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Kyasanur forest disease
|Kyasanur forest disease|
|Classification and external resources|
Kyasanur forest disease (KFD) is a tick-borne viral hemorrhagic fever endemic to South Asia. The disease is caused by a virus belonging to the family Flaviviridae, which also includes yellow fever and dengue fever.
The disease was first reported from Kyasanur Forest of Karnataka in India in March 1957. The disease first manifested as an epizootic outbreak among monkeys killing several of them in the year 1957. Hence the disease is also locally known as Monkey Disease or Monkey Fever. The similarity with Russian Spring-summer encephalitis was noted and the possibility of migratory birds carrying the disease was raised. Studies began to look for the possible species that acted as reservoirs for the virus and the agents responsible for transmission. Subsequent studies failed to find any involvement of migratory birds although the possibility of their role in initial establishment was not ruled out. The virus was found to be quite distinctive and not closely related to the Russian virus strains. Antigenic relatedness is however close to many other strains including the Omsk hemorrhagic fever (OHF) and birds from Siberia have been found to show an antigenic response to KFD virus. Sequence based studies however note the distinctivenss of OHF. Early studies in India were conducted in collaboration with the US Army Medical Research Unit and this led to controversy and conspiracy theories.
Subsequent studies based on sequencing found that the Alkhurma virus, found in Saudi Arabia is closely related. In 1989 a patient in Nanjianin, China was found with fever symptoms and in 2009 its viral gene sequence was found to exactly match with that of the KFD reference virus of 1957. This has however been questioned since the Indian virus shows variations in sequence over time and the exact match with the virus sequence of 1957 and the Chinese virus of 1989 is not expected. This study also found using immune response tests that birds and humans in the region appeared to have been exposed to the virus. Another study has suggested that the virus is recent in origin dating the nearest common ancestor of it and related viruses to around 1942, based on the estimated rate of sequence substitutions. The study also raises the possibility of bird involvement in long-distance transfer. It appears that these viruses diverged 700 years ago.
There are a variety of animals thought to be reservoir hosts for the disease, including porcupines, rats, squirrels, mice and shrews. The vector for disease transmission is Haemaphysalis spinigera, a forest tick. Humans contract infection from the bite of nymphs of the tick.
The symptoms of the disease include a high fever with frontal headaches, followed by haemorrhagic symptoms, such as bleeding from the nasal cavity, throat, and gums, as well as gastrointestinal bleeding.
An affected person may recover in two weeks time, but the convalescent period is typically very long, lasting for several months. There will be muscle aches and weakness during this period and the affected person is unable to engage in physical activities.
Prevention and treatment
Prophylaxis by vaccination, as well as preventive measures like protective clothing, tick control, and mosquito control are advised. An attenuated live vaccine is now available. Specific treatments are not available.
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