The Colorado Department of Agriculture confirmed that three horses residing in three Colorado counties (Larimer, Pueblo, and Weld) were diagnosed with West Nile virus (WNV) on Aug. 29.
These mark Colorado’s first confirmed equine cases of WNV in 2019 and were diagnosed by Colorado State University’s Veterinary Diagnostic Laboratory in Fort Collins in late August.
WNV transmission occurs when infected mosquitoes feed on animals, as well as humans, after having fed on infected birds.
Clinical signs of WNV in horses include:
- Mild anorexia and depression;
- Fine and coarse muscle and skin fasciculation;
- Hyperesthesia (hypersensitivity to touch and sound);
- Changes in mentation (mentality), when horses look like they’re daydreaming or “just not with it”;
- Occasional drowsiness;
- Propulsive walking (driving or pushing forward, often without control); and
- Spinal signs, including asymmetrical weakness; and
- Asymmetrical or symmetrical ataxia (incoordination).
Officials urge horse owners to minimize horse exposure to mosquitoes during the peak mosquito feeding periods at dawn and dusk.
In addition to applying mosquito repellant to your horses, the following mosquito control efforts can help eliminate mosquito breeding sites:
- Drain unnecessary standing water in wheelbarrows, tires, etc.
- Clean water containers (bird baths, plant saucers, etc.) at least weekly.
- Schedule pasture irrigation to minimize standing water.
- Keep swimming pools optimally chlorinated and drain water from pool covers.
- Stock water tanks with fish that consume mosquito larvae (Contact local mosquito control for assistance), or use mosquito “dunks” available at hardware stores.
West Nile virus has no cure; however, some horses can recover with supportive care. Equine mortality rates can reach 30-40%. The American Association of Equine Practitioners includes WNV as one of the core diseases all horses should be vaccinated against at least annually.