Definition of myiasis:Invasion of animal and human tissues by larvae od dipterous fliesEtiological Classification of Myiasis-Causing Flies:

Obligatory (Specific):1. Both Dermatobia and Cordylobia are obligatory parasites,

whose larval stages can occur only in the living tissue of animal or human hosts.

2. Other obligatory flies include the genera Oestrus, Rhinoestrus, Gasterophilus, Hypoderma, Chrysomyia, and Wohlfahrtia vigil.

3. The type of tissue affected varies with the species of the parasite.

Facultative (Semi-specific): 1. Flies of this group normally develop in decomposing tissue.2. They are considered facultative parasites.3. Larvae of these flies parasitize wounds and other damaged

tissues, and some species further invade living tissues adjacent to the wound.

4. Important genera in this category include Musca, Calliphora, and Lucilia.

Accidental (Non-specific) Agents1. Accidental myiasis occurs when egg-stage of flies are ingested

in contaminated food or come in contact with the genitourinary tract.

2. Flies of the families Muscidae, Calliphoridae, and Sarcophagidae may be involved

Clinical classification of myiasis:1. Bloodsucking larvae of the African species Auchmeromyia

luteola are atypical myiasis-causing species, they do not live in the host, but suck the blood of sleeping humans (sanguinivorous myiasis).

2. Cutaneous myiasis: Furuncular:a. The Cuterebridae, Gasterophilidae and Oestridae are

responsible for furuncular myiasis in animals and all are obligate parasites.

b. The most important cuterebrid in man is Dermatobia hominis (human bot fly) Its larvae create boil-like swellings where they enter the skin.

c. The sarcophagid Wohlfahrtia vigil and Wohlfahrtia opaca and the calliphporid Cordylobia larvae tend to penetrate the host's skin, producing furuncles.

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Subdermal migratory:a. In human Gasterophilus and Hypoderma larvae can not develop beyond the first instar but produce and wander in tunnels in the epidermis (cutaneous larva migrans).b. Hypoderma penetrate more deeply than Gasterophilus; so may invade nervous system. Wound myiasis: Calliphoridae, Sarcophagidae, Muscidae

are very important in wound myiasis.o It may be benign, as when secondary species confine their

activities to diseased and dead tissue. Oro It may be malign, as when the obligate and primary species

attack living tissue .oThree major species of obligate parasites encountered in

wound myiasis are Cochliomyia hominivorax, C. bezziana, and W. magnifica.

3. Myiasis of the body cavities In head passages: Rhinoestrus, Oesterus and

cochliomyia homnivorax can invade nasal, ocular and aural cavities in human

a. Nasal: Tickling, sneezing, pain and nasal obstruction. Bloody discharge that becomes purulent and fetid. Invasion pf CNS → death.

b. Aural: pain, discomfort, deafness, tinnitus, and drum perforation.

c. Ocular: External (Oestrus), internal (Oestrus, Rhinoesterus, Dermatobia, Gasterophilus). Normally, Oestrus induces a painful form of conjunctivitis. However, larvae can penetrate the eye.

Anal/ vaginal/ urogenital:a. Wohlfahrtia can lay many eggs in the soiling and sores round

the anus and vagina to develop into larvae within few hours.b. Musca, Calliphora, Sarcophaga and Psychoda can oviposit

eggs on the vulva or vaginal area to develop into larvae that may enter the urinary bladder.

Intestinal: Eggs and larvae of Musca, Fannia scalaris (latrine), F. canicularis (little house fly) Chrysomiya, Calliphora, and others are deposited on foodstuffs and can survive in the intestines to induce irritation→ pain, vomiting, diarrhea and even ulceration.

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