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é ^ ^ ^ W O R L D H E A L T H O R G A N I Z A T I O N

^ ^ ^ ^ O R G A N I S A T I O N M O N D I A L E D E L A S A N T E

GUIDE FOR THE CONTROL OF EMERGENCIES CAUSED BY YELLOW FEVER IN AFRICA Dakar, 30 May to 3 J u n e 1983

VIR/YF/83.5 ENGLISH ONLY

INOEXEO

PUBLIC HEALTH PROBLEMS ASSOCIATED WITH EPIDEMIOLOGY OF YELLOW FEVER IN NIGERIA

by

P r o f e s s o r A k i n y e l e F a b i y i and Dr A.0.0.Sorungbe

Y e l l o w l e v e r i s one of +-.he most a c u t e i n f e c t i o u s d i s e a s e s known to man. The v i r u s o f yellov/ f e v e r , an RMA v i r u s o f the i n s e c t - t r a n s m i t t e d group 3 d o c s not o n l y cause e p i d e m i c s , but i s a l s o known t o be endemic i n i n t e r - t r o p i c a l zones o f A f r i c r f a n d Gouth A m e r i c a . Y e l l o w f e v e r can vary i n i n t e n s i t y r a n g i n g from h y p e r a c u t e , which c o u l d be f a t a l w i t h i n 2-3 days, to the l a t e n t t y p e . The t y p i c a l d i s e a s e i s c h a r a c t e r i z e d b y sudden onset w i t h two-phased development, each phase s e p a r a t e d b y a s h o r t p e r i o d o f r e m i s s i o n . The f i r s t phase i s g e n e r a l l y i n f e c t i o u s w i t h - out s i g n s of l o c a l i z a t i o n , w h i l e the second phase i s u s u a l l y h e p a t o r e n a l . Y e l l o w f e v e r i s t r a n s m i t t e d i n West A f r i c a by members o f the m o s q u i t o f a m i l y of a ^ d i n a e , genus Aedes.

The s o c e l l e d " c l a s s i c a l " y e l l o w f e v e r o c c u r s u s u a l l y d u r i n g epidemics*

when ti-ie d i s e a s e i s o b s e r v e d i n many i n d i v i d u a l s , i s e a s i e r t o d i a g n o s e c l i n i c a l l y , s u b j e c t o f course t o l a b o r a t o r y c o n f i r m a t i o n . T h i s form o f y e l l o w f e v e r has an i n c u b a t i o n p e r i o d o f 3-6 days a f t e r t h e b i t e o f an i n f e c t e d mosquito, a l t h o u g h the i n c u b a t i o n p e r i o d may be l o n g e r i n some c a s e s . The d i s e a s e i s u s u a l l y sudden and i s marked by s h i v e r i n g , tempera- t u r e o f 39°c-40°c, i n t e n s e headache w i t h v e r t i g o , g e n e r a l i z e d m u s c u l a r p a i n s , nausea and v o m i t i n g , c o n j u n c t i v i t i s , b l o a t e d f a c e sometimes w i t h a s c a r l e t i n a type o f r a s h . The u r i n e a t t h i s s t a g e i s d a r k c o l o u r e d and does not c o n t a i n a l b u m i n . These syndromes l a s t about 2-4 d a y s , w i t h d e c r e a s e i n i n t e n s i t y o f the headache, b u t t h e c o n g e s t i v e c o n d i t i o n c o n t i n u e s w i t h minor"'hemorrhages and e p i s t a x i s . At t h i s s t a g e F a g e t ' s s i g n o f h i g h t e m p e r a t u r e (?9°c-40°c) and a f a l l i n p u l s e r a t e (from 110-80 or 130-90 b e a t s per minute) occurs.-

G e n e r a l l y , bv the 3 r d or 4th day from o n s e t , a r e m i s s i o n o c c u r s , c h a r a c t e r i z e d bv f a l l i n t e m p e r a t u r e t o 38°c, d i s a p p e a r a n c e o f headache, and i m p r o v e i i e n t ' i n the g e n e r a l c o n d i t i o n o f the p a t i e n t ^ T h i s c o n d i t i o n i.s h. o w e v e r s h o r t - l i v e d , ' l a s t i n g o n l y a f e w h o u r s , and i s f o l l o w e d b y h e p a t o r e n a l phase, which i s c V i a r^ ^ c t e r i z e d by a r i s e i n t e m p e r a t u r e , reappearance o f g e n e r a l symptoms, appearance o f j a u n d i c e ( i f i t h a d n o t o c c u r r e d d u r i n g the r e m i s s i o n s t a g e ) , v o m i t i n g , b u t t h i s time more

f r e q u e n t and nay c o n t a i n d i g e s t e d b l o o d ( b l a c k v o m i t u s ) . O t h e r

syndromes i n c l u d e hemorrhage e s p e c i a l l y o f the gum, b u c c a l mucosa, u t e r u s , stomach, and i n t e s t i n e ; a l b t i m i n u r i a , which may be o f sudden o n s e t and

D i r e c t o r , V i r u s R e s e a r c h L a b o r a t o r y , U n i v e r s i t y C o l l e g e H o s p i t a l , I b a d a n , N i g e r i a .

**

S e n i o r C o n s u l t a n t E p i d e m i o l o g i s t , F e d e r a l M i n i s t r y o f H e a l t h , L a g o s , N i g e r i a .

Ce document ne constitue pas une 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 Santé. Les opinions exprimées dans les articles signés n'engagent que leurs auteurs.

The issue of this document does not constitute formal publication. It should not be reviewed, abstracted or quoted without the agreement of the World Health Organization. Authors alone are responsible for views expressed in signed articles.

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V I R / Y F/83.5 page 2

i s g e n e r a l l y a common f e a t u r e o f y e l l o w f e v e r . I n a d d i t i c ) n , c a r d i a c i n v o l v e m e n t , e s p e c i a l l y o f t h e n y o c a r d i u m i s o b s e r v e d . P r o g r e s s i v e

t a c h y c a r d i a i s c o n s i d e r e d a n o m i n o u s s i g n . N o t a l l c a s e s o f y e l l o w f e v e r are however t y p i c a l o r c l a s s i c a l , a s d e s c r i b e d a b o v e , o r o f t h e same

g r a v i t y ; t h u s v a r i a t i o n s i n s y m p t o m s a n d / o r i n g r a v i t y P'Hy a f f e c t t h e c o u r s e o f the d i s e a s e .

D u r i n g n o n - e p i d e n i c p e r i o d s , i n f l u e n z a - l i V ; e ( w i t h o u t p u l m o n a r y

i n v o l v e m e n t ) f o r m s o f y e l l o w - f e v e r h ? v e b e e n d e s c r i b e d ^ The c i . s e a s e c a n be e v a l u a t e d by e i t h e r s e r o l o g y o r v i r u s i s o l a t i o n o r b o t h ; r e c o v e r ^ ' o c c u r s w i t h i n 2-3 d a y s .

The f o r e g o i n g h a v e b e e n d e l i b e r a t e l y e m p h a s i z e d . T h i s was n e c e s s a r y b e c a u s e most o f t h e problem.s e n c o u n t e r e d i n t h e e p i d e m i o l o g i c a l s t u d i e s of y e l l o w f e v e r i n N i g e r i a are i n t i m a t e l v t i e d i n w i t h th*- c l i n i c a l s y n d r o m e s a s s o c i a t e d w i t h t h e d i s e a s e .

I n N i g e r i a d u r i n g B r e t r o s p e c t i v e e v a l u a t i o n o f c a s e s o f v e l l o w f e v e r e p i d e m i c s r e p o r t e d t o t h e F e d e r a l M i n i s t r v o f H e a l t h b y d i f f e r e n t S t a t e s i n t h e F e d e r a t i o n , f o r a 15 y e a r p e r i o d "ï 1'^68-1982) , no l e s s t h a n

17 e p i d e m i c s were r e c o r d e d . These e p i d e m i c s spartned e i g h t o f t h e f i f t e e n y e a r s s t u d i e d . O v e r a l l , 1 7 5 c a s e s w i t h 5 d e a t h s w e r e r e p o r t e d f r o m a

t o t a l of e l e v e n s t a t e s ( o u t o f 19 S t a t e s ) .

The d i a g n o s i s o f y e l l o w , f e v e r i n I ' i g e r i a o' t e n n r e s e n t s v i t h v a r i o u s p r o b l e m s , e v e n d u r i n g e p i d e m i c s , and i s e v e n more d i f f i c u l t i n s u b a c u t e and a t y p i c a l form.s. I l a l a r i a , w h i c h i s e n d e m i c i n t h e c o u n t r y , u s u a l l v shows c l i n i c a l s y m p t o m s i n v a r i a b l y a l m o s t i d e n t i c a l w i t h t h e e a r l y s t a g e s o f y e l l o w f e v e r : s u d d e n o n s e t , h e a d a c h e , g e n e r a l i z e d a c h e s , and v,in;itiiig„

I n a d d i t i o n i n c a s e s o f p r i m a r y m a l a r i s ( e s o e c i a l l y P . f a l r . i p f. r n n i ) P l a s m o d i u m may be r a r e i r , hlood f i l, . ; s . M o s t 1 i e n t s p r e s e n t i i , P w i t h the symptoms a b o v e a r e g e n e r a l l y t r e a t e d f o r m a l a r i a , w V i i c h may^'not h e l p 4 'v,?^"^® ^'^^^ a s s o c i a t e d y e l l o w f e v e r , p l a s m o d i t i - %'ould be r a r e i n t h e b l o o d .stream. T'est o i t h e s n i . a l i e n r s v;ould n o t r- t u r n t o t h e c l i n i c

îi^îl

may n o t h a v e b e e n " c u r e d " o f t h e i r I n f e c t i o n w i t h m a l a r i a l x r e a t m e n t . Under t h e s e c i r c u m s t a n c e s , c a s e s o f y e l l o v f e v e r c a n '-o

' ^ f î c ! ; S ^ ' ' ^ ! ^ In o t h e r c a s e s , t h e p r e s e n c e o f s c a r l e t i n a r a s h c o u l d be c o n - J o S i f o v t ^ " m e a s l e s , a l t h o u g h s u c h a c a s e may r e a d i l y be e l i m i n a t e d i f K o p l i c k ' s s p o t s a r e p r e s e n t .

o-i.r, g r e a t e r i m p o r t a n c e i s t h e d i a : . n o s i s o f c a s e s p r e s e n t i n g . : w i t h :-my

^if^S ^fï^rl^''^^ h e p a t i t i s . G e n e r a l l y , c l i n i c a l c a s e s w i ' h m a l a i s e , f e v e r , d a r k u r i n e , j a u n d i c e a r c a s s o c i a t e d n o t o n l y w i t h h e p a t i t i s v i r u s e s b u t c-lso w i t h a g e n t s w h i c h cause h e p a t o - b i l i a r y d i s o r d e r s

( l e p t o s p i r o s i s , h e p a t o - t o x i n s e t c ) .

The t r a n s m i s s i o n o f y e l l o w f e v e r by v e c t o r m o s q u i t o e s o f t h e f a m i l y A e d i n a e h a s b e e n w e l l e s t a b l i s h e d . I n ÎLlgeria, a s i n s e v e r a l o t h e r p a r t s o f A f r i c a , n e d e s a e g y p t i . A. s i m p s o n i . / i . a f r i c a n s h a v e b e e n i n c r i m i n a t e d f o r m a i n t a i n i n g a c t i v e f o c i o f y e l l o : - / f . - v e r . T r T t h e s e v e c t o r r - : t h e

e x t r i n s i c i n c u b a t i o n p e r i o d (th?<t i i ^ t h e p e r i o d f r o m i n g e s t i o n r.z i n f e n t e d b l o o d t o w h e n s u c h m o s q u i t o e s c a n t r ^ n s i n i t i n f e c t i c u s v i r u s ) i s a b o u t 12 d a y s , s u c h m o s q u i t o e s r e m a i n i n f e c t i o u s f o r l i . f e ( a b o u t 6 o r m o r e m c n t h s ) . E x p e r i m e n t a l l y , w i t h A , a e g y p t i , t h i s i j e r i o d v a r i e s w i t h t l i e t e i . - i o e r a t u r e ,

I n A f r i c a , t h e m o n k e y w h i c h a c t s a s t h e m a i n r e s e r v o i r o f y e l l o v ;

f e v e r i n t h e f o r e s t i s l e s s s e n s i t i v e t o t h e v i r u s : u n l i k e i n t h e A m e r i c a s where the m a i n f o r e s t m o n k e y r e s e r v o i r ( e . g . A o t u s ; i s more s u s c e p t i b l e t o y e l l o w f e v e r v i r u s , a n d u s u a l l y d i e s o f t h e i n f e c t i o n ; t h u s m a k i n g i t p o s s i b l e a s an i n d e x t o d e t e c t e p i z o o t i c s . The A f r i c a n m o n k e y s s u r v i v e y e l l o w f e v e r i n f e c t i o n , t h e a t t e n t i o n o f epidenàologist c o u l d n o t b e d r a w n t o s u d d e n m o r t a l i t y o c c u r i n g among t h e m .

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VIR/YF/83.5 page 3

The l o c a l i z a t i o n o f f o c i o f y e l l o w f e v e r i n f e c t i o n s a t l e a s t i n A f r i c a i s v e r y d i f f i c u l t . I n a d d i t i o n , i n a r e a s where a c t i v e s y s t e m i c v a c c i n a t i o n o f human p o p u l a t i o n has taV^en p l a c e , a c t i v e f o c i o f i n f e c t i o n c o u l d n o t be r e a d i l y d e t e c t e d , e x c e p t from o c c a s i o n a l d e a t h s o f i n d i v i - d u a l s who may have been i n f e c t e d b e f o r e moving t o an a r e a w i t h l a r g e nurabersof vaccinées. G e n e r a l l y , s e r o l o g i c a l s u r v e y s have been s u c c e s s f u l though i n a r e a s where s y s t e m i c v a c c i n a t i o n s have n o t t a k e n p l a c e .

E p i d e m i o l o g i c a l s u r v e y s i n N i g e r i a a r e u s u a l l y c a r r i e d o u t t o

i n v o l v e man, m o s q u i t o e s , and w i l d a n i m a l s ; l i m i t e d d a t a from s u c h s u r v e y s can be summarized as f o l l o w s :

(a) I n s e v e r a l p a r t s o f N i g e r i a t h e r e a r e s t i l l f o c i o f y e l l o w f e v e r v/hich a r e n o t w e l l d e m a r c a t e d , t h e r e f o r e i n s p e c t i o n and c o n t r o l a r e d i f f i c u l t ,

(b) S e r i o u s e p i d e m i c s o f y e l l o v - f e v e r have o c c u r r e d a t t h e end o f the r a i n y s e a s o n when m a s s i v e m o s q u i t o r e - i n v a s i o n o c c u r s , ( c ) Areas o f y e l l o w f e v e r e p i d e m i c s a r e g e n e r a l l y c o n f l u e n c e s o f

r i v e r s , edges o f t h e r a i n f o r e s t s , d e r i v e d s a v a n n a , and r i c e — p-rowing p l a c e s . A r e a s o f e n d e m i c i t y i n c l u d e n o t o n l y t h e above b u t

also

heavy damp g u i n e a and e q u a t o r i a l f o r e s t s . These a r e a s are d i f f i c \ ; l t t o p e n e t r a t e .

(d) The e x t e r m i n a t i o n o f m o s q u i t o v e c t o r s has p r o v e n t o be n o t o n l y d i f f i c u l t b u t a l m o s t i m p o s s i b l e .

(e) The o n l y e f f e c t i v e c o n t r o l f o r t h e p r o t e c t i o n o f man, t h r o u g h w h i c h t h e c y c l e o f t r a n s m i s s i o n c o u l d be b r o k e n , i s by c o n t i - nuous and s u s t a i n e d v a c c i n a t i o n w i t h s t a b i l i z e d and r e l i a b l e y e l l o w f e v e r v a c c i n e s ,

A w e l l - e q u i p p e d , and w i t h p r o p e r l y t r a i n e d s t a f f , v i r u s l a b o r a t o r y c o u l d e f f e c t i v e l y be o f g r e a t v a l u e d u r i n g e p i d e m i c s and f o r s u r v e i l l a n c e s f o r y e l l o w f e v e r . Such l a b o r a t o r i e s a r e v e r y few and i n some c a s e s non- e x i s t e n t i n s e v e r a l c o u n t r i e s o f A f r i c a . I n N i g e r i a o n l y one s u c h

l a b o r a t o r y e x i s t s .

I n a d d i t i o n t o t h e s c a r c i t y o f v i r u s l a b o r a t o r i e s , c o m m u n i c a t i o n , and t r a n s p o r t s y s t e m s i n some c o u n t r i e s a r e r u d i m e n t a r y ^ t h u s i t may be d i f f i c u l t t o communicate i n f o r m a t i o n on h e a l t h p r o b l e m s t o h e a d q u a r t e r s where c r u c i a l d e c i s i o n s have t o be t a k e n . Roads a l s o p r o v e t o be impe- d i m e n t s to e p i d e m i o l o g i c a l s u r v e y s . I n some a r e a s , t h e few a v a i l a b l e r o a d s a r e i m p a s s a b l e i n t h e r a i n y s e a s o n .

There i s a n e c e s s i t y f o r t h e o r o p e r t r a i n i n g o f p h y s i c i a n s , n u r s e , h e a l t h o f f i c e r s e t c . on wrhat t o l o o k f o r i n s u s p e c t e d c a s e s o f y e l l o w f e v e r . I n d e e d , f o r m e d i c a l s t u d e n t s and graduante p h y s i c i a n s emphasis s h o u l d be made t h a t t h e y s h o u l d c o n s i d e r e v e r y case o f j a u n d i c e as y e l l o w f e v e r u n t i l p r o v e n o t h e r w i s e by l a b o r a t o r y e v a l u a t i o n s . D i f f e r e n t i a l d i a g n o s i s o f y e l l o w f e v e r from dengue, i n f l u e n z a , t y p h o i d , m a l a r i a , h e p a t i t i s and o t h e r j a u n d i c e s s h o u l d be emphasized and e v a l u a t e d f o r e f f e c t i v e and u s e f u l i n f o r m a t i o n i n c o m b a t i n g e p i d e m i c s o f y e l l o w f e v e r .

L a b o r a t o r i e s s h o u l d be e s t a b l i s h e d , p r o p e r l y e q u i p p e d w i t h r e a g e n t s

and s t a f f e d w i t h competent v i r o l o g i s t and s u p p o r t i n g a u x i l l i a r y s t a f f .

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