The cattle screwworm: Chiapas leads the way in Mexico

The cattle screwworm , scientifically known as Cochliomyia hominivorax , has become a serious threat to animal health in Mexico. According to a recent bulletin issued by the United States-Mexico Commission for the Prevention of Foot-and-Mouth Disease (CPA), Chiapas is the state with the most registered cases , accounting for more than 60% of the reports nationwide.

This parasite is a fly larva that infests living tissue , causing deep, painful lesions, mainly in the navel of newborn animals , although it also affects other wounds. The infestation, known as myiasis , can cause serious infections, weight loss, decreased milk or meat production, and even death if not treated promptly.

At the economic level, the impact is considerable: it affects small and medium-sized livestock farmers , compromises food security, and requires the allocation of more resources to veterinary treatments and health surveillance.

Between November 2024 and July 2025 , 3,324 cases of screwworm were confirmed nationwide. Of these, 2,074 were in Chiapas , distributed across 88 municipalities. The most affected areas include:

• Ocosingo : 236 cases
• Pijijiapan : 140
• Tonalá : 130
• Meritorious of the Americas : 117
• Marquis of Comillas : 80

These data reveal that the Chiapas jungle and rural regions with high livestock activity are the most vulnerable.

After Chiapas, Tabasco is the state with the second highest number of cases, with 567 reported in 17 municipalities. Balancán stands out as the most critical area, with 317 infections, followed by Macuspana (45) and Tenosique (41).

Campeche , for its part, occupies third place with 313 cases . Municipalities such as Candelaria (90) , Kalakmul (66) and El Carmen (53) concentrate the majority of the reports.

The CPA bulletin also details the most common types of lesions associated with screwworms. Of the 4,123 cases of myiasis reported between January 2024 and July 2025, larvae were found in:

• Navel of newborns : 1,308 cases
• Traumatic wounds : 920
• Dehorning : 224
• Areted : 186
• Vulva : 161
• Barbed wire injuries : 111

In addition, wound infections from papillomatosis, castration, dermatitis, ulcers , and bat bites were documented.

Although most cases are in cattle (2,738) , the plague has also been detected in dogs (207), horses (173), pigs (129), sheep (61), goats, cats, poultry and even a wild bird . This host diversity amplifies the challenge for sanitary control and underlines the need for integrated regional measures.

Senasica and other authorities are working on screwworm monitoring and control campaigns, especially in rural areas. Some strategies include:

• Training livestock farmers to identify early signs of infestation
• Application of larvicides and immediate wound healing
• Immediate notification of suspected cases to health authorities
• Coordination between states, municipalities and the federation to address outbreaks

Prevention is key. It's recommended to regularly inspect animals , especially after births, castrations, or fights, and apply disinfectant to any open wounds.

The spread of the screwworm in Mexico represents a serious threat to animal health and the economy of livestock-raising regions. Chiapas , as the state with the highest incidence, requires priority attention, but the fight against this pest must be national and ongoing. The active participation of producers, veterinarians, and authorities is essential to halt its spread and protect both livestock and the livelihoods of thousands of rural families.