Kyasanur Forest Disease is a hemorrhagic fever caused by a virus. It is transmitted to humans by a tick bite or contact with an infected animal. The virus is endemic to the South-Western part of India. While the disease has a low mortality, it is spreading beyond its original endemic region and is now considered to be emerging.
The official number of cases per year are still low and the disease is currently not that prevalent. However, systematic surveillance of this disease is severely lacking.
New infections per year
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What causes Kyasanur Forest Disease
Kyasanur Forest disease (KFD) is caused by the Kyasanur Forest disease virus which is a member of the Flaviviridae virus family. Common hosts of this virus are monkeys and small animals (shrews and rodents).
Several species of ticks can transmit the virus, but Haemaphysalis spinigera is the main vector of disease. It is a forest tick prevalent in the state Karnataka of India where most cases were recorded.
The virus can be transmitted to humans after a tick bite or through contact with an infected animal. Particularly dangerous is the contact with a sick or recently deceased monkey. When an infected monkey dies, ticks fall from its body generating hot-spots of infectious ticks which can latch on to the humans.
Humans are dead-end hosts of the virus, and no human-to-human transmission of this virus has been described.
Where is Kyasanur Forest Disease found
Kyasanur Forest disease was first discovered in 1957 in the Kyasanur forest area in the Karnataka state of India. During this outbreak, several cases of a febrile disease in humans were reported. They coincided with numerous monkey deaths in the region. Hence, Kyasanur Forest disease is also known as “monkey fever”.
Since then, Kyasanur Forest disease has spread to new districts of Karnataka and other states within India, including Tamil Nadu, Kerala, Gujarat and Goa. The disease is now endemic in various districts of Karnataka, Tamil Nadu and Kerala states.
People who frequently visit forests in the endemic areas such as forest workers, shepherds, hunters and farm-workers are at a particularly high risk of infection. Most cases occur in the dry season from December to May when the ticks are most active.
Very similar variants of this virus have also been identified in Saudi Arabia and China.
What are the symptoms of Kyasanur Forest Disease
Some infections with the virus are asymptomatic, while others might be mild to severe.
The initial symptoms begin after an incubation period of 3 to 8 days. They usually start abruptly and include high-grade fever, chills and headache. 3 to 4 days after the initial symptom onset, vomiting, gastrointestinal symptoms and bleeding problems may occur. An important diagnostic sign seen in some patients is blisters on the upper, inner mouth. Other symptoms of the acute phase of Kyasanur Forest disease are low blood pressure and heart rate as well as low platelet, red blood cell, and white blood cell counts.
Most patients begin to recover after 14 days. However, 10-20% of patients experience a second phase of disease after a 1 to 2 -week period of remission. The symptoms of the second wave include fever and neurological complications, such as tremors, mental disturbances, severe headache, stiff neck and blurring of vision.
The disease fatality rate is in the range of 3-10%.
How can Kyasanur Forest Disease be prevented
Farmers, shepherds, veterinarians, local dwellers and travelers visiting forest areas are at elevated risk of infection.
Prevention involves avoiding tick bites by using special repellents, wearing long pants and long sleeves as well as avoiding areas inhabited by ticks. Skin and clothing should be frequently examined for the presence of ticks and in case ticks are found, they should be removed without touching them with bare hands. De-ticking farm animals before transportation or slaughter is required in endemic areas.
Clothing and wearing gloves are also important when handling the blood and tissue of infected animals, especially in endemic areas. It is recommended to thoroughly cook meat and other animal products before consumption and avoid oral contact with raw animal products.
A vaccine against Kyasanur Forest disease has been developed and is used in India in areas endemic to the virus. It is well tolerated and relatively protective but efforts to enhance its long-term efficacy are needed.
How is Kyasanur Forest Disease diagnosed
The clinical signs of Kyasanur Forest disease are indistinguishable from other viral fevers, such as Dengue, and cannot be relied on for disease diagnosis. Hence, several diagnostic tests have been developed, including PCR and ELISA assays.
Infection can be confirmed using Polymerase chain reaction (PCR) tests, such as the ones made available by the WoIDMo. However, it cannot detect the virus after 8-10 days from the onset of symptoms. ELISA tests can also be used and detect antibodies 7 to 9 days after the onset of symptoms. Hence, ELISA tests are useful for confirmation at later stages of infection.
Early diagnosis and fast treatment reduces the severity of the disease and prevents deaths.
How is Kyasanur Forest Disease treated
Currently, no specific treatment is available for Kyasanur Forest disease. Treatment consists of supportive measures, such as maintenance of hydration, blood pressure and blood cell counts.
Patients in the second phase of the disease may require pain reliefs and antipyretics for the management of headache and fever. Anti-epileptics are used for patients with seizures.
There is currently few evidence supporting the use of intiviral drugs. Ribavirin, an antiviral drug could be used. Treatment is most effective when it is started early in the course of the disease and preferably within 48 hours after the onset of symptoms.
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