West Nile fever: A new virus on the prowl?

Kerala is going through yet another flu season. And this time, there is the added worry over the West Nile fever
Image used for representational purposes only
Image used for representational purposes only

KOCHI: Dengue, hepatitis, leptospirosis, and murmurs about a silent Covid wave… Kerala has been going through a sick phase of late. Adding to the public anxiety, one more has joined the list: West Nile fever.

The state reported the first case of West Nile fever in 2011. The virus was later detected in 2013, 2019 and 2022 as well. This year, so far, at least 10 confirmed West Nile cases and two suspected deaths – one in Palakkad and the other in Thrissur – have been reported in the state.

Nine of the 10 cases were reported in May. Experts, however, allay concerns and say West Nile fever is preventable, and treatable, if detected early.

West Nile fever is transmitted by mosquitoes infected with the virus. “The virus gets transmitted when mosquitoes draw blood from infected birds. When these mosquitoes bite humans or animals, the virus yet again gets transmitted,” explains Dr Harikumar S, assistant director (public health), Directorate of Health Services, Kerala.

“However, the virus will not be transmitted from one infected person to another through a mosquito bite. Similarly, there will be no transmission by touching or coming in close contact with an infected person.”

The symptoms of West Nile fever, according to the World Health Organization (WHO), include:

  • Fever

  • Headache

  • Tiredness

  • Body ache

  • Nausea

  • Vomiting

  • Occasionally, a skin rash (on the trunk of the body)

  • Swollen lymph glands.

Symptoms of severe disease (also called neuroinvasive disease), such as West Nile encephalitis meningitis or West Nile poliomyelitis:

  • Headache

  • High fever

  • Neck stiffness

  • Stupor

  • Disorientation

  • Coma

  • Tremors

  • Convulsions

  • Muscle weakness

  • Paralysis

Symptoms usually appear 3 to 14 days after being bitten by an infected mosquito. “Only a small number of people infected with the virus develop serious symptoms. According to data, one in 150 cases are serious,” Dr Harikumar notes.

“About 20 per cent of people infected with the virus may develop mild symptoms that can last from a few days to weeks. About 80 per cent of people infected with the virus do not develop symptoms.”

However, if the infection is severe, West Nile fever may affect the brain. “Early detection is crucial. Because the disease can also lead to encephalitis or meningitis, and can even lead to death,” says Dr Althaf A, epidemiologist and professor of community medicine at Government Medical College, Thiruvananthapuram.

“Even if the patient survives, he or she may suffer from morbidity. Recovery from severe illness might take several weeks or months. Some effects on the central nervous system might be permanent. About 1 out of 10 people who develop severe illness affecting the central nervous system succumb. Thus, it is important to consult a doctor at the earliest once the symptoms manifest.”

Severe illness can occur in people of any age. However, people over the age of 60 are said to be at a greater risk for complications (1 in 50 people). People with certain medical conditions, such as cancer, diabetes, hypertension, kidney disease, and those who have received organ transplants, are also at greater risk.

Consulting a doctor at the earliest is important. “Among symptomatic patients, fever is the major symptom of the disease. About 1 in 5 people who are infected develop a fever with other symptoms such as headache, body aches, joint pains, vomiting, diarrhoea, and rashes. Most people with febrile illness due to the West Nile virus recover completely, but fatigue and weakness can last for weeks or months,” says Dr Althaf.

“In case of fever, people should consult a doctor and the actual cause must be diagnosed and treated properly. If delayed, it can lead to complications and even death. As people get older, their immunity decreases and the chances of getting affected by the disease are high. Thus, the elderly population, and people with co-morbidity should be cautious.”

According to Dr Hari, mild symptoms usually resolve without treatment. “But in case of symptoms like severe headache and confusion, the person should immediately seek treatment,” he says. “Pregnant and lactating mothers should consult a doctor immediately if symptoms are observed.”

Kerala’s surveillance system needs to be strengthened to prevent the occurrence of the disease, the doctors highlight. “Migration, increasing travel, and climate change are factors in the emergence of new infectious diseases,” says Dr Althaf, adding that comprehensive preventive strategies are vital.

“With the increasing migration and travel to other states/countries, possibilities of spread are high. Also, we are experiencing a climatic change. Thus, it is important to strengthen surveillance. As we are in the post-pandemic phase, we need to be more cautious.”

Over the years, surveillance in the state has, indeed, improved, and it has helped in the detection and prevention of the disease spread, says Dr Hari. “We have new technologies and diagnostic equipment available. It has helped in the detection of the presence of the virus. It helps in early detection and prevention. People should refrain from self-medicating,” he adds.

What’s the West Nile story?

It is named after the West Nile district of Uganda, where the virus specimen was first isolated in 1937. It was later identified in birds (crows and columbiformes) in the Nile Delta region in 1953. The virus is commonly found in Africa, Europe, the Middle East, North America and West Asia. WNV sustains in nature via a cycle involving transmission between birds and mosquitoes. Humans, horses and other mammals can be infected.

Govt directive

With at least nine West Nile fever cases reported in the state this month alone, the health ministry has directed the district medical officers to intensify the pre-monsoon cleaning drives and efforts to control mosquitoes with the cooperation of the local bodies.

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