I^û^^^ ^ ^ S ^
WORLD HEALTH
ORGANIZATION
VIR/RC/74.36 ENGLISH ONLY
(Arbo)
ORGANISATION
M O N D I A L E D E L A SANTÉ
MEETING OF DIRECTORS OF WHO REFERENCE CENTRES FOR ARBOVIRUSES, CHLAMDYDIAE AND RICKETTSIAE Geneva, 1-5 A p r i l 1974
INDEXED
j>y^\ H E O ' / ^ ' .
YELLOW FEVER IN THE AMERICAS by 1 Thomas P. Monath, M.D. Chief, Vector-Borne Diseases D i v i s i o n Center f o r Disease C o n t r o l Ft. C o l l i n s , Colorado
2 7
E f f o r t s t o e r a d i c a t e Aedes a e g y p t i d u r i n g t h e f i r s t 30 y e a r s o f t h i s c e n t u r y r e s u l t e d i n the v i r t u a l d i s a p p e a r a n c e o f urban e p i d e m i c s o f y e l l o w f e v e r b u t uncovered t h e u n d e r l y i n g sylvan transmission cycle. S i n c e 1930, o n l y 14 e p i d e m i c s o f urban y e l l o w f e v e r have o c c u r r e d ; each f o l l o w e d i n t r o d u c t i o n o f t h e v i r u s from a j u x t a p o s e d j u n g l e f o c u s , and none r e s u l t e d i n a c o n t i n u i n g endemic p r e s e n c e . The l a s t o u t b r e a k was r e c o r d e d i n P o r t o f S p a i n , T r i n i d a d i n 1954. S i n c e 1930, t h e annual i n c i d e n c e o f human c a s e s o f j u n g l e y e l l o w f e v e r has been low and f a i r l y constant. P e r i o d i c a l l y an i n c r e a s e i n v i r u s a c t i v i t y i s m a n i f e s t e d by c a s e s c l u s t e r e d i n t i m e and space w i t h i n t h e endemic zone. A few e p i d e m i c s have broached t h e b o u n d a r i e s o f t h e endemic wet f o r e s t s o f South A m e r i c a , e x t e n d i n g i n t o A r g e n t i n a t o t h e s o u t h o r i n t o C e n t r a l America t o the n o r t h . Y e l l o w f e v e r v i r u s i s endemic i n B r a z i l , B o l i v i a , P e r u , and Colombia, i n f o r e s t e d and s p a r s e l y - p o p u l a t e d a r e a s under l i m i t e d c u l t i v a t i o n , d r a i n e d by t r i b u t a r i e s o f t h e Amazon and Orinoco R i v e r s . The i n c i d e n c e o f c a s e s i n t h e l a s t f i v e y e a r s , r e f l e c t i n g o n l y t h e a c t i v i t y of y e l l o w f e v e r i n i t s s y l v a n c y c l e , i s shown i n T a b l e 1. Brazil. Y e l l o w f e v e r c a s e s a r e s p o r a d i c a l l y r e c o g n i z e d i n t h e s t a t e s o f P a r a , Amazonas, A c r e , Mato G r o s s o , G o i a s , and i n t h e t e r r i t o r i e s o f Roraima and Rondoma. No d i s c r e e t o u t b r e a k s o c c u r r e d from 1969 t o December, 1972 when s i x c a s e s were c o n f i r m e d i n f o u r m u n i c i p a l i t i e s of s o u t h - c e n t r a l G o i a s S t a t e . A n o t h e r 31 c a s e s were r e c o r d e d from t h i s r e g i o n i n 1973, t h e l a s t i n t h e month o f April.•'• A t l e a s t 30 c o u n t i e s o f G o i a s S t a t e were a f f e c t e d ; 2 scattered c a s e s were a l s o r e c o g n i z e d i n c o n t i g u o u s a r e a s o f M i n a i s Gérais. A. a e g y p t i was r e p o r t e d l y absent from t h e a r e a . The o u t b r e a k o c c u r r e d v e r y near t h e c i t y o f B r a s i l i a . Bolivia. Y e l l o w f e v e r i s r e c o g n i z e d a n n u a l l y i n an a r e a e x t e n d i n g westward from t h e l o w l y i n g Amazonian f o r e s t s o f e a s t e r n B o l i v i a t o t h e C o r d i l l e r a O r i e n t a l . The d e p a r t m e n t s o f S a n t a C r u z , Cochabamba, and L a Paz a r e g e n e r a l l y a f f e c t e d . As i n B r a z i l , t h e i n c i d e n c e o f c a s e s was low from 1969 t o 1972. I n January, 1972 a m i n o r o u t b r e a k ( e i g h t c o n f i r m e d c a s e s ) o c c u r r e d i n I n q u i s i v i P r o v i n c e i n e a s t e r n L a Paz Department. I n December, einother s m a l l e p i d e m i c began i n n o r t h - e a s t e r n Cochabamba and ended i n March, 1973; 24 c a s e s were r e c o g n i z e d . A n o t h e r 30 c a s e s were o f f i c i a l l y r e p o r t e d i n e a s t e r n La Paz Department i n May, 1973.
The issue of this document does not constitute formal publication. It should not be reviewed, abstracted or quoted without the agreement of the W o r l d Health Organization. Authors alone are responsible for views expressed in signed articles.
C e document ne constitue pas une publication. Il ne doit faire l'objet d'aucun compte rendu ou r é s u m é ni d'aucune citation sans l'autorisation de l'Organisation Mondiale de la S a n t é . Les opinions e x p r i m é e s dans les articles s i g n é s n'engagent que leurs auteurs.
VIR/RC/74.36 page 2
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Peru. From December, 1969 t o A p r i l , 1970 an o u t b r e a k of jungle y e l l o w f e v e r J u n i n Department, w i t h a t o t a l of 79 c a s e s r e c o r d e d . The a f f e c t e d r e g i o n l i e s i n zone of C e n t r a l P e r u , bounded t o the west by the Andes and t o the e a s t by Amazonas s t a t e s of B r a z i l . No f u r t h e r c a s e s were r e c o g n i z e d i n 1971, but i n i;)72 and 1973, v i r u s a c t i v i t y was r e f l e c t e d by a t o t a l of 39 r e c o r d e d c a s e s from Huanaco and Puno
occurred i n the e n d e m i c and A c r e increased departmen-fcs^
Colombia. A steady d r i b b l e of c a s e s a r e r e c o g n i z e d a n n u a l l y . A l t h o u g h i n the p a s t , y e l l o w f e v e r has f r e q u e n t l y appeared i n the Magdalena R i v e r v a l l e y , i n r e c e n t y e a r s the l l a n o s of e a s t e r n C o l o m b i a d r a i n e d by t r i b u t a r i e s of the O r i n o c o and Amazon r i v e r s have b e e n affected. Venezuela. In May, 1972 y e l l o w f e v e r was r e c o g n i z e d f o r the f i r s t time s i n c e 1966. t o t a l of 22 c a s e s were r e p o r t e d from L a r a , Apure, B a r i n a s and P o r t u g u e s a s t a t e s i n the s o u t h w e s t e r n p a r t of the c o u n t r y . T h i s a r e a , d r a i n e d by the O r i n o c o r i v e r , i s c o n t i g u o u s w i t h endemic r e g i o n s of C o l o m b i a . A. a e g y p t i was e i t h e r absent or p r e s e n t a t a very low l e v e l . 3 Other a r e a s . Y e l l o w f e v e r has not been r e p o r t e d from Ecuador s i n c e 1967. Prior to 1969, s c a t t e r e d c a s e s were r e c o g n i z e d a n n u a l l y a l o n g the b o r d e r s of V e n e z u e l a and Guyana; t h i s r e g i o n has s u b s e q u e n t l y remained s i l e n t . S p o r a d i c c a s e s have been c o n f i r m e d i n S u r i n a m i n 1969 and 1972. Panama has p e r i o d i c a l l y e x p e r i e n c e d e p i z o o t i c s of y e l l o w f e v e r i n D a r i e n p r o v i n c e , m a n i f e s t e d by i l l n e s s and d e a t h s among w i l d h o w l e r monkeys and by an i n c r e a s e d p r e v a l e n c e o f y e l l o w f e v e r a n t i b o d i e s i n s p i d e r monkeys."* The most r e c e n t v i r u s a c t i v i t y p r o b a b l y o c c u r r e d n e a r t h e Colombian b o r d e r d u r i n g the r a i n y season of 1970. S t u d i e s conducted i n 1973 showed no e v i d e n c e f o r westward movement of the v i r u s toward p o p u l a t e d a r e a s o f Panama r e c e n t l y d i s c o v e r e d t o be r e - i n f e s t e d by A. a e g y p t i . ^ S u r v e i l l a n c e of y e l l o w fever
i
Y e l l o w f e v e r i s m a i n t a i n e d i n n a t u r e by "wandering e p i z o o t i c s " i n w h i c h the v i r u s s l o w l y p a s s e s between t e r r i t o r i a l bands of monkeys w h i c h are decimated or immunized and subsequently repleted with susceptibles. Because the endemic a r e a s have few m e d i c a l s e r v i c e s and a r e d i s t a n t from d i a g n o s t i c l a b o r a t o r i e s , s u r v e i l l a n c e of human c a s e s i s at b e s t d i f f i c u l t , and the number o f r e p o r t e d c a s e s v a s t l y u n d e r e s t i m a t e d . At p r e s e n t s u r v e i l l a n c e depends upon the h i s t o p a t h o l o g i c d i a g n o s i s of v i s c e r o t o m y specimens c o l l e c t e d from f a t a l c a s e s i n r u r a l a r e a s . The governments of B r a z i l and C o l o m b i a i n c o l l a b o r a t i o n w i t h WHO, m a i n t a i n two r e f e r e n c e c e n t r e s f o r the p a t h o l o g i c d i a g n o s i s o f ' yellow fever. I n t e r e s t i n g l y , a l t h o u g h t h e r e has been a d e c l i n e i n emphasis o f v i s c e r o t o m y s e r v i c e s s i n c e the 1930's and 1940's, the i n c i d e n c e of r e p o r t e d c a s e s i n the l a s t decade a p p r o x i m a t e s t h a t of the v i s c e r o t o m y e r a . One may r e a s o n a b l y q u e s t i o n the p r o p r i e t y , i n 1974, o f such a p a s s i v e , l o o s e l y c o n s t r u c t e d s u r v e i l l a n c e system. Improved s u r v e i l l a n c e i s n e c e s s a r y f o r the f o l l o w i n g reasons : 1. The t r u e m o r b i d i t y of j u n g l e y e l l o w f e v e r has never been a c c u r a t e l y d e f i n e d i n the endemic zones. What f r a c t i o n of the whole " I c e b e r g " i s r e p r e s e n t e d by v i s c e r o t o m y monitoring? The p r i o r i t i e s of s u r v e i l l a n c e a c t i v i t i e s and v a c c i n a t i o n campaigns would u n d o u b t e d l y be changed by i n f o r m a t i o n of t h i s s o r t . The s e l e c t i o n of a r e a s f o r i n t e n s i f i e d s u r v e i l l a n c e i s r e l a t i v e l y simple. In the U c a y a l i - A p u r i m a c v a l l e y s of c e n t r a l Peru, f o r example, s p o r a d i c and c l u s t e r e d c a s e s a r e r e c o r d e d a n n u a l l y . 2. A m p l i f i c a t i o n o f v i r u s a c t i v i t y s h o u l d be e a r l y d e t e c t e d near d e n s e l y p o p u l a t e d a r e a s i n f e s t e d w i t h A. a e g y p t i . There i s u n i v e r s a l agreement^-'' t h a t t h e p r e s e n t c o n f i n e m e n t o f y e l l o w f e v e r t o i t s s y l v a n c y c l e r e p r e s e n t s an u n s t a b l e c o n d i t i o n . Recent e p i d e m i c s o f
VIR/RC/74.36 (Arbo) page 3 dengue i n the C a r i b b e a n and n o r t h e r n South A m e r i c a have u n d e r s c o r e d h i s t o r i c a l f e a r s of p o t e n t i a l urban y e l l o w f e v e r o u t b r e a k s . The r i s k s a r e e a s i l y a s s e s s e d i n terms of the r e p o r t e d p r e s e n c e of the urban v e c t o r , A. a e g y p t i . In Surinam, f o r example, where A. a e g y p t i i n d i c e s a r e h i g h , y e l l o w f e v e r has been r e p o r t e d i n 1969 and 1972. In C o l o m b i a , dengue spread i n l a n d i n 1971 from B a r r a n q u i l l a on the c o a s t towards M e d e l l i n , a f f e c t i n g a p p r o x i m a t e l y 416 000 p e r s o n s . A. a e g y p t i p o p u l a t i o n s had become r e - e s t a b l i s h e d i n t h i s r e g i o n f o l l o w i n g c u r t a i l m e n t of e r a d i c a t i o n e f f o r t s i n 1969, T h i s area i s c o n t i g u o u s w i t h the Magdalena V a l l e y , where y e l l o w f e v e r has been p e r i o d i c a l l y a c t i v e and may be endemic, 3, I t i s n e c e s s a r y t o m o n i t o r n a t u r a l c o r r i d o r s t h r o u g h w h i c h y e l l o w f e v e r may spread from i t s customary bounds. Examples o f such c o r r i d o r s a r e the D a r i e n P r o v i n c e of e a s t e r n Panama and the M i s i o n e s P r o v i n c e of A r g e n t i n a . What e p i d e m i o l o g i c a l methods can be adapted t o e f f e c t i n t e n s i f i e d s u r v e i l l a n c e of y e l l o w fever? A l t h o u g h a d m i t t e d l y d i f f i c u l t t o a p p l y , t e c h n i q u e s a r e a v a i l a b l e f o r the d i a g n o s i s of n o n - f a t a l as w e l l as f a t a l c a s e s . These i n c l u d e the c o l l e c t i o n of p a i r e d s e r o l o g i c a l samples and of a c u t e b l o o d s f o r v i r u s i s o l a t i o n a t t e m p t s . P r e s e r v a t i o n and shipment of t h e l a t t e r i s always a problem. L i q u i d n i t r o g e n can be used; a l t e r n a t i v e l y , Dr Downs has s u g g e s t e d the use of tube c u l t u r e s of m o s q u i t o c e l l c u l t u r e s , w h i c h can be m a i n t a i n e d at ambient t e m p e r a t u r e s f o r p r o l o n g e d p e r i o d s i n the f i e l d . S e r o l o g i c a l surveys, both prosp e c t i v e and r e t r o s p e c t i v e are u s e f u l f o r d e f i n i n g i n f e c t i o n r a t e s i n a g i v e n a r e a . On the b a s i s of a g e - s p e c i f i c a n t i b o d y r a t e s , p o p u l a t i o n s r e p e a t e d l y i n f e c t e d can be d e f i n e d . The r e s u l t s of s e r o l o g i c a l s u r v e y s a r e more e a s i l y i n t e r p r e t e d than i n West A f r i c a , s i n c e t h e p r o v a l e n c e of a n t i b o d i e s t o o t h e r group B a r b o v i r u s e s i s r e l a t i v e l y low. S t u d i e s of monkey of p r e d i c t i v e v a l u e . that v i r u s a c t i v i t y i s detected early? Does p o p u l a t i o n s and of v e c t o r m o s q u i t o s p r o v i d e s e c o l o g i c a l i n f o r m a t i o n In endemic a r e a s , e x a m i n a t i o n o f i n c i d e n c e t a b l e s c l e a r l y d e m o n s t r a t e s h i g h i n c e r t a i n y e a r s , low i n o t h e r s . Can a b u i l d - u p of a c t i v i t y be the v i r u s "wander" down p r e d i c t a b l e pathways, r i v e r v a l l e y c o r r i d o r s ?
S u r v e i l l a n c e of the k i n d s u g g e s t e d r e q u i r e s c o l l a b o r a t i v e e f f o r t s o f h e a l t h m i n i s t r i e s and l a b o r a t o r i e s o r i n s t i t u t e s v e r s e d i n the t e c h n i q u e s of a r b o v i r u s r e s e a r c h . There a r e fewer such i n s t i t u t e s , fewer a r b o v i r o l o g i s t s , and fewer funds t h a n i n former y e a r s . L i m i t e d programmes w i t h s p e c i f i c g o a l s might n e v e r t h e l e s s be s u p p o r t e d by c o n c e r n e d g o v e r n ments and PAHO/WHO. Yellow fever c o n t r o l . The p r e v e n t i o n of urban y e l l o w f e v e r o u t b r e a k s i s one of the agreed g o a l s of the A. a e g y p t i e r a d i c a t i o n programme. In 1947 and a g a i n i n 1972 t h e D i r e c t i n g C o u n c i l of PAHO r e s o l v e d t o pursue e r a d i c a t i o n i n a r e a s of the hemisphere i n f e s t e d and r e i n f e s t e d by A. a e g y p t i . J u n g l e y e l l o w f e v e r can be p r e v e n t e d o n l y by v a c c i n a t i o n . Large s c a l e v a c c i n a t i o n campaigns have been conducted d u r i n g and f o l l o w i n g o u t b r e a k s of the d i s e a s e , f o r example, i n G o i a s S t a t e i n 1972. E f f o r t s are g e n e r a l l y made t o v a c c i n a t e i m m i g r a n t s , l a b o u r e r s , and t o u r i s t s e n t e r i n g endemic r e g i o n s . S e v e r a l l i m i t e d permanent v a c c i n a t i o n programmes are also i n effect. V a c c i n a t i o n of a l l s u s c e p t i b l e s i s n o t , however, an a c c e p t e d o r o r g a n i z e d g o a l i n most of South A m e r i c a .
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REFERENCES 1. 2. 3. 4. PAHO Weekly E p i d e m i o l o g i c a l R e p o r t (1973) X L V ( 4 5 ) , 263 F. P i n h e i r o ( u n p u b l i s h e d ) WHO Weekly E p i d e m i o l o g i c a l Record (1973) No. 35, p. 345
G a l i n d o , P. & . S r i h o n g s e , S. (1967) E v i d e n c e o f r e c e n t j u n g l e y e l l o w f e v e r i n e a s t e r n Panama, B u l l . Wld H l t h Org., 36, 151-161
5. 6. 7.
Gorgas Memorial L a b o r a t o r y and M i d d l e America R e s e a r c h U n i t ( u n p u b l i s h e d i n f o r m a t i o n ) Reeves, W. C, (1972) Recrudescence o f a r t h r o p o d - b o r n e v i r u s d i s e a s e s i n t h e A m e r i c a s , PAHO S c i . Pub., 238, pp. 3-14 Downs, W. G. (1970) The problem o f y e l l o w f e v e r i n t h e A m e r i c a s . In: International C o n f e r e n c e on t h e A p p l i c a t i o n o f V a c c i n e s a g a i n s t V i r a l , R i c k e t t s i a l , and B a c t e r i a l D i s e a s e s of Man, PAHO/WHO, pp. 29-30 ~ PAHO Weekly E p i d e m i o l o g i c a l R e p o r t , (1972) XLIV, 62
8.
TABLE 1.
ANNUAL INCIDENCE OF YELLOW FEVER CASES
1969 8 4 7 28 1 48 * January-September.
1970 2 2 2 7 75 88
1971
1972
1973*
Total
Argentina Bolivia Brazil Colombia Ecuador Guyana Peru Surinam Venezuela Total
8 11 9 28
9 12 3 7 1 22 54
75 40 4 32 3 154
2 102 69 30 142 2 25 372