Keeping the screwworm at bay

What Minnesota farmers need to know

GILFILLAN ESTATE -- Animal health experts met at Minnesota Farmfest on Tuesday. They talked with local farmers about how to keep a dangerous pest called the New World screwworm out of northern herds. The panel met in the Livestock Tent.

The talk featured Dr. Angela Varnum, a vet with the University of Minnesota Extension, and Dr. Brian Hoefs, head of the Minnesota Board of Animal Health. Kelly Schmidt from the Minnesota Beef Council led the talk.

The United States got rid of the screwworm back in 1966. But new cases in Texas this summer brought the parasite back into the news. Screwworms are fly maggots that eat living flesh instead of dead tissue. Female flies lay eggs near open wounds, fresh belly buttons on newborn calves, skin cuts, and body openings like nostrils or under tail areas. They can attack cattle, horses, pets, wildlife, and even people.

Dr. Varnum and Dr. Hoefs told farmers that there are no cases of screwworm in Minnesota right now, and the danger here remains low.

“The New World screwworm is not in Minnesota,” Varnum said. “Our outlook is that it is important here in Minnesota, but it is not urgent. We have different risks here in Minnesota than in other parts of the U.S., primarily one of those being our climate.”

Varnum said cold weather helps keep the fly away during the winter.

“The New World screwworm won’t be a localized problem in the wintertime,” Varnum said.

Hoefs explained that the parasite cannot live through cold northern winters because the larvae die in soil colder than 40 degrees. But state leaders warn that moving cattle from other states is the biggest way the pest could travel north in warm months.

“The fly doesn’t fly that far in her lifetime, an absolute maximum of maybe 10 or 12 miles,” Varnum said. “So although this is a flying insect, it is not a matter of the fly traveling on its own power. It is our domestic animals traveling.”

The pest has lived for years in South America and Central America. For a long time, the U.S. and Mexico released sterile flies in Central America to stop the insect from moving north. But recent problems with that program let the flies spread north through Mexico to the U.S. border.

Moving farm animals and pets across state lines is the main worry for health officials. Hoefs noted that rescue dogs can also spread the pest.

“Us northern states have a lot of people moving animals in and around those areas infested,” Hoefs said. “We are talking about cattle transfers and people vacationing with their pets. About a third of the cases we are seeing in Mexico are in dogs. They have a feral dog issue down there, and New World screwworms are having a heyday.”

To keep farms safe, Minnesota set up new rules for animals coming from areas with screwworms.

“If you are traveling to an area that is endemic with New World screwworm, and you are bringing your animals with, there is going to be a quarantine and treatment required before you can come home,” Hoefs said.

Even though the parasite is dangerous, it is easy to treat with common animal medicines like ivermectin.

“If you report the New World screwworm, your animal is treated and not killed,” Varnum said. “The main problem with not reporting is that we don’t know where it is traveling. Reporting is the only way state and federal agencies know where sterile flies are needed to control its spread on a broader level.”

Hoefs reassured farmers that officials want to help sick animals get well, pointing to the first case found in Texas.

“This is very treatable,” Hoefs said. “Patient zero in Texas was treated, cured, and continues to grow. There is no reason not to report it.”

To wipe out the pest, experts release millions of sterile male flies. Female screwworm flies only mate once in their lives. If they mate with a sterile male, their eggs never hatch.

For local livestock owners, checking animals every day is the best defense. Varnum advised checking newborn calves, cuts, skin folds, and natural openings.

Varnum remembered the first time she saw a screwworm on a horse, noting how the larvae hide in skin folds.

“I remember the first time I saw it on a mare--the infestation was hidden deep under her front leg in that armpit fold where you wouldn’t normally look,” Varnum said. “We applied rubbing alcohol to the area, which cuts off their air supply and forces the larvae to back up to the surface so you can see them and collect them.”

Varnum urged farmers to trust their senses and speak up quickly if anything looks suspicious.

“Use all your senses,” Varnum said. “You might see a wound that is not healing like it normally would, or visible maggots burrowing deep into the flesh. Other indicators are your sense of smell and how you watch the animal’s behavior. Sometimes they are very irritated, and there is a characteristic foul stink from the decaying tissue.”

Varnum stressed that early reporting is critical for keeping the whole region safe.

“If you see something, say something,” Varnum said. “If you see something and you are unable to know exactly what it is, you can collect a sample of the maggots in alcohol. It is only identified in a lab, and that is why we have to put it in alcohol. Even rubbing alcohol works. It is much more achievable than it sounds when reading about this insect in popular media.”

State leaders ask farmers to work closely with local vets and report any strange wounds right away.

“Early awareness is key in all of these situations,” Hoefs said. “The quicker we get on top of it, the quicker we can get it taken care of and out of your hair so you can move on with your business.”

Farmers can contact the Minnesota Board of Animal Health or their local Extension office for more details. Farmfest continues through Thursday at the Gilfillan Estate near Morgan.