Myiasis is a revolting condition seen occasionally in dogs and other animals. It is the infestation of the dog by the maggots of some species of flies. The two different types of myiasis relate to the types of maggots infesting the animal. Myiasis involving maggots, which can also live on dead tissue, is termed facultative myiasis. While if the maggots require a live animal they cause obligate myiasis.

Screwworms cause obligate myiasis. In Central and South America, the New World screwworm or American screwworm, Cochliomyia hominivorax, occurs. While in Africa and Asia the Old World screwworm Chrysomya bezziana, infests animals. These flies normally live in tropical and sub tropical regions but occasionally they are seen elsewhere when bought in by an imported animal.

Screwworms normally attack dogs and other animals via laying eggs in a pre-existing wound to the skin or mucous membrane. In the absence of a suitable wound, the adult flies lay their eggs on intact mucous membranes. The maggots bore their way into the tissue of the dog appearing like screws drilled into the affected tissue. If a dog scratches the infested site, the maggots bore deeper into the tissue to prevent their removal.

Cases of facultative myiasis occur worldwide. House flies (Musca domestica) blowflies or bottle flies (Calliphora species, Phaenicia species, Lucilia species and Phormia species) and flesh flies (Sarcophaga species) all cause myiasis. Normally these flies lay their eggs on decaying meat or fecal matter. Untreated infected wounds or matted coats contaminated with feces or urine attracts such flies.

The maggots eat dead or decaying tissue. Some species can bore into the skin causing a large subcutaneous lesion containing numerous maggots. Dogs with myiasis have a pungent odor. Without treatment, an infested dog may die of shock or infection.

Treatment requires the shaving of the infested area and the manual removal of maggots. The removal often requires sedation or anesthesia of the dog. After visible maggots have been removed, daily examination of the lesion ensures that no maggots from eggs laid more recently develop. Examination of samples from the lesion for bacteria allows the correct antibiotic treatment for any infection present in the area.

An owner of a dog presenting with myiasis requires education on the proper care of their dog. They need to provide a sanitary living area regular grooming and prompt treatment of any wounds. Some cases of Myiasis in a dog may be used as evidence for neglect of the animal.

Reference sources

Pet Place.com

Merck Veterinary Manual

Myiasis in pet animals in British Columbia: The potential of forensic entomology for determining duration of possible neglect, Gail S. Anderson and Niki R. Huitson Can Vet J. 2004 December; 45(12): 993-998

UGA College of Veterinary Medicine

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