Field investigators of the Virus Research Centre(VRC) in Pune came to Shimoga district in Karnataka in 1957 to follow up on the mysterious death of tens of monkeys. The investigation would begin a decades spanning search for the origins of a baffling disease that would go on to afflict humans.

Even as the researchers were looking into the deaths of the apes, reports came that people in the villages around the forest were taking ill with strange symptoms- including high fevers that last for around two weeks, headache, body pain, diarrhea and sometimes even passing stool with blood. Only those who had gone to the forest and “smelt” or “seen” the dead monkeys fell sick, the villagers noted.

The only disease that the researchers knew could kill both monkeys and humans was the dreaded yellow fever. And it was largely absent in India.

Mystery deepens

When the researchers started collecting mosquitoes from the forests of Shimoga, they found that just a single mosquito attacked a human during three hours. In other words, not many mosquitoes bit humans during daytime when humans went to the forest. And yellow fever was inflicted by mosquito bites.

Another bafflement was that no monkeys or humans outside Shimoga seemed to be afflicted. Surely, mosquitoes could fly for miles to other districts?

Though the test results conducted at the lab in Pune showed that there was an arthropod-borne virus at play, belonging to the family flaviviridae- the same one to which yellow fever, dengue and Zika viruses belong, no virus was found in the mosquitoes collected. Analysis at a New York lab showed that the virus wasn’t yellow fever. It turned out that it was related to a tick-borne virus prevalent in Russia, the Russian spring-Summer encephalitis.

The researchers, noticing the large number of ticks on the monkey carcasses began collecting ticks. On the third day of that endeavor, two of the team members fell sick. Two weeks later, the same fate befell another. The virus was found in all of their blood samples.

Harry Hoogstraal, the famous American entomologist called it “possibly the most dramatic epidemiological detective story of our time.”

Kyasanur Forest Disease

The disease, dubbed the Kyasanur forest disease(KFD) remained confined to just five Karnataka districts for five decades. It had claimed the lives of more than 500 people over a span of 6 decades.

The first human case outside the region was reported in 2006, in the Gulbarga district bordering Maharashtra. Six people came down with the disease in 2012- they handled monkey carcasses in the Bandipur National Park that bordered Tamil Nadu and Kerala. The next year, monkeys in the neighboring Tamil village of Nilgiri were found dead of the virus.

That same year, the first human infection of the disease was reported from Wayanad in Kerala. Monkey deaths and human infections continued in the following years in many places including Kerala and Goa. In Goa, of the 50 or so people infected, five died.

All the places where the disease sprung up lied along the Western Ghats.

Theories abound

There were theories.

For instance, migratory birds might carry ticks and viruses. But, if that’s the case, why would they drop the ticks and viruses only in Shimoga? And if the virus was indigenous, how come the sudden outbreak?

Then, there was also the possibility that the virus had arrived from Russia.

But long research revealed that no birds carried any foreign ticks or viruses. In fact, the only birds capable of distributing ticks, it was found, was ground-foraging ones like the jungle fowl, that too just locally.

In other words, the virus ought to be indigenous.

With this information, the researchers began collecting ticks again. Analysis at the VRC lab in Pune showed that the ticks indeed carried the KFD virus.

And from the thousands of tick pools that were collected, a pattern began to emerge. The key, it was found was the Haemaphysalis spinigera- a tick which infested and bit human beings. The study of its evolution from larvae to adult showed that the maturing period coincided with the season when monkeys and humans get infected.

But the infected ticks were found in isolated foci- pointing to the possibility of some animal which coulee be circulating the virus in its blood on which the ticks fed.

Monkeys, being the obvious suspects were closely observed.

Over the next seven years, the researchers looked into more than a thousand monkey deaths and autopsied about 400.

But it was found that multiple animals- including the livestock held by humans carried around the ticks.

Still a mind-bender

Many aspects of the disease still puzzle researchers. Like its biphasic nature.

Some of the infected people recover after two weeks. In some, the symptoms may be absent for about a week before they relapse. Most of the patients do recover. But they remain weak for months on end.

Now that KFD sprouts up in places outside of Karnataka, a challenge that researchers face is identifying the hosts(for the ticks) in such places. Detailed field investigations are called for.

Meanwhile, people living in areas with the potential of infection are keeping their fingers crossed.

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