|Yellow Fever Overview|
Yellow fever is an important public health problem which causes an estimated 200,000 cases and 30,000 deaths each year. This mosquito-borne viral disease primarily affects monkey primates, but is easily transmissible to man by suitable mosquito vectors of the Aedes mosquito. Trans-ovarian transmission has also been demonstrated, thereby ensuring virus survival and continuation of the transmission in enzootic foci in tropical regions of the continent.
It may cause devastating outbreaks particularly in susceptible unprotected populations living in areas where the risk factors for transmission continue to exist. The disease is usually underreported and it is difficult to ascertain the true case load even during outbreaks. There is no definitive treatment, but it can be prevented through vaccination with a live attenuated Yellow fever vaccine.
Since 1980, there has been a resurgence of the disease worldwide, but especially in the tropical regions of sub-Saharan Africa, from where more than 80% of the cumulative total number of cases have been reported.
Prior to this, mandatory preventive vaccinations between 1925 and 1953 in Francophone West Africa kept the number of cases very low. Chief among the reasons for this resurgence is the build-up of susceptible populations following the cessation of the preventive vaccination exercises.
In the WHO African Region,31 countries are known to be at risk for the disease, with 27 of them at moderate or high risk by virtue of having reported confirmed cases in the past.
The first symptoms of the disease usually appear 3–6 days after infection. The first, or “acute”, phase is characterized by fever, muscle pain, headache, shivers, loss of appetite, nausea and vomiting. After 3–4 days, most patients improve and symptoms disappear. However, in a few cases, the disease enters a “toxic” phase: fever reappears, and the patient develops jaundice and sometimes bleeding, with blood appearing in the vomit (the typical "vomito negro"). About 50% of patients who enter the toxic phase die within 10–14 days.
This text was partially adapted from texts available on the sites: World Health Organization, Centers for Disease Control and Prevention, WHO – Regional Office for Africa, and U.S Department of Health and Human Services