Myiasis may be defined as the infection of vertebrates with the larvae maggots) of Diptera flies which feed on the tissues of the host. The maggots are usually identified by the form of their posterior spiracles, but this may be difficult to define in the early molts. Hearing the larvae to adults makes identification easier, especially with immature stages Myiasis is a far greater problem in sheep, cattle, and deer than in man.
There is no form of myiasis found exclusively in man For the purposes of a textbook of medicine, it is permissible to abandon the scientific classification of the responsible specie* and consider the clinical type of myiasis produced. For a description of the genera of flint, u textbook of entomology should be consulted Primary- myiasis occur* in the absence of debility of the host or tissue injury; this is in contrast to secondary myiasis.
Furuncular Myiasis is a good descriptive term, because the skin lesion looks like a boil but in fact contains a maggot which breathes through a holt- in the tip of the lesion When mature, the in at; got drops to the ground to pupate. There art* two distinct types occurring in Africa and the Americas, respectively. The African Tumbu fly ‘Cordylobin anthro/Mphanai. The eggs are sometimes laid on clothing or else the larvae actively seek the host and burrow into the skin to feed. Multiple lesions are common.
The normal hosts are wild rodents. The human botfly Dermutobia homims • The botfly is found in South America, Central America, and Mexico. The eggs are frequently laid on a hematophagous insect ■mosquito or stable flyi by the female and thence transported to the host. The secondarily infected “boil”-like lesion also occurs in other mammals in endemic areas.
The application of petroleum jelly to the lesion to block the spiracles often brings the suffocating larvae wriggling out backward, especially when mature Immature larvae can Ik- excised, but if possible it is better to let them mature and drop out
Creeping myiasis is a form of larva migrans caused by flies of the genera Gastrophilus and Hypoderma. The former larvae do not mature and. being restricted to the stratum comeum, leave an obvious trail. Hypoderma penetrates more deeply and can complete its development in some instances and perforate the skin to escape.
The behavior of these two species is easily understood if their lives in their normal hosts are mentioned. Gastrophilus, normally a parasite of Equidae. has a period of migration as a young larva in the tongue epithelium but matures in the lumen of the intestine Hypoderma is classically a parasite of bovids // hoi is migrates via nerve trunks to gain the spinal canal and paravertebral muscle mass, and II Uneatus penetrates, migrating via the mucosa of the upper icut and gaining the same muscles via the esophagus. Both cause voluminous subcutaneous paravertebral abscesses, ruining the hide It is not surprising, therefore, that when man is the host, the larvae may wander widely and even gain the eye, causing blindness.
A painful conjunctivitis can be produced by the first-stage maggots of Oestrus ovis hatching from eggs laid by the female near the conjunctiva. Hypoderma maggots may penetrate the globe of the eye. Such maggots can be irrigated from the conjunctiva or mechanically removed.
Other Forms of Primary Myiasis
Genitourinary myiasis owing to F.innin or Calliphora maggot* has been rarely reported. the egg* being laid in the vicinity of the urethra Maggot* of thev p’nera and the genera Sarcophagi! and Mux-a have been found in freshly passed stools and can develop in the fecal st ream. TMmNoroethylene is efltetivt Intwtinil myiasis is cosmopolitan and relatively common In North America the drone fly (Tubifera tenaxl larvae is the most
frequently encountered species. The larvae of Auchmero-myia luteola (the Congo floor maggot i are temporary blood-sucking parasites of Africa; the larvae emerge from hiding places at night to suck blood, but after a meal retire to rest.
Invasion of the body by maggots can occur in very debilitated individuals and in those with destructive or ulcerative lesions. Thus wounds may be infected by maggots of various fly genera, including Wohlfahrtia. Callitroga, and t’hrysomyia Similarly, my i a si* of the none, upper respiratory passages, or ear i> caused by the screwworm fly maggots mvuding infected debilitated tissues. They should In- picki-d out with forceps, otherwise they can penetrate the base of the skull and invade the brain.
Prevention of Myiasis
Reduction of screw worms, botflies, and warble fly maggots m sheep and cattle reduces the chances of human infection. This can be done w ith various dip> of insecticides. Auchmeromyia larvae can be killed by dusting houses with insecticides. Clothing should be ironed and not hung out of doors for Cordylobia to lay eggs on it Repellents and bed nets will reduce the incidence of Der-matobia lesions. The proper control of refuse disposal will reduce the number of blue- and greenbottle flies. It is worth noting that the eradication of the screwworm fly from Curasao by releasing sexually sterile males is one of the few instances of a successful form of biologic control.