West Nile Virus | 01 Jun 2022

Why in News?

Recently, a 47-year-old man in Thrissur, Kerala died due to West Nile Virus (WNV). This has caused the Kerala health department to be on alert.

• Malappuram’s 6-year-old boy also died of the same infection, earlier in 2019.
• WNV was first reported in the state of Alappuzha in 2006. Later in 2011, it was also reported in Ernakulam, Kerala.

What is WNV?

• About:
  • The West Nile Virus is a flavivirus related to the viruses that are also responsible for causing St. Louis encephalitis, Japanese encephalitis, and yellow fever.
  • It is a mosquito-borne, single-stranded RNA virus.
• Global Prevalence:
  • Along all major bird migratory routes, WNV outbreak sites are found.
  • Africa, Europe, the Middle East, North America, and West Asia are the regions where the virus is commonly found.
  • Usually, WNV infections peak during the period when mosquito vectors are most active and the ambient temperature is high enough for virus multiplication for most of the countries.
• Prevalence in India:
  • In Mumbai in the year 1952, the antibodies against WNV were first detected in humans.
  • Since then, the virus activity has been reported in southern, central, and western India.
  • In Andhra Pradesh and Tamil Nadu, WNV was isolated from Culex vishnui mosquitoes.
  • In Maharashtra, it was isolated from Culex quinquefasciatus mosquitoes.
  • In Karnataka, it has been isolated from humans.
  • Further, WNV neutralizing antibodies were found to be present in human serum collected from Tamil Nadu, Karnataka, Andhra Pradesh, Maharashtra, Gujarat, Madhya Pradesh, Odisha, Rajasthan and Assam.
  • In 1977, 1978 and 1981, serologically confirmed cases of WNV infections were reported in Vellore and Kolar districts, and in West Bengal in 2017.
  • During an acute encephalitis outbreak in Kerala, the complete genome sequence of WNV was isolated in 2013.
  • The association of WNV with eye infection in Tamil Nadu had been clearly established during an epidemic of mysterious fever in the first half of 2010.
• Origin:
  • WNV was first isolated in a woman in the West Nile district of Uganda in 1937.
  • It was identified in birds in the Nile delta region in 1953. Before 1997, WNV was not considered pathogenic for birds.
  • Human infections attributable to WNV have been reported in many countries for over 50 years.

• Transmission Cycle:
  • Principal vector for transmission is the culex species of mosquitoes.
  • Birds act as the reservoir host of the virus.
  • Infected mosquitoes transmit WNV between and among humans and animals, including birds.
  • When a mosquito feeds on infected birds, they become infected.
  • The virus circulates in the blood of those infected mosquitoes for a few days, eventually getting into the mosquito’s salivary glands.
  • The virus may get injected into humans and animals during later blood meals (when mosquito bites). Therein, WNV can multiply and possibly cause illness.
  • WNV can also get transmitted from an infected mother to her child through blood transfusion or via exposure to the virus in laboratories.
  • No instance of transmission by contact with infected humans or animals has been reported.
  • It does not spread “through eating infected animals, including birds.
  • Generally, the incubation period for WNV disease is 2-6 days. However, this may range from 2-14 days, and can also be several weeks in people whose immunity is compromised.
  • According to the World Health Organization (WHO), no human-to-human transmission of WNV through casual contact has been reported till date.
• Symptoms:
  • In 80% of the infected people, the disease is asymptomatic.
  • In the rest of the 20% cases, West Nile fever or severe WNV is observed with symptoms such as fever, headache, fatigue, body aches, nausea, rash, and swollen glands.
  • Severe infection may even cause neurological diseases like West Nile encephalitis or meningitis or West Nile poliomyelitis or acute flaccid paralysis.
  • Also, there are reports of WNV-associated Guillain-Barré syndrome and radiculopathy.
  • Around 1 in 150 individuals with WNS is likely to develop a more severe form of disease.
  • It may take several weeks or months to recover from severe illness.
  • Nervous system damage can last forever.
  • In persons with co-morbidities and immuno-compromised persons (such as transplant patients), the disease may turn out to be fatal.
• Measures of Prevention:
  • The establishment of an active animal health surveillance system to detect new cases in birds and horses should be essentially established.
  • As WNV outbreaks in animals precede human cases, it is necessary to provide early warning for veterinary and human public health authorities.
  • The European Centre for Disease Control and Prevention (ECDC) has suggested that 28-day blood donor deferral or nucleic acid testing of prospective donors who have visited or lived in an affected area should be implemented by the European Union (EU).
  • Besides, testing for WNV infection must be done for the donors of organs, tissues and cells, who are living in or returning from an affected area.
• Treatment:
  • As of now, no treatment/vaccine for WNV is available.
  • Only supportive treatments can be provided to neuroinvasive WNV patients.

Source: IE