Helminths in the etiology of anemia in the tropics, with special reference to hookworms and schistosomes

PARASITOLOGICAL

EXPERIXIENTAI. PAR.ASIT”LOGY 14, 240-262

Helminths Special

(1963)

in the Etiology Reference to Henry Wellcome

REVIEWS

Foy Trust

of Anemia Hookworms and

George

Research

in the Tropics, and Schistosomes S. Nelson

Laboratories,

The anemias of the tropics have the same fundamental pathology as those of temperate climates, but they are usually more prevalent and severe, often with a multiple etiology. Helminths play an important role in the genesisof iron deficiency anemiasand accentuate those due to other causes. Taking the minimum hemoglobin levels suggestedby the World Health Organization (1959) as a basis, whole communities in many tropical areas have levels less than half that regarded as normal. In determining the frequency and severity of anemia in any area a reliable and reproducible method for estimating the hemoglobin is necessary.This should enablelarge numbers to be examined with reasonableaccuracy and rapidity. The cyanomethemoglobin method (King and Gilchrist, 1947) fulfils most of these requirements and is the one of choice. To assessthe prevalence of anemia an arbitrary standard should be selected, say 8-10 gm/lOO ml and the percentage of the population which falls below this level determined. Packed-cell volumes are a valuable adjunct but their determination in the field is time consumingeven with the micro method. Marrow punctures can be done in the field but satisfactory differential diagnosis of the various types of anemia will require investigation in hospitals where responseto treatment can also be observed. The effect of altitude on 240

with

Nairobi,

Kenya

hemoglobin levels may have to be taken into account, but the most badly affected areas in the tropics are almost all at low altitudes (Smith, 1925; Holmes et al., 1950; Foy, Kondi, and Hargreaves, 1952; Walker, 1956). In comparing the hemoglobin levels of one region with another it is important to select samplesfrom similar groups. Pregnant women and children are most likely to be affected by anemia, and samples should not be unduly weighted with these. Schools,plantations, and estatesare convenient for collecting large and uniform samples; hospital records are biased and frequently unreliable. The anemias of the tropics and elsewhere may be classified into four main groups: iron deficient, hemolytic, megaloblastic, and aplastic. These often overlap since an iron deficient anemia may be associatedwith megaloblastosis or a hemolytic anemia may be accompanied by deficiency of folic acid or B/12. TYPES

OF ANEMIA THEIR

SEEN

RELATION

IN THE TO

TROPICS

AND

HELMINTHIC

1NFEcT10~s

Iron

Deficiency

Anemia

This is by far the most common anemia in the tropics, especially in the hot, damp river valleys, and lacustrine and coastal regions where 70-95s of the anemias are iron deficient. Important factors in the etiology are iron loss due to chronic bleeding and

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poor absorption or deficiency of iron in the diet. Contributory factors are iron losses from the skin due to excessive perspiration and from the intestine due to increased desquamation as a result of bacterial or parasitic infections. It is possible that the iron-containing enzymes may also be depleted in the gross iron deficiency anemias (Beutler, 1957; Gubler et al., 1957; Beutler et al., 1958). The helminths associated with the tropical iron deficiency anemias are those which cause direct blood loss, such as Ancylostoma duodenale, Necator americanus, Schistosoma haematobium, S. mansoni and S. japonicum. Of these, hookworm is by far the most important. Of less significance is the blood loss caused by such parasites as Paragonimus westermani, Strongyloides stercoralis, and Fasciolopsis buski. Hemolytic

Anemia

The most common cause of intravascular blood destruction in the tropics is malaria, particularly in children, in whom the anemia is usually normocytic and normochromic. The iron liberated from the destroyed red cells is largely reutilized for hemoglobin synthesis; malaria anemia generally responds to antimalarial treatment and requires no iron. Included in the group of hemolytic anemias are the anemias associated with hypersplenism (pseudo-Banti) and hepatomegaly, common sequelae of schistosomiasis, malaria, and kalaazar. Other causes of hemolytic anemia in the tropics are the presence of abnormal hemoglobins or the deficiency of red cell enzymes such as glucose-6-phosphate dehydrogenase, abnormalities which are genetically determined and ethnologically distributed (Singer, 1953 ; Foy et al., 19.54, 1955; Lehmann, 19.54, 1960; Allison et al., 1961a,b; Sheba, 1962). It is unlikely that helminths play any part in the genesis of these hemolytic anemias, although they may aggravate the picture by causing direct blood loss.

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Megaloblastic

Anemia

Nonpernicious megaloblastic anemia is much commoner in the tropics than in temperate climates. This may be because of dietary deficiency of B/12 and folic acid, defects in absorption, or because the type of diet eaten in these areas produces an intestinal flora which competes for essential hemopoietic substances or prevents their production or absorption. In the humid tropical lowlands megaloblastic anemia is less common; no satisfactory explanation has been given for this. Pernicious anemia occurs in most tropical peoples but it is not known whether its incidence is the same as in other races. Helminths are not commonly involved in the etiology of megaloblastic anemias in the tropics, although in northern regions Diphyllobothrium latum is a causative parasite. This worm is common in man in Finland, Sweden, North America, and in the Eskimos of northern Canada (Laird and Meerovitch, 1961), the infection being contracted by eating fresh-water fish containing the plerocercoid stage of the parasite. Diphyllobothrium species are reported in several tropical areas but these are unlikely to be D. Zatum; related species are not uncommon in wild carnivores. Megaloblastic anemia is not a feature of infection with the other species of tapeworms which are so prevalent in man in the tropics, but any possible association has not been critically investigated. Taenia saginata does not take up CoGo-labeled B/12 and the dry weight of the worms contains only 0.046 ug per gram of B/12 in contrast to D. Zatum, which has 2.3 pg per gram (Scudamore et al., 1961). It is interesting to note that the dry weight of Ascaris lumbric,oides contains almost as much B/12 ( 1.9 yg per gram) as D. latum but does not take up Co”O or compete actively with man for B/12. Twenty to sixty per cent of the population of Finland is infected with D. datum but only O.Ol-0.9% develops anemia (Laine et al.,

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1959; Scudamore et al., lot. cit.). The anemia is typically megaloblastic and resembles pernicious anemia, including the presence of subacute combined degeneration of the cord, occurs at any age, and is cured by the removal of the worms. The incidence of anemia is always higher when the worm is located high in the intestinal tract, where it absorbs as much as 80% of a dose of labeled B/12, compared with only 4070 when located lower in the tract. The worm changes its position in the gut, and as a result of these changes there are variations in the absorption of B/12 which are probably responsible for the spontaneous relapses and remissions of the disease. The mechanism of anemia production by D. la&m has been extensively studied in Finland and Sweden as well as North America (Totterman, 1944; Bonsdorff et al., 1947, 1952, 1956; Nyberg et al., 1952, 1958a,b, 1960; Brante and Ernberg, 1958; Kaipainen et al., 1959; Laine et al., lot. cit.; Markkenen et al., 1960; Scudamore et al., 1961). The worm produces megaloblastic anemia by interfering with the absorption of B/12 through splitting the combination of the vitamin and intrinsic factor. Variations in the B/12 content of the diet may also affect the incidence of the anemia. The serum B/12 in anemic patients infected with D. latunz is always low (SO-100 ypg/lOO ml) and even in those without anemia it is rarely normal. There is also a lowered urinary excretion of B/12 as shown by the Schilling test. There are considerable differences in the amount of B/12 taken up by different geographical strains of D. latum (Brante and Ernberg, 1958). In Finland the amount absorbed is from 14 to 84% (Nyberg, 195813); lower absorption values, 3-14s are reported from Sweden and Canada (Scudamore, lot. cit.). The reasons for this variation are not understood. No comparable studies on the effect of other tapeworms and their relation to anemia have been made in the tropics. In parts of

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Kenya 98% of the adult population is infected with T. saginata. No critical work has been done to determine whether tropical megaloblastic anemia is more prevalent in areas where this parasite is common. Aplastic

Anemia

Erythroid aplasia is common in children recovering from marasmus and kwashiorkor and may be associated with infections such as measles, mumps, chicken pox, bacterial dysentries, and staphylococcal and streptococcal infections (Lien-Keng, 1957; Fey et al., 1961; Neame and Naude, 1961; Kondi et al.: 1962a,b). It is unlikely that helminths play any role in their etiology, although they may worsen the situation and prevent full hematological responses to specific treatment. Hookworm

Anenzia

The main endemic areas of hookworm lie between latitude 35” North and 30’ South, thus embracing a large part of the habitable surface of the earth. The distribution of hookworm anemia in these endemic areas is very patchy. In the Americas and Africa, N. americanus is the prevalent worm. In the Far East both species are widespread, while in the Mediterranean and subtropical areas, A. duodenale predominates. More than 100 years ago Bilharz (1852) and Griesenger ( 1854) suggested that hookworm played a part in the genesis of “Egyptian chlorosis,” but little attention was paid to this problem until Perroncito (1880, 1882) described severe anemia in workers heavily infected with A. duodenale in the St. Gothard Tunnel and the French coal mines. Later Ashford (1900) discovered that the anemia in Puerto Rico was associated with hookworms. These findings led to the investigations by Stiles (1902)) who found that the prevalent hookworm in the southern United States was N. americanus. In 1909, the Sanitary Commission of the Rockefeller Foundation organized a program for the eradication of hookworm

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disease in the United States, and later the International Health Board demonstrated the benefits to be derived from antihookworm campaigns in different parts of the world. Darling et al. (1920), Lane (1922), Stoll (1923), and Chandler (1929) showed that the severity of anemia was related to the load of worms and introduced methods for estimating worm loads from the number of eggs in a known quantity of stools. These pioneers demonstrated the importance of hookworm as a cause of morbidity in the tropics and its part in the etiology of tropical iron deficiency anemia. Workers in China, Mexico, U.S.A., India, Palestine, Egypt, Brazil, East and Central Africa, Mauritius, Malaya, South America, and the Seychelles have demonstrated the association of hookworm with anemia, and confirmed the relationship between its severity and worm loads (St011 and Tseng, 1925; Cart-, 1926; Augustine and Smillie, 1926; Chandler, 1929; Scott, 1933, 1937; Napier, 1941; Fonseca, 1948; Forde Tredre, 1948; Beet, 1949, 1951; Lehmann, 1949; Daffay and Bhende, 1957; Roche et al., 195713; Tasker, 1958; Nelson, 1959; Foy and Kondi, 1958a, b, 1961; Stott, 1960; Layrisse et aZ., 1961; Jordon and Randall, 1962 ; Charmot and Reynaud, 1961; Beaver, 1961). In spite of these careful studies other workers found that the correlation between hookworm disease and anemia was frequently very low and considered that other factors were concerned in the etiology of the anemia. They have described situations where either hookworm loads are heavy but anemia absent or where hookworm loads are light but severe anemia prevalent (Gordon, 192 5 ; Fiilleborn, 1929; Cort et al., 1929; Hynes et aZ., 1945; Dick and McCarthy, 1946; The Australian Health Department, 1947; Wellbourn, 1949; Mackey, 1953; Chernin, 1954; Yamasaki and Saruta, 1954; Quattrocchi and Russo, 1954; Kennedy, 1956; Oldmeadow, 1956; Hughes, 1959; Brumpt et al., 1961). The difference of opinion concerning the relation of hook-

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worm to anemia can usually be accounted for by variations in the iron content of the diet, or to other factors described below. In areas where hookworms are absent and anemia is said to be prevalent, little information is available regarding the type of anemia and in many of these regions malaria is known to be endemic. In many tropical countries hookworm disease is second only to malaria as a cause of ill health and nearly 100% of cases with iron-deficiency anemia are also infected with hookworms. Stoll (1947) estimated that some 460,000,000 people were infected with these helminths. The findings of a joint symposium of specialists from C.C.T.A. and W.H.O.,l in Brazzaville (1961) re-emphasized the major importance of hookworms as a cause of both anemia and morbidity in the tropics, and suggested means of control and investigation (Beaver, 1949, 1950, 1961; Charmot and Reynaud, lot. cit.). The following factors affect the severity of hookworm anemia: loads and species of parasite, blood and iron losses due to hookworm, dietary factors, iron losses due to other causes, immunity, and the ecology and economic status of the community. Failure to give due weight to all these factors led one of the authors (H.F.) to conclude that hookworms were probably not very important in the etiology of tropical iron deficiency anemia (Foy et al., 19.57, 1958b). Our views on this problem have changed mainly as a result of the introduction of radioisotopic techniques for estimating blood loss. FACTORS

AFFECTING

OF HOOKWORM

SEVERITY ANEMIA

Effect of Loads and Species of Parasites on the Development of Anemia Since worm loads and speciesare closely associated with the presence and severity of 1 C.C.T.A.-W.H.O. ration Technique sation.

en

= Commission Afrique-World

pour Health

la

Coop& Organi-

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anemia, reasonably accurate methods for assessing these must be used if a correlation is to be found between loads of worms and the degree of anemia. Numbers of hookworm vary from a few to several thousand but rarely have more than 3000 N. americanus or 2000 A. duodenale been recovered from one patient. Burdens of less than 100 N. americanus or 50 A. duodenale seem to be well tolerated, but greater numbers than this will cause ill health and anemia. In most surveys hookworm infection has been judged by the presence of eggs in the stools, usually on one examination of a wet smear. This method is sufficiently accurate for classification into light, medium, and heavy infections, but the very light infections are often missed. Indirect methods for estimating worm loads have been devised using a flotation technique for calculating the number of eggs per gram of stools. Egg counts per gram of stool vary enormously from a few up to 100,000 (Brumpt and HO-Thi-Sang, 1961), A. duodenale usually producing more eggsper worm than N. americanus. The accuracy of the indirect methods is upset by the variation in the daily output of eggs, the small amount of material taken in relation to the total volume of the stool, and the lack of uniformity in the distribution of eggsin the sample.Beaver thinks that the “standard fecal smear” is as reliable and easier than other indirect methods, but Yajima (1960) considers that the number of hookworms in the host cannot be easily estimated from the number of eggs in the feces. Hurley (1959) has devised an indirect method for estimating worm loads which dependson the number of eggs passedper gram of stool multiplied by the daily weight of the stool. Only rarely have loads and species been estimated by counting the number of adult worms expelled after multiple vermifuges; this is the only really satisfactory method for making an assessmentof the relation between

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anemia and hookworm loads (Beaver, 1950; Foy and Kondi, 1960). Egg-positive stools are likely to be present in a large proportion of the population in any area at risk, and loads of adult worms in such a population vary enormously. Generally speaking, high worm loads will be associated with greater blood lossesthan lighter loads, and A. duodenale causes greater blood loss for similar loads than does N. americanus. This may be because of its greater size, its armed mouthparts, its more migratory habits leaving more bleeding points in the gut, or to the fact that it may secrete more powerful anticoagulants (Foy et al., 1958b, 1960). Amount of Blood in Hookworm

and Iron Infections

Lost

(a) Blood losses. There is now no doubt that heavy hookworm loads cause serious blood loss and lead to gross anemia (Roche et al., 1957b,c; Foy et al., 1958a, 1960; Layrisse et al., 1961; Gilles et al., 1961). In the past it has not been easy to assess with any accuracy the amount of blood lost from infections with hookworms. Writh the introduction of radioactive labels (Fe”” and Cr5r) the estimation of blood lossis both easy and accurate (Gerritsen et al., 1954; Roche et al., 1957a,b,c, 1959; Foy et al., 1958a, 1960; Layrisse et al., 1961; Gilles et al., 1961). There is fairly close agreement between authors concerning the amount of blood lost with different worm burdens. Estimates vary from negligible amounts to 200 ml a day? differ in the same person on different days, and are not always the same in different individuals with similar worm loads (Fig. 1) For example, over a period of 26 days 625 ml of blood were lost in a patient having 200 A. duodenale. In another having 116 AT. americanus and 50 A. duodenale, 1535 ml of blood were lost in 35 days, a mean daily loss of 24 and 44 ml, respectively. Worm loads

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N. omericono II00 Hb. 3.8 grs /lOOml Morrow Erythronormoblostic Gastric acidity normal

100

50

FIG.

1.

Fecal

blood

loss and

hemoglobin

from 800 to 1000 N. americanus caused daily blood losses of 25-35 ml ; similar loads of A. duodenale can cause two to three times this blood loss (Foy, Kondi, and Austin, 1958, 1960). Tasker (1958) found that with 100-1500 N. americanus the daily blood loss was from 8 to 90 ml; Roche and PerezGimenez (1959) found losses ranging from 9 to 108 ml daily, and Gilles et al. ( 1961) record losses varying from 83 to 163 ml daily in a patient who later expelled 1900 N. americanus. In Venezuela, where the infection is predominantly N. americanus, Layrisse and his collaborators (1961) have calculated that a daily egg output of 1000 eggs per gram stool will cause a loss of approximately 2.4 ml of blood daily. Since the loss of blood varies greatly from day to day in the same patient, isolated estimations will not give a complete picture of the blood losses. The most satisfactory method is to determine the blood loss by plotting radio activity for every stool passed over a period of 25 days after an iv injection of Fe69 or Cr51. Vermifuges are then given until no more worms are passed, continuing

response

before

and

after

vermifuge.

meanwhile to estimate stool radioactivity until it is less than 1% of the administered dose. From such figures the total amount of blood lost over the whole period of stool collection can be estimated and the mean daily loss calculated for the pre- and postvermifuge period. Using this technique, Foy and Kondi (1958a, 1960) found in 15 cases that the mean daily loss before vermifuges varied from traces to 40 ml daily with a range of 2-180 ml for worm burdens that varied between 80 and 850 N. americanus and 7-2400 A. duodenale, some of the patients having mixed infections. With such losses it is no wonder that the mean hemoglobin levels are low in many tropical areas where hookworms are present and that patients with hemoglobin values of 1.5 gm/lOO ml are common. Removal of the worms always leads to a cessation or great diminution in blood loss (Fig. 1). If the stores of iron have been exhausted, as shown by marrow hemosiderin estimation, there will be no improvement in the hemoglobin level as a result of the vermifuge, unless therapeutic iron is given, since

246

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worming cannot replace depleted iron stores. If the worms are left ilz situ and iron is given the hemoglobin will rise in spite of continuing blood loss (Rhoades et al., 1934a, b). Distinguishing between intestinal and fecal iron losses, Roche et al. (1957a), Layrisse et al. (1959), and Aparcedo et al. (1962) have estimated that up to 60% of the iron liberated from the intestinal blood loss is reabsorbed and utilized for hemaglobin synthesis. It sometimes happens that patients with severe iron deficiency anemia are sent to hospitals from rural dispensaries, and no blood can be demonstrated in the feces and no hookworms are recoverable on worming. Such patients are generally found to have taken vermifuges but not iron, hence the presence of anemia but no worms. Other patients report with a normal hemoglobin level, considerable blood loss, and on vermifuging they are found to have heavy worm loads. In these cases adequate therapeutic iron has been given, but the patient has not been vermifuged, hence the absence of anemia in the presence of heavy worm loads and high blood losses. Situations like these explain some of the misconceptions which have arisen about the relation of hookworms to anemia and the efficacy of iron treatment. The lost blood in hookworm infections is due mainly to the blood being pumped through the worm in the act of sucking (Roche and Torres, 1960). Important contributary sources of loss are the bleeding points left in the gut as the hookworm browses along the mucosa, which will vary according to the migratory habits of the hookworms, the ability of the host to seal off the bleeding points quickly, and to variations in the secretions by the hookworm of anticoagulants. The time factor as well as worm loads will affect the development and severity of the anemia; a light load will produce just as

NELSON

severe an anemia if blood loss continues over a long period. The amount of blood retained by individual hookworms is negligible; the radioactivity of 2000 worms was found to be equivalent to 0.003 ml per worm (Foy et al., 1958a, 1960; Lay&se, 1959). Worms do not, in fact, retain any constant or significant amount of blood. (b) Iron Zosses. The significant factor in blood loss is the accompanying loss of iron: and the importance of hookworm in the etiology of anemia will depend on the balance between iron loss and iron intake. The amount of iron lost will depend upon the hemoglobin level at the time the blood loss occurred, iron loss decreasing as the hemoglobin falls. A patient with 15 gm/lOO ml hemoglobin losing 100 ml of blood will lose 50 mg of iron; one with a hemoglobin of 7 gm/lOO ml will lose only 25 mg of iron (Foy et al., 1958a). A hemoglobin level might ultimately be reached where the iron loss would be balanced by the iron intake and the hemoglobin level stabilized. Unless, however, therapeutic iron is given the iron stores will remain depleted. The average daily iron loss from hookworm infection has been estimated by a number of different workers and found to be from 5 to 9 mg (Gerritsen, 1954; Foy and Kondi, 1958a, 1960; Roche, 1957a, b; Gilles et al., 1961; Layrisse et al., 1961). Such losses will deplete the iron stores and lead to anemia unless supplementary iron is available to balance the loss. Dietary

Factors Aflecting Hookworm

Anemia

Since the anemia of hookworm disease is hypochromic and due to iron loss produced by intestinal bleeding, the iron content of the diet will have an important influence on the presence or absence of anemia. In many areas where hookworm loads are high, and the blood losses considerable, anemia may be minimal because the iron loss is balanced by the high iron content of the

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diet. In other areas where hookworm loads are considerably lighter the intestinal blood loss may be less, but anemia may be more severe because the iron content of the diet is too low to compensate for the losses sustained. Calorically adequate tropical diets usually contain from 12 to 60 mg of iron daily compared with 10-18 mg in European diets. However, in parts of India the iron content of the diet may fall as low as 4 mg daily (Indian Council of Medical Research, 1951; Aykroyd et al., 1951; Mitra, 1953). In parts of South Africa the iron content may be excessive, reaching more than 200 mg daily, mostly derived from iron vessels used in the preparation of food and drink (Walker et al., 1953, 1955, 1956). If the fluid in which food is prepared is discarded there is likely to be a loss of iron. In the tropics less iron will be present in the diet if cooking is done in aluminium or earthenware utensils. Two to ten per cent dietary iron is normally absorbed and utilized for hemoglobin production, varying with the type of food eaten (Moore, 1955). Absorption increases in anemia to 30-SO%, depending on the body’s iron stores, erythropoietic activity, and hypoxia (Bothwell et aE., 1958; Demulder, 1958; Pirzio-Birolo et al., 1958; Schulz and Smith, 1958; Mendel, 1961). Tropical diets are generally bulky, consisting largely of carbohydrates rich in phytates and phosphates and usually low in calcium. Such diets may hinder iron absorption either by forming insoluble phytates and phosphates or producing a type of intestinal flora which reduces iron absorption (Macdonald, 1939 ; McCance and Widdowson, 1942 ; Kinney et al., 1949; Hegsted et al., 1949; Foy et al., 1959; Hussain and Padwardhan, 1959a). Bulk alone as well as absence of folic acid also adversely affect iron absorption. Experimental studies on animals have shown that the load of intestinal parasites may be affected by the diet. Usually a deficiency of vitamins and essential minerals

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results in heavy worm loads, but sometimes a deficiency may prevent the establishment of infections. This subject has been extensively reviewed by Hunter (1953) and Frye (1955). Holmes and Darke (1959) noted that there was a diminution in nitrogen absorption in patients with heavy hookworm infections, but it is doubtful if this affects the degree of anemia. Layrisse (1959) and his associates have shown that patients with heavy hookworm loads had low serum B/12 levels and impairment of folic acid absorption, but there was no megaloblastosis and their patients all recovered with iron therapy alone. There is no evidence to show that diet apart from the iron content is of much significance in the etiology of hookworm anemia, or that it affects the chances of infection. By far the most important factor determining the development of the anemia is the dietary iron content. If this is high enough and absorption is not interfered with, it will compensate for the intestinal blood loss from hookworms, and anemia is unlikely to occur. The importance of iron in the etiology of hookworm anemia is further demonstrated by the absence of anemia in communities where the daily iron intake is high in spite of heavy hookworm loads, and also by the well-established fact that hookworm anemia responds to therapeutic iron even if the worms are left in situ (Fig. 1) and that the anemia recurs once iron is stopped. Iron Losses Due to Factors Other than Hookworm which Aggravate the Anemia These include iron loss in sweat, dermal iron losses from the gut due to desquamation, and the effects of menstruation and pregnancy. Dermal iron loss. Losses in tropical climates are probably greater than in temperate ones because excessive sweating leads to increased desquamation. Using chemical methods, derma1 iron losses due to excessive sweating have been variously estimated at 6 mg or more

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daily (Mitchell and Hamilton, 1949), 05 l.Omg daily (Dubach et al., 1948), and 0.05-0.1 mg hourly (Johnson et al., 1950). More recent estimations have shown an iron content of 0.3-6.0 mg/3-4 liters of whole sweat with cell content of 0.5-2.5% (Foy and Kondi, 1957). Hussain and Patwardhan (1959b) found the average iron value of cell-rich sweat 1.6 mg per liter; assumingan average loss of 3-6 liters sweat in 24 hours, this would produce an iron lossof 4.8-9.7 mg. These authors also found that after iron therapy the iron content of cell-rich sweat increased significantly, probably due to an increased amount of iron in the desquamated cells. Jacobs and Jenkins (1960) found the iron content of infants finger nails as high as 1 mg per gram, decreasing in anemic states. The iron content of sweat is almost exclusively in the cellular portion; this is measured by the sweatocrit and is higher in the apocrine than the eccrine sweat. It has been shown that the skin desquamationrate varies from person to person and in the sameperson, at different times being higher in people wearing clothes (Foy et al., 19.57, 1958). Twenty-four hour whole body sweat collections are therefore necessary; surface counting using Fe55 has recently been used to estimate dermal iron losses. Intestinal iron loss.Loss of epithelium from the bowel, normally SO-80gm of mucosal cells daily, involves an iron lossof 0.5-1.5 mg (Hahn et aZ., 1939; Smith, 1952; Witts, 1956). In the inhabitants of the tropics iron losses from the gut must frequently be in excessof normal not only an account of the high incidence of bacterial, helminthic, and protozoa1 infections which cause excessive epithelial loss but also due to the associated iron lossesfrom bleeding. Exudative enteropathy, such as occurs in patients with tropical sprue, has been measured by using Cr51 and 1131PVP” (Rubini et al., 1961). The same technique has been 2 PVP

= Polyvinyl-pyrrolidone.

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used in a few casesof hookworm infection, and the stools show little radioactivity; so far only a limited number of patients with small hookworm loads have been investigated. Iron loss from menstruation

and pregnancy.

The iron requirements of girlhood, with its high growth-rate and rapid expansion of blood volume, together with menstruation, can cause marked iron deficiency. In many developing countries, particularly India and the Far East, the low age at marriage, accompanied by pregnancy before the age of 16, are important contributory factors in the production of iron deficiency anemias. In the samplesexamined by Foy and Ko’ndi in Assam 80% of the women patients were below the age of 18 and many were pregnant for the secondor third time (Foy and Kondi, 1957, 195813).Similar marriage customs prevail throughout the rural Far East, where Chen (1940) reports that in Yunan 87y of the girls are married and have children between the ages of 16 and 18 years. Menstrual iron lossesvary from person to person, and in the same person at different periods. In some women they are considerable (Foy and Kondi, 1957). All these different sourcesof iron loss will affect the severity of hookworm anemia, but they are usually of less significance than the iron lost from the activity of the worms. Effect

of Immunity

on Hookworm

Anemia

The development of immunity may affect the incidence and severity of anemia by preventing the establishment of heavy loads. There is evidence of an age resistance and immunity to super infection with hookworms and related nematodes in experimental animals. It has been shown by Krupp (1959) that when dogs are given heavy hookworm infections there is a depression of egg production, and only a limited number of worms can populate the intestine regardless of the number of infective larvae given. Taliaferro (1929. I, Yamanaka \, 1940). II Culbertson (1941).

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(1960), and Stoll (1961) have all reviewed this problem and emphasized that there is little experimental evidence to support the view that man can acquire any significant or lasting immunity to hookworms. However, epidemiological evidence strongly suggests that the hookworm disease would be even more serious in hyperendemic areas if it were not for some degree of immunity preventing overwhelming infections. Jarrett et al. (19.58), using irradiated larvae as a living “vaccine” against Dictyocaulus and other nematodes, have revolutionized techniques for preventing parasitic infections in some animals. This method has been used successfully by Dow et al. (1959) to immunize dogs against hookworm, but because of the high incidence of side effects there is little hope, at present, of applying this technique to the study and control of infections in man. Ecological and Economic Factors Affecting Prevalence of Hookworm Anemia Hookworm transmission is most active in low-lying, hot, humid areas, but it also occurs at higher altitudes such as in the foothills of the Himalayas in Darjeeling, Kashmir, Ceylon, the Andes of South America, and the high plateaus of Africa. More continuous transmission with heavier loads, accompanied by severe anemia, occurs in areas where high temperatures and humidity coincide. In such areas 25,000 larvae can be recovered from a spot where SO;000 eggs were deposited 6 days previously, and the larvae may survive for several weeks (Beaver, 1961). In regions where transmission is interrupted by long dry seasons, as in many parts of India and Africa, worm burdens are lower and the anemia less severe. With soil-transmitted helminths, larvae survive better in damp, sandy soil with a high humus content than in predominantly clay soils. Although the usual means of transmission of hookworm is through the skin from

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contaminated soil, infection can sometimes occur by mouth. The social and agricultural practices of the community as well as its sanitary habits have a considerable effect on the incidence and loads of worms. Economic status affects the amount and type of food eaten, but it is unlikely to alter seriously the iron intake, except in cases where the calorie content is greatly reduced. The anemias of frank malnutrition, such as marasmus and kwashiorkor, are generally less serious than those seen in hookworm disease in spite of the reduced protein and calorie intake and very low serum proteins. The lower hemoglobin levels found in the less privileged members of the community exposed to hookworm infection are generally due to poor sanitation, the general absence of footwear and, even more important, their rural living conditions which favor high transmission. It is in such communities that chronic bleeding from heavy worm loads exhausts the iron stores and produces gross hypochromic anemia. Clinical and Laboratory Findings in Hookworm Anemia In the more backward indigenous peoples of endemic areas anemia is usually the presenting sign of hookworm disease, but in the immigrant races and the more sophisticated members of such communities subjective symptoms are usually the first evidence of infection. Most patients show a striking “paradoxical tolerance” to the anemia, even when gross; this is no doubt due to the gradual development of the anemia resulting in cardiac and respiratory compensation. There may be dyspnoea, weakness, and giddiness but patients with hypochromic anemia are usually less severely ill than those with megaloblastic anemia and they are generally ambulant. Edema is uncommon in East Africa but is said to be more frequent in the Far East and

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other parts of Africa (Brumpt and HO-ThiSang, 1961; Charmot and Reynaud; 1961) and to be related to the degree of anemia, but if there is a correlation between anemia and edema it is not very close. Koilonychia, although seen, is rare in spite of the long duration of the illness (Foy et al., 1958b; Charmot and Reynaud, 1961; Brump and Ho-Thi-Sang, 196 1) . Gastric achlorhydria is uncommon. The indirect bilirubin is never raised unless megaloblastic or hemolytic anemia is also present. Enlargement of the liver and/or spleen are usually present only in patients with concomitant malaria, kala-azar, or schistosomiasis. In endemic hookworm areas children may become infected between the age of 1 and 2 years, and if worm burdens are heavy they will become anemic in a few weeks due to a combination of low iron intake, rapid growth, and blood volume expansion. Death rates from hookworm and its accompanying anemia are not easy to determine, and figures quoted in the literature leave much to be desired. Charmot and Reynaud (1961) recorded eleven deaths in a series of 116 cases of hookworm anemia, 92 of them children. The anemia is usually hypochromic, with hemoglobins as low as 1.5 gm/lOO ml (range, 1.5-12.0 gm/lOO ml) with a low mean corpuscular hemoglobin concentration (20-25s ) and low serum iron ( 15-100 pg/lOO ml) and normal to high unsaturated iron binding capacity (220-400 yg/lOO ml) (Srikantia and Belavady, 1962). Hemosiderin is absent from the usually active erythronormoblastic marrow, a sign of the exhaustion of the iron stores. Eosinophilia is generally high, especially initially and is probably evidence of an allergic reaction. Giant stab-cells occur in the marrow of 5070 of the iron deficient anemias in India, in 20% of those seen in Africans, but are absent in Seychellois. These differences have not been explained

NELSON

but may be associated with dietary deficiency or upsets in absorption of folic acid. The saline fragility of the red blood cells is not altered, and the total serum proteins are not usually reduced, although, as is commonly found in tropical races, the albumin to globulin ratio is reversed due either to production of immune globulins or to ethnological factors (Foy et al., 19.54). Occasionally there may be megaloblastosis or hemolysis, but they are not specifically associated with the hookworm infection. Hypoplasia and aplasia are rare except in patients that also have kwashiorkor or marasmus. Treatment of Hookworm

Anemia

Treatment should be directed toward restoring the hemoglobin and the removal of worms by giving oral iron and vermifuges. Ninety-eight per cent of iron deficiency anemias in the tropics respond completely to iron therapy (Rhoades et al., 1934a,b; Foy et al., 1958a,b, 1960, 1961; Stott, 1960; Charmot and Reynaud, 1961), but if intercurrent complaints such as tuberculosis, syphilis, or infections with Giardia, Strongyloides, BalanEntamoeba histolytica, malarial tidium, plasmodia, etc., are present, full responses will only be obtained if these are treated (Foy and Kondi, 1961). The failure of iron therapy is nearly always due to not taking the iron. In a group of out-patients treated in the Seychelles (Foy and Kondi, 1961) , the hemoglobin rose only 2.0 gm/lOO ml in a period of 6-8 weeks, but in a closely supervised group of hospitalized patients, the mean hemoglobin rise in the same period was 6.2 gm/ml. The difficulty of ensuring that patients take their iron is very real and has led to the view that oral iron is useless in the treatment of iron deficiency anemias associated with hookworm, and parenteral iron has been advocated. The advantage of parenteral therapy is the certainty that it has been given, but it is no more effective than properly administered

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oral iron. Although therapeutic iron will raise the hemoglobin level to normal values it will fall again once iron is stopped unless the worms are removed. The object of vermifuging is to reduce the worm loads to a level that will diminish intestinal blood loss to insignificant amounts. It is not essential, and indeed it is almost impossible, to secure an egg-negative stool, and even multiple vermifuges will not do this. Necat’or americanus is much more resistant to all vermifuges than is A. duodenah but is relatively more sensitive to tetrachlorethylene, while A. duodenale is highly sensitive to bephenium salts. Since auto-infection such as occurs in Strongytoides and Enterobius is not a feature of hookworm infection, there is no danger in leaving a few worms in the bowel. Most vermifuges will remove 20-70% of the worm loads after one dose, and three or four will ensure that the majority of the worms are expelled. In infected communities three or four doses a year of an effective vermifuge will maintain the worm burden at a sufficiently low level to prevent anemia. Removal of worms will not, however, result in any improvement of the blood picture unless iron is also given since it will not replace depleted iron stores. The replacement of iron stores takes many months if dietary iron is the only source, hence the necessity of combined iron therapy and vermifuges in treatment. It is no longer necessary to delay the administration of the modern nontoxic vermifuges till the hemoglobin has risen. If tetrachlorethylene is used as a vermifuge it is perhaps wise to follow it with a saline purge if a stool has not been passed within 4 hours. Out of 116 patients, Charmot and Reynaud (1961) reported 4 deaths which they attribute to tetrachlorethylene, and Stein et al. (1956) and Grossowicz et al. (1957) have shown that carbon compounds denude the liver B/12 stores and lift blood levels of the vitamin.

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Prevention

of Hookworm

Anemia

Since the anemia is due to hookworm infection and blood loss from the gut, prophylactic measure should be directed to preventing infection, removing or reducing loads of worms, and ensuring a positive iron balance. Infection can be prevented if everyone in the community uses an effective privy. However, in most countries where hookworm is rife, economic and social conditions do not readily lend themselves to the provision of such amenities. Inadequate facilities and poorly constructed latrines are often worse than nothing at all. Sanitary improvements must go hand in hand with improvement in the economic and cultural development of the community. In areas where infection is acquired predominantly through the feet, wearing shoes offers the possibility of preventing or reducing the chances of infection. In Egypt whole communities have been protected by enforcing the use of shoes (Ministry of Health, 1959). The calloused sole of the foot in those unaccustomed to footwear may afford some protection against infection, but the more delicate tissues between the toes and on the side of the foot are still vulnerable and important sites of penetration. In the past 10 years there has been an enormous increase in the purchase and use of shoes in under-developed countries such as India and Africa; the improvement of social status acquired by shoe wearing has no doubt contributed to this (Okpala, 1961). We are aware that peasantry the world over tend to use shoes only on high-days and holidays and to avoid them for reasons of economy or comfort during their working hours, but their use is steadily increasing and will undoubtedly affect the incidence of the disease. Drug prophylaxis is both possible and successful, especially on estates and plantations where the labor force can be easily

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mobilized for treatment. Three or four treatments a year with one or other of the modern vermifuges will reduce hookworm loads so that significant blood loss is stopped and the incidence and the severity of anemia reduced. Even one treatment can effectively reduce worm loads (Goodwin and Standen, 1958; Goodwin et al., 1958). Reinfection will of courseoccur, but if adequate worming is done heavy loads will not develop. Vermifuge campaigns may not initially reduce the percentage of egg-positive stools but they will at once reduce worm burdens, which is the object of any such campaign. The drugs of choice for mass treatment are tetrachlorethylene or “Alcopar.” Tetrachlorethylene is not without disadvantages for massuse and should be used with discrimination. Alcopar is completely nontoxic and if given in sufficient dosage will reduce loads of both N. americanusand A. duodewale; it is especially effective in A. duodenale infections (Ahmad et al., 1959; Ghysels and Sartiaux, 1959; Nagaty et al., 19.59; Juminer et al., 1960; Lambotte et al., 1960; Young, 1960; Gilles et al., 1961; Mackerras, 1961; Queensland Institute Medical Research, 1961) The maintenance of a positive iron balance by fortification of somesuitable article of diet with an iron salt has been achieved in limited areasin a number of countries (China, South East Asia, the Phillipines, South America, and India). The results of these measures are not easy to assess,but theoretically it would seem an obvious method of replacing iron lossesparticularly as it has been shown that anemia can be cured in spite of heavy worm loads if iron is given, Proper levels of fortification must be worked out so as to avoid the possibility of iron overload and the development of cytosiderosis. Fifteen milligrams of ferrous sulfate (FeS04 *7H20) will provide 5 mg of elemental iron, and this is a suitable daily fortification level for adults with a reduced dose for children.

An article of diet in common use must be chosenand fortification must not interfere with either its appearance or palatability lest such changes hinder or stop consumption. Luxury articles, usedonly infrequently, should be avoided. It is unfortunately true that in situations where the treatment of soil-transmitted helminths is most essential the meansof control are limited by difficulties that are often hard to overcome. The purpose, however, is not eradication of worms, which is unrealistic to attempt, but the reduction of loads to a level that makes anemia unlikely. SCHISTOSOYIASIS

AND ANEMIA

The complicatiosnsof schistosomiasisare serious in many parts of the tropics, but far less is known about the hematological effects of such infections than is the casewith ancylostomiasis. An editorial in the Journal of Tropical Medicine and Hygiene (1953) stated that “schistosomiasisremains the largest unsolved problem in tropical medicine.” Shousha ( 1949), in a report to the World Health Organization, paints a very grim picture and says, “The clinical picture of schistosomiasis, with its symptomology of anemia, underdevelopment, undernourishment, asthenia, and general debility, is stark and terrible, especiaIly when one considersthat it spreadsitself over a vast part of the world and involves over 1.5’0million people.” The problem of schistosomiasismay be %ark and terrible” in parts of Egypt where the people are very heavily infected with both Schistosoma haematobium and Schistosoma mansoni, but in many parts of the world, although children may be severely affected, the majority of adults develops some resistance to superinfection. Even more so than with hookworms it is the species and strain of schistosome which determines the clinical picture. Strains of S. japonicum nonpathogenic to man have been described by Hsu and Hsu (1956)) and marked biological and morphological differ-

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ETIOLOGY

ences exist with geographical strains of the other species of schistosomes. In schistosomiasis, as with most helminth infections, including hookworm, it is believed that the severity of the disease is related to the intensity of the infection, but few studies have been made correlating schistosome loads with clinical symptoms, particularly with anemia. The anemia in schistosome infections results from either blood loss and toxic manifestation in the early stages or to the development of hepatosplenic syndrome (pseudo-Banti) in the later stage of the infection. The schistosomes of importance in the etiology of anemia are S. mansoni, S. haematobium, and S. japonicum. The pseudo-Banti syndrome is most commonly associated with infections of S. mansoni and S. japonicum. The effect of S. haematobium is mainly due to blood loss from the bladder and chronic disturbances of the urogenital system, but when associatedwith S. mansoni, S. haematobium contributes to the development of the pseudo-Banti syndrome with its associated anemia. Anemia in the Early Stagesof Schistosomiasis Day (1921) and Hutchinson (1928) thought that schistoso’miasiswas the most common cause of anemia in Egypt, and Girges (1932, 1934) refers to schistosomal anemia as “youth’s insidious enemy.” More recent observations by Saif (1959) confirm that schistosomeinfections are still responsible for a great deal of anemia in Egypt. Workers in other parts of the world have also reported S. mansoni as a common cause of anemia (Molina and Pons, 1936; Janssen, 1948; Pessoa and Coutinho, 1952; Greany, 1952; Fraga de Azevedo, 1958; Nelson, 1958a,b; Jordan, 1961). Beet (1949) considered that S. haematobium was associated with anemia. Pesigan et al. (1951) reported that the hemoglobin levels in people infected with S. japonicum

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in the Phillipines were below normal, especially in children. The anemia in the initial stagesof schistosomiasisis believed to be iron deficient and due to blood loss. Consequently the factors which affect the relation between anemia and schistosomiasiswill generally be the same as those which operate with ancylostomiasis. The prevalence of schistosome anemia will depend upon such factors as loads and species of parasites, iron content of the diet, agricultural and social habits oi the population at risk, as well as such factors as climate and the presence and abundance of appropriate vectors. In areas where schistosomiasisis prevalent hookworms are also likely to be present and an anemia due to ancylostomiasis might easily be attributed to schistosomiasisor vice versa. There is still a conflict of opinion regarding the part that schistosomesplay in the etiology of anemia; this is mainly because the various factors affecting the correlation between the presence of schistosomes and anemia have not been clearly defined. Using Fe59, Gerritsen et al. (1954) found that the blood loss in the urine of adult Africans infected with S. haematobium was between 1.3 and 6.1 ml per diem. This was not considered sufficient to produce anemia, but it might contribute to an anemia from other causes. Growing children with an expanding blood volume who often have heavier infections may suffer more severely from anemia, especially in the early stages of the diseasewhen direct blood lossesare greater. Walker et al. (1954) found no significant blood loss in mine workers infected with S. mansoni. These studies were done on adults in South Africa where the iron intake is very high. Observations on heavily infected patients in countries where the iron intake is lower might produce different results. A reappraisal of this problem should be carried out in areas of varying endemicity, using

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techniques similar to those employed for hookworm studies. A great deal could also be learnt from a study of the anemia which is known to develop in monkeys experimentally infected with S. japonicum (Vogel and Minning, 1953). Anemia in the Late Stages of Schistosomiasis Enlargement of the liver and spleen has been reported as a common feature of S. mansoni infections (Day, 1921; Girges, 1932; Heisch, 1948; Janssen, 1948; Greany, 19.52; Pitchford, 1952; Nelson, 1958 a,b). In some areas a proportion of these cases develop what has been called “Egyptian splenomegaly,” pseudo-Banti, or the hepatosplenic syndrome-the most common and most serious complication of schistosomiasisalways associated with severe anemia in the late stages. A high incidence of Egyptian splenomegaly was reported in Egypt by Roger (1902) and Ferguso’n (1911). During the next 40 years there was a large and controversial literature dealing with the etiology of this condition; this has been extensively reviewed by Girges (1934) and Erfan (1947). The majority opinion was that both the splenomegaly and anemia were complications of schistosomiasis.Fairley ( 1951) suggested that malnutrition played a part in the etiology of hepato8splenomegaly. A similar hepatosplenomegaly associatedwith schistosomiasiswas seenin Nyasaland by Dye (1924)) in Kenya by Trim (1936), in Puerto Rico by Koppisch (1943), and by workers in South America, notably Da Silva (1949), Meira (1951)) and Dias (1952). Gelfand (1950) in Rhodesia and Nelson (1958a,b) in Uganda found that cirrhosis of the liver and splenomegaly were just as common in persons without schistosomiasisas in those with the infection. In these areas schistosomiasisis widespread but the parasites are either less pathogenic or the people are more resistant to the infections than in Egypt and South America,

NELSON

where gross splenomegaly and liver cirrhosis are common complications of schistosomiasis. Splenomegaly is very prevalent in the tropics. It is associated with malaria, kalaazar, and schistosomiasisas well as a number of other diseases;it is nearly always characterized by anemia. The mechanismsresponsible for the anemia of schistosomal splenomegaly are not fully understood; it has many features in common with the Banti syndrome. its differentiation from true Banti not always being easy. In schistosomiasisthere is a diffuse hy,perpIastic periportal cirrhosis of the liver resulting in progressive splenomegaly. The mechanismsof the production of these abnormalities has been described by Bogliolo (1957). The anemia may be moderate or severe, hemolytic, pancytopenic, or normocytic. Jaundice is uncommonand suggeststhat hemolysis is minimal. The part that the enlarged spleenand/or liver plays in the etiology of the anemia is obscure. No critical work has so far been carried out on the various types of hemolytic anemia that are so common in the tropics, and the part that the splenomegaly of schistosomiasisplays in the prevalence of this type of anemia has not been determined (Bergenheim and Fahraeus, 1936; Knisely, 1936a,b; Fahraeus, 1939; Mackenzie et al., 1940; Whipple, 1941; Dacie, 1954; Crosby, 1961). The late stages of S. haematobium infection are associated with disturbances of the urogenital tract, with chronic cystitis, hydronephrosis, pyelonephritis, and occasionally bladder cancer. All these conditions may be associated with anemia. Prates and Gillman (1959) and Trout et al. (1960) have shown that there is no excessive excretion of indolic compounds in schistosomiasisand conclude that they are not related to bladder cancer, which is common in patients with S. haematobium in Portuguese East Africa. Fripp in Uganda (1960) has found a positive correlation between the excretion of l3-glucuronidaseand the output of

HELMINTHS

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THE

S. haematobium eggs in the urine which disappears on treatment with “Nilodin.” The precise relation of these findings to tryptophan metabolism, anemia, and bladder cancer needs further investigation. It is clear that the anemias appearing in the late stages of schistosomiasis are of a complex nature, and not due entirely to direct blood loss, as in hookworm infection. In recent years there has been renewed interest in schistosomiasis, particular stress being given to field projects attempting to assess the morbidity due to the parasites. It is important in these projects to determine the relative importance of schistosomiasis as a cause of anemia. SUMMARYANDCONCLUSIONS

1. There is overwhelming evidence that the prevalent iron deficiency anemia in the tropics is usually associated with blood loss from infections by A. duodenale and/or N. americanus. Hookworms are among the most important causes of ill health in many underdeveloped countries and 460,000,OOO are said to be infected. 2. Using isotopic techniques it has been shown that blood losses in hookworm infections may be as much as 200 ml daily. The loss is due to bleeding from the intestine as the worms browse along the mucosa or as a result of blood being pumped through the worms as they feed. The loss is greater from A. duodenale than N. ame-ricanus and it is proportional to the number of parasites. 3. The amount of iron lost depends upon the volume of blood lost, but allowance has to be made for the low iron content of anemic blood. The severity of the anemia depends on the balance between iron intake and iron loss; if the intake is adequate anemia is unlikely to occur even with heavy worm burdens. 4. Calorically adequate tropical diets contain a sufficiency of iron, but they are usually bulky with a high content of phytates and

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255

phosphates which may interfere with iron absorption. Other factors which affect the iron balance, such as loss in sweat or in intestinal exudates and the effect of menstruation and pregnancy, must be considered when assessing the importance of hookworms as a cause of anemia. 5. There is always a close correlation between hookworm infections and anemia if the loads and species of parasites and the iron intake are taken into consideration. 6. Hookworms and the associated anemia are most prevalent in the less privileged groups of the community where insanitary and rural living conditions favor transmission. Diet, apart from the iron content, is of little significance in determining the severity of hypochromic anemia, and the total serum proteins are not reduced, the serum iron is low, and the unsaturated iron binding capacity is raised. 7. Hookworm anemia responds to oral iron even when the worms are left in the bowel and bleeding continues, but unless the worms are removed the anemia will recur once the iron is stopped. Effective treatment requires both iron and a vermifuge. 8. Prophylaxis should aim at preventing transmission by improved sanitation and the wearing of shoes, periodic vermifuges to reduce worm loads, and the addition of iron salts to some suitable article of diet. These measures are not easy to implement in the areas where they are most needed. 9. Less is known about the anemia in schistosomiasis than in ancylostomiasis, but S. mansoni, S. japonicum, and S. haematobium in the later stages of infection are responsible for certain types of anemia in the tropics and subtropics. In the early stages of these infections the combination of blood loss and toxemia results in a hypochromic anemia which is most prevalent in children. Since hookworms occur in most areas where schistosomiasis is common, it is difficult to assess the importance of the latter in the etiology

FOY

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AND

of the anemia. Anemia is a constant feature of the hepatosplenomegaly or pseudo-Banti syndrome, which are complications of S. mansoni and S. japonicum infections. 10. The hepatosplenomegaly is mainly the result of heavy infections but other factors such as the strains of the parasite and associated malnutrition play a part in the etiology. The anemia may be hypochromic, megaloblastic, or hemolytic; the hypersplenism often results in pancytopenia. Specific treatment or splenectomy may be effective if the cirrhosis is not too far advanced. It is suggested that the anemias in schistosomiasis should be studied using the techniques which have given such excellent results in hookworm anemia. REFERENCES AND RASOOL, G. 1959. Bephenium X., Hydroxynaphthoate against hookworm in West Pakistan. Journal of Tropical Medicine and Hygiene 62, 284. ALLISON, A. C., AND CLYDE, D. F. 1961a. Malaria in African children with deficient erythrocyte British gIucose-6-phosphate dehydrogenase. Medical Journal 1, 1346. ALLISON, A. C., CHARLES, L. J., AND MCGREGOR, I. A. 1961b. Erythrocyte G6PD deficiency in West Africa. Stature 190, 1198. APARCEDO, L., LAYRISSE, M., AND R~CHE, M. 1962. Further evidence for reabsorption of haemoglobin iron lost into the intestine in hookworm infected subjects. Proceedings of the Society for Experimental Biology and Medicine 110, 67. ASHFORD, B. K. 1900. Ancylostomiasis in Puerto Rico. New York Medical Journal 71. 552. AUGUSTINE, D. L., AND SMILLIE, W. G. 1926. The relation of the type of soils of Alabama to the distribution of hookworm disease. American Journal of Hygiene 6 (March Supplement), 36. AUSTRALIAN HEALTH DEPARTMENT. 1947. Report of New Guinea Nutrition Survey Expedition, Department of External Affairs, Canberra. AYKROYD, W. R., PATWARDHAN, V. N., AND RANGANATHAN, S. 1951. “The Nutritive Value of Indian Foods and the Planning of Satisfactory Diets.” Health Bull. No. 23, Govt. India Press. Simla. AZEVEDO, FIUIGA DE. 1958. Human bilharziasis in the British Cameroons. Bulletin of the World Health Organization 18, 1052. BEAVER, P. C. 1949. Quantitative hookworm diagAHMAD,

NELSON nosis by direct smear. Journal of Parasitology 36, 125. BEAVER, P. C. 1950. The standardization of fecai smears for estimating egg production and worm burden. Journal of Parasitology 36, 451. “Control of Soil-Transmitted BEAVER, P. C. 1961. Helminthic Diseases.” Conseil Scientifique Afrique/World Health Organisation, Brazzavflle. BEET, E. A. 1949. Observations on haemoglobin values in African children. Transactions of the Royal Society of Medicine and Hygiene 45, 317. BEET, E. A. 1951. Observations on African children. Archives of Disease in Childhood 26, 119. BERGENHELM, B., AND FAHRAEUS, R. 1936. Uber spontane Hemolysin-bildung im Blut, unter Besonderer Berucksichtigung der Physiologie der Milz. Ges. Exptl. Med. 97, 555. BEUTLER, E. 19.57. Iron enzymes in iron deficiency. American Journal of the Medical Sciences 234, 517. BEUTLER, E., AND BLAISDELL, R. K. 1958. Iron enzymes in iron deficiency. II. Catalase in human erythrocytes. Journal of Clinical Investigation 37, 833. BILRARZ, T. 1852. C. Th. v. Siebold. “Ein Beitrag zur Helminthographia humana, aus brief&hen Mittheilungen des Dr. Bilharz in Cairo, nebst Bemerkungen von Prof.” 2. Wissensch. 2001. Leipzig 4, 53. BOGLIOLO, L. 1957. Anatomical picture of the liver in hepatosplenic Schistosomiasis mansoni. Annals of Tropical Medicine and Parasitology 61, I. BONSDORFF, VON B., AND GORDIN, R. 1947. In which part of intestinal canal is fish tapeworm found. D. latunt and pernicious anaemia. Acta Medica Scandinavica 129, 142. BONSDORFF, VON B., AND GORDI.N, R. 19.52. Antianemic activity of dried fish tapeworm; D. latum and pernicious anaemia. Acta Medica Scandinavica 142, Supplement 226, 283. BONSDORFP, VON B. 1956. D. latum as a cause of pernicious anemia. Experimental Parasitology 5, 207. BOTHWELL, T. H., PIRZIO BIROLI, G., AND FINCH, C. A. 1958. Iron absorption. I. The Journal of Laboratory and Clinical Medicine 61, 24. BRANTE, G., AND ERNBERG, T. 1958. The mechanism of pernicious anaemia studied with CoSolabelled vitamin B/12. Acta Medica Scattdinavica 160, 91. BRUMPT, L. C., AND HO-THI-SANG. 1961. “Prophylaxis of Ankylostomiasis.” Commission pour la Cooperation Technique en Afrique/Conseil Scientifique Afrique/World Health Organisation, Brazzaville. Specialists Meeting on Ankylostomiasis.

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Commission pour la Cooperation Technique en Afrique/Conseil Scientifique Afrlque/World Health Organisation 1961. Specialists Meeting on Ankylostomiasis, Brazzavllle. CHANDLER, A. C. 1929. “Hookworm Disease.” MacMiin, New York. CHARMOT, G., AND REYNAUD, R. 1961. “Blood Disorders in Ankylostomiasis.” Conseil Scientifique Afrique/World Health Organisation. Brazzaville Specialists Meeting on Ankylostomiasis. CHEN, TA. 1940. “Emigrant Communities South China.” New York. CHERNIN, E. 1954. Problems in tropical public health among workers at a jute mill near Calcutta. American Journal of Tropical Medicine 3, 338. CORT, W. W., SCHAPIRO, L., SWEET, W. C., STOLL, N. R., AND RILEY, W. A. 1929. Hemoglobin levels in Panama as a measure of the intensity of hookworm infestations. American Journal of Hygiene (Monograph Series) 9, 139. CROSBY, W. H. 1961. Role of spleen in marrow function. Blood l9, 801. CULBERTSON, J. T. 1941. “Immunity Against

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Animal Agents.” Columbia Univ. Press, New York. DACIE, J. V. 1954. “The Haemolytic Anaemias.” Churchill, London. DAFFAY, V. G., AND BHENDE, Y. M. 1937. i\nemia in ankylostomiasis. Blood l9, 1143. DARLING, S. T., BARBER, M. A., AND HACKER, H. P. and Malaria Research in 1920. “Hookworm Malaya, Java, and the Fiji Islands.” Rockefeller Foundation, International Health Board, Publ. No. 9, 191. Report of Uncinariasis Commission to the Orient. DA SILVA, C. T. 1949. “Estudo clinic0 da Esquistossomose Mansoni.” Laeiment Rio de Janeiro. DAY, H. B. 1921. The out-patient treatment of bilharziasis. Lancet 1, 525. DEMULLIER, R. 1958. Iron. Archives of Internal Medicine 102, 254. DIAS, C. B. 1952. “A Sindrome Hepatico-explenica na Esquistossomiase Mansonica.” Belo Horizonte, p. 449 (Tese). DICK, G. W. A., AND MCCARTHEY, D. D. 1946. The absence of anemia in hookworm infestation in E. African personnel. East African Medical Journal 29, 19. Dow, C., JARRETT, WFH., JENNINGS, F. W., MCINTYRE, W. I. M., AND MULLIGAN, W. 1959. Production of active immunity against canine hookworm uncinaria stenocephala. American Vet. Medical

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Journal of the Royal Army Medical Corps 43, 161. EDITORIAL, 1953. Schistosomiasis. Journal of Tropical Medicine and Hygiene 66, 73. EGYPTIAN MINISTRY OF HEALTH (CAIRO). 1959.

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R. 1939. The erythrocytes plasma interface. Lancet 9, 630. FAIRLEY, N. H. 1951. Schistosomiasis and some of its problems. Transactions of the Royal Society of Tropical Medicine FERGUSON, A. R. 1911.

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Associated bilharziasis and primary malignant disease of the urinary bladder. Journal of Pathology and Bacteriology 16, 76. FONSECA, L. C. 1948. Dietary deficiency in the Pathogenisis of hookworm anaemia. Hospital, 33, 559. FORDE TREDRE, R. 1948. “The Health of the East African Worker with Particular Reference to the Sisal Industry.” Ross Institute Report. London School of Hygiene and Tropical Medicine. FOY, H., KONDI, A., AND HARGREAVES, A. 1952. Anaemias of Africans. TraNsactions of tke Royal Society of Tropical Medicine and Hygiene 48, 327. FOY, H., KONDI, A., TINIMS, G. L., BRASS, W., AND BUSRP.A, F. 1954. The variability of sicklecell rates in the tribes of Kenya and the southern Sudan. British Medical Journal 1, 294. FOY, H., BRASS, W., MOORE, R. A,, Tmaas, G. L., KONDI, A., AND OLUOCR, T. 1955. Two surveys to investigate the relation of sickle-cell trait and malaria. British Medical Journal 2, 1116. FOY, H., AND KONDI, A. 1957. Anaemias of the tropics. Journal of Tropical Medicine and HyFOY,

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