The fight to regain control over the screwworm after breaking the barrier that held it back in Panama
Moncho Torres
Metetí (Panama), Aug 5 (EFE).- Since the beginning of this century, a biological barrier had been established in the Darién rainforest, the natural border between Panama and Colombia, against the screwworm—which can cause serious injuries to warm-blooded animals—impeding its spread from South America. However, a combination of factors caused it to penetrate northward, and now the fight is underway on several fronts to regain control.
Known scientifically as Cochliomyia hominivorax , or the "man-eating screw fly," this insect seeks out warm-blooded animals with open wounds and lays its eggs there. Upon hatching, its larvae, or maggots, begin feeding on the tissue. If left untreated, it can cause severe wounds, loss of function of the infected organ, and even death, especially if it attacks newborns.
Although it can affect humans and dogs, it is generally cattle that are most affected by this pest, because they are large animals and the extensive livestock farming model in Central America and Mexico, in which animals are left to graze for days without much attention, is more likely to cause any wound to become infected by the screwworm without being treated in time.
"The animal suffers a lot because it's something that eats away at its flesh. And the animal loses weight, it doesn't eat... a lot of problems, a lot of worms, too many," Nelson Moreno, who has been in charge of a cattle farm in the Darién province for 27 years, told EFE.
Accompanied by dozens of cattle, Moreno explains that it is necessary to monitor the livestock "every day" because in a week the screwworm "eats the meat and kills them," or "they lose an ear, they lose a leg."
A fight that began in the 1950sThe Panama-United States Commission for the Eradication and Prevention of Screwworms in Livestock (COPEG) details on its website how the program against this pest, endemic to much of the continent, began in the U.S. in the 1950s as a response by ranchers to reduce the constant losses caused by this larva, from which it was declared free in 1966.
In addition to raising awareness among farmers, a key element in the process was the implementation of the sterile insect technique, which involves mass breeding and sterilizing screwworm flies through radiation. When millions of them are then released into areas affected by the pest, they mate with wild females without producing offspring, drastically reducing the insect population.
After the United States, this plan continued its successful expansion throughout Central America, and in 1994, COPEG was created in Panama. In 2006, the country was declared free of screwworms, with the exception of the Darien province. This border became the last permanent biological barrier against the pest, preventing its spread northward.
That same year, a plant with the capacity to produce 100 million sterile insects per week was opened in Panama, becoming the only one operating after two others in the United States and Mexico closed or changed operations.
Until January 2023, when the screwworm emergency situation in Panama was reactivated, triggering an unstoppable northward advance: first in Costa Rica, then spreading to the rest of the countries until reaching Mexico.
A battle against millions"We dispersed the few screwworm populations that remained in Darién province and neutralized them. But we reached a point where the cycles got out of control," Dr. Carlos Moreno, general director for Panama of COPEG, one of the leading experts on the subject, told EFE.
Thus, he continues, "it's not the same as having, for example, 10 of your soldiers go into battle against 100. Perhaps those 10 against 100 with a good strategy will do it, but it's not the same as your 10 going into battle against an enemy of millions. That doesn't do it, no matter how much strategy there is, so that's what happened."
Dr. Moreno believes the resurgence of the pest in the region was due to several factors, such as the impact of the pandemic, which affected health monitoring and control systems, and climate change, with a 2-3 degree temperature increase that has created optimal conditions for the pest to establish and thrive.
There is also a lack of awareness among some livestock producers, because "unfortunately, an entire generation—almost 15, 20, or 30 years of producers in these countries—had forgotten what screwworm looked like, what it caused, what it did, and what they could do to control and mitigate the risk" of the disease, in addition to "the introduction of contaminated or infected animals across borders without any type of verification control."
"Fortunately, producers in my country have already understood that something needs to be done. So we've returned to all the suppression strategies, which are education, awareness, and action. We shouldn't wait for the Holy Spirit to come down and solve the problem, but rather take direct action," says Dr. Moreno.
On the other hand, while the plants in the United States and Mexico, each capable of producing around 500 million sterile flies per week, are not reactivated "in the next two years" to combat the screwworm, the Panama factory maintains its maximum production, destined for the battlefront in Mexican territory.
"We have to try to keep the disease at bay so it doesn't spread further, trying to contain it, in Mexico. That's precisely what we're trying to do: try to stop it from spreading further or buy us enough time while we can strategically have the elements (mentioned). We're trying to stop it, to buy time, and then try to hit it harder," the specialist concludes.
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