Arizona agriculture officials say cattle imported from Mexico will undergo multiple layers of inspections as the state works with federal partners to prevent the spread of the New World screwworm, a destructive livestock pest that has prompted heightened border surveillance and plans for a new sterile fly distribution facility in southern Arizona.
Ryan Wolker, State Veterinarian with the Arizona Department of Agriculture, said the process for importing cattle has remained largely consistent with previous reopening periods following the detection of New World screwworm in Mexico, but Arizona has added another inspection after cattle cross into the United States.
Before cattle are allowed to enter the United States, each shipment undergoes three inspections on the Mexican side of the border, Wolker said.
The process begins with a veterinarian approved by Mexico's national animal health authority, who examines the animals, administers an approved antiparasitic treatment and verifies the required documentation before the cattle move to a border pre-inspection facility.
There, a second Mexican government veterinarian performs another inspection before the cattle are transferred to a U.S. Department of Agriculture Animal and Plant Health Inspection Service facility, which is also located on the Mexican side of the border. USDA veterinarians conduct a third inspection, looking for wounds or signs of infestation that could indicate the presence of New World screwworm larvae.
If no concerns are identified, the cattle are treated with an organophosphate solution designed to eliminate ticks and other parasites before they are cleared to cross into the United States.
"There are essentially three sets of eyes on the Mexican side of the border before these animals are ever even crossed into the United States," Wolker said.
Once cattle enter Arizona, state officials conduct an additional inspection. Livestock inspectors with the Arizona Department of Agriculture verify documentation after the cattle are resorted, record each animal's electronic identification tag, and ensure a USDA-accredited veterinarian completes paperwork for transportation to destinations throughout the country.
The added inspection brings the total to four separate reviews before cattle continue through the U.S. livestock system.
Despite increased concern over the pest, Wolker said Arizona has not detected New World screwworm within the state.
The department has submitted more than 1,200 fly trap samples for foreign animal disease testing and continues responding to reports of maggots found on livestock and other animals. Those investigations have consistently identified other species that cause myiasis rather than New World screwworm, he said.
While surveillance continues, Arizona is also preparing for a long-term strategy centered on the sterile insect technique, which federal officials previously used to eliminate New World screwworm from the United States and much of Central America.
A planned facility near Douglas will not produce sterile flies but instead will serve as a distribution hub, Wolker said. The insects will continue to be produced at an existing facility in Edinburg, Texas, before being transported to Arizona for release across the Southwest.
Distribution centers are necessary because sterile flies can only be transported about 400 miles once they reach a certain stage of development before their effectiveness begins to decline, Wolker said. The Douglas facility would primarily support Arizona, California and New Mexico.
Millions of sterile flies can be released by aircraft or from strategically placed ground dispersal stations. The approach relies on the biology of the New World screwworm, whose females typically mate only once during their lifetime. By releasing large numbers of sterile male flies, officials aim to prevent reproduction and interrupt the insect's life cycle.
"You basically stop the life cycle," Wolker said.
The sterile insect technique was widely used during eradication campaigns in the 1960s and 1970s that pushed the pest south through Latin America to Panama, where sterile fly releases continue today to maintain a biological barrier.
Wolker said future improvements could make the program even more effective. The USDA's Agricultural Research Service is working to advance a technology known as NovaFly, which is designed to produce only sterile male flies for release.
Historically, sterile fly production yielded roughly equal numbers of males and females, but the newer system would allow all released insects to be sterile males, increasing the efficiency of eradication efforts.
There's no set date for the completion of the Douglas-area distribution facility, which is expected to operate from Bisbee Douglas International Airport, Wolker said.
In the meantime, state officials are encouraging ranchers, livestock producers and pet owners to remain vigilant by closely monitoring animals for wounds or unusual maggot infestations and reporting suspected cases immediately.
"The most important tool that ranchers and producers and pet owners have at their disposal is their eyes," Wolker said, adding that early detection will be critical to preventing the pest from becoming established in Arizona.
