MYASIS

Definition :

Myiasis is defined as the infestation of live vertebrates (humans and/or animals) with dipterous larvae.

Dipterous larvae can feed on the host's living or dead tissue, liquid body substance, or ingested food and cause a broad range of infestations depending on the body location and the relationship of the larvae with the host.

The majority of flies causing myiasis can be categorized into 1 of 2 groups, based on relationship with their hosts. Obligate parasites grow only on healthy tissue of live hosts whereas facultative parasites, associated usually with carrion , feces or decaying plant material, can develop on necrotic tissue of living animals and tend not to invade healthy tissue. Accidental infestations represent a third category in wich the eggs of larvae are inhaled or swallowed with contaminated food.

Facultative myiasis, is the the most important myiasis developed in veterinary world.

In normal conditions, adult flies of different genera of those parasites  lay their eggs in feces or in decaying animal carcasses. In facultative myiasis, the adult flies are attracted to a moist wound, skin lesion, or soiled hair coat. A common site is the breech, where flies may be attracted to wool / fur soaked with urine or feces.

As adult female flies feed in these sites, they lay eggs, which hatch within 24 hr if conditions are moist. Larvae (maggots) move independently about the wound surface, ingesting dead cells, exudate, secretions, and debris, but not live tissue. This condition is known as fly strike or strike.

The larvae irritate, injure, and kill successive layers of skin and produce exudates. Maggots can tunnel through the thinned epidermis into the subcutis. This process produces tissue cavities in the skin that measure up to several centimeters in diameter. Once established, strikes can spread rapidly and attract more blow flies, secondary as well as primary. Mild strikes can cause rapid loss of condition, and bad strikes can be fatal. Unless the process is halted by appropriate therapy, the infested animal may die from shock, intoxication, histolysis, or infection. A peculiar, distinct, pungent odor permeates the infested tissue and the affected animal. Advanced lesions may contain thousands of maggots.

What to watch on your Pet

Prevention

The hair coat should be kept clean of urine or feces and should not be permitted to become matted. Contaminated wounds and matted hair coats soaked in urine or feces rapidly attract adult myiasis-producing flies.

Diagnosis

Affected animals become depressed, stand with their heads down, do not feed, and attempt o bite the infested areas. Screwworm may be suspected if the larvae are associated with wounds.The species of myiasis-producing flies can be definitively identified by closely examining the larvae. 

Treatment

If these larvae are detected in small animals, immediate therapy is necessary. The hair coat should be clipped to determine the extent of the lesion and to remove many of the larvae present in the hair. Removing maggots from existing deep tissue pockets 

by. jeffry wahyudi, DVM