The first (1st) case of West Nile Virus in California in 2024 was confirmed in Placer County. On July 25, 2024, a 6-year-old Andalusian cross stallion in Placer County with an unknown vaccine history displaying neurologic signs was confirmed positive for West Nile Virus. The stallion is alive and recovering.
To date for 2024, a total of one (1) horse has been confirmed positive for WNV in California. The positive horse is located in Placer (1) County. Zero (0) horses were unvaccinated, zero (0) horses were undervaccinated, zero (0) horses were vaccinated, and one (1) horse had unknown vaccine history. One (1) horse is alive and recovering and zero (0) horses were euthanized or died.
In 2023, a total of thirty-one (31) horses were confirmed positive for WNV in California. The positive horses were located in Butte (1), Fresno (2), Kern (2), Kings (1), Madera (1), Merced (2), Napa (1), Orange (1), Placer (1), Riverside (4), Sacramento (3), San Bernardino (1), San Joaquin (2), San Luis Obispo (2), San Mateo (1), Santa Clara (1), Siskiyou (1), Stanislaus (2), Tulare (1) and Yuba (1) Counties. Fifteen (15) horses were unvaccinated, four (4) horses were undervaccinated, nine (9) horses were vaccinated, and three (3) horses had unknown vaccine history. Twenty-two (22) horses are alive and recovering, eight (8) horses were euthanized or died, and one (1) horse has unknown status.
For 2022, a total of sixteen (16) horses were confirmed positive for WNV in California. The first case was confirmed on July 13, 2022 and the last case on October 26, 2022. Horses ranged in age from under 1 year to 15 years (mean 6, median 5), with 10 males and 6 females affected, with multiple breeds reprsesented, but an overrepresentation of Quarter Horse breeds/crosses (over half of confirmed cases).
The positive horses were located in Kern County (3), Kings County (1), Los Angeles (1), Nevada County (1), Sacramento County (2), San Luis Obispo County (1), San Joaquin County (1), Stanislaus County (1), Tehama County (2), and Tulare County (3). Ten (10) horses were unvaccinated, four (4) horses had unknown vaccine history, and two (2) were vaccinated. Eleven (11) horses recovered, one (1) horse died, and four (4) horses were euthanized.
For 2021, a total of thirteen (13) horses were confirmed positive for West Nile Virus in California. The first case was confirmed on June 28, 2021 and the last case was confirmed on October 6, 2021. Horses ranged in age from 1 to 14 years old (mean 4 years, median 3 years), with 9 females and 4 males affected, and multiple breeds represented.
The positive horses were located in Amador County (1), Fresno County (2), Kings County (1), Merced County (1), Sacramento County (2), San Joaquin County (3), Stanislaus County (1), and Yuba County (2). Nine (9) horses were unvaccinated, two (2) horses had unknown vaccine history and two (2) were vaccinated. Eleven (11) horses are alive, one (1) horse died, and one (1) horse was euthanized. CDFA continually monitors and investigates equine neurologic cases for the presence of WNV in California. CDFA urges horse owners to consult their veterinarian concerning a WNV vaccination program to ensure maximum protection of their horses.