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Myiasis

Myiasis is an animal or human disease caused by parasitic dipterous fly larvae feeding on the host's necrotic or living tissue. Colloquialisms for Myiasis include fly-strike and fly-blown.

Zumpt describes myiasis as "the infestation of live human and vertebrate animals with dipterous larvae, which at least for a period, feed on the host's dead or living tissue, liquid body substances, or ingested food."

Classifications

Two different classifications of myiasis can be adopted:

  • The classical classification describes the myiasis by the infected area of the host. For example : dermal, sub-dermal, cutaneous, nasopharyngeal, ocular, intestinal/enteric or urogenital.
  • Another classification is based on the relationship between the host and the parasite and provides insight into the biology of the fly species causing the myiasis and its likely effect. Thus the myiasis is described as either obligatory, facultative or accidental.

Flies responsible for Myiasis

There are three main fly families causing economically important myiasis in livestock and also, occasionally, in humans:

  • Oestroidea (botflies)
  • Calliphoridae (blowflies)
  • Sarcophagidae (fleshflies)

The adult flies are not parasitic, however when they lay their eggs in open wounds and these hatch into their larval stage (a.k.a. maggots or grubs), the larvae feed on live and/or necrotic tissue causing myiasis to develop.

Control Methods - Prevention and Treatment

The first control method is preventive and aims to eradicate the adult flies before they can cause any damage and is called vector control. The second control method is the treatment once the infestation is present, and concerns the infected animals (or humans).

Prevention

The principal control method of adult populations of myiasis inducing flies involves insecticide applications in the environment where the target livestock is kept. organophosphorus or organochlorine compounds may be used, usually in a spraying formulation. One alternative prevention methods is the SIT (Sterile Insect Technique) where a significant number of artificially reared sterilized (usually through irradiation) male flies are introduced. The male flies compete with wild bred males for females in order to copulate and thus cause females to lay batches of unfertilised eggs which can't develop into the larval stage.

Another prevention method involves removing the environment most favourable to the flies. One example of this is the crutching of sheep, which involves the removal of skin folds between the rear legs, which is a favourable environment for the larvae.

Treatment

This applies once an infection is underway. First the larvae must be eliminated through pressure around the lesion and the use of forceps. Secondly the wound must be cleaned and disinfected. Further control is necessary to avoid further reinfection.

It is also possible to treat livestock with the use of slow release boluses containing ivermectin which can provide long term protection against the larvae development.

Sheep may be dipped, which involves drenching the sheep in insecticide to prevent the growth of the larvae.

Use of Myiasitic maggots in Medicine

Through the ages maggots have been used in medicine in order to clean out necrotic wounds. Companies exist which produce sterile maggots which may be used to clean wounds and promote healing. (to be finished... )