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Myiasis

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Myiasis
Other namesFlystrike, blowfly strike, fly-blown
Cutaneous myiasis in the shoulder of a human
Pronunciation
SpecialtyInfectious disease

Myiasis is the parasitic infestation of the body of a live animal by fly larvae (maggots) which grow inside the host while feeding on its tissue. Although flies are most commonly attracted to open wounds and urine- or feces-soaked fur, some species (including the most common myiatic flies—the botfly, blowfly, and screwfly) can create an infestation even on unbroken skin and have been known to use moist soil and non-myiatic flies (such as the common housefly) as vector agents for their parasitic larvae.

Because some animals (particularly non-native domestic animals) cannot react as effectively as humans to the causes and effects of myiasis, such infestations present a severe and continuing problem for livestock industries worldwide, causing severe economic losses where they are not mitigated by human action.[1] Although typically a far greater issue for animals, myiasis is also a relatively frequent affliction of humans in rural tropical regions where myiatic flies thrive, and often may require medical attention to surgically remove the parasites.[2]

Myiasis varies widely in the forms it takes and its effects on the victims. Such variations depend largely on the fly species and where the larvae are located. Some flies lay eggs in open wounds, other larvae may invade unbroken skin or enter the body through the nose or ears, and still others may be swallowed if the eggs are deposited on the lips or on food.[2] There can also be accidental myiasis which E. tenax can cause in humans via water containing the larvae or in contaminated uncooked food. The name of the condition derives from ancient Greek μυῖα (myia), meaning "fly".[3]

Signs and symptoms

How myiasis affects the human body depends on where the larvae are located. Larvae may infect dead, necrotic (prematurely dying) or living tissue in various sites: the skin, eyes, ears, stomach and intestinal tract, or in genitourinary sites.[4] They may invade open wounds and lesions or unbroken skin. Some enter the body through the nose or ears. Larvae or eggs can reach the stomach or intestines if they are swallowed with food and cause gastric or intestinal myiasis.[2]

Several different presentations of myiasis and their symptoms:[2]

Syndrome Symptoms
Cutaneous myiasis Painful, slow-developing ulcers or furuncle- (boil-) like sores that can last for a prolonged period
Nasal myiasis Obstruction of nasal passages and severe irritation. In some cases facial edema and fever can develop. Death is not uncommon.
Aural myiasis Crawling sensations and buzzing noises. Smelly discharge is sometimes present. If located in the middle ear, larvae may get to the brain.
Ophthalmomyiasis Severe irritation, edema, and pain. Fairly common.

Wound

Wound myiasis occurs when fly larvae infest open wounds. It has been a serious complication of war wounds in tropical areas, and is sometimes seen in neglected wounds in most parts of the world. Predisposing factors include poor socioeconomic conditions, extremes of age, neglect, mental disability, psychiatric illness, alcoholism, diabetes, and vascular occlusive disease.[5][6][7][8][9]

Eye

Myiasis of the human eye or ophthalmomyiasis can be caused by Hypoderma tarandi, a parasitic botfly of caribou. It is known to lead to uveitis, glaucoma, and retinal detachment.[10] Human ophthalmomyiasis, both external and internal, has been caused by the larvae of the botfly.[10]

Cause

Life cycle

The life cycle in sheep is typical of the disease. The female flies lay their eggs on the sheep in damp, protected areas of the body that are soaked with urine and feces, mainly the sheep's breech (buttocks). It takes approximately eight hours to a day for the eggs to hatch, depending on the conditions. Once hatched, the larvae then lacerate the skin with their mouthparts, causing open sores. Once the skin has been breached, the larvae then tunnel through the sores into the host's subcutaneous tissue, causing deep and irritating lesions highly subject to infection. After about the second day, bacterial infection is likely and, if left untreated, causes bacterial bloodstream infections or sepsis. This leads to anorexia and weakness and is generally fatal if untreated.[citation needed]

Human vectors

There are three main fly families causing economically important myiasis in livestock and also, occasionally, in humans:[citation needed]

Other families occasionally involved are:[citation needed]

Specific myiasis

Caused by flies that need a host for larval development[citation needed]

Semispecific myiasis

Caused by flies that usually lay their eggs in decaying animal or vegetable matter, but that can develop in a host if open wounds or sores are present[citation needed]

Flesh flies, or sarcophagids, members of the family Sarcophagidae, can cause intestinal myiasis in humans if the females lay their eggs on meat or fruit.[citation needed]

Accidental myiasis

Also called pseudomyiasis. Caused by flies that have no preference or need to develop in a host but that will do so on rare occasions. Transmission occurs through accidental deposit of eggs on oral or genitourinary openings, or by swallowing eggs or larvae that are on food.[citation needed] The cheese fly (Piophila casei) sometimes causes myiasis through intentional consumption of its maggots (which are contained in the traditional Sardinian delicacy casu marzu).[11][12] Other flies that can accidentally cause myiasis are:[citation needed]

The adult flies are not parasitic, but when they lay their eggs in open wounds and these hatch into their larval stage (also known as maggots or grubs), the larvae feed on live or necrotic tissue, causing myiasis to develop. They may also be ingested or enter through other body apertures.[citation needed]

Diagnosis

Myiasis is often misdiagnosed in the United States because it is rare and its symptoms are not specific. Intestinal myiasis and urinary myiasis are especially difficult to diagnose.[2]

Clues that myiasis may be present include recent travel to an endemic area, one or more non-healing lesions on the skin, itchiness, movement under the skin or pain, discharge from a central punctum (tiny hole), or a small, white structure protruding from the lesion.[13] Serologic testing has also been used to diagnose the presence of botfly larvae in human ophthalmomyiasis.[10]

  • Ultrasound showing maggot infestation[14]
  • Ultrasound showing maggot infestation[14]
  • Ultrasound showing maggot infestation[14]
    Ultrasound showing maggot infestation[14]

Classifications

German entomologist Fritz Zumpt describes myiasis as "the infestation of live human and vertebrate animals with dipterous larvae, which at least for a period, feed on the host's dead or living tissue, liquid body substances, or ingested food". For modern purposes however, this is too vague. For example, feeding on dead or necrotic tissue is not generally a problem except when larvae such as those of flies in the family Piophilidae attack stored food such as cheese or preserved meats; such activity suggests saprophagy rather than parasitism; it even may be medically beneficial in maggot debridement therapy (MDT).[citation needed]

Currently myiasis commonly is classified according to aspects relevant to the case in question:

  • The classical description of myiasis is according to the part of the host that is infected. This is the classification used by ICD-10. For example:[15]
  • Another aspect is the relationship between the host and the parasite and provides insight into the biology of the fly species causing the myiasis and its likely effect. Thus the myiasis is described as either:[15]
    • obligatory, where the parasite cannot complete its life cycle without its parasitic phase, which may be specific, semispecific, or opportunistic
    • facultative, incidental, or accidental, where it is not essential to the life cycle of the parasite; perhaps a normally free-living larva accidentally gained entrance to the host[2]

Accidental myiasis commonly is enteric, resulting from swallowing eggs or larvae with one's food. The effect is called pseudomyiasis.[16] One traditional cause of pseudomyiasis was the eating of maggots of cheese flies in cheeses such as Stilton. Depending on the species present in the gut, pseudomyiasis may cause significant medical symptoms, but it is likely that most cases pass unnoticed.[citation needed]

Prevention

The first control method is preventive and aims to eradicate the adult flies before they can cause any damage and is called vector control. The second control method is the treatment once the infestation is present, and concerns the infected animals (including humans).[citation needed]

The principal control method of adult populations of myiasis inducing flies involves insecticide applications in the environment where the target livestock is kept. Organophosphorus or organochlorine compounds may be used, usually in a spraying formulation. One alternative prevention method is the sterile insect technique (SIT) where a significant number of artificially reared sterilized (usually through irradiation) male flies are introduced. The male flies compete with wild breed males for females in order to copulate and thus cause females to lay batches of unfertilized eggs which cannot develop into the larval stage.[citation needed]

One prevention method involves removing the environment most favourable to the flies, such as by removal of the tail of sheep (docking). Another example is the crutching of sheep, which involves the removal of wool from around the tail and between the rear legs, which is a favourable environment for the larvae. Another, more permanent, practice which is used in some countries is mulesing, where skin is removed from young animals to tighten remaining skin – leaving it less prone to fly attack.[17]

To prevent myiasis in humans, there is a need for general improvement of sanitation, personal hygiene, and extermination of the flies by insecticides. Clothes should be washed thoroughly, preferably in hot water, dried away from flies, and ironed thoroughly. The heat of the iron kills the eggs of myiasis-causing flies on washed clothes.[13]

Treatment

This applies once an infestation is established. In many circles the first response to cutaneous myiasis once the breathing hole has formed, is to cover the air hole thickly with petroleum jelly. Lack of oxygen then forces the larva to the surface, where it can more easily be dealt with. In a clinical or veterinary setting there may not be time for such tentative approaches, and the treatment of choice might be more direct, with or without an incision. First the larva must be eliminated through pressure around the lesion and the use of forceps. Secondly the wound must be cleaned and disinfected. Further control is necessary to avoid further reinfestation.[citation needed]

Livestock may be treated prophylactically with slow-release boluses containing ivermectin, which can provide long-term protection against the development of the larvae. Sheep also may be dipped, a process which involves drenching the animals in persistent insecticide to poison the larvae before they develop into a problem.[citation needed]

Epidemiology

The most common infected animal worldwide is the domestic sheep, for more information see fly strike in sheep. This condition is caused by the blowfly (particularly Lucilia sericata and its sister species L. cuprina), especially where the weather is often hot and wet.[18] Blowfly strike accounts for over A$170 million a year in losses in the Australian sheep industry, the largest such losses in the world. Given the seriousness of the risk, Australian sheep farmers commonly perform preventive measures such as mulesing designed to remove the most common targets for the flies. The docking of lambs' tails (another frequently-soiled area that flies target) is also commonly practiced by sheep farmers worldwide. Maggots also occasionally [citation needed] infest the vulvar area, causing the condition called vulvar myiasis.

Such problems are not peculiar to Australia and New Zealand; they occur worldwide, especially in countries where livestock, particularly sheep, are kept under hot, wet, conditions, including most of Africa and the Americas, ranging from the cold temperate regions in the north, to corresponding latitudes in the south. Myiasis is also not restricted to sheep; screwworm flies (Cochliomyia hominivorax in particular) regularly cause upwards of US$100 million in annual damages to domestic cows and goats,[19] though the impact has been heavily mitigated in recent years by the sterile insect technique. [citation needed]

History

Myiasis in a cat's flesh
Myiasis in a dog's flesh

Frederick William Hope coined the term myiasis in 1840 to refer to diseases resulting from dipterous larvae as opposed to those caused by other insect larvae (the term for this was scholechiasis). Hope described several cases of myiasis from Jamaica caused by unknown larvae, one of which resulted in death.[20]

Even though the term myiasis was first used in 1840, such conditions have been known since ancient times. Ambroise Paré, the chief surgeon to King Charles IX and King Henry III, observed that maggots often infested open wounds.[21]

Maggot therapy

Main article: Maggot therapy

Throughout recorded history, maggots have been used therapeutically to clean out necrotic wounds, an application known as maggot therapy.[citation needed]


References

  1. ^ Otranto, Domenico (2001). "The immunology of myiasis: parasite survival and host defense strategies". Trends in Parasitology. 17 (4): 176–182. doi:10.1016/S1471-4922(00)01943-7. PMID 11282507.
  2. ^ a b c d e f John, David; Petri, William, eds. (2006). Markell and Voge's Medical Parasitology (9th ed.). Missouri: Saunders Elsevier. pp. 328–334. ISBN 978-0-7216-4793-7.
  3. ^ μυῖα. Liddell, Henry George; Scott, Robert; A Greek–English Lexicon at the Perseus Project.
  4. ^ Ockenhouse, Christian F.; Samlaska, Curt P.; Benson, Paul M.; Roberts, Lyman W.; Eliasson, Arn; Malane, Susan; Menich, Mark D. (1990). "Cutaneous myiasis caused by the African tumbu fly (Cordylobia anthropophaga)". Archives of Dermatology. 126 (2): 199–202. doi:10.1001/archderm.1990.01670260069013. PMID 2301958.
  5. ^ Namazi MR, Fallahzadeh MK (November 2009). "Wound myiasis in a patient with squamous cell carcinoma". ScientificWorldJournal. 9: 1192–3. doi:10.1100/tsw.2009.138. PMC 5823144. PMID 19882087.{{cite journal}}: CS1 maint: unflagged free DOI (link)
  6. ^ "Screwworm flies as agents of wound myiasis". Fao.org. Retrieved 2013-11-05.
  7. ^ El-Azazy, O.M.E. (1989). "Wound myiasis caused by Cochliomyia hominivorax in Libya". Vet. Rec. 124 (4): 103. doi:10.1136/vr.124.4.103-a. PMID 2929078. S2CID 26982759.
  8. ^ Huntington, T. E.; Voigt, David W.; Higley, L. G. (January 2008). "Not the Usual Suspects: Human Wound Myiasis by Phorids". Journal of Medical Entomology. 45 (1): 157–159. doi:10.1603/0022-2585(2008)45[157:NTUSHW]2.0.CO;2. PMID 18283957.
  9. ^ Cleveland Clinic (13 August 2010). Current Clinical Medicine: Expert Consult - Online. Elsevier Health Sciences. pp. 1396–. ISBN 978-1-4377-3571-0. Retrieved 22 April 2013.
  10. ^ a b c Lagacé-Wiens, P. R.; et al. (January 2008). "Human ophthalmomyiasis interna caused by Hypoderma tarandi, Northern Canada". Emerging Infectious Diseases. 14 (1): 64–66. doi:10.3201/eid1401.070163. PMC 2600172. PMID 18258079.
  11. ^ Peckenscneider, L.E., Polorny, C. and Hellwig, C.A., 1952 Intestinal infestation with maggots of the cheese fly (Piophila casei). J Am Med Assoc. 1952 May 17;149 (3):262-3.
  12. ^ "Gastrointestinal Myiasis – Report of a case, Alonzo F. Brand, M.D., Arch Intern Med (Chic). 1931;47(1):149–154. doi:10.1001/archinte.1931.00140190160017". Archives of Internal Medicine. 47 (1): 149–154. January 1931. doi:10.1001/archinte.1931.00140190160017. Archived from the original on 9 January 2018. Retrieved 17 February 2018.
  13. ^ a b Adisa, Charles Adeyinka; Mbanaso, Augustus (2004). "Furuncular myiasis of the breast caused by the larvae of the Tumbu fly (Cordylobia anthropophaga)". BMC Surgery. 4: 5. doi:10.1186/1471-2482-4-5. PMC 394335. PMID 15113429.{{cite journal}}: CS1 maint: unflagged free DOI (link)
  14. ^ a b c "UOTW #22 - Ultrasound of the Week". Ultrasound of the Week. 14 October 2014. Retrieved 27 May 2017.
  15. ^ a b Janovy, John; Schmidt, Gerald D.; Roberts, Larry S. (1996). Gerald D. Schmidt & Larry S. Roberts' Foundations of parasitology. Dubuque, Iowa: Wm. C. Brown. ISBN 0-697-26071-2.
  16. ^ Zumpt, Fritz Konrad Ernst (1965). Myiasis in man and animals in the old world. Butterworth.
  17. ^ "Standard Operating Procedures - sheep Mulesing". teacher's notes. New South Wales Department of Primary Industries. March 8, 2004. Retrieved 2007-01-09.
  18. ^ "Royal (Dick) School of Veterinary Studies". Veterinary Record. 160 (19): 669. 2007-05-12. doi:10.1136/vr.160.19.669-b. ISSN 0042-4900. S2CID 219190547.
  19. ^ Hill, Dennis S. (1997). The economic importance of insects. Springer. p. 102. ISBN 0-412-49800-6.
  20. ^ "Introduction to myiasis | Natural History Museum". Nhm.ac.uk. Retrieved 2013-11-05.
  21. ^ Sherman, RA, Hall, MJR, Thomas, S (2000). "Medicinal Maggots: An ancient remedy for some contemporary afflictions". Annual Review of Entomology. 45: 55–81. doi:10.1146/annurev.ento.45.1.55. PMID 10761570.
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