WORLD
HEALTH
ORGANISATION MONDIALE De LA SANTÉ VC/Aedes Sera./9. ORIGINAL: ENGLISH
OkGANlZATiON SEMINAR ON THE ECOLOGY, BIOLOGY, CONTROL AND ERADICATION OF AEDES AEGYPTI Geneva, l6-20 Aup:ust Agenda Item 1.1 1965
AEDES AEGYPTI AND YELLOW FEVER by Fred L. Soper, M.D, Aedes a e g y p t i - t r a n s m i t t e d y e l l o w f e v e r - aegypti y e l l o w f e v e r f o r short - long, one of the great scourges of t r o p i c a l , s u b t r o p i c a l , and even temperate regions of the Americas, has been brought under complete c o n t r o l i n the Western Hemisphere. Only two small l o c a l outbi'eaks have occurred d u r i n g the past 28 years, the f i r s t at Senna Madureira i n the heart of the Amazon V a l l e y i n B r a z i l i n 19^2, the l a s t at \:Jhether the n a t i o n s of the Americas are t o be present
Port of Spain, T r i n i d a d , i n 1954.
spared f u t u r e epidemics of urban y e l l o w f e v e r depends on the completion of the Vfell -advanced programme f o r the e r a d i c a t i o n of Aedes^, a e p y p t i . The p o t e n t i a l danger i s c l e a r l y revealed by the 1963-1964-1965 outbreak of dengue i n c e r t a i n Caribbean i s l a n d s and Venezuela, This outbreak has been
.
d r a m a t i c a l l y l i m i t e d to areas I s t i l l I n f e c t e d w i t h a e g y p t i .
So long as the e r a d i c a t i o n
of aepypti i s incomplete, tha('continuing t h r e a t of r e i n f e s t a t i o n of eradicated areas i s very r e a l , as shown i n recent years by the r e i n f e s t a t i o n s of Colombia and of B r i t i s h and French Guianas. The most recent break i n the advancing e r a d i c a t i o n
programme i s the 1965 r e i n f e s t a t i o n of E l Salvador at a time when neighbouring c o u n t r i e s are not known to be i n f e s t e d . ( I n i t i a l i n v e s t i g a t i o n suggests t h i s
r e i n f e s t a t i o n came through the i m p o r t a t i o n from the United S t a t e s of o l d automobile t y r e s , a f a v o u r i t e breeding place f o r aegypti i n t h i s modem age.)
Man's v i c t o r y of urban y e l l o w f e v e r i n the Americas d i d not come e a s i l y , d i d not come r a p i d l y , and d i d not come cheaply. The conquest of yellow f e v e r was not
complete w i t h the i n i t i a l g l o r i o u s v i c t o r i e s i n Havana, Rio de J a n e i r o , Panama, Veracruz and Mew Orleans. Those f a c i n g the problems of a e g y p t i - t r a n s m i t t e d diseases
VC/Aedes Sem./9.65 page 2
i n o t h e r r e g i o n s may s i n c e 1900. was
s a i n much from a s t u d y of the c t r u s g l e aGain::t yello:.' f e v e r evidence
T h i s d a t e i s chosen s i n c e i t v/as the y e a r i n w h i c h c o n v i n c i n c
p r o d u c e d i n c r i m i n a t i n c Aedec a e g y p t i as the v e c t o r of y e l l o w f e v e r . The a t t a c k on y e l l o v ; f e v e r began i n Havana i n 1901. f o l l o w e d by s u c c e s s The v i c t o r y of Gor^jas i n Janeiro,
Havana was Brazil,
i n o t h e r c i t i e s of Cuba, i n Santos and R i o de
i n Veracruz
and Tampico, M e x i c o and i n the c i t i o c of Panama. t h a t i t was
V e r y e a r l y i n the s t r u g g l e a g a i n s t y e l l o w f e v e r i t became obvious not necessary fever;
t o c o m p l e t e l y e l i m i n a t e a e g y p t i t o s t o p the t r a n s m i s s i o n of y e l l o w r a p i d l y when the b r e e d i n g of a e g y o t i o c c a r r e d i n i n the l a r g e stopped,
yellow fever disappeared
l e s s t h a n 5^ o f the h o u s e s .
F u r t h e r , once y e l l o w f e v e r d i s a p p e a r e d
endemic c e n t r e s , a f t e r a p e r i o d o f some months o r a y e a r o r more, the d i s e a s e spontaneously i n the towns and v i l l a g e s of the e n t i r e t r i b u t a r y area.
These i m p o r t a n t
o b s e r v a t i o n s are r e a d i l y e x p l a i n e d on the b a s i s of the d e l i c a t e
i n t e r r e l a t i o n s h i p o f the s u p p l y of y e l l o w - f e v e r v i r u s , the d e n s i t y of the ae _f ,ypti m o s q u i t o , and t h e a v a i l a b i l i t y s i o n of y e l l o w f e v e r . t h e s e f a c t o r s , v/hich may (a) of s u s c e p t i b l e p e r s o n s needed f o r c o n t i n u e d trcin.smisof
T h i s i n t e r r e l a t i o n s h i p rnay be d i s t u r b e d by a d r o p i n any occur r e a d i l y because:
t h e v i r u s of y e l l o w f e v e r i s a v a i l a b l e f o r the i n f e c t i o n of the a.o_gypti individual •t h e i n f e c t e d a e g y p t i must s u r v i v e an 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 of b e f o r e becoming i n f e c t i v e ; nine
m o s q u i t o o n l y d u r i n g the f i r s t t h r e e days of the d i s e a s e i n the case; (b)
days o r more, d e p e n d i n g on the t e m p e r a t u r e ,
once
I n f e c t i v e , a e g y p t i remains so f o r l i f e , but doer, n o t t r a n s m i t the v i r u s t o t h e next generation; though i t may s u r v i v e f o r f i v e o r s i x months i n the l a b o r a t o r y ,
t h e e f f e c t i v e e p i d e m i o l o g i c s u r v i v a l p e r i o d i s g e n e r a l l y n o t over s i x o r s e v e n weeks ; (c) and the
p e r s o n s o f a l l r a c e s , b o t h s e x e s , and a l l ages are s u s c e p t i b l e , but
r a p i d l y a c q u i r e d immunity i s l i f e l o n g ; and no s e c o n d a t t a c k s .
t h e r e are no r e l a p s e s , no c a r r i e r s t a t e
page 3
Tne unbrol-.en "Gile.s of - r i c t o r i e s l e d v a r i o u s vrorkers even before 1910 dream of the c r a d i c a t i o i i oï y e l l o v fever;
to
tne opportvinity to underbake the orr.};
or.Tî v.'ith the c r e a t i o i i of the Roei .ief eller Fo;uida-':ioi? (1913) arid the i -ecog -iitlcai 'jf the yelj.ovj -f evei' t h r e a t to /vsia inherent li-. tra.-Cfic throursh the Panamr. Ganaj ;^egirining r.914.
j_i 191") the Roc:>:ef elj.er Pcjixdation dedicated i t s e l f to the task of the crddicatr'-or. of yeliov,- f e v e r •'rom ':,he world; was rhoser to load tbl^j ef:''or't. on th'.: obrer'/atr.onr. v:: Surgeon G a r e r a i Willi'.aiii G. Gore abased
Tar. plpi. o? a c t i o n wa^ f a i r l y simple^
or.perlerne of oh'j ;o:"e\-ioi.v : 1;3 yoars „
A rceonnaxssannti
of the oontinenc -'x I c e i i t i f y endémie y-^] Ic-r-fci^'er' centner T;as tc be f o l l c w e d te;"por?.].-y in'iensiya oa-n^paigiVJ -'^^ '^'""î- «eutr?*^ to rednc:e t h ; aogypt:'. iride:: b-^lc" the ohresliold r.eed.ec fo-'^ eort:.r .ueà trai:sn-,-j.ssio^. c:C y e l l c v ; fevex , Tne caKpatgn
against aegypti wo-jld be n-,air.tainec' ir. eacli endeT.ie centre imv.lj. y e l l o w ":e'r?r spontaneously disappeared from the bown-j ana v l l i a g o s of the surroui-.d^ng area tlirough e.-;di"ustion of the •^•r.pcep•viole ^jopula'cion bj" i-nmu:iization. Once a l l the \or
endemic areas had beer, covered i n t h i s manner, y e l l o w f e v e r could not recui-
lack of yel.lovr f e v e r - v l r u F even though thr; camoaign against the aeg ;^2tl mosquitc weT'p abandoned.
In 1916 a re connais s anne of the h i s t o r i c ye HOT J --fryer regions of the yAnerican i n d i c a t e d very few remaining endemic centre,- and r e l a t l y e l y easy v i e t o r y v/as anticipated,, A f t e r dela.ys due tc World War 1 / the e r a d i c a t i o n e f f o r t got underVJ.ctory i n ^,'^uador vras f o l l o w e d by successes i n Peril,
l a y i n Ecuador i n I 9 l 8 .
Colombia, C e n t r a l Ame-ica, Mex:ioc ard Venezuela, and by 19^5 v i e t o r y seemed near Brazil. .
lîie f i r s t suggestion c f f a i l u r e cexr.e w i t h the appearajice of y e l l o w fearer i n north-' -E't ^ I f o l l o w j . n g the xnt-"od^i,Gtxon of non-^mnui-ie troops i n 19^6. i n t e n s i f i e d attac]: on aeKjptl An
elimiinatad t h i s threai;, and d u r i n g 1927-19?8 a
p e r i o d of 12 months passed w i t h a r-ingle reported sporadic case of y e l l o w f e v e r . This calm was but the ln ?.l before the stcnTi. I n May 1928 y e l l o w fever Yellow fever
appeared i n Rio de uaneirc- where i t had been uniaiov.'n f o r 20 y e a r s .
tool: f u l l advantage of the high a e K / ^ t i - i n d e r . i n R i o <le J a n e i r o , a busy trop;'.cal
VC/Aedes
Sem„/9»65
seaport with a population o f 1 700 the
000
people;
15 months were required t o e l i m i n a t e
d i s e a s e from t h e c i o y and three years from the towns and v i l l a g e s o f the s u r r o u n d ! I n t h e meantime, y e l l o w fever had been recorded along the north coast of B r a z i
area.
and i n t h e Amazon V a l l o y a t Belein ;-nd Kanaos. The source o f i n f e c t i o n f o r Rio de Janeiro was not established at the time.. The
o u t b r e a k i n R i o de J a n e ' i o , however, emphasized the f a c t t h a t yellow fever - i n i t s c l a s s i c a l , , c l i n i c a l m a n i f e s t a t i c n a most dramatic d i s e a s e - had been able XQ c o n t i n u e unobserved d u r i n g a considerable period o f time and t o enter i i i o de Janeiro without i n d i c a t i o n o f the source o f i n f e c t i o n . The e v e n t s o f t h e next few years vrere t o reveal not one, but two mechanisms f o r the persistence o f yellow f e v e r during the R o c k e f e l l e r Foundation campaign of
eradication. The -introduction i n 1930 o f routine microscopic examination o f l i v e r t i s s u e from
f e b r i l e cases d y i n g a f t e r less t h a n 11--days ' i l l n e s s revealed a L- '.ent endemic r u r a l y e l l o w - f e v e r throughout a l a r g e a r e a o f n o r t h - e a s t B r a z i l which had been unsuspected by t h e y e l l o w fever workers i n t h e nearby c o a s t a l port c i t i e s . y e l l o w f e v e r depended on an unusual a r i d area. The endemicity This r u r a l endemic
d i s t r i b u t i o n o f the aegypti mosquito i n t h i s s e m j so high that most cases occurred
o f y e l l o w fever here was
i n c h i l d r e n u n d e r f i v e years o f agej
p r a c t i c a l l y no cases occurred beyond age 15.
The a t t a c k on aegyp_bi was c a r r i e d t o t h e r u r a l areas with the r e s u l t t h a t yellow f e v e r disappeared i n August 193^. I t i s now 31 years since the disease has been found i n
t h i s previously l a t e n t endemic area,. T h i s l.at n t endemic aegypti yellow fever explained the unexpected j'cllow f e v e r a ^ o r g troops i n 19ro, but i t s l i m i t e d extent and great distance from Rio de J a n e i r o maee ir. unacceptable braiitiful capital. The s e c o n d unrecognized e a s i l y handled; i n 1932 mechanism f o r the persistence of yellow fever was not so • as the source o f v i r u s f o r t h e 1928 outbreak i n B r a z i l ' s
yellow fever v/as proven t o occur i n the absence of Aedes Following t h i s r e v e l a t i o n ,
a e g y p t i i n the V a l e do Canaan, E s p i r i t o Santo, B r a z i l .
continuing studies l e d t o the r e c o g n i t i o n o f Jungle yellow fever as a disease of f o r e s t vertebrates, e s p e c i a l l y primates, transmitted by f o r e s t mosquitos other than Aedes aeo-
VC/Aedes Sem ./9.65 page 5
Observations
were made on the i n v a s i o n of s e v e r a l towns by Jungle v i r u s leading t o Thus came an understanding of the o r i g i n of the 1928
aogypti-transmitted outbreaks.
yellow-fover i n v a s i o n of Rio de J a n e i r o and the e q u a l l y enigmatic outbreaks of aeg^vpti yellovj f e v e r i n Socorro, Colombia and Guasapti, Venezuela, i n 1929 and t h a t i n Santa Cruz de l a S i e r r a ^ B o l i v i a i n 1932. Since no means were knoim f o r preventing yellow fever among f o r e s t animals, i t became obvious t h a t the er-adication of yellow f e v e r , as planned by the R o c k e f e l l e r Foi'ndaticn, v\ras i m p o s s i b l e . The aegypti yellow f e v e r of c i t i e s and towns could
always recur throngh i n t r o d u c t i o n of v i r u s by persons i n f e c t e d i n nearby f o r e s t s . F o r t u n a t e l y , i n 1933, a year a f t e r the f i r s t observation-of jungle yellow fever and before the g r a v i t y of i t s t h r e a t was f u l l y apparent, i t was shown t h a t aegypti had been eradicated i n s e v e r a l B r a z i l i a n c i t i e s . planning f o r e r a d i c a t i o n ; i t occurred V7hen
This was .not a r e s t i l t of d e l i b e r a t e
not a n t i c i p a t e d , as the r e s u l t o f
meticulous a d m i n i s t r a t i o n and the i n t r o d u c t i o n of the capture of a d u l t mosquitos t o p i n p o i n t the l o c a t i o n of hidden breeding of aegypti not e a s i l y found by the search f o r l a r v a l foci,. The n a t i o n a l e r a d i c a t i o n of aegypti as a permanent prevention of urban and maritime yellow fever was proposed and u n o f f i c i a l l y adopted as the o b j e c t i v e of B r a z i l ' s Yellow Fever Service i n 193^.''" Impossible as t h i s task then appeared,
• experience was to show t h a t e r a d i c a t i o n i s a c t u a l l y e a s i e r than c o n t i n u i n g e f f e c t i v e aeg^/pti c o n t r o l . Once a l a r g e c i t y i s f r e e of a e g y p t i , i t i s more economical t o
clean the suburbs and t r i b u t a r y v i l l a g e s than t o maintain permanent c o n t r o l i n the city. Continuing p e r i p h e r a l expansion was p o s s i b l e i n B r a z i l w i t h no increase o f
manpower beyond t h a t p r e v i o u s l y used i n a e g y p t i - c o n t r o l work i n the p r i n c i p a l c i t i e s . Aegypti e r a d i c a t i o n c a l l s f o r the systematic a t t a c k on aegypti wherever i t be found regardless of the immediacy of disease t r a n s m i s s i o n . fruitful in Brazil; This p o l i c y has been most
s e v e r a l towns were i n f e c t e d by cases from nearby jungle outbreaks
i n 1934, 1935 and 1936, but only a s i n g l e small outbreak has occurred i n the l a s t three decades.
Aegypti e r a d i c a t i o n became the o f f i c i a l o b j e c t i v e by Decree No. 8675 of 4 February 19^2.
VC/Aedes Sem ./9.65 page 6
In 1964 the e r a d i c a t i o n of aegypti i n T i r a z i l had advanced t o the point where r e i n f e s t a t i o n across i n t e r n a t i o n a l f r o n t i e r s was a major problem. In 19-17 B r a z i l
proposed, and the nations of the Americas became committed t o , the e r a d i c a t i o n o f aegypti i n the Western Hemisphere. This i n t e r n a t i o n a l development i s a c o n t i n u a t i o n
of the phenomenon of p e r i p h e r a l expansion w i t h i n the i n d i v i d u a l n a t i o n . T h i s e f f o r t was w e l l timed; the i n t e r v e n i n g I8 years have seen yellow f e v e r
confirmed f o r T r i n i d a d and a l l the c o u n t r i e s of the mainland, except Canada and t h e U n i t e d States i n North, E l Salvador i n C e n t r a l , and C h i l e and Uruguay i n oouth A m e r i c a In s p i t e of t h i s widespread d i s t r i b u t i o n of y e l l o w - f e v e r v i r u s , a s i n g l e s e r i e s o f only four cases o f aegypti yellow f e v e r has been recorded 1954). Thus the endemic aegypti yellow f e v e r of the Americas, the yellow f e v e r of h i s t o r y , the only yellovj f e v e r loio'^n previous t o 1932, has disappeared vrhether i t r e t u r n s w i l l depend on the completion mosquito from the remaining i n f e s t e d areas before s i n c e 1934; (Port of Spain, T r i n i d a d ,
o f the e r a d i c a t i o n of the a e g y p t i 'eradicated" areas become r e i n f e s t e d
The p e n e t r a t i o n of urban areas has become r a r e indeed s i n c e the 1930's (19^2 and 1954) but the p o t e n t i a l t h r e a t from the f o r e s t i s permanent. The e r a d i c a t i o n of aegypti i n the Americas i s p o s s i b l e because i t has never adapted t o l i f e i n the f o r e s t av/ay from human h a b i t a t i o n . Apparently t h i s i s a l s o
t r u e f o r the aegypti i n other parts of the world av/ay from i t s o r i g i n a l home i n A f r i c a vjhere i t s t i l l breeds i n the f o r e s t . Whether e r a d i c a t i o n of the domestic aegypti i n A f r i c a would be followed by ready r e i n f e s t a t i o n w i t h aegypti from the f o r e s t depends on the a d a p t a b i l i t y o f the f o r e s t a e g y p t i t o domestic water c o n t a i n e r s . This has not y e t been determined. Until i t i
the aegypti y e l l o w f e v e r of A f r i c a can be prevented by a n t i - a e g y p t i measures i n t h e l a r g e c i t i e s and by v a c c i n a t i o n of the i n t e r i o r p o p u l a t i o n . satisfactory. N e i t h e r method i s wholly-
VC/Aedes Sera./9.65 page 7
Yellov/ f e v e r has never t r a v e l l e d t o A s i a vjith man
and aegypti by boat -
probably because there has been no epidemic i n the port c i t i e s of the east coast of Africa. The absence of y e l l o w f e v e r i n these c i t i e s may not be e q u a l l y important
i n preventing the movement of yellow f e v e r by a i r . Jungle yellow fever i n the Americas and i n A f r i c a i s a permanent source of yellow f e v e r - V i r u s , a p o t e n t i a l t h r e a t t o u n i n f e c t e d regions i n these days of r a p i d t r a v e l , t o a l l regions i n f e s t e d w i t h a e g y p t i . Should aegypti e r a d i c a t i o n i n A s i a
and the VJeatem P a c i f i c be considered because of i t s t r a n s m i s s i o n of other d i s e a s e s , freedom from a l l t h r e a t of y e l l o w f e v e r can be c i t e d as an added inducement.