Background
New World Screwworm (NWS) infestation occurs when NWS fly larva feed on living tissues of mammals, including humans. If left untreated, NWS can be fatal. Female NWS flies lay their eggs, which develop into larva, at body orifices or open wounds. Cattle are at an increased risk for NWS infestations due to the numerous possibilities for open wounds including castration, dehorning, and fresh branding sites that provide an excellent environment for NWS flies to lay their eggs. NWS flies have a short reproduction cycle. NWS eggs hatch into dangerous parasitic larva (maggots) within 24 hours after eggs are laid in an area. After feeding for 5-7 days, the larva leaves the body tissue and drops to the ground and pupate into adult NWS flies within an additional 3-5 day.
Stop NWS by Protecting Your Herd:
Preventing an infestation of NWS is key–treatment can be difficult, and eradication is expensive. NWS are attracted to the open wounds and mucus membranes where they lay their eggs, and they can be carried by both domestic and wild animals. We recommend taking steps to quickly identify and treat open wounds and keeping wildlife away from your cattle to the extent possible.
- Frequently inspect cattle and pay close attention to insect bites, cuts, and dehorning/branding sites. Immediately treat any open wounds, scratches, or scabs.
- Closely monitor new calves and mothers. NWS flies often lay eggs on the navel areas of calves, and the vulva and perineum of cows. On bulls and steers, monitor the sheath/prepuce as well.
- Pay close attention to nasal passages and eyes for signs of larvae (maggot) infestation.
- Minimize access of wild animals (birds, feral hogs, etc.) to cattle to the greatest extent possible.
- Practice biosecurity measures like frequently cleaning clothing, boots, vehicles, and equipment on your farm or ranch.
Animals suffering from NWS infestation may exhibit the following signs:
- Bloody or light-colored drainage from a cut or wound.
- A cut or wound that rapidly enlarges for seemingly no reason.
- White or cream-colored runny substance (the eggs) in and around a wound.
- Presence of fly larvae (maggots) in wounds.
- Irritated behavior, foul odor, fever, reduced appetite, and signs of pain, including repeated head shaking.
If you see any of these signs in your cattle, contact your veterinarian immediately and then contact USDA APHIS. Remember to kill and preserve the larvae by placing directly into concentrated (70%) ethyl or isopropyl alcohol to help with future identification efforts.
What is NCBA doing?
NCBA has a strong, grassroots policy on combating pests and foreign animal disease. Under that direction, NCBA will continue working with Congress and USDA to fund and expand the sterile male fly program to properly protect the American cattle herd from NWS infestation. NWS are devastating parasites that can be lethal for livestock, wildlife, and humans. NWS was previously eradicated from the United States in the late 1960s using sterile male NWS flies. Sterile insect technique (SIT), using sterile male NWS flies to mate with female NWS flies, who only mate once in their lifetime, is a technique that has been very successful in eradicating and halting the spread of NWS.
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