Scientists have traced the source of a re-emerging disease, Kyasanur Forest Disease (KFD) or “monkey fever”, to cashew plantations in Goa. Some plantation workers tested positive after returning home to Belgaum while others tested positive in Goa. Cashew nut workers face occupational exposure to KFD, the scientists say in a study in the International Journal of Infectious Diseases.
Monkey fever is so named because it affects black-faced langurs and red-faced bonnet monkeys. The disease is spread by tick bites. Symptoms include high fever with headache, followed by haemorrhagic symptoms such as bleeding from the nose, throat and gums as well as gastrointestinal bleeding, besides muscle stiffness, tremors, absent reflexes and mental disturbances.
In some cases, it can be fatal; in others, an affected person may recover in two weeks. The convalescence period, however, is typically very long, lasting for several months.
The vector ticks are known to thrive in the Western Ghats. First recognised in 1956 in Shimoga, Karnataka, the disease has been reported in recent years from Bandipur National Park of Karnataka (2012), Mudumalai Tiger Reserve of Tamil Nadu and Wayanad in Kerala (2012-13), Malappuram (2014), Pali village of Sattari in Goa (2015) and Sindhudurg in Maharashtra (2016).
In 2015, when the disease was first detected in Goa, it was limited to Sattari taluka. In the following two years, cases have been detected in Dharbandora and Pernem. As many as 82 cases have been registered between January and June; monkeys of one species have been seen dying of the infection.
Along with the Belgaum Disease Surveillance Unit, researchers studied the occupational exposure of cashew nut workers in Goa. During March-June 2016, blood samples of 76 suspected cases were tested in Belgaum, and the fever was confirmed in 13. Samples were also tested of six cases referred from the Disease Investigation Unit and Directorate of Health Services, Goa, and three were found positive.
“Our study showed that the persons fell ill after cashew nut harvesting in Goa on return to their residences in Belgaum within the incubation period of 6-7 days,” Dr D T Mourya, director of National Institute of Virology, told The Indian Express. “This corroborates the assumption that these cases had acquired infection at Goa, as it takes a minimum of four days’ incubation period for the appearance of antibodies. The only source of infection would be through monkeys and ticks during cashew nut harvesting in Sattari.”
Sattari is known to have KFD activity affecting humans and monkeys since 2015. Workers from Belgaum visit Sattari every year during February-May for cashew collection.
“Monkeys pick up KFD virus infections from infected ticks. After the death of a monkey, infected ticks drop from the body of the animal and this generates hot spots of infectious ticks,” Mourya said.
Despite monkeys dying in large numbers, the virus was being passed on from one generation of ticks to the next as they had found smaller mammal hosts such as rodents. The Western Ghats are full of wildlife sanctuaries and there is a high risk of spread of KFD among people in and around forest areas.
NIV has developed an inactivated chick embryo tissue culture vaccine against KFD. “Diagnostic tests provided by NIV have also helped identify KFD across five states. These diagnostic tests have now been transferred to Zydus Cadila and will be available in the market soon,” Mourya said.