FPIDFMIOLOGY OF FILARIASIS

mainly investigated, a l though o ther parts o f the country

were visited to a lesser extent. Onchocerc ias i s was found

only in villages along the former two rivers. No infected

individuals w e r e r e c o r d e d from 9 8 7 p e o p l e s a m p l e d at

thirty-five loca l i t i es in the r eg ions o f C a c h e u , O i o and

Tombali outside the known foci.

O f 516 people examined in six villages along the Geba river

102 (19 % ) were infected with the disease. The data show

that the disease was more prevalent in the older age groups.

Skin densities were relatively low with the majority o f infec­

ted individuals having less than 15 mff/mg.

Investigations in villages along the Corubal river showed that

316 (37 % ) o f 833 individuals examined were infected. An

analysis o f the disease in relation to age and sex shows that

although larger numbers o f older people were infected the

disease was also significant in younger males. Skin densities

were also higher than for individuals from villages along the

G e b a river.

Typical symptoms o f onchocerciasis were seen in infected

individuals and 48 o f the infected people were blind (31

males and 17 females). In most cases this was due to the pre­

sence o f microfilariae in the eye.

The data presented indicate that the more important o f the

two foci is that o f the Corubal river. Irrigation schemes along

the upper reaches o f the Geba river have drastically reduced

water flow and transmission is bel ieved to be only sporadic

or even absent because o f the paucity o f S. damnosum s.l. in

this area.

SIMULIIDAE

' "TPhe distribution o f Simuliidae in Guinea Bissau was inves-

I tigated (Gracio et al., in press) and identification o f the

cytospecies o f the Simulium damnosum complex made at

l o c a l i t i e s w i t h i n a n d a d j a c e n t to t h e C o r u b a l f o c u s

(Charalambous et al., in press).

Only S. sirbanum and S. konkourense were found along the

Corubal river be tween March 1990 and November 1992. The

former species predominated at localities along the upper

reaches and the largely zoophil ic S. konkourense was the

m a i n c y t o f o r m a l o n g t he l o w e r r e a c h e s o f t he r iver .

Morphometric analysis o f cytotyped larvae showed these two

cytotaxa o f S. damnosum could be separated using the num­

ber o f rows o f hooks in the posterior circlet and the number

o f hypstomial setae. Unfortunately, this differentiation o f the

two cytotypes contained a large percentage o f overlap so

that unequivocal identifications could only be made for spe­

cimens in the extremes o f the combined range (Lowry et al.,

in prep.).

Entomological surveys showed the presence o f the following

simuliid species associated with the Geba and Corubal river

basins : Simulium alcocki, S. gartnsi, S. djallonense, S. cervi-

cornutum, S. unicornutum, S. ruficorne, S. adersi, S. tridens

and S. hargreavesi.

p a r e f i l a r i a l d e v e l o p m e n t in t h e t w o c y t o s p e c i e s .

Insufficient numbers o f S. konkourense precluded the com­

pletion o f the experiment .

REFERENCES

ABREU M.M. , MARINI A. : Contribuicäo para o estudo da oncocercose na Guiñé Portuguesa (Foco do Rio Corubal). Bol. Cult. Guiñé Port., 1964, 19, 433-453 (also published in Rev. Est. Ger. Univ. Mozambique, 1964, 1, 3-23.

ABREU M.M. , MARINI A. : Contribuicäo para o estudo dos Simuliidae (Díptera : Nematocera) da Guiñé Portuguesa. Estudo realizado na bacia hidrográfica do Rio Corubal. Bol. Cult. Guiñé Port., 1965, 20, 35-65.

CHARALAMBOUS M., SHELLEY A.J . & GRACIO A.J . dos Santos : Cytogene-

tical analysis of the Simulium damnosum complex (Diptera : Simuli idae) in Guinea Bissau. Medical and Veterinary Entomology, in press.

GRACIO A . J . dos Santos, SHELLEY A J . , RAYBOULD J . & NHAQUE A.T . :

The blackfl ies (Diptera : Simuli idae) o f Guinea Bissau. Systematics , distribution and b ioeco log ica l data. Acta Parasitológica Portuguesa. 1994, 2 (1), in press.

LECUONA M . O . : Nota previa sobre a existencia da oncocer-cose na Guiñé Portuguesa (primeiro caso registado). An. Inst. Med. trop., 1956. 13 (1/2), 83-87.

LECUONA M . O . : Primeiros dados sobre a distribuieäo da oncocer­cose na Guiñé Portuguesa. An. Inst. Med. trop., 1959, 16(1/4), 199-208.

LECUONA M . O . : A oncocercose e o seu interesse médico-social na Guiñé Portuguesa. Subsidios para o estudo epidemiológico do foco de Sonaco. Bol. Cult. Guiñé Port., I960, 15(58), 193-237.

LOWRY C.A., CHARALAMBOUS M., SHELLEY A.J . , GRACIO A.J . dos Santos

& HOWARD T.M. : Identification of larvae in the Simulium dam­nosum complex (Diptera : Simuliidae) from Guinea Bissau using multivariate morphometric analysis. In preparation.

TENDEIRO J . : Estudos sobre simúlios na Guiñé Portuguesa. García de Orta, 1963, 7 7 (2), 243-252.

TRANSMISSION OF ONCHOCERCA VOLVULUS, 0. OCHENGI AND TYPE D FILARIAE BY SIMULIUM DAMNOSUM S.L. IN NORTH CAMEROON AND ITS INFLUENCE ON THE EPIDEMIOLOGY OF HUMAN ONCHOCERCIASIS WAHL G.*, ENYONG P.**, SCHIESEL J.M.***, NGOSSO A.****, TUBBESING H.*****, MOYOU R.**, & RENZ A.******

KEY WORDS : Onchocerca volvulus. Onchocerca ochengi. Simulium damnusum. North Cameroon.

INTRODUCTION

E arlier studies in North-Cameroon showed that the pro­

portion o f non- Onchocerca volvulus filarial larvae in

the onchocerc ias i s vectors (Simulium damnosus s.l.) was

BITING BEHAVIOUR AND HOST CAPACITIES

dult S. sirbanum and S. konkourense were co l lec ted

biting man and large numbers o f the former cytospe­

cies were experimental ly infected with O. volvulus to com-

* Institut für Tropenmedizin, Universität Tübingen, Germany. ** Medical Research Station, Kumba, Cameroon. *** Lehrstuhl für Populationsgenetik, Universität Tübingen, Germany. **** Hôpital Central, Yaounde, Cameroon. ***** Hôpital Protestant, Ngaoundéré, Cameroon. ****** Fachgebiet Parasitologic Universität Hohenheim, Germany.

Parasite. 1994. ?. I S 7

Article available at http://www.parasite-journal.org or http://dx.doi.org/10.1051/parasite/199401s1007

EPIDEMIOLOGY OF FILARIASIS

Table I. - Simulium damnosum s.l. biting- and infection rates in a Sudan- (Kama) and Guinea savanna village (Galim) of North-Cameroon. Ov = O. volvulus, Oo = O. ocbengi, TD = Type D filariae, SEAS = season, DS/RS = dry/rainy season, DAY = number of cat­ching days, FLIES L3+ = flies with L3 in the head, thorax or abdomen, % diss fl = % of dissected flies, mL3 / in f fl = mean number of L3 in the head, thorax or abdomen per infected fly, DBR = Dayly Biting Rate. ABR = Annual Biting Rate. DTP = Daily Transmission Potential, ATP = Annual Transmission Potential.

Table II. - Endemicity of human onchorcerciasis in a Sudan- (Kama) and Guinea savanna village (Galim) of North-Cameroon, m/f ex = males/females examined, m/f st = males/females expected in OCP standard population (Moreau etal.. 1978), % snip+ - % of examined with one or two positive skin snips, mf/snip = arithmetic mean number of microfilariae per 1 positive snip, % nod+ = % of examined with palpable nodules, nod/pat = a. mean number of nodules per positive patient, oconch = ocular onchocerciasis, % corr+ = percentage corrected for OCP standard population.

8 Parasite, 1994, J, I S

KI ' IDKMIOl .OGY O F l'ILAKIASIS

astonishingly high (Duke , 1967 ; Renz et al.. 1989) . T w o ma jo r fo rms o f l a rvae w e r e d e s c r i b e d , T y p e D l a rvae (Duke , 1967) and Type G larvae (Renz et al., 1989) . While the latter was identified as O. ocbengi from cattle (Wahl et al.. 1991) , the former was recently discovered to stem from an Onchocerca spec ies in wart hogs (Wahl and Bain, 1993) . In an epidemiological field study in two villages in North-Cameroon w e assessed the yearly co-transmission o f these filariae by man-bi t ing S. damnosum s.l. and its poss ib le impact on the local epidemiology o f human onchocercias is .

MATERIAL AND METHODS

• he biting and infection rate o f Simulium damnosum s.l. was assessed during two years near o n e village in a

cattle-raising area in the Guinea Savanna (Galim, estimated population : humans : 350 . cattle : 7 ,000) and another in the Sudan savanna ( K a m a , 5 0 0 ) . whe re only nomad ic catt le (estimated 5 0 0 ) are present from January to April. Flies were caught by volunteers in exhaustors ("sucking tubes") from 7.00 h to 18.00 h at the nearly perennial rivers (Vina du Sud and B e n o u é ) during 1-30 days per month (mean : 6.8, total : 162 days). A proportion o f the flies was subsequently dis­sec t ed , fresh or after d e e p freezing , in the laboratory . Filarial infective larvae (L3) in the flies were identified mor­phologically and a proportion o f them was sent to Tubingen for identification by specific DNA probes. Sibling species o f S. damnosum s.l. were identified by cytotaxonomy o f larvae in the nearby rivers and morpho logy o f adult flies. T h e endemicity o f human onchocerciasis in the two villages was assessed in random samples o f autochtonous volunteers by parasitological examination (2 skin snips from the iliac crest, palpation o f nodules) and by thorough ophthalmologica l examination with a slit lamp. "Ocular onchocercias is" was defined as sclerosing keratitis, chorioretinitis and/or microfi­lariae in the cornea and/or anterior chamber .

RESULTS

. squamosum w a s the p r e d o m i n a n t s p e c i e s in the G u i n e a s a v a n n a - s i t e in b o t h ra iny and dry s e a s o n

(98 .4 % o f 63 identified larvae, 97 .4 % o f 2 .970 identified adults). In the Sudan savanna-site the vectors in both sea­sons were mainly S. squamosum and S. damnosum s.str. (65 .7 % and 32 .9 % respectively o f 7 0 larvae, 62 .9 % and 37.1 % o f 2 , 6 0 6 adults) . Both spec i e s were attracted 2-3 times more to a cattle than to a human bait. Flies caught on cattle and on man carried all three types o f filarial larvae. T h e infection rates and the proportions o f the different fila­riae were not different in the two vector species and bet­w e e n flies caught on cattle and on man.

The morphological identification o f 8 8 "wild" infective larvae of O. volvulus. 160 O. ocbengi and 29 Type D L3 w-as confir­med for 90.1 %, 85.7 % and 100 % of the larvae respectively by sequential hybridisation o f single L3 with an O. volvulus-specific and an O. ochengi/O. volvulus-specific DNA probe.

In Kama a moderate Annual Biting Rate ( 1 6 , 8 0 0 ) led to a moderate Annual Transmission Potential o f 411 L3 per man per year (Table I ) . About half o f these larvae (48 .9 % ) were O. volvulus. 31.1 % were O. ocbengi and 20 % Type D. In Galim the biting rate was 8.7 times higher ( 1 4 7 , 5 0 0 ) and the

ATP 8 5 . 6 t imes higher ( 3 5 , 0 0 0 ) than in K a m a . However , only 7 % o f all L3 were O. volvulus ; the remaining ones were O. ocbengi. Nevertheless, the O. volvulus-transmission potential in Galim ( 2 , 4 4 6 ) was 12.2 t imes higher than in Kama ( 2 0 1 , Table I ) .

O n c h o c e r c i a s i s was h y p e r e n d e m i c and seve re in K a m a with 64 .8 % microfilariae carriers, a mean microfilarial load o f 56 % per positive snip and 32 .6 % o f the population sho­wing ocular implications (Table II). In Galim, onchocerc ia­sis was hypoendemic with only 17.9 % skin snip-positives, 1.9 microfilariae per positive snip and 2.9 % ocular oncho­ce rc i a s i s (Table II).

Figure 1. - Onchocerca spp. Transmission Potential and Microfilarial Density of (). volvulus in a Sudan (Kama) and Guinea savanna village (Galim) of North-Cameroon : Surface areas repre­sent values from Tables I+II and are proportional between villages. Ov = O. volvulus. Oo = O. ocbengi. TD = Type D filariae, ATP = Annual Transmission Potential, Ov-MF/SNIP = arithmetic mean num­ber of O. volvulus microfilariae per 1 (positive and negative) snip.

DISCUSSION

I h e p r o p o r t i o n o f n o n - O volvulus f i larial l a rvae in onchocerc ias is vectors in North-Cameroon (51 .2 - 9 3 % )

is amazingly high. Most o f these "animal filariae" ( 6 0 . 9 -100 % ) are O. ocbengi from cattle. In the rainy season in the Sudan savanna, every third infected 5. damnosum s.l. carries onchocerca l larvae from wart hogs.

Th is high propor t ion o f animal filariae reflects the high degree o f zoophi ly o f the onchoce rc i a s i s vectors , which greatly decreases (by the square power ) their vector capa­city (Garret-Jones, 1964) . Furthermore, it must b e supposed that many (if not most ) o f the animal filarial L3 enter man when the vectors bite, and thus provoke an immunological

Parasite, 1994, /, I S 9

E P I D E M I O L O G Y O F FILARIASIS

reaction. In Galim the annual transmission o f O. volvulus

was high (2 ,500 L3 /man) and would normally cause hyper-

endemic onchocerc ias i s . However , the mean microfilarial

d e n s i t y in t he w h o l e p o p u l a t i o n w a s s t r i k i n g l y l o w

(0 .034 / sn ip ) and 107 (!) times lower than in K a m a ( 3 6 . 2 9 ) ,

w h e r e the O. fo/fw/ws-transmission was 12 t imes lower

(Figure 1 ) . This cou ld poss ib ly b e due to the very high

transmission o f O. ocbengi in Galim ( 3 3 , 0 0 0 L3/man x year)

which might induce a partial crossreactive immunity in the

local populat ion. This hypothesis is s t rengthened by first

immunological studies which demonstrated a high degree

o f homology be tween O. volvulus and O. ocbengi in pro­

tein profile and serological recognition, and showed signifi­

c a n t d i f f e r e n c e s in t he s e r o l o g i c a l r eac t iv i ty b e t w e e n

patients from Galim and Kama (Hoch et al., 1992) . It is thus

conc luded that the proximity, throughout the year, o f large

numbers o f cattle infected with O. ocbengi probably protect

the local human population from severe onchocerc ias is

ACKNOWLEDGEMENTS

T h e t echn ica l ass i s tance o f M. D. Eka le is gratefully ac ­

knowledged . This investigation received financial support

from the Commission o f European Communit ies ( T S 2 / 0 1 8 4 -

D (AM) and T S 3 / C T 9 2 - 0 0 6 ) .

REFERENCES

DUKE B . O . L . : Infective larvae, other than Onchocerca vol­vulus in Simulium damnosum. Annals of Tropical Medicine and Parasitology, 1967, 61, 200-205.

GARRET-JONES C. : The human b lood index o f malaria vec tors in relation to epidemiological assessment. Bulletin of the World Health Organization, 1964, 30, 345-362.

HOCH B . , WAHL G . , ENYONG P . , LÙDER C.G.K. , HARNETT W . &

RENZ A. : Serologica l recogni t ion of specif ic and cross-reactive antigens of O. ochengi and O. volvulus by infected cattle and humans. Tropical Medicine and Parasitology, 1992, 43, 206-207.

MOREAU J . P . , PROST A. & PROD'HON J . : Essai de normalisation

de la méthodolog ie des enquê tes c l in ico-paras i to-logiques sur l ' o n c h o c e r c o s e en Afrique de l 'Ouest. Médecine Tropicale, 1978, 38, 43-51.

RENZ A., SCHIBEL J . , EICHNER M . & ENYONG P . : Animal filariae

in anthropophilic Simulium spp. in North Cameroon. Tropical Medicine and Parasitology, 1989, 40, 386-387.

WAHL G . , EKALE D., ENYONG P . & RENZ A. : The development

of Onchocerca ochengi and O. dukei microfi lariae to infective stage larvae in Simulium damnosum s.l. and in members of the S. medusaeforme group, following intra­thoracic inject ion. Annals of Tropical Medicine and Parasitology, 1991, 85, 324-328.

WAHL G . & BAIN O. : Development in Simulium damnosum s.l. o f two Onchocerca spec ies from the African wart hog, O. ramachandrini and Onchocerca n. sp. to infec­tive larvae resembling Type D-larvae Duke, 1967. 1993, submitted.

PREPATENCY PERIOD AND SOME ASPECTS OF THE EPIZOOTIOLOGY OF ONCHOCERCA OCHENGI INFESTATION IN CATTLE IN THE ADAMAWA PLATEAU, CAMEROON ACHU-KWI*, DAIBER W.H.**, RENZ A.***, WAHL G.** &

WANJI S.****

KEY WORDS : Onchocerca ochengi. epizootiology. prepotency,

infective larvae, cattle. Cameroon.

SUMMARY

In an onchocerciasis endemic area, calves which were one to 24 months old, were examined for palpable Onchocerca ochengi

nodules and microfilariae in skin snips. A highly infested bait oxen was used for the production of infective larvae through the vector Simulium squamosum. A prepotent period of about 1 0 months for the appearance of palpable nodules and skin microfilariae was identified, and the prevalence of nodules (80.5 %) and the microfilarial density (0.74 microfilariae per mg skin biopsy) was highest in the 19-24 months old animals. Peaks of 4.8 infective larvae per blood fed fly were reached during infective larvae production. The ease of counting palpable nodules, collecting blood and skin snips, performing nodu-lectomy, isolating adult worms, keeping these in vitro and producing infective larvae provides favorable conditions for the use of this animal model for in vivo chemotherapy and vaccine development research.

INTRODUCTION

l though there is a high prevalence o f bovine onchoce r -

/ i cos i s in North C a m e r o o n c o u p l e d with a high inci­

dence o f multiple-species concurrent infestations (Wahl et

al., in press) , very little knowledge exists on the biology,

immunology and pathology o f Onchocerca ochengi in par­

t icu la r . T h e r e is e m p h a s i s on the s tudy o f th is f i laria

b e c a u s e its life cyc le , infective larvae (Wahl et al., 1 9 9 1 )

and nodule formation are very similar to those o f O. volvu­

lus. T h e n e e d for e x p a n d e d r e sea r ch on mos t o f t he se

a s p e c t s o f b o v i n e o n c h o c e r c o s i s ha s b e e n g r o w i n g in

recent years because o f its possible implication in the con­

trol (zooprophylaxis and crossreactive concomitant immu­

nity) o f human onchocerc ias is in a highly endemic region

(Renz etal.. 1989 ; Wahl, 1991 ; Hoch et al, 1993 ) .

In this survey w e investigated the rate o f acquisition o f pal­

pable nodules and skin microfilariae o f O. ochengi during

natural infestation in cattle with a view to find out the pre-

patent per iod o f the parasitism. Another object ive was to

find out h o w feasable it was to use cattle naturally infested

with O. ochengi to p roduce infective larvae which were

needed for immunological studies.

* Institute of Animal Research, Wakwa, B.P. 65. Ngaoundere, Cameroon. ** Institut für Tropenmedizin, Wilhelmstrasse 27, 72074 Tübingen, Germany. *** Fachgebiet Parasitologic Universität Hohenheim, Emil-Wolff-Strasse 34, 70599 Stuttgart, Germany. **** Museum National d'Histoire Naturelle, 6 1 , rue Buffon, 75231 Paris Cedex, France.

10 Pnrnsitp 1 OOzl ? 1 S