Kyasanur Forest DiseaseA98.-

Discovered in 1955-1957 in a forest area on the southwest coast of India (Mysore); described as a zoonosis that affected several monkeys ("monkey disease"); later humans also became ill; initially classified as a variant of Russian encephalitis, in 1990 it was recognized as a separate disease.Enzootic between ticks and small rodents, monkeys and humans are accidental hosts

Kyasanur Forest Disease is a serious infectious disease caused by the KFD virus. KFD occurs mainly in the Indian states of Karnataka, Tamil Nadu and Kerala and was first detected in the Kyasanur forest in southern India.

Transmission to humans occurs mainly through tick bites or contact with infected animals. Carriers are shield ticks (Hemaphysalis spinigera) that transmit the KFD virus to humans and animals such as monkeys and rodents.

Kyasanur Forest Disease Virus (KFDV) and Alkhurma Hemorrhagic Fever Virus (AHFV) are tick-borne flaviviruses that cause life-threatening hemorrhagic fever in humans with a mortality rate of 3-5% for KFDV and 1-20% for AHFV. Kyasanur Forest Disease Virus is a biosafety level 4 pathogen due to the severity of the diseases they cause and the lack of effective countermeasures. In recent years, Kyasanur Forest Disease Virus has spread beyond its original endemic zones and has thus become a public health concern (Bhatia B et al. 2020).

Since KFDV is of zoonotic origin and is transmitted by vectors, the viruses circulate between a tick vector and a vertebrate host. Haemaphysalis spinigera and Ornithodoros savignyi are the main tick vectors involved in the transmission of KFDV (Charrel RN et al. 2007; Trapido H et al. 1959). H. spinigera is common in India, Sri Lanka and Vietnam. About 95 % of KFDV isolates were obtained from this tick species. Ticks ingest vertebrate blood at various stages of development and become infected with the virus, which is then transmitted to the host. Seasonal outbreaks of KFDV and AHFV in humans occur in spring and summer, which correlates with the maximum activity of the respective tick vector (Stone R 2014; Al-Tawfiq JA et al. 2017). KFDV has been isolated in rodents, birds, cattle and bats, but only primates appear to develop disease (Stone R 2014). Humans become infected with KFDV through bites from infected ticks or by handling infected mammals and bird species. To date, no human-to-human transmission has been reported for KFDV.

Between 400 and 500 people contract KFD every year. Hunters, herders, forest workers and farmers in the Indian states of Karnataka, Tamil Nadu and Kerala are naturally at a higher risk of contracting KFD.

The first symptoms usually appear 3 to 8 days after infection with the virus with sudden chills, fever and headache. 3 to 4 days after the onset of symptoms, severe muscle pain, vomiting, gastrointestinal symptoms and bleeding may occur. Most patients recover one to two weeks after the onset of symptoms. A second wave of symptoms occurs in about 10 to 20% of patients, including severe headaches, mental disturbances, tremors and visual disturbances.

The recovery phase usually lasts several months. During this time, muscle pain and weakness also occur and the patient is unable to engage in physical activity.

Detection of the pathogen using virus isolation and detection of antibodies in the blood using polymerase chain reaction (PCR).

So far, only symptomatic measures are known. Supportive care is crucial, including hydration, oxygenation, blood pressure control and treatment of additional infections. A vaccine against KFD is available and is recommended in parts of India where Kyasanur Forest Disease occurs.

With prompt medical care, most patients recover from KFD without complications. However, around 3 to 5 % of people with this disease die.

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2. Bhatia B et al. (2020) Kyasanur Forest Disease and Alkhurma Hemorrhagic Fever Virus-Two Neglected Zoonotic Pathogens. Microorganisms 8:1406.
3. Charrel RN et al. (2007) Alkhurma hemorrhagic fever virus in Ornithodoros savignyi ticks. Emerg. Infect Dis 13:153-155.
4. Kandi V et al. (2024) Kyasanur Forest Disease: A Comprehensive Review. Cureus 16:e65228.
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6. Trapido H et al. (1959) Kyasanur Forest disease. VIII. Isolation of Kyasanur Forest disease virus from naturally infected ticks of the genus Haemaphysalis. Indian J Med Res 47:133-138.