Cuterebra in Cats

What are cuterebra?

Cuterebra (pronounced cuter-ree-brah) are larvae of the botfly who are obligate parasites to rabbits and other lagomorphs. Cats are accidental hosts who become infected when they come into contact with infective larvae (also known as bots or maggots).

• Cuterebriasis is the medical term for infection with Cuterebra
• Myiasis is the medical term for infection by fly larvae (larvae sounds slightly nicer than maggot). There are many different species of fly, including the botfly.

The botfly is found throughout the Americas (Western Hemisphere) and occurs in cats who live in rural settings. Infection generally occurs in late summer to early autumn (fall), although that time frame can be longer in warmer climates. It affects young to middle cats most often. This is no doubt due to their propensity to roam further than older cats.

Transmission

The adult botfly is the size of a bumblebee and lays between 5-15 eggs near the openings of burrows and on vegetation.

Cats become infected when they explore rabbit or rodent burrows. As the cat passes, eggs hatch into larvae in response to heat and motion where they stick to the fur of the passing host.

From there, they enter the body via the mouth, nose or an open wound. Once inside the host, they remain localised in the nasopharyngeal region for several days before migrating through the tracheal wall, into the thoracic cavity, through the diaphragm, and into the abdominal cavity, from there they migrate to the dermis (skin) where they remain, feeding on surrounding tissue. A local swelling (known as a warble) develops with an air hole (fistula) which enables the larvae to breathe.

Approximately 30 days later, and an inch in length, the larvae wriggle out of the hole and onto the ground where burrows into the ground and pupates, developing into an adult botfly. Adult botflies have no mouthparts and cannot eat. They mate, lay more eggs and die.

Clinical signs

There are many forms of Cuterebriasis, affecting different parts of the body; however, the focus of this article relates to Cutaneous Cuterebra myiasis, which is a Cuterebra infection of the skin.

Cutaneous Cuterebra myiasis

The most common form of Cuterebriasis occurs when the larvae migrate to below the skin where it forms warble. Common locations include the head, neck, and thorax.

• A large lump up to 1 inch long with a breathing hole in the centre, it is usually possible to see the tip of the larvae inside the hole. There may be some clear or pus-like discharge.
• Pain and inflammation can occur, and the cat may lick at the area.
• Secondary infection can develop in some cats.

While the thought of a larvae/maggot living under the skin is disgusting to most, this form of infection is generally not serious but does require veterinary attention. In rare cases, cuterebriasis can kill a cat due to anaphylaxis or in cases where the brain is involved.

Other forms of myiasis exist which include:

• Cerebrospinal
• Nasal
• Respiratory
• Ocular

These forms are beyond the reach of this article which is focused on subcutaneous (skin) infection.

Diagnosis

Diagnosis can be made during the physical exam, and no diagnostic tests are necessary. The area will be clipped, which will reveal the characteristic lump with a circular air hole and the head of the larvae at, or near the surface.

Treatment

Although the cuterebra would leave on its own, removal is necessary to prevent anaphylaxis or recurrent infection from the parasite. As they grow, the spines burrow into the skin which is extremely painful. Do not try to remove the larvae at home as not only is removal extremely painful to the cat, but it is easy for the larvae to break apart during extraction which can cause a severe allergic reaction and secondary infection.

• Your veterinarian will clip the fur, administer a local anesthetic and sterilise the area.
• The breathing hole is enlarged, and the larvae are carefully removed using forceps. Larvae may retreat, making it difficult to grasp. Your veterinarian can apply a layer of petroleum jelly to the fistula for a period to block the air hole, which makes retrieval easier.
• Dead or damaged tissue will be debrided (removed).
• The hole is then flushed with sterile saline and cleaned with antiseptic.
• Antibiotics to prevent secondary infection of the wound.

Prevention

Monthly flea medications such as Revolution or Advantage may reduce the incidence of cuterebriasis in cats and dogs.

If botflies live in your area and your cat has outdoor access, check him daily for lumps. If you do find any, seek veterinary attention. Indoor cats are generally safe and should not be at risk for cuterebriasis.

Image courtesy Katja Schulz, Flickr