Influence of Environment on Clinical Trachoma in Saudi Arabia

INFLUENCE OE ENVIRONMENT ON CLINICAL IN SAUDI ARABIA A R T H U R A.

BOBB, J R . , M.D.

AND ROGER L.

TRACHOMA

NICHOLS,

M.D.

Boston, Massachusetts A previously published survey of tracho­ ma in over 3,000 young subjects in the Eastern Province of Saudi Arabia demon­ strated highly significant differences in the incidence of trachoma between adjacent communities. 1 T h e Third Report of the W H O E x p e r t Committee on Trachoma also emphasized that marked differences may occur in the general level of severity of trachoma and in the incidence and distribu­ tion of disabling complications and sequelae, between one area and another, and some­ times between neighboring districts. These differences were thought to depend largely on the type and distribution of associated in­ fections of the conjunctiva.Detels, Alexander and Dhir 3 compared the clinical prevalence and sequelae in tra­ choma occurring in genetically similar pop­ ulations of Indians in the Punjab and in British Columbia, Canada. They concluded that environment is the main cause of the differences found in trachoma in these In­ dian subjects. T h e data led these authors to affirm that trachoma in persons over 20 years of age remained subject to environ­ mental influences; an adverse environment after that age appeared to lead to trachoma of increased gravity. Decreased opportunity for reinfection with trachoma in British Co­ lumbia was thought to be one of the princi­ pal factors which permitted active trachoma to subside into inactive trachoma without sequelae. Mann,* in her extensive surveys in westFrom the Medical Department, Arabian Ameri­ can Oil Company, Dhahran, Saudi Arabia and the Department of Microbiology, Harvard University School of Public Health. This study was supported by the Arabian American Oil Company and by USPHS General Research Grant FR-S446-04 and USPHS Research Grant AI-06251-02 from the National Institute of Allergy and Infectious Dis-

ern and northern Australia, Papua, and New Guinea, found that trachoma may vary re­ markably within a short distance and may show specific peculiarities within a given vil­ lage. There was no correlation between prev­ alence of the disease and degree of visual impairment. The longer trachoma had been endemic in a region the earlier the age at which the disease first appeared. T h e more recent the appearance of trachoma in a com­ munity, the milder clinical course the disease seemed to take. I n our previous microbiologie studies, 1 prevalence rates of trachoma inclusions in Arabian children, with ages ranging from a few days to 4 years, varied to a statistically significant degree with the socioeconomic environments of the subjects. Children living in relatively modern surroundings (townsites) were found to have inclusion positivity rates never exceeding 5% ; children of the same age in less adequate environments (oases) had inclusion positivity rates ap­ proaching 5 0 % . These differences, together with other microbiologie and clinical varia­ tions found in oasis and townsite groups, led us to study the clinical aspects of trachoma in older subjects in these two areas. In comparing townsite versus oasis villages, we were fortunate to find a situa­ tion in which many of the epidemiologic variables alleged to influence trachoma— race, cultural patterns, climate, geographical separation, nutrition, extrinsic contacts— were minimized or eliminated. W e present here clinical data on trachoma in subjects from neighboring communities in Saudi Arabia. Marked contrasts in trachoma were found in these adjacent populations. T h e clinical data reported are from older children living in a townsite or in the Qatif oasis (both surveyed in the previous microbiologic s t u d y ) , and in a third oasis village, 235

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al-Hasa, all in the Eastern Province of Saudi Arabia. This paper is part of a con­ tinuing study which seeks to determine the epidemiologic factors influencing trachoma in Saudi Arabia. MATERIALS AND METHODS

The study was designed to examine the effect of socioeconomic conditions upon the clinical course of trachoma. Therefore indi­ viduals were accepted for examination only if they had lived their entire lives in either the townsite or in the oasis milieu; persons with mixed environmental background were excluded from the study. Only school children were examined. To control the selection of subjects, all students with appropriate environmental background in a given class were examined. The stu­ dents were selected for age by accepting or rejecting entire classes, not individuals. Since the townsites had been in existence less then 20 years, this age represented the

FEBRUARY, 1969

upper limit of the study and older sections of the populace were not examined. Ages ranged from 5 to 19 years ; mean ages were 9.3, 10.0 and 10.4 years in the townsite, Qatif and al-Hasa oases respectively. Twenty-one boys and 32 girls were exam­ ined in the townsite or Qatif oasis, respec­ tively; mean ages of these two groups were 9.6 and 9 years. Ophthalmologic findings among girls did not differ markedly from those among the boys and the data from both sexes were considered together. The socioeconomic environments in the modern townsites and the traditional villages in the oases of the Eastern Province of Saudi Arabia have been described in pre­ vious reports. 1 ' 5 - 6 Persons living in the townsite had the advantage of relatively modern homes with electricity and running water (fig. 1). Sewage and garbage disposal were enforced. Window screens were used and fly counts were comparatively low. Farm animals were infrequently seen within

'>%■■'■ v.;

Fig. 1. (Bobb and Nichols). A townsite village in Saudi Arabia.

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Fig. 2 (Bobb and Nichols). An oasis village in Saudi Arabia.

the courtyard. The average number of occu­ pants of each house was approximately six. Seventy-seven percent of those living in the townsite were families of employees of the Arabian American Oil Company (Aramco) ; as such they were entitled to free modern medical care. In contrast the homes in the oasis were more crowded, with an average occupancy of nine persons. The construction was of baked mud and stone, or of palm fronds (fig. 2). Public sanitation was inadequate. Electricity and running water were rarely available. Fly counts were high. Farm animals were fre­ quently kept in the homes. Only 19% of these oases dwellers were families of Aramco em­ ployees; the remainder were constrained to use local medical facilities, which were less adequate. The physical environments of the subjects living in these two areas, although in sharp contrast, were perhaps less important than other aspects of their way of life. In general the heads of households in the townsites had

a higher level of income and a better educa­ tional background. Families of employees of Aramco were exposed to specific health edu­ cation regarding personal, family, and com­ munity hygiene, including eye care. Geographically, the townsite and Qatif oasis villages were separated by less than 10 miles ; al-Hasa, an oasis with living condi­ tions similar to those in the Qatif oasis, was 80 miles distant. All inhabitants were Mos­ lem ; the Qatif oasis was composed of the Shia sect whereas the townsite and al-Hasa oasis were predominantly Sunni. Ethnically the subjects were thought to be similar. All shared the same climate. The numbers of subjects examined in townsites, Qatif or alHasa oases were 176, 207 and 53 respec­ tively. It was not possible to control the study so that the examiner was unaware of the village of origin of the subjects. We believe the prejudice thus introduced to the study is small. The examination was carried out with the

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Haag-Streit slitlamp 900. The power source was a 6-volt storage battery in the oasis and a transformer in the townsite. The examina­ tion of every subject included the eyelid margins, the palpebral and bulbar conjunc­ tiva, the corneoscleral limbus and the cornea. The examination technique consisted of dif­ fuse illumination, sclerotic scatter, direct focal illumination and examination by retroillumination. The magnification used was usually 10X followed by 16X ; higher mag­ nifications were used only occasionally. The following trachoma lesions were re­ corded in detail : 1. Follicles were seen mainly in the palpe­ bral conjunctiva, frequently at the corneo­ scleral limbus and occasionally in the bulbar conjunctiva. Follicles were scored from 1 + to 3 + , depending on the amount of con­ junctiva involved. 2. In the palpebral conjunctiva, papillae were seen which appeared as closely packed elevations, each with a central capillary. 3. Cicatrization was graded from 1 + to 3 + on the basis of amount of conjunctiva involved. The biomicroscope usually was not needed to see the sequelae of entropion, trichiasis and contraction of the fornices. 4. Keratopathy was noted as superficial punctate lesions of the epithelium, subepithelial infiltrates and pannus. With the biomicroscope the examiner was able to determine if the pannus was active or inactive. The limbal border was identified with the slitlamp in several ways: (a) identification in the focal beam of the corneal border of the lim­

FEBRUARY, 1969

bal opacity which appeared as a serrated line,7 (b) identification in the focal beam of the change from limbal to corneal curva­ ture,8 and (c) determination of the position of the recurrent vessels which bend in the middle one-third of the corneoscleral limbus. Neovascularization was affirmed if the length of the vessel below the loop of the re­ current vessel was twice that of the portion of the corneoscleral limbus situated between the scierai border and the loops, and could be presumed if these two lengths were equal. Although an attempt was made to use all three methods for identification of the corne­ oscleral limbus, for practical purposes the recognition of the end of the limbal opacity was the most useful. The corneal infiltration and neovascularization were each recorded in millimeters of extension below the limbal opacity of the upper corneoscleral limbus. RESULTS

When subjects with diagnoses of active clinical trachoma were combined with sub­ jects with healed clinical trachoma, point prevalence rates were 93%, 98% and 100% in the townsite, Qatif oasis, or al-Hasa oasis respectively (table 1). Thus nearly all sub­ jects in this study had clinical stigmata of trachoma, active or healed. Statistically, these rates were significantly different only between the townsite and Qatif oasis popula­ tions. Greater disparities were found in point prevalence rates of active clinical trachoma. Only 3 % of the sample in the townsite had

TABLE 1 POINT P R E V A L E N C E RATES O F ACTIVE P L U S H E A L E D CLINICAL TRACHOMA IN S U B J E C T S LIVING IN MODERN H O U S I N G ( T O W N S I T E ) CONTRASTED W I T H T H O S E F O U N D I N S U B J E C T S L I V I N G I N TRADITIONAL HOMES IN OASES VILLAGES IN S A U D I A R A B I A

Village

No. Examined

Subjects With Active or Healed Clinical Trachoma No. %

Townsite

176

163

93

Qatif oasis

207

202

98

53

53

100

Al-Hasa oasis

Statistical Significance Townsite vs. Qatif X 2 = 4.20, n = l, p= <0.05 Qatif vs. al-Hasa Not significantly different Townsite vs. al-Hasa Not significantly different

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TRACHOMA IN SAUDI ARABIA TABLE 2

POINT PREVALENCE OF ACTIVE CLINICAL TRACHOMA IN SUBJECTS LIVING IN MODERN HOUSING (TOWNSITE) CONTRASTED WITH THAT FOUND IN SUBJECTS LIVING IN TRADITIONAL HOMES IN OASES VILLAGES IN SAUDI ARABIA

Village

No. Examined

Subjects With Active Clinical Trachoma No. %

Townsite

176

6

3

Qatif oasis

207

58

28

53

19

36

Al-Hasa oasis

active disease compared to rates of 28% and 36% respectively in the Qatif or al-Hasa oases. Thus the townsite subjects differed markedly from groups in either of the oasis villages in respect to diagnoses of active clinical trachoma, with probability values less than 0.001 in each chi-square test of sig­ nificance (table 2 ) . The percentages of subjects with healed trachoma were in an order inverse to that of active trachoma in these villages ; the differ­

Statistical Significance Townsite vs. Qatif X 2 = 39.6, n = l,p=<0.001 Qatif vs. al-Hasa Not significantly different Townsite vs. al-Hasa X 2 = 40.8, n = i, p = <0.001

ences gave a high degree of statistical valid­ ity to the comparisons between the townsite and oasis samples (table 3). Active pannus was diagnosed in these three samples with frequencies which varied to a statistically significant degree. This diagnosis was made in 2%, 9% and 25% of the subjects examined in the townsite, Qatif or al-Hasa oases respectively (table 4 ) . Herbert's pits were found in 5%, 28% and 47% of the subjects in the townsite,

TABLE 3 CLINICAL EVIDENCE OF THE POINT PREVALENCE OF HEALED TRACHOMA IN SUBJECTS LIVING IN MODERN HOUSING (TOWNSITE) IS CONTRASTED WITH THAT FOUND IN SUBJECTS LIVING IN TRADITIONAL HOMES IN OASES VILLAGES IN SAUDI ARABIA

Village

No. Examined

Subjects With Healed Clinical Trachoma No. %

Townsite

176

157

89

Qatif oasis

207

144

70

53

34

64

Al-Hasa oasis

Statistical Significance Townsite vs. Qatif X 2 = 20.7, n = l,p= <0.001 Qatif vs. al-Hasa Not significantly different Townsite vs. al-Hasa X 2 = 16.7, n = l, £ = < 0 . 0 0 1

TABLE 4 T H E POINT PREVALENCE OF ACTIVE PANNUS IN SUBJECTS LIVING IN MODERN HOUSING (TOWNSITE) IS CONTRASTED WITH THAT FOUND I N SUBJECTS LIVING I N TRADITIONAL HOMES IN OASES VILLAGES IN SAUDI ARABIA

Village

No. Examined

Subjects With Active Pan 1US No. %

Townsite

176

4

2

Qatif oasis

207

18

9

53

13

25

Al-Hasa oasis

Statistical Significance Townsite vs. Qatif X 2 = 6.11, » = l , p = < 0 . 0 2 Qatif vs. al-Hasa X 2 = 8.62, n = l , / > = < 0 . 0 0 5 Townsite vs. al-Hasa X 2 = 26.19, n-i, p= <0.001

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F E B R U A R Y , 1969

TABLE 5 T H E POINT PREVALENCE OF HERBERT'S PITS IN SUBJECTS LIVING IN MODERN HOUSING (TOWNSITE) IS CONTRASTED WITH THAT FOUND IN SUBJECTS LIVING IN TRADITIONAL HOMES IN OASES VILLAGES IN SAUDI ARABIA

No. Examined

Village

Subjects With Herbert' s Pits No. %

Townsite

176

8

Qatif oasis

207

57

28

53

25

47

Al-Hasa oasis

TABLE 6 ARITHMETIC MEANS IN MILLIMETERS BEYOND THE CORNEAL LIMBUS OF CORNEAL VASCULARIZATION AND INFILTRATION IN SUBJECTS LIVING IN VARYING SOCIOECONOMIC ENVIRONMENTS IN SAUDI ARABIA

Village

Townsite Qatif oasis Al-Hasa oasis

No. Examined 176 207 53

Arithmetic Means in Millimeters Vascularization

Infiltra­ tion

1.5 3.3 3.9

1.1 2.1 2.5

5

Statistical Significance Townsite vs. Qatif X a = 34.1, n = l , p = < 0 . 0 0 1 Qatif vs. al-Hasa .Y» = 6.651, » = 1, p= <0.01 Townsite vs. al-Hasa X 2 = 56.6, » = ! , / > = <0.001

townsite or oasis dwellers ; records were not kept by local attending physicians, with the exception of the medical clinics of Aramco. However, the townsite and villages in the oasis were sampled to assess the availability of eye medication in the homes. All house­ holds were numbered from aerial photo­ graphs ; selection of homes for the sample was based on a random numbers table. All medications were inspected. Antibiotic oph­ thalmic ointment was found in 34% (21/62) of homes in the townsite and 70% (60/86) of homes in the oasis village. A similar investigation into the nutrition of these children failed to reveal significant differences. Gross evidence of clinical mal­ nutrition was not found during the survey.

Qatif oasis, or al-Hasa oasis respectively. Point prevalence rates for this clinical sign were significantly different in each of these sample groups (table 5). Infiltration and vascularization were esti­ mated in millimeters from the upper corneoDISCUSSION scleral limbus. For subjects living in the An opportunity to investigate trachoma townsite, the Qatif or al-Hasa oases the re­ epidemiologically occurred when microbio­ spective arithmetic means for vascularization logie and clinical data from more than 3,000 and infiltration were as follows: vasculari­ subjects under 5 years of age revealed zation—1.5 mm, 3.3 mm, 3.9 mm; and in­ filtration —1.1 mm, 2.1 mm, 2.5 mm (table TABLE 7 6)· ARITHMETIC MEANS OF FOLLICLES AND CICATRIFollicles and cicatrization were recorded ZATION SCORED ON A BASIS OF ZERO TO 3 IN SUBJECTS LIVING IN VARYING SOCIOECONOMIC with an arbitrary score of 1 + to 3 + ; the sub­ ENVIRONMENTS IN SAUDI ARABIA ject was given a score of zero if these clinical signs were not found. Arithmetic means for Arithmetic Means of Clinical Scores subjects in the townsite, Qatif or al-Hasa No. Village Examined oases respectively were as follows: fol­ Follicles Cica­ trization licles—0.01+ , 0.3+ , 0 . 3 + ; cicatrization— 1.0+, 1.6+, 2.0 + . Townsite 176 0.01 1.0 Qatif oasis 207 1.6 0.3 It proved to be impossible to estimate ac­ Al-Hasa oasis 2.0 53 0.3 curately medical care to the eyes received by

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marked differences in the disease in popula­ tions living less than 10 miles apart. 1 Many of the écologie variables which frequently hinder or render invalid epidemiologic com­ parisons of this nature were spontaneously controlled in this study, as described above. Differences in the environments of townsite and oases subjects appeared to reside mainly in the living conditions and habits of per­ sonal hygiene created by variation in socioeconomic status. Trachoma was holoendemic in each of these three population samples, as it has been for years in the Eastern Province as a whole. Clinical signs of trachoma were found in 96% (418/436) of the entire sam­ ple ; there was a maximum difference of only 7% between the prevalence rates of tracho­ ma, active plus healed, in any of these three villages. Thus lifelong residence in the rela­ tively beneficent environment of the townsite did not protect townsite subjects from infec­ tion with trachoma, 93% of whom had clini­ cal evidence of the disease (table 1 ). However, the clinical course which ensued from this infection differed drastically in subjects born and raised in the townsite when compared with subjects who were life­ long residents of the oases. The townsite subjects were much less prone to retain clin­ ically active disease (table 2) and were much more likely to have healed infections (table 3) than were the oases populations under study. These differences are highly signifi­ cant statistically. All other measures of clinical trachoma— active pannus, Herbert's pits, cicatrization, follicles, corneal vascularization and infiltra­ tion—were consistent in that the intensity and gravity of trachoma in the townsite sub­ jects were much less than in the oasis groups. In an earlier paper describing the microbi­ ologie epidemiology of trachoma in Saudi Arabia1 it was noted that the disabling com­ plications of trachoma were observed fre­ quently in oasis dwellers but were rare in in­ habitants of the townsites. The present paper

241

supports that statement. Because the townsites had been in existence only about 20 years, subjects in this study were young, with a mean age of 10 years. Despite com­ parable early ages, oasis dwellers were found to exhibit trachoma of a gravity far exceed­ ing that observed in townsite subjects. Detels and associates3 described a situa­ tion in which environmental factors, acting on subjects 20 years of age or more, in­ fluenced substantially the sequelae of tracho­ ma. The Canadian environment exerted a favorable effect on severe scarring; in con­ trast, continued residence in India led to trachoma of increased gravity. There is rea­ son to believe that a similar epidemiologic situation obtains to some extent in Arabia. Oasis subjects with a mean age of 10 years were found with vascularization averaging 3.4 mm ; active pannus was noted in 12% of this sample. It is reasonable to predict that active pannus, continuing to influence ad­ versely a vascularization already encroaching on the pupillary area, would lead in future to interference in vision in an unknown num­ ber of these young residents of the oases. In contrast, only 2% of townsite children examined were found to have active pannus (table 4). Moreover, rates for continued mi­ crobiologie infection in the townsites have been shown to be less than the rates among oases subjects to a degree which is statisti­ cally highly significant.1 Living in a more fa­ vorable environment as they become adults, the townsite children are not expected to de­ velop the disabling consequences of tracho­ ma in any sizeable numbers. Blindness was not observed in any subject in this study, a not unexpected finding in view of the fact that students were examined only in schools where no special facilities for teaching the blind were available. Can the diminution in intensity and grav­ ity of trachoma in the townsite be ascribed to specific medical treatment? In recent years controlled studies of trachoma treat­ ment with antibiotics have failed to demon­ strate the effectiveness of systemic sulfona-

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mides and ophthalmic ointments used alone or in conjunction.9"11 Poor results have been reported in mass treatment campaigns12 or in human volunteers13 when topical ointments were used alone. Although general medical care as well as specific eye treatment un­ doubtedly was more adequate in the townsite populace, it was interesting to find antibiotic ointment for the eyes in twice as many homes in the oases as in the townsites. In our experience, few if any of these subjects in townsites or oases used ointment in a man­ ner adequate to constitute effective treat­ ment. We believe that the differences in trachoma observed in these communities can not be ascribed, in any large measure, to medical treatment, whether at home or in the clinics. This concept agrees with the findings of Dawson, Hanna and Jawetz9 who found "the good environment seemed to be the ov­ erriding beneficial influence" when com­ pared with treatment with tetracycline topi­ cal ointment and suif a by mouth. Taylor and associates,14 in studying eye in­ fections in the Punjab, suggested that the most important vehicle for the spread of eye infections is the village woman's shawl, a general purpose garment used for cleaning the faces of the children. A similar garment is used in Arabia and we agree with Taylor's imputation regarding the role it plays in spread of trachoma. In addition, children and adults in oases villages customarily sleep on mats in a single room. Exudate from the eyes contaminates the mats and provides an ideal hand-to-eye transmission route. Sur­ vival time of the trachoma agent on cloth is ample to permit dissemination by this route.15 Habits and customs in general were simi­ lar in townsite and oasis ; however, the higher economic level of the townsite per­ mitted less crowding in the homes and run­ ning water facilities in each home. The presence of water in the home for washing and for laundry may be quite important in the control of this disease. The higher educa­ tional level, together with industrial employ­

FEBRUARY, 1969

ment of the heads of households, contributed to improvements in personal hygiene and community sanitation in the townsites. Various authors have described the influ­ ence on trachoma of such factors as "envi­ ronment," "way of life," and "living condi­ tions."1-4-14 The Third Report of the W H O Expert Committee on Trachoma lists the following among the environmental factors affecting transmission of trachoma : race, cli­ mate, insect vectors, density of population, diet and nutrition, cultural and social cus­ toms, general economic level, extrinsic con­ tacts, educational level, and the presence of other ocular or general diseases.2 This study does not negate the importance of any of these alleged influences. Rather our clinical data, together with the microbio­ logie data presented earlier,1 demonstrate that marked differences in trachoma do occur in circumstances where several of these factors can not impinge on the course of the disease. Race, climate, cultural pat­ terns, geography, nutrition, and extrinsic contacts must be equated in these sample groups and cannot, therefore, be invoked to explain the contrasts found. We return, then, to person-to-person con­ tact in conditions of crowding and inade­ quate hygiene as the most probable explana­ tion of the transmission of trachoma in Saudi Arabia. Such an unfavorable environ­ ment provides the conditions conducive to reinfection or continued infection wherein trachoma progresses to a disabling disease. These observations, of course, are not origi­ nal. MacCallan,16 Nataf,17 Thygeson18 and others have published similar findings years ago. However, it is our intent in this paper to draw conclusions from clinical observa­ tions relating them to microbiologie data ; our major purpose in Saudi Arabia is to more nearly define the epidemiology of trachoma, relying heavily on microbiologie data and its correlation with clinical signs. The clinical data presented here serve to strengthen the validity of our concepts based on microbiologie data from young children.

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Future publications will explore the microbi­ ologie and clinical interrelationships relating to intensity of infection and chronicity of disease as well as the epidemiologic signifi­ cance of immunologie types of trachoma strains found in this area. SUMMARY

1. F o u r hundred and thirty-six school children in the Eastern Province of Saudi Arabia were examined with a slitlamp for signs of trachoma. These subjects had been born and raised either in a relatively modern "townsite" village or the less adequate envi­ ronment of two oasis villages. 2. Trachoma was holoendemic in all three villages; 9 6 % of the entire sample and 9 3 % of townsite dwellers showed signs of the dis­ ease. 3. T h e clinical consequences of this infec­ tion differed with the place of residence of the subject. Statistically significant differ­ ences between townsite and oasis children were shown in point prevalence rates of ac­ tive or healed trachoma, active pannus and Herbert's pits. Measurement of follicles, ci­ catrization, vascularization and infiltration demonstrated that the intensity and gravity of trachoma in the oasis subject exceeded the severity of the disease found in townsite children. 4. Many epidemiologic variables alleged to be important in influencing trachoma—race, climate, cultural patterns, geography, nutri­ tion and extrinsic contacts—could be equated in townsite and oases subjects, em­ phasizing the potential of crowding and poor personal hygiene in producing an environ­ ment in which trachoma may progress to the point of impairment of vision. 1 Shattuck Street (02115) REFERENCES

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Saudi Arabia. Am. J. Ophth. 63:1372/346, 1967. 2. World Health Organization, Expert Commit­ tee on Trachoma, Third Report. World Health Org. Tech. Rep. Ser. No. 234, 1962. 3. Detels, R., Alexander, E. R. and Dhir, S. P. : Trachoma in Punjabi Indians in British Columbia: A prevalence study with comparisons to India. Am. J. Epidem. 84:81, 1966. 4. Mann, I. : Correlation of race and way of life in Australia and the territory of Papua and New Guinea with incidence and severity of clinical trachoma. Am. J. Ophth. 63 :1302/276, 1967. 5. Snyder, J. C, Nichols, R. L., Bell, S. D. Jr., Haddad, N. A., Murray, E. S and McComb, D. E. : Vaccination against trachoma in Saudi Arabia : Design of field trials and initial results. Industry and Tropical Health IV. Boston, Harvard School of Public Health, 1963, p. 65. 6. Bell, S. D. Jr., Nichols, R. L. and Haddad, N. A. : The immunology of the trachoma agent with a preliminary report on field trials of vaccine. Invest. Ophth. 2:471, 1963. 7. Thygeson, P. : The limbus and cornea in exper­ imental and natural human trachoma and inclusion conjunctivitis. Ann. N.Y. Acad. Sei. 98 :201, 1962. 8. Wilson, R. P.: A short slitlamp study of the corneal vessels in Egyptian trachoma with a discus­ sion of their diagnostic value in doubtful cases. Folio Medica Orientalia 1 :S2, 1932. 9. Dawson, C. R., Hanna, L. and Jawetz, E : Controlled treatment trials of trachoma in Ameri­ can Indian children. Lancet 2 :961, 1967. 10. Foster, S. O., Powers, D. K. and Thygeson, P. : Trachoma therapy : A controlled study. Am. J. Ophth. 61: 451, 1966. 11. Woolridge, R. L , Cheng, K. H., Chang, I. H., Yang, C. Y., Hsu, T. C. and Grayston, J. T. : Failure of trachoma treatment with ophthalmic an­ tibiotics and systemic sulfonamides used alone or in combination with trachoma vaccine. Am. J. Ophth. 63:1577/551, 1967. 12. Agarwal, L. P. and Malik, S. R. : Tetracycline in trachoma. Brit. J. Ophth. 39:759, 1955. 13. Grayston, J. T. : Biology of the virus. Invest. Ophth. 2:460, 1963. 14. Taylor, C. E., Gulati, P. V. and Harinarain, J. : Eye infections in a Punjab village. Am. J. Trop. Med. Hyg. 7 :42, 1958. 15. Sowa, S., Sowa, J., Collier, L. H. and Blyth, W. : Trachoma and allied infections in a Gambian village. Medical Research Council, Special Report Series No. 308, London: Her Majesty's Stationery Office, 1965, p. 71. 16. MacCallan, A. F. : The epidemiology of trachoma. Brit. J. Ophth. 15:370, 1931. 17. Nataf, R. : Le Trachome. Paris, Masson et Cie., 1952. 18. Thygeson, P. : Epidemiologic observations on trachoma in the United States. Invest. Ophth. 2 :482, 1963.