CDFA Working to Protect California from New World Screwworm

The U.S. Department of Health and Human Services recently reported a travel-associated human case of New World Screwworm (NWS), the first of its kind in the US, following an infected person recently returning from an outbreak-affected country. According to the USDA, human risk is low, and the agency adds that there have been no detections in American livestock.

While there is no evidence to suggest that the fly that produces screwworm larvae has made it to the U.S., the northward spread of NWS through Central America and deep into Mexico over the past year, and the potential threat it poses to California's animal agriculture, has mobilized CDFA to take proactive measures.

What animal health concern does NWS pose?

Screwworm larvae consume the living flesh of warm-blooded animals. A female fly can lay 200 to 300 eggs at a time on an open wound or a body orifice, and in its 10- to 30-day lifespan can lay up to 3,000 eggs. Once hatched, the larvae burrow into the flesh, causing a painful infestation known as myiasis. If left untreated, the infestation can be fatal to the host due to secondary infections or toxicity.

CDFA's 'One Team' approach

CDFA is coordinating with partners to address the threat. For several months, the agency has been actively working with other border states, the United States Department of Agriculture (USDA), and private veterinarians to achieve the best prevention, detection, and response practices. We are collaborating with key California agencies like the California Department of Fish and Wildlife (CDFW), the California Department of Public Health (CDPH), Cal EPA, and the Governor's Office of Emergency Services to develop NWS protocols for a comprehensive emergency response plans. Just this week, CDFA hosted a planning exercise with federal and state partners to clarify roles in case of a screwworm introduction in the US.

We are developing protocols for critical response approaches like fly traps, insecticide use, sterile fly production techniques, alternative animal-carcass disposal methods, and animal movement control. This early coordination is designed to ensure that response efforts align and complement each other.

To minimize the devastating impact of these fly larvae and to ensure animals recover, swift and accurate reporting is a must. CDFA urges private practitioners, producers, and hobbyists to report any suspected NWS findings to a CDFA district office or the sick animal hotline. Suspected or known NWS is considered a foreign animal disease and must be reported to state or federal animal health officials within 24 hours of discovery for further evaluation. Upon diagnosis, CDFA will work with the producer to quarantine the premises and the infested animal, to prevent further spread. The quarantined animal will receive daily care and treatment until the larvae are eliminated.