In News:

• The Kerala health department is on alert after the death of a 47-year-old from Thrissur due to the West Nile Virus.

What’s in Today’s Article:

• West Nile Virus – About, transmission, incubation, symptoms, WNV in India, preventive measures, treatment

West Nile Virus (WNV)

• The West Nile Virus is a mosquito-borne, single-stranded RNA virus.
  • RNA virus is the virus that has single-stranded as well as double-stranded RNA as its genetic material.
  • Noticeable disease caused by RNA virus is (severe acute respiratory syndrome) SARS, influenza, common cold, Hepatitis B and C.
• It is a flavivirus related to the viruses that cause St. Louis encephalitis, Japanese encephalitis, and yellow fever.
  • The Flaviviridae are a family of positive, single-stranded, enveloped RNA viruses. Members of this family belong to a single genus, Flavivirus.
  • They are found in arthropods, (primarily ticks and mosquitoes), and can occasionally infect humans.

Transmission

• 
• Culex species of mosquitoes act as the principal vectors for transmission.
• It is transmitted by infected mosquitoes between and among humans and animals, including birds, which are the reservoir host of the virus.
  • Mosquitoes become infected when they feed on infected birds, which circulate the virus in their blood for a few days.
  • The virus eventually gets into the mosquito’s salivary glands.
  • When mosquitoes bite, the virus may be injected into humans and animals, where it can multiply and possibly cause illness.
• It can also spread through blood transfusion, from an infected mother to her child, or through exposure to the virus in laboratories.
• It is not known to spread by contact with infected humans or animals.

Incubation                                                        

• According to the US Centre for Disease Control and Prevention (CDC), the incubation period for WNV disease is typically 2 to 6 days.
  • It can range from 2 to 14 days, and can be several weeks in immunocompromised people.
• To date, no human-to-human transmission of WNV through casual contact has been documented.

Symptoms

• The disease is asymptomatic in 80% of the infected people.
• The rest develop what is called the West Nile fever or severe West Nile disease. For them, the symptoms include:
  • fever, headache, fatigue, body aches, nausea, rash, and swollen glands.
  • It usually turns fatal in persons with co-morbidities and immuno-compromised persons (such as transplant patients).
• Severe infection can lead to neuroinvasive disease such as West Nile encephalitis or meningitis or West Nile poliomyelitis or acute flaccid paralysis.
  • Neuroinvasive disease are capable of infecting the nervous system and especially the central nervous system.
• WNV-associated Guillain-Barré syndrome and radiculopathy have also been reported.
  • Guillain-Barre syndrome is a rare disorder in which immune system of one’s body attacks its own nerves.
  • Radiculopathy is a mechanical compression of a nerve root usually at the exit foramen or lateral recess.

WMV in India

• In India, antibodies against WNV were first detected in humans in Mumbai in 1952 and virus activity has since been reported in southern, central, and western India.
• WNV has been isolated in India:
  • from Culex vishnui mosquitoes in Andhra Pradesh and Tamil Nadu,
  • from Culex quinquefasciatus mosquitoes in Maharashtra, and
  • from humans in Karnataka.

Preventive measures

• Since WNV outbreaks in animals precede human cases, the establishment of an active animal health surveillance system is helpful in providing early warning.
• The peak for WNV infections generally coincides with the period when mosquito vectors are most active and the ambient temperature is sufficiently high for virus multiplication.
• Hence, health authorities globally advice for personal protective measures to reduce the risk of mosquito bites such as
  • using mosquito repellents, and
  • for public health departments to ensure larval source reduction especially at breeding and resting sites for the mosquito vectors.

Treatment

• No WNV-specific prophylaxis, treatment or vaccine is available.
• So, only supportive treatments are given to neuroinvasive WNV patients.