The Kerala alert: drawing attention to the little-known West Nile Virus

There needs to be greater surveillance across India for the West Nile Virus

Updated - March 23, 2019 08:34 am IST

Published - March 23, 2019 12:02 am IST

The death of a child in Kerala’s Malappuram district has drawn attention to the epidemiology of the little-known West Nile Virus in India. Though awareness is low, the virus is endemic to several States. The first documented WNV case in Kerala was in Alappuzha in 2011, with the numbers then growing. However, official records do not reflect this, given the difficulty of diagnosing WNV in its acute phase. This microbe is serologically similar to the Japanese Encephalitis virus, which means a go-to test, ELISA, often fails to differentiate JE antibodies from WNV antibodies. More tests are typically needed to confirm WNV, and while the results appear in journals, they don’t always make it to State surveillance systems. This is why, though a 2014 Journal of Clinical Virology paper identified the 2011 Alappuzha outbreak as WNV, with around six deaths, Kerala’s health department is calling the Malappuram death the State’s first. The confirmation triggered an alert, but it doesn’t mean Kerala did not have WNV deaths before.

Nevertheless, the alert is a welcome move. It means that State health authorities will look harder for the disease. Historically, wherever Indian researchers have looked for the WNV, they have found it. The first sign of its presence came from positive antibody tests among residents of Bombay in 1952. Thereafter, it began showing up in encephalitis patients in many of the places it was tested for, including Maharashtra, Assam and Madhya Pradesh. In Malappuram too, the rapid diagnosis was driven by heightened surveillance in Kerala following the 2018 Nipah outbreak. Patient samples were sent to the Manipal Centre for Virus Research, which deployed the Plaque Reduction Neutralisation Test, more specific than ELISA. If more States used such diagnostics, it would help determine just how widespread WNV is in India. There is a good chance the virus is a significant cause of Acute Encephalitis Syndrome, the infamous basket of illnesses with no known aetiology that affect over 10,000 Indians each year. Still, WNV rarely kills. In less than 1% of infections, the virus travels to the brain, triggering potentially fatal encephalitis. Otherwise, it merely causes a mild flu-like illness. This could change. Viruses are known to adapt for both greater virulence and more efficient transmission. Urbanisation and land-use changes are bringing the virus’s zoonotic hosts, such as birds, in more frequent contact with humans. Given increased mobility, viruses can hitch a ride to new regions via infected humans and vectors. All this makes the WNV a formidable foe. India’s best defence is better surveillance, which will help doctors reach patients early to prevent complications. Kerala could not prevent the death in Malappuram, but other States should adopt its model of heightened surveillance.

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