Kyasanur forest disease

Kyasanur forest disease (KFD) was first recognized in 1957 as a new disease entity affecting man and monkeys in Karnataka, India. The disease is named after the Kyasanur forest area of Shimoga district in Karnataka (often called monkeys disease by the  villagers). The causative agent belongs to genus Flavivirus of the family Flaviviridae and is transmitted through ticks.

Epidemiology: The transmission cycle of KFD involves mainly monkeys and ticks. But there appears to be a wide range of natural hosts other than monkeys, such as rats, shrews, birds, reptiles and cattle. Man acquires infection from bites of infected ticks during his visit to the forest. Man is a “dead-end” or tangential host and has no significance in the natural cycle of the KFD virus. There is no evidence of person-to- person transmission of KFD virus.

A seasonal pattern of incidence of KFD has been noted. The highest number of human and monkey infections occur during the dried months, particularly from January to June. This period coincides with the peak nymphal activity of ticks. This period also correlates with the period of greatest human activity of the forest.

Tick vectors: More than 15 species of ticks are involved in the ecology of the virus. The major vectors for man are Haemaphysalis spinigera, H. papauana, H. kinneari and H. turturis.

Clinical features: The incubation period in man is 3-8 days. The disease has a sudde n onset with fever, headache, conjunc tivitis, vomiting and diarr hoea. Gastrointestinal disturbances and haemorrhages occur in severe cases. Recovery from an attack is generally slow. The case fatality rate is about 5-10 %.

Differential diagnosis: In the absence of any history of direct exposure, Kyasanur forest disease is confused with enteric fever, influenza or pyrexia of unknown origin. In the endemic areas Kyasanur forest disease should be suspected in all patients with a sudden onset of fever. Kyasanur forest disease etiology could be established by isolating the virus from the blood or by serological tests.

Control and prevention

• Control of ticks: KFD is a tick-borne disease and control of ticks should be undertaken. Insecticidal treatment of animals is a useful measure to free them from ticks.

• Vaccination of population at risk: A killed KFD vaccine is available and may be offered to the population at risk in KFD endemic areas.

•  Health education: individuals at risk should be protected from tick bite by adequate clothing and by the use of insect repellents. They should examine their bodies at the end of each day for ticks and remove them promptly. The habit of sitting or lying down on the ground should be discouraged.