FPIDFMIOLOGY OF FILARIASIS
m a i n l y i n v e s t i g a t e d , a l t h o u g h o t h e r parts o f t h e c o u n t r y w e r e visited to a l e s s e r e x t e n t . O n c h o c e r c i a s i s w a s f o u n d only in villages a l o n g t h e f o r m e r t w o rivers. N o i n f e c t e d i n d i v i d u a l s w e r e r e c o r d e d f r o m 9 8 7 p e o p l e s a m p l e d at thirty-five l o c a l i t i e s in t h e r e g i o n s o f C a c h e u , O i o a n d T o m b a l i o u t s i d e t h e k n o w n foci.
O f 516 p e o p l e e x a m i n e d in six villages along t h e G e b a river 102 ( 1 9 % ) w e r e infected with t h e disease. T h e data s h o w that t h e disease w a s m o r e prevalent in t h e older a g e groups.
Skin densities w e r e relatively l o w with t h e majority o f infec- ted individuals having less than 15 mff/mg.
Investigations in villages along t h e Corubal river s h o w e d that 3 1 6 ( 3 7 % ) o f 8 3 3 individuals e x a m i n e d w e r e infected. An analysis o f t h e disease in relation to a g e a n d s e x s h o w s that although larger n u m b e r s o f older p e o p l e w e r e infected t h e disease w a s also significant in y o u n g e r males. Skin densities w e r e also higher than for individuals from villages along the G e b a river.
Typical s y m p t o m s o f o n c h o c e r c i a s i s w e r e s e e n in infected individuals a n d 4 8 o f t h e i n f e c t e d p e o p l e w e r e b l i n d ( 3 1 males a n d 17 females). In most c a s e s this w a s d u e to t h e pre- s e n c e o f microfilariae in t h e eye.
T h e data p r e s e n t e d indicate that t h e m o r e important o f t h e two foci is that o f t h e Corubal river. Irrigation s c h e m e s along the u p p e r r e a c h e s o f the G e b a river h a v e drastically r e d u c e d w a t e r flow a n d transmission is b e l i e v e d to b e o n l y sporadic or e v e n absent b e c a u s e o f the paucity o f S. damnosum s.l. in this area.
SIMULIIDAE
' " T P h e distribution o f Simuliidae in G u i n e a Bissau w a s inves- I tigated ( G r a c i o et al., in p r e s s ) a n d identification o f t h e c y t o s p e c i e s o f t h e Simulium damnosum c o m p l e x m a d e 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 t o t h e C o r u b a l f o c u s ( C h a r a l a m b o u s et al., in p r e s s ) .
O n l y S. sirbanum a n d S. konkourense w e r e found along t h e Corubal river b e t w e e n March 1 9 9 0 a n d N o v e m b e r 1 9 9 2 . T h e former s p e c i e s p r e d o m i n a t e d at localities a l o n g t h e u p p e r r e a c h e s a n d t h e largely z o o p h i l i c S. konkourense w a s t h e m a i n c y t o f o r m a l o n g t h e l o w e r r e a c h e s o f t h e r i v e r . M o r p h o m e t r i c analysis o f cytotyped larvae s h o w e d t h e s e t w o cytotaxa o f S. damnosum could b e separated using t h e num- b e r o f rows o f h o o k s in t h e posterior circlet a n d t h e n u m b e r o f hypstomial setae. Unfortunately, this differentiation o f t h e t w o c y t o t y p e s c o n t a i n e d a large p e r c e n t a g e o f o v e r l a p s o that u n e q u i v o c a l identifications c o u l d o n l y b e m a d e for s p e - c i m e n s in t h e e x t r e m e s o f t h e c o m b i n e d range (Lowry et al., in p r e p . ) .
E n t o m o l o g i c a l surveys s h o w e d t h e p r e s e n c e o f t h e following simuliid s p e c i e s associated with t h e G e b a a n d 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 i n t h e t w o c y t o s p e c i e s . Insufficient n u m b e r s o f S. konkourense p r e c l u d e d t h e c o m - pletion o f t h e e x p e r i m e n t .
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 o f the Simulium damnosum complex (Diptera : S i m u l i i d a e ) in G u i n e a B i s s a u . Medical and Veterinary Entomology, in press.
GRACIO A . J . dos Santos, SHELLEY A J . , RAYBOULD J . & NHAQUE A . T . : T h e b l a c k f l i e s ( D i p t e r a : S i m u l i i d a e ) o f G u i n e a B i s s a u . S y s t e m a t i c s , d i s t r i b u t i o n and b i o e c o l o g i c a 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 oncocer- cose 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 dam- nosum 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 N o r t h - C a m e r o o n s h o w e d that t h e pro- portion o f n o n - Onchocerca volvulus filarial larvae in t h e o n c h o c e r c i a s i s v e c t o r s (Simulium damnosus s.l.) w a s
BITING BEHAVIOUR AND HOST CAPACITIES
dult S. sirbanum a n d S. konkourense w e r e c o l l e c t e d biting m a n a n d large n u m b e r s o f t h e f o r m e r c y t o s p e - c i e s w e r e e x p e r i m e n t a l l y infected with O. volvulus t o c o m -
* Institut für Tropenmedizin, Universität Tübingen, Germany.
** Medical Research Station, Kumba, Cameroon.
*** Lehrstuhl für P o p u l a t i o n s g e n e t i k , Universität T ü b i n g e n , Germany.
**** Hôpital Central, Yaounde, Cameroon.
***** Hôpital Protestant, Ngaoundéré, Cameroon.
****** Fachgebiet Parasitologic Universität Hohenheim, Germany.
Parasite. 1994. ?. I S 7
Article available athttp://www.parasite-journal.orgorhttp://dx.doi.org/10.1051/parasite/199401s1007
EPIDEMIOLOGY O F 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 cat
ching days, FLIES L 3 + = flies with L 3 in the head, thorax or abdomen, % diss fl = % of dissected flies, m L 3/ i n f fl = mean number of L 3 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
K I ' I D K M I O l . O G Y O F l'ILAKIASIS
a s t o n i s h i n g l y high ( D u k e , 1 9 6 7 ; R e n z et al.. 1 9 8 9 ) . T w o m a j o r f o r m s o f l a r v a e w e r e d e s c r i b e d , T y p e D l a r v a e ( D u k e , 1 9 6 7 ) and T y p e G larvae ( R e n z et al., 1 9 8 9 ) . W h i l e the latter w a s identified as O. ocbengi from cattle ( W a h l et al.. 1 9 9 1 ) , the f o r m e r w a s r e c e n t l y d i s c o v e r e d to stem from an Onchocerca s p e c i e s in wart h o g s ( W a h l and Bain, 1 9 9 3 ) . In an e p i d e m i o l o g i c a l field study in t w o villages in North- C a m e r o o n w e a s s e s s e d the yearly c o - t r a n s m i s s i o n o f t h e s e filariae b y m a n - b i t i n g S. damnosum s.l. a n d its p o s s i b l e impact o n the local e p i d e m i o l o g y o f h u m a n o n c h o c e r c i a s i s .
MATERIAL AND METHODS
• h e biting a n d infection rate o f Simulium damnosum s.l.
w a s a s s e s s e d during t w o y e a r s n e a r o n e village in a cattle-raising area in the G u i n e a S a v a n n a (Galim, estimated population : h u m a n s : 3 5 0 . cattle : 7 , 0 0 0 ) and a n o t h e r in the S u d a n s a v a n n a ( K a m a , 5 0 0 ) . w h e r e o n l y n o m a d i c c a t t l e (estimated 5 0 0 ) are present from J a n u a r y to April. Flies w e r e caught b y v o l u n t e e r s in e x h a u s t o r s ("sucking t u b e s " ) from 7 . 0 0 h to 1 8 . 0 0 h at the nearly perennial rivers (Vina du Sud a n d B e n o u é ) during 1-30 days per m o n t h ( m e a n : 6 . 8 , total : 162 d a y s ) . A proportion o f the flies w a s s u b s e q u e n t l y dis
s e c t e d , fresh o r after d e e p f r e e z i n g , in t h e l a b o r a t o r y . Filarial infective larvae ( L 3 ) in the flies w e r e identified mor
phologically and a proportion o f t h e m w a s sent to T u b i n g e n for identification by specific DNA p r o b e s . Sibling s p e c i e s o f S. damnosum s.l. w e r e identified b y c y t o t a x o n o m y o f larvae in t h e n e a r b y rivers a n d m o r p h o l o g y o f adult flies. T h e e n d e m i c i t y o f h u m a n o n c h o c e r c i a s i s in the t w o villages w a s a s s e s s e d in r a n d o m s a m p l e s o f a u t o c h t o n o u s volunteers by parasitological e x a m i n a t i o n (2 skin snips from the iliac crest, p a l p a t i o n o f n o d u l e s ) and by t h o r o u g h o p h t h a l m o l o g i c a l e x a m i n a t i o n with a slit lamp. " O c u l a r o n c h o c e r c i a s i s " w a s defined as sclerosing keratitis, chorioretinitis a n d / o r microfi
lariae in the c o r n e a a n d / o r anterior c h a m b e r .
RESULTS
. squamosum w a s t h e p r e d o m i n a n t s p e c i e s in t h e G u i n e a s a v a n n a - s i t e in b o t h r a i n y a n d d r y s e a s o n ( 9 8 . 4 % o f 6 3 identified larvae, 9 7 . 4 % o f 2 . 9 7 0 identified adults). In the S u d a n savanna-site the v e c t o r s in b o t h s e a s o n s w e r e m a i n l y S. squamosum a n d S. damnosum s.str.
( 6 5 . 7 % a n d 3 2 . 9 % r e s p e c t i v e l y o f 7 0 larvae, 6 2 . 9 % and 3 7 . 1 % o f 2 , 6 0 6 a d u l t s ) . B o t h s p e c i e s w e r e a t t r a c t e d 2-3 times m o r e to a cattle than to a h u m a n bait. Flies c a u g h t o n cattle and o n m a n carried all three t y p e s o f filarial larvae.
T h e infection rates a n d the p r o p o r t i o n s o f the different fila
riae w e r e not different in the t w o v e c t o r s p e c i e s and b e t w e e n flies c a u g h t o n cattle a n d o n m a n .
T h e m o r p h o l o g i c a l identification o f 8 8 "wild" infective larvae o f O. volvulus. 160 O. ocbengi and 2 9 T y p e D L3 w-as confir
m e d for 90.1 %, 8 5 . 7 % and 100 % o f the larvae respectively by sequential hybridisation o f single L3 with an O. volvulus- specific and an O. ochengi/O. volvulus-specific DNA p r o b e . In K a m a a m o d e r a t e Annual Biting Rate ( 1 6 , 8 0 0 ) led to a m o d e r a t e Annual T r a n s m i s s i o n Potential o f 4 1 1 L3 p e r m a n p e r y e a r ( T a b l e I ) . A b o u t half o f t h e s e larvae ( 4 8 . 9 % ) w e r e O. volvulus. 3 1 . 1 % w e r e O. ocbengi a n d 2 0 % T y p e D. In G a l i m the biting rate w a s 8.7 t i m e s h i g h e r ( 1 4 7 , 5 0 0 ) and the
ATP 8 5 . 6 t i m e s h i g h e r ( 3 5 , 0 0 0 ) than in K a m a . H o w e v e r , only 7 % o f all L3 w e r e O. volvulus ; the remaining o n e s w e r e O. ocbengi. Nevertheless, the O. volvulus-transmission p o t e n t i a l in G a l i m ( 2 , 4 4 6 ) w a s 1 2 . 2 t i m e s h i g h e r than in K a m a ( 2 0 1 , T a b l e I ) .
O n c h o c e r c i a s i s w a s h y p e r e n d e m i c a n d s e v e r e in K a m a with 6 4 . 8 % microfilariae carriers, a m e a n microfilarial l o a d o f 5 6 % p e r positive s n i p a n d 3 2 . 6 % o f the population s h o w i n g o c u l a r implications ( T a b l e II). In Galim, o n c h o c e r c i a sis w a s h y p o e n d e m i c with o n l y 1 7 . 9 % skin snip-positives, 1.9 microfilariae p e r positive snip a n d 2.9 % o c u l a r o n c h o c e r c i a s i s ( T a b l e II).
Figure 1. - Onchocerca s p p . T r a n s m i s s i o n P o t e n t i a l and Microfilarial Density of (). volvulus in a Sudan (Kama) and Guinea savanna village (Galim) of North-Cameroon : Surface areas repre
sent 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 num
ber 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 l a r i a l l a r v a e in o n c h o c e r c i a s i s v e c t o r s in N o r t h - C a m e r o o n ( 5 1 . 2 - 9 3 % ) is a m a z i n g l y high. Most o f t h e s e "animal filariae" ( 6 0 . 9 - 1 0 0 % ) are O. ocbengi from cattle. In the rainy s e a s o n in the Sudan s a v a n n a , e v e r y third infected 5. damnosum s.l.
carries o n c h o c e r c a l larvae from wart h o g s .
T h i s h i g h p r o p o r t i o n o f a n i m a l filariae r e f l e c t s t h e high d e g r e e o f z o o p h i l y o f t h e o n c h o c e r c i a s i s v e c t o r s , w h i c h greatly d e c r e a s e s ( b y the s q u a r e p o w e r ) their v e c t o r c a p a city ( G a r r e t - J o n e s , 1 9 6 4 ) . F u r t h e r m o r e , it must b e s u p p o s e d that m a n y ( i f not m o s t ) o f the animal filarial L3 e n t e r man w h e n the v e c t o r s bite, and thus p r o v o k e an i m m u n o l o g i c a l
Parasite, 1994, /, I S
9
E P I D E M I O L O G Y O F FILARIASIS
r e a c t i o n . I n G a l i m t h e a n n u a l transmission o f O. volvulus w a s high ( 2 , 5 0 0 L 3 / m a n ) a n d w o u l d normally c a u s e hyper- e n d e m i c o n c h o c e r c i a s i s . H o w e v e r , t h e m e a n microfilarial d e n s i t y i n t h e 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 . 0 3 4 / s n i p ) a n d 1 0 7 (!) t i m e s l o w e r than in K a m a ( 3 6 . 2 9 ) , w h e r e t h e O. f o / f w / w s - t r a n s m i s s i o n w a s 1 2 t i m e s l o w e r ( F i g u r e 1 ) . T h i s c o u l d p o s s i b l y b e d u e t o t h e v e r y h i g h transmission o f O. ocbengi in G a l i m ( 3 3 , 0 0 0 L 3 / m a n x y e a r ) w h i c h might i n d u c e a partial c r o s s r e a c t i v e immunity in t h e l o c a l p o p u l a t i o n . T h i s h y p o t h e s i s is s t r e n g t h e n e d b y first i m m u n o l o g i c a l studies w h i c h d e m o n s t r a t e d a high d e g r e e o f h o m o l o g y b e t w e e n O. volvulus a n d O. ocbengi in pro- tein profile and s e r o l o g i c a l r e c o g n i t i o n , a n d s h o w e d signifi- c a n t d i f f e r e n c e s i n t h e s e r o l o g i c a l r e a c t i v i t y b e t w e e n patients from G a l i m a n d K a m a ( H o c h et al., 1 9 9 2 ) . It is thus c o n c l u d e d that t h e proximity, t h r o u g h o u t t h e year, o f large n u m b e r s o f cattle infected with O. ocbengi p r o b a b l y protect the local h u m a n p o p u l a t i o n from s e v e r e o n c h o c e r c i a s i s
ACKNOWLEDGEMENTS
T h e t e c h n i c a l a s s i s t a n c e o f M. D . E k a l e is gratefully a c - k n o w l e d g e d . T h i s investigation r e c e i v e d financial s u p p o r t from t h e C o m m i s s i o n o f E u r o p e a n C o m m u n i t i e s ( T S 2 / 0 1 8 4 - D ( A M ) a n d T S 3 / C T 9 2 - 0 0 6 ) .
REFERENCES
DUKE B . O . L . : Infective larvae, other than Onchocerca vol- vulus in Simulium damnosum. Annals of Tropical Medicine and Parasitology, 1967, 61, 200-205.
GARRET-JONES C. : T h e h u m a n b l o o d i n d e x o f m a l a r i a v e c 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. : S e r o l o g i c a l r e c o g n i t i o n o f s p e c i f i c a n d c r o s s - reactive antigens o f 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 m é t h o d o l o g i e d e s e n q u ê t e s c l i n i c o - p a r a s i t o - l o g i q u e s sur l ' o n c h o c e r c o s e en Afrique d e l ' O u e s t . 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. : T h e d e v e l o p m e n t
o f Onchocerca ochengi a n d O. dukei m i c r o f i l a r i a e t o infective stage larvae in Simulium damnosum s.l. a n d in m e m b e r s o f the S. medusaeforme group, following intra- t h o r a c i c i n j e c t i o n . Annals of Tropical Medicine and Parasitology, 1991, 85, 324-328.
WAHL G . & BAIN O. : D e v e l o p m e n t in Simulium damnosum s.l. o f t w o Onchocerca s p e c i e s from t h e African wart hog, O. ramachandrini and Onchocerca n. s p . to infec- tive larvae r e s e m b l i n g T y p e D-larvae D u k e , 1 9 6 7 . 1 9 9 3 , submitted.
PREPATENCY PERIOD AND SOME ASPECTS OF THE EPIZOOTIOLOGY OF O NCHOCERCA 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
lthough there is a high p r e v a l e n c e o f b o v i n e o n c h o c e r - / i c o s i s in N o r t h C a m e r o o n c o u p l e d with a h i g h i n c i - d e n c e o f m u l t i p l e - s p e c i e s c o n c u r r e n t infestations ( W a h l et al., in p r e s s ) , very little k n o w l e d g e e x i s t s o n t h e b i o l o g y , i m m u n o l o g y a n d p a t h o l o g y o f Onchocerca ochengi in par- t i c u l a r . T h e r e i s e m p h a s i s o n t h e s t u d y o f t h i s f i l a r i a b e c a u s e its life c y c l e , infective larvae ( W a h l et al., 1 9 9 1 ) a n d n o d u l e formation a r e very similar t o t h o s e o f O. volvu- lus. T h e n e e d f o r e x p a n d e d r e s e a r c h o n m o s t o f t h e s e 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 h a s b e e n g r o w i n g in r e c e n t y e a r s b e c a u s e o f its p o s s i b l e implication in t h e c o n - trol ( z o o p r o p h y l a x i s a n d c r o s s r e a c t i v e c o n c o m i t a n t i m m u - nity) o f h u m a n o n c h o c e r c i a s i s in a highly e n d e m i c r e g i o n ( R e n z etal.. 1 9 8 9 ; W a h l , 1 9 9 1 ; H o c h et al, 1 9 9 3 ) .
In this survey w e investigated t h e rate o f acquisition o f pal- p a b l e n o d u l e s a n d skin microfilariae o f O. ochengi during natural infestation in cattle with a v i e w t o find o u t t h e p r e - p a t e n t p e r i o d o f t h e parasitism. A n o t h e r o b j e c t i v e w a s t o find o u t h o w f e a s a b l e it w a s t o u s e cattle naturally infested w i t h O. ochengi t o p r o d u c e i n f e c t i v e l a r v a e w h i c h w e r e n e e d e d for i m m u n o l o g i c a l 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
