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Myiasis

ISSN 2398-2942


Synonym(s): Fly strike

Introduction

  • Myiases (Greek MYIA = fly) are infestations of humans and animals with maggot larvae of flies, which feed on dead or living host tissue for a variable period.
  • Classification is based on their location on the host body (dermal, subdermal, nasopharyngeal, internal organs, intestinal and urogenital) or, in parasitological terms, according to the type of hostparasite relationship (obligatory, facultative or pseudomyiases).
  • Cause: maggot larvae of flies of the orderDiptera.
  • Signs: fly strike occurs mostly in warm weather, and is usually preceded by soiling or moist dermatitis. Fly larvae cause alopecia and erosion/ulceration and may enter body cavities. Secondary skin infection is common and peritonitis/septicemia may be associated with entry to the body cavity.
  • Diagnosis: clinical signs.
  • Treatment: clip and clean area, remove maggots, antibiotics, fluid therapy.
  • Prognosis: poor in severe cases, otherwise dependant on predisposing conditions.

Acute presentation

  • Soiling and alopecia/erosion.
  • Punched-out round holes that may coalesce to form broad defects.
  • Ulceration/necrosis of large areas of skin may occur.
  • Visible fly larvae, often embedded in exposed or neglected wounds.
  • Infested wounds have a characteristic strong offensive smell and ooze a sero-sanguineous exudate or frank blood.
  • Entry into body cavities possible (favorite areas include nose, eyes, mouth anus, genitalia).

Geographic incidence

  • Worldwide.
  • In USACuterebrasp larvae also involved, which develop as single maggots in a subcutaneous pocket over several weeks.
  • Cordylobia anthropophaga.

Age predisposition

  • Usually isolated animals.
  • Many in a group affected in very poor housing/hygiene.

Cost considerations

  • May be high as treatment of disease may be time-consuming.

Pathogenesis

Etiology

  • Dipterafly larvae, especiallyLucilia sericataand other Calliphora spp.
  • The Old World Screwworm fly (Chrysomya bezziana) has recently been causing aggressive myiasis in pet dogs in Hong Kong. Because Hong Kong is a source of pet migration or a transit point to Australia, the fly could threaten Australia.
  • Cochliomyia hominovoraxis still reported in the US.

Predisposing factors

General
  • Some maggots (egCalliphorids)are only present on dead tissues.
  • Some maggots (egSarcophagids) only attack living tissue.
  • Draining wounds or urine soaked coats.
  • diseases, especially those causing diarrhea and soiling of the perineum or a decrease in grooming activity.
  • Obesity.
  • Warm weather.
  • Unattended wounds.
  • Poor hygiene/lack of adequate observation of pet.

Pathophysiology

  • Laying ofDipteraeggs on unattended wounds.
  • Maggots damage skin and burrow under skin.
  • As skin breaks down and liquefies it becomes more suitable for further infestation.
  • Body cavities may be entered leading to peritonitis Peritonitis /septicemia Shock: septic.
  • Some larvae (egCuterebra) can penetrate intact skin and produce nodular lesions. Eggs are deposited on vegetation and animals become infested as they pass through contaminated areas. As dogs and cats are abnormal hosts the larvae undergo aberrant migrations. In the late fall the larvae enlarge producing a swelling and a fistula develops.

Timecourse

  • Can be very rapid (hours) - some fly species are viviparous and deposit live maggots directly onto the skin. In ideal conditions even eggs will hatch within 8 hours.
  • Blowflies (Calliphoridae) and fleshflies (Sarcophagidae) cause myiases of relatively short duration, by both obligate and/or facultative parasites, which mature within 47 days, usually at the host's body orifices and in wounds (egCochliomyia hominivorax, andChrysomya bezziana).
  • Botflies (Oestridae) are obligate parasites that are harbored and feed for several weeks to months in the host's nasopharyngeal tract.

Diagnosis

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Treatment

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Prevention

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Outcomes

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Further Reading

Publications

Refereed papers

  • Recent references from PubMed and VetMedResource.
  • Anderson G S, Huitson N R (2004) Myiasis in pet animals in British Columbia: the potential of forensic entomology for determining duration of possible neglect. Can Vet J 45 (12), 993-998 PubMed.
  • Chemonges-Nielsen S (2003) Chrysomya bezziana in pet dogs in Hong Kong: a potential threat to Australia. Aust Vet J 81 (4), 202-205 PubMed.
  • Ferroglio E, Rossi L, Trisciuoglio A (2003) Cordylobia anthropophaga myiasis in a dog returning to Italy from a tropical country. Vet Rec 153 (11), 330-331 PubMed.
  • Otranto D (2001) The immunology of myiasis: parasite survival and host defense strategies. Trends Parasitol 17 (4), 176-182 PubMed.
  • Luján L, Vázquez J, Lucientes J, Pañero J A, Varea R (1998) Nasal myiasis due to Oestrus ovis infestation in a dog. Vet Rec 142 (11), 282-283 PubMed.
  • Manchón M, Ruiz de Ybáñez R, Alonso F D (1998) Intestinal myiasis in a dog. Vet Rec 143 (17), 479-480 PubMed.
  • Azeredo-Espin A M, Madeira N G (1996) Primary myiasis in dog caused by Phaenicia eximia (Diptera:Calliphoridae) and preliminary mitochondrial DNA analysis of the species in Brazil. J Med Entomol 33 (5), 839-843 PubMed.
  • Dongus H, Hirschberger J, Gothe R (1996) Cordylobia anthropophaga as a cause of cutaneous myiasis in a dog in Germany. Tierarztl Prax 24 (5), 493-496 PubMed.
  • Hendrix C M, King-Jackson D A, Wilson P M, Blagburn B L, Lindsay D S (1995) Furunculoid myiasis in a dog caused by Cordylobia anthropophaga. J Am Vet Med Assoc 207 (9), 1187-1189 PubMed.