Understanding West Nile fever & Effective Preventive Measures

  •   Fri, May 17 2024
  •   Dr Rohit Pai

May 17, 2024

We have hardly come out of multiple Covid waves, a new virus has come to the fore. This virus has caused several outbreaks in the past in North Africa, Europe, United states and India. The largest outbreak occurred in 2018 with 991 cases. It was reported in Kerala in 2011, 2013, 2019, 2022. This year 10 confirmed cases have been reported in Kerala with 2 suspected deaths one in Palakkad and the other in Thrissur.

Transmission - Transmission is by mosquito bite. The virus also infects birds and circulates in bird mosquito bird cycle. Humans and horses act as incidental hosts and is note helpful in transmission as viremia is short lived and low grade. Transmission may occur from mother to child in utero, through blood or organ transplantation. Mosquitoes that transmit this virus are the Culex mosquitoes. These mosquitoes are also responsible for transmitting Japanese encephalitis, St Louis encephalitis, Western and Eastern equine encephalitis. The mosquito injects the victim with saliva laden with viruses while it is feeding. In the initial phase virus replicates in the skin cells and skin resident immune cells called as dendritic cells. The virus subsequently replicates in the draining lymph nodes. Then the virus spreads to the visceral organs including spleen. CNS invasion may occur during this phase.

Risk factors - About 25% of those infected develop West Nile fever. 1 out of 250 develop neuroinvasive disease.

Symptoms - Most infections are asymptomatic; symptoms occur in only 20 % of the cases. The typical incubation period is 2 to 14 days. Usual presentation is indistinguishable from dengue. Patients may present with the following symptoms.

  • Fever
  • Headache
  • Body pain
  • Pharyngitis
  • Vomiting, diarrhea and abdominal pain
  • Generalized lymphadenopathy
  • Rash on chest, back and arms

Neuroinvasive Disease - Encephalitis is more common in the older patients whereas meningitis is seen in children. Meningitis is characterized by fever, headache and photophobia. Encephalitis ranges in severity from mild confusion state to severe encephalopathy, coma and death. Extrapyramidal symptoms like tremor, myoclonus, parkinsonian symptoms. It can also cause poliomyelitis like illness with flaccid weakness of limbs. This is due to involvement of part of nervous system called anterior horn cells. Testing of the virus can be done by ELISA and RT PCR. MRI brain will be required to show evidence of encephalitis.

Treatment - Treatment of West Nile virus infection is usually supportive with medication for headache, vomiting and intravenous fluids for hydration. Patients need to me monitored for raised intracranial pressure and seizures. If patients develop polio like illness ventilatory support may be required. Agents like corticosteroids and intravenous immunoglobulin have been used with varied outcome.

Prognosis - Serious outcome are limited to patients with neuroinvasive disease. Among the neuroinvasive cases mortality was seen in 2 % of patients with meningitis,14 % with encephalitis ,13 % with polio like presentation. Long term outcomes include muscle weakness, fatigue, memory problems

Prevention - This includes personal protection to avoid mosquito exposure and mosquito control. There are no human vaccines at present to prevent West Nile infection.

 

 

 
Dr Rohit Pai
Dr Rohit Pai is a consultant of neurology at KMC Hospital, Mangaluru.
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