THERE’S now been four confirmed cases of New World screwworm fly in livestock in the southern United States, following the first case detected in a calf in Texas a week ago.

The flesh-eating insect pest has been bearing down on the US in recent weeks, having spread rapidly across Mexico since 2024.

Over the weekend USDA reported a second case a few miles from the original detection, and overnight confirmed two more – one in a calf and the other, a dog – in west Texas, some 600km to the southeast of the first outbreak.

Since the first detection was made on 3 June, Canada has imposed a temporary ban on livestock movements out of Texas into Canada. The US itself had enforced bans on Mexican live cattle imports for the past 18 months, in an effort to keep the exotic inspect pest at bay.

Impact of the Canada ban on livestock is expected to be next to zero, commentators have said this week (see details below).

No trading partners have yet imposed any NWS-related restrictions on US beef or other red meat products, and the US Meat Export Federation reaffirmed its statement overnight that it did not expect any disruption for US red meat exports.

“The World Organisation for Animal Health code is clear that meat trade is not to be impacted (and presents no risk), but we continue to monitor the situation,” MEF said in a communication.

“There has been a fair amount of speculation in the US market as to the implications the arrival of NWS has both for US supply and demand,” Steiner Consulting said in commentary this week.

“The previous outbreak in the Florida Keys in 2016 took about a year to control. It is not known how NWS was introduced to Florida, but at the time USDA was able to control it by releasing sterile flies, something that it is currently doing in Texas,” Steiner said.

“However, the current situation is much more challenging. There are hundreds of miles (of Mexican/US border) that present significant transmission risk, while in the case of Florida, the outbreak happened along a narrow chain of islands linked by a single road. It made it far easier to control,” Steiner said.

While the US had suspended cattle trade out of Texas to control the spread, it would be difficult to control the movement of wildlife over very difficult terrain, it said.

There has been a steady increase in the number of NWS cases reported in Mexico, in part because the US has shifted sterile fly production and distribution resources closer to the US border.

“The inability to control the infestation in Mexico will make the control of this latest infestation significantly more difficult, and may last much longer than what the market appreciates,” Steiner said.

“For the moment demand risk is limited, although if the infestation spreads, it is hard to know the response from the US public, in the age of social media,” it said.

Should the infestation spread, there will be negative cattle supply impacts both due to livestock losses but also due to the restrictions put in place.

Getting on with reality

Respected Oklahoma State University extension leader Derrell Peel said for many months US producers and markets had operated under the threat of NWS coming into the US.

“Now that it’s here, we can get on with the reality of dealing with it,” he said.

Derrell Peel

“The bad news is that NWS will be costly and a management headache for affected producers and those nearby, along with industry and agency folks tasked with controlling and eradicating the pest. Time spent planning and anticipating an outbreak now shifts to actions,” he said.

“The psychological impact has been mostly one of relief, especially in futures markets.  The arrival of NWS has been one of many sources of uncertainty hanging over US cattle markets for months.  Confirmation of NWS in the country removes one source of uncertainty and allows the market to focus on the reality, which has largely been priced into the market,” Dr Peel said.

The ‘good’ news in all this was that NWS was not a broader market issue, he said.

“NWS will affect relatively few animals and is not something that will affect the cattle supply or beef production. It also is not a food safety issue and there are no impacts on meat.  Beef market supply and demand fundamentals are not affected and no significant market impacts are anticipated,” Dr Peel said.

Additionally, no major trade impacts were warranted or expected relative to NWS, he said.

“However, the reaction of trade partners is unpredictable. Canada’s temporary ban on livestock from Texas, is seen as a largely symbolic political move, as it will affect a very small volume of trade. Although there is significant bilateral cattle trade between Canada and the US, very few Texas cattle are typically involved. Canada is well north of the climate boundary for NWS and the threat is minimal.”

Another part of the uncertainty about NWS was the continued closure of the Mexican border, Dr Peel said.

“It is uncertain if the fact of NWS in the US will change political decisions regarding the status of border. The market will continue to wait for news about when the border might open,” he said.

“Once again, the impacts are more related to the uncertainty than the reality.  When it happens, opening the border will likely be a deliberate and relatively slow process.  Over time, Mexican cattle flows into the US may rebuild with marginal impacts on feeder cattle supplies in the country but no immediate disruptive shocks to cattle markets are anticipated.”

Like most disasters, the impacts of NWS on the US would be primarily local, Dr Peel said.

“It will take significant efforts and dollars to ensure a perimeter around the outbreak and effective animal movement controls to contain the pest along with diligent monitoring and treatment of any affected animals. It is uncertain at this point how large of a region might be involved in this outbreak, but no major cattle or beef market impacts are anticipated.”