On October 28, 2026, a domestic cat in Grant County, New Mexico became the first cat in the United States diagnosed with New World screwworm, a parasite eradicated from the country in 1966 that returned on June 3, 2026, in a 3-week-old calf in Zavala County, Texas. By November 12, USDA had confirmed 128 animal cases across Texas, New Mexico and Arizona, 126 of them domestic animals. Nine of the ten pet cases were dogs.
What the 2026 numbers actually say
The spread is uneven. August produced 4 domestic cases, September 3, October 33, and November 1 to 11 another 42, with 41 still active. Detections span three states and movement restrictions in parts of 21 Texas counties. South of the border the scale is different: CDC counts more than 209,400 animal cases and more than 2,850 human cases across Mexico and Central America since 2023.
| Period | US domestic cases | What changed |
|---|---|---|
| June to July 2026 | A handful, cattle only | First case June 3, Zavala County, Texas |
| August 2026 | 4 | First horse and sheep |
| September 2026 | 3 | Slower month |
| October 2026 | 33 | First dog in Arizona, first cat in New Mexico |
| November 1 to 11, 2026 | 42 | Three states, 41 cases still active |
Why cats are a harder case than cattle
A calf with an infested navel is inspected twice a day by someone paid to look. A cat with a 1 cm bite abscess under the tail base is inspected by nobody, and a cat in pain hides rather than limps. The feline evidence is thin: FDA's authorization rests on two cats in Malaysia with Old World screwworm (Chrysomya bezziana), both cured, and 11 naturally infested dogs in Brazil.
From egg mass to fly in three weeks
A female lays 100 to 300 eggs in one mass, in overlapping rows like roof tiles, on the edge of a wound or a body opening. Each egg is about 1 mm and hatches in 10 to 12 hours by USDA's description, 12 to 24 hours in most extension guidance. The mature third instar reaches 17 mm and feeds head-down with only its rear spiracles at the surface, which is why a light rinse reveals nothing. After 5 to 7 days of feeding the larva drops to the soil, pupates and emerges 6 to 8 days later. One female can lay up to 3,000 eggs in a 10 to 30 day life.
Screwworm or ordinary fly strike?
| Feature | Ordinary blowfly strike | New World screwworm |
|---|---|---|
| Eggs per mass | 100 to 200 | 100 to 300 |
| Hatch time | About 24 hours | 10 to 12 hours |
| Tissue eaten | Dead and dying tissue | Living tissue, including tendon |
| Wound over 48 hours | Slow, stays near the surface | Deepens and widens, new tracts appear |
| Larvae visible | Usually yes, on the surface | Often no, buried head-down |
| Without treatment | Slow healing, secondary infection | Death in 7 to 14 days from toxaemia |
For the domestic version of the left column, see fly strike in cats.
Five signs in a cat, and the ruler test
- A wound larger on day two than day one: a bite abscess, a scratch, a surgical incision.
- A putrid smell that survives one chlorhexidine bath.
- Bloody discharge and small new holes beside the original wound: larval breathing tracts.
- Restlessness, no appetite, a cat that stops grooming one flank.
- Visible movement in the wound, usually only the rear ends of larvae.
Photograph the wound next to a ruler every 24 hours. A wound that grows by more than a few millimetres a day is a same-day appointment, not a wait-and-see.
What the vet does in the first visit
The core treatment is mechanical: remove every larva, flush the tracts with saline, debride dead tissue, and repeat in 24 hours because a second wave can hatch. In the two-cat Malaysian series, both were hospitalised for 10 and 11 days while wounds were flushed until they re-epithelialised. Expect sedation for a deep wound, pain relief, antibiotics and a fly-proof bandage. Larvae that drop out must be destroyed, not swept into the garden, because that is how the next generation reaches the soil.
The drugs that are authorized, and the ones that are not
As of November 3, 2026, FDA has issued 16 emergency use authorizations and 3 conditional approvals for animal drugs against screwworm. For cats, the specific authorization is Credelio CAT (lotilaner), authorized November 21, 2025 for treatment only: 6 mg/kg, which is 2.7 mg per pound, given with food, as a 12 mg tablet for cats 2.0 to 4.0 lb and a 48 mg tablet for 4.1 to 17.0 lb, not split because the tablets are not scored, and not for cats under 8 weeks or 2.0 lb. Nitenpyram has an over-the-counter authorization for dogs and cats from June 11, 2026. Two cautions: isoxazolines carry a class warning for tremors, ataxia and seizures, and no product is authorized for prevention in cats, so a monthly flea tablet is your vet's judgement call, not a guarantee.
What does not work is what most owners reach for. Heartworm preventives deliver 4 to 6 micrograms per kilogram; the cattle dose against screwworm is around 200. A monthly Heartgard-type chewable therefore provides no meaningful protection, and imidacloprid products such as Advantage II and Seresto collars act in skin, not in the tissue where larvae live.
Travelling with a cat into an affected area
Driving into Mexico or Central America with a cat, or returning from a stay there, means treating every scratch as a potential egg site. Check head to tail twice a day, keep the cat indoors at dawn and dusk, cover open wounds, and keep it away from livestock and stray dogs. The same applies for 30 days after you get home, because a larva that entered abroad can mature after arrival; the Arizona index dog was found with a wound on its back. For the paperwork side of a border crossing, see cross-border cat travel.
If you find maggots in a wound
- Do not squeeze, pick, or apply oil, alcohol or petrol. Buried larvae rupture and the wound deepens.
- Photograph the wound and the larvae with a scale in frame.
- Cover the wound with a clean dressing and confine the cat in a carrier.
- Call the clinic, say "possible screwworm", and give the county and any travel in the past 30 days.
- Collect any larva that drops out in a sealed container for identification.
- Go in the same day. A cat that is already off food needs an emergency visit, not a next-week slot.
US veterinarians must report suspected cases to the state animal health official and APHIS; a 20 km infested zone and movement controls follow one confirmation. Ordinary wound care is covered in home wound care for cats, and the abscess that so often precedes this in cat bite abscess.
This article is educational and does not replace a veterinary examination. Screwworm myiasis cannot be diagnosed from a photograph, and any emergency-use drug decision belongs to a veterinarian who has seen the wound.
Terms mentioned in this article
Frequently asked
Can an indoor cat get New World screwworm?
Yes, but only through a break in the skin. The fly needs an open wound or a body opening to lay on, so a healed cat with no cuts has almost no route in. The realistic indoor risk is an untreated bite abscess, a scratch, or a recent surgical incision; the New Mexico cat was a domestic cat, and the Arizona index dog was found with an infested wound on its back. Keep wounds covered and check them daily for 72 hours.
Is the flea tablet my cat already takes protective?
Not by itself as a prevention claim. FDA has authorized lotilaner (Credelio CAT, 6 mg/kg with food) for treating screwworm myiasis in cats, and nitenpyram has an over-the-counter authorization for dogs and cats since June 11, 2026, but no product is authorized for prevention in cats. Heartworm preventives are dosed at 4 to 6 micrograms per kilogram, far below the roughly 200 micrograms per kilogram used in cattle, so a monthly chewable is not a shield.
What does a screwworm wound look like after 48 hours?
It gets bigger and deeper rather than crusting over. Expect a putrid smell that survives one antiseptic bath, bloody discharge, and small new holes beside the original wound where larvae surface to breathe. Larvae are usually not visible because they feed head-down, so absence of visible maggots does not rule it out. Untreated cases can die of toxaemia in 7 to 14 days, which is why a wound that grows each day is a same-day appointment.