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April 27, 2017
Infectious Disease Outbreaks: Yellow Fever in South America
Introduction
virus do not exhibit symptoms. Among symptomatic cases,
Since 1980, emerging infectious diseases (EID) have
victims often develop fever, nausea, muscle pain, and
resulted in more frequent outbreaks that are causing higher
vomiting. In most instances, related symptoms resolve
numbers of human infections. EID are either new diseases
within four days. According to the CDC, roughly 15% of
or existing ones that have emerged in new areas. In recent
those who contract yellow fever develop severe symptoms,
decades, new EID have included Severe Acute Respiratory
including organ failure. The “yellow” in the name of the
Syndrome (SARS) and HIV/AIDS. EID that have spread to
disease refers to the jaundice—yellowing of the skin and
new geographical areas have included yellow fever and
whites of the eyes, often indicating liver damage—that
Zika. Zoonotic pathogens (organisms that spread from
typically occurs among severe cases. About half of those
animals to humans, often through a vector like a mosquito)
who experience severe yellow fever die within 10 days.
sicken some 1 billion people annually, roughly 15 million
While specific treatment for the virus does not exist, yellow
of whom die. Notable EID outbreaks caused by zoonotic
fever can be prevented through vaccination. Eradication is
pathogens include SARS (2003), Avian Influenza H5N1
not considered feasible, as the disease is also found in
(2005), Pandemic Influenza H1N1 (2009), Middle East
primates, from which mosquitos can transmit the disease to
Respiratory Syndrome coronavirus (MERS-CoV, 2013),
humans.
West Africa Ebola (2014), Zika (2015), and Central Africa
Yellow Fever (2016) and South America Yellow Fever
Yellow Fever Outbreaks in South America
(2016-2017).
Yellow fever is reemerging in South America. It is
sickening and killing primates and people in numbers not
On average, Congress has provided about $130 million
seen for decades. A growing number of cases are being
annually through regular appropriations to the U.S. Agency
detected in primates in forested areas across Argentina,
for International Development (USAID) and the U.S.
Bolivia, Colombia, Guyana, Paraguay, Peru, Suriname,
Centers for Disease Control and Prevention (CDC) for
Uruguay, and Venezuela. Experts are tracking this
global pandemic preparedness efforts. Emergency
phenomenon and working to avoid a scenario in which the
responses to EID outbreaks have varied, however, but tend
disease moves from being transmitted by Haemogogus
to follow introduction of the disease into the United States.
(forest-dwelling) mosquitos to Aedes (urban-dwelling)
For example, the 114th Congress appropriated roughly $5
mosquitos. To date, most human cases in South America
billion and $2 billion to help control the West Africa Ebola
have been detected among people who either reside in or
and Zika outbreaks, respectively, but other Congresses did
have traveled to forested or rural areas, including through
not provide funds to address SARS or yellow fever
ecotourism.
outbreaks. Due to the unpredictable nature of EID
The scope of yellow fever outbreaks vary across the region:
outbreaks, some question whether Congress will continue to
emphasize infectious diseases that reach the U.S. shores or
In Bolivia, Colombia, Ecuador, and Suriname, the
whether the 115th Congress might develop a more proactive
disease was detected in ecotourists. These cases were
approach.
rapidly detected and did not cause further transmission.
The reemergence of yellow fever in several South
A yellow fever outbreak that began in Peru in 2016
American countries is the latest event highlighting the
sickened 78 people and killed 26 of them. That outbreak
global threat of EID outbreaks. The importation of the
was the largest seen in Peru since 2006. No new cases
disease from Angola—where an outbreak of unprecedented
have been reported since February 2017.
proportions occurred in 2016—and the frequency at which
Brazil is working to contain an outbreak that began in
EID outbreaks are spreading globally have sparked further
2016. Health experts are concerned about the continued
concern. For more information on the outbreak in Angola,
spread of the disease across Brazil, particularly as
see CRS In Focus IF10603, Infectious Diseases Outbreaks:
outbreaks approach densely populated urban areas with
Yellow Fever in Central Africa, by Tiaji Salaam-Blyther.
populations who frequently travel throughout the region,
Moreover, some global health experts have expressed
including to the United States. As of April 20, 2017, the
concerns about the vulnerability of the United States to EID
disease has infected 681 people in Brazil, 234 of whom
(including yellow fever) and about the capacity of the
have died. Health officials are investigating an
international health system to control future outbreaks.
additional 768 suspected cases and 35 deaths.
Background on Yellow Fever
Yellow Fever Vaccination
Yellow fever is a disease transmitted by mosquitoes
In Brazil, most human yellow fever cases are occurring in
endemic in 47 countries across sub-Saharan Africa (SSA)
parts of the country that had not been considered at risk of
and South America (see Figure 1). Roughly 90% of annual
yellow fever transmission. The largest clusters of cases are
yellow fever cases occur in SSA. Many who contract the
in the states of Minas Gerais (471 confirmed cases and 252
https://crsreports.congress.gov
Infectious Disease Outbreaks: Yellow Fever in South America
cases under investigation) and Espirito Santo (185
to stop the central African yellow fever outbreak was the
confirmed cases and 289 cases under investigation). Most
largest such effort in recent history, and trends indicate that
people in these areas were not vaccinated against the
other EID might require similar responses. Questions
disease, and now local health officials are implementing
abound, however, about whether sufficient resources exist
mass vaccination campaigns in these areas.
globally to handle simultaneous outbreaks of a similar
magnitude. Other issues raised by the outbreak include:
Some health experts assert that Brazil and Peru experienced
larger outbreaks than other South American countries
Global Risks—WHO has warned that the global risk of
because of their relatively low vaccination rates. The World
future yellow fever outbreaks is heightened by climate
Health Organization (WHO) recommends that at least 80%
change, increased international trade and travel, and the
of a population receive yellow fever vaccinations to prevent
resurgence of the urban-dwelling Aedes mosquito (which
outbreaks. By the end of 2015, roughly 46% of Brazilians
can spread other tropical diseases). Brazilian officials
and 67% of Peruvians were vaccinated. Meanwhile, its
detected yellow fever, for example, in a person traveling
neighboring countries, which reported only isolated
from Angola. Almost 80% of South Americans live in
imported cases, exceeded WHO’s vaccination guidelines
urban areas, elevating the region’s vulnerability to urban
(Bolivia, 91%; Colombia, 92%; Ecuador, 78%; and
epidemics. Populations in the United States are also
Suriname, 86%).
vulnerable to yellow fever, as many are not vaccinated
against the disease.
WHO and several international organizations created the
International Preparedness—Many low- and middle-
International Coordination Group on the Provision of
income countries (LMIC) lack the ability to detect, prevent,
Vaccines (ICG) in 1997 to manage the production and
and contain EID outbreaks. Some observers worry that
distribution of vaccine stockpiles for cholera, meningitis,
yellow fever transmission may be occurring in Venezuela,
and yellow fever. The stockpile was created to avert the
but that deteriorating conditions in the country limit
spread of deadly infectious disease outbreaks from
detection and surveillance capacity. Health experts are also
countries without sufficient capacity to control them. In
wary about the growing proportion of urbanization in LMIC
2016, the global vaccine stockpile was depleted several
that is driven by population growths in slum areas that lack
times and was unable to meet the global need.
adequate access to clean water and sanitation. Yellow fever
cases in the states of Rio de Janeiro and San Paolo are
Yellow fever vaccine shortages forced WHO to employ a
“
troubling to health experts who fear a spread of the disease
fractional” dosing campaign during the 2016 central
to major cities in the states where tens of millions of people
African yellow fever outbreak. Fractional doses use one-
live, many in informal settlements.
fifth of the standard dosage and provides protection against
the disease for one year. Standard doses provide lifetime
Congressional Response—Some groups advocate for more
protection in most cases. Brazil, typically a yellow fever
funding to strengthen health systems worldwide and
vaccine donor country, is reportedly considering using this
improve pandemic preparedness efforts like the Global
strategy to contain the outbreak and has received 3.5
Health Security Agenda. They argue that emergency
million doses from WHO.
responses are more costly than preventive measures and
assert that ignoring poor health conditions worldwide
Outlook
imperils health security. Others question how broad-based
Recent EID outbreaks in South America are raising
health systems support could be adequately measured and
questions about how the United States and other countries
monitored, and argue for stronger political will in many
can address this challenge. The mass vaccination campaign
LMIC to address the issue.
Figure 1. Areas at Risk of Yellow Fever Transmission: Sub-Saharan Africa and South America
Source: Adapted by CRS from CDC webpage on Yellow Fever at https://www.cdc.gov/yellowfever/, accessed on January 27, 2017.
Notes: Data for sub-Saharan Africa and South America were developed in July 2015 and March 2014, respectively.
Tiaji Salaam-Blyther, Specialist in Global Health
IF10642
https://crsreports.congress.gov
Infectious Disease Outbreaks: Yellow Fever in South America
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