Kyasanur Forest Disease Virus Transmission

Overview

Have you heard of the Kyasanur Forest disease, or perhaps monkey fever? The Kyasanur Forest disease virus is responsible for causing this disease, which is a viral haemorrhagic infection, transmitted by ticks. This virus is distributed around the southern region of India and can lead to devastating consequences if not dealt with properly. 

Introduction to Kyasanur Forest Disease virus 

Kyasanur Forest disease virus (KFDV) is a member of the Flaviviridae family. It is known for causing the Kyasanur Forest disease (KFD), commonly known as monkey fever, a viral haemorrhagic disease that is transmitted through ticks and infects humans and smaller mammals. The virus has been assigned to the risk group 4 pathogens¹ and every year, there have been around 500 cases, along with a 1 to 3% fatality rate.²

The virus was first discovered in 1957 when it was found in monkeys located in the Kyasanur Forest in India. This epizootic outbreak has raised interest in the research of KFDV and through sequencing, it was found that its genetic composition shares similarities with the Alkhurma Haemorrhagic Fever virus.

Distribution and cases

The virus first originated from the Kyasanur Forest, located near the southwestern coast of India. Over the decades, the virus has been distributed to forests across India and reached the southernmost and southeastern regions. The spread of KFDV has not been properly identified and remains unknown, but it is believed that the availability of the vectors and the presence of the host play a large contributing factor.³ 

Between the first discovery to the present, there have been several outbreaks of the KFD. After the initial discovery of KFDV, the cases of the disease decreased gradually, but in 2012, there was a sudden increase in the number of cases, where the human and monkey samples from the southernmost district of the state were found to be tested positive for the virus.⁴

There also was a major epidemic of the disease in 2015 when there was an outbreak within a population of women working in a forest located in the Wayanad district of Kerala, India.⁵ As time passed, the virus was no longer contained within this tribal community and spread to the general public, which led to further outbreaks up until 2017. 

Signs and symptoms 

Symptoms of KFDV can take up to 8 days to appear⁶ and some of the initial symptoms include:

• Chills
• Fever
• Headache 

Later-stage signs and symptoms might also appear 3 to 4 days after the initial presentations, such as:

• Muscle pain
• Vomiting
• Gastrointestinal symptoms
• Bleeding
• Mucosal inflammation 
• Conjunctival congestion

Kyasanur forest disease is a biphasic illness for around 15% of the patients, meaning they will experience a second round of symptoms. These symptoms include fever and neurological manifestations, for example, confusion, drowsiness, loss of consciousness and transient disorientation.⁶ Patients recovering from the relapse symptoms might display hand tremors or unsteadiness for a few weeks, but long-term complications are not common.⁷

How is KFD transmitted?

Ticks–It can be transmitted to humans through an infected tick bite.¹ The tick responsible is the hard tick, Haemaphysalis spinigera, acting as a reservoir host for the virus.⁹

During a tick bite, the virus along with the saliva components can enter the host body at the site.¹ The virus would then infect its target cells, including macrophages, dendritic cells and monocytes, and replicate within the host cells to produce further viral particles to infect more cells. 

Monkeys and rodents–Tick feed on infected hosts, such as rodents, shrews and monkeys. Infected ticks then transmit the virus to humans.

Other animals– larger animals can also act as hosts for KFDV, but they are not as common and play less of a significant role in the viral transmission. According to one study, the consumption of unpasteurised milk from infected animal hosts, such as cows, sheep and goats, does not transmit the virus.¹⁰

Human contact– There is currently no evidence that the infection is transmitted between humans. 

Risk factors

There are several risk factors that would increase the likelihood of getting infected by KFDV. One of these contributing factors would be the location of where people stay for a prolonged period. Places that require extended exposure to rural or outdoor settings, such as farmers, hunters, etc. would be more at risk of being in contact with the infected ticks. Another factor would be the time, in which the drier seasons, from November to June, appear to have more cases due to the activity of the ticks. 

Diagnosis

The modern techniques for testing revolve around the detection of the virus directly from the patient samples, whereas the tests (haemagglutination inhibition test, virus neutralisation test and complement fixation test)⁸ used before were time-consuming and not as efficient for testing the early stages of the disease. 

The polymerase chain reaction (PCR) is a common serological method to test for the presence of the virus within the patient's blood sample. Another recent diagnostic test includes the enzyme-linked immunosorbent assay (ELISA), which can detect antibodies produced in response to KFDV in patient serum samples. Both of these methods are more sensitive and specific, which would be useful for determining the early stages of the infection. 

Treatment

There is currently no cure for Kyasanur Forest disease,³ but there are several actions that could be taken to aid with the recovery from the Kyasanur Forest disease. Early hospitalisation is important to control the infection effectively, taking action earlier can avoid a severe progression of the disease to its more impact on the neurological functions. Another solution would be supportive therapy, such as maintaining proper hydration and taking action for bleeding disorders. The type of therapy would depend on the severity of each case and the symptoms that have arisen. 

Prevention

Vaccination

Vaccines are available for the general public to take as a preventative measure, which is a vaccine for a whole virus that has been tissue culture derived and formalin-inactivated.¹¹ However, the suitability has been challenged due to the short-term effectiveness and the need for additional boosters. Newer models of vaccines for KFDare undergoing research and development, where the vaccines are based on a vesicular stomatitis virus that expresses the KFDV precursor membrane and its envelope proteins.^{11, 12} They have shown promising effectiveness in inducing a strong immune response and being able to defend the body from the incoming infection. 

Insect repellent and protective clothing

Other precautions to take include the use of insect repellent and wearing protective clothing. The repellent used should be Environmental Protection Agency-registered to ensure they contain the appropriate substances to effectively prevent tick bites. All clothing and gear should be treated with permethrin as they can incapacitate any ticks that try to come into contact, making it highly effective in protecting against them. Be mindful that the permethrin does not last for a long time and requires reapplication if the clothing was worn for too long or has been washed multiple times. 

Tick avoidance and awareness

Travellers who visit the endemic regions of India should be particularly mindful and should avoid staying in the forests where the ticks reside.

Summary 

The Kyasanur Forest disease virus is a tick-borne member of the Flaviviridae family that leads to the epizootic Kyasanur Forest disease. Hard ticks act as the reservoir for this virus and transmit the virus to humans through their bites. There are several preventative precautions to take, including vaccinations, insect repellent and protective clothing to avoid tick bites, especially for those travelling to the endemic areas within India. If you have been bitten, seek medical help as soon as possible to avoid the invasive progression of the disease.