West Nile Virus Cases Rise Across the U.S. This Summer

The West Nile Virus situation is worsening throughout the United States:Death in Colorado and First Cases in Multiple States

Colorado recently confirmed a tragic turn in its West Nile season: an elderly man in Montrose County died due to the virus—marking the first fatality there this year. Health officials confirmed the cause following diagnostic tests.

In Salt Lake County, Utah, authorities reported the first human case of 2025. The patient required hospitalization after developing a severe form of WNV. Mosquitoes carrying the virus have already been detected in the region prompting local officials to urge preventive measures.

Midland County, Michigan, is also grappling with a spike in mosquito infection rates. Testing revealed 13 WNV-positive mosquito samples—more than triple the area’s typical annual average. While no human cases have emerged so far, the high vector activity underscores significant concern about potential spread.

In Morgan and Greene counties, Illinois, mosquitoes tested positive for WNV. These findings have triggered increased larvicide treatments and public advisories emphasizing insect repellent use, protective clothing, and reporting of standing water.

Meanwhile, Harris County, Texas reported its first human infection of the year. The individual, now fully recovered, illustrates the silent volatility of WNV—previous years saw up to three virus-related deaths there.

Wider National Trends: Confirmed Cases and Ongoing Surveillance

Recent data from the CDC (via ArboNET) reveals that WNV activity has been reported across the contiguous United States, typically peaking between June and October and especially in late August through September.

By August 26, 2025, the CDC recorded preliminary human WNV case counts in key states: Colorado (74 cases), California (17), Georgia (2), and Iowa (1). These figures are expected to rise as more data comes in from state health departments.

In Maryland, state health officials confirmed their first 2025 human case, though the individual is recovering. The department emphasized ongoing risk and encouraged vigilant mosquito bite prevention.

In New York City, two human cases were confirmed, one mild (West Nile fever), the other more serious (neuroinvasive disease). Mosquito pools across all five boroughs have tested positive, and blood donations from Brooklyn and Staten Island flagged additional potential cases.

What Is West Nile Virus? Symptoms, Risk & the Bigger Picture

West Nile virus is the leading mosquito-borne disease in the continental U.S., primarily transmitted via Culex mosquito bites. Human infection occurs when mosquitoes bite infected birds and then humans.

• Asymptomatic cases: Around 80% of infected individuals show no symptoms.
• Mild illness: About 20% may experience flu-like symptoms—fever, headache, body aches, rash.
• Severe illness: Less than 1% develop neuroinvasive complications such as meningitis or encephalitis, with roughly 10% of these cases resulting in death.

There is no vaccine or antiviral treatment available for humans with West Nile virus. Prevention relies on symptom relief (e.g., pain relievers, hydration), and serious cases require hospitalisation for supportive care.

Why 2025 Is Especially Concerning

This year’s early mosquito testing and case detections reflect broader environmental conditions that favor WNV spread. Record-high vector activity in multiple states aligns with a trend of warmer, prolonged summers and wetter conditions, a pattern exacerbated by climate change.

A 2025 CDC toolkit underscores the virus’s decade-long toll: since its U.S. debut in 1999, WNV has caused over 31,800 neurologic illness cases and approximately 2,900 deaths.

How to Protect Yourself This Season

Public health agencies across impacted areas are issuing consistent advice. These simple steps remain the frontline defence:

• Use EPA-registered insect repellents (DEET, picaridin, oil of lemon eucalyptus).
• Wear long sleeves and pants, especially during dawn and dusk, when mosquitoes are most active.
• Eliminate standing water—empty bird baths, buckets, tyres, and gutters to reduce breeding sites.

The rise in West Nile cases—from Colorado to Connecticut, New York, Maryland, and beyond—signals a serious public health alert. Climate dynamics, high mosquito infection rates, and confirmed human cases call for urgent attention.

While the majority of infections remain mild or hidden, the stakes are higher for older adults and those with weakened immune systems.