Cases of West Nile fever caused by the virus of the same name have been reported from three districts in Kerala: Thrissur, Kozhikode and Mallapuram. Hence, the Kerala health department directed all districts in the state to be on alert in a public notice issued on 7 May 2024.
There are over 10 confirmed cases of West Nile fever in Kerala, of which nine have recovered while one person continues to be treated at a private hospital in Kozhikode. All these cases were confirmed through tests done by National Institute of Virology, Pune.
West Nile virus in Kerala
The first case of West Nile fever was reported in Kerala in Alappuzha district in 2011. Since then, there have been routine outbreaks. The virus was first isolated in a woman in Uganda’s West Nile district in 1937.
In a recent meeting, the Kerala health department gave instructions to intensify pre-monsoon cleaning activities as the West Nile virus spreads mainly through infected mosquito bites. Moreover, District Vector Control Units have already collected samples of mosquito pools from different areas and sent them for testing. The state health department has also directed districts to increase awareness campaigns about West Nile fever.
What is West Nile fever?
According to the World Health Organization (WHO), West Nile fever, which spreads through a mosquito-borne virus, can sometimes lead to a fatal neurological disease in humans. Currently, there are no vaccines that protect humans against this virus.
Dr Netto George Mundadan, assistant professor, department of infectious diseases, Government Medical College, Kottayam, Kerala, says the bite of an infected Culex mosquito leads to the spread of the West Nile virus. Hence, the infection spikes during rainy reason. He adds, “Birds are the primary hosts of the West Nile virus, and it can pass on from them to mosquitoes. Humans are just an incidental host for this virus.” He shares that the same mosquito also carries Japanese encephalitis. Besides, the West Nile virus does not spread from human to human.
Discussing the fact that cases of West Nile fever were recorded in Kottayam district in Kerala in 2023, Dr Mundadan says that several cases go undiagnosed. Dr Anoop Kumar A S, director, critical care medicine, Aster Hospitals, North Kerala, says that almost 80% of the infected people are asymptomatic — only 20% develop symptoms.
Common symptoms of West Nile fever
According to the US Centers for Disease Control and Prevention (CDC), 1 in 150 people infected with the West Nile virus develop encephalitis (brain inflammation) or meningitis (inflammation of membranes surrounding the brain and spinal cord). Additionally, it says that people with medical conditions like cancer, diabetes, hypertension and kidney disease, those over the age of 60 and people who have undergone organ transplants are at greater risk of severe illness.
Diagnosis and treatment
Dr Mundadan says that one of the most commonly used tests used to diagnose the West Nile virus is the IgM (Immunoglobulin M) antibody test. Dr Kumar adds that there are issues in detecting specific antibodies as well. He explains that in a majority of viral infections, once it subsides, the person’s antibody level for the condition also reduces over the course of a few weeks or months. “However, in the case of the West Nile virus, the IgM antibody response may persist in the body for as long as six years,” he shares. Hence, when a person tests positive for the IgM antibody for West Nile virus, it cannot be confirmed if they had a recent infection — dead viral remnants continue to show up in the tests. A similar scenario was seen during the COVID-19 pandemic when several people continued testing positive even months after recovering from the condition.
Dr Kumar points out that other viruses can cross-react with West Nile antibodies. “So, if you contract another viral infection like Japanese encephalitis, you may test positive for the IgM antibody against West Nile. You will then require additional tests to confirm the presence of West Nile virus,” he explained.
Further, Dr Mundadan added that West Nile fever has no specific treatment; only symptomatic treatment can be provided. He adds that it usually takes one to two weeks to recover from the infection fully.
West Nile fever: Prevention
According to a statement by the Kerala state health ministry, eradication of mosquitoes is key to preventing the transmission of West Nile fever. The ministry has asked people to take every possible measure to avoid mosquito bites. This includes:
- Wearing long-sleeved shirts and long pants to avoid mosquito bites
- Using mosquito nets or electric mosquito-repellent devices
- Using mosquito repellent ointments
- Prevent the collection of stagnant water in and around the house
Takeaways
- Kerala is reporting cases of West Nile fever caused by the virus of the same name. Thus, the state health department is currently on alert.
- 80% of the infected people are unlikely to show symptoms. Of the remaining 20%, some may have a severe form of the illness.
- The government has advised people to avoid mosquito bites by wearing appropriate clothing, using mosquito nets and repellents, and preventing the collection of stagnant water in and around their houses.
