Mexico's screwworm (gusano barrenador) outbreak spreads to livestock and pets

Authorities in Chihuahua have confirmed five cases of the screwworm parasite (gusano barrenador) in cattle, with 14 additional suspected infections and many unreported. Municipalities affected include Parral, San Francisco del Oro, Allende, Coronado, Jiménez, La Cruz and Delicias. The regional cattle union, led by Álvaro Bustillos Fuentes, is using sterile‑fly releases as the primary containment tool, relying on the Panama plant (100 million flies) and a new facility in Metapa de Domínguez, Chiapas (starting at 20 million, scaling to 120 million). The state has established a 20‑km sanitary fence and deployed Senasica‑coordinated brigades to treat livestock with doramectina, Exzolt and ivermectin, provided free to producers.

The infestation has reached 29 Mexican states, with a national total of 34,742 reported cases and 1,792 active infections as of November 2024. Aguascalientes reported 62 cumulative cases, 21 active, spread across most of its municipalities. In Coahuila, a suspected case was detected in a dog from the ejido La Mota, prompting municipal animal‑health authorities to initiate testing and warn owners to monitor pets for open wounds. Veterinarians across the region are urging constant surveillance of dogs and other warm‑blooded animals, emphasizing early treatment to prevent severe tissue damage.

Political leaders, including PRI deputy Arturo Medina, have called on the federal government to strengthen zoosanitary controls and avoid future export disruptions that could cost cattle producers 40‑60 % of their revenue per head. The coordinated response aims to protect Mexico’s cattle export market to the United States while controlling the spread of the parasite in both livestock and companion animals.