Russia's Federal Service for Supervision in the field of Consumer Rights Protection and Human Well-Being or Rospotrebnadzor, on August 30, 2021, alerted its public of a possible rise in West Nile Virus (WNV) infections this autumn. It cited heavy precipitation as favourable circumstances for mosquitoes that carry the virus.

"Given the prevailing favourable climatic conditions in the current year - the abundance of precipitation predicted in most of Russia, including the central part, warm and prolonged autumn, in the autumn period there may be a high number of vectors and the risk of transmission of the pathogen remains," the federal agency's statement read.

More than 80% of West Nile fever is recorded in the country's southern district. The government agency further confirmed that the situation was under control. But what is this virus and how has it affected people in the past? Let's find out.

What is West Nile Virus?

According to the World Health Organization, WNV is a member of the flavivirus genus and belongs to the Japanese encephalitis antigenic complex of the family Flaviviridae. It is spread by mosquitoes of the Culex species. While the virus can cause a fatal neurological disease in humans, about 80% of those infected do not show any symptoms, says the WHO.

It is the leading cause of mosquito-borne diseases in the continental United States and is commonly spread by the bite of an infected mosquito, according to the Centers for Disease Control and Prevention (CDC).

WNV originated in the West Nile district of Uganda in 1937. Later it was identified in crows in the Nile Delta region in 1953. In 1999, WNV caused an outbreak in the United States. Since then, WNV has become endemic, with sporadic epizootics. Between 1999 and 2019, a total of 51,702 cases have been reported to the CDC — including 24,227 (48.8%) cases of West Nile Neuroinvasive disease, the more severe disease process of encephalitis or meningitis, and 2,376 (4.6%) deaths, shows a report published in the PLOS Neglected Tropical Diseases Journal by researchers from Texas.

In almost eight months of 2021 (till August 24, 2021), a total of 102 cases of WNV had been reported to the CDC. Of these, 64 (63%) were classified as neuroinvasive disease and 38 (37%) were classified as non-neuroinvasive disease.

As far as the history of West Nile Fever cases in India is concerned, serologically-confirmed cases of WNV infections were reported from Vellore and Kolar districts during 1977, 1978 and 1981, according to National Health Portal of India. The presence of WNV was also documented in the north-eastern region of India during the year 2006 from four districts of Assam, says NHPI. In 2019, a seven-year-old boy from Kerala's Malappuram district succumbed due to the virus, according to a Down To Earth report.

To know more about the prevalence of the virus, FactChecker spoke to Kerala's former state epidemiologist Dr A Sukumaran. "Malappuram and Kozhikode had reported cases two years back but it has been very sporadic," said Sukumaran. "There were two confirmed cases in Malappuram and three in Kozhikode and a few suspected cases. One child died but we could confirm it only after his death," he added.

The epidemiologist said the virus is not very prevalent but the surveillance is not very strong either. "There could be cases but we are not picking it. Focussed testing is required," he said.

When asked about the difference between WNV, malaria and dengue, Sukumaran said while dengue and malaria are spread by the Aedes and female Anopheles mosquitoes respectively, WNV is spread by the Culex mosquito. The Culex mosquito carries the infection after biting infected birds and it is generally active during summer. "All three are mosquito-borne infections but West Nile virus is less serious than dengue and malaria. However, a severe form of the disease affects the central nervous system. In that case, the fatality is high," Sukumaran told FactChecker.

West Nile Virus: Symptoms and Risk

While most cases of WNV are asymptomatic, about 20% of people infected with the virus develop WNV fever or WNV severe disease. About 1 in 5 who develop febrile illness (fever) will show symptoms such as fever, headache, tiredness, body ache, nausea, vomiting, occasionally with a skin rash (on the trunk of the body) and swollen lymph glands. Most people with WNV febrile fever recover completely, although weakness could last for weeks or months, according to the CDC.

But the WNV infection can also lead to a severe neuroinvasive disease, such as West Nile encephalitis (inflammation of the brain) or meningitis (inflammation of the membranes that surround the brain and spinal cord) with symptoms including headache, high fever, neck stiffness, stupor, disorientation, coma, tremors, convulsions, muscle weakness, and paralysis. According to the WHO, about 1 in 150 persons infected with WNV develop a more severe form of the disease.

While serious illness can occur in people of any age, people over 50 years and some immunocompromised persons for instance, transplant patients, are at a higher risk of catching the virus.

West Nile Virus: Diagnosis & Treatment

Reverse transcription polymerase chain reaction (RT-PCR) analysis and virus isolation by cell culture are some of the assessment methods used in diagnosing WNV, says the WHO. Over-the-counter pain relievers can be used to reduce fever and relieve mild symptoms.

In severe cases, such as neuroinvasive disease, patients often need to be admitted to hospital to receive supportive treatment, such as intravenous fluids, respiratory support, pain medication and prevention of secondary infections.

West Nile Virus: Prevention

While there is no vaccine available for humans as of now, there are two intramuscular vaccines available for horses, according to the Rutgers Equine Science Center. The most common vaccine is the West Nile-INNOVATORTM vaccine which requires two injections, spaced three to six weeks apart. Another vaccine administered to horses is the RECOMBITEK Equine West Nile Virus Vaccine.

For humans, an effective way of prevention from WNV is through integrated mosquito surveillance and control programmes in areas where the virus occurs, according to the WHO. This could help identify local mosquito species that play a role in WNV transmission including those that might serve as a "bridge" from birds to human beings. Also, health agencies suggest that use of mosquito nets, insect repellents, wearing light coloured clothing (long-sleeved shirts and trousers) and avoiding outdoor activity at peak biting times can prove helpful.

While handling sick animals or their tissues, gloves and protective clothing should be worn to reduce the risk of animal-to-human transmission. Lastly, blood and organ donation restrictions and laboratory testing should be considered during an outbreak to reduce risk of transmission through blood transfusion and organ transplant.