Dog owners have a new treatment option if their pets become infested with the potentially deadly New World screwworm, as federal officials continue preparing for the parasite's possible spread in the United States. Food and Drug Administration (FDA) issued an Emergency Use Authorization on August 13 for Trio, a monthly chewable medication made by Zoetis, to treat New World screwworm infestations in dogs and puppies. The drug is not authorized to prevent screwworm infestations.
The authorization comes as officials remain on alert after New World screwworm, a parasitic fly whose larvae feed on living tissue, was detected in the U.S. this year. The FDA said most dogs in the country currently face a low risk because of their geographic location, but dogs living in, traveling to or returning from areas where infestations have been identified should be closely monitored. New World screwworm larvae feed on the living tissue of warm-blooded animals.
Female flies lay eggs around wounds or body openings, and larvae can hatch within about 24 hours before burrowing into the wound and feeding. Even wounds as small as a tick bite can attract the flies. Kevin Esch, executive vice president and president of research and development at Zoetis, told Newsweek that the resulting damage can progress rapidly.
"A New World screwworm infestation in a dog can be very serious because unlike most maggots that feed on dead tissue, screwworm larvae invade and eat living tissue," Esch said. The infestation can cause rapidly enlarging and deepening wounds, severe pain and tissue destruction, while secondary bacterial infections can lead to sepsis and shock, he added. "In a heavy infestation or when it isn't recognized promptly, a dog can become critically ill within 24 to 72 hours," Esch said.
The first signs may be easy to mistake for an ordinary wound or skin infection, making regular checks particularly important. Esch said owners should watch for a wound that suddenly becomes larger or appears to be "eaten away" over hours or a day. Swelling, redness, drainage, foul odors and visible maggots are also warning signs, particularly around the ears, mouth and nose or beneath thick or matted fur.
More serious symptoms include lethargy, fever, loss of appetite, weakness and pale gums, Esch said. The USDA lists irritated behavior, head shaking, the smell of decay and maggots in wounds among the signs that should prompt concern. "These habits are especially important for pet owners who live in or travel to the geographic areas of concern, where vigilance matters most," Esch said.
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