Anemia and malaria at different altitudes in the western highlands of Kenya

Acta Tropica 91 (2004) 167–175

Anemia and malaria at different altitudes in the western highlands of Kenya Willis S. Akhwale a,c , J. Koji Lum a,1 , Akira Kaneko a,b,∗,1 , Hideaki Eto a , Charles Obonyo d , Anders Björkman b , Takatoshi Kobayakawa a a

b

Department of International Affairs and Tropical Medicine, Tokyo Women’s Medical University, 8-1 Kawada-Cho, Shinjuku-Ku, Tokyo 162 8666, Japan Malaria Research Laboratory, Unit of Infectious Diseases, Karolinska Hospital, Stockholm, Sweden c Kisii District Hospital, Kisii, Kenya d Kenya Medical Research Institute, Kisumu, Kenya

Received 15 March 2003; received in revised form 11 November 2003; accepted 3 February 2004 Available online 1 June 2004

Abstract Malaria associated severe anemia in children is the most important complication of Plasmodium falciparum infection in sub-Saharan Africa. To evaluate anemia and malaria in an area with recurrent malaria epidemics in the western highlands of Kenya, we conducted cross-sectional surveys in four “lowland” (1440–1660 m) and two “highland” (1960 and 2040 m) villages in 2002. Among 1314 subjects randomly selected from all age groups, the overall prevalence of anemia (hemoglobin, Hb < 11 g/dl) was 14% and P. falciparum infection 17%. In children ≤5 years, anemia prevalence ranged from 57% at 1440 m to 11% at 2040 m and correlated with altitude (r = −0.88, P < 0.05). Similarly, P. falciparum prevalence ranged from 31 to 0% and correlated with altitude (r = −0.93, P < 0.01). Malnutrition defined by a body mass index <15th percentile characterized 39% of the population and the hookworm prevalence was 3.9%. In the lowland villages, anemia was most common in children ≤5 years of age (34%) followed by women of childbearing age (16%). A similar pattern was also observed in the highland villages. In these vulnerable populations, hemoglobin concentration was significantly associated with malaria infection, but not with malnutrition or hookworm infestation and comparisons of anemia prevalence between highland and lowland villages revealed that two-thirds of anemia could be attributed to malaria infection. The prevalence of severe anemia (Hb < 8 g/dl) was 1.5%; of these, 90% resided in lowland villages, 70% were under-fives, while 20% were women of childbearing age. In severely anemic subjects, the Hb concentration decreased further with malnutrition (P < 0.05). Anemia was more prevalent in the lowland villages characterized by high prevalence of P. falciparum infection. We conclude that malaria may also be the main cause of anemia in the highland fringe areas of sub-Saharan Africa. Measures that reduce the prevalence of malaria will consequently reduce anemia in both, young children and adult women and the need for blood transfusions associated with the risk of HIV-transmission. © 2004 Elsevier B.V. All rights reserved. Keywords: Plasmodium falciparum; Anemia; Malaria epidemics; Malnutrition; Hookworm; Highland fringe; Kenya

∗

Corresponding author. Tel.: +81-3-5269-7422; fax: +81-3-5269-7422. E-mail address: [email protected] (A. Kaneko). 1 These authors contributed equally to this work.

0001-706X/$ – see front matter © 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.actatropica.2004.02.010

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1. Introduction Anemia is a common and potentially serious condition encountered in many countries of sub-Saharan Africa (Nussenblatt and Semba, 2002). About three quarters of children less than 5 years of age in eastern Africa suffer from anemia defined by hemoglobin (Hb) concentrations below 11 g/dl of blood (DeMaeyer and Adiels-Tegman, 1985). Malaria is the predominant cause of both acute and chronic anemia (Ekvall et al., 2001), but malnutrition and micronutrient deficiencies are also involved in the pathogenesis of anemia and severe malaria (Snow et al., 1991; Shankar, 2000; Nacher et al., 2001). Severe anemia is the most common in small children 6–24 months old, but is also found in pregnant women (Lackritz et al., 1997). In pregnancy, iron deficiency is thought to be the main cause of anemia but malaria may also contribute (Brabin et al., 1990). Severe anemia has been shown to be responsible for 11–13% of maternal deaths (Shulman et al., 1999). The most common treatment of severe anemia in Kenyan hospitals is blood transfusion, and although this may decrease short-term mortality, the risk of HIV-transmission is considerable (Obonyo et al., 1998). Previous studies on anemia in Kenya have been conducted in areas with stable malaria endemicity (Zucker et al., 1994; Newton et al., 1997; Lackritz et al., 1997; Brooker et al., 1999) with Plasmodium falciparum malaria identified as the main cause of anemia. However, anemia and its potential causes have been much less investigated in areas with unstable and epidemic malaria such as the highlands of western Kenya. We therefore conducted cross-sectional surveys of anemia, nutrition, and malaria in villages at different altitudes at Kisii District in the western highlands of Kenya.

2. Materials and methods

area is densely populated with 700 people/km2 (CBS, 2001). Kisii district receives moderate to heavy rainfall through the year that peaks from March to June and is associated with increased malaria transmission by Anopheles gambiae (Malakooti et al., 1998; Hay et al., 2002). Subsistence farming, tea cultivation, and livestock rearing are the main economic activities. The Kisii District Hospital located at an altitude of 1660 m serves as the principal health institution of the district. From 1992 to 2001 there were 106,784 patients admitted to the hospital with a discharge diagnosis of malaria, 3.8% of whom died during hospitalization. From 1998 to 2001, 35% of 50,350 in-patients received blood transfusions. The malaria admission peak (17,000) in 1998 was followed by peaks in case fatality (5.5%) and blood transfusion (43%) rates in 1999 (W.S. Akhwale, unpublished data). The six villages selected for cross-sectional studies are located within the hospital catchment area at altitudes ranging from 1440 to 2040 m. The four between 1440 and 1660 m are referred to as “lowland” villages, while the two at 1960 and 2040 m are “highland” villages. Lowland Riana and Marani, and highland Masimba villages are located close to public health centres, while lowland Mosocho and Nyagoto, and highland Ramasha villages are more than 5 km from the nearest health centre. 2.2. Cross-sectional surveys In January and February 2002, we conducted cross-sectional surveys among all age groups in the four lowland and the two highland villages. In addition to malariometric indices, hemoglobin concentrations, stool parasitological profiles, and anthropometric measurements were obtained. Blood was taken by finger prick for microscopic examination of malaria and Hb measurement.

2.1. Study area

2.3. Malariometric indices

Kisii District is located at the southern end of the western Kenyan highlands at altitudes ranging from 1400 to 2200 m above sea level. This hilly area borders a lowland holoendemic malaria region to the west that extends to the shores of Lake Victoria. The

The spleen size of each subject was assessed in the recumbent position according to Hackett’s method by a single investigator. Microscopic examination of malaria was made from thick and thin blood smears stained with 10% Giemsa. Parasite density was esti-

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mated by counting asexual malaria parasites against 200 leukocytes in a thick film assuming a leukocyte count of 8000 ␮l−1 of blood. Body temperature was recorded using a digital ear-thermometer (Matsushita, Japan). All parasite positive cases were treated with sulfadoxine/pyrimethamine combination in accordance with the national guidelines. 2.4. Hb concentrations Hb concentration of peripheral blood was measured on the spot using a hemoglobinometer (HemoCue AB, Sweden) according to the product instruction. Although the World Health Organization (WHO) proposed levels of Hb concentrations for different groups of individuals that could be considered as the lower limits of normality, such a definition of anemia involves the adoption of rather arbitrary criteria (Weatherall, 1996). On the one hand, malaria-related anemia is defined as anemia (Hb < 11 g/dl) in the presence of malaria parasitaemia of any density in endemic areas (Menendez et al., 2000). In this paper, anemia is referred to as Hb concentration less than 11 g/dl and severe anemia as Hb less than 8 g/dl (Verhoef et al., 2001). This definition of anemia may be rather conservative for adult males. 2.5. Stool parasitological profiles Each study subject was given a plastic stool container and asked to return an approximately bean-sized stool sample within the following 24 h. The samples obtained were examined for ova of intestinal helminthes using formalin-ethyl acetate sedimentation method (Truant et al., 1981). 2.6. Anthropometric measurements Heights were measured using a purpose-built board, while those of children less than 2 years old were measured in a recumbent position. Weights were measured using a digital scale (Matsushita, Japan), while those of infants were measured with a spring balance (Salter, UK). Malnutrition was defined as a body mass index (BMI) below the 15th percentile corrected for age, sex, and race (Frisancho, 1988; Van der Sande et al., 2001).

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2.7. Data analysis Standard statistical methods were used including the G-test for homogeneity for comparison of binary variables among age groups and villages. ANOVA was used for comparisons of continuous variables among individuals and linear regression was used for continuous variables among groups (Sokal and Rohlf, 2000). P < 0.05 was considered statistically significant. 2.8. Ethical considerations The study was approved by the Ministries of Health and Education in Kenya, and the ethics committee of Tokyo Women’s Medical University. Survey subjects were briefed on purposes and procedures of the study prior to the surveys and a written informed consent was obtained from each adult subject, while in the case of children a written informed consent by their guardian determined the child’s participation.

3. Results 3.1. Malaria prevalence A total of 1314 survey subjects were randomly selected from six villages; of whom, 414 were ≤5 years, 404 (6–15 years), 294 (16–30 years), and 202 were >30 years of age. Table 1 shows the prevalences of anemia, malaria, hookworm infestation, and malnutrition among all age groups and Fig. 1 shows anemia and P. falciparum prevalences in children ≤5 years within villages by altitude. The overall parasite and spleen rates were 18 and 16%, respectively. The prevalences of P. falciparum and Plasmodium malariae were 17 and 0.6%, respectively. No case of Plasmodium ovale was detected. There were four cases (1.8%) of mixed infections of P. falciparum and P. malariae. The overall prevalences of P. falciparum malaria and enlarged spleen were significantly higher in the lowland villages (24 and 23%, respectively) than in the highland villages (2 and 1%, respectively) (P < 0.001, Table 1). The prevalence of P. falciparum in children ≤5 years of age was significantly correlated with altitude (Fig. 1).

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Table 1 Anemia, malaria, hookworm, and malnutrition prevalences by altitude within villages of Kisii District, January 2002 Village

Altitude (m)

All (n)

≤5 years (n)

Anemiaa (%)

Severe anemiab (%)

P. falciparum (%)

Spleenc (%)

Hookworm (%)

Malnutritiond (%)

Riana Mosocho Marani Nyagoto Masimba Ramasha

1440 1510 1600 1660 1960 2040

200 219 202 300 201 192

68 35 114 65 76 56

31 14 19 8 7 7

5.5 1.4 1.0 0.7 0.5 0.5

22 31 25 18 1 3

47 23 20 31 3 0

2.8 7.1 2.4 5.0 2.6 1.6

46 34 39 39 44 29

a b c d

Hb < 11 g/dl. Hb < 8 g/dl. Enlarged spleens in children 2–12 years. BMI < 15th percentile.

3.2. Malnutrition and hookworm

3.3. Anemia prevalence by altitude, age, and sex

In 39% of the study population, the BMI was below the 15th percentile indicating malnutrition (Van der Sande et al., 2001; Frisancho, 1988). We obtained stool samples from 796 subjects: 184 subjects were ≤5 years of age, 288 subjects were 6–15 years of age, and 324 subjects were >15 years of age. The prevalences of Ascaris lumbricoides, hookworm, and Trichuris trichuri were 10, 4, and 0.1%, respectively. Although the prevalences of A. lumbricoides decreased with age; 15% (≤5 years), 12% (6–15 years), and 6.8% (>15 years), those of hookworm were not significantly different between age groups. The overall prevalences of malnutrition and hookworm infection did not correlate significantly with altitude (Table 1).

Among a total of 1314 study subjects, 181 (14%) had anemia (Hb < 11 g/dl). The overall prevalence of anemia was higher in the lowland villages (18%) than in the highland villages (7.1%) (P < 0.001, Table 1). The prevalence of anemia in children ≤5 years of age was significantly correlated with altitude (Fig. 1); however, when this correlation was controlled for P. falciparum infection, it was no longer significant. Proximity to a health facility was not associated with the prevalence of anemia (P > 0.05). Table 2 shows prevalences of anemia, P. falciparum infection, and malnutrition by age and sex in the pooled lowland villages. In lowland villages, anemia prevalence varied significantly among age and sex groups (P < 0.01). It was highest in children ≤5 years old (34%) and lowest in young adults 11–15 years old (2.5%). In under-fives, anemia was more prevalent in boys (40% versus 28%, P < 0.05), whereas in adults aged 16–30 years anemia was more common in females (14% versus 1.6%, P < 0.001). The P. falciparum infection rate was highest in children below 10 years (30%) and decreased with age without any significant difference between sexes. The malnutrition rate was highest in males >30 years (61%) and lowest in females aged 16–30 years (20%). Fig. 2 shows age-related anemia and P. falciparum infection rates in the highland villages in comparison with those in the lowland villages. In the highland villages, as in the lowland villages, anemia prevalence was highest in small children ≤5 years of age (12%). In highland villages, anemia prevalence was not significantly different between males and females in the

60

Anemia P. falciparum

Prevalence (%)

50 40 30

(r= -0.88, P<0.03)

20 10

(r= -0.93,P<0.08)

0 1400 1500 1600 1700 1800 1900

2000 2100

Altitude (meter)

Fig. 1. Prevalences of anemia (Hb < 11 g/dl) and P. falciparum in children ≤5 years of age by altitude in Kisii District of the highland fringe of Kenya, January 2002. Also shown are the regression lines.

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Table 2 Anemia, P. falciparum, and malnutrition prevalences by age and sex in the lowland villages (1440–1660 m), Kisii District, 2002 Age (years)

0–5 6–10 11–15 16–30 >30 a b

Anemiaa (%)

n (m:f)

282 158 120 193 168

(151:131) (84:74) (79:41) (61:132) (67:101)

P. falciparum (%)

Malnutririonb (%)

Male

Female

Male

Female

Male

Female

40 13 3 2 10

28 12 2 14 18

31 31 25 15 15

26 34 22 19 12

44 41 47 38 61

34 43 34 20 48

Hb < 11 g/dl. BMI < 15th percentile.

three age groups shown in Fig. 2, but in adults aged 16–30 years the trend was that it was higher in females (5.3%) than in males (0%), similar to lowland villages. In the highland villages, the P. falciparum infection rate was highest in males >15 years of age.

tration in both lowland and highland villages. In lowland villages, there were also significant associations between Hb concentration and spleen size (all ages), parasite density (0–10 years), and also body mass index (males >30 years).

3.4. Factors influencing Hb concentrations

3.5. Severe anemia

Table 3 shows results of linear regression analysis for factors influencing Hb concentrations in individuals and age is a significant predictor of Hb concen-

Among the 20 subjects with severe anemia, 14 were children aged ≤5 years and 4 were women in childbearing age. Furthermore, 14 of these subjects had

Lowland males

Lowland females Highland females

Highland males

P. falciparum

45

45

40

40

35

35

prevalence (%)

Prevalence (%)

Anemia (Hb<11g/dl)

30 25 20 15

25 20 15

10

10

5

5 0

0 0-5

(A)

30

6--15

Age (years)

0-5

16+

(B)

6--15

16+

Age (years)

Fig. 2. (A) Anemia (Hb < 11 g/dl) and (B) P. falciparum prevalences by age and sex: lowland (1440–1660 m, malaria mesoendemic) vs. highland (1960–2040 m, malaria hypoendemic) villages in Kisii District, 2002.

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Table 3 Variables identified by linear regression analysis that were significant contributors to low Hb concentrations in lowland and highland villages Independent variable

Age (years) Spleen size log10 (PD + 1) Body mass index Hookworm

Lowland villages

Highland villages

P

R

Age group

P

R

Age group

<0.001 <0.001 <0.001 <0.001 NS

0.35 0.04 0.07 0.13

0–15 years All ages 0–10 years Males >30 years

<0.001 NS NS NS NS

0.31

0–15 years

R : proportion of variance due to the factor. PD + 1: parasite density per microliter of blood +1.

either P. falciparum infection or enlarged spleen, or both and 18 resided in the lowland villages. In these subjects, hemoglobin concentrations significantly correlated with the BMI percentile (r = 0.48, P < 0.05).

4. Discussion 4.1. Malaria epidemics The records from Kisii District Hospital reflected the malaria epidemics of 1998/1999 in the highland fringe of western Kenya. Shretta et al. (2000) reported that the epidemics of 1998/1999 were accompanied by widespread chloroquine treatment failure, as Kenya was implementing a change of first-line treatment policy from chloroquine to sulfadoxine/pyrimethamine. Malarial anemia has been attributed to chloroquine resistant P. falciparum infections (Lackritz et al., 1997; Weber et al., 1997; Ekvall et al., 1998). Blood transfusion is the principal treatment for severe malarial anemia; hence the remarkably high-blood transfusion rate (35%) among in-patients at Kisii District Hospital during the malaria epidemics in 1998/1999 clearly highlights the potential of transmitting other disease pathogens including HIV and hepatitis. 4.2. Anemia and malaria We observed that the P. falcpiparum prevalence varied among villages of Kisii district, decreasing with increasing altitude from 1440 to 2040 m. The malaria prevalence was about 10 times greater in the lowland villages than in highland villages. Our

observations of malaria epidemics and geographic variation along with seasonal variations previously observed by Malakooti et al. (1998) highlights the unstable nature of malaria in the highland fringe areas of western Kenya. The prevalence of anemia also varied with altitude and among the under-fives it increased over five-fold from the village at highest altitude to that at the lowest altitude. In general the lower a village’s altitude is, the higher its malaria and anemia prevalence. Ellman et al. (1998) reported a similar relationship in Tanzanian villages located between 900 and 1200 m, where the prevalence of severe anemia ranged from 2.4 to 15% and parasite rates from 33 to 84%. The same authors also showed that a 1000 m rise in altitude has no direct physiologic effect on Hb level. These observations suggest that malaria may also be the most important cause of anemia in highland fringe areas in sub-Saharan Africa. 4.3. Vulnerable groups Children ≤5 years of age and adult women of childbearing age residing in the lowland villages were most vulnerable to anemia. Comparisons of anemia in children aged ≤5 years in lowland (34%) and highland (12%) villages suggested that about two-thirds of childhood anemia in the lowland villages can be attributed to malaria. We observed the prevalence of anemia decreased with age and was lowest at puberty, supporting the views that the association between young age and anemia could be due to age-related differences of cumulative malaria exposure leading to acquisition of immunity to malaria (Marsh and Snow, 1997). On the other hand, a similar cline was observed

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in the highland villages with malaria hypoendemicity. This may be due to age-related maturation of the immune system that favor higher Hb concentrations at puberty, independent of cumulative exposure of malaria infections (Baird, 1998; Kurtis et al., 2001). In children aged ≤5 years residing in the lowland villages with malaria mesoendemicity, anemia affected more males than females for as yet unclear reasons. A similar observation was made in malaria endemic regions of Malawi and Ghana (Brabin et al., 2001; Owusu-Agyei et al., 2002) and thus, the sex differences in childhood anemia presents a potential area for further studies. The higher prevalence of anemia among women 16–30 years compared to males in both lowland and highland villages indicates that the nutritional demands of menstruation, pregnancy, and lactation contribute to anemia in this group. Comparison of anemia prevalence between women 16–30 years of age residing in the lowland villages (14%) and those in the highland villages (5.3%) indicates that P. falciparum malaria exacerbates intrinsic anemia in women of childbearing age at about the same rate as observed in childhood anemia and explains almost two-thirds of it. 4.4. Predictors of Hb concentration Both age and malaria infections were important predictors of Hb concentration. In the lowland villages, we observed significant associations between Hb concentration and parasite density (children) and splenomegaly (all age groups). Splenomegaly may thus prove useful in screening for anemia especially in semi-immune populations. In contrast, nutritional status as indicated by BMI and hookworm infection did not contribute significantly to variations in Hb in the vulnerable populations. 4.5. Adult males In males >30 years of age in the lowland villages, we observed the highest malnutrition rate and a significant association between Hb concentration and BMI. Health-related factors other than malaria infection such as HIV/AIDS, tuberculosis, and liver diseases may be involved, but the importance of a past history of malaria cannot be excluded.

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We observed a relatively high P. falciparum infection rate in highland males aged >15 years (Fig. 2). This pattern is consistent with views of minimal indigenous transmission in highland villages, and adult male acquisition of malaria during socio-economic activities in the lowland villages. A similar pattern was observed in Rwanda and Burundi where adult males residing in highland homes were at greater risk for malaria because they travelled most often to endemic areas (Gascon et al., 1988; Van der Stuyft et al., 1993). Future studies including entomological surveys are necessary to clarify the human and vector contact related to malaria transmission in the highlands of Kisii district. 4.6. Severe anemia Although as mentioned above, malnutrition in the vulnerable population was not a significant contributor to anemia, subjects with severe anemia had significantly lower Hb concentrations when they were undernourished, compatible with previous studies which describe a complex cyclical interplay between malnutrition, anemia, and malaria (Fleming and Werblinska, 1982; Nacher et al., 2001; Shankar, 2000; Verhoef et al., 2001). Poor nutrition may predispose children to malaria infections and thus anemia by impairing the immune function (McGregor et al., 1983). Since malnutrition and micronutrient deficiencies are common in many regions where malaria is endemic (Nussenblatt and Semba, 2002), further research is needed to elucidate the role of malnutrition on malaria and anemia. 4.7. Conclusion The higher prevalence of anemia in areas of higher malaria endemicity in this study and the association between severe anemia and malnutrition underscores the need to devise control strategies that address both malaria and malnutrition. Comparisons between the highland and lowland villages suggest that reducing exposure to malaria infection may reduce the prevalence of anemia in both, young children and adult women by two-thirds. Overall an effective malaria control program ought to lead to a reduction in the prevalence of anemia and hence the incidence of severe anemia and the need for blood transfusions.

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Acknowledgements We thank the people of Kisii District, who participated in the study and the staff of the Ministry of Health at the Kisii District Hospital, who assisted in the surveys. We particularly appreciate the work by James Omambia in compiling hospital data, Håkan Ekvall and Hee I.L. Lee for comments on the manuscript. The 1998 surveys were conducted as part of the development study in Kenya by Japan International Co-operation Agency (JICA). W.S.A. was a research fellow under JICA long-term training program. This study was supported in part by a grant-in-aid for scientific research (13576030, 14570224) from the Ministry of Education, Culture, Sports, Science, and Technology of Japan and by grant for international health research from the Ministry of Health and Labour of Japan, Tokyo, Japan.

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