Update on Yellow Fever in the Americas
Yellow fever continues to be an important public health problem in the Americas. Between 1985 and 1999, Bolivia, Brazil, Colombia, Ecuador, Peru, Venezuela and French Guiana reported 2,935 cases and 1,764 deaths (See Table 1). During this period, more than 80% of all yellow fever reports in the American Region came from Bolivia and Peru. In 1999, Bolivia, Brazil and Peru accounted for 33%, 36% and 27% of all cases, respectively. However, from January to May 2000, a total of 66 confirmed cases were reported in Brazil, which represent more than 90% of all the cases notified in the Region during this period. Reports from the Brazilian Ministry of Health show that most of those cases come from the State of Goiás and neighboring States, where an extensive epizootic has been taking place since the beginning of the year (see Table 2).
All cases notified in the Region since the 1940s have been of the jungle form of yellow fever, transmitted by mosquitoes of the genus Haemagogus. However, the overwhelming spread of the Aedes aegypti mosquito threatens to re-urbanize the disease. The seriousness of the current yellow fever situation in the Region demands a firm commitment by the countries to a strong and effective strategy for controlling the disease. The Pan American Health Organization (PAHO)’s recommendations focus on the prevention of its re-urbanization, through surveillance, vaccination and vector control.
The establishment of a sensitive surveillance system is critical to the control and prevention of yellow fever. Currently notified cases tend to be of the severe clinical form of the disease, and therefore correspond to only a fraction of the total number of yellow fever virus infections, since as much as 50% of all cases can be asymptomatic.
In order to provide immediate protection to residents in enzootic areas and to prevent the introduction of yellow fever into nearby urban areas infested with Aedes aegypti, high levels of vaccination should be maintained among individuals living in both areas. During its Seventh Plenary Session in 1997, PAHO’s Directing Council exhorted its Member States to include yellow fever vaccine in their national immunization programs in all areas at risk of transmission of the disease. The countries and territories that have included universal children immunization against yellow fever are Trinidad and Tobago, Guyana and French Guiana. Brazil, Ecuador and Peru have given priority to the immunization of children in enzootic areas. Trinidad and Tobago and Guyana have implemented “catch-up” campaigns in all age groups in the entire country, and Brazil and Ecuador have used the same strategy for enzootic areas and regions with a high risk of transmission of the disease. Peru, Bolivia, Suriname and Venezuela have developed plans to introduce the yellow fever vaccine in their children vaccination schedule, as well as the vaccination of all age groups in enzootic areas.
Present day control strategies against the urban vector Aedes aegypti are based primarily on the reduction of breeding sources through their elimination. Social communication, community participation and health education are fundamental elements in these strategies. Insecticides are widely used where there are high vector population densities.
* Provisional data
1985-1995 1996 1997 1998 1999* 2000* Country Cases Deaths Cases Deaths Cases Deaths Cases Deaths Cases Deaths Cases Deaths Bolivia
319 30 21 63 47 57 39 68 33 1 0 Brazil 202 88 15 12 3 3 34 15 75 28 66 35 Colombia 55 47 8 4 5 4 1 0 2 2 Ecuador 45 29 8 8 31 4 3 1 5 3 F. Guiana - - - - - - 1 1 - - Peru 1431 914 86 34 44 20 165 49 56 33 2 1 Venezuela 2 1 - - - - 15 4 1 1 Total 2159 1398 147 79 146 78 276 109 207 100 69 36
PAHO. Division of Vaccines and Immunization.
State Cases Deaths Amazonas 1 0 Bahia 8 2 Brasilia, D.F. 1 1 Goiás 43 22 Mato Grosso 4 3 Minas Gerais 1 1 Sao Paulo 2 2 Tocantins 6 4 Total 66 35
CENEPI-FUNASA-Ministry of Health of Brazil.
For the case definition of yellow fever, select this link.
Source: PAHO. Division of Vaccines and Immunization and Division of Disease Prevention and Control.
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Epidemiological Bulletin, Vol. 21 No. 2, June 2000