Cuterebra (Botfly) or Warbles in Cats

What are Cuterebra or warbles?

Cuterebra is the scientific name of the North American rabbit or rodent botfly. Cuterebra larvae develop within the tissues of certain animal hosts and, during this phase of their life cycle, they are commonly referred to as “warbles”.

What is the Cuterebra (botfly) lifecycle?

The adult botfly deposits its eggs near or in the opening of rodent and rabbit burrows. After hatching, the botfly larvae enter the host's body through an opening such as the nose, mouth, or skin wound. The botfly’s preferred hosts are typically rodents and rabbits. After several days, the botfly larvae migrate to the tissues beneath the skin, where they encyst (burrow in) and continue their development.

After about a month of living in the host’s skin, the larvae crawl out to pupate (develop into a pupa, or immobile cocoon-like stage) in loose soil, debris, or forest detritus. Adult Cuterebra flies mate within a few days of emerging, laying more eggs, and starting the cycle again.

How did my cat get warbles?

Cats are accidental hosts of Cuterebra larvae. They are usually infected when they are hunting rodents or rabbits and encounter the botfly larvae near the entrance to a rodent's burrow. Most cases of warbles in cats occur around the head and neck.

How do I know if my cat has warbles?

The early stages of Cuterebra infection or warbles are rarely visible on the outside of the skin. Most cases of warbles are detected when the larva enlarges and becomes a noticeable swelling seen or felt beneath the skin. A small “breathing hole” is often visible in the skin over the warble. The hole enlarges when the warble has fully matured and is about to leave the host.

Sometimes, nothing abnormal is noticed until after the larva leaves the host. Most cats develop a deep abscess or skin infection in the empty cyst after the warble has left the skin. In many cases, the secondary bacterial infection that develops in the empty cyst causes more damage than the primary attack by the Cuterebra warble. 

Rarely, the Cuterebra larvae migrate away from the skin, causing inflammation and damage where they travel. Affected areas can include the eyes and surrounding tissues, the brain, nose, larynx, and trachea. They can even cause serious widespread disease, such as sudden inflammatory response syndrome (SIRS) and disseminated intravascular coagulation (DIC).

How is the condition treated?

Treatment depends on when the condition is discovered. If the condition is diagnosed before the warble leaves the skin, the warble will be removed and the injured tissues will be removed (debrided), sometimes surgically. Antibiotics are usually prescribed to combat any secondary bacterial infection. Surgery may be required to close the injured site in some cases. Anti-histamines or corticosteroids are also sometimes used to prevent an allergic reaction when the Cuterebra is removed.

If the condition is diagnosed after the warble has left the skin, your veterinarian will clean and debride the infected area and also prescribe antibiotics.

What is the prognosis for my cat?

When only a few warbles are involved, the prognosis is good for complete resolution, and few, if any, permanent side effects occur. The prognosis is worse if a cat is infected with multiple warbles or if a warble migrates through or develops near a nerve or other sensitive tissue or organ. Seizures have sometimes been caused by the presence of a Cuterebra in the nervous system.

How can I prevent my cat from getting warbles?

Cuterebra is a common fly in North America. The best way to prevent a cat from getting warbles is to keep them from hunting rodents. When this is impossible, and if you live in an area with numerous rodents, rabbits, or other small mammals, you should regularly inspect your cat for signs of warbles. The earlier a warble is removed, the less likely the chance of severe or permanent damage to your cat.