Symptoms Of Kyasanur Forest Virus In Humans

  • Mfon EkanemBSc (Hons) Human Biology & Infectious Diseases - University of Salford, UK

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Kyasanur Forest virus causes the Kyasanur Forest disease and is usually transmitted between animals. However, in certain cases, this virus can infect humans too.

This article will explore and explain more about this virus, its transmission, disease symptoms, origins, management and prevention.

A brief overview of Kyasanur Forest virus 

Kyasanur Forest disease, also defined as monkey fever, is found in the Western Ghats of India.1 This disease is caused by the Kyasanur Forest virus, which belongs to the family of arboviruses. Other known viruses also belong to this family such as Dengue virus, West Nile virus, and Zika virus. These viruses are zoonotic diseases, which are diseases that are transmitted between animals and humans   via stinging vectors, for example, mosquitos.1


Kyasanur Forest disease was first identified in 1957 when it was discovered in a monkey from the Kyasanur Forest in Karnataka state in India. After identification, 400-500 cases have been reported each year.

Origins and transmission of Kyasanur Forest virus

As reported previously, Kyasanur Forest disease originated in India from the Kyasanur Forest virus.2 The virus is transmitted between animals through vectors, which in this case are hard ticks (Hemaphysalis spinigera).  After infection, the hard ticks remain infected until death, possibly transmitting the virus to multiple individuals or animals.

The virus was first isolated from a sick monkey, giving its origin to the name monkey fever.2 It commonly affects shrews, rodents, and monkeys, after coming into contact with a tick bite. However, as we know this virus can also be transmitted to humans, but how does that occur?  In humans, transmission can occur after a tick bite or after contact with an infected animal (usually a sick or dead monkey), while person-to-person infection is uncommon.2

Incubation period

What is the incubation period?

In any viral disease, the incubation period is the length of time between the first contact and infection with the virus and the first appearance of any symptoms. In the case of Kyasanur Forest disease, incubation can range from 3-8 days, following virus exposure.3,4 The incubation period can however, vary based on factors, such as: 

  • The amount of virus the person has been exposed to 
  • The immune system of the infected person
  • The way the  person has been infected

Distribution and risk of infection

Kyasanur Forest virus has always been contained within the central and western districts of Karnataka states in India, but also in other states in India such as Tamil Nadu and Kerala.4 Additionally, a very similar virus called Alkhurma haemorrhagic fever virus has been discovered in Saudi Arabia.

Partaking in occupational and recreational activities in  outdoor settings in the Karnataka state, can put people at risk of infection. Other than outdoor activities, more cases have been reported during the dry season which can last from November to June.

Common symptoms

Most patients infected with Kyasanur Forest virus recover without any complications.3 Generally after viral incubation, symptoms can appear abruptly within 1-2 weeks. 

 Common symptoms can include:3 

  • High fever (up to 40°C) 
  • Haemorrhage 
  • Headache
  • Bleeding from gums
  • Nasal cavity 
  • Gastrointestinal bleeding3  

Other major symptoms can also include chills, vomiting, diarrhoea, sore throat, muscle pain and extreme physical weakness.3 Occasionally, people can develop blisters in the mouth or soft palate, and bleeding which can manifest as a nose bleed, by coughing blood (usually from the lungs), as bleeding of the gums, and as blood in stools.3 Other common symptoms can include low blood circulation, reduced heart rate and insomnia.3 Due to the severity of these symptoms, limiting and preventing the spread of this virus is  of vital importance.

Optical manifestations

The disease can have optical manifestations such as: 

  • Blood in the eye membrane (conjunctiva)
  • Blood in the vitreous humour (the gel-like substance of the eye that helps keep its shape and provides nutrients)
  • Blood in the retina
  • Inflammation of the eye iris (iritis
  • Opacity of the lens 
  • Inflammation of the cornea (keratitis).

The main features of the disease

The symptoms which make the presence of the virus recognisable are usually:3 

  • Pneumonia, complicated by pulmonary haemorrhage (haemorrhagic pneumonia) 
  • Enlargement of the liver with tissue degeneration (hepatomegaly with parenchymatous degeneration) 
  • Kidney disorders such as nephrosis 
  • Presence of characteristic cells, called reticuloendothelial cells, in the liver and spleen
  • An increase in the elimination of red blood cells (erythrophagocytosis) in the spleen.

Blood dysfunctions related to Kyasanur Forest Disease

Kyasanur Forest virus cancause some abnormalities in the blood like a reduction in white (leucopenia) and red blood cells, as well as a reduction in platelets (thrombocytopenia).³

Patients have also shown anaemia and high liver enzyme levels.³

Recovery and relapse

Patients can recover as early as 2 weeks after infection.³ However, about 10-20% of people have recurring symptoms, which can last from 2-12 days.

While this second phase of infection can be characterised by the same symptoms of Kyasanur Forest disease, additional symptoms can be:³

  • Neurological complications
  • Mental disturbances
  • Stiff neck
  • Confusion
  • Abnormal reflexes
  • Tremors
  • Lower heartbeat (bradycardia)
  • Haemorrhages (gastrointestinal bleeding or bronchopneumonia)
  • Coma
  • Death

Studies also show that while bonnet monkeys and langurs suffer the same symptoms after infection, death happens in about 85% of cases.³


Which methods can be recommended to diagnose the disease?

Early diagnosis is vital to prevent the infection from proceeding further.3 Diagnosis based on symptoms alone is harder because they can be common symptoms of other viral infections too.


Specific treatment to cure Kyasanur Forest disease in humans does not exist as timely intervention is of more vital importance, this can include:3,4

  • hospitalisation
  • supportive therapy
  • maintenance of blood pressure, hydration, and optimal blood condition
  • antipyretics (drugs reducing fever) and  pain reliefs
  • antimicrobial therapy 
  • blood transfusion (in case of infection)

Prevention and control

Because of the increase in tick-borne diseases, many measures have been put into place to prevent the virus from spreading such as:

  • quarantine
  • tick control
  • vaccination

However, further personal protections should be considered by people, such as tick repellents, long sleeves and more courses of vaccines to prevent the disease.


In conclusion, the Kyasanur Forest virus causes the Kyasanur Fforest disease  which can be transmitted from animals to humans. It is most commonly spread through infected tick bites, and less likely, but not completely uncommon, through contact with infected animals. Infection results in severe symptoms such as high fever, haemorrhage, and physical weakness.

The best course of action when suspecting infection is early detection and treatment, to facilitate symptom management.

While this disease is mainly located in India, being aware of it and its  symptoms can help you take necessary precautions when travelling to affected areas.

Summary of key points

  • Kyasanur Forest virus is a zoonotic disease found in India
  • Kyasanur Forest virus is transmitted through hard ticks or infected animals
  • Infected ticks remain infected until death
  • The incubation period can last from 3-8 days
  • Major symptoms include high fever, headache, multiple haemorrhages and muscle weakness
  • Early detection and treatment of infection can avoid the onset of worse symptoms
  • Early detection of infection can be made by PCR or ELISA
  • There is no specific cure for Kyasanur Forest disease
  • People visiting this side of India should exercise caution and take preventive measures


What is the mortality rate of the Kyasanur Forest virus?

The mortality rate ranges from 3-15 %.

How do you manage Kyasanur Forest disease?

Kyasanur Forest disease can be managed by supportive therapies and early hospitalisation.

What are the risk factors of Kyasanur Forest disease?

Anyone working or doing recreational activities in rural or outdoor settings, in the Karnataka state is at risk of infection by infected ticks.

What is the other name for Kyasanur Forest disease?

Kyasanur Forest disease can also be called monkey fever.


  1. Chakraborty S, Sander W, Allan BF, Cristina F. Retrospective Study of Kyasanur Forest Disease and Deaths among Nonhuman Primates, India, 1957–2020. Emerging Infectious Diseases [Internet]. 2021 Jul 1;27(7):1969–73. Available from:
  2. Kyasanur Forest Disease (KFD) | CDC [Internet]. 2019. Available from:
  3. Mourya D, Munivenkatappa A, Sahay R, Yadav P, Viswanathan R. Clinical & epidemiological significance of Kyasanur forest disease. Indian Journal of Medical Research [Internet]. 2018;148(2):145. Available from:
  4. Muraleedharan M. Kyasanur Forest Disease (KFD): Rare Disease of Zoonotic Origin. Journal of Nepal Health Research Council [Internet]. 2016 Sep 1 [cited 2024 May 5];14(34):214–8. Available from:
  5. Shah SZ, Jabbar B, Ahmed N, Rehman A, Nasir H, Nadeem S, et al. Epidemiology, pathogenesis, and control of a tick-borne disease- kyasanur forest disease: current status and future directions. Front Cell Infect Microbiol. 2018;8:149.
  6. Shah SZ, Jabbar B, Ahmed N, Rehman A, Nasir H, Nadeem S, et al. Epidemiology, pathogenesis, and control of a tick-borne disease- kyasanur forest disease: current status and future directions. Frontiers in Cellular and Infection Microbiology [Internet]. 2018 [cited 15 february 2024];8. Available from:

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Mfon Ekanem

Bachelor of Science in Human biology and Infectious Diseases – Bsc(Hons), University of Salford, United Kingdom

Mfon is a recent graduate with a Bachelor of Science degree in Human Biology and Infectious Diseases, with a comprehensive understanding of genetics and physiology. With a profound passion for both medicine and writing, Mfon is dedicated to delivering engaging and accurate content tailored for both general audiences and enthusiasts of the medical field alike.

Throughout her academic journey, Mfon has gained knowledge of the human body, focusing particularly on the mechanisms of infectious diseases and their impact on human health. She has developed a keen insight into the complex interplay between pathogens and host organisms, as well as the body's defence mechanisms against diseases.

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