A deadly fly is spreading through Central America. Experts blame illegal cattle ranching

An outbreak of screwworm — a fly that infects the open wounds of warm-blooded animals — is the direct result of cattle smuggling through protected areas across Central America, conservation groups said.The fly appeared in Panama last year and quickly traveled north to Guatemala. Now, officials are concerned it will spread uncontrollably into Mexico and the US.Eradicating the fly could cost millions of dollars and prove disastrous for agribusiness and countries that rely on beef exports.Conservation groups are arguing for border shutdowns and increased regulation of the cattle industry, especially around protected areas where smuggling routes have cleared forests.

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MEXICO CITY — Illegal cattle ranching in Central America has led to the spread of a deadly parasite long thought to be eradicated, and conservationists are calling for tighter controls before it reaches Mexico and the US.

An outbreak of new world screwworm (Cochliomyia hominivorax) — a fly that infects warm-blooded animals — is the direct result of cattle smuggling through protected areas across Central America, conservationists said. Unregulated movement of livestock has accelerated transmission, and could cost the region millions of dollars if officials don’t act soon.

“The screwworm outbreak highlights an urgent need for tighter regulation in the cattle trade across Mesoamerica, as the unchecked movement of illegal cattle exacerbates both environmental and health issues,” said Chris Jordan, Latin America Director for Re:wild, a conservation group. “…Tackling this requires cooperation from companies, industry leaders and governments, who must step up to prevent contraband cattle from crossing borders unchecked.”

New world screwworms lay their eggs in the open wounds of cattle and other animals, with the resulting larva feeding on live flesh until the host dies. It can be disastrous for agribusiness and countries relying on beef exports.

A joint US campaign in the 1980s and 90s helped eradicate screwworm from Central America and Mexico. But last year, the fly reappeared unexpectedly, this time in Panama. Experts believe it traveled from South America through the thick jungles of the Darien Gap, which had previously kept the parasite at bay for nearly thirty years.

Experts still don’t know if the fly made it through the Darien Gap via cattle or another warm-blooded animal.

It spread to Costa Rica this year and then exploded in Nicaragua before moving quickly into Honduras and Guatemala, according to researchers at the National Autonomous University of Mexico, who are tracking the outbreak. Now, there’s a chance that it could cross the border into Mexico, where it would be nearly impossible to stop.

“The consequences of this plague would be catastrophic, affecting productivity and international markets,” the National Confederation of Livestock Organizations said in a letter to Mexican officials this month. “The economy of the livestock sector would be devastated.”

Predicted routes for screwworm spread, with confirmed sites in blue. Image courtesy of WCS.

There’s a strong correlation between the spread of the fly and cattle smuggling routes, many of which cross through protected areas, according to WCS. Maps of deforestation from illegal cattle ranching overlap with many of the worst outbreak sites.

WCS and other conservation groups are hoping the economic threat of the fly will lead to stricter regulations for the cattle ranching industry, which will result in better conservation of protected areas.

“What we see is a kind of win-win where if we can stop illegal cattle ranching, then we can save wildlife, save local and national economies, save the livestock sector and save human health,” said Jeremy Radachowsky, WCS Director for Mesoamerica and the Caribbean.

Drug traffickers and other organized crime groups in Central America rely on illegal cattle ranching to launder money. They clear protected forests in unpopulated areas so the cattle can graze, then mix them with legal herds that have undergone pest treatment and other health checks.

Because cattle are so often tied to organized crime, officials trying to avoid trouble tend to let transport trucks cross the border without checking their documentation.

One of the hardest-hit areas in the region is the Bosawás Biosphere Reserve in northern Nicaragua, where an influx of non-Indigenous squatters, known as colonos, displace native communities while setting up their cattle ranches. The herds move between several intermediary buyers before arriving to slaughterhouses with false ear tags, making it impossible to know where they came from.

The screwworm is now present in at least seven of Nicaragua’s departments, according to the World Organization of Animal Health (WOAI), which confirmed the cause was the illegal movement of animals.

“As long as that flow of illegal cattle keeps coming from Nicaragua…then [the screwworm] is just going to keep reinfecting,” said Radachowsky.

On the other side of the border, cattle ranching has devastated Honduran protected areas like Patuca National Park and Río Plátano Biosphere Reserve, which lost around 13% of its primary forest cover between 2002 and 2020, according to Global Forest Watch. In September and October, WOAI registered screworm cases in the national park and other border areas farther south.

The fly has also affected domesticated animals like cats, dogs and horses, as well as vulnerable wildlife like three-toed (fam. Bradypodidae) and two-toed sloths (Choloepus spp.), porcupines (Erethizontidae), deer, tapirs and howler monkeys (gen. Alouatta), according to Costa Rica’s National Food Safety and Quality Service. But it’s almost impossible to track how much the fly is affecting wild populations.

A vet works on an infected tapir in Costa Rica. Image by Jorge Rojas.

“There are going to be a lot of affected wild animals,” said Dr. Jorge Rojas-Jiménez, a wildlife veterinarian specializing in tapirs in Costa Rica. “The problem is that we’re only seeing the animals that arrive at rescue centers, or when people find them. We really can’t know for sure what the total impact will be.”

Now that the screwworm has entered Guatemala, officials are concerned it might reach the Maya Biosphere Reserve on the country’s northern border with Mexico. The reserve has suffered from a “lack of governance,” according to multiple environmental NGOs, with out-of-control forest fires decimating thousands of hectares of rainforest at the hands of illegal cattle ranchers.

There are believed to be 50,000 illegal cattle in the country, according to the National Council for Protected Areas.

To stop the fly from entering Mexico and the US, governments will release sterile males into the air to stifle reproduction. But conservation groups are also lobbying them to stop the problem at its source, increasing restrictions on illegal cattle ranching and closing the border. In the long run, that could be what helps save multiple protected areas.

“If we were to eliminate some of that [cattle] demand, it would have a trickle-down effect all the way into the forest that we care about the most,” Radachowsky said.

Banner image: Cattle graze on deforested land in northern Guatemala. Image by Rhett A. Butler.

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