Explained | What is the West Nile virus, causing the latest health scare in New York City?

The story so far: The West Nile virus, which causes potentially dangerous diseases of the central nervous system in human beings, has been found in two people in New York City and detected in a record number of mosquitoes across all five boroughs, the city’s health department announced on August 16. The news comes at a time when the city is already battling a monkeypox outbreak alongside the Covid-19 pandemic. Across the U.S., 54 cases of West Nile virus infection and four deaths have been reported so far this year.

The infection has also soared in Italy, per EuroNews reports. Europe has reported over 100 cases of the virus so far this year, with Italy having the highest number among all the countries.

The NYC outbreak

According to the New York City health department, 1,068 positive mosquito pools have been identified across the five boroughs so far – the highest number ever recorded. The number of positive pools detected at the same time last year was 779. Each day, an average of 77 mosquitoes were caught in the trap, compared to last year’s 75.

The West Nile virus was first detected in New York City more than 20 years ago. In the last decade, an average of 16 persons per year are diagnosed with the West Nile neuroinvasive disease – a severe illness that targets the brain and the spinal cord, causing muscle weakness and altered mental status.

The virus is now considered endemic in New York State and shows up in at least parts of it every year in the summer months.

Infection by the West Nile virus

Humans can contract the West Nile virus through an infected mosquito bite. According to the U.K. National Health Service, the virus is not contagious. However, Johns Hopkins Medicine says that there is a rare possibility of human-to-human transmission through blood transfusion, organ transplant, or through placenta to the foetus.

It is usually the Culex species of mosquitoes that carry the West Nile virus. It has also been detected in birds. The West Nile virus can make birds like crows and jays sick and eventually kill them. There is no evidence of humans catching the virus directly from birds, the U.S. Centres for Disease Control and Prevention (CDC) said.

What are the symptoms of the viral infection?

Most cases of the West Nile virus do not present any symptoms. According to CDC, around one in five people infected with the virus show flu-like symptoms like fever, body ache, vomiting, diarrhoea, and rashes. About one in 150 people are severely affected by the virus and develop serious illnesses related to the central nervous system, like encephalitis and meningitis. Other symptoms of severe illness can include high fever, headache, neck stiffness, disorientation, coma, tremors, convulsions, muscle weakness, vision loss, numbness and paralysis.

Although there is no specific age at which the virus can affect humans, people over 50 years of age are at a higher risk of a more severe form of the infection.

What treatment is available?

Currently, there are no vaccines available to treat infection by the West Nile virus. In most cases, the infection heals itself. Medication may be needed to treat the flu-like symptoms caused by the virus. Most health departments recommend covering the body and using mosquito repellents to prevent West Nile virus infections.

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