The disease is caused by the yellow fever virus. Humans and monkeys are the principal animals to be infected. The virus is carried from one animal to another (horizontal transmission) by a biting mosquito
Symptoms: The virus remains silent in the body during an incubation period of three to six days. There are then two disease phases. While some infections have no symptoms whatsoever, the first, “acute”, phase is normally characterized by fever, muscle pain (with prominent backache), headache, shivers, loss of appetite, nausea and/or vomiting. Often, the high fever is paradoxically associated with a slow pulse. After three to four days most patients improve and their symptoms disappear.
However, 15% enter a “toxic phase” within 24 hours. Fever reappears and several body systems are affected. The patient rapidly develops jaundice and complains of abdominal pain with vomiting. Bleeding can occur from the mouth, nose, eyes and/or stomach. Once this happens, blood appears in the vomit and faeces. Kidney function deteriorates; this can range from abnormal protein levels in the urine (albuminuria) to complete kidney failure with no urine production (anuria). Half of the patients in the “toxic phase” die within 10-14 days. The remainder recover without significant organ damage.
Treatment: There is no specific treatment for yellow fever.
Yellow fever vaccine is safe and highly effective. The protective effect (immunity) occurs within one week in 95% of people vaccinated. A single dose of vaccine provides protection for 10 years and probably for life. Over 300 million doses have been given and serious side effects are extremely rare. (neurotropic disease and multiple organ failure)
The risk to life from yellow fever is far greater than the risk from the vaccine, so those who may be exposed to yellow fever should be protected by immunization.
Vaccination is highly recommended for travellers to high-risk areas. A vaccination certificate is required for entry to many countries, particularly for travellers arriving in Asia from Africa or South America. Fatal cases in unvaccinated tourists have been reported.