Cuterebriasis in Pets – Creepy Crawlies in our Critters

You’ve probably seen the viral videos. You know the ones. A veterinarian uses forceps to gently pull a wriggling critter from under the skin of a kitten. To a lay person, the sight is both enthralling and grotesque. To a veterinarian, it is wholly gratifying. What did the veterinarian actually remove? A larvae of Cuterebra spp. that causes cuterebriasis. This week’s post sheds more light on this relatively common infestation. Happy reading!


Cuterebriasis – What is it?

Cuterebra spp. are
more commonly known as rodent bot flies. During summer months, the flies lay
their eggs at the entrances of rodent and rabbit burrows. The warmth of a rabbit’s
/ rodent’s body stimulates the eggs to hatch. The larvae attached themselves to
the animal’s hair coat and then migrate through the host, usually ending their
journey in subcutaneous (under the skin) tissues. After ~1 month, a warble with
a breathing hole forms under the skin. Once they have completed their
development, the larvae leave the body to pupate on the ground. Our pets become
infected when they sniff in and around rabbit and rodent burrows.

A Cuterebra spp. larva

Cuterebriasis – What does it look like?

There is no age, breed, or sex predilection for developing
cuterebriasis. Interestingly, one study found more than 80% of affected dogs
weight less than 4.5 kilograms (9.9 pounds). Infestation is most commonly documented
during warm weather months. The clinical signs that develop depends on the
migratory path taken by the larvae in the body. For example, if the larvae only
migrate under the skin, there is often no other clinical abnormality beside the
warble and breathing hole. Should the larvae migrate through nervous tissue, a
variety of clinical signs – ataxia (unsteadiness while walking), head tilt,
vision loss, seizures, body temperature fluctuations, and paralysis – may result.
Similarly, if the larvae migrate through ocular tissues, conjunctivitis, eye
discharge, eyelid swelling, and inflammation in the eyes often occur. Sneezing,
nasal discharge, coughing, and abnormal breathing are common when the larvae
migrate through the upper respiratory tract.

Cuterebriasis – How is it diagnosed?

A skin swelling with a breathing hole is a reliable
confirmation of cuterebriasis, and such lesions are most commonly found on the
head and neck of cats. Larvae may be visible through the breathing hole. Cuterebriasis
should be considered in any patient with eye abnormalities, neurologic
deficits, and/or nasal signs. In such case, a veterinarian will recommend some
testing that may include:

  • Blood & urine tests to evaluate the function of major organs
  • Diagnostic imaging (radiographs/x-rays +/- sonography) of the chest and abdomen
  • Advanced imaging of the brain (i.e.: CT scan, MRI)
  • Cerebrospinal fluid analysis (aka spinal tap)
  • Skin biopsy

Cuterebriasis – How is it treated?

The best treatment – whenever possible – is to remove larvae
from the patient. Obviously, this requires said larvae to be in an approachable
location. It is very important the larvae are removed intact to avoid reactions,
secondary infections, and anaphylaxis. When the larvae are located in
inaccessible locations (i.e.: the brain), a medication called ivermectin has
been used successfully.

Antihistamines and anti-inflammatory corticosteroids may be helpful
to reduce the potential for adverse reactions as the larvae die. Patients with
secondary bacterial infections often need antibiotics, and those who develop
seizures benefit from anti-convulsant medications. Cats with subcutaneous and
upper respiratory tract cuterebriasis generally have good prognoses while those
whose central nervous systems are involved have poorer outcomes.

The take-away message about cuterebriasis in pets…

Cuterebriasis – an infestation by the rodent bot fly – is common
in dogs and cats during warm weather months. Early identification is important
so effective therapy can be initiated quickly.

Wishing you wet-nosed kisses,