Source: LiveMint

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Context

• The Kerala government has reported West Nile fever cases in several districts.
• The health department ordered all districts to be vigilant and issued directives to take mosquito control measures by stepping up pre-monsoon cleaning drives and surveillance activities.

Details

• West Nile fever (WNF) is a viral infection caused by the West Nile virus (WNV), primarily transmitted to humans through the bite of infected mosquitoes.
• WNF occurs primarily in regions where the virus is endemic, with periodic outbreaks reported in various parts of the world, including Africa, Europe, the Middle East, North America, and Asia.
• Mosquito species of the genus Culex are the primary vectors responsible for transmitting WNV to humans and other vertebrate hosts.

Etiology

• WNV belongs to the family Flaviviridae, genus Flavivirus, and is classified into various lineages or strains based on genetic differences.
• The virus primarily circulates between birds and mosquitoes, with humans and other mammals serving as incidental hosts.
• WNV can cause a spectrum of clinical manifestations, ranging from asymptomatic infection to severe neurological disease.

Transmission

• Mosquito-Borne Transmission: WNV is primarily transmitted to humans through the bite of infected mosquitoes, primarily Culex species, which acquire the virus by feeding on infected birds.
• Blood Transfusion and Organ Transplantation: Transmission can also occur through blood transfusion, organ transplantation, and perinatal transmission from mother to fetus.
• Rare Modes of Transmission: Rare cases of WNV transmission have been reported through breastfeeding, and laboratory exposure.

Clinical Presentation

• The majority of WNV infections (~80%) are asymptomatic, with individuals showing no clinical signs or symptoms.
• Mild Disease (West Nile Fever): Symptomatic infection may present as a self-limited febrile illness, with symptoms such as fever, headache, body aches, fatigue, rash, and occasionally gastrointestinal symptoms.
• Severe Disease (Neuroinvasive Disease): In a small proportion of cases (<1%), WNV infection can progress to severe neurological disease, including meningitis, encephalitis, acute flaccid paralysis, and rarely, death.

Diagnosis

• Laboratory diagnosis of WNV infection involves detecting viral nucleic acid (RNA) or specific antibodies (IgM and IgG) in serum, cerebrospinal fluid (CSF), or other clinical specimens using molecular and serological assays.
• Cross-reactivity with other flaviviruses, such as dengue virus and Zika virus, can complicate serological diagnosis and require confirmatory testing.

Treatment

• There is no specific antiviral treatment for WNV infection, and management primarily involves supportive care to alleviate symptoms and complications.
• Hospitalization may be necessary for patients with severe neurological disease or complications such as dehydration, respiratory failure, or secondary bacterial infections.
• Vector control measures, including larval habitat reduction, insecticide spraying, and mosquito repellents, play a crucial role in preventing WNV transmission.

Sources:

LiveMint

PRACTICE QUESTION Q.  Comprehensive strategies combining vector control, surveillance, and public education are essential for reducing the burden of and mitigating the risk of severe diseases. Comment. (250 words)