Beware the ticks of Kyasanur

Kyasanur forest disease, a viral infection that can be fatal, has spread beyond the forests of Shivamogga in Karnataka, where it was first discovered 60 years ago, to Kerala, Goa and Maharashtra in the past few years, and its further spread along the Western Ghats is a real possibility as encroachment of forests increases.

Published : Jun 07, 2017 12:30 IST

A magnified image of Haemaphysalis spinigera, the tick that carries the KFD virus.

A magnified image of Haemaphysalis spinigera, the tick that carries the KFD virus.

“A zoonosis is an animal infection transmissible to humans. There are more such diseases than you might expect. AIDS is one. Influenza is a whole category of others. Pondering them as a group tends to reaffirm the old Darwinian truth (the darkest of his truths, well known and persistently forgotten) that humanity is a kind of animal, inextricably connected with other animals: in origin and in descent, in sickness and in health. Pondering them individually… provides a salubrious reminder that everything, including pestilence, comes from somewhere.”

—David Quammen, Spillover: Animal Infections and the Next Human Pandemic.

SHESHAPPA NAIK, 72, a resident of Chaduva village in the Western Ghats of Karnataka, had an areca nut plantation on the fringes of a deciduous forest. He was an active farmer and would walk the two-kilometre trail that ran along the forest from his home to his plantation every day. His village consists of scattered settlements on the periphery of the forest and has 600 residents, all members of the Idiga community. On January 17, a fellow villager reported that a bonnet macaque, the pink-faced monkey, the most common primate species of south India, was found dead along this trail. Roughly a week later, Naik fell ill with a high fever and acute body ache. On January 28, he was admitted to the taluk hospital in Thirthahalli where he was diagnosed with a viral infection called Kyasanur forest disease (KFD), a zoonotic disease endemic to the region. On February 2, Naik died.

Of the 37 “human” cases that were identified as having contracted monkey fever, as KFD is popularly known, in the villages falling under the Kudumallige gram panchayat this year, Naik was one among the three fatalities. Since 1957, when KFD was first diagnosed as a distinct disease in the forests of Shivamogga (formerly Shimoga) district, it recurs annually in the same months and takes its share of human lives from communities that live along, or inside, the forests in the area.

Until a few years ago the virus was restricted to a small swathe of the Western Ghats located in Karnataka. What is scary is that it is spreading along the forests both to the south, appearing in the Wayanad region in Kerala in 2014, and to the north, where KFD’s first victim was diagnosed in eastern Goa in the same year. In 2016, the virus expanded its footprint, leaping across the State boundary to Sindhudurg district in Maharashtra.

To find the victims of KFD in Goa, one has to drive east, away from the touristy beaches to Valpoi, a town in the Western Ghats surrounded by forests that abound with cashew plantations. At the Community Health Centre (CHC)— a large modern hospital that is testimony to Goa’s relatively advanced public health care system—Ahmed (42, name changed), a cashew farmer diagnosed with KFD, lay writhing in agony on a hospital bed with a fever of 103 °Fahrenheit when this correspondent visited him on March 28. “As I do every year, I went to the cashew plantation 10 days ago. I saw the carcass of a langur but did not understand its significance. I got a high fever in a few days,” he said in Konkani. Dr Gajanan Naik, the Health Officer at the CHC who translated Ahmed’s statement, was confident that his patient would make a full recovery.

In Banda, a town in Sindhudurg district, Rajan Gawas (40), a multipurpose health worker, took this correspondent to the spot in the forest, just off the highway connecting Panjim and Mumbai, where he collected ticks—vectors that could be tested for the KFD virus—in January. “We use a Turkish towel to sweep a portion of the undergrowth and ticks cling on to the towel,” he explained. He contracted the virus during this assignment but was fortunate to have completely recovered after a painful month of recuperation. Before he entered the forest this time around, he generously lathered his exposed arms and feet with dimethyl phthalate, a tick repellent whose effects last for a couple of hours. “I don’t want to take a chance again. Makad taap [monkey fever in Marathi] almost killed me. The high fever is one thing, but the headache is something else! I became mad for a few days!” Gawas said.

According to official data, over the past 60 years, KFD has killed 512 people in Karnataka. In the initial years, a lot of deaths went unreported. Many of the deaths have been reported from villages in and around the forests of Shivamogga district, which is recognised as ground zero. The virus has been responsible for more than 50 deaths in Kerala, Goa and Maharashtra in the past few years. The disease has a fatality rate that hovers between 5 and 10 per cent, which means that there have been more than 10,000 laboratory-confirmed cases of KFD since it was first discovered. More than three times this number of people have been reported as having symptoms of KFD. People with co-morbid diseases such as diabetes are more vulnerable to death because of the virus.

According to Sandhya V.K., a microbiologist at the Virus Diagnostic Laboratory (VDL) in Shivamogga—a specialist laboratory that was set up in 1959 to carry out research on the disease—KFD is an arthropod-borne virus disease, which means that it relies on vectors such as flies, fleas, ticks, mosquitoes and lice to spread. The virus that causes KFD is a member of the genus Flavivirus of the family Flaviviridae and is transmitted to monkeys and humans mainly by infected ticks (in the nymph stage) known as Haemaphysalis spinigera . Nine other ticks in the same genus can also act as vectors. The other diseases caused by viruses in the family Flaviviridae are yellow fever, dengue, Japanese encephalitis and Zika—all of which have attracted a great deal of medical attention all over the world because of the severity of their attacks and the spread of their outbreaks.

Extensive epidemiological studies have been done on KFD over the past six decades, and the way in which it spreads is well known now. During the monsoons between June and September, when the Western Ghats receive plentiful rain, the adult ticks mate while having a blood meal on bovines and other large mammals inhabiting the forest. The female tick lays between 3,000 and 4,000 eggs at the end of the south-west monsoon and then dies. The larvae that emerge lurk in the undergrowth and on the underside of leaves. Small mammals such as shrews and squirrels that scurry around the foliage act as blood meals during this stage of the tick’s life. Usually, by the end of December, the tick has transitioned into a nymph and is dangerous to humans and monkeys. Mammals, apart from humans and monkeys, are only passive carriers of the virus as they have natural immunity. Even cattle appear immune to the KFD virus.

Monkeys are particularly affected by the KFD virus and have high viremia, that is, if an infected tick bites them, uninfected ticks that subsequently cling on to the monkey also become vectors of the deadly virus. Humans who enter the forests are particularly vulnerable as the hungry nymph is looking for the next warm mammal to feast on. Infected monkeys become extremely dehydrated and sluggish and come close to human settlements looking for water. Many of them die at this point. The nymphs that were feasting on the monkeys drop off, and it is at this point that any human in the vicinity becomes vulnerable.

The virus is passed on through both transovarian (all the larvae that are born from an infected tick will carry the KFD virus) and transstadial (uninfected ticks get it from infected animals) ways. In the forests of Shivamogga, the disease peaks in January and February every year, whereas in Goa and Sindhudurg, the highest number of victims occur towards the end of March and the first two weeks of April when they go into the forests to harvest cashew. The incubation period of the virus in humans is between two and seven days. KFD’s symptoms are quite gory, and it is worth quoting at length from a paper by the virologists Devendra T. Mourya, Pragya D. Yadav and Deepak Y. Patil that describes the symptoms in some detail: “The onset is sudden, with chills followed by severe frontal headache. Fever soon follows headache and rapidly rises to 104 °F. This raised temperature is continuous and lasts for 5-12 days, or even longer. There is severe myalgia [muscular pain due to viral infections], which is reminiscent of dengue. Body pains are of high intensity at the nape of the neck, lumbar region and calf muscles. Diarrhoea and vomiting occur by the third or fourth day of illness. Bleeding from the nose, gums and intestines begins as early as the third day, but a majority of cases run a full course without any haemorrhagic symptoms. Gastrointestinal bleeding is evidenced by haematemesis or fresh blood in the stools. Some patients have persistent cough, with blood-tinged sputum and occasionally substantial haemoptysis. Physical examinations during the first few days of illness reveal an acutely ill, febrile patient with a severe degree of prostration. There is usually conjunctival suffusion and photophobia.... Neck stiffness, mental disturbance, coarse tremors, giddiness, and abnormality of reflexes are noted.” The patients who are lucky enough to recover from this are still susceptible to getting reinfected with the disease in the next few months.

Much of what is known about KFD is from the early years after its discovery when intense curiosity about it fuelled research. These early researchers were valiant and hiked through thick forests collecting ticks and cutting up monkeys. The advances they made helped in publicising many aspects of the disease as is evident from an article on KFD published in The British Medical Journal in 1960. That fascinating story of discovery and adventure is told in the next few paragraphs. Archival material was provided by the VDL and was sourced from a brilliant research article by the science journalist Nithyanand Rao.

On the trail of the virus In early 1956, a suspiciously large number of monkey deaths were reported from the Kyasanur forest in Soraba taluk of Shivamogga with human deaths also being reported in the vicinity. Kyasanur, now denuded of its thick forest cover, lies between the towns of Sagara and Soraba. The humans who were infected suffered from high fever, severe headache, myalgia and nausea. In many case haemorrhagic symptoms such as conjunctivitis or blood in the stool were also present. A change in the mental state of the person was also noticed. The problem recurred in 1957, prompting the Medical Officer of Health in Sagara to seek the help of the Director of Public Health in Bangalore (now Bengaluru) on March 12, 1957.

On March 23, the Virus Research Centre (VRC), now the National Institute of Virology, in Pune (then Poona) was apprised of the situation. On March 27, the first strains of the virus, later named KFD, were isolated, and a special ward for KFD patients was opened at the hospital in Sagara. The first two patients were VRC tick collectors. Over the next few years, bacteriologists, virologists, serologists and entomologists descended on the forest and got their hands dirty eviscerating bonnet monkeys and common langurs in the area. Samples were regularly sent on ice to the VRC. Before this, there was only one disease that was known to affect both monkeys and humans and that was yellow fever, but it was clear that this was something different.

The Rockefeller Foundation was interested in discovering and cataloguing arthropod-transmitted viruses and had set up the VRC in 1952. The work of scientists from the foundation was particularly valuable. Specialists from the United States Department of Agriculture were also involved in this research. The contributions of P.K. Rajagopalan, who was 27 when he first came to Shivamogga, and Jorge Boshell-Manrique, a well-travelled Columbian physician and epidemiologist whom Rajagopalan describes as his teacher, helped tremendously during the time. Rajagopalan, who lived at the field research station of KFD in Sagara for 13 years, even contracted KFD.

In 1959, a system of rewarding those who brought information about monkey deaths was begun in order to track KFD cases quickly. The renowned ornithologist Salim Ali was roped in as scientists pondered over how this mysterious virus that had sprung up a few years ago could have travelled to the region. Could it be spread by ticks clinging on to birds migrating from Russia? Along with birds, small mammals were also studied. The search then extended to sheep and goats that had been imported to Shivamogga from the maidan (plain) areas. A research team also went down south to Tibetan refugees inhabiting Hunsur, Kakanakote and the Bandipur area to see whether they were the carriers. This early spurt in research came to an end for two reasons: first, the Rockefeller Foundation stopped funding in the 1960s, and secondly, several workers at the National Institute of Virology became infected with KFD. Thus, this important saga of discovery came to an abrupt end. Work at the National Institute of Virology was resumed only after the establishment of a laboratory in 2005 that was equipped to handle the virus.

Vaccine Back in Chaduva, Dr S.K. Kiran, Taluk Health Officer of Thirthahalli, explained why it was hard to keep ahead of the seasonal monkey fever outbreaks. “The disease does not recur in the same villages every year,” he said. Chaduva village was not affected by KFD last year. This principle also holds true for newer areas where KFD has occurred such as Sindhudurg. Last year, most of the cases were discovered in Dodamarg, but this year there have been no cases in that town and all the cases are in Banda. So how does one stay ahead of the disease? “Real-time reporting of the death of a monkey is most important. A monkey death sounds the alarm call for us,” Dr Kiran said.

As soon as a monkey death is reported, officials from the Health, Forest and Animal Husbandry Departments rush to the “hot spot” where an area of 50 metres is “cordoned off” using a white powder that is a mixture of the insecticide malathion and ash. The monkey corpse is sent for an autopsy. Ticks are collected and sent for testing. The carcass is subsequently burnt. From 1990, when a vaccine for KFD began to be used, villagers living within 5 km radius of a monkey death are vaccinated, but the virus has an immunity rate of only 62.4 to 82.9 per cent. It also needs two doses separated by a month initially followed by a booster dose. In Goa, for instance, out of 76 positive cases, 11 cases had already received one dose of the KFD vaccine in 2017.

It is also not given to individuals who are more than 65 years old, which meant that Naik was not vaccinated. There are also other issues with the vaccination. Considering the low strike rate of the disease and its erratic spread, there is a casualness about it among villagers. The formalin-based injection also burns for a few seconds, which leads to a reluctance to get vaccinated. Thus, there can only be prevention. Villagers are advised not to collect minor forest produce during the period, and if they have to go to the forest, they are advised to take a hot water bath as soon as they return. Everyone is susceptible, and treatment is symptomatic. Once the virus is detected, the vaccine is useless, and the patient can only be treated for the symptoms of fever and dehydration.

The area of KFD has been spreading since it was first discovered, though it is clear that its range is across the Western Ghats. In a spatial depiction of this spread prepared by Dr Kiran, one can see that in 1957 it was restricted to Kyasanur. Until 1972, KFD was restricted to the three taluks of Sagara, Soraba and Shikaripura. By 1970, it had spread to all the districts in Karnataka adjoining the Ghats. In the 1980s, cases were reported from the adjoining districts of Chikkamagaluru and Dakshina Kannada. In 1982, a KFD epidemic swept through four villages in Belthangady taluk of Dakshina Kannada, some 200 km away from Kyasanur. In the next decade, it spread to Uttara Kannada and Udupi. Cases were also reported from the district of Belagavi. In 2012, cases were reported from Chamarajanagar and Mysuru in southern Karnataka, and a few cases were also discovered in the Nilgiris district in Tamil Nadu. In 2013, animal handlers at Bandipur Tiger Reserve got the disease while handling sick monkeys. Over the past few years, KFD has transcended State borders.

How is KFD spreading?

An interesting question is how the KFD virus is spreading. Are the blood hosts such as monkeys travelling up and down the Western Ghats and carrying the virus to newer areas or has the virus always been there and is being discovered only now?

Dr Utkarsh Betodkar, State epidemiologist of Goa, said: “The disease was always there. Possibly, there were no outbreaks because of which it was not diagnosed but more people are going into the forest now.”

G. Arunkumar, professor and head of the Department of Virus Research at Manipal University, said: “KFD was never looked for beyond Karnataka. When in 2012, KFD was detected in Chamarajanagar, Karnataka, we at the Manipal Centre for Virus Research started looking for KFD in Wayanad district of Kerala adjoining Chamarajanagar. We did find one case each in 2013 and 2014. In 2015, we detected more than 100 cases in Wayanad through the acute febrile illness (AFI) surveillance at Sultan Bathery hospital. The same year while investigating an unusual acute diarrhoeal disease in North Goa (Valpoi), we quickly realised that we were dealing with KFD. We initiated our AFI surveillance in Goa in November 2016 and detected more cases in Valpoi and through our sentinel centre at Mapusa hospital in North Goa, we detected KFD cases in Sindhudurg. KFD cases have been detected in Nilambur forest area [in Kerala] too. So it is very clear that KFD is distributed along the Western Ghats region. KFD must have existed unrecognised for several years. Now everyone is realising that KFD is there.”

Dr Yogesh Salhe, District Health Officer of Sindhudurg, said: “People are going into the jungle for various reasons. The virus was not available but it came through the migration of wild animals. The virgin area is having more number of deaths. The old area does not have so many deaths. They develop resistance.”

Researchers have established a clear link between increased encroachment of forests and the incidence of KFD. Nithyanand Rao, in his article, writes that the KFD outbreak in Belthangady taluk was preceded by extensive deforestation as land was cleared to start export-oriented cashew plantations. Similarly, Dr Kiran said that a connection could be made between an increase in areca nut prices and the increase in incidents of KFD.

According to Prof. Anindya Sinha, a primatologist at the National Institute of Advanced Studies in Bengaluru, there is a small possibility that troops of bonnet monkeys and common langurs that usually have ranges of only a few kilometres radius could be interacting with neighbouring troops and spreading the ticks.

This article began with an epigraph from David Quammen’s excellent work on zoonotic diseases. Some of the diseases that he lists, each more exotic than the other, include monkeypox, bovine tuberculosis, Lyme disease, West Nile fever, Marburg virus disease, rabies, hantavirus pulmonary syndrome, anthrax, Lassa fever, Rift Valley fever, ocular larva migrans, scrub typhus and Bolivian hemorrhagic fever. He writes: “We should appreciate that these recent outbreaks of new zoonotic diseases, as well as the recurrence and spread of old ones, are part of a larger pattern, and that humanity is responsible for generating that pattern. We should recognise that they reflect things that we’re doing, not just things that are happening to us. We should understand that, although some of the human-caused factors may seem virtually inexorable, others are within our control.”

A study done in the Western Ghats showed that 25.6 per cent of its forest cover was lost between 1973 and 1995. Deforestation and encroachment have continued over the past two decades. It is almost as if the forest is fighting back with diseases such as KFD.

The death toll due to KFD stood at 14 until the end of April in Karnataka (3), Goa (1) and Maharashtra (10). The numbers may seem small, but the future implications of monkey fever are large as communities increase their encroachments into the forests of the Western Ghats. And the lessons for public health are many as this zoonotic disease can only be contained. The virus that causes KFD can never be destroyed unless all the forests of the Western Ghats, along with all the animals, disappear.


Quammen, David (2016): Spillover: Animal Infections and the Next Human Pandemic .

Mourya, Devendra T., Pragya D. Yadav and Deepak Y. Patil (2014): “Highly Infectious tick-borne viral diseases: Kyasanur Forest Disease and Crimean-Congo haemorrhagic fever in India”, WHO South-East Asia Journal of Public Health , Vol. 3, Issue. 1, January-March.

Rao, Nithyanand (2016): “The Seven-Decade Transnational Hunt for the Origins of a Strange Indian Disease”, The Wire , November 19.

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