Yellow Fever Cases Decreasing In Most States In Brazil

The Pan American Health Organization (PAHO) released its latest update on the current yellow fever outbreak in Brazil. While the number of cases in the state of Minas Gerais, the country’s 2nd most populous city (population: 20.8 million), has declined; there have been increasing reports in Espirito Santo, in southeastern Brazil.

Yellow fever vaccine recommendations in Brazil.

The yellow fever virus, like the related Zika and dengue viruses, is spread by mosquitoes. It is more lethal than its cousins, with a significant fatality rate. Case fatality rates for reported cases are in the order of 15 to 50%.

The virus normally spreads in what is known as a jungle or sylvatic cycle, with transmission between mosquitoes and monkeys. Occasionally a person becomes infected, but human cases are generally rare in the jungle cycle.

US CDC | The Jungle (Sylvatic) Cycle

However, if the virus finds its way into cities, it is able to infect Aedes mosquitoes, which live in close proximity to people, and that can trigger a cycle of urban yellow fever. The World Health Organization (WHO) said that to-date there is no evidence of human cases of yellow fever virus infection transmitted by Aedes aegypti, the vector that could sustain urban transmission of yellow fever.

Yellow fever cases moving towards the Atlantic coast

Though Minas Gerais, an interior state in Brazil, has been the epicenter of the country’s yellow fever outbreak, there has not been a new patient after Mar 6. That decreasing trend is not seen in Espirito Santo, where the southern part of the state is reporting an increase in the number of cases. Rio de Janeiro also recorded an increase in cases between Mar 15 and 25. Both states, Espirito Santo and Rio de Janeiro, are in the middle of a massive yellow fever vaccination campaign.

Since the beginning of the outbreak in December of 2016 through Apr 6, there have been a total of 2,210 cases of yellow fever recorded, including 604 confirmed cases. Five states have reported confirmed cases, including Espirito Santo, Minas Gerais, Rio de Janeiro, and Sao Paulo. Among the confirmed cases, the case-fatality rate is 33%.

Infection in Nonhuman primates

As of Apr 6, Brazil reported 2,871 nonhuman primates (NHP) epizootics, of which 474 were confirmed yellow fever infections, 997 remain under investigation, and 77 were discarded.

The Pan American Health Organization also said epizootic (from Greek: epi- upon + zoon animal) cases have been reported from Federal district and 21 states, including ones that border 9 neighboring countries: Argentina, Bolivia, Colombia, Guyana, Paraguay, Peru, Suriname, Uruguay and Venezuela. Epizootic cases can precede human transmission, and PAHO said they represent a risk of spreading the virus to neighboring countries.

The WHO and PAHO emphasize the importance of vaccination, noting that countries must assess vaccine coverage in areas with a strong risk of yellow fever transmission.

PAHO | The Yellow Fever vaccine.

The Yellow fever vaccine is a live, weakened virus. It is given as a single shot. For people who remain at risk, a booster dose is recommended every 10 years. Yellow fever vaccine may be given at the same time as most other vaccines. The vaccine provides effective immunity within 30 days for 99% of persons vaccinated.