Jungle Yellow Fever in south America

Feb 13 2008

Yellow fever is a zoonosis of the tropical regions of South America and Africa, which occurs in two distinct epidemiologic cycles: jungle and urban.

In the jungle cycle, the virus spreads among monkeys and humans, who may be infected when they enter the jungle and are bitten by mosquitoes infected with the yellow fever virus. Urban yellow fever has long been eradicated from the Americas, with the last cases occurring in Brazil in 1942.

Since the 1970s, the area where jungle yellow fever (JYF) cases have occurred has been restricted to the northern region of the South American continent. From 1985 to December 2007, 3,837 cases of JYF have been reported, with 2,229 deaths.

In 2007 and the beginning of 2008, Brazil reported an intense and extensive epizootic of Jungle Yellow Fever in an area encompassing 6 states (Goi?s, the Federal District, Mato Grosso do Sul, Minas Gerais, Tocantins, and S?o Paulo). The State Health Departments have confirmed the epizootic based on laboratory and clinical epidemiological criteria. In the past two months, 26 confirmed human cases were reported in 3 Federal States (Goi?s, Mato Grosso do Sul, and the Federal District); 13 of the patients died. The affected areas have high vaccination coverage. Nevertheless, as part of ongoing control measures, health authorities have intensified vaccination for people living in or traveling to affected areas.

On 15 January 2008, the national health authorities of Paraguay reported their first confirmed cases of Jungle Yellow Fever. One of the cases was confirmed using molecular techniques; the other four, by epidemiological nexus. As of 11 February 2008, 4 other suspected cases of JYF have been reported. All the confirmed cases reported by the national health authorities come from a rural area of San Pedro department in the northern part of the country. National health authorities have intensified epidemiological surveillance for the detection and investigation of suspected cases, and yellow fever vaccination for people living in or traveling to the affected area.

On 17 January 2008, the national health authorities of Argentina reported finding dead monkeys in Pi?alito Park, San Pedro department, Misiones province. On 4 February 2008, yellow fever was confirmed in one of the primates using molecular techniques. Although there is high vaccination coverage in the area, national health authorities have intensified vaccination for people living in or traveling to the affected area with no previous vaccination history.

For many years, jungle yellow fever has caused numerous high-mortality epidemics. The clinical manifestations of infection from the yellow fever virus can vary greatly, from asymptomatic or subclinical forms with non-specific symptoms, to hemorrhagic fever, which develops in 15-25% of infected patients and which presents a case fatality of around 50%.

Currently, the recommended strategy for vaccination against yellow fever is to focus on protecting the population living in or traveling to areas with any risk of transmission, where epizootics or human cases were recently reported, thus avoiding massive vaccination and re-vaccination.

The Pan American Health Organization is providing technical support to these countries through advisors in its Country Offices and at Headquarters in Washington, DC, in accordance with requests from the countries.

The Pan American Health Organization, founded in 1902, works with all the countries of the Americas to improve the health and quality of life of their peoples. It serves as the Regional Office of the World Health Organization (WHO).