Kyasanur Forest Disease Virus (KFDV) belongs to the genus Flavivirus within the family Flaviviridae. Flaviviruses belong to a diverse group of RNA viruses that are primarily transmitted by arthropods such as mosquitoes and ticks. The Flavivirus genus includes other viruses like Dengue, Zika, West Nile, and Japanese encephalitis.

Kyasanur Forest Disease Virus (KFDV) is a tick-borne virus causing Kyasanur Forest Disease (KFD), primarily found in India. Identified in 1957 in Karnataka's Kyasanur forest, it spreads through the bite of infected ticks, notably Haemaphysalis spinigera. This virus originally affected monkeys, but can now infect humans, leading to symptoms like fever, headache, and muscle pain, progressing to severe complications like haemorrhage and neurological issues. KFD outbreaks periodically threaten public health, prompting vaccination campaigns and tick habitat reduction efforts.¹

In this article, we will delve into the transmission, signs and symptoms, risk of exposure, diagnosis, treatment and prevention of disease caused by the Kyasanur Forest virus.

Transmission of Kyasanur Forest Disease

Kyasanur Forest Disease Virus (KFDV) primarily circulates between ticks and small mammals in forested areas of South Asia.² Here's a breakdown of the natural reservoirs and hosts, as well as the modes of transmission to humans:

1. Monkeys (Primates)

Among the various species of monkeys, such as langurs and bonnet macaques, there exists a significant role in the preservation of the Kyasanur Forest Virus (KFDV). These primates serve as natural reservoirs, carrying the virus without displaying symptoms, thereby contributing to the virus's sustainability within the ecosystem.³

2. Rodents

Rodents, such as rats and squirrels, are known to serve as reservoir hosts for KFDV, enabling ongoing virus transmission in the wild. Despite being infected, these animals do not display any symptoms, further contributing to the sustained spread of the virus.⁴

3. Shrews

Some types of shrews, which are small insectivorous mammals, have been linked to the possible transmission of KFDV as well. Similar to other host species, shrews can carry the virus and pass it onto ticks, playing a role in its spread.⁴

4. Tick bites

KFDV is mainly transmitted to humans through the bite of ticks carrying the infection. Ticks acquire the virus by feeding on infected reservoir hosts, such as monkeys, rodents, and shrews. When infected ticks bite humans, they can transmit the virus, leading to human infection.

5. Direct contact with infected animals

Humans can also become infected with KFDV through direct contact with infected animals or their tissues, such as blood, during hunting, handling, or butchering of infected animals. This mode of transmission is relatively rare but can occur in individuals who come into close proximity with infected animals.⁵

6. Occupational exposure

People who spend time working or participating in activities in forested regions, including forestry workers, researchers, and hunters, face a high risk of coming into contact with KFDV-infected ticks. Occupational exposure to tick-infested environments increases the likelihood of tick bites and subsequent transmission of the virus to humans.⁵

Symptoms of Kyasanur Forest Disease 

The incubation period of Kyasanur Forest Disease (KFD) typically ranges from 3 to 8 days. 

After this period, the symptoms may appear suddenly which include:

• Chills
• Fever
• Headache

3-4 days after initial symptom onset:

• Severe muscle pain
• Vomiting
• Gastrointestinal symptoms
• Bleeding problems

Possible complications associated with the infection include:

• Abnormally low blood pressure
• Low platelet count
• Low red blood cell count
• Low white blood cell count

Some patients recover without complications after 1-2 weeks. However, for some individuals, typically around 10-20% of cases, Kyasanur Forest Disease (KFD) follows a two-phase pattern. This means that after an initial period of symptoms, there's a second wave of symptoms that arises at the start of the third week of illness.

Symptoms include:

• Fever
• Severe headache
• Mental disturbances
• Tremors
• Vision deficits

The approximate mortality rate for Kyasanur Forest Disease (KFD) falls within the range of 3 to 5%.

Risk of exposure to Kyasanur Forest Virus

The risk of exposure to Kyasanur Forest Disease (KFD) depends on the following factors:

1. Geographic location

KFD is endemic to certain regions of India, particularly in the Western Ghats, including parts of Karnataka, Goa, Maharashtra, and Kerala. Travelling to or residing in these regions increases the risk of exposure.⁶

2. Outdoor activities

Engaging in outdoor activities such as hiking, camping, or trekking in forested areas where ticks are prevalent can increase the risk of exposure to KFD.⁷

3. Contact with infected animals

KFD primarily circulates among small mammals such as rodents, shrews, and monkeys. The risk of virus transmission in humans can increase if there is contact with the blood or tissues of infected animals or they are bitten by infected ticks that have fed on these animals.

4. Seasonal variations

The risk of KFD transmission may vary seasonally, with higher incidence typically occurring during the warmer months when tick activity is increased.

5. Occupational exposure

Individuals who work in forestry, agriculture, or other outdoor occupations in endemic areas may have a higher risk of exposure to KFD due to their increased likelihood of encountering infected ticks or animals.

Diagnosis of Kyasanur Forest Disease

The diagnosis of Kyasanur Forest Disease (KFD), caused by the Kyasanur Forest virus (KFDV), is carried out by the following methods:

1. Clinical evaluation

Physicians evaluate the patient's symptoms, which may include fever, headache, muscle pain, and gastrointestinal symptoms like nausea, vomiting, and diarrhoea. Severe cases can involve bleeding manifestations, neurological symptoms, and multi-organ failure.⁸

2. Epidemiological history

Knowledge of the patient's recent travel history or residence in endemic areas, particularly regions where KFD is prevalent such as South Asia, is crucial for isolating potential exposures and guiding diagnostic efforts.

3. Laboratory tests

The laboratory tests required to diagnose Kyasanur Forest Disease (KFD) include the following:

Serological tests

Enzyme-linked immunosorbent assay (ELISA) or other serological tests detect antibodies against KFDV in the patient's blood serum. IgM antibodies typically appear during the acute phase, while IgG antibodies may persist longer.⁹

Viral isolation

Attempts to isolate KFDV from blood samples during the acute phase can be made. However, this method is less common due to its complexity and the requirement for specialised facilities.

PCR testing

Polymerase chain reaction (PCR) assays detect viral RNA in blood samples, offering a rapid and specific diagnosis, particularly during the early stages of illness.

Blood tests

A complete blood count (CBC) is performed to assess abnormalities such as leukopenia (low white blood cell count) and thrombocytopenia (low platelet count).⁸

Liver function tests

To assess liver involvement, as KFD can cause hepatitis.¹

Treatment of Kyasanur Forest Disease

The treatment and management approaches for Kyasanur Forest Disease involve:

1. Supportive care

There is no specific antiviral treatment available for KFD. Therefore, supportive care forms the cornerstone of management. This includes maintaining hydration, and electrolyte balance, and managing symptoms such as fever, headache, and muscle pain.

2. Hospitalisation

Severe cases of KFD may require hospitalisation, especially if there are complications such as hemorrhagic manifestations or neurological symptoms.

3. Monitoring and management of complications

Complications such as hemorrhagic manifestations (bleeding) and neurological symptoms may occur in severe cases. These complications need to be managed appropriately. Blood transfusion may be necessary in cases of severe bleeding.⁸

Prevention of Kyasanur Forest Disease

Preventing Kyasanur Forest Disease (KFD) primarily involves measures to reduce exposure to the tick vectors and the virus they carry. Here are some key preventive measures:

1. Avoidance of tick habitat

To prevent the transmission of the virus, it is advised to minimise exposure to areas where ticks are prevalent, such as dense forests, especially during peak tick activity seasons (usually the post-monsoon period in endemic regions).

2. Protective clothing

Wear appropriate clothing such as long-sleeved shirts, long pants tucked into socks, and closed shoes when entering tick-infested areas to reduce skin exposure to ticks.

3. Use of tick repellents

Apply insect repellents containing DEET (N, N-diethyl-meta-toluamide) or permethrin to exposed skin and clothing to repel ticks. 

4. Tick checks

Thorough tick checks should be conducted on clothing and skin after outdoor activities in areas where ticks may be present. Any attached ticks should be promptly removed using fine-tipped tweezers, grasping the tick as close to the skin surface as possible and pulling upward with steady, even pressure.

5. Vaccination

In endemic areas, vaccination against KFD is an important preventive measure. The KFD vaccine is available and has been shown to confer immunity against the virus for a certain period.

6. Public awareness and education

Public health education campaigns should be conducted to raise awareness about KFD, its symptoms, transmission, and preventive measures. The general public should be made aware of the importance of protective measures and prompt medical attention if they experience any symptoms suggestive of KFD.

7. Livestock protection

Implement measures to protect livestock (e.g., cattle) from tick infestations, as they can serve as amplifying hosts for the virus. This may include tick control programs and keeping the animal enclosures away from tick-infested areas.

8. Surveillance and control

Implement active surveillance for KFD cases and tick populations in endemic areas to detect outbreaks early and initiate appropriate control measures. Vector control strategies should be used to reduce tick populations in high-risk areas.

Summary

Kyasanur Forest Virus (KFD) is a tick-borne viral disease prevalent in forested regions of India. Belonging to the Flavivirus genus, it primarily infects monkeys and small mammals, with ticks acting as vectors. Transmission to humans occurs through tick bites or contact with infected animals.

Symptoms include fever, headache, muscle pain, and bleeding tendencies, progressing to severe manifestations like haemorrhage and neurological complications. Vaccination and control measures targeting tick populations are crucial for prevention. KFD poses a significant public health concern in endemic areas due to its potential for outbreaks and the absence of specific antiviral treatments.