Myiasis (Maggots) in Dogs

Overview of Canine Maggot Infestation

Myiasis is a the term used to describe a maggot infestation. Maggots are fly larva that feed on necrotic and dying tissue. Especially prone are those dogs confined to the outdoors with situations in which their skin remains moist. This includes dogs with draining wounds, urine or fecal stained hair coats, or bacterial skin infections. Sustained skin moisture can cause damage, inflammation and infection setting up a favorable environment for maggots. This applies especially to weak and debilitated dogs.

The majority of maggots found on pets are larva from blowflies (family Callliphoria). The blowfly lays many eggs on decaying, infected or inflamed tissue. In favorable weather (warm and moist) the eggs hatch within 24 hours. The cone shaped larva uses its specialized mouth parts, including hooks, to lap up liquids and pierce the skin. After feeding and maturing for 5-7 days, the maggots leave the animal and enter the soil. Adult flies then emerge a few weeks later. Some maggots only invade dead or dying tissue. Unfortunately, some do not know when to stop and leave the decaying tissue to start feeding on healthy tissue.

What to Watch For

Signs of maggots in dogs may include:

• Moist skin areas, especially around wounds or where urine or feces touch skin
• Small thin tubular worms found in wounds that range in size from 1/4 inch to one inch, often approximately the size of a grain of rice. They are rarely found alone.

Diagnosis of Maggots in Dogs

Diagnosis of myiasis is based on visualizing the maggots on the skin or in the wounds. Fly eggs can sometimes be found. Eggs (also called fly blow) are small white and sticky. They usually can only be removed by shaving the hair.

After diagnosing myiasis, the underlying infection or skin problem that led to the maggot infestation should also be investigated and treated.

Treatment of Maggots in Dogs

Treatment of myiasis in dogs is to remove the maggots physically. Maggots are quite hardy and can be difficult to kill safely.

Shaving the hair from the affected area is the first step. After hair removal, the extent of the maggot infestation can now be seen. Frequently, the maggots hide under the hair coat and extend a lot further than initially suspected.

After shaving, physically removing the maggots – sometimes one at a time – is the next step. Frequently, there are hundreds of tiny maggots that burrow under the skin, and removal of all maggots may take several hours.

Many potent insecticides can kill maggots but they put the weak and debilitated dog in danger of insecticide poisoning. Options for anti-parasite drugs that kill maggots may include the following:

• Non-alcohol based pyrethrin or pyrethroid spray on lesions can kill maggots (Note – do not use on cats).
• Injectable anti-parasite drugs such as Ivermectin can be used in dogs that are negative for heartworm disease. These drugs need to be used with caution in dog with sensitivity to avermectins.
• Topical application of Selamectin (Revolution) or Imidacloprid + moxidectin (Advantage Multi or Advocate).
• Another anti-parasite drug used is Capstar which can be given as an oral pill, rectally or dissolved in water and dripped directly in the wound.

After removal of the maggots, the skin must be allowed to heal. In severe cases, sections of skin die and must be removed. If a significant amount of skin has been damaged, skin grafts may be required.

Wound care will also include topical wound therapy, frequent rechecks for new emerging maggots, antibiotics and pain medications.

Home Care and Prevention

If caught early, the skin can be shaved and the maggot removed. Frequently, the owners are unaware of the maggots due to the hair coat covering the area. Most maggot infestations should be examined and treated by a veterinarian.

The best way to prevent myiasis is to prevent skin diseases or infections that attract blowflies. Wounds should be cleaned and treated promptly. Urine and feces should be thoroughly washed off daily. Weak and debilitated dogs should remain primarily indoors and frequently checked for urine staining or fecal matter. Skin infections should be treated promptly.