The threat of New World screwworm (NWS) continues to plague cattle producers in Mexico. Eradicated from the continental U.S., this parasitic fly poses growing risks to livestock, wildlife and humans as its range has expanded moving northward in Mexico.
In November, NWS reappeared in Mexico, marking its first confirmed sighting since U.S. eradication efforts pushed it south in the 1970s. To protect the U.S., ruminant movement from Mexico was halted. In February, live ruminant imports briefly resumed under strict pre-clearance protocols.
However, the fly has now spread closer, approximately 700 miles from the U.S. border, effectively a trailer ride from southern border ports. On May 11, Secretary of Agriculture Brooke Rollins announced the suspension of live cattle, horse and bison imports from southern border ports into the U.S.
The NWS larvae infest open wounds and feed on live tissue, unlike other maggots that feed on dead tissue. Infected animals experience significant pain, swelling, foul odor and infection. If left untreated, the infestation can lead to severe tissue damage, and even death. A female fly typically lays eggs near open wounds, mucous membranes or body orifices.
In cattle, the primary risk of screwworm infestation comes from exposed tissue such as areas created during branding, tagging, dehorning or castration. Even minor injuries, such as a tick bite, and the umbilicus of newborns are vulnerable.
The NWS female fly only mates once in its lifetime. Control measures have historically focused on sterile insect technique by releasing sterile male flies. The USDA is evaluating and supporting control measures in collaboration with Mexico as the fly continues to move north. In the U.S., the USDA, state animal health officials and industry stakeholders are collaborating to develop educational materials and response plans in preparation for potential NWS outbreaks.
So, what can cattlemen and other animal owners do to prepare?
• Examine animals daily especially after processing.
• Build a relationship with a veterinarian and have a plan in place for communication and treatment if an animal shows signs of illness or disease.
• Utilize biosecurity protocols to limit animal movement and unnecessary exposure to disease.
• Stay alert of disease announcements in the operation’s area.
• Report clinical signs consistent with NWS to a veterinarian or the state veterinarian’s office. — Rosslyn Biggs, DVM, Oklahoma State University Extension beef cattle specialist
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