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Y ellow fever
Rev Assoc Med B ras 2017; 63(4):291-292 291
EDITORIAL
Yellow fever
Febre amarela
Helio Arthur Bacha1*, Gustavo Henrique Johanson 2
1MD, Infectious Disease Specialist, Hospital Israelita Albert Einstein, Sociedade Brasileira de Infectologia. MSc in Medicine – Infectious and Parasitic Diseases, Faculdade de Medicina da Universidade
de São Paulo (FMUSP). PhD in Medicine – Infectious and Parasitic Diseases, FMUSP. Fellow American College of Physicians, São Paulo, SP, Brazil
2MD, Infectious Disease Specialist, Hospital Israelita Albert Einstein. MSc in Tropical Medicine and International Health from London School of Hygiene & Tropical Medicine, University of London. Specialist Degree
in Tropical Medicine and Hygiene from the Royal College of Physicians of London. Specialist Degree in Travel Medicine from the International Society of Travel Medicine, São Paulo, SP, Brazil
*Correspondence:
Yellow fever
Yellow fever is a potentially very serious disease, with high
mortality, caused by a Flavivirus, which is a genus of the
Flaviviridae family, inoculated in humans by arthropod
vectors with two cycles of transmission: urban and syl-
vatic (jungle).1 In Brazil, there is no record of urban trans-
mission of the disease since 1942, but human cases in the
sylvatic cycle do occur.2
Yellow fever is still relevant in countries on three con-
tinents: Africa, South America and Central America, with
an annual estimate of 84,000 to 170,000 serious cases and
about 29,000 to 60,000 deaths, according to the World
Health Organization (WHO).
The peak transmission season in Brazil is between
December and May, with epizootic cases having occurred
in non-human primates in atypical periods in the last year.
Cases of sylvatic yellow fever were recorded in the
states of Goiás, Mato Grosso do Sul, Pará, Tocantins,
Distrito Federal, Minas Gerais and São Paulo. The Bra-
zilian Ministry of Health issued an official document,
Informative Note No. 02/2017, which regulated the ex-
pansion of the areas of obligatory vaccination coverage
in the country, also vaccinating its inhabitants and visitors.
It should be noted that myths, misinformation and
neglect about yellow fever have caused diffuse panic in
several countries.3
Epidemiology
Two distinct cycles of disease transmission occur in en-
demic areas (sylvatic and urban), with symptoms indis-
tinguishable from each other. In sylvatic-cycle infections,
the vector species are necessarily of the Haemagogus and/
or Sabethes genera, which normally inhabit the tree cano-
py, as well as the susceptible reservoir, non-human pri-
mates, and occasionally humans. In urban-cycle infections,
the vector responsible for the transmission of the virus
is of the Aedes genus, with Aedes aegypti, an insect extreme-
ly adapted to urban conditions, as the main disease trans-
mitter. In this case, humans are the only susceptible res-
ervoir. In terms of transmission potential, sylvatic-cycle
vectors are more efficient than those of the urban cycle.
This, combined with mass vaccination campaigns in the
country, led to the last case of urban-cycle infection in
Brazil occurring more than seven decades ago, precisely
in 1942, in the state of Acre. It is worth remembering that
epizootic (death of monkeys due to yellow fever) is a red
flag to verify the circulation of yellow fever virus in the
region, which, per se, can generate immediate action of
the sanitary authorities to elaborate contingency plans
for halting transmission to humans.
The sylvatic form of transmission does not occur so
markedly in other endemic countries as it does in Brazil.
This is particularly true for the African continent, where
approximately a thousand cases occurred in 2016 with
urban transmission, with the countries most affected, in
descending order, being Angola, Democratic Republic of
Congo, Ethiopia and Uganda
gencies/yellow-fever/en/).
In Latin America, apart from Brazil, a recent outbreak
struck Peru, which notified health authorities of more
than twice as many cases of yellow fever as normal.
In Brazil, an increase in the number of cases of yellow
fever started to be noticed at the end of 2016, extending
from the summer of 2017 to the present, with more than
680 cases reported and a case fatality rate of 34% (moni-
toring of yellow fever cases and deaths – Report 37, Min-
istry of Health). As previously reported, all cases have
sylvatic transmission. The most affected states are Minas
Gerais and Espírito Santo, but São Paulo and Rio de Ja-
neiro (which traditionally does not register cases of the
disease) are also on the list.
The intensification of sylvatic transmission of yellow
fever with increasing numbers of patients every 5 to 8
years is a known fact that can be explained by the increase