Conservationists monitoring illegal cattle movement in Central American forests have discovered a disturbing trend: wildlife, including jaguars, pumas, and tapirs, are rapidly becoming infected with the new world screwworm. This parasitic fly, which has already been detected in 34 animals in the US—mostly in Texas, with one in New Mexico—is now endemic in wildlife far from cattle infestations, according to a study by the Wildlife Conservation Society (WCS).
Endemic Presence in Wildlife
Camera traps set up by the WCS captured images of various mammals with unmistakable wounds caused by the screwworm. The infected animals shared water sources with cattle moved across national borders without health checks. Jeremy Radachowsky, director of the Mesoamerica and Caribbean program at WCS, stated, "We see infestations in the deepest parts of the interiors of the forest, so now it’s become endemic in wildlife, far from the cattle infestations."
Current Eradication Efforts Insufficient
The US is currently dropping 100 million sterile flies in the south-west and Mexico to slow the fly's northward movement, but experts say this is insufficient for eradication. Phillip Kaufman, professor and head of entomology at Texas A&M University, explained, "What we lack are sufficient flies in order to start pushing the population back south." To eradicate the pest, approximately 500 million sterile flies would be needed. New facilities in Mexico and Texas are being built to expand breeding capacity, but they will not be operational until late 2026 and 2027, respectively.
Innovations and Root Causes
Potential innovations include raising only sterile male flies and designing better bait traps. However, Kaufman cautioned, "We have to have things that work. We can’t stop doing things we know work in order to try things that don’t have any data to support." Radachowsky emphasized that efforts have focused on the fly itself rather than addressing the root cause: illegal cattle trafficking. "If you’re only using sterile fly technique and you have other factors that are moving beyond your efforts to blanket those areas with sterile flies, you’re never going to have the capacity to clear huge areas," he said.
Historical Context and New Challenges
The screwworm was eradicated from the US in 1966, but the situation has changed dramatically. Radachowsky noted, "In the 60s, when we first eradicated screwworm, we didn’t have this high density of cattle like we do now. The human population and cattle population is just incredibly different from what it was back then, and the [illicit] cattle movements didn’t exist before." The fly re-entered Mexico in 2022 and spread rapidly northward through Central America, moving thousands of kilometers in only four or five months along illegal cattle-trafficking routes.
Research Limitations and Future Risks
In the US, the screwworm is considered a foreign animal disease pest, restricting research. Kaufman said, "We were not permitted to have the fly in research facilities in the US for the last 50 years, because it’s such a dangerous organism." Scientists are only now beginning to study attractants for bait traps through USDA grants. Conservationists are extremely worried about the potential for infectious disease transmission beyond screwworm, including tuberculosis, brucellosis, and hoof and mouth disease. Radachowsky warned, "It frightens me that we’re not learning the main lesson here. More disease monitoring is needed to examine wildlife populations in the Americas."
