Myiasis (Maggots) in Dogs

The most visible sign of myiasis is unmistakable. The small, white larva of a fly will be present on the broken skin of the dog, and most often will be wriggling and moving. Sometimes the dog’s fur obscures the wound, particularly with long, matted fur. Miniscule sticky, white eggs can often be found on the fur of the afflicted animal. A dog with untreated myiasis will develop a foul, decaying smell as the maggots secrete an enzyme that necrotizes healthy skin tissues. In severe cases, they may lose their appetite as well as becoming lethargic and depressed.

• Foul smell
• Visisble larva on skin

Types

Myiasis

This type of infestation is caused by an infestation of maggots, which is the larval stage of the growth of many flies. Pre-existing wounds and skin damage are susceptible to this type of infestation, and many maggots will be present with this type of infestation and it can lead to necrosis and additional infections.

Cuterebriasis

With cuterebriasis, the infestation is actually by the grub of a fly in the Cuterebra family. The female of the Cuterebra fly, also known as the botfly, lays her eggs on the ground near the homes of rodents such as rats or rabbits. They burrow into their host and grow until they emerge a month later. These grubs can be found either singly or in small groups, but are not generally found in the large number that the maggots of blowflies are.

Diagnosis of a blowfly maggot infestation is often much simpler than the task of treating it, as the maggots can clearly be seen in most wounds. The area will be shaved to give the examining veterinarian a better view of the affected tissues. In serious infestations, the wounds can extend further than it may appear due to the amount of necrotized flesh the maggots are creating. Cultures of any affected tissues will help to reveal if any bacterial or fungal infections are present in the wounds. 

Botflies create a lump with a breathing hole on the surface of the skin as they grow. These breathing holes are usually visible when the area is shaved and occasionally the breathing tube of the grub itself can be seen poking out. In rare cases where the grub migrates into the lungs or brain diagnosis becomes more challenging and additional imaging techniques such as CT scans and magnetic resonance imaging may be helpful in spotting either the larvae or their migratory tracks.

The primary treatment of myiasis is the physical removal of the maggots or grubs. This process is usually done by hand and is a delicate procedure. With blowfly maggots there can be large numbers of the larvae, and they must be removed carefully as the enzymes that they use to necrotize living flesh can be released in larger quantities if the body is crushed or pulled apart and in large enough quantities, can cause additional tissue death and possibly shock. Often skin that has been damaged by the maggots needs to be debrided to remove dead tissue and promote healing. 

Botfly grubs are usually only present as singletons or in small groups, but they too contain toxins within their bodies that can be detrimental to your pet’s health. Because of both the delicacy of the operation and to avoid discomfort on the part of the dog, it is usually done under general anesthesia. Any infections that are uncovered by the cultures taken of the infected tissues will be addressed at this time as well, and antibiotics or antifungals will be prescribed as needed.