New World Screw Worm: Deadly Parasite Now Threatening Pets

By Dr. Andrew Jones December 5, 2025 0 Comment

A Growing Parasite Threat for Dogs and Cats

Screwworm alert.
There are growing concerns about a new parasite that is making its way toward the United States. It is called the New World screwworm, and it has the potential to affect farm animals as well as our dogs and cats.

This is what you need to know.

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What Exactly Is the New World Screwworm?

It sounds like something from a horror film, but it is very real.
The New World screwworm used to exist in the US. It was eradicated, but it has started to move north again through Central America and Mexico.

Why does this matter?

Screwworms are dangerous parasites that target any warm-blooded mammal, including:

  • cattle

  • horses

  • wildlife

  • dogs

  • cats

A screwworm begins as a fly. Similar to a housefly, but far more harmful. The female fly seeks out an entry point on a live animal.

That can be:

  • a mucous membrane

  • the gums

  • the nostrils

  • the lips

  • the external genital area

  • and most commonly, an open wound

Once she finds a wound, she lays her eggs. Those eggs hatch into larvae, which look like maggots. These maggots do not consume dead tissue. They eat live flesh.

That is what makes screwworm infestation so dangerous.

How Screwworms Infect Animals

Picture this.


Your cat has a small ear wound from a bite. A screwworm fly lands on that wound and lays hundreds of eggs. Within days, the eggs hatch and the larvae burrow deeper into the tissue. They eat through the skin, muscle and surrounding tissue, causing:

  • severe inflammation

  • infection

  • tissue necrosis

  • extreme pain

If left untreated, screwworm infestation can be fatal.

The fly can travel over 100 miles in a day, which is why the spread has been quick.

Where Screwworms Are Showing Up

  • Screwworms were eradicated in the US in 1966.

  • In 2023, a significant outbreak occurred in Panama.

  • In 2024, screwworms were confirmed in Mexico.

This means the parasite is once again approaching the US border.

Signs Your Pet May Have Screwworm Infestation

You are looking for a wound that:

  • is rapidly enlarging

  • smells foul or necrotic

  • drains continuously

  • does not look like a normal abscess

And most importantly:

You may actually see maggots inside the wound.

If you see anything like this on your dog or cat, you need to visit your veterinarian right away.

Early infestation can be hard to spot because the larvae hide beneath the skin for the first three days. Once they multiply, the damage becomes visible.

How Screwworm Infestation Is Treated

There are reliable treatments available.

Common veterinary insecticides

Examples include:

  • ivermectin

  • and recently, Credelio (now authorized by the FDA for New World screwworm in cats)

These medications kill the larvae.

Wound care

Treatment also requires:

  • anesthesia

  • clipping and cleaning the wound

  • flushing with chlorhexidine

  • removing dead tissue

  • starting oral antibiotics, such as clavulanate

  • using a safe topical antibacterial, such as propolis spray

Propolis is one of my favorite natural antibacterial options. It works very well and is safe for dogs and cats.

How to Protect Your Pets

The most important thing is wound management.
Screwworms need an open wound to enter.

Step 1: Clean all wounds immediately

Use chlorhexidine to flush and disinfect. This helps prevent infection and speeds up closure.

Step 2: Apply a topical natural antibacterial

Propolis spray is an excellent option.

Step 3: Use manuka honey

A thin layer twice a day promotes rapid healing and prevents bacterial growth. Most small wounds will close within 3 to 5 days.

Step 4: Monitor every wound daily

If you see:

  • rapid enlargement

  • a foul smell

  • or maggots of any size

go straight to your veterinary clinic.

Should You Panic?

No.
Your dog or cat is not at high risk right now.

But awareness is important. Screwworms are spreading north, and pet parents should know the signs and act quickly.

If you stay on top of wound care, recognize changes early and use the holistic tools available, you can dramatically reduce the risk.

Final Thoughts

I hope this gives you a clear understanding of what screwworms are and how to protect your pets. Awareness is key. Quick action is essential. And good wound care goes a long way.

Thank you for watching this edition of Veterinary Secrets on the New World Screwworm Infestation. And when you click the link in the box below, I will send you a copy of my free book.

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