Kyasanur Forest Disease: an old dog up to same old tricks

Contributed by Dr R Surendran, Dr Ashwini Tayade

At least 65 people have tested positive in the ongoing outbreak of KFD in Karnataka, but the number of suspected cases —awaiting confirmation through blood tests — has touched 204. At least 38 monkeys have died in the plantations. Aralagodu is the epicentre of the outbreak, but infected areas are also being reported in villages across four districts of Karnataka (Shivamogga, Udupi, Dakshina Kannada, and Uttara Kannada) – and in Kerala (Wayanad) and Maharashtra (four cases).

KFD virus was first reported in Kyasanur village of Shivamogga district, way back in 1957. The virus belongs to the family Flaviviridae, whose other members are responsible for causing Yellow Fever, Zika and Dengue. Multiple species of ticks of the genus Haemaphysalis are the principal vectors. Infections peak between November and March, which coincides with the larvae-nymph cycles of ticks. Since 1957, it has flared up in sporadic outbreaks. Post-2013, it has even expanded its range, with fatal consequences in Maharashtra, Kerala and Goa. According to State data, in the past 15 years, KFD has infected 2,067 people and killed 42. The demographic group most vulnerable to KFD are people more than 40 years old.

Nearly every study on the disease so far has highlighted the role of forest degradation in the spread of KFD. SK Kiran, who has helmed multiple research papers on KFD, says that villagers living near highly-fragmented forests are more susceptible to the disease. He says, “Tick densities remain high in these forests, and with the presence of monkeys, peacocks, rodents and other reservoirs, there is always a chance of the disease spilling over to the village. This risk factor is not given its due in the health response to KFD [The Hindu - 26 Jan 2019].

Vaccination with formalin-inactivated tissue-culture vaccine has been the primary strategy for controlling KFD. The strategy involves mass vaccination in areas reporting KFD activity (i.e., laboratory evidence of KFD virus [KFDV] in monkeys, humans, or ticks) and in villages within a 5-km radius of such areas. Two vaccine doses are administered at least 1 month apart to persons 7–65 years of age. Vaccine-induced immunity is short-lived, so the first booster dose of vaccine is recommended within 6–9 months after primary vaccination; thereafter, annual booster doses are recommended for 5 years after the last confirmed case in the area. Though a vaccination programme began on November 30, it was too late for Aralagodu. The first dose hardly provides protection, while the efficiency of the second dose (administered after a month) is only of 63% efficacy. Of the seven dead, two persons had received their first dose, while one had been administered the second dose. A study done by S.K.Kiran et al, investigating and outbreak of KFD in 2013-2014 reveals - low vaccine coverage, low vaccine effectiveness, and spread of disease to areas beyond those selected for vaccination and to age groups not targeted for vaccination. To control disease, vaccination strategies need to be reviewed [Emerg Infect Dis. 2015 Jan; 21(1): 146–149].