Yellow Fever

It is a severe infectious and life threatening disease characterized by toxic jaundice, yellow skin, high fever, severe bodyache, nausea, vomiting and albuminuria accompanied by haemorrhages from stomach, nose and mouth.

Occurrence: The disease is found in certain parts of Africa, West Indies, South and Central America. It is endemic in West Africa. Ethiopia was badly affected by severe epidemic in 1960-62 with 200,000 cases and 30,000 deaths. In 1978,epidemicsoccurred inColumbia and Peru of South America andGhana andGambia inAfrica. Yellow fever does not exist in Asian countries. Fatality rate varies from 5 to 50 percent.

Agent: It is a virus (flavivirus).The virus can be isolated from blood during the first 4 days of illness. Virus can be• cultured in growing chick embryo and tissue culture. It can be destroyed by heat and chemical agents but can be preserved for years at 21.1 oC.In continued culture, it loses its pathogenicity but retains its antigenicity. There are two epidemiological types: (1) Jungle or Sylvan type. Jungle yellow fever is primarily a disease of monkeys. It is transmitted from monkey to monkey by certain species of mosquitoes found on tree tops. Some monkeys succumb to the disease while others recover from it. Other animal reservoirs may also exist. (2) Urban/rural type: Here man is the reservoir of infection. Disease spreads from man to man by aeries mosquitoes. Transovarian transmission in mosquitoes may contribute to maintenance of infection. Period of communicability : Patient is infective for the first 4 days of disease and probably for the later part of incubation period. After an extrinsic incubation period of 10 to 14 days, the mosquito becomes infective and remains so till death. Host : All ages,sexes and races are affected.Forest visitors like wood cutters and hunters are exposed to the risk of infection. The bring the infection from jungles and start the human cycle of yellowfever. One attack confers lifelong immunity.Infants upto 6 months are protected by passive immunity from mother. Second attackis unknown.Mild inapparent infection are common in endemic areas.Environment: A temperature of 23.7C is favourable for the spread of the disease.Reservoir: Man,aedes aegypti and monkey.Incubation period: 3to 10 days.average 6 days