California investigates two new equine infectious anemia cases

CURRENT BRIEF VERSION: Two Quarter Horse geldings, ages 7 and 8, tested positive for equine infectious anemia, or EIA, on March 19 in Stanislaus County, California. The cases were reported through EDCC Health Watch, and 25 potentially exposed horses on the premises have been tested, placed under quarantine, and will remain under movement restrictions pending initial results and 60-day retesting. Epidemiologic tracing is ongoing, with investigators suspecting iatrogenic transmission rather than insect spread. EDCC Health Watch distributes verified disease reports using information from the Equine Disease Communication Center, an independent nonprofit that provides open-access equine infectious disease information. (equusmagazine.com)

Why it matters: EIA remains rare in the U.S., but it carries outsized operational consequences because infected horses are lifelong carriers and the disease is reportable, untreatable, and tightly regulated. Horses that test positive may die, be euthanized, or spend life under strict quarantine at least 200 yards from unaffected equids. For veterinarians, this case is another reminder that California regulators continue to see many EIA detections tied to iatrogenic exposure, especially in Quarter Horse populations, making injection hygiene, single-use equipment, careful handling of blood products, and protection of multidose vials central to prevention. A Coggins test detects antibodies to the virus and is widely required for interstate movement. USDA says national prevalence has fallen to about 0.004%, while California recorded 15 cases in 2024 after 6 in 2023, underscoring how even a small cluster can trigger intensive tracing and quarantine work. Clinical signs, when they occur, can include weight loss, weakness, poor stamina, fever, depression, and anemia. (aphis.usda.gov)

What to watch: Watch for confirmatory and follow-up test results from the exposed horses, plus any additional findings from the trace-back investigation into the suspected source of blood-borne transmission. Recent March reports from Texas, where two positive horses were euthanized, are a reminder that sporadic EIA detections continue to surface and require rapid containment. (equusmagazine.com)