Studies on onchocerciasis in the United Cameroon Republic II. Comparison of onchocerciasis in rain-forest and Sudan-savanna

209 TRANSACTIONS OF THE ROYAL SOCIETY OF TROPICAL MEDICINE AND HYGIENE. Vol. 68. No. 3. 1974.

STUDIES ON ONCHOCERCIASIS IN THE UNITED CAMEROON REPUBLIC II. COMPARISON OF ONCHOCERCIASIS IN RAIN-FOREST AND SUDAN-SAVANNA J.*ANDERSON*, H. FUGLSANG*, P. J. S. H A M I L T O N t AND T. F. dE C. MARSHALLt-

Introduction In the companion paper (ANDERSONet al., 1974) the association between Onchocerca volvulus infection and certain skin and eye lesions was confirmed in both rain-forest and Sudan-savanna areas of Cameroon. The present paper describes the differences in the pattern of onchocerciasis seen in the two areas, and correlates them with the intensity of infection as measured by the number of nodules and by microfilarial concentrations in the skin and eye. A defined population of 1,151 persons aged 5 years and over from 8 groups of heavily infected rain-forest villages, was compared with a similarly defined population of 1,220 persons from 8 groups of heavily infected savanna villages.

Materials and methods Details of the methods used, together with a map of the survey area, are given in this issue of the Transactions (At,mE,SON et al., 1974). From the 22 groups of villages included in that study the parasitological and clinical data from 8 of the most heavily infected rain-forest villages (Nos. I-8) have been analysed in detail in this paper and compared with those from 8 of the most heavily infected savanna villages (Nos. 12-19). Only data from persons aged 5 years and over were included, and in 2 villages, one in the rain-forest and one in the savanna, only persons aged 20 years and over had been examined. A diagnosis of onchocerciasis was made if 1) microfilariae of O. volvulus were found in a skin snip at the shoulder or buttock, 2) there were 3 or more nodules, or 3) microfilariae were seen in the eye, whether in the cornea, anterior chamber, retrolental space, or vitreous.

Results

1. Prevalence of onchocerciasis. Table I lists the 16 groups of villages, together with their main tribe. 1,151 people were examined in the rain-forest, and 1,220 in the savanna. The response rates in the defined populations were 89% and 88% respectively. The prevalence of onchocerciasis was 95-4% in the rainforest villages (range 87.0 to 97-1) and 92-5% in the savanna (range 84.6 to 99-2). The over-aU prevalence of nodules was 69-5% in the rain-forest (range 60.6 to 80.7), while it was significantly lower in the savanna (54.3%, range 40-0 to 70.5). Table I I gives the distribution of the population of each area by sex and age. From Figure i (A and B) it can be seen that in the rain-forest the prevalence of onchocerciasis in both sexes was already over 80% in the 5-9 year old group, while in the savanna that level was not reached before the age of 10-14 years. By the age of 20 almost 100°/0 of males and females were infected in both areas. Also shown is the prevalence of nodules by area, sex, and age. In general it was slightly higher in males than females in both rain-forest and savanna. In the rain-forest males, nodules were present in 30% of the age group 5-9, and in 76% by the age of 15-19. Thereafter there was a steady increase to 89% in the oldest group. In the savanna males the prevalence was only 10% in the youngest group, rising quickly to 66% by the age of 15-19, but never reaching 80% at any age. The females in both areas showed a steady increase in nodule prevalence with age, but again in the savanna they appeared later and never reached the rain-forest levels. *Medical Research Council grantholders, Helminthiasis Research Unit, P.O. Box 55, Kumba, S.W. Province, Cameroon. tTropical Epidemiology Unit, Department of Medical Statistics and Epidemiology, London School of Hygiene and Tropical Medicine, Keppel Street, London, WC1E 7HT. We wish to thank Dr. B. O. L. Duke and Professor G. S. Nelson for helpful criticism and encouragement. We are grateful to our assistants, Mr. S. Ayonge and Mr. C. Fisiy, for their continued enthusiasm, and acknowledge the help of our savanna interpreter, Mr. S. Farikou. We are also grateful to Miss Gillian Kearney of the Department of Medical Statistics and Epidemiology, London School of Hygiene and Tropical Medicine.

210

STUDIESON ONCHOCERCIASISIN THE UNITEDCAMEROONREPUBLIC

TABLE I. Population by area, village group, and tribe, showing response rate, percentage with onchocerciasis and with nodules. RAIN-FOREST Village

main tribe

response rate (%)

total no. seen

% pos.

% with (nodules)

1. Ngongo

Bakundu

93

97

95.9

75.0

2.

Baduma

Bakundu

93

169

96.4

70.2

3.

Ekonje Boanda

Bakweri Bakweri

98 89

69 70

97.1

75.5

4.

Mafanja

Bakweri

83

221

94.6

60.6

5.

Mfaitok

Bayangi

97

155

96.8

80.7

6.

Makobe M. Meteke*

Balue Mbonge

98 88

125 110

95.7

62.1

7.

Mundame

Balong

86

46

87.0

73.9

8.

New Ngongo

Meta

75

89

93.3

73.0

89

1,151

95.4

69.5

Total

SAVANNA 12.

Koumban

Mboum

90

275

93-8

44.6

13.

Bedara

Mboum

95

147

98.0

70.5

14. Mbora New Bedara

Mboum Mboum

90 94

46 86

99.2

70-5

15. Mbai Mboum* Mbai Mbeo*

Mboum Mboum

? ?

198

95-0

70-2

16.

Foulb~

87

78

85-9

59.0

17. Djarendi Lingerba

Voko Voko

82 89

84 78

84.6

40.7

18.

Gorheck

Dourou

68

103

89.3

45-6

19.

Ndiki

Mboum

97

125

88.8

40.0

88

1,220

92.5

54- 3

Naari

Total *Only people of 20 years and over were seen.

Altogether there were 1,098 persons (556 males and 542 females) with onchocerciasis in the rainforest villages and 1,128 (567 males and 561 females) in the savanna. The following account compares the clinical manifestations in these two groups of confirmed cases. To simplify the presentation the ocular findings in the right eye only have been shown. 2. Nodules. Table I I I shows that in the rain-forest, nodules were present on the upper part of the body (head and neck, upper limb, thorax) in 32.0% , and on the lower part (pelvis, lower limb) in 67.8~g. The corresponding savanna figures were 15.5% (upper) and 55.1% (lower). The difference between rain-forest and savanna was statistically significant (P~.001) for both upper and lower nodules. Most of the upper nodules were on the thorax, and they were present on the head and neck in only 1.4% in the rain-forest and 0.5% in the savanna. The lower nodules in both areas were distributed mainly around the pelvis, but in the rain-forest many were also found around the knee. Nodule distribution is analysed by area, sex, and age in Figure 2A. In the lower part of the body the pattern was the same as for the

J. ANDERSON, H. FUGLSANG~ P. J. S. HAMILTON AND T. F. DE C. MARSHALL

211

prevalence of all nodules taken together (Figure 1B), but in the upper part there were relatively more nodules in the younger age groups in both areas. TABLE II. Population by area, sex, and age, N = 2371. Rain-forest

Savanna

Males

Females

Males

Females

Age

No.

(%)

No.

(%)

No.

(%)

No.

(%)

5-9

62

(10.8)

66

(11.4)

68

(11-2)

61

(10"0)

10-14

64

(11.2)

64

(11.1)

81

(13-3)

63

(10.3)

15-19

37

(6.5)

61

(10-5)

46

(7.5)

83

(13-6)

20-29

102

(17-8)

135

(23.3)

150

(24.6)

189

(30.9)

30-39

102

(17.8)

100

(17.3)

118

(19.4)

91

(14.9)

40--49

96

(16.8)

70

(12.1)

57

(9-4)

75

(12.3)

50+

109

(19.2)

83

(14.3)

89

(14.6)

49

(8-0)

Total

572

(100)

579

(100)

609

(100)

611

(100)

RP,IN FOREST Males

SAVANNA

Females

Males

Females

HI

A. Onchocerc~asis

-~

i

i

I-1i

-7 i

i

I I

I I _J_ I

.-J._

l°°Fo

__

FIG. 1. Prevalence of onchocerciasis (A) and one or more nodules (B) by area, sex and age.

B. Nodules

Figure 2B gives the mean number of nodules per person by area, sex, and age. Here again the figures were higher in the rain-forest for both the upper and lower parts of the body, and these differences were particularly striking in the older age groups. In males aged 50 years and over the mean number of nodules per person was 4-6 in the rain-forest and 2.2 in the savanna. 3. Microfilariae in the skin. (Table I I I and Figure 3A). Positive shoulder snips were present in 86.1% in the savanna, while the corresponding rain-forest figure was 75.6%. This difference was highly significant (P<.001). Positive buttock snips were found in 97.4% in the rain-forest and in 99"1°"/o in the savanna, but this difference was not significant. The mean number of microfilariae per mg. of skin at the shoulder and buttock was higher in the savanna in both sexes at all ages, with the exception of the 5-9 year old males, in whom the mean con-

212

STUDIES ON ONCHOCERCIASIS IN THE UNITED CAMEROON REPUBLIC

centration was very slightly higher in the rain-forest. While the females showed a gradual increase in skin density with age, the 15-19 year old males in both areas had already reached peak levels o f 85 and 154 microfilariae per mg. o f skin at the buttock in the rain-forest and savanna respectively. T h e concentration at the shoulder was particularly high in the savanna males, and the peak level o f 45 microfilariae per mg. o f skin was reached in the 15-19 year old group. TABLE I I I . Prevalence of positive shoulder and buttock skin snips by area together with prevalence of nodules in upper and lower part of the body in cases of onchocerciasis. Rain-forest (1,098)

Savanna (1,128)

Prevalence

Prevalence

Sig. of diff.

Microfilariae in shoulder snip

75.6

86.1

+ + +

Microf-dariae in buttock snip

97.4

99' 1

NS

Nodules on head, neck, arms, and thorax

32.0

15" 5

~- + ~-

Nodules on pelvic girdle and legs

67.8

55- 1

- ' + ~-

N = 2,226

(%)

(%)

+++ ++ NS

= = =

RAIN FOREST Males

P <0.001 0.02>P>0.001 No Significance SAVANNA

Females Prevalence Males

Females

H ead ,neck arms and thorax 0

•

100 -%

Abdoment pelvis and I ow er

exfremitles

FIG. 2. Prevalence (A) and mean number (B) of nodules on the upper and lower parts of the body by area, sex and age.

O

Mean No. B°

Head ~neck arms and thorax

A ~ d omen t

pelvis and

Lower limbs

4. Clinical manifestations in the skin and lymphatic system (Table IV and Figure 4). M a r k e d differences between the rain-forest and savanna were found in pronounced skin atrophy (16.3% and 23.0% res-

J. ANDERSON, H. FUGLSANG, P. J. s. HAMILTON AND T. F. DE C. MARSHALL

213

pectively), shin depigmentation (36.0% and 4.3%), inguinal and/or femoral lymphadenopathy (43.3% and 27.0%), and hanging groin (8.8% and 1.6%). All these differences were statistically significant. Sex differences within area were not marked, and most of these signs showed a gradual increase of prevalence with age. An exception in the savanna was visible inguinal and/or femoral lymphadenopathy, the prevalence of which remained more or less at the same level from the age of 10 years in both sexes, and which was much more common among the males. R/kIN FOREST Males

Females

Mean No. 60,1._

SAVANNA

Ma les

Females

40/

A. Shoulder

180 160] 140 -

Buttock

--- - -

120 m

100! -

FIG. 3. Mean number of microfilariae (A) per rag. of skin at left shoulder and buttock, together with the prevalence of microfilariae (B) in the right cornea, anterior chamber, retrolentai space and/or vitreous by area, sex and age. The prevalence of 20 or more microfilariae is shown in black.

6O

4oi 2O

Prevalence

80 - % 60'

B.

Cornea 2O 0

6O

chamber

40[%

Retrolental space and/or vitreous "

,~

To~

~?

~o

n, ~,.-, ~o~oo

~4--1-L-,

,

5. Microfilariae in the eye (Table V and Figure 3B). When considering the prevalence of microfilariae in the eye and of the resultant clinical manifestations, it must be emphasized that some eyes were so diseased that not all the signs could be evaluated. Those eyes were therefore excluded from the calculations of prevalence, and a downward bias was no doubt introduced for the appropriate sign. In the savanna there was too much corneal opacification to comment on other signs in the anterior segment in 3.4% of the males and in 1.3% of the females. The corresponding rain-forest figures were 0.4% and 0.2%. Details in the posterior segment were invisible because of anterior segment pathology in 6"9~o of the males and in 3.4% of the females in the savanna. The corresponding rain-forest figures were 1"6~o and 2.6%. The over-all prevalence of microfilariae in the cornea was 44-4% in the savanna and significantly lower (P~.001) in the rain-forest (23.9%). This striking difference was due to the higher prevalence in

214

STUDIES ON ONCHOCERCIASIS IN THE UNITED CAMEROON REPUBLIC

both males and females in the savanna. In both areas peak levels were reached in the 15-19 year old males, and later in the females. Corneas containing more than 20 microfilariae were seen in 7% of the savanna males, and in only 2% of the rain-forest males. TABLE IV. Prevalence of skin and groin changes by area. Rain-forest (1,098)

Savanna (1,128)

Prevalence (%)

Prevalence (%)

Sig. of diff.

Pronounced skin atrophy

16.3

23.0

+ + +

Shin depigmentation (any degree)

36" 0

4" 3

+ + +

Groin lymphadenopathy (visible)

43' 3

27.0

+ + +

Hanging groin

8-8

1.6

+ + +

Lymphoedema of external genitalia

1.4

0- 9

NS

N = 2,226

RAIN FOREST Males

SAVANNA

Females

Males

Females

Skin atrophy

, • Shin

FIG. 4. Prevalence of skin atrophy, shin depigmenration, groin lympadenopathy, and hanging groin by area sex and age.

deplgmentatlc~l

2O 0 ~ 80I%

0 Groin

lymphadenopclthy

8oF.,.

402o 6of 0 40 %

Hanging groin •

~

o)r-I+

t~ 09 T h e over-all prevalence of microfilariae in the anterior chamber was almost identical in the rain-forest (36.6%) and the savanna (37-0%), but Figure 3B shows that in the males, with the exception of the youngest and oldest age groups, the sign was slightly more prevalent in the savanna, whereas in the females it was slightly more common in the rain-forest. The peak figure of 62.8% was reached in the 15-19 year old savanna males. There were no marked differences between the rain-forest and savanna with respect to anterior chambers containing more than 20 microfilariae. The prevalence of microfilariae in the retrolental space and/or vitreous was significantly higher in the savanna (8.8%) than in the rain-forest (3.1%). The highest prevalence was 16.5% in the 30-39 year old savanna males.

215

J. ANDERSON, H. FUGLSANG, P. J. S. HAMILTON AND T. F. DE C. MARSHALL

TABLE V. Prevalence of microfilariae in the cornea, the anterior chamber, and the retrolental space and/or vitreous (by area) Rain-forest (1,098)

Savanna (1,128)

Prevalence (%)

Prevalence (%)

Sig. of diff.

Cornea

23-9

44"4

-+ + +

Anterior chamber

36.6

37- 0

NS

3" 1

8- 8

+ + 4-

N -

2,226

Microfilariae present in : - -

Retrolental space and/or vitreous

Microfilarial invasion o f the eye was thus maximal in the savanna m a l e s - - i n the cornea, the anterior chamber, and the posterior segment. 6. Clinical manifestations in the eye (Table VI and Figure 5). T h e prevalence o f snowflake corneal opacities was significantly higher ( P ~ . 0 0 1 ) in the rain-forest (17.9%) than in the savanna (10.4%). T h e y were more common in females than in males in both areas, and their highest prevalence was between the ages o f 10 and 19 years in both sexes. Sclerosing keratitis was far more prevalent in the savanna (6-6%) than in the rain-forest (1-6%), where it was seen only in its milder forms. I n the savanna it was most common in the males, in whom it was often combined with anterior uveitis. It occurred even before the age o f 10 years, and was seen in 25.9°/0 o f the savanna males over 50 years. TABLE VI. Prevalence of eye signs, impaired vision and blindness by area. Rain-forest (1,098)

Savanna (1,128)

Prevalence (%)

Prevalence (%)

Sig. of diff.

17.9

10' 4

: - :-

1.6

6-6

- ÷ i-

Iritis, any degree, torpid and past

11-4

9.7

NS

Loss of pupil ruff (any degree)

19.4

17.8

NS

Optic atrophy

3" 5

1" 6

-

Choroidoretinitis

4-1

3" 5

NS

Vision 6/36 to no perception of light (right eye)

7.4

9' 1

NS

Blind in right eye

3-7

6 "4

-:- +

Blind in both eyes

2"0

5.1

~+ -~-

N

2,226

Snowflake corneal opacities Sclerosing keratitis (any degree)

Signs o f previous iritis, or torpid iritis, were seen in 11"4% in the rain-forest and in 9.7°,/0 in t h e savanna. I n the rain-forest they were equally common among males and females and complications were less severe than in the savanna, where more males than females were affected. T h e prevalence o f disappearance o f the pupillary ruff was similar in rain-forest and savanna, and the sign increased steadily with age in all groups. Optic atrophy and choroidoretinitis were both relatively rare. Optic atrophy was seen in 3.5% in the rain-forest and in 1 . 6 % in the savanna, while the corresponding figures for choroidoretinitis were 4.1 °'/'0 and 3.5°"0. Both conditions were more common in males.

7. Impaired vision and blindness (Tables VI and Figure 5). 2"0 °//o were blind in both eyes in the rain-forest, and 5.1% in the savanna. Figure 5 shows that in both areas blindness (defined as inability to

216

STUDIESON ONCHOCERCIASISIN THE UNITEDCAMEROONREPUBLIC

count fingers at 3 metres with the better eye) started earlier in males than in females, and that it reached a particularly high level in the savanna males, 30-7% in the over 50 age group. The corresponding figure for the savanna females was I0.6%, whereas the blindness rates for rain-forest males and females over 50 years of age were 6.5% and 12.2% respectively.

RAIN FOREST Males Females

SAVANNA Males Females 3O

Corneal

snowflake opacities

2(?

30 - %

Sclerosing keratitis . (any degree)

10

40 - %

~oL

~

FIG. 5. Prevalence of corneal snowflake opacities, sclerosing keratitis, iritis, optic atrophy, choroidoretinitis and blindness by area, sex and age.

1

Iritls (any degree) 20r%

Optic atrophy

~

,_.r-r] 20r%

Onchocercal choroldoretinitis

r-~

,-~

'2F

3O 2G

Blindness

10 0

~o~

o

o

.

.

.

.

~,~'

.

~

8. Causes of blindness (Table VII). Sclerosing keratitis and iritis, often combined, were the main causes in the savanna, where these lesions were of overwhelming importance in the males and responsible for 64% (30 out of 47 cases) of blindness among them. In the rain-forest the causes of blindness were more equally distributed between the anterior and posterior segments, and sex differences were relatively minor. Trachoma in the rain-forest was not severe and did not cause blindness. In the savanna it was responsible for 8-5% of the blindness among the males and 9.1% among the females. Discussion The differences between the rain-forest and savanna were not only in the onset and intensity of infection, but also in the pattern of clinical manifestations. In summary, infections started earlier in the rain-forest and nodules were more numerous and widely distributed, but microfilarial density in the skin was higher in the savanna; shin depigmentation, lymphadenopathy, and hanging groin were more frequent in the rain-forest, but severe skin atrophy was more common in the savanna; microfilariae were more prevalent in the savanna corneas, but in the anterior chamber the prevalence was similar in both areas; snowflake corneal opacities were seen mainly in earlier infections particularly in the rain-forest, whereas

217

J. ANDERSON, H. FUGLSANG, P. J. s. HAMILTON AND T. F. DE C. MARSHALL

severe sclerosing keratitis was confined to the savanna; iritis was equally prevalent in both areas, but more severe in the savanna; posterior segment lesions were almost equally frequent in both areas, but blindness was most prevalent in the savanna males. These findings are in over-all agreement with those from similar comparative studies by BUDDEN (1963) and MONJUSlAtr et al. (1965). All these differences might be explained by differences in intensity and duration of transmission, biting behaviour of the vector, pathogenicity and behaviour of the local strain of parasite, or by variations in host response due to race, nutrition, immunity, or the presence of concomitant infections with other organisms. TABLE VII. Main cause of blindness, distribution by area and sex. Rain-forest N ~ 2226

Males 556

Savanna

Females 542

Males 567

Females 561

Sclerosing keratitis

0

0

5

0

Sclerosing keratitis -- iritis

0

0

15

1

Complications of iritis

3

4

10

2

Uncomplicated cataract

2

3

2

3

Optic atrophy

3

2

3

0

Choroidoretinitis

3

1

6

2

Total corneal opacity

1

0

1

2

Trachoma

0

0

4

1

Leucoma

0

0

1

0

12

l0

47

11

Total

There were 6 cases of blindness in the 3 Rain-Forest and 3 Savanna village groups surveyed but not analyzed in this paper.

1. Prevalence and intensity of skin infection. The earlier onset of infection in the rain-forest is probably due to the widespread and continuous man-fly contact there (DUKE et al., 1972), as opposed to the more focal and less continuous contact in the savanna (CROSSKEY, 1955; LE BEm~Eet al., 1964). It is also possible that differences in the intensity and pattern of transmission were responsible to some extent for the more gradual build-up of infection in the females as contrasted with the steep build-up in the males in both areas. It is more likely, however, that males and females have different susceptibilities to infection and/or subsequent development of the parasite on account of hormonal factors, as suggested by animal experiments in other parasitic diseases (SMITHERSand TERRY,1969). With the earlier onset of infection in the rain-forest a higher intensity of infection might be expected to follow. In the present study it was higher when measured by the prevalence and number of nodules, but not when measured by the concentration of microfilariae in the skin. Among the females there was a direct correlation at all ages between the mean number of nodules and the concentration of microfilariae in the skin within area, but in the males in both areas peak levels of skin microfilarial concentrations were reached in the 15-19 year old group, when the mean number of nodules per person was still relatively low. However, NNOCHIRI (1964) found adult O. volvulus worms lying free in the tissues and in deeper impalpable nodules, while DuKE (1970) confirmed the latter finding. In both positions they were fully productive and surrounded by little or no fibrous tissue. It is therefore possible that these younger men had relatively more female worms in those positions. With encystment they may become less productive, as suggested by the levelling off of the concentration ofmicrofilariae in the skin. It is still not known why nodules develop (ISRAEL, 1959; BROWNE, 1961). Their formation may have a direct relationship to the senescence and subsequent death of the adult worms, but it is more probable that they result from immune reactions. T h e higher prevalence and mean number of nodules in the rain-forest would suggest a more highly de-

218

STUDIES ON ONCHOCERCIASIS I N THE UNITED CAMEROON REPUBLIC

veloped immunity there, which may have resulted from the fact that the infections were acquired in younger and therefore more immunologically competent children. This may be analogous to findings in schistosomiasis by CLARKE (1966). BUCK et al. (1971) found a strong association between microfilarial skin densities and the prevalence of O. volvulus microfilariae in the urine, but they showed that serum antibody levels as detected by indirect haemagglutination tests with O. volvulus antigen in patients showing microfilariae in the urine were generally lower than in those without this manifestation. This may also suggest that the higher microfilarial skin densities in the savanna might be a reflection of lower immunity. NIEL et al. (1972) tested sera from 150 patients with onchocerciasis against antigen from adult O. volvulus and Ascaris suum. They used a double diffusion technique in agar gel and obtained similar reactions with both antigens, suggesting the existence of cross-immunity. Judged by the results of treatment with piperazine in the present study infestation with A. lumbricoides was ubiquitous from early childhood in the rain-forest villages, but it was never found in the savanna villages, a finding in agreement with BUCK et al. (1969) from nearby savanna villages in Chad. It is possible therefore that the ascaris infections in the rain-forest might also have conferred some degree of heterologous immunity against O. volvulus. It is also possible that cross-immunity with Loa loa and Dipetalonema perstans played a r61e, since these infections were commoner in the rain-forest. Duke introduced and elaborated the hypothesis of different Onchocerca-Simulium complexes (DUKE, 1966, 1967, 1970; LEWIS and DUKE, 1966; DUKE et al., 1966, 1967). The present study suggested a savanna onchocerceca strain which produced few nodules and high microfilarial densities in the skin, compared with a rain-forest strain producing relatively many nodules but few microfilariae. Just as there is evidence of different pathogenicity of rain-forest and savanna strain microfilariae (see below) it is likely that the strains have different antigenic properties. The pattern of prevalence and intensity of infection was similar in different tribes among heavily infected villages within the same area. It is therefore unlikely that the differences found between areas could be explained on a tribal basis. There was some difference in the nutritional state between the savanna and rain-forest (ANDERSONet al., 1974), but it is difficult to know what influence this might have had on intensity of infection since little is understood about the metabolism of the parasite. Certainly heavy microfilarial loads were seen in well nourished as well as in poorly nourished individuals.

2. Nodule distribution and its relationship to skin microfilarial density. In Central America there seems to be a relationship between vector biting habits, nodule distribution, and skin microfilarial densities (LAGRAULET et al., 1964). In all areas of Africa, where Simulium damnosum and S. naevei both bite predominantly on the ankle and leg, nodules are most common around the pelvis. This seems to be the site of predilection for infections introduced through the leg, but less so when introduced through the upper parts of the body. Thus in children head nodules were not infrequent, and it is likely that the infective bites were on the scalp. The head of a child is nearer to the ground than is that of an adult, and on its mother's back the head of an infant may be the only area exposed. There were no marked differences in clothing customs either between the rain-forest and savanna or between males and females. In chimpanzees DUKE (personal communication) found that wherever he inoculated infective larvae of O. volvulus, whether of the West African forest or savanna or Guatemalan strains, the adult worms were invariably found at autopsy close to the hip joints. The studies on O. gutturosa in cattle by EICHLER and NELSON (1971) and on O. cervicalis in horses by MELLOR (1973) have also shown that the adult worms have predilection sites in the neck ligaments far from the skin around the umbilicus, which is the vector's biting area of choice and also the area of maximum microfilarial skin density. In the present study skin snips were only taken from the buttock and shoulder, but it was evident from more detailed examinations that the area of maximum skin microfilarial density was in the same anatomical area as the nodule. Thus a 5-year old boy in the savanna had a head nodule and microfilariae in a skin snip at the outer canthus of the eye, but no microfilariae in snips at the shoulder, buttock, or ankle. Several school children with head nodules from the same area had maximum skin concentrations at the outer canthus. 3. Clinical manifestations in the skin and lymphatic system. Some workers (WOODRUFF et al., 1963) have found it strange that itching does not necessarily accompany the presence of microfilariae in the skin. The symptom has been attributed to the death of microfilariae mainly because it is so greatly aggravated by diethylcarbamazine (d.e.c.) treatment. It has been shown (CONNOR et al., 1970; FUGLSANGand ANDERSON, 1973; ANDERSON and FUGLSANG, 1973a) that d.e.c, also causes migration of microfilariae as a

J. ANDERSON, H. FUGLSANG, P. J. s. HAMILTON AND T. F. DE C. MARSHALL

219

prelude to their death. Since the itching commences so rapidly it is possible that in some cases this migration is also partly responsible for the symptom. Itching was most common in early infections~ and usually intermittent. It was often absent in long standing heavy infections in whichmanymicrofilariae must certainly have been dying. After taking d.e.c, they started itching within half an hour. It was suggested by CONNOR et al. (1970) that d.e.c, caused the microfilariae to release an antigen that lead to eosinophilotaxis with consequent microfilarial disintegration, whereas in untreated patients the slower disintegration of microfilariae lead to reactions of the delayed hypersensitivity type. In the savanna, BuCK et al. (1969) found that there was a suppression of delayed hypersensitivity reactions in heavily infected people having nodules or skin atrophy. Our finding that skin atrophy was more common in the savanna, whereas shin depigmentation, lymphadenopathy, and hanging groin were commoner in the rain-forest, again suggested the possibility that the immunological response was more active in the rain-forest, or that development of tolerance had occurred in the savanna. In both areas many persons seemed to live from the age of 20 in equilibrium with their parasite. Their skin was atrophic, perhaps due to lack of nutrients which may have been taken up by the millions of larvae present, but there were few, if any, signs of acute irritation. There was certainly no direct correlation between all skin manifestations and microfilarial skin densities, and an extreme example is provided by the severe changes of sowda (ANDERSONet al., 1973), in which microfilariae are very difficult to detect. All these differences in clinical manifestations could also be due to differences in the pathogenicity and antigenic structure of the parasite. In that case there is probably not just one rain-forest and one savanna strain, but also minor variations even within similar ecological areas (DUKE et al., 1966). Shin depigmentation was thus rare in the savanna villages in this study, but it was seen frequently by the authors in nearby northern Nigeria. However, the problems of immunity in onchocerciasis are complex, since they involve immunity to infective larvae, adult worms, and microfilariae, either separately or in combinations. 4. Microfilariae in the eye. (a) Cornea. It is probable that microfilariae enter the cornea from the surrounding skin via the conjunctiva (RODGER, 1959). In support of this was the strong correlation in the present study between the prevalence and intensity of microfilarial invasion of the cornea with the skin density at the shoulder, as illustrated by the savanna males. DUKE and ANDERSON (1972) have also produced experimental evidence that the microfilariae of the Cameroon Sudan-savanna strain of O. volvulus are 2-3 times more virulent than microfilariae of the Cameroon forest strain in their powers of invading the rabbit cornea and in their ability to produce corneal lesions. These two factors, high local concentration and higher microfilarial pathogenicity, may together account for the greater invasion of the cornea in the savanna. Immunological factors must also be considered. In this study snowflake opacities, which follow the death of microfilariae in the anterior part of the corneal stroma, were seen mainly in younger persons. It was also noted by BUDDEN(1962) that snowflake opacities were particularly evident in expatriate patients. CHOYCE (1972) found them in 48°,<0of 800 cases seen in London, and stated that he saw numerous patients with well marked onchocercal punctate keratitis who had only been exposed to the bites of infected flies for a very short period. It is therefore likely that the snowflake opacity is the response of a cornea to which the microfilaria is relatively foreign. By analogy with the skin, in later infections microfilariae were able to live and die in the cornea without giving rise to major reactions. With massive invasion, however, in which hundreds of living larvae may be seen (ANDERSON and FUGLSANG, 1973b) the cornea was more severely damaged. The presence of these enormous numbers of living parasites might have caused physical damage and also deprived the cornea of essential nutrients, thus aggravating the inflammatory reactions already present. This 'sclerosing keratitis' was therefore not simply a confluence of snowflake fluffy opacities which had formed around dead microfilariae. Additional evidence was that the extent and severity of sclerosing keratitis were not increased by d.e.c, treatment, during which large numbers of microfilariae died in the cornea. (b) Anterior chamber and iris. Although the prevalence and intensity of microfilariae in the anterior chamber followed the same age and sex patterns as those for the cornea and skin in both areas, there were far fewer microfilariae in the anterior chamber in the savanna than might have been expected from the rain-forest figures. When allowance was made for the higher proportion of savanna eyes in which microfilariae in the anterior chamber could not be evaluated, there was still relatively little difference between rain-forest and savanna, though the highest prevalence was again found in the savanna males (Figure 3B). It is not yet known by which route microfilariae enter the anterior chamber, but these results suggested that it might be different from the path of entry into the cornea. Additional evidence for this was found

220

STUDIES ON ONCHOCERCIASIS I N THE UNITED CAMEROON REPUBLIC

in an 18 year old man examined in Yemen. Despite the fact that 50 or more microfilariae were seen in both anterior chambers, only one was seen in each cornea, and skin snips at the shoulder and buttock were negative on two occasions, while a few microfilariae were found later at the ankle. Cases were not infrequently seen in the present study, particularly in the rain-forest, in which the anterior chambers contained many microfilariae while the corneas remained clear. In rabbit experiments microfilariae were never seen in the anterior chamber after sub-conjunctival inoculations (DUKE and ANDERSON, 1972). The fnding of microfilariae in the urine (Buck et al., 1971), in the cerebrospinal fluid (MAzzoTTI, 1959), and in the lymphatics (CoNNOR et al., 1970), and their demonstration in the sputum within an hour of treatment with d.e.c. (FuGLSANG and A~qDERSON, 1973) suggest that the microfilariae may be carried all over the body, including into the anterior chamber of the eye, via the lymphatic system and blood. The higher prevalence of lymphadenopathy and the relatively high prevalence of microfilariae in the anterior chamber may both be due to a relatively high number of 'circulating' microfilariae in the rain-forest. The presence of microfilariae in the anterior chamber was accompanied by a high prevalence of torpid iritis, but the finding of more severe iritis leading to blindness in the savanna males might suggest that the savanna strain microfilariae were more pathogenic not only to the cornea but also to the iris. However, the response of the iris to irritation is often unpredictable, and the presence of many microfilariae circulating in the anterior chamber without any evidence of anterior uveitis is a common finding (APPELMANS,1958; CHOYCE, 1972). (C) The posterior segment. It is likely that microfilariae reach the retrolental space and vitreous via routes similar to those by which they enter the anterior chamber, since the retrolental space and vitreous are both permeated by aqueous humour. The prevalence of microfilariae in the posterior segment might therefore be expected to follow the same pattern as microfilariae in the anterior chamber, but the sign was not sufficiently frequent for a clear pattern to emerge. It was obvious though that the prevalence was higher in males, particularly in the savanna. NEUMANN and GUNNERS (1973) found microfilariae of O. volvulus close to the short posterior ciliary arteries and nerves, and thus there were suggestions of an invasion of the posterior segment directly from the surrounding tissues, but an additional invasion by microfilariae via the blood stream as suggested above might also be considered. At one time it was thought that there was no direct relationship between prevalence of posterior lesions and microfilarial skin densities in the upper parts of the body (KERsHAW et al., 1954), and even that microfilariae were not present in the eyes in certain cases of posterior segment lesions (RODGER, 1960). In the present survey, however, in both rain-forest and savanna the prevalence of optic atrophy and of choroidoretinitis largely corresponded to the prevalence and intensity of microfilarial invasion of the skin and eye. Microfilariae were found behind the lens in 24.5% of cases of Ridley fundus and related lesions, a figure much higher than the over-all average (6.0%). In over 50% of these cases microfilariae were seen in the anterior chamber. D'HAussY (1958) similarly found a direct relationship between these lesions and microfilarial invasion of the eye.

5. Impaired vision and blindness. Skin microfilarial densities in combination with microfilarial invasion of the eye were higher and achieved earlier in the savanna males than in any other group. However, the incidence of prevalence of blindness of both anterior and posterior segment origin was disproportionately high in this group. It was as if there was a critical intensity of early infection which was only reached by the savanna males. The obvious differences in the build-up of infection between males and females were also reflected in the onset of blindness, and hormonal factors may therefore have played a protective role in both areas in keeping the blindness rates in females low during their reproductive years. It would seem that in the savanna such factors were strong enough to offset the suggested higher pathogenicity of the strain of parasite. However, further studies on all aspects of strain differences are required, as well as more information of the S. damnosum transmission potentials in the savanna as compared with the rain-forest. Nutritional factors have often been incriminated in the explanation of the differences in severity of ocular onchocerciasis as seen in rain-forest and savanna. In particular RODGER (1957, 1958, 1962) has consistently suggested by a relative deficiency of vitamin A in the savanna might be associated with the development of certain posterior segment lesions. In the present survey 4 cases of Bitot's spots were seen in the savanna, but they were not associated with generalized conjunctival xerosis. More definite signs of pronounced vitamin A deficiency such as keratomalacia were not seen, and there was no blindness among pre-school children. ROBERTS(1963) thought that ocular involvement in horses parasitized by O. cervicalis may be determined by a deficiency of riboflavine. The staple food in the savanna area in this survey was millet, and this cereal is rich in riboflavine. Some cases of bleeding hypertrophic gums were seen among

221

J. ANDERSON~ H. FUGLSANG~ P. J. s. HAMILTON AND T. F. DE C. MARSHALL

the savanna children, suggesting a deficiency o f vitamin C, but it would be far-fetched to attribute much importance to this observation until more is known about the metabolism o f the parasite. Cases o f goitre were common in the savanna focus, but they showed the same intensity o f infection in the skin and eye as persons without this complication. T r a c h o m a was a cause o f blindness only in the savanna, b u t there was no clear evidencce that this infection had aggravated onchocercal eye lesions, since cases o f trachoma did not show a higher prevalence or intensity o f microfilarial invasion of the cornea. Outside the survey, however, 2 patients were seen in whom enormous numbers o f living microfilariae were lying particularly among the vessels o f a trachoma pannus, and it was possible that the presence o f these vessels had facilitated the entry of microfilariae into the cornea. Summary

T h e results o f an onchocerciasis survey o f total populations aged 5 years and over in 16 heavily infected villages in Cameroon rain-forest and savanna zones are reported. Using standardized parasitological and clinical techniques the same observers examined the intensity o f infection and clinical manifestations in 1,098 cases in the rain-forest and compared them with those found in 1,128 cases in the savanna. T h e following T a b l e summarizes the main findings : - Infection rate among 5-9 year olds Prevalence of nodules Mean number of nodules per person Microfilarial skin density Skin atrophy Shin depigmentation Groin lymphadenopathy Hanging groin Microfilarial invasion of cornea Microfilarial invasion of anterior chamber Microfilarial invasion of vitreous Snowflake corneal opacities Sclerosing keratitis Iritis Optic atrophy Choroidoretinitis Blindness

Rain-forest 80-90 o o

Savanna 60-70" ~,

+÷~. --' ÷

-

4+ -5 ~ + ÷

+++ ++ + .-

-

++ i

+

+

-4 ÷

..L

2.0%

5.1 ",,

- at low level + + - at medium level ÷+÷ = at high level I t is suggested that the differences between rain-forest and savanna may be due to variations in host response resulting from differences in the intensity and patterns of transmission. Different pathogenicity o f the rain-forest and savanna strains o f parasite is also considered to be o f importance, and it is suggested that concomitant infections may influence the immunological response. Hormonal factors are considered to be important in influencing the differences in the patterns and severity o f infections between males and females. REFERENCES ANDERSON, J. & FUGLSANG,H. (1973a). Trans. R. Soc. trop. Med. Hyg., 67, 710. - &~ (1973b). Br. J. Ophthal., 57, 712. - - , - & ZUBAIBY, A. (1973). Trans. R. Soc. trop. Med. Hyg., 67, 30. , - - , HAMILTON, P. J. S. & MARSHALL, T. F. DE C. (19~74). Ibid., 68, 190. APPELMANS, M. (1958). Bull. M~m. Soc. ft. Ophtal., 71, 244. BROWNE, S. G. (1961). Trans. R. Soc. trop. Med. Hyg., 55, 258. BUCK, A. A., ANDERSON, R. I., KAWATA, K. & HITCHCOCK, J. C. (1969). Am. J. trop. Med. Hyg., 18, 217. - - , - - , COLSTON, J. A. C., WALLACE, C. K., CONNOR, D. H., HARMAN, L. E., DONNER, M. W. & GANLEY, J. P. (1971). Bull. Wld Hlth Org., 45, 353. BUDDEN, F. H. (1962). Br. J. Ophthal., 46, 1. (1963). Trans. R. Soc. trop. Med. Hyg., 57, 64. CHOYCE, D. P. (1972). Proc. R. Soc. Med., 65, 955. CLARKE, V. DE V. (1966). Cent. Afr. J. Med., 12, Suppl.

222

STUDIES ON ONCHOCERCIASIS IN THE UNITED CAMEROON REPUBLIC

CONNOR, D. H., MORRISON, N. E., KERDEL-VEGAS, F., BERKOFF, H. A., JOHNSON, F., TUNNICLIFFE, R., FAILING, F. C., HALE, L. N. & LINDQUIST,K. (1970). Hum. Path., |, 553. CROSSKEY, R. W. (1955). Ann. trop. Med. Paras#., 49, 142. D'HAussY, R. (1958). Bull. Mdm. Soc. fr. Ophtal., 71, 258. DUKE, B. O. L. (1966). Ann. trop. Med. Parasit., 60, 495. - (1967). Ibid., 6 1 , 326. (1970). Ibid., 64, 421. (1970). Trans. R. Soc. trop. Med. Hyg., 64, 791. - & ANDERSON,J. (1972). Z. Tropenmed. Parasit., 23, 354. , LEWIS, D. J. & MOORE, P. J. (1966). Ann. trop. Med. Parasit., 60, 318. , MOORE, P. J. & DE LE6N, J. R. (1967). Ibid., 61, 332. , - & ANDERSON,I. (1972). Ibid., 66, 219. EICHLER, D. A. & NELSON, G. S. (1971). J. Helminth., 45, 245. FUGLSANG, H. & ANDERSON,J. (1973). Lancet, ii, 321. ISRAEL, M. S. (1959). Trans. R. Soc. trop. Med. Hyg., 53, 142. KERSHAW, W. E., DUKE, B. O. L. & BUDDEN, F. H. (1954). Br. Ivied. J., 2, 724. LAGRAULET,J., MONJUSIAU,A. & DURAND, B. (1964). M3d. Trop., 24, 566. LE BERRE, R., BALAY, G., BRENGUES,J. & Coz, J. (1964). Bull. Wld Hlth Org., 31, 843. LEWIS, D. J. & DUKE, B. O. L. (1966). Ann. trop. &led. Parasit., 60, 337. MAZZOTTI,L. (1959). Rev. Inst. Salubr. Enferm. trop. (Mex.), 19, 1. MELLOR, P. S. (1973). J. Helminth., 47, 97. MONJUSlAU, A. G. M., LAGRAULET,J., D'HAussY, R. & GOCKEL, C. W. (1965). Bull. Wld Hlth Org., 32, 339. NEUMANN, E. & GUNDERS,A. E. (1973). Am. J. Ophthal., 75, 82. NIEL, G., GENTILINI, M., COUTURE,J., PINON, J.-M. & DANIS, M. (1972). Bull. Soc. Path. ~xot., 65, 569. NNOCHIRI, E. (1964). Ann. trop. Med. Parasit., 58, 89. ROBERTS, S. R. (1963). Am. J. Ophthal., 55, 1049. RODGER, F. C. (1957). Trans. ophthal. Soc. U.K., 77, 267. (1958). Brit. J. Ophthal., 42, 21. - (1959). Trans. R. Soc. trop. Med. Hyg., 53, 138. (1960). Am. J. Ophthal., 49, 560. (1962). Bull. Wld Hlth Org., 27, 429. SMITHERS, S. R. & TERRY, R. J. (1969). Adv. Parasit., 7, 41. WOODRUFF, A. W., BARNLEY,G. R., HOLLAND,J. T., JONES, D. E., McCRAE, A. W. R. & MCLAREN, D. S. (1963). Trans. R. Soc. trop. ivied. Hyg., 57, 50.