Kyasanur forest disease, a tick-borne infection plaguing India
In recent weeks, India has confirmed several deaths caused by Kyasanur Forest Disease (KFD), commonly known as “monkey fever”. It is a serious viral infection transmitted by ticks and is endemic to the Western Ghats, a mountain range located in southern India.
Among other symptoms, patients experience frontal headache, severe prostration, chills, high fever, conjunctivitis, bleeding from the nose, mouth and gastrointestinal tract. They may also have abnormally low blood pressure and low platelet, red and white blood cell counts.
Mortality rate up to 15%
The incubation period for KFDV is three to eight days. After one to two weeks of symptoms, some patients recover without complications. However, in some people (10 to 20%), the disease is biphasic, that is, it causes a second wave of symptoms at the beginning of the third week. These include fever and signs of neurological disorders such as severe headache, mental disturbances, tremors and visual disturbances.
KFDV is classified as a Biosafety Level 4 (BSL4) pathogen, the highest available. The mortality rate ranges from 3 to 15%.
Transmission to humans can occur through contact with an infected animal, most notably a sick or recently deceased monkey. However, the main vectors of KFDV are ticks. Hemaphysalis spinigera And Hemaphysalis tuturiswhich are endemic to southern India and transmit the virus to monkeys and humans.
These parasites absorb the blood of vertebrates at different stages of development, acquiring and transmitting the pathogen to various hosts – birds and mammals. It is also transmitted from tick to tick when feeding together. Asymptomatic replication of KFDV has been documented in most birds and mammals, including birds, cattle, and bats, but human-to-human transmission has not been described.
Large animals such as goats, cows and sheep can be infected with KFDV, but they play a limited role in the spread of the disease. Although these species provide blood to ticks that act as vectors for the virus, direct transmission of the pathogen from large animals to humans is extremely rare. Additionally, there is no evidence of disease transmission through unpasteurized milk from any of these animals.
First identified in 1957.
The disease is named after the forest area located in the Shimoga district of the Indian state of Karnataka, where it was first identified. In 1957, there was a spate of black-faced langur deaths in the region (Presbytus entellus) and a red-faced hooded monkey (Macaca radiata). This coincided with reports of febrile illnesses in humans, leading to the coining of the colloquial terms “monkey disease” or “monkey fever”.
One of the first cases of CFD was described in a young man who climbed a tree to collect what he thought was honey from a bee hive. However, it turned out to be a dead monkey, hanging from a branch and covered in flies everywhere. It is very likely that the corpse was infested with mites.
Between 2003 and 2012, a total of 3,263 human cases were reported in Karnataka, with 823 confirmed cases and 28 deaths. Since 2012, Kyasanur forest disease has spread to new districts and states in India, and human incidence has increased to approximately 500 cases per year.
The largest human outbreaks occurred in 1957–1958 (681 cases), 1983–1984 (2589 cases), 2002–2003 (1562 cases) and 2016–2017 (809 cases). Monkey migration may expand the geographic spread of KFDV as infected ticks cross national borders through associated natural areas.
Ineffective vaccine
There is no cure for this pathology. In the past, India has used inactivated whole virus vaccine to prevent infections. However, even with multiple booster doses, vaccinees still develop viremia and clinical disease following KFDV infection, demonstrating limited efficacy.
Prevention, early detection, supportive care and symptom management are the main measures to reduce the impact of the disease caused by this virus. However, the main barriers are associated risk factors such as limited disease awareness, human-induced forest degradation and exploitation, and poor diagnosis and surveillance.
Deforestation appears to be one of the main reasons for the spread of Kyasanur forest disease. Unfortunately, due to agricultural intensification and increased human activity, there has been a huge loss of forest cover in the Western Ghats mountain ranges where the virus is geographically prevalent. This increased the risk of diseases emerging in new areas.
The growing threat of ticks
The Kyasanur forest disease is a prime example of the growing threat posed by emerging tick-borne zoonoses. Experts expect them to increase worldwide and disproportionately affect poor and marginalized social groups.
Besides Kyasanur forest disease, the most common tick-borne diseases are: Lyme disease, babesiosis, ehrlichiosis, Rocky Mountain spotted fever, Crimean-Congo hemorrhagic fever, anaplasmosis, rickettsiosis, southern tick rash, tick-borne recurrent virus. fever, Powassan disease, Bourbon virus infection, and tularemia.
Read more: Why Lyme disease cases are rising in Spain, Europe and the US.
There is an urgent need to take an approach One health prevent and control these new diseases that will increasingly affect low- and middle-income populations.
The increasing impact of ticks on public health requires personal protective measures. When we are in areas where we may encounter these ectoparasites, the most effective ways to avoid their bites are to wear long pants and long-sleeved shirts, and to apply repellent to the skin and clothing. The skin should be periodically checked for attached mites, which should be removed as soon as possible.