The threat of New World Screwworm, Cochliomyia hominivorax, continues to affect cattle producers in Mexico, said Dr. Roslyn Biggs, Oklahoma State University Extension beef cattle specialist, in a letter called Cow-Calf Corner.
Although eradicated from the continental US, this parasitic fly still poses serious risks to livestock, wildlife, pets and humans as its infestation front advances northward through Mexico, Biggs said.
US CASE ISOLATED
In August 2025, US public health authorities confirmed a human case of NWS in the US in a patient returning from El Salvador, she said. This case appears to be isolated with no further human or animal spread detected domestically.
In September, Mexico confirmed a detection of NWS less than 70 miles from the US border, Biggs said. The infected animal was an eight-month-old calf in a herd moved from southern Mexico.
The USDA continues to work closely with Mexican authorities supporting sterile fly releases across Mexico, she said.
Although risk to livestock and wildlife remains low, surveillance measures have been elevated across the southern border in Texas, Arizona and New Mexico, Biggs said1. Thousands of traps have been dispersed with more than 13,000 surveillance samples testing negative for NWS.
TREATMENMT OPTIONS EVALUATED
Treatment options also have been evaluated with the US Food and Drug Administration conditionally approving Dectomax-CA1 (doramectin) injectable solution for the prevention and treatment of NWS larval infestations and prevention of NWS reinfestation for 21 days in cattle only, she said.
To reduce the risk of parasite resistance development, producers and veterinarians have been encouraged to use antiparasitic drugs like Dectomax-CA1 only when medically necessary, in accordance with the product labeling, and as part of a strategic parasite management, Biggs said.
Producers and veterinarians were encouraged to remain vigilant by:
- Examining animals daily, especially after any handling or procedures.
- Cultivating a solid veterinary relationship and maintain a response plan for suspected cases.
- Observing biosecurity and minimizing unnecessary animal movement or exposure.
- Watching for local disease notices.
- Reporting any clinical signs consistent with NWS (lesions, maggots, odor, extreme irritation) to their veterinarian or state veterinarian.
This column reflects the latest information available as of Oct. 15, Biggs said. These are evolving situations. She encouraged animal owners to stay informed and to watch for news updates as new information becomes available.
Cattle futures were blasted last week with rumors the Mexican border might reopen to Mexican feeder cattle in the near future. However, this proved to be nothing more than wishful thinking on the part of US cattle traders.
Also, the US is not prepared with its own sterile fly facility yet to reduce the risk of infection.
CATTLE, BEEF RECAP
The USDA reported formula and contract base prices for live FOB steers and heifers this week ranged from $234.59 per cwt to $236.77, compared with last week’s range of $236.75 to $249.43 per cwt. FOB dressed steers and heifers went for $368.31 per cwt to $373.39, compared with $373.28 to $378.93.
The USDA choice cutout Tuesday was down $1.67 per cwt at $377.58 while select was up $1.32 at $361.25. The choice/select spread narrowed to $16.33 from $19.32 with 136 loads of fabricated product and 31 loads of trimmings and grinds sold into the spot market.
The USDA-listed the weighted average wholesale price for fresh 90% lean beef as $401.55 per cwt, and 50% beef was $159.45.
The USDA said basis bids for corn from feeders in the Southern Plains were unchanged at $1.05 to $1.20 a bushel over the Dec corn contract, which settled at $4.31 1/2, down $0.02 3/4.
The CME Feeder Cattle Index for the seven days ended Monday was $346.79 per cwt, up $3.46. This compares with Tuesday’s Nov contract settlement of $334.97, down $7.60.