In general, the infection is of two types. Ectoparasitic (Auchmeromyia leuteola) and Endoparasitic (Cutaneous and Tissues or cavities). Examples of the cutaneous type are the Dermatobia hominis and Corylobia antrhopophaga. Examples of the Tissues or cavities type are the Sarcophaga, Wohlfartia, Fannia Oestrus, Chrysomia and Callitroga.
Deep Tissue Myiasis
Larvae of the flies belonging to the families Callitroga (Cochliomyia), Chrysomyia, Sarcophaga, Wohlfartia, Fannia and Oestrus invade tissues extensively when the eggs are laid on open wounds, damaged tissues or discharging surfaces, by the adult flies. The larvae of Wohlfartia can penetrate even unbroken skin. The lesions are commonly seen in the nasal cavities, paranasal sinuses, middle ear and orbit. Cartilage and bone may also be destroyed by the screw shaped larvae which may extend intracranially leading to fatal meningitis. The lesions are very painful and the larvae may be discharged from these sites. Treatment is manual removal of larvae or extraction after spraying the area with chloroform. Repeated sessions may be necessary. Secondary infection has to be treated with broad spectrum antibiotics like ampicillin.
Flies of the genus Chrysomyia and Oestrus may lay their eggs in the conjuctival sac. The larvae hatch out and produce lesions resembling acute conjunctivitis with severe irritation. Rarely corneal ulceration and loss of sight may occur. Removal of the maggot after anaesthetizing the eye and application of topical antibiotic drops will relieve the condition.
The larvae or pupae of Musca, Fannia, Sarcophaga and Tubifera may be passed in stools or appear in vomitus. The eggs may be laid by the flies around the lips or anus while sleeping, especially if there are foul smelling discharges around these orifices. The larvae hatch out from a few hours to two days and are swallowed to reach the upper gastrointestinal tract or they may crawl up into the rectum and large intestine. They develop in the stomach or in the intestines. Sometimes, larvae may be swallowed along with infested food stuffs. The larvae cause symptoms of gastritis or colitis which may persist from weeks to months. If reinfection does not occur, the condition is self-limiting. Treatment consists of administration of purgatives and reassurance about the self-limiting nature of the illness.
Larvae of Muscae, Fannia or Sarcophaga may enter the bladder, when the eggs are laid around the external genitalia and produce symptoms of lower urinary tract infection with proteinuria, pyuria and hematuria. The larvae may pass in urine. Rarely urinary system may be involved by maggots eroding their way from the gastrointestinal tract.