State recorded outbreak in the past & there is no reason to panic, says Health Minister Veena George
The West Nile virus (WNV), a mosquito-borne arbovirus of the family Flaviviridae, belonging to the Japanese encephalitis antigenic complex, has become a cause of concern across Kerala.
The southern state reported 12 confirmed and four suspected cases in the last week, triggering widespread panic. The state is now under high alert amid reports that WNV is spreading around the world and causing human infections in every continent except Antarctica.
The single-stranded RNA virus has been detected in Malappuram, Kozhikode and Thrissur districts, and the state health department suspects that the recent death of a resident of Palakkad district is also due to the virus.
Health minister Veena George told Down to Earth that the deceased person had symptoms of the disease but confirmation could be done only after the test result is published by the National Institute of Virology in Pune.
The virus is transmitted from person to person through the biting of infected mosquitoes, which acquire the virus from infected birds (mostly migratory).
Thrissur district has reported three cases, while Kozhikode has seven confirmed and two suspected cases. One of these two suspected patients has been on a ventilator at the Baby Memorial Hospital in Kozhikode City. In Malappuram, two confirmed cases have been reported so far, while one other remains unconfirmed. The deceased person has presently been classified as unconfirmed.
‘State prepared for crisis’
The state has been on alert since the last two days, George said, and all preparations are being made to prevent its spread to other regions and ensure quick treatment for those infected.
There is no need for people to panic, she added, because the state has been experiencing the presence of the virus since 2011 and is completely prepared to cope with any critical situation.
According to her, those with signs of fever or other symptoms of WNV infection should seek immediate treatment at a hospital.
A state-level mechanism is already in place to advise doctors, nurses and paramedical staff on how to treat patients with the disease and administer medicines, the minister noted.
The state government has ordered local bodies and district administrations to take mosquito control measures to destroy the breeding grounds of Culex mosquito, the primary vector.
To reduce the likelihood of receiving a mosquito bite, health authorities all over the world advise using personal preventive measures like insect repellents.
Public health authorities are also responsible for ensuring that larval sources are reduced, particularly at breeding and resting locations for mosquito vectors. In California, the Minister of Health has recommended that individuals wear clothing that completely covers their bodies, use nets and repellants and maintain a clean environment in their homes.
The outbreak of the virus occurs in animals before humans, said Aneesh. So, establishing an active animal health surveillance system to detect new WNV cases in birds and animals is crucial, highlighted TS Aneesh, a public health expert and the nodal officer for the Kerala Disaster Management Authority.
Transmission & pathogenesis
WNV has the potential to cause neurological damage and death in individuals, said Aneesh.
A significant majority of those who are afflicted will not exhibit any symptoms, he said. Depending on the circumstances, some people may experience mild symptoms like fever, headache, body ache or sore throat, the expert noted, adding:
In some instances, however, the infection can be fatal due to severe complications such as encephalitis (inflammation of the brain) and meningitis, both of which have the potential to be lethal.
The virus spreads to humans through the bites of Culex species of mosquitoes carrying the disease. The incubation period of the virus is between three and fourteen days, according to Aneesh. The disease also spreads through mice and other animals and birds infected with the virus.
A blood test is done to diagnose the infection. No vaccination or prevention method specific to WNV is available yet, and the only treatments administered to neuroinvasive WNV sufferers are supportive remedies.
“It’s similar to dengue and there are no current hotspots,” said Kozhikode District Collector Snehil Kumar Singh.
The virus enters the bloodstream of the mosquito when it bites an infected animal or bird and circulates through its bloodstream of mosquitoes for a few days till it reaches its salivary glands.
The vector then passes HNV to people it bites. The virus multiplies in the human body and causes illness in some cases, according to V Ramankutty, a public health expert based in Thrissur. He added:
WNV can also be transmitted through blood transfusions, transmission from an infected mother to her child as well as exposure to the virus in laboratories.
It is not known to spread through interaction with animals or humans infected with the disease. According to the Centers for Disease Control and Prevention (CDC) in the United States, the disease also does not spread “through eating infected animals or birds”.
The recovery process of a severe infection can take a few weeks to many months.
The virus is typically lethal in those who have comorbidities as well as immunocompromised individuals (such as transplant patients), said Aneesh. The mortality rate of the disease is quite low, compared to that of Japanese encephalitis, which exhibits comparable symptoms.
In most countries, the peak of WNV infections correlates with the time of year when mosquito vectors are at their most active and the temperature of the surrounding environment is high enough for the virus to multiply.
India’s first case was in Mumbai
In 1937, the virus was initially detected in a female inhabitant of the West Nile province of Uganda. Crows and other Columbiformes like doves and pigeons were among the birds found to have the virus in the Nile delta region in 1953.
Until 1997, WNV was not recognised as a pathogen that could cause bird mortality. However, after that year, a more virulent strain of the virus was responsible for the deaths of many bird species in Israel, exhibiting symptoms of encephalitis and paralysis.
The WNV strain, believed to be the same strain circulating in Israel and Tunisia, made its way to New York in 1999 and caused a widespread outbreak across the United States and the Americas, ranging from Canada to Venezuela.
WNV outbreak areas are located along key bird migration routes. As of now, the virus is most frequently discovered in West Asia, Africa, Europe and the Middle East, as well as in North America.
In India, the first case of WNV infection in a person was reported in Mumbai in 1952. Since then, virus activity has been documented across India’s southern, central and western regions.
WNV has been isolated in India from Culex vishnu mosquitoes in Andhra Pradesh and Tamil Nadu, Culex quinquefasciatus mosquitoes in Maharashtra and humans in Karnataka.
In 2013, the whole genome sequence of WNV was recovered from human samples collected during an outbreak of severe encephalitis in Kerala between May and June of 2011.
In 2022, a 47-year-old man from Thrissur district was the first to die of the disease in the country.
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