|Epidemiological Alert: Increase in Circulation of Jungle Yellow Fever Virus in the Americas|
Washington, DC, January 27, 2009 (PAHO)—Since October 2008, an intense increase in the circulation of the jungle yellow fever virus has been observed in the Americas, affecting Argentina and Brazil in the southern part of the continent, Colombia and Venezuela in the Andean region, and Trinidad and Tobago in the Caribbean.
The objective of this communication is to alert the countries of the Region so that they can strengthen their surveillance, prevention, and control activities for yellow fever within their territories and for persons traveling towards affected or risk areas.
Situation of Yellow Fever in the Region
Argentina and Brazil
Since October 2008, monkey deaths (epizootics) have been observed in southern Brazil; and starting in November of that same year, in northeastern Argentina. The affected area includes municipalities in the State of Rio Grande do Sul in Brazil, and localities in the provinces of Misiones and Corrientes in Argentina, adjacent to Rio Grande do Sul.
In Brazil, up to 15 January 2009, the State of Rio Grande do Sul has reported 228 monkey deaths in 62 municipalities. Of these, 23 municipalities had probable or laboratory-confirmed epizootics. Some of these epizootics were registered in municipalities located outside the area previously considered at risk.
Argentina has presented three epizootic events in different localities in the Province of Misiones and in seven localities of the Province of Corrientes, confirming yellow fever in one of them.
With regard to human cases, four laboratory-confirmed cases of jungle yellow fever have been reported, all involving deaths: two cases in Rio Grande do Sul with the probable infection sites in Pirapo and Santo Ángelo; and two cases in Argentina, with the probable infection site in the area of Fachinal, Province of Misiones. The last outbreaks of jungle yellow fever recorded in both Rio Grande do Sul and in Corrientes were in 1966.
Trinidad and Tobago
Two epizootics have been reported of laboratory-confirmed yellow fever, in the districts of Mayaro and Nariva, respectively located in southern and southeastern Trinidad. Epizootics in Trinidad and Tobago have not been reported since 1998.
A monkey death in the State of Guarico is under investigation. The last human case reported in the country was in 2005.
Between Epidemiological Week (EW) 51 in 2008 and EW 1 in 2009, two (fatal) human yellow fever cases have been reported in the Department of Meta, both falling within the pattern of sporadic cases expected in the country.
Response to the Situation
The countries have taken action to prevent the occurrence of more human cases, strengthening epidemiological surveillance, which includes active case-finding of febrile, jaundiced (icteric), and ictero-hemorrhagic cases. Investigation of any rumors of monkey deaths has also been intensified. At the same time, in the affected areas, vaccination coverage is being increased among the resident population. Furthermore, the indication to vaccinate has been strengthened for travelers to these areas. In addition, for the purpose of preventing urban transmission by the Aedes aegypti mosquito, vector control activities have been strengthened.
Yellow Fever Vaccination
One of the most important mechanisms for preventing yellow fever is vaccination. However, the priority of its use, its indications, and counter-indications should all be considered when applying it. PAHO recommends a rational use of vaccines, prioritizing the population residing in a risk area as well as travelers going to or through these areas. Special attention should be paid to vaccinating people who live in risk areas (where epizootics or cases have been identified), and those who, though residing in low-risk areas (where vaccination coverage is generally low), work or participate in recreational activities inside risk areas. The yellow fever vaccine should not be administered to people with acute febrile diseases, to those with hypersensitivity to eggs and their derivatives, or to those who have diseases or who receive treatment that supresses the immune system.
Timely detection of outbreaks allows for the effective implementation of control measures. To this end, it is important to use all yellow fever surveillance mechanisms in both humans and primates: monitoring of compatible clinical cases; surveillance of febrile icteric syndromes; epizootic surveillance; intensified monitoring of A. aegypti infestation indices in urban areas close to the disease focus; monitoring of vaccination coverage; and monitoring of post-vaccination events presumably attributable to vaccination against yellow fever in affected and bordering areas.
Yellow fever transmission in the Americas continues to be of the jungle cycle. However, in order to avoid the reurbanization of this disease—of which there already was an outbreak, confirmed at the beginning of 2008 and successfully controlled—A. aegypti control measures are critical, mainly in cities and in localities bordering affected areas. These measures also allow for the prevention of dengue outbreaks.
In light of the intense circulation of the yellow fever virus observed in the Region, countries should include in their communication activities clear educational directives on the rational use of the vaccine, on the population to be vaccinated, on personal protection measures (such as avoiding activities taking place in forests), and on vector control measures.
PAHO, founded in 1902, works with all the countries of the Americas to improve the health and quality of life of their peoples. It also serves as the Regional Office for the Americas of the World Health Organization (WHO).
For additional technical information on Yellow fever and control activities, see PAHO’s practical handbook.
Regional Office for the Americas of the World Health Organization