First Human Screwworm Case Confirmed in Mexico City
Mexico City has documented its first human case of myiasis caused by Cochliomyia hominivorax, commonly known as screwworm, according to the General Directorate of Epidemiology (DGE) of the Ministry of Health. The initial case in the capital was recorded during the first week of May.
Nationally, a total of 235 human cases of myiasis have been accumulated as of May 22, 2026. This represents a substantial increase of 118 cases compared to the entire year of 2025, which saw 117 reported cases.
Geographic Distribution of Cases
As of week 19, Veracruz leads the country with 58 human screwworm cases, followed by Chiapas with 41, Guerrero with 23, and both Oaxaca and Yucatán each reporting 22 cases. Other affected states include Puebla (19), Quintana Roo (9), Hidalgo and San Luis Potosí (8 each), Tabasco (7), Campeche (6), State of Mexico (4), Michoacán and Querétaro (2 each), and Jalisco, Morelos, and Tamaulipas (1 each).
Notably, states such as Guerrero, Hidalgo, Jalisco, State of Mexico, Michoacán, Morelos, Puebla, Querétaro, San Luis Potosí, Tamaulipas, and Mexico City had no human cases reported in 2025. This year, the infestation has also extended to domestic animals, with 15 cases reported in dogs within four months.
Animal Cases Also on the Rise
A report from the World Organisation for Animal Health (OMSA) on screwworm foci in Mexico and Central America indicates that from January 1 to May 5, 2026, Mexico confirmed 154 cases in animals. These include cattle (119), horses (7), pigs (7), sheep (4), and antelopes (2). OMSA also identified 8,113 animals susceptible to this pest.
Health Authorities Urge Prevention
In response to these figures, the Ministry of Health has called on the public to strengthen preventive measures against myiasis. Emphasizing proper care for any skin lesions, the ministry advises immediately washing and disinfecting cuts, scrapes, or even insect bites with soap and water, and keeping them covered with sterile gauze or bandages until they heal. This is crucial as flies are attracted to open wounds for egg-laying.
“Maintaining good personal hygiene is also key to reducing risks, especially for children, the elderly, individuals with limited mobility, vulnerable populations, and those in frequent contact with animals,” stated the agency.
Additional recommendations include wearing protective clothing, such as long sleeves and pants, during outdoor activities or near animals, and using approved repellents on skin and clothing to deter flies.
Pet Care and Warning Signs
For pets, constant vigilance is recommended. Owners should regularly inspect areas like ears, paws, tail, snout, and fur for any wounds, irritations, or skin lesions. If any are found, it is important to clean and protect them, and to seek immediate veterinary attention. Pet owners are also advised to prevent their animals from licking or scratching affected areas, as this can worsen the injury.
Immediate medical or veterinary attention is crucial if signs such as the presence of maggots in wounds, foul odor, severe inflammation, tissue damage, pain, irritation, or non-healing lesions are observed.
For suspected cases of screwworm myiasis, the public can contact the following numbers: 800 751 2100 or 079 (55) 5337-1845 (Epidemiological and Sanitary Intelligence Unit, UIES).
Understanding Cochliomyia Hominivorax
According to the DGE, Cochliomyia hominivorax is a fly exclusive to the American continent. Its larvae are obligate parasites capable of invading the tissues of any live warm-blooded animal, including humans, causing myiasis. The common name, “screwworm,” refers to the feeding behavior of the larvae, which bore or “screw” into healthy tissues.
Infestation occurs when the female fly lays its eggs in open wounds or natural orifices (nose, ears, eyes, genitals). Even minor skin lesions, such as insect bites, can serve as oviposition sites.
Clinical Picture and Diagnosis
The monthly report on the current situation of C. Hominivorax myiasis in humans indicates that the clinical picture is characterized by intense pain, a sensation of movement in the lesion, serosanguineous discharge, and a foul odor. Progressive tissue destruction, local inflammation, and, in advanced cases, involvement of deep structures may be observed.
Diagnosis of myiasis is primarily clinical, based on direct observation of larvae in the lesion, supported by physical examination (including otoscopy or other studies depending on the location). Confirmation is made through taxonomic identification of the parasite.
In case of a suspected case, biological samples must be collected, preserved, and sent to the corresponding State Public Health Laboratory, in accordance with the Standardized Procedures Manual for the Epidemiological Surveillance of human C. hominivorax myiasis.
Treatment involves the complete mechanical extraction of larvae, wound cleaning, and debridement. Agents that facilitate larval expulsion (occlusion or topical substances) may be used. Antibiotics are administered if a secondary infection is present.
