Mexico - September 2026

On 24 August the US government led by President Donald Trump partly reopened its border to livestock imports from Mexico after closing it due to concerns over the spread of the New World Screwworm (NWS) fly. However, difficulties in eradicating the flesh-eating parasite mean that the risk of new restrictions remains high.

NWS is a fly whose larvae cause serious infections in livestock and other animals by burrowing into their flesh. It had been eradicated from the US and Mexico following concerted international efforts in recent decades, but in November 2024 it was detected in Chiapas state in southern Mexico after spreading north through Central America. The US closed its border to livestock imports in response and subsequently lifted and reimposed restrictions several times as NWS flies moved progressively closer to the US, before closing the border to Mexican cattle again in July 2025. 

This has had a devastating effect on Mexico’s livestock sector. National daily La Jornada reported in July that the Consejo Mexicano de la Carne, a meat business association, had calculated that from November 2024 to June 2026 around 2.06m cattle slated for export, worth around M$34.82bn (US$2.06bn), went unsold because of the restrictions. From January-June this year some 748,000 animals intended for export were stuck in Mexico, worth a total of US$1.04bn, according to the same figures.

Rogelio Pérez Sánchez, director of strategy and international relations at the Confederación Nacional de Organizaciones Ganaderas (CNOG) livestock business association, added that the sector had also suffered an opportunity cost of US$2.5bn. “There was a negative impact on farmers because there was no incentive to expand their herds due to expectations of low prices,” he said, indicating that, in the face of uncertainty around export markets, producers decided to delay investments.

Given these difficulties, it is no surprise that Mexico’s livestock sector rejoiced in late July this year when the US Department of Agriculture (USDA) announced a phased reopening of the border from 24 August. Starting with the crossing between Agua Prieta, Sonora state, and Douglas, Arizona, the reopening is being “guided by overlapping safeguards and a science-based import protocol jointly agreed upon between the United States and Mexico,” according to a USDA statement. There were some teething troubles, with exports suspended again on 28 August as the inspection chute couldn’t handle larger animals, but the crossing reportedly reopened on 8 September. Further reopenings at the Santa Teresa and Columbus crossings with Chihuahua state will depend on “Mexico’s progress in meeting Action Plan milestones and addressing critical issues,” as well as the level of risk of NWS in Sonora or Chihuahua states, the USDA added.

As of 8 September, there were 2,083 active confirmed cases of NWS in Mexico, and 30 out of 31 of the country’s states had recorded cases of NWS. A rising caseload in the border state of Sonora was a particular cause for concern as it has been singled out by USDA for monitoring, with 39 active NWS cases in the state as of 8 September. The fact that NWS has also established a foothold in the US is a further worry, with dozens of confirmed cases in Texas and New Mexico this year, as it will make eradicating the fly once again a more difficult prospect.

Eradication efforts centre on the sterile insect technique (SIT), in which specially bred sterile flies are released in their millions to outcompete wild males and suppress successful reproduction, meaning that populations fall and ultimately die out. The issue is that an estimated 500m sterile flies per week will be needed to eradicate NWS over a vast area across North and Central America, and there are only two facilities currently producing them. The first, in Panama, can make 100m sterile flies a week, with a second plant in Chiapas state also ramping up production to an expected 100m per week by the end of the year. This means that the number of sterile flies available to be released is far short of what is needed. A planned US domestic facility is expected to start producing flies in late 2027, ramping up to 300m per week by 2028, which will make the 500m target achievable, but if the fly continues to spread to new areas before the US facility reaches maximum capacity, it is likely that even more sterile males will be needed to eradicate it.

As a result, there is no guarantee that the fly will be eradicated, and if it is, it is likely to take years to do so. It took decades to push NWS out of North and Central America during the 20^th century, and any residual populations are likely to result in a renewed spread northwards. Eradication efforts may need to extend even further south this time around, with a US congressional report from August raising the possibility that the Darién Gap, a densely forested strip of land between Panama and Colombia, would no longer act as a biological barrier to NWS as the cattle population there has boomed in recent years. Some scientific research has even suggested that sterile males are becoming less effective at competing with wild males for mates, according to the report. This would call into question the future viability of the strategy if it is proven that natural populations are increasingly able to mate despite the presence of sterile male flies.

Of course, it may be that successfully managing caseloads in Mexico’s northern states is sufficient to convince US officials to fully reopen the border to livestock imports, so NWS may not have to be completely eradicated from the country to allow livestock exports to continue. However, the thresholds governing when livestock exports can resume are being set by the US, potentially handing Washington even more leverage over Mexico at a time when the two nations are continuing to renegotiate the US-Mexico-Canada Agreement (USMCA) trade deal [EB-26-08].

This increases the likelihood that livestock exports will become caught up in wider bilateral discussions, exposing Mexico’s livestock producers to continued risk that exports will be halted once again, although so far there is no suggestion that the import restrictions are motivated by politics rather than USDA’s technical assessments of the threat to the US livestock sector. Although President Claudia Sheinbaum has pointed out that Mexican cattle previously destined for export have simply been redirected to the domestic market, livestock farmers earn around US$300 less for each head of cattle sold in Mexico than in the US, according to Mexico-based agrifood consultancy Grupo Consultor de Mercados Agrícolas (GCMA), meaning that the economic impact is reduced not eliminated.

In conclusion, the phased reopening of the US border to livestock exports from Mexico is encouraging for the livestock sector, but it appears highly likely that the number of animals sold to US buyers will remain lower than pre-NWS levels for the foreseeable future. This could be due to difficulties in reducing caseloads sufficiently to satisfy US officials, shortfalls in the production of sterile flies, or political pressure to use livestock imports as leverage in wider trade negotiations. Other risks include the trafficking of unmonitored cattle from Central America, which will increase the risk of outbreaks in southern Mexico, as well as climate change, which is making it easier for the flies to move into new geographical areas where they previously could not reproduce. As a result, the sector is likely to continue to face headwinds in the coming months and years.