2024 peak year for Kyasanur Forest Disease, Karnataka health officials confirm as cases rise

Cases higher this year due to low rainfall, expert says

By Seema Prasad
Published: Monday 12 February 2024
Kyasanur forest disease is transferred to humans either by making contact with animals such as monkeys, livestock, shrews and rodents harbouring infected ticks or directly through tick bites. Photo for representation: iStock

A viral outbreak of the Kyasanur Forest Disease (KFD), a tick-borne, hemorrhagic fever, is on the rise in Karnataka, state health officials said. Two deaths and 53 confirmed cases spread across Uttara Kannada, Chikkamagaluru and Shivamogga districts have been reported this year as of February 3. 

This recent surge is part of a larger trend of cases peaking every four to five years since 1957, when KFD was first identified in the Kyasanur Forest in Shivamogga District, government officials told Down to Earth (DTE).

“After the 2019 outbreak, this is the next peak of KFD cases,” Prashant Bhat, Udupi district vector-borne diseases control programme officer, said to DTE.

Bhat, a senior epidemiologist with Karnataka’s department of health and family welfare, added, “The ongoing trend over the past several decades shows that once in every four to five years, a peak emerges, with minor fluctuations in the two major hotspots (Shivamogga and Uttara Kannada). It is the pattern the disease outbreak follows.” 

KJ Harshavardhan, deputy chief medical officer of the Virus Diagnostics Laboratory (VDL) in Shivamogga, concurred that 2024 is the peak year after a gap period and the state is witnessing a surge at present. 

“This year, there has been an increase in the number of cases due to decreased rainfall. Generally, the rain washes away the infected ticks in the nymph stage, and the spreading of the disease is contained,” Harshavardhan added.

The transmission season for KFD is from November to May when nymphal activities of ticks are in high gear, infecting animals and people. It commonly occurs as a seasonal outbreak in the endemic districts of Shivamogga, Chikkamagaluru, Uttara Kannada, Dakshina Kannada and Udupi.

Bhat explained: 

The KFD virus resides in the Haemaphysalis spinigera species of ticks. The life cycle includes eggs that will hatch into larvae and develop into nymphs between November to May. The nymphal stage is an active form of the life cycle, crucial for the disease to spread, where the ticks actively try to feed on vertebrates and human beings.

For seven decades, from 1957 to 2012, KFD was limited to Karnataka. However, after 2013, cases have been reported in adjacent states along the Western Ghats such as Tamil Nadu, Kerala, Goa and Maharashtra.

Kyasanur Forest Disease is a viral hemorrhagic fever diagnosed in people from the Western Ghats states. It is caused by the KFD virus, an arbovirus belonging to the Flaviviridae family of RNA viruses, primarily found in ticks and mosquitoes.  

The disease is transferred to humans either by making contact with animals such as monkeys, livestock, shrews and rodents harbouring infected ticks or directly through tick bites.

Forest dwellers, wood collectors, wildlife personnel, people inhabiting endemic forest areas and people venturing into the endemic forest areas for work or recreational activities are most at risk, according to the National Centre for Disease Control. Person-to-person transmission has not been observed. 

Suspected cases are confirmed using RT-PCR tests or serologic testing using enzyme-linked immunosorbent serologic assays.

Symptoms of the disease include high-grade fever, headache, myalgia, extreme weakness, nausea, vomiting, diarrhea, muscle pain, and occasional neurological hemorrhagic manifestations. There is no specific antiviral medicine available. The treatment is symptomatic and supportive like keeping hydrated, managing blood pressure and heart rate.

While most people recover without complications, KFD has a 2-10 per cent mortality rate. In about 20 per cent of the patients, the disease occurs in two phases as a biphasic illness. The fever returns in 1–2 weeks, causing severe hemorrhagic or neurological symptoms in the next phase lasting about 12-14 days, according to a 2018 study titled Clinical & epidemiological significance of Kyasanur forest disease led by the National Institute of Virology, Bengaluru.

In October 2022, Karnataka’s department of health and family welfare suspended the formalin-inactivated tissue-culture vaccine developed at the National Institute of Virology in Pune to protect against KFD. An investigation by the Mint newspaper found that even after the Central Drugs Standard Control Organisation (CDSCO) withdrew permission to manufacture the vaccine from at least 2002, the Bengaluru-based Institute of Animal Health and Veterinary Biologicals (IAHVB) continued doing so.

IAHVB and the VDL in Shivamogga had provided the vaccine to the public regardless of the vaccine failing potency tests. Several studies have shown that the vaccine was not entirely effective against KFD.

Rajesh Surgihalli, district health officer, Shivamogga, told DTE that with the increased campaigning, people are coming forward themselves if they have a fever for two days. “People are also asking for the vaccine. In nine months to one year, we will have a new vaccine,” he said.

A new vaccine doesn’t mean the cases will decrease, but it will have a positive effect on mortality, resulting in fewer deaths, Harshavardhan added.

Disease surveillance is an ongoing activity in the endemic areas during the season. Remote areas, where the cattle graze, and where people go to the forest for wood collection, are known to the field staff and are monitored, the officials said.

“However, deep in the forest where the monkeys die, we don’t know how to access it yet. Other animals could be the carriers as well. Identification of hotspots to assess them is the challenge,” Surgihalli said.

Deforestation and encroachment of forests also lead to increased transmission of the disease. Harvesting of areca nuts and cashew nuts is done from November to January, which is when villagers venture into the forest and become more vulnerable to tick bites. 

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