Yellow fever

Yellow fever also known as Black Vomit and American plaque is a viral disease primarily of monkeys and transmitted to man by female Aedes mosquitoes. It is caused by Flavivirus of the family flavivirideae and is characterized by fever, acute hepatic  and renal involvement and jaundice and haemorrhagic manifestations. Yellow fever in man is an accidental zoonosis.

Epidemiology: There are 2 epidemiological patterns of transmission. Urban yellow fever involves transmission by A. aegypti from an infected to a susceptible individual, and jungle yellow fever normally involves transmission by mosquito vectors among monkeys. Outbreaks of yellow fever were a major problem in the construction of the Panama Canal, leading to Walter Reed’s instrumental works in establishing the relationship between yellow fever and mosquito vectors in 1901. Today yellow fever occurs primarily in the tropical countries.Yellow fever does not exist in India. Its public health importance has, however, been recognized and yellow vaccine is regularly manufactured in India. Rigid requirements of immunization against yellow fever and/or quarantine measures are enforced for all travelers coming from yellow fever endemic areas.

Clinical feature: The incubation period is 3-6 days. The onset of yellow fever is marked by anorexia (loss of appetite), nausea, vomiting and fever. The multiplication of the virus results in liver damage, causing jaundice from which the disease derives its name. Various haemorrhagic manifestations become apparent. Gastric haemorrhages result in “Black vomit” which was used as the name of the disease in the past. Bleeding from gum, epistaxis, melena and uterine haemorrhages are common. The symptoms generally last for one week, after which either recovery begins or death occurs. The mortality rate is about 5 %.

Laboratory diagnosis: Diagnosis of yellow fever can be done by the isolation and detection of the virus, by demonstrating the development of specific antibodies during the course of the disease and by the pathological examination of liver in the fatal cases. Molecular diagnosis is done by reverse transcription- polymerase chain reaction (RT-PCR) using its specific primers.

Control and prevention: There is no effective antiviral drug at present for treating the disease. It can be prevented by vaccination, using the 17D strain of yellow fever virus. Yellow fever has been largely controlled by effective mosquito eradication programme.