Kyasannnur Forest Disease

Kyasanur Forest Disease (KFD) is a highly infectious, tick-borne viral haemorrhagic fever that affects humans and monkeys, caused by the Kyasanur Forest Disease Virus (KFDV), a member of the genus Flavivirus within the family Flaviviridae. The disease was first identified in 1957 in the Kyasanur Forest region of Shimoga District, Karnataka, India, from which it derives its name. KFD is an important zoonotic disease of public health significance in India, transmitted primarily through tick bites and maintained in nature via a complex cycle involving ticks, monkeys, and small mammals.

Historical Background

The first outbreak of Kyasanur Forest Disease occurred in Kyasanur village, located in the Western Ghats region of Karnataka, where several monkeys were found dead, followed by cases of acute febrile illness among forest workers and villagers. Investigations by the Virus Research Centre (now National Institute of Virology, Pune) led to the isolation of the virus from Haemaphysalis spinigera ticks and affected monkeys.
Since its discovery, KFD has remained endemic to parts of southern India, with recurring seasonal outbreaks. Initially confined to Shimoga, Chikkamagaluru, and Uttara Kannada districts, the disease has progressively spread to Kerala, Goa, Tamil Nadu, and Maharashtra, particularly along the Western Ghats hill ranges, which provide ideal ecological conditions for tick survival and transmission.

Causative Agent and Virology

The causative organism, the Kyasanur Forest Disease Virus (KFDV), is an RNA virus belonging to the Flavivirus genus, which also includes viruses responsible for dengue, yellow fever, and tick-borne encephalitis.
Key virological features:

• Genome: Single-stranded, positive-sense RNA.
• Shape: Spherical, enveloped virus (~40–50 nm diameter).
• Stability: Sensitive to heat, lipid solvents, and common disinfectants.

Genetically, KFDV is closely related to the Alkhurma haemorrhagic fever virus (AHFV) found in Saudi Arabia, suggesting a possible evolutionary link.

Reservoirs and Transmission Cycle

KFD is maintained in nature through a zoonotic transmission cycle involving ticks, wild mammals, and monkeys. Humans are accidental hosts and do not contribute significantly to further transmission.
Principal vectors:

• Haemaphysalis spinigera, a hard tick species, is the primary vector.
• Other Haemaphysalis species may also participate in virus maintenance.

Reservoir hosts:

• Small mammals such as rodents (Rattus spp., Funambulus tristriatus) and shrews act as reservoir hosts, sustaining the virus in forest ecosystems.
• Monkeys, particularly Semnopithecus entellus (Hanuman langur) and Macaca radiata (bonnet macaque), act as amplifying hosts, suffering high mortality during outbreaks and serving as sentinels of viral activity.

Human infection route:

• Humans acquire infection primarily through tick bites while working or walking in forested areas.
• Secondary exposure may occur via handling infected monkey carcasses or contact with contaminated vegetation where infected ticks reside.
• There is no evidence of person-to-person transmission.

Epidemiology and Geographic Distribution

KFD occurs predominantly in the Western Ghats region of South India, an area characterised by dense forests, high rainfall, and suitable habitats for ticks.
Endemic and affected states:

• Karnataka: Shimoga, Chikkamagaluru, Uttara Kannada, Dakshina Kannada, Udupi, and Chamarajanagar districts.
• Kerala: Wayanad, Malappuram, and Palakkad districts.
• Goa, Maharashtra, and Tamil Nadu have also reported sporadic outbreaks.

The disease typically appears during the dry pre-monsoon season (November to May), coinciding with increased human activity in forests and the life cycle peak of infected ticks.

Clinical Manifestations

The incubation period of KFD in humans is usually 3–8 days after an infected tick bite. The disease progresses in two distinct phases:
First (febrile) phase:

• Sudden onset of high fever, chills, severe headache, and muscle pain.
• Photophobia, conjunctival congestion, and facial flushing.
• Nausea, vomiting, and diarrhoea.
• Lymphadenopathy and bradycardia are common.

After about one week, the fever subsides, and some patients recover; however, about 10–20% enter a second phase.
Second (haemorrhagic/neurological) phase:

• Occurs after a short afebrile period (1–2 weeks).
• Characterised by bleeding from gums, nose, gastrointestinal tract, and petechial haemorrhages on skin.
• In severe cases, encephalitic symptoms such as confusion, tremors, and mental disturbances may develop.
• The case fatality rate (CFR) ranges between 3% and 10%, depending on outbreak intensity and healthcare access.

Pathology

Post-mortem studies have shown involvement of the liver, spleen, lymph nodes, and bone marrow. The virus causes haemorrhagic lesions, necrosis, and depletion of immune cells, explaining the bleeding tendency and immunosuppression observed in patients.

Diagnosis

Diagnosis is based on clinical suspicion in endemic areas supported by laboratory confirmation using:

• ELISA (IgM and IgG detection) for recent and past infection.
• RT-PCR (Reverse Transcription Polymerase Chain Reaction) for detection of viral RNA in blood samples.
• Virus isolation in cell cultures or laboratory animals (for research).

Serological surveys are often conducted to monitor disease prevalence and outbreak risk.

Treatment and Management

There is no specific antiviral treatment for KFD. Management is supportive and symptomatic, focusing on maintaining hydration, controlling fever, and managing haemorrhagic complications.
Supportive care includes:

• Fluid and electrolyte balance.
• Blood transfusions in cases of severe bleeding.
• Pain management and rest.
• Antibiotics to prevent secondary infections.

Hospitalisation is recommended for severe cases to monitor vital signs and potential neurological involvement.

Prevention and Control

Since no curative treatment exists, prevention and vector control form the cornerstone of KFD management.
Key preventive measures include:

1. Vaccination:
   • A formalin-inactivated KFD vaccine developed by the National Institute of Virology (NIV), Pune, is used in endemic districts of Karnataka.
   • Two primary doses given one month apart, followed by booster doses every 5 years.
   • Coverage remains limited due to logistical challenges in remote areas.
2. Tick Control:
   • Application of acaricides (insecticides) in forest fringes, cattle shelters, and human habitations.
   • Use of protective clothing and tick repellents for forest workers.
3. Surveillance and Monitoring:
   • Early detection of monkey deaths to predict viral activity.
   • Establishment of sentinel surveillance in endemic zones.
   • Community education and health awareness campaigns.
4. Public Health Education:
   • Avoiding handling of dead monkeys without protection.
   • Minimising forest exposure during outbreak periods.
   • Strengthening rural healthcare and diagnostic infrastructure.

Ecology and Environmental Factors

Environmental changes such as deforestation, agricultural expansion, and human encroachment into forests have facilitated closer contact between humans, ticks, and wildlife reservoirs, leading to new foci of infection. The Western Ghats, being a biodiversity hotspot with humid forests and thick undergrowth, provide ideal conditions for tick proliferation and disease persistence.

Recent Trends and Spread

In recent years, KFD has expanded beyond traditional endemic zones, with cases reported in Kerala (Wayanad, Malappuram), Goa, Maharashtra (Sindhudurg), and Tamil Nadu (Nilgiris). This spread is attributed to:

• Movement of infected ticks via migratory animals.
• Changing climate and forest ecology.
• Increased human intrusion into forested areas.

Key Facts and Figures

Public Health Significance

Kyasanur Forest Disease remains a priority zoonotic disease under India’s Integrated Disease Surveillance Programme (IDSP). It illustrates the complex interconnection between wildlife, environment, and human health, fitting the One Health framework that integrates veterinary, medical, and ecological approaches.