Detection and Containment of a Livestock Screwworm Outbreak in Querétaro
The National Agri-Food Health, Safety and Quality Service (Senasica), an agency dependent on the Secretary of Agriculture and Rural Development (Sader), precisely executed a containment protocol after the identification of a case of livestock screwworm (Cochliomyia hominivorax) in the municipality of Ezequiel Montes, state of Querétaro. This episode, detected at the beginning of October 2025, highlights the constant threat that parasitic diseases represent for national livestock production and the effectiveness of the surveillance systems implemented.
The event originated during one of the routine zoosanitary inspections applied to a shipment of cattle originating in the south-southeast region of Mexico. An authorized responsible veterinary doctor, acting as the first inspection filter, observed a suspicious skin lesion on one of the specimens. After a thorough clinical examination, the presence of dipteran larvae was confirmed, constituting the only affected animal of a total of 67 head of cattle that made up the shipment. This specific discovery immediately activated Senasica’s rapid response machinery.
Protocol of Action and Epidemiological Control Measures
The notification triggered a phased and multifaceted response designed to eradicate the focus and prevent the spread of the pest. Immediately, specialized personnel from Senasica went to the site to carry out primary interventions. These consisted of the exhaustive healing of the wound of the infected bovine, the collection of biological samples for laboratory diagnosis and the application of prophylactic treatment with ivermectin to the rest of the animals in the flock. Ivermectin, a powerful broad-spectrum antiparasitic, is essential to eliminate any non-visible initial stage larvae and break the parasite’s life cycle.
In parallel, the Incursion Attention Protocol was activated, a standardized action plan that coordinates resources and defines tactical actions for situations of this type. As part of this strategy, Sader, under the direction of Julio Berdegué, mobilized four field brigades made up of twenty veterinary medicine professionals. The mission of these teams is to reinforce active epidemiological surveillance in the region, carrying out a sweep to rule out the presence of more cases.
Interinstitutional coordination was a key pillar in containment. Senasica worked hand in hand with the Government of the State of Querétaro and the State Committee for the Promotion and Protection of Livestock (CEFPPEQ). This collaboration made it possible to establish a well-defined health fence, delimiting an area of priority attention with a radius of forty kilometers around the initial outbreak. Within this area, retroactive epidemiological tracing operations are being carried out, clinical inspection of animals in neighboring herds and the systematic healing of any wound, no matter how minor, in livestock, since these constitute the preferred oviposition site for the screwworm fly.
The livestock screwworm is considered one of the most devastating pests for livestock. Unlike other flies, Cochliomyia hominivorax is an obligate parasite that deposits its eggs in the living tissue of warm-blooded animals, including humans. The larvae, upon hatching, feed on living flesh, causing deep tissue injuries, intense pain, loss of body condition, secondary infections and, in severe cases, the death of the animal. Its ability to spread is extremely fast, so early detection is the most effective tool to avoid catastrophic economic losses for producers.
Given this panorama, the authorities strongly call on livestock owners to maintain a state of permanent health alert. It is recommended to inspect the animals daily, pay special attention to any wound, no matter how small it may seem, and apply immediate cures using authorized insecticides. Immediate notification is a civic and productive responsibility. Any suspicion of the presence of this pest must be reported without delay through official channels: the free telephone number 800 751 2100, the WhatsApp messaging service at 55 3996 4462, or the email [email protected].
The prompt intervention in Querétaro demonstrates the solidity of Mexico’s health defense system. However, the battle against pests is continuous and requires the collaboration of all links in the production chain. Joint surveillance between authorities and ranchers is the most robust barrier against biological threats of this caliber.
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