Myiasis

• First Described: Myiasis in humans and animals has been recognized for centuries. The most well-accepted description of myiasis was reported in 1965 by Fritz Zumpt, a German entomologist. 1 Infestations with Cuterebra spp. in cats in the United States were first described in the late 1800s. 2 • Cause: A variety of fly species that obligately or facultatively infest the skin of vertebrates. The most common species that infest dogs and cats belong to the order Diptera; families Oestridae (bot flies or warble flies), Calliphoridae (blow flies), Sarcophagidae (flesh flies), and Muscidae (house flies). Examples include Cuterebra spp., Hypoderma spp., and Dermatobia hominis, Oestrus spp. (Oestridae); Cochliomyia hominivorax, Lucilia spp., and Chrysomya spp. (Calliphoridae); Sarcophaga spp. and Wohlfahrtia spp. (Sarcophagidae); and Musca domestica (Muscidae). • Affected Hosts: Dogs, cats, and a large number of other vertebrate host species, especially livestock and wildlife species. • Geographic Distribution: Worldwide, although the geographic distribution of individual fly species varies. • Route of Transmission: For Cuterebra spp., eggs or larvae that are normally deposited around rodent or lagomorph burrows contaminate the skin and migrate into tissues. For most other fly species, eggs or larvae are deposited directly on to the vertebrate host. This may be where wounds or skin maceration are present, around body orifices (e.g., nasal cavity, perianal region), or on intact skin of weak or debilitated animals that are unable to groom. • Major Clinical Signs: Cutaneous ulceration, which may have a putrid odor; subcutaneous masses (“warbles”), which may be pruritic or have evidence of larval movement; upper respiratory signs (e.g., sneezing, nasal discharge, stertorous respiration); neurologic signs (e.g., seizures, paralysis); ophthalmologic signs (impaired vision, uveitis, corneal edema, ocular discharge, distortion of the globe). • Differential Diagnoses: Depend on parasite location and include a variety of other infectious diseases and neoplasia of the skin, ocular tissues, upper respiratory tract, and CNS; and migrating foreign bodies (e.g., plant awns). Aberrant CNS migration by Cuterebra spp. has been identified as a cause of feline ischemic encephalopathy in some regions. • Human Health Significance: Humans can be infested by some of the same Diptera species that infest dogs and cats; myiasis is more often seen in impoverished people living in unhygienic conditions, travelers returning from tropical jungles, and children. Infestations are not directly transmitted from dogs and cats to humans. Blow fly larvae, especially Lucilia sericata, are also used as a recognized treatment in humans for debridement of necrotic wounds.