West Nile Virus Cases Rise Across the US as Drought Creates New Mosquito Risks

A mosquito-borne illness that can cause severe inflammation of the brain and spinal cord is spreading across parts of the United States, with health officials warning people to take extra precautions during the summer months.

West Nile virus has been detected in at least 30 US states so far this year, with more than 180 human cases recorded nationally, according to data from the Centers for Disease Control and Prevention (CDC). At least eight people have died.

Arizona has reported the highest number of cases, with 73 infections and five deaths. California has also experienced a notable rise, reporting 30 human cases and three deaths, according to state health data. That figure is around three times the number recorded in the state at the same point last year.

The increase is particularly concerning because severe West Nile infections can cause neurological complications. While many people who contract the virus experience no symptoms or develop only mild illness, a small proportion can become seriously ill.

A virus that can affect the brain

West Nile virus is mainly transmitted through the bite of an infected mosquito. Mosquitoes become infected after feeding on birds carrying the virus and can then pass it to humans and other animals.

According to the Centers for Disease Control and Prevention, most people infected with West Nile virus do not develop symptoms. Others may experience fever, headache, body aches, vomiting, skin rashes or swollen lymph glands.

The more serious form of the disease, known as West Nile neuroinvasive disease, can cause inflammation of the brain or the membranes surrounding the brain and spinal cord.

Symptoms can include a high fever, confusion, tremors, muscle weakness, vision problems, paralysis and, in the most serious cases, coma or death.

There is currently no specific antiviral treatment or vaccine for people infected with West Nile virus. Medical care generally focuses on managing symptoms and supporting patients while their bodies fight the infection.

Older adults and people with weakened immune systems are among those at greater risk of developing severe disease.

California sees a significant increase

California has become one of the states attracting particular attention this summer.

State figures show 30 human cases so far in 2026, including three deaths. Few details have been released publicly about the deaths, although local health authorities said at least one person was aged between 80 and 90 and died following complications associated with the infection.

The rise in cases has also affected individual communities.

In Elk Grove, California, a 70-year-old man was recently hospitalised after developing a serious illness associated with West Nile virus. According to ABC10, the patient underwent a spinal tap as doctors investigated his condition.

A member of his family, Jeanetta McDowell, urged people to take mosquito protection seriously.

Her advice was simple: use insect repellent, cover exposed skin and take steps to reduce the risk of mosquito bites.

Idaho reports severe disease

California is not the only state to have recorded serious infections.

Idaho has reported its first severe West Nile virus case of the season. The patient is a 65-year-old resident of Canyon County who developed meningitis linked to the virus.

The Idaho Department of Health and Welfare said the case should serve as a reminder that people need to protect themselves from mosquito bites.

Dr Christine Hahn, Idaho's state epidemiologist, encouraged residents to take preventative measures during the mosquito season.

West Nile virus is not a new threat in the US. The infection causes more than 130 deaths in the contiguous United States in an average year, demonstrating that severe disease can occur even though most infections are relatively mild.

Why drought may be making the problem worse

The spread of West Nile virus might appear surprising in areas experiencing drought. Mosquitoes generally need water to reproduce, so it could be assumed that dry conditions would reduce mosquito populations.

Scientists say the reality is more complicated.

In parts of the western US, drought can create conditions that increase the risk of West Nile transmission. As larger bodies of water shrink, mosquitoes and birds can become concentrated around the remaining sources of water.

That closer proximity can create more opportunities for the virus to move between infected birds and mosquitoes.

Matthew Aliota, a professor at the University of Minnesota who studies viruses transmitted by mosquitoes and other vectors, previously explained the phenomenon to The Independent.

According to Aliota, drought can paradoxically increase transmission by concentrating mosquitoes and birds around shrinking water sources.

This year, the US has experienced significant drought across parts of the country. CNN reported earlier this year that historic drought conditions contributed to major wildfires and record-low snowpack in some regions.

The effects, however, are not uniform across the country.

Some states have seen mosquito activity below normal levels. Colorado, North Dakota and Minnesota are among the areas where mosquito numbers have been lower than usual this summer.

How people can protect themselves

Health officials say individuals can take several straightforward steps to reduce their exposure to mosquitoes.

The most important measures include using insect repellent when spending time outdoors and wearing clothing that covers the arms and legs. People should also check around their homes for standing water.

Mosquitoes can lay eggs in surprisingly small amounts of water. Containers, buckets, plant pots, blocked drains and other objects that collect rainwater can therefore become potential breeding sites.

Removing standing water regularly can help reduce the number of mosquitoes around homes and gardens.

The Idaho Department of Health and Welfare recommends combining personal protection with efforts to reduce mosquito breeding areas.

For people living in areas where West Nile virus is circulating, these precautions are particularly important during the warmer months, when mosquito activity generally reaches its highest levels.

A growing seasonal concern

West Nile virus remains a seasonal public health concern in the United States, but the latest figures highlight how environmental conditions can influence the spread of mosquito-borne diseases.

The situation also demonstrates why lower mosquito numbers do not necessarily mean lower infection risk. In drought-affected areas, changes in water availability can alter the behaviour and concentration of mosquitoes and birds, potentially creating conditions that favour transmission.

For most people, infection will not result in serious illness. However, the possibility of neurological disease, hospitalisation and death means that prevention remains important.

As summer continues, health authorities are urging residents to avoid mosquito bites wherever possible, remove standing water around their homes and seek medical advice if they develop concerning symptoms after spending time in areas where West Nile virus has been detected.

The message from public health officials is straightforward: mosquito bites may seem like a minor nuisance, but the virus they can carry can have serious consequences.

Sources

• Centers for Disease Control and Prevention (CDC)
• California West Nile Virus and Mosquito-Borne Disease Information
• Idaho Department of Health and Welfare
• ABC10
• CNN
• The Independent