West Nile Virus: Which Symptoms After a Mosquito Bite Require Attention?
On 9 July 2026, Greece’s National Public Health Organization, EODY, announced the country’s first diagnosed case of West Nile virus infection for the current transmission season. The patient was over 60 years old, had developed meningoencephalitis and was most likely exposed in Agia Paraskevi, Attica. The situation subsequently evolved. According to the EODY epidemiological report published on 22 July 2026, 21 locally acquired cases had been recorded, including 20 involving the central nervous system. No deaths had been reported. This does not mean that almost every infection causes neurological disease. Mild and asymptomatic infections are rarely diagnosed, while surveillance is more likely to detect patients who require hospital care. EODY estimates that every recorded neuroinvasive case may correspond to approximately 140 additional people with mild or asymptomatic infection. How is the virus transmitted? West Nile virus is transmitted mainly through the bite of infected common mosquitoes, usually species belonging to the Culex genus. Mosquitoes acquire the virus by feeding on infected birds and may subsequently transmit it to humans. The virus is not spread through ordinary social contact, touching, kissing or living with an infected person. Rare transmission through blood transfusion, organ transplantation or from mother to baby has been reported, but specific blood-safety measures are introduced in affected areas. Does every mosquito bite represent a risk? No. Most mosquitoes do not carry West Nile virus, and a red, itchy bump that appears around the bite is usually a local reaction to mosquito saliva, not a symptom of West Nile infection. An asymptomatic person does not need laboratory testing after every mosquito bite. What matters is the development of systemic or neurological symptoms within the relevant incubation period, particularly during the mosquito transmission season. When do symptoms appear? Symptoms generally develop 2–14 days after the bite of an infected mosquito, although the incubation period may be longer in immunocompromised people. They do not appear immediately after the bite. According to EODY: - approximately 80% of infected people remain asymptomatic, - approximately 20% develop a mild illness, - fewer than 1% develop severe disease involving the central nervous system. What are the symptoms of mild illness? Mild West Nile illness may resemble a flu-like syndrome and include fever, headache, pronounced fatigue, muscle and joint pain, nausea, vomiting, diarrhoea, reduced appetite, abdominal discomfort, a skin rash or swollen lymph nodes. Symptoms usually improve within several days, although fatigue, headache, muscle pain or difficulties with concentration may occasionally persist for weeks or months. These symptoms are not specific to West Nile virus and may be caused by many other infections. A diagnosis cannot be made solely because the person remembers a recent mosquito bite. Which symptoms require immediate attention? Severe West Nile disease may cause encephalitis, meningitis or acute flaccid paralysis. The CDC recommends immediate medical assessment when high fever, neck stiffness, muscle weakness, confusion or tremors occur. Other warning signs include: - an unusually severe or progressively worsening headache, - disorientation, lethargy or behavioural changes, - difficulty walking or pronounced instability, - seizures, - sudden weakness in one or more limbs, - paralysis, - visual disturbances, - reduced consciousness. Seizures, loss of consciousness, severe confusion, sudden paralysis or breathing difficulty constitute an emergency and require immediate emergency medical assistance. Who is at greater risk? Severe disease can occur at any age, but the likelihood increases considerably with age. EODY identifies age over 50 as an important risk factor, with risk continuing to rise among older age groups. Additional higher-risk groups include: - immunocompromised people, - organ transplant recipients, - patients receiving immunosuppressive treatment, - people with chronic underlying medical conditions. In the report of 22 July, the median age of patients with neurological manifestations was 72. This reinforces the importance of consistent mosquito-bite prevention among older adults without implying that younger people cannot develop severe disease. Is there a treatment or vaccine? There is currently no human vaccine or specific antiviral medicine for West Nile virus infection. Management is supportive. Mild illness generally resolves without specific treatment, while people with neurological disease may require hospitalisation, intravenous fluids, close monitoring and, in severe cases, respiratory support. Preventing mosquito bites therefore remains the most important protective measure. How can infection be prevented? Recommended measures include: - using an approved insect repellent according to the label, - wearing loose-fitting clothing that covers the arms and legs, - installing or repairing screens on windows and doors, - using mosquito nets where necessary, - limiting outdoor exposure between dusk and dawn, when common mosquitoes are often most active, - emptying, covering or removing containers that collect standing water, - regularly changing water in animal bowls and other outdoor containers, - cleaning gutters and areas where water accumulates. EODY recommends mosquito-bite precautions throughout Greece, not only in municipalities where cases have already been recorded, because the areas in which the virus will circulate cannot be predicted with certainty. The bottom line An ordinary mosquito bite is not, by itself, a reason for panic or laboratory testing. Medical attention is nevertheless necessary if fever is followed within the next 2–14 days by symptoms affecting consciousness, the neck, muscle strength, walking or neurological function. Severe West Nile disease is rare compared with the total number of infections, but it can have serious and long-lasting consequences. The appropriate response is not fear of every mosquito. It is consistent prevention and early recognition of genuine neurological warning signs. Read the full article
