“The stench…it’s like roadkill stewed in infection,” explains Jose Santiago Gallardo Espinosa, a cattle producer from Chiriqui, Panama, describing an animal that has been infected with New World screwworm (NWS). “You’ll smell it before you see it.”
He goes on to describe the appearance. “That little dehorning scrape you didn’t worry about? Now, it’s a fist-sized hole pulsating with maggots. Not on top, under the skin. Hundreds of cream-colored worms with screw-like spines, eating your cow alive.”
It’s a Plague in Panama
Gallardo is a Panamanian livestock production specialist and animal science professional with a diverse and practical background in cattle production, agricultural policy and international ranch management. He currently serves as the technical assistance team manager at Cooleche, R.L., where he leads strategic initiatives in cattle production and technical outreach.
“This ain’t ‘just flies.’ We’ve buried calves eaten alive in 48 hours,” Gallardo stresses. “Post-calving cows are sitting ducks, I found one last week with maggots deep in her vulva, she was trembling as she tried to nurse her calf.”
To catch NWS and stop the spread, Espinosa encourages daily wound checks including navels on newborns, vulvas on fresh cows, sheaths on bulls, branding cuts and tagging nicks. Some red flags include a wound that swells overnight or oozes cloudy fluid and a milk tank mysteriously dropping.
“Treat every scratch like a ticking bomb,” he says adding if you find one with a wound acting a little strange, you should “peel back skin edges, and if you see rice-grain maggots with dark spines — sound the alarm.”
He says more than 6,500 cases have erupted across Panama, marching north through Central America like a plague.
“For years, our U.S.-Panama barrier kept NWS at bay,” Gallardo says. “We’d see maybe 25 cases a year — it was a nuisance, not a crisis. Then 2023 hit, and overnight our pastures became war zones.”
He says the reality in Panama is rainy season is maggot season.
“Here, in Chiriquí’s dairy country, it is the perfect storm,” he says. “Rainy season humidity of 90%, 85°F heat and flies everywhere. A single-infected cow bleeds $10/day in lost milk — its life or death for small dairies.”
NWS in Nicaragua
Ernesto José Sequeira Enríquez, an agronomist from Camoapa, Nicaragua, says NWS was eradicated from Nicaragua in the 1990s. He says he first encountered it during an internship in Brazil where he experienced the serious challenge the fly causes.
“When cases began appearing here again last year, I was able to use what I learned in Brazil to prepare veterinary supplies and train people on prevention and treatment,” he explains.
He says it’s essential to enforce a daily inspection routine, checking every animal carefully for open wounds.
“When you find an infected animal, you’ll typically see a bleeding wound,” Sequeira says. “If the infestation has progressed, there will be a strong, foul smell due to tissue damage and the presence of larvae.”
He encourages U.S. producers to be prepared with sufficient supplies of veterinary medicines and insecticides for both treatment and prevention and to adjust management practices to reduce risk. For example:
- When dehorning, branding or ear tagging, apply insecticide spray to the wound immediately.
- Ensure proper care of newborn calves by disinfecting the navel with iodine solution as soon as possible, since that is the most common entry point for infestation.
“Although complete control of screwworm is not possible, taking preventive measures significantly reduces the economic and productivity impact of it,” he says. “Early detection and consistent preventive practices are critical to minimizing losses.”
Sequeira stresses a producer’s eyes and hands are their best tools to fight NSW.
“My warning to U.S. ranchers is this isn’t just a Panama problem,” he summarizes. “Newborn calves are maggot magnets. If you lose one calf to a navel infestation, you’ll never sleep again. Make inspections sacred — no excuses. Report fast and hide nothing.”
It’s Endemic in Brazil
Marcelo Costa is a veterinarian, professor and cattle business consultant in Brazil and Paraguay. In 1999, Costa was taught embryo transfer at Camp Cooley in Franklin, Texas. He then returned to his family’s third generation ranching operation where they started Camp Cooley Brazil.
“I have been dealing with screwworm all my life since it is endemic in Brazil,” Costa says. “Screwworm-infected animals happen all months of the year.”
Like others, he has experienced finding infected animals with bleeding, foul-smelling wounds. He says animals show discomfort and may not follow the herd as normal.
“Newborn calves are usually the more attacked category because of the navel’s wet and bloody tissue,” he says. “If a screwworm infects the navel, it may open a door at the site for more severe infections that may cause diarrhea, pneumonia and other diseases.”
Costa stresses how much NWS costs producers beyond animal loss and decreased productivity.
“One of the biggest problems with NWS is the increased labor with vigilance and animal treatment,” he summarizes.
Guatemala Producers Are Learning to Cope with NWS
“Screwworm came to teach us the times are changing, and that any type of production is possible and open to any complication,” says Oscar León, a livestock production specialist and agricultural business administrator from Guatemala City, Guatemala. “Brazil learned how to cope with it, and Guatemala is in the process of it. The U.S. is not exempt from it, unfortunately. But with the adequate measures and prevention techniques, one can learn and teach others. We can make the impact less harmful on our production and wallets.”
León currently manages his family’s cattle operations and leads LAVAT S.A., a company that imports and distributes innovative animal health and nutrition products tailored to the needs of the Guatemalan livestock sector.
He explains it is important for producers to look for and treat any open wound or bruise as they are the first indicators.
“If an open wound smells like the scent of rotten meat, you will find the presence of screwworms feeding off live tissue,” he says. “Prevention and early timing are the best ways to treat screwworm. Make sure to take your time, observe your cattle, search for a bruise or wounds and treat them properly.”
He also stresses the importance of making sure everyone who works in the farm or ranch is aware of NWS and knows how to react if an infection is found.
Educating U.S. Producers
Chris Womack, a veterinarian and rancher from San Angelo, Texas, says he remembers helping his dad treat calves with NWS infestations.
“I can still remember the smell,” Womack says. “I thought it was cool because I was a little kid, and we dug maggots out of the calves. I can still smell it like it was yesterday, and it was horrible to look at them.”
Womack shares a historic context of NWS, which he says means “man-eater,” on the “Registered Ranching” podcast with Tucker Brown.
Womack also describes the emotional toll on the producer when faced with NWS.
“If you’re a steward of an animal and it has half of its head rotting off, or its abdomen is a gaping wound because the maggots are eating it up, or it gets in their ear and they’re walking around in circles with brain damage because they got meningitis, well, it’s devastating.”
Womack summarizes NWS isn’t just an agricultural issue, it’s a human health concern. Historical accounts and recent data from Panama show NWS can affect humans, particularly vulnerable populations like homeless individuals or those in areas with limited medical access.
Womack says the experiences with NWS during his childhood is the reason he is a veterinarian today. He says there is a generational ignorance in the U.S. regarding NWS, and that is something he is committed to fixing.
“The only way we can overcome ignorance is education,” he stresses.
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