Yellow fever virus belongs to Flaviviridae family. It is acute febrile vector borne disese that occur in Africa and South america. Last century there was an large epidemics in Caribbean and North america and in Ethiopia in 1960- 1962.
There are seven genotypes of virus, five in Africa and two in south America. It is transmitted from mosquito that belongs to species of Aedes and haemogogus (WHO). Aedes aegypti is responsible for urban outbreaks. Mosquto can become infeted from first to third day of fever and those mosquto remained infected for life. Virus enter through bite of mosquto where it multiply. It spread to local lymphatic, liver, spleen, kidney, bonemarrow, myocardium. So necrotic lesion in liver, kidney and degenerative changes in spleen, lymphnode can occurred. Cerebral changes occur with oedema and petechial haemorrhages. Death usually result of liver and kidney or heart failure. Immunty is antibody mediated which is lifelong. Clinical features are fever, chills, headache, nausea, vomiting, bradycardia.
Most of patient recover in initial phase of 7 days and it can progress into severe form of disease with fever, jaundice, renal failure and haemorrhagic manifestation. 200000 cases are reported per year and 90% are in Africa( IDSA). Disease transmission in south america is lower than Africa because of mass immunization programme. 1990- 2000 , resurgence of disease occur in Brazil due to poor vaccinaton and migration of affected people from other countres( IDSA). 9 caes were reported in US and Europe from travellers during period of 1970- 2002( IDSA). Virus can isolate from blood in the few days and can use serological method like Ig M antibody by ELISA, IFA, HI. Neutralizing antibodies produce about 1 week of illness that response to destroy the virus. There is no antiviral treatments for this. Vigorous mosquto control and vaccinaton of all person at least 10 days before arrival into endemic country are preventive measures of yellow fever. 95% vaccinated people persist for at least 30 years and vaccination is contraindicated for infants who younger than 9 month, during poignancy and persons who allergy to eggs. 17 D vaccine is safe.
More than 400 million doses of vaccine had been administered and less reported adverse effect. In 2000 vaccine associated viscerotropic disease was discovered. There are two major epidemiological cycles of transmission. They are urban and jungle. Urban yellow fever involve person to person transmission by domestc aedes mosquto which breed in accumulation of water in human settlement. Jungle one is transmitted from monkeys to monkey by arboreal mosquto like Haemagogus spp. Yellow fever has not spread in Asia even vector mosquito are available. It infect thousands of people because of poor immunization. Humid and semihumid savanna rain forest where the sylvatic cycle is more prevalent because of large population of monkeys.
Most cases are reported in boys and men age 15 to 45 who are engage in agricultural or forestry activities. Disease transmission is increase with immigration, high urbanisation, poor maintenance of vaccnation programme. Regular epidemics occur in sub saharan africa and in Nuba mountain of southern sudan in 1940 there was an epidemic. Removing of breeding places of mosquito is major preventive measure.
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