# West Nile virus animal infections

> Live situation record from CLSTR: https://clstr.news/situations/west-nile-virus-animal-infections
> Updated: 2026-08-11T18:12:10.000Z. Sources: 16. Developments: 4.

In early August 2026, Germany reported a surge of West Nile virus cases in horses, linked to unusually wet weather that boosted mosquito and tick populations. The virus, first seen in European birds in the 1960s and in German birds in 2018, was causing neurological disease in a minority of infected horses, prompting many owners to seek prophylactic vaccination.

In the United States, the Utah Department of Agriculture confirmed two positive cases in horses: a 4-year-old gelding in Weber County that recovered from symptoms, and a second horse in Box Elder County. Simultaneously, Delaware reported its first detection of 2026 in a sentinel chicken flock in eastern Kent County. While no human cases have been reported in these U.S. incidents, officials have urged vaccination and mosquito control.

By mid-August, the virus was detected in mosquito samples in other parts of the U.S. In Boston, the Boston Public Health Commission reported the first positive mosquito test of the summer in the Jamaica Plain neighborhood. In Montana, the Department of Public Health and Human Services confirmed that two mosquito pools in Roosevelt County tested positive. While no human or horse cases have been reported in Montana this summer, epidemiologists warned that the virus can cause severe neurological complications, including paralysis or death, in a small percentage of infected individuals.

In Europe, Belgium confirmed its first case of West Nile virus in a horse located in Vilvoorde. The animal exhibited severe neurological symptoms and was euthanized. Health authorities noted that because horses often display clearer symptoms than humans, they serve as an early warning system for viral circulation.

## Timeline

### 2026-08-11: West Nile virus detected in mosquito samples in Boston and Montana

West Nile virus has been detected in mosquito samples in Boston's Jamaica Plain and Roosevelt County, Montana, prompting health officials to issue bite prevention warnings.

5 sources. https://clstr.news/cluster/west-nile-virus-detected-in-mosquito-samples-in-boston-and-montana

### 2026-08-07: West Nile virus confirmed in Belgian horse

Belgium has confirmed its first case of West Nile virus in a horse in Vilvoorde. Authorities advise mosquito prevention as the virus is transmitted via bites and can cause neurological issues.

2 sources. https://clstr.news/cluster/west-nile-virus-confirmed-in-belgian-horse

### 2026-08-06: West Nile Virus Detected in Utah Horses and Delaware Chickens

West Nile virus was found in two Utah horses and in a Delaware sentinel chicken flock, prompting health alerts and urging horse vaccination and mosquito control across the US.

5 sources. https://clstr.news/cluster/west-nile-virus-detected-in-utah-horses-and-delaware-chickens

### 2026-08-05: West Nile Virus Spreads Among German Horses Amid Rising Insect Activity

Germany's wet winter fuels mosquito and tick growth, driving West Nile virus spread in horses; severe cases affect 8% with up to 50% mortality, prompting more owners to vaccinate.

4 sources. https://clstr.news/cluster/west-nile-virus-spreads-among-german-horses-amid-rising-insect-activity

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Cite as: West Nile virus animal infections. CLSTR, https://clstr.news/situations/west-nile-virus-animal-infections