Screwworm in the US: what it changes for travelling with a pet
This isn't one more rule in a manual: it's an active health situation that changes week to week. This article explains the mechanism, because that's the only part that will hold.
What happened
On 3 June 2026, the US Department of Agriculture confirmed the first animal case of New World screwworm on American soil since 1966. The parasite — a fly whose larvae develop in the open wounds of warm-blooded animals — had been eradicated from the United States after a decades-long campaign.
It primarily affects livestock, but dogs, cats and, rarely, humans are possible hosts. That's why the regulatory response reached pet movement at all, when the subject initially looked like a purely agricultural one.
The mechanism: containment zones and movement certificates
When a case is confirmed, veterinary authorities establish a containment zone around it. Its size isn't arbitrary: it starts from a minimum radius of roughly 20 kilometres, based on the fly's daily flight distance and lifespan, and can extend considerably further depending on local geography and climate.
Inside a zone, a warm-blooded animal can't leave without prior authorisation. Leaving requires an inspection and a movement certificate that travels with the animal. That mechanism is the stable part — the zones themselves open and close as detections come and go.
More than forty states responded, each in its own way
There was no single federal answer covering the movement of a pet between two states. Each state set its own entry conditions for animals coming from affected areas, and the forms vary noticeably.
Depending on the state, you'll find an entry permit to request several days ahead, a short-window veterinary certificate explicitly attesting the absence of the parasite, a systemic treatment given one to two weeks before travel, or a monitoring period after departure. Some states outright prohibited certain animal transfers out of affected areas.
What it changes in practice
If your route touches neither a containment zone nor an affected state, nothing changes for you. That covers the large majority of trips.
If your departure point sits in an affected state, though, checking is no longer optional and the answer isn't what it was three months ago. A veterinary certificate that was enough in spring may not be now, and the lead time involved — a permit to request in advance, a treatment to administer days before — can't be recovered the night before departure.
For entry into the US from a country where the parasite is present, a federal requirement is added: a certificate signed by an official government veterinarian in the country of origin, stating that the dog was inspected within five days before shipment and is free of screwworm, or was treated until fully clear before leaving.
Why this page won't tell you where the zones are
Because it would be wrong next week. Containment zones open and close as detections and releases happen, and an article freezing a list of counties would quietly become false — including for its reader.
The current state of play lives at one place: the official tracking map and the Department of Agriculture's status page, both in the sources below. If you're departing from or crossing an affected area, that's where to look, on the day, and nowhere else.