Reprinted from Mosqurro News, Vol. 18, No. 3, September, 1958

G0

THE 1957 STATUS OF YELLOW FEVER IN THE AMERICAS
FRED L. SOPER *

The professor of infectious diseases in a
medical school, located in a city once the
scene of a disastrous epidemic of yellow
fever, inquired recently if the disease still
exists in the Americas.

The statistics of the Pan American San-
itary Bureau list 77 cases officially reported
during 1957, surely an insignificant num-
ber when related to the hundreds of mil-
lions of population of the Western Hemi-
sphere. One might, then, be tempted to
answer the query with a statement to the
effect that yellow fever virus still exists in
the Americas but that it is a public health
problem of very minor importance. Such
a reply would overlook these facts: these
77 cases come from seven countries, (Fig.
1), Bolivia, Brazil, Colombia, Guatemala,
Panama, Peru and Venezuela; field studies
have proven yellow fever virus to be pres-
ent in British Honduras, where human
cases were not observed during the year;
and the range of the virus during 1957
from northwest to southeast has been over
3,500 miles.

A look at yellow fever in the Americas
through the eyes of foreign health ad-
ministrators might alter the indifference
of the professor of infectious diseases.

The Committee on International Quar-
antine of WHO and the World Health
Assembly, in meetings devoted to the prep-
aration, adoption and modification of the
International Sanitary Regulations, be-
tween 1949 and 1956, encountered greater
difficulty in harmonizing the views of dif-
ferent countries, and groups of countries,
on regulations for yellow fever than was
encountered in the solution of all other
differences.

During early 1956, the WHO sponsored
a visit of representatives of Egypt, Philip-
pines, Indonesia, British Africa, Belgian

* Director, Pan American Sanitary Bureau, Re-
gional Office of the World Health Organization.

Africa, India, France, and Iraq to several
countries in America to get first hand im-
pressions of yellow fever here. After one
day at the Pan American Sanitary Bureau
in Washington the group visited Cuba
where there is an active campaign for the
eradication of the Aédes aegypti mosquito
as a part of the continent-wide program
to permanently prevent all urban yel-
low fever in the Americas. Then on to
the then recently reactivated jungle fever
zone of Honduras (Fig. 2) where it was
learned that after an apparent silence of
15 months, yellow fever virus had not
only persisted in Honduras but had moved
northward into Guatemala (1).

In moving from Honduras to Guate-
mala yellow fever virus had left the range
of its most widespread vector in the for-
ests of South and Central America, Hae-
magogus spegazzinii, and had demon-
strated its adaptability to Haemagogus
mesodentatus (2) whose range extends
well up into Mexico (Fig. 3).

In Costa Rica the group visited the San
Juan de Dios Hospital where scores of
cases of jungle yellow fever were under
direct observation in 1951-52, and learned
from those who had handled the cases
that the clinical picture and high mor-
tality of the jungle disease are in all ways
similar to those of urban yellow fever.

In Panama the group learned the de-
tails of the cases of jungle yellow fever
infected in 1948 only some ten miles from
Panama’s International Airport at Tocu-
men, and of the 1949 to 1951 march of
the epizootic through Western Panama to
the frontier with Costa Rica. It was noted
that the five hospitalized cases of 1948
were diagnosed post-mortem two months
after the first case and two weeks after
the last one, and then only because the
Santo Tomds Hospital has a full time
pathologist. The group could not but
wonder how many similar episodes may
 

      
 

i park " o

SANTAMDER (91
CALDAS (2)
BOVACA (2)
META (2}
NARINOLI
cague tats)

  
 
  
 
 
 
  
  
   

AAAGUA LI
SUCRE (I)
TACHIRAL2)

VENEZUELA (5}

 

 

  
 
  
  
     

oe
"7

   

TERRITORIO
ROMDONIA (HF

  
 
   

      

SANTA CRUZ (I)
La Paz (5)

BOLIVIA (6)

=

1956

 

  

BRAZIL SEM 12} BRAZIL
(9) SANTA CRUZ (21: (8)
BOLIVIA(4)
1954 1955
CAYO DISTRICT Poy os,
GUATEMALA (31.\C7 3 5
TACHIRA (1) *PETEN(SI COLOMBIA(35) VENEZUELA(6)
GUATEMALA aoe oe asin) y; mantaas (4)
PANAMA {1} i Ss ‘ VENEZUELA (3) PANAMA (2)

COLOK (2)

SANTANDER (16)

BOTACA (2)

CALDASI9):

CUNDINAMARCA (ST
RETACSL
AMA2OWAS(3}
Ga Paz (is)

PERU(3}

BOLIVIA(IS}

1957

 

 

      
   
  

    

 

 

% DISCOVERY OF THE SPECIFIC LESIONS OF YELLOW FEVER IN THE LIVER OF VERTEBRATES CTHER THAN MAN

PASO/WHO 4-58

Fic. 1.—Number of cases of yellow fever from countries of the Americas, by political divisions and years, 1954 to 1957.

 

Foz

SMEN OLINDSOPT

€ -oN ‘QI “IOA
SEPTEMBER, 1958

Mosquito News

205

 

 

JUNGLE YELLOW FEVER

. NS . di)
ae i?

oe FEBRUARY 1957
a ee JUNE 1987
X ° SEPTEMBER 1954

‘49
JULY-AUGUST 1954

 

    

 
 

 
 
 

 

ag er wed
Stiveae 7 ey

E

:

A NICARAGUA

IN CENTRAL AMERICA— 1948-1957

CRAVBBEAN
StAR
DECEMBER 1953

ARCH 1993

: HONDURAS ma ene
a FEBRUARY 1956 : oars 1953
: M

(
JULY-AUGUST 1953

 

{ AUGUST-
NOVEMBER
'o

JUNE-SEPTEMBER 1952

 

OCTOBER 195!
MARCH 1952

JANUARY 1952
FEBRUARY 1952

  
  
  
 
   

JULY-SEPTEMBER 1952

AUGUST 195'- SEPTEMBER 1952

JAMUARY 1950 i
err iUNE 1851 L UGUST~ SEPTEMBER 19891
; APRIL 1951 we i957

nat

3
fcoLomara

)
AUSUST 1956

  
  
  
 

 

 

 

PASO/ AHO 5-58

Fic. 2.—Jungle yellow fever in Central America—1948-1957.

have passed unnoted during the four dec-
ades yellow fever had been absent from
the records of Panama and the Canal
Zone. That this may have happened is
suggested by the appearance in August
1956, of a case of yellow fever in the
Santo Tomas Hospital (3), originating in
the same jungle area which supplied the
cases in 1948.

In Bogota, Colombia the visitors saw, at
the Carlos Finlay Institute, the record of
repeated and continuing incidence of yel-
low fever, year after year, and visited the
yellow fever study area at San Vicente de
Chucuri, Santander (Fig. 4), where in
spite of repeated intensive vaccination
campaigns, yellow fever cases have been
confirmed in twelve of the last twenty-two
years. San Vicente de Chucuri is appar-
ently a permanent enzootic focus, in
which, interestingly enough, monkeys are

not present in numbers sufficient to main-
tain the virus unless there be some as yet
unidentified reservoir or long-lived insect
vector. Marsupials are suspected.

At Trinidad, B.W.L., the group learned
of the early serendipitous discovery of yel-
low fever virus in jungle areas in April
1954, four decades after the last report of
yellow fever from the Island, and of the
urbanization of the jungle infection at
Port-of-Spain some months later. Port-
of-Spain was the first city in twelve years
to report aegypti-transmitted yellow fever
and the first maritime port in America to
be infected in 25 years. Here, also, it was
possible to see the intimate contact, through
well paved roads, which exists between
jungle and urban areas. The Aédes
aegypti mosquito has been widespread in
human habitations along the rural high-
ways, near the infected forests. In Trini-
Moseurtro News

VoL. 18, No. 3

 

 

 

 

 

 

 

   
 
 

vomoman NORIMERN LIMIT OF RANGE OF HOWLER MONKEYS

     

[> Memotean AORTHERN LIMIT OF RANGE OF CEBUS MONKEYS

The sonennicst cone one hance oF
tewieats Coes ranca

ee

= 75

 

 

 

 

 

 

 

1
PatOr eno 38

 

 

ree

 

Fic. 3.—Northern limits of the range of monkeys
in Central America.

dad, reports were also heard of positive
neutralization tests carried out in 1953 of
young teen-age Trinidadians born long
after the last reported yellow fever, indi-
cating the possibility of previous unrecog-
nized outbreaks on the Island.

The visiting group could not fail to
note that in spite of evidence indicating
the presence of yellow fever virus in Trini-
dad during a twelve-month period and its
spread throughout the Island, less than a
score of cases were reported internation-
ally. Obviously many more must have
occurred.

At Belém, the gateway to the Amazon
Valley, the group from overseas learned
of the isolation of yellow fever virus, also
serendipitous, from six febrile persons in
1954 not far from the city, when yellow
fever was not known to be active in the
area. The group also learned of repeated
isolations of virus from naturally infected
Haemagogus mosquitoes captured in 1955
in the Utinga forest at the edge of the
city.

At Rio de Janeiro, the terminal point
of its American tour, the group visited the

 

      

=
6

/ de Janeiro

/ QE ET

EE Ta
eye)

meee x)
Pea cra)

BRAZIL

  
  

     
 

eae Mee)
aol

 
 

     
   

 
 

We Ptaces tnawn to nove been olmost canstontty infected
% A mca who wos «afected im Sucre Stote in 1954 traveled to Coracas ond died there

 

 

 

FIIOF weg a ea

Fic. 4.—Intervals between the appearance of
yellow fever in specific areas, (Courtesy American
Journal of Tropical Medicine and Hygiene.)

National Yellow Fever Service and heard
the story of the 1928-to—1931 struggle to
free South Brazil of endemic yellow fever,
(Fig. 5), which followed the reinfection
of Brazil’s beautiful capital, 20 years after
Oswaldo Cruz’ first victory over the dis-
ease in 1908 (Fig. 4).

As stated, the objective of the trip was
to give the group a first hand opportunity
to see the conditions under which yellow
fever occurs in the Americas, in order to
judge the threat which yellow fever here
may be to other regions. The hope that
the trip might result in an immediate les-
sening of the fear in the Orient of infec-
tion from America was not fulfilled. On
the eve of his departure one member of
the group declared that his anxiety re-
garding the possibility of the infection of
Asia with yellow fever had doubled dur-
ing the trip. This may well have been
the reaction of the entire group, visiting
SEPTEMBER, 1958

Mosquito News

207

 

 

     
   

sAo Luis
5 PORNAIBA

Manis ‘ORTALEZA

e@
PS aLvapoR

     

di.néus,

  

   
  

PARANAGUA

F LORIANOPOLIS

 

 

CASES ON BOARO SHIPS OM THE LA PLATA RIVER

 

PASO/WHD $-59

LOCALITIES KNOWN TO HAVE HAD CASES OF
YELLOW FEVER FOLLOWING 1928 OUTBREAK
IN RIO DE JANEIRO

Fic. 5.—Localities known to have had cases of
yellow fever following the 1928~1929 outbreak
in Rio de Janeiro.

the Americas in a year during which only
28 cases of yellow fever have been reported.

The indifference of the American pro-
fessor of infectious diseases contrasted with
the great concern of the health authorities
of other regions emphasizes the need of an
objective statement of the status of yellow
fever in the Americas at the end of 1957.

With yellow fever, as with many other
infectious diseases, long-term observations
are needed for any objective appraisal of
the situation, care being taken to make due
allowance for any changes which may
occur in basic epidemiological conditions.

During the century and a half previous
to rgoo yellow fever occurred on both the
Atlantic and Pacific coasts of North, Cen-
tral and South America, and was very ac-
tive in the Caribbean and Gulf areas. All
countries of the Americas, not excepting
even Canada, suffered incursions of yellow
fever.

Following the confirmation in 1900 by
the Reed Commission of Carlos Finlay’s
theory of the transmission of yellow fever
by the Aédes aegypti mosquito, dramatic
results were obtained by the reduction of
the breeding of this mosquito in endemic
centers such as Havana, Panama, and Rio
de Janeiro. There was a striking disap-
pearance of the disease, not only from the
cities where anti-mosquito measures were
applied, but also from surrounding and
tributary areas. And in rg15, on the basis
of this experience, the International Health
Board of the Rockefeller Foundation, un-
der the leadership of Wickliffe Rose and
General Gorgas, sponsored a program for
the eradication of yellow fever from the
Americas, (Fig. 6), based on the reduction
of the Aédes aegypti breeding in the
endemic centers until the disease should
spontaneously disappear. As a result of
this program, the last focus of self-sustain-

 

v

q Pee

   

CARIBBEAN AREA.

 

ai
PO

 

 

 

 

 

 

 

 

SAAT ES SEL LOY FE
4 a

  

Fic. 6.—Areas reported with yellow fever 1900
to 1931. (Courtesy The Jefferson Medical Col-

lege of Philadelphia.)
208

Mosquito News

VoL. 18, No. 3

 

ing man-aegypti-man yellow fever infec-
tion disappeared from the rural endemic
area of northeast Brazil in 1934 (Fig. 7).

 

 

@ JUNGLE YELLOW FEVER
dursan YELLOW FEVER
é
‘
x

Vy
“Et

=

Dy

 

 

 

AREAS REPORTED WITH YELLOW FEVER
S932 TO !1957

Fic. 7.—Areas reported with yellow fever 1932
to 1957. (Courtesy The Jefferson Medical Col-
lege of Philadelphia.)

As the man-aegypti-man yellow fever
was being eliminated, observation led to
the discovery (4) in 1932 and succeeding
years, of enzootic and epizootic yellow
fever of the tropical forests of America.
This was jungle yellow fever, the dis-
covery of which gave a ready explanation
of the source of virus for some previously
unexplained aegypti-transmitted outbreaks
in cities and towns isolated from any
known source of infection: Rio de Janeiro,
Brazil, in 1928; Socorro, Colombia 1929;
Guasapati, Venezuela 1929; and Santa
Cruz de la Sierra, Bolivia 1932 (5).

This discovery showed that the dream
of eradicating yellow fever VIRUS was
chimerical. The almost simultaneous per-
fection of methods for the eradication of
the highly domesticated Aédes aegypti led

inevitably to a program for the eradication
of this African invader from the Americas.

Even though conditions in the period
between 1900, when the gegypti-transmis-
sion of yellow fever was confirmed, and
1931, when the last series of urban out-
breaks ended, were quite different from
those of the period following 1932, the
year in which jungle yellow fever was
confirmed and aegypti-eradication begun,
it is instructive to compare the distribution
of yellow fever in these two periods.

The yellow fever reported between 1900
and 1931 (Fig. 6), was distributed around
the periphery of South America, around
the Caribbean Sea and the Gulf of Mexico,
and along the Pacific Coast of Mexico,
and Central America. It was almost en-
tirely urban yellow fever although the con-
temporaneous description of the Trinidad
outbreak of 1914 clearly identifies that
episode as jungle yellow fever. The re-
ports for this early period are almost en-
tirely of outbreaks diagnosed clinically and
epidemiologically, whereas the reports for
the later period 1932 to 1955 (Fig. 7),
have come in large part as the result of
routine viscerotomy and the histopatho-
logical confirmation of unsuspected cases.
This is true even of the few cases of Aédes
aegypti transmitted yellow fever which
have been reported. Yellow fever has
been found widely distributed in the in-
terior of the continent and even when re-
ported close to the coast has only in one
instance (Port-of-Spain 1954) infected any
international port. The aegypéi-trans-
mitted yellow fever reported during this
period was of two types: endemic rural
yellow fever; and isolated urban outbreaks
occurring very close, and secondary, to
known infected jungle districts. The
rural endemic yellow fever of northeast
Brazil was terminated in 1934 by extend-
ing anti-aegypt measures to large rural
areas and has not recurred.

In the period from 1932 to 1955 a huge
amount of epidemiological information
about both urban and jungle yellow fever
was collected and studied (6).

This period includes the last three vears
SEPTEMBER, 1958

Mosquito News

209

 

(1932-1934) of endemic aegypti-trans-
mitted yellow fever in northeast Brazil,
and the period from 1935 to 1942 when
urbanization of jungle virus occurred in
13 towns of Brazil, Paraguay, Bolivia and
Colombia, in areas from which the aegypti
mosquito has since been eradicated.

In order to bring the yellow fever situa-
tion of recent years into clearer focus, the
distribution of the 1606 cases of yellow
fever reported during the decade 1948-
1957 have been brought together in Table
1 (Fig. 8). During this ten-year period,
yellow fever occurred from Guatemala on
the north to Argentina on the south and
filled in many previous blank spots in the
map of jungle yellow fever. The human
cases were confirmed in 14 countries—
Guatemala, Honduras, Nicaragua, Costa
Rica, Panama, Colombia, ' Venezuela,
British Guiana, Trinidad, Ecuador, Peru,
Bolivia, Brazil and Argentina—without
the occurrence of any aegypti-transmitted
outbreaks! Brazil, Colombia and Bolivia
reported cases in each of the ten years. In
addition yellow fever in monkeys was con-
firmed in British Honduras, Venezuela in
nine years and Peru in seven. Ecuador
reported cases in the Amazon Valley in

1949 and on the Pacific slope in 1951.
This is the first report of jungle yellow
fever west of the Andes in Ecuador and
the first yellow fever on the Pacific slope
of South America to be reported since
1921.

In 1950 yellow fever extended much
farther south in Bolivia than it had been
found during 18 years of observation. In
Brazil, the Southern States of Mato Grosso,
Goias, Minas Gerais, Sido Paulo and Par-
ana were invaded from the Amazon Basin,
1950 to 1953, for the third time since
1934. In late 1957 deaths in Mato Grosso
and Goias indicated that a fourth epizo-
otic wave was beginning.

In 1954, northeastern Venezuela, after
apparent freedom from yellow fever for
twenty years, was shown to be infected.
This area was probably the source of virus
for the outbreak of the same year in Trin-
idad, already referred to, and is also not-
able as originating the first infectious case
of yellow fever known to travel by air
from the jungle to a distant segyp#i-in-
fested urban center—Sucre State to Ca-
racas. In 1955 and again in 1956, jungle
yellow fever was reported in the State of
Aragua in north central Venezuela, far

TABLE 1.—Reported Cases of Yellow Fever in the Americas, 1948-1957

 

 

 

 

Area 1948 1949 1950 1951 1952 1953 1954 1955 1956 1957 Total

Total 54 174 391 312 341 89 97* 42 28 78 1606*
Argentina ** I - - - - ~ - - “ - I
Bolivia 30 «6156354 3 1 18 2 7 6 1g 596
Brazil ** 3 6 4 50 221 39 9 8 2 10 = 352
British Guiana ** I - - - - 7 - - ~ - I
British Honduras - - - - - i - - _ #ee _
Colombia ** 12 3 12 26 16 II 12 22 16 35. «165
Costa Rica - - - 180 93 5 - - - - 278
Ecuador - I i 42 ~ - - - - ~ 43
Guatemala - - - - - - - _ ee 3 3
Honduras ** - - - - - ~ I — &ke Z I
Nicaragua ** - ~- - - 7 8 - - - - 15
Panama 5 4 2 3 I - - - 1 2 18
Peru I 4 16 4 I - 26 - - 3 55

Trinidad and Tobago ** - - - - - - 18* - - - 13*
Venezuela ** I - 3 4 I 8 29 5 3 6 60

 

* Jungle yellow fever, with the exception of 3 cases in Trinidad in 1954.

** All cases with laboratory confirmation.

*** Evidence of activity of the virus of yellow fever in howler monkeys (Alouatta sp.)
 

   
 
 
  
 

ZULIA (4)
TRUJILLO (3)
TACHIRA (4)

    
     
 
 
 

  
  

ANTIOQUIA (I pu.-, VENEZUELAS
SANTANDER (6) Vee Un $y
COLOMBIA | . ,

wy 2 oes

CAQUETA (2) SNe

  

SAN MARTIN (3)—

   

BRAZIL
Ww

    

     
   
  
  
  
 
 
 

ZULIA (1y

COLOMBIA  FTACHIRA (25
‘(?T) ope ;

SANTANDER (25)
CALDAS (101
BOTACA (45.
CUMDINAMARCA (5).
TOLIMA (3).
META (14}

HUANUCO (4)

BRAZIL
(2)

     

tee

 

 

 

   

BRITISH GUIANA (1)
BERBICE (1)

   

SAN MARTIN U1)

  
   

PANOS (1).

 
 

Peru
ay 2a

         
 
 
  

  

A
o-

OLIVIA TS BRAZIL

301" BI

SANTA CRUZ (29)

Lew nah,
3 *. ‘,

{ Ganoenvina’?
1948 MISIONES a ee

ae PIO GARDE OO SUL {iD

 

 

 

 

 
    
 
 
  
 

PANAMA (3)
COLON (3)

ANTIOGUIA 12)
BOYACA (1)

‘Santa cauz (93)
BOLIVIA (94)

1949

BRAZIL
(6h

    
 
  

 

 

 

ot

SMANT OLINOSO|L

€ *ON ‘I “TOA
 

 

    
   
  

VENEZUELA (3)
BOLIVAR (2)

PUTUMAYO (5)
COLOMBIA (12)
LORETO Uh
PERY (16)

MARANHAO (1)

BOLIVIA (354)
CHUQUISACA (307)

TARISA (28)
SANTA CRUZ (5).

1950.

  
     
  
    
 
 
   

ALAJUELA (252
HEREDIA (4) “WENEZUELA (3)

BOLIVAR (3)

N, SANTANDER (3)

SANTANOER (14)

BOYACA (2}

HUANUCO (1)}—
JURIN {1}

ECUADOR (65) JF Semcy FMATE BROSSO ‘GOlKS

MINAS GERAIS
w

SAO PAULO (4)

 

 

   
  
   
   
  
 
    
 
 
 
   
  
 
 

ZELAYAU
CHONTALES (5)
ALAJUELA (1
HEREDIA (PF
SAN JOSE (4)
PUNTARENAS (12)

N, SANTANDER (6)

SANTANDER (1)

VENEZUELA (1)

pourvar (1!

BRAZIL
(223)

  

ATO GROSSO! :
{ 7 @oas =
i ue)

LA PAZ G1}

BOLIVIA UI) MINAS GERAIS

SAO PAULO (1G2)

I952

PARAKZ 176)

 

 

 
    
 
  
     
       
    
 
 
   
   
 
 

CABO GRACIAS A DIOS (1)
ZELAYA (3)

JINOTEGA (Ih
SANTANDER (5}
GALDAS (4)
BOYAGA (1)
GASANGRE (It

Uy
2

. Amal
oH

gt

>

BRAZIL
(39)

 
 

AGRE (I)

BOLIVIA (18)
La PAZ UI)

     
       
 

Sass!

i LOCALITIES

“ not SPECIFIE
4 uty pee

   
 
 

?
Vee
; SAO PAULO (15)
PARANA (22)

1953

 

 

Fic. 8—Number of cases of jungle yellow fever from countries of the Americas, by political divisions and by years, 1946-1953.
(Courtesy American Journal of Tropical Medicine and Hygiene.)

 

gS61 ‘aawalaas

SMAN] OLINOSOW

1%
212

Moseurro News

Vor. 18, No. 3

 

from any previous reported focus of infec-
tion and only some 50 miles from the
Capital.

In Panama, as already noted, yellow
fever appeared in 1948 as a jungle infec-
tion east of the Canal, spread during the
next five years across the Canal and up
the Isthmus to Costa Rica and Nicaragua
(7).

Thine events of the next three years, 1954,
1955, 1956, (Fig. 1), were to show that
jungle yellow fever had not yet exhausted
its ability to surprise the epidemiologists.

In Central America, in 1954, (Fig. 2),
the enzootic which had previously been
traced easily in Costa Rica and Nicaragua
by the finding of sick and dead monkeys,
was followed with difficulty across Hon-
duras to the Ulua Valley near the frontier
with Guatemala.

During 1955, no yellow fever activity,
either in man or in monkeys, was reported
in Central America. Surprisingly, early
in 1956, activity among monkeys was re-
ported in Honduras, in the same area
where the activity had ceased 15 months
before (1). Simultaneously, yellow fever
among monkeys was observed across the
border in Guatemala indicating progres-
sion of the epizootic wave. The year
1956 was one of considerable yellow fever
activity in monkeys in Guatemala, without
the occurrence of reported human cases.
The activity in monkeys continued in
1957 in Guatemala and British Honduras;
though human cases were confirmed in
Guatemala.

The recurrence in Panama of jungle
yellow fever in 1956(3) and 1957 in the
same districts where cases occurred in
1948, and the present epizootic wave,
which has now reached Guatemala, when
taken together raise the question of
whether a second wave may follow the
preceding one so soon in Central America
where the susceptible monkey population
was greatly reduced by mortality from
yellow fever just a few years ago.

In Brazil, the 1950-53 outbreak in the
Southern States stopped unexpectedly.
Apparently drought conditions curtailed

this epizootic before it completed its sweep
through the forests of southern Brazil,
practically all of which were invaded dur-
ing the 1934 to 1940 epizootic. The only
cases reported in Brazil during 1954 were
found through routine virus isolations in
an otherwise silent area near Belém at the
mouth of the Amazon. In 1955 likewise
yellow fever reported from Brazil was
limited to this same area. In 1956 and
1957 there were a few scattered cases in
the Amazon Valley.

The cumulative reports of yellow fever
since 1932 and the unfolding picture of
yellow fever since 1946, reveal clearly the
absolute necessity of continuous observa-
tion and study if any appreciation, even
approximate, of the sweep of epizootic
cycles is to be obtained, for some of these
cycles require a decade or longer for com-
pletion.

Even the 25-year period has been too
short (Fig. 7), to give the whole picture
of jungle fever in the Americas. This is
due to the relatively long intervals which
have occurred in certain areas between
epizootic waves, as well as to the failure
to recognize and report many, if not almost
all, of the resultant human cases. The
progress of a wave depends upon at least
three coincident factors: the introduction
of the virus; the existence of an adequate
population of susceptible vertebrates; and
weather suitable to multiplication and
maintenance of adequate numbers of mos-
quito vectors. The study of the intervals
between the appearance of yellow fever in
specific areas indicates that yellow fever
persists almost constantly in certain small
areas, returns repeatedly after short periods
of freedom in other areas, and recurs only
after long and irregular absences in yet
others.

Rio de Janeiro, already referred to as
having been reinfected by jungle yellow
fever virus in 1928, twenty years after the
city had been freed of endemic yellow
fever by Oswaldo Cruz, was again bom-
barded by jungle virus in a number of
known infectious cases coming into the
city from nearby infected areas in 1938.
SEPTEMBER, 1958

Mosourro News

213

 

During the past 19 years jungle yellow
fever has not been observed in areas close
to Rio nor have recognized cases appeared
from further afield. Other areas have re-
ported the recurrence of yellow fever after
intervals of two or three years up to ten,
twenty and even forty years.

This discussion of the status of yellow
fever in 1957 has been largely limited to
the official reports of the distribution of
jungle yellow fever.

Since endemic gegypti-transmitted yel-
low fever no longer exists in the Americas,
the problem of yellow fever during the
past 20 years has been related to enzootic
and epizootic yellow fever as a source of
virus for jungle yellow fever cases, and
to jungle yellow fever cases as a source of
infection for Aédes aegypti-infested towns.

The questions to be answered in assess-
ing the yellow fever situation as a threat
to man are: What is the importance of
jungle yellow fever to rural populations of
tropical America? What is the threat of
the urbanization of jungle yellow fever
virus in cities and towns in enzootic and
epizootic areas? What is the international
threat of jungle yellow fever?

Jungle yellow fever is clinically and
pathologically indistinguishable from ur-
ban yellow fever and is just as dangerous
to the person infected in or near the forest
as to the city victim. The jungle disease
is however generally limited to those living
or working in or very close to the tropical
forest or entering the forest for recreation
or travel, Figure 9 shows the transmis-
sion cycle of jungle yellow fever in tropi-
cal America.

Where the homes are closely surrounded
by forest in a permanently enzootic focus
(Ilheus, Brazil) or where Indian tribes
live in the forest, the people get infected
with yellow fever even during the early
years of life. Where road or lumber gangs
enter the forest and where the forest is
being cleared for agriculture the disease
becomes almost occupational in its distribu-
tion and attacks a high percentage of
young adult males at their most productive
period (Espirito Santo, 1940; 108 deaths,

THE TRANSMISSION CYCLE OF JUNGLE
YELLOW FEVER IN TROPICAL AMERICA

MONKEYS: )
Hoemageges

C °

C “5

eegysti

FOREST CANOPY
440 FLOOR

© Rapleced by K sesovestetre is Geatada

‘UneantZaniOn OF
SUNGLE YELLOW FEVER

THE TRANSMISSION CYCLE OF NON-URBAN YELLOW FEVER In
placea with FEW or NO MONKEYS eg. Son Vicente de Chucuri, Cotombia

VERTEBRATE HOST
MARSUPIALS?:

IME EXTRA-HUWAN RESERVOIR

OF YELLOW FEVER VIRUS APPEARS
10 BE EXTHA-PRIDATE' A PLACES
SUCH AS THESE,

baal aes VECTOR
MOSQUITOES?

AN

After segrstt
URBANIZATION, ETC. mnEN 8

Fic. 9.—Diagrams of the transmission cycle of
jungle yellow fever in tropical America. (Cour-
tesy Boletin de la Oficina Sanitaria Panamericana.)

100 in males over 16) (San Vicente de
Chucuri, Colombia 1936-1955; 55 deaths,
45 farmers, 7 women, 3 children).

Where relatively light work, such as cof-
fee picking, brings both women as well
as men close to the forest, the disease tends
to attack both men and women and even
a considerable number of the children
who accompany their parents to the fields.
Thus it is clearly not necessary to chop
down a tree to get yellow fever.

The development of a satisfactory yel-
low fever vaccine in 1936 greatly reduced
the threat of jungle yellow fever, and has,
in fact, practically eliminated it for those
who are vaccinated.

The American nations are fortunate in
having free access to vaccine, produced in
the Oswaldo Cruz Institute, in Brazil, and
in the Carlos Finlay Institute, in Colom-
bia, in both with the collaboration of the
Pan American Sanitary Bureau. Vaccina-
tion produces long lasting, probably perm-
anent, immunity.

What is the threat of urbanization of
214 Mosgurro News Vou. 18, No. 3

 

 

   
     
     
  
   
   
 
 

BANAMA 1S. ANDS

GD SERMUDA
/ BRITISH VIRGIN ISLANDS
/ GUS. VIRGIN ISLANDS
/ | ANGUILLA
. , ST.KITTS, NEVIS
|| / @ antigua, Barsuoa

| / / P&P MONTSERRAT
fi fy GUADELGUPE
/ / DOMINICA

| “i /, “_® MARTINIOUE

3BY

———_ GRENADINES
€) GRENADA

TOBAGO
QB TRINIDAD

     
 

  

AREAS IN WHICH AEDES AEGYPTI STILL EXISTS

AREA DECLARED RECEPTIVE TO YELLOW FEVER BY THE
U.S. PUBLIC HEALTH SERVICE

ZONES WITH ERADICATION CAMPAIGN

P| ZONES WITHOUT ERADICATION CAMPAIGN

AREAS IN WHICH AEDES AEGYPT! iS NO LONGER o
REPORTED

 

ZONES PREVIOUSLY INFESTED

 

 

PASO/ WHO 5-58

 

 

STATUS OF AEDES AEGYPT/ ERADICATION CAMPAIGN IN THE WESTERN HEMISPHERE- 3! DECEMBER 1957

Fic. 10.—Status of the Aédes aegypti eradication campaign in the Western Hemisphere on December 31,
1957. (From the Annual Report for 1957 of the Director, Pan American Sanitary Bureau.)
SEPTEMBER, 1958

jungle yellow fever virus near infected
forests?

All observed urbanization of jungle yel-
low fever virus has occurred in towns rela-
tively close to infected forests. The possi-
bility of the introduction of yellow fever
virus from forest to urban areas has been
greatly reduced by the vaccination of large
blocks of the populations living in jungle
yellow fever areas: in Brazil, Colombia,
Venezuela, Trinidad, Panama, Costa Rica,
Nicaragua, Honduras, Guatemala and
Mexico. However, vaccination is never
complete, and absolute protection of towns
can come only from the eradication of the
aegypti mosquito.

The program for the eradication of the
Aédes aegypti mosquito from the Amer-
icas has progressed to the point (Fig. 10),
where there is very little opportunity for
cases from infected jungle areas to infect
cities without undertaking an international
trip. From Argentina to Guatemala, the
aegypti mosquito has either been eradi-
cated or is under heavy attack in all of
the countries where jungle yellow fever
has been reported in the past 25 years. To
prevent reinfestation of those areas which
have been, or are being, cleared of Aédes
aegypti it is essential that aegypti be eradi-
cated also from the United States, Cuba,
the Dominican Republic, Haiti, Puerto
Rico, Jamaica, and the other Caribbean is-
lands—where conditions for jungle yellow
fever do not exist—as well as from Mexico
where jungle yellow fever could occur, and
which also has Aédes aegypti.

What is the international threat of jun-
gle yellow fever? In its extra-human res-
ervoir the virus of yellow fever apparently
moves through contiguous or nearly con-
tiguous forest areas quite independently
of man. The forest areas may all be in
one large country like Brazil, or in half a
dozen small ones like the Central Ameri-
can countries. The virus takes cognizance
only of ecological boundaries, not of na-
tional ones (8).

It so happens that jungle yellow fever
has never been observed to move inter-
nationally along human routes of travel.

Mosgurto News

215

But in Venezuela in 1954 a man in the
early—i.e. infectious—stage of jungle yel-
low fever traveled by plane from Sucre
State to Caracas, a distance of several hun-
dred miles. Facilities for both highway
and air travel are constantly improving in
the outlying areas of jungle yellow fever
countries. This places those areas in closer
contact, through man, with heavily used
national and international routes of travel.
Aegypti-infested countries, that could
formerly rely on relative isolation from
virus-infested jungles to protect them from
yellow fever, may soon find that they are
no longer effectively isolated.

Summary. Yellow fever virus is always
present, with variable year-to-year distribu-
tion, throughout the tropical and subtropi-
cal forests of America from Mexico to
Argentina.

In the decade 1948-1957 there was labo-
ratory evidence of virus activity in 15 coun-
tries and territories. From four to eight
countries were known to be involved each
year. In three instances the presence of the
virus was observed only in howler mon-
keys (Alouatta sp.). The countries in-
volved were British Honduras, Guatemala
and Honduras, in the years 1956 and 1957.

Jungle yellow fever is a serious threat
to rural populations and is a permanent
source of virus for the reinfection of such
cities and towns, as may be infested with
Aédes aegypti, in the same country with
infected forests and even of such cities and
towns in other countries.

Maximum guarantees against yellow
fever depend on the widespread vaccina-
tion of rural populations and on the eradi-
cation of the Aédes aegypti mosquito from
all of the Americas.

References

1. Jounson, C. M. and Farnswortu, S. F.
Results of recent studies of yellow fever in Middle
America. Preliminary Note. Bol. Of. San. Pan.
1956, vol. 41, pp. 182~183.

2. Gatinpo, P., Ropanicue, E., and Trapipo,
H. Experimental transmission of yellow fever by
Central American species of Haemagogus and
Sabethes chloropterus. Amer. Jour. Trop. Med.
and Hyg., 1956, vol. 5, pp. 1022-1031.
 

216

Mosquito News

Vou. 18, No. 3

 

3. Weekly Epidemiological Report, PASB/
WHO, No. 35, August 28, 1956.

4. Soper, F. L., Penna, H. A., et al. Yellow
fever without Aédes aegypti. Study of a rural
epidemic in the Valle do Chanaan, Espirito Santo,
Brazil, 1932. Amer. Jour. Hyg. 1933, vol. 18,
pp. 555-587.

5. StrovE, G. K., Ed. Yellow Fever.
York. McGraw-Hill, 1951.

6. Yettow Frver CONFERENCE, 21-22 DE-

New

CEMBER 1954. Amer. Jour. Trop. Med. and
Hyg., 1955, vol. 4, pp. 571-661.

7. Trapipo, H. and Gauinpo, P. The epidemi-
ology of yellow fever in Middle America. Exper.
Parasit., 1956, vol. 5, pp. 285-323.

8. BosHELL-MANRIQUE, J. Yellow fever in Cen-
tral America—The post-war spread as a threat.
Yellow fever—a symposium in commemoration of
Carlos J. Finlay. The Jefferson Medical College of
Philadelphia, 22-23 September 1955, pp. 61-69.
April 1, 1968
fie

ae re

NOTES ON NO. 164 of FLS BIBLIOGRAPHY

1958 (Sept.). The 1957 status of yellow fever in the Americas. Mosquito
News 18 (3): 203-216.

Page 210

The map for 1946 shows no yellow fever for south Brazil. Asa
matter of fact, no cases were reported there for the year. However,
jungle yellow fever had moved from the Amazon Valley into the valley
of the River Plate on the divide in Mato Grosso in 19). This had spread
into Goias and Minas Gerais, reaching to the Rio Grande on the frontier
with Sao Paulo. The infection apparently died out during the year 1945,
Sao Paulo being spared the next year.

However, viscerotomy revealed a very probable case of yellow fever
at Dourados in southern Mato Grosso in 1946. This was given a diagnosis
of leptospirosis--not yellew fever--at the time. Reexamination in 1917
by FLS led to the belief that this had been a case of yellow fever ard
that there was a possibility that yellow fever virus had moved through
southern Mato Grosso into Paraguay and would eventually be manifested
further south.

As a matter of fact, single cases were proven by viscerotomy for
the province of Misiones in Argentina and the state of Rio Grande do
Sul in Brazil in 1948.