WORLD H E A L T H ORGANIZATION ORGANISATION M O N D I A L E D E L A SANTÉ MEETING O F DIRECTORS OF WHO REFERENCE CENTRES FOR ARBOVIRUSES, aiLAMYDIAE AND R I C K E T T S I A E
VIR/RC/74.23 ENGLISH ONLY
(Arbo)
Geneva,
1-5 A p r i l 1 9 7 4
E P I D E M I O L O G I C A L TRENDS OF C E R T A I N ARBOVIRUS D I S E A S E S YELLOW F E V E R IN WEST AND CENTRAL A F R I C A by Dr Y. R o b i n , D i r e c t o r , WHO R e g i o n a l Institut 1, 1.1 Central Africa review i t is a striking fact that there have never been important epidemics o f cases i n Pasteur, Reference Dakar, Centre for Arboviruses,
Senegal
Historical To begin fever
with,
yellow Zaire
i nCentral A f r i c a .
The most t h a t h a s o c c u r r e d
has been a few grouped
i n 1958. Since 1970, there seems t o h a v e b e e n r e s u m e d a c t i v i t y (4 c a s e s ) i n 1971 and again o f the virus, as reported (65 cases from - 42
Cameroon 1972.
(1 c a s e - 1 d e a t h ) a n d E q u a t o r i a l G u i n e a (2 cases - 2 deaths)
i n 1970,
Angola
deaths) and Z a i r e
Cameroon
(2 c a s e s - 2 d e a t h s ) i n
Obviously notified, 1.2
t h er e a l
number o f y e l l o w seem t h a t
fever
cases
i s very could
much h i g h e r
than
the
number
but i t would situation the
no i m p o r t a n t
epidemic
have o c c u r r e d
unnoticed.
Present Despite
institution
o f a s u r v e i l l a n c e system
i n 1968,
notvery
much i s known
about
the
present
situation. population i n several countries ' ^' I'*' idea of Central 1"^' o f the o f the Africa: While circulation of populations. makes t h e
1.2.1 S e r o l o g i c a l s t u d i e s a m o n g _ t h e _ h u m a n Serological these yellow they surveys fever are surveys have been c a r r i e d Chad, not out
Central A f r i c a n Republic, have s t i l l
C a m e r o o n , a n d G a b o n ^' ^'
made i t p o s s i b l e t o o b t a i n a t r u e the
v i r u s because o f v a c c i n a t i o n s and other useful for assessing present ^. h a s never been a r e a l epidemic, the
i n f e c t i o n s caused o f the
by Group B v i r u s e s ,
nevertheless there
degree o f r e c e p t i v i t y size
Although
receptive population
danger o f one o c c u r r i n g e v e r
1.2.2 S e r o l o g i c a l s t u d ^ 3'''2Di_*ii:Ë_YÎEÎ2^E2*25 Millan sera et a l , rarely found carriers of yellow fever antibodies i n s t u d i e s o f 694 (6/36).
from w i l d and domestic animals:
a f e w among s q u i r r e l s
(2/68) a n d monkeys
The
issue of this document does not constitute It should not be reviewed, Authors alone in signed
Ce
document ne constitue pas une publication.
formal publication.
Il ne doit faire l'objet d'aucun compte rendu ou résumé ni d'aucune citation sans l'autorisation de l'Organisation Mondiale de la S a n t é . Les opinions exprimées dans les articles s i g n é s n'engagent que leurs auteurs.
abstracted or quoted without the agreement of the World Health Organization. are articles. responsible for views expressed
VIR/RC/74.23
(Arbo)
page 2 In the C e n t r a l A f r i c a n R e p u b l i c and Chad, D i g o u t t e ^' ^ c a r r i e d out s e r o l o g i c a l s t u d i e s on w i l d a n i m a l s ( b i r d s , r o d e n t s and lai-ge mammals); these s t u d i e s however, d i d not r e v e a l any a n t i b o d i e s f o r y e l l o w f e v e r on i t s own. On tho o t h e r hand, r e a c t i o n s of the t y p e c a u s e d by m u l t i p l e i n f e c t i o n w i t h Group B v i r u s e s were f r e q u e n t . 1,2.3 S t u d ^ of th2_'^£2t2£S
In C e n t r a l A f r i c a , w h i l e s t u d i e s have p r o v i d e d many f a c t s c o n c e r n i n g p o t e n t i a l v e c t o r s i n the C e n t r a l A f r i c a n R e p u b l i c , Cameroon and Gabon , t h e r e have been very few s t u d i e s on the Congo or Chad ^, I t c o u l d be s a i d however, t h a t g e n e r a l l y s p e a k i n g , v e c t o r s are present everywhere.
Aedes a e g y p t i has been found everywhere i n towns, most o f t e n as a p e r i d o m e s t i c p e s t , s i n c e the problem of water s t o r a g e does not a r i s e i n the humid zones of C e n t r a l A i r i c a . A. a f r i c a n u s has been w e l l s t u d i e d , above a l l i n Cameroon and the C e n t r a l A f r i c a n Republic, In those c o u n t r i e s i t i s very abundant and very a g g r e s s i v e near the ground (palm g r o v e s , marshy l o w l a n d s , f o r e s t g a l l e r i e s ) . I t b i t e s day and n i g h t , but m o s t l y a t dawn and dusk, A. s i m p s o n i i s a l s o p e r i d o m e s t i c i n i t s e c o l o g y (banana p l a n t a t i o n s ) . It i s active d u r i n g the d a y - t i m e but becomes l e s s a n t h r o p o p h i l i c from e a s t t o west. Where i t i s a n t h r o p o p h i l i c , i t may cause t r a n s m i s s i o n between humans and thus s t a r t an e p i d e m i c ( E t h i o p i a , 1960-1962).
The
t h r e e v e c t o r s t h e r e f o r e , so f a r r e c o g n i z e d as major v e c t o r s o f y e l l o w f e v e r ,
are
omnipresent i n C e n t r a l A f r i c a . 1. 3 Future prospects
S t u d i e s a r e s t i l l needed i n o r d e r t o d e t e r m i n e how y e l l o w f e v e r v i r u s m a i n t a i n s i t s e l f in i t s sylvatic cycle. E f f o r t s must be c o n c e n t r a t e d on r e g i o n s where i t i s s u s p e c t e d t h a t the v i r u s i s permanently a c t i v e : Cameroon (Ayos Region) and the C e n t r a l A f r i c a n R e p u b l i c (South West Region) ^. 2 . 2 .1 West A f r i c a Historical review
U n l i k e C e n t r a l A f r i c a , West A f r i c a has known v a s t e p i d e m i c s o f y e l l o w f e v e r d u r i n g i t s history. The r e v i v a l o f y e l l o w f e v e r f i r s t became m a n i f e s t a t D i o u r b e l i n S e n e g a l i n the form o f an e p i d e m i c i n 1 9 6 5 . In 1 9 6 9 , t h e r e was an e p i d e m i c i n f i v e West A f r i c a n c o u n t r i e s : M a l i , Upper V o l t a , N i g e r i a , Togo and Ghana. In 1 9 7 0 , y e l l o w f e v e r was r e c o r d e d i n Ghana, N i g e r i a and Togo and i n 1 9 7 2 a g a i n i n Ghana. On the o t h e r hand, no case o f y e l l o w f e v e r has been r e p o r t e d from I v o r y Coast s i n c e 1 9 4 8 , from Dahomey s i n c e 1 9 5 1 , from Guinea s i n c e 1 9 5 2 and from S i e r r a Leone s i n c e 1 9 5 5 , 2.1 Present situation
The whole s u r v e i l l a n c e system depends i n e f f e c t on the i n t e r e s t shown i n t h i s d i s e a s e b d o c t o r s i n t h e s e n t i n e l h o s p i t a l s and the p r e v e n t i v e m e d i c i n e d e p a r t m e n t s . So f a r , the svstem has not produced t h e r e s u l t s a n t i c i p a t e d , so much so t h a t a p a r t from s t u d i e s c a r r i e d out by a few teams, knowledge o f the e p i d e m i o l o g i c a l s i t u a t i o n i n r e g a r d t o y e l l o w f e v e r i n west A f r i c a has made l i t t l e p r o g r e s s .
VIR/RC/74.23 page 3 2.2.1 Serological_studies_ainong_the_human surveys population almost the whole a r e a o f the y e l l o w tackled. been of
(Arbo)
Serological West A f r i c a . it the is difficult virus.
among the human p o p u l a t i o n have c o v e r e d i n t e r f e r e n c e from v a c c i n a t i o n s and from them as regards the enable conclusions
Because of the to draw any
heterologous to be not
Group B r e a c t i o n s , fever This is the
circulation problem
However,
s u r v e i l l a n c e of c h i l d r e n should
case i n the Kedougou r e g i o n , where i n c h i l d r e n who r e a c t i o n s have been r e c o r d e d . In the low campaigns, interpretation level which very fever virus survey English-speaking i s easier. of a c t i v i t y do give the
have c e r t a i n l y
vaccinated, regular
serological yellow recent vaccination
s t r o n g l y suggest This i s the
r e c e n t a t t a c k by Sierra
c o u n t r i e s where t h e r e have been no case with fever of the y e l l o w virus. receptive
Leone where a
showed a v e r y
In any The source capable
case,
serological
surveys then
some i d e a o f the
s i z e o f the
population.
danger o f an e p i d e m i c w i l l o f the v i r u s ( s y l v a t i c o f b r i n g i n g about
depend on
the e x i s t e n c e n e a r the presence i n s u f f i c i e n t beings.
population numbers, o f
concerned of a vectors
c y c l e ) and
transmission
between human vertebrates primates
2.2.2 It the
S e r o l o g i c a l s t u d i e s among w i l d s u r v e i l l a n c e o f the Institut by Pasteur,
i s essentially the
t h a t has
been the
subject
of a j o i n t mainly the
study Zika
between ORSTOM and results virus. covers I t may
Dakar, w i t h
a s s i s t a n c e from WHO.
I n t e r p r e t a t i o n of
i s made d i f f i c u l t however be
i n t e r f e r e n c e from o t h e r Group B a r b o v i r u s e s , t h a t the be zone where y e l l o w 11 N. between 9 and
concluded
f e v e r i s most h i g h l y endemic zone t h a t
the Guinea
savanna a r e a s
It i s therefore i n this
particularly 2.2.3
strict
s u r v e i l l a n c e should vectors
e x e r c i s e d ^,
Study o f the
The l i s t o f known p o t e n t i a l v e c t o r s c o m p r i s e s 11 s p e c i e s a t t h e moment, but i t i s not e x h a u s t i v e and l a b o r a t o r y s t u d i e s s h o u l d b r i n g t o l i g h t o t h e r p o t e n t i a l v e c t o r s . Major v e c t o r s a r e p r e s e n t everywhere ^' ^"^. A. still surveyed A. On aegypti ^. A. i s present africanus does not everywhere. focus In S e n e g a l , o f 1965 t o the the o n l y are forest zone where d e n s i t y over 50 galleries. indexes are
dangerous i s the e p i d e m i c
where they
i n almost a l l the
villages
remains r e s t r i c t e d bite man.
simpsoni the
o t h e r hand, Aedes o f the i n d i s c r i m i n a t e l y and
D i c e r o m y i a genus r e a d i l y probably being
bite
i n the
villages,
attacking
the
whole p o p u l a t i o n 2 children 2.3 Future
t h e cause o f t h e
infections
found i n
prospects r e s e a r c h on y e l l o w restricted three links zones f e v e r i s a long-terra t a s k . However, we ( E a s t Senegal, The scanty an results obtained of
Epidemiological seem out carrying and the out
of proportion in certain the
t o the amount o f work i n v o l v e d . i n the yellow
have had man,
opportunity Coast) abandoned vertebrates be
t h e Korhogo R e g i o n i n I v o r y other not they should
combined s t u d i e s on vectors. are f o r they
fever virus cycle: seem a m b i t i o u s ,
Although these foundation
programmes may o f a system
the v e r y
of e f f e c t i v e s u r v e i l l a n c e .
VIR/RC/74,23
(Arbo)
page 4 REFERENCES 1. Boche R., M i l l a n J . , k R a v i s s e P. (1972), P a r i s , 832-836. Cordellier R. & D o u c h i t e B. (1973), 103-138. F i n a l Report, 5th T e c h n i c a l Conference, OCEAC, Final Final Report, 1st Joint Meeting OCCGE-OCEAC,
2.
Report,
13th T e c h n i c a l
Conference,
OCCGË,
Bobo-Dioulasso, 3. Cordellier Yaoundé, 4. Cordellier
R. & G e o f f r o y B. (1970), 447-452. R. & G e o f f r o y B. (1972),
C a h i e r s ORSTOM, s i T i e
Entomologie
mi -dicalo Si
parasitologie, 5.
v o l . X, n
2, 43-60. R. (1973), Final RcporL,
Cornet M., Le G o n i d e c G., Bernadou J . , Robin Y., & T a u f f l i o b 13th T e c h n i c a l Conference, Final OCCGE, B o b o - D i o u l a s s o , Report, 5th T e c h n i c a l 98-102.
6. 7.
D i g o u t t e J . P. (1970), D i g o u t t e J . P. & P a j o t Yaoundé, 421-433. D i g o u t t e J . P. Yaoundé,
Conference,
OCEAC, Yaound--, 434-43(i.
F. X . (1970), F i n a l Report,
5th T e c h n i c a l Conforonco, OCEAC,,
8.
P a j o t F. X . (1971), F i n a l Report,
6th T e c h n i c a l
Conference,
OCEAC,
184-192. F i n a l Report, 6th T e c h n i c a l Conference,
9.
G a t e f f C., Labusquière R. & B o i s s o n P. (1971), OCEAC, Yaoundé, 121-135.
10.
Germain M., Eouzan J . P., F e r r a r a L., B u t t o n J . P. (1972), C a h i e r s ORSTOM, série E n t o m o l o g i e médicale Se p a r a s i t o l o g i e , v o l . X, n 2, 35-42. Germain M., M i l l a n Conference, J , , Eouzan J . P. k M a r t e l A. (1970), 437-446, C a h i e r s ORSTOM, série E n t o m o l o g i e médicale, Final Report, 5th Technical
11.
OCEAC, Yaoundé,
12.
Hamon J . , P i c h o n G. & . Cornet M. (1971), vol. IX,
n ° 1, 3-60. B u l l . Soc. P a t h , e x o t . Conference, In t h e P r e s s . OCEAC, Yaoundé, 457-462, Report,
13. 14. 15.
L e Gonidec G., St D h i v e r F. (1973), L o u r i e B. (1970), Millan 6th Final Report,
5th T e c h n i c a l
J . , Germain M., G a r c i n H., R i c k e n b a c h A. & B u t t o n J . P. (1971), Technical Conference, OCEAC, Yaoundé, 173-183. 6th T e c h n i c a l
Final
16.
Millan
J . , k Lamberton A. (1971),
F i n a l Report,
Conference,
OCEAC,
Yaoundé,
164-172. 18. Pajot F. X . (1972), C a h i e r s ORSTOM, série E n t o m o l o g i e médicale Se p a r a s i t o l o g i e , v o l . X,
n ° 2, 27-33. 19. Rickenbach Yaoundé, 20. A. & B u t t o n . J . P. (1973), F i n a l Report, 8 t h T e c h n i c a l Conference, OCEAC,
346-351. F i n a l Report, 8th Technical Conference, OCEAC, Yaoundé, 352-352c,
S u r e a u P. (1973),