Cuterebra spp.

Also known as: Rabbit Botfly — Rabbit Warble Fly

Introduction

Cuterebra spp. can infect rabbits, dogs, cats and ferrets and lead to a nodular lesion of the skin due to the presence of the Cuterebra spp. larvae causing myiasis.

Identification and Life Cycle

Adult Cuterebra flies resemble the bumblebee and have vestigial mouthparts. They do not feed nor bite.

Fully-developed third-stage larvae are up to 45mm, black or dark-brown, and have black spines covering their bodies. Earlier stages are much paler and sometimes white, but still have the dark spines which help with identification.

It is impossible to determine which species of Cuterebra is present by observing the larvae.

Female Cuterebra flies lay their eggs along rabbit runs or near rodent burrows. As the host brushes past, the first-stage larvae hatch instantly and crawl into the host's fur. The larvae then enter the host through its natural body openings. Migration occurs to the skin and the third-stage larvae become clinically noticeable in the subcutaneous tissue, usually in the cervical region. The larvae communicate with the air through a breathing hole. After about 30 days, the larvae exit the skin, fall to the soil and pupate.

Aberrant migration can occur to the brain, pharynx, nostrils and eyelids.

Clinical Signs

Lesion occur generally in late summer or autumn as 1-2cm nodules over the head, neck and trunk. A fistula will develop from which the larvae emerge.

There may be secondary infections and purulent material exiting the mass.

Animals are usually clinically normal, unless aberrant migration has occurred and then a range of clinical presentations is possible.

Rabbits may sometimes present with anorexia and weakness.

Diagnosis

Definitive diagnosis requires finding and identifying the larvae. The larvae is usually found in its third stage and will be heavily spined.

Treatment

Under sedation or general anaesthesia, the breathing hole in the skin should be enlarged with mosquito forceps and the larvae should be extracted gently. Care should be taken not to crush the larvae as this may lead to anaphylaxis, a chronic foreign body reaction and secondary infection.

The area should be flushed thoroughly, debrided if necessary and allowed to heal by granulation.

Oral analgesics and antibiotics may be required.

No parasiticides are approved for the treatment and control of Cuterebra and so in rabbits infections should be avoided by preventing contact between rabbits and flies, either by keeping the rabbit indoors during fly season or by installing protective screens. It may be a difficult condition to prevent in dogs and cats, but the condition is very rare in these species.

Cuterebra spp. Learning Resources
Flashcards Test your knowledge using flashcard type questions	Rabbit Medicine and Surgery Q&A 16

References

Merck and Co (2008) Merck Veterinary Manual Merial

Bowman, D. (2008) Georgis' Parasitology for Veterinarians Elsevier Health Sciences

Harvey, R. (2009) A colour handbook of skin diseases of the dog and cat Manson Publishing