By Michael Hsu
Earlier this fall, the New World screwworm – the flesh-burrowing larva of a blowfly (Cochliomyia hominivorax) – was detected in cattle in Mexico just 70 miles from the U.S. border. Most recently, in late November, another case was confirmed in Nuevo León, a state of Mexico adjacent to Texas.
While the screwworm is not currently present in the U.S., Mexico and Central American countries have been reeling due to the resurgent parasite. There have been more than 140,000 cases in animals and over 1,000 in humans during this outbreak dating to 2023 – and the cases continue to track northward.
Members of the California agriculture community are just as worried as their counterparts in Texas, where an outbreak could cost livestock producers $732 million per year and cause up to $1.8 billion in losses for the Texas economy, according to U.S. Department of Agriculture estimates.
Among California’s top gross-value commodities in 2024, dairy products/milk are number one ($8.61 billion) and cattle and calves are number four ($4.98 billion) – both categories that could be most affected by the screwworm.
“Controlling for and preventing impact from the New World screwworm are the majority of the questions I’m receiving now,” said Brooke Latack, University of California Cooperative Extension livestock advisor for Imperial, Riverside and San Bernardino counties. Imperial County, adjacent to Mexico, houses about 329,000 head of cattle.
“There is definitely concern about the screwworm down here for producers, industry members and the veterinarians that serve the area,” Latack said.
For dairy, the risk is especially severe, as even small disruptions can lead to major financial losses, said Daniela Bruno, UCCE dairy advisor for Fresno, Madera and Kings counties.
“Unlike beef cattle, which can be held back from market during a quarantine, dairy cows produce milk every day that must be processed immediately – if a farm is quarantined or a plant shuts down, milk spoils quickly and has to be dumped,” Bruno explained.
She said that producers should look into diversifying processing options, reviewing their insurance coverage and bolstering biosecurity against threats like screwworm and avian flu, which has reemerged in California dairies.
Burrowing fly larvae cause ‘horror movie’ damage to animals
It’s not just the economic impact that is particularly unnerving about New World screwworm. While mortality rates vary based on the species and other factors, it can be up to 100% in newborn calves.
“It can affect and kill any warm-blooded animal – any bird, any mammal, including humans,” said Gaby Maier, Cooperative Extension specialist for beef cattle herd health and production at the UC Davis School of Veterinary Medicine. “But we are particularly concerned about our cattle here.”
Maier pointed to recent data from the outbreak in Panama, which indicated that 83% of screwworm cases were in bovines, with all other animals trailing far behind (human cases are relatively rare).
Source : ucanr.edu