Myiases are often classified according to the anatomical position in, or on, the animal that the larvae infest. Broadly speaking, they may be described as dermal, sub-dermal or cutaneous, nasopharyngeal, ocular, intestinal/enteric or urinogenital. When open wounds are involved, the myiasis is known as traumatic and when boil-like, the lesion is termed furuncular. If the path of the larvae beneath the skin can be traced, the myiasis is designated as creeping and a rare form of bloodsucking myiasis is described as sanguinivorous. However, it is probably of more biological interest to classify myiases in terms of the relationships between host and parasite, since this provides insight into the biology of the fly species causing the myiasis and its likely pathological effect. Accordingly myiases may be described as obligatory, facultative or accidental.
Obligatory ectoparasites must have a living host to complete their development and are unable to survive in the absence of the host. In contrast, facultative parasites can develop in both living and dead organic matter. The facultative species can be subdivided into primary and secondary facultative ectoparasites. The primary species usually adopt an ectoparasitic habit and are capable of initiating myiases, but may occasionally live as saprophages in decaying organic matter and animal carcasses. The secondary facultative ectoparasites normally live as saprophages and, usually, cannot initiate a myiasis but may secondarily invade pre-existing infestations.
The final group of species to be described causes accidental or miscellaneous cases of myiasis. These are species that are only rare or chance agents of myiasis, which may invade an inappropriate host or which may cause a myiasis when fly eggs are accidentally ingested.
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