Disease Activity Report: March 8-22, 2026 — EIA Surge in California and Texas

Spring 2026 is arriving with a notable uptick in equine disease activity. Over the past two weeks, 13 new disease alerts were reported across 9 U.S. states and Ontario, Canada, with a concerning cluster of Equine Infectious Anemia (EIA) cases emerging in California and Texas.

Two-Week Snapshot: March 8-22

Equine Infectious Anemia: California and Texas on Alert

The biggest story of the past two weeks is the surge in EIA cases — a disease that carries no cure and requires lifetime quarantine or euthanasia of positive horses.

Four EIA alerts were reported between March 19-20:

• Stanislaus County, CA — 2 confirmed, 25 exposed (Official quarantine)
• Merced County, CA — 1 confirmed, 1 exposed (Official quarantine)
• Milam County, TX — 1 confirmed (Official quarantine)
• Harris County, TX — 1 confirmed (Official quarantine)

The two California cases in adjacent San Joaquin Valley counties are particularly concerning. With 26 horses potentially exposed across the two facilities, state veterinary officials have imposed official quarantine and are conducting Coggins testing on all contact animals.

Why this matters: EIA is transmitted by blood-feeding insects (primarily horse flies and deer flies). As spring temperatures rise across California's Central Valley, vector activity will increase, making early detection critical. Horse owners in central California should ensure all horses have current Coggins tests and report any signs of fever, weight loss, or anemia to their veterinarian immediately.

Strangles: Oregon's Harney County Outbreak Grows

Strangles accounted for 5 of the 13 alerts this period, with Oregon's Harney County seeing the most significant activity:

• Harney County, OR — 9 confirmed cases at a farm facility (March 9, Official quarantine)
• Linn County, OR — 1 confirmed, 4 exposed (March 10, Official quarantine)
• Columbia County, FL — 1 confirmed, 8 exposed at a private facility (March 20)
• Marquette County, MI — 1 confirmed, 2 exposed (March 12)
• Wellington, ON (Canada) — 1 confirmed at a training facility (March 19)

Harney County alone has now reported 17 total cases over the past 30 days, making it the most active county in the nation for disease activity. The multi-horse farm outbreak suggests ongoing transmission despite quarantine measures.

EHV-1: Two Neurologic Cases and a Resolved Outbreak

Equine Herpesvirus activity included both concerning new cases and encouraging news:

• Anne Arundel County, MD — 1 confirmed EHV-1 Neurologic case with 29 exposed horses at a boarding facility (Official quarantine)
• Waukesha County, WI — 1 EHV-1 Neurologic case with 38 exposed horses — now resolved
• Maricopa County, AZ — 1 EHV-1 case with 32 exposed at a private facility (Official quarantine)

The Wisconsin resolution is welcome news, showing that proper quarantine protocols and veterinary care can successfully contain neurologic herpesvirus outbreaks. However, the Maryland boarding facility case is a reminder of how quickly EHV-1 can put dozens of horses at risk in a shared environment.

Equine Influenza: Kansas Reports New Case

A single Equine Influenza case was reported in Ellis County, KS on March 15 at a boarding facility under voluntary quarantine. While isolated, this case is a reminder that influenza remains active heading into spring show season.

Vaccination Data: A Sobering Reality

Our tracking data across all 552 cases with known vaccination status paints a stark picture.

Vaccination Gaps by Disease

The data becomes even more telling when broken down by disease.

These visuals underscore a clear message: routine vaccination dramatically reduces disease risk. While no vaccine is 100% effective, the data consistently shows that the vast majority of disease cases occur in horses that are not up to date on their vaccinations.

Most Active Counties — 30-Day View

Virginia continues to show elevated activity from outbreaks that began in late February, with Louisa and Loudoun counties accounting for 25 combined cases across multiple diseases.

Spring Season Advisory

As we head deeper into spring, several factors are increasing disease transmission risk:

• Show season is ramping up — More horses traveling and congregating means more disease exposure opportunities
• Vector season is beginning — Warmer temperatures bring horse flies, mosquitoes, and other disease vectors
• Breeding season is underway — Horses at breeding facilities face increased contact with animals from multiple farms

What Horse Owners Should Do Now

• Schedule spring vaccinations — Ensure your horses are current on core vaccines (EEE/WEE, West Nile, Tetanus, Rabies) and risk-based vaccines (Influenza, EHV, Strangles) before peak season
• Get a current Coggins test — Required for travel in most states and critical for EIA surveillance
• Practice biosecurity at events — Don't share water buckets, tack, or equipment; avoid nose-to-nose contact with unfamiliar horses
• Monitor temperatures daily — Fever (above 101.5F) is often the first sign of infection; early detection enables faster response
• Check your destination — Before traveling, review disease activity in your destination state on our interactive map
• Isolate returning horses — Keep horses separated for 14-21 days after returning from events or shows

What We're Watching

• California EIA cluster — Will Coggins testing of exposed horses reveal additional positives in the San Joaquin Valley?
• Oregon Strangles — Can Harney County's outbreak be contained before spreading to neighboring counties?
• Spring vector emergence — First mosquito-borne disease reports typically begin in April; early vaccinations are critical
• Virginia activity — Multiple concurrent outbreaks in northern Virginia bear close monitoring

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Stay informed with real-time outbreak data on our interactive map, or browse alerts by state. All data sourced from the Equine Disease Communication Center (EDCC). Follow us for the latest updates on equine disease activity nationwide.