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Myiasis ( ), also known as flystrike or fly strike, is the parasitic infestation of the body of a live animal by fly () that grow inside the host while feeding on its tissue. Although flies are most commonly attracted to and urine- or feces-soaked fur, some species (including the most common myiatic flies—the botfly, Calliphoridae, and screwfly) can create an infestation even on unbroken skin. Non-myiatic flies (such as the common housefly) can be responsible for accidental myiasis.
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. Although typically a far greater issue for animals, myiasis is also a relatively frequent disease for humans in rural tropical regions where myiatic flies thrive, and often may require medical attention to surgically remove the parasites. (2025). 9780721647937, Saunders Elsevier. ISBN 9780721647937
Myiasis varies widely in the forms it takes and its effects on those affected. 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 food. There can also be accidental myiasis that Eristalis 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"..
Several different presentations of myiasis and their 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. |
Other families occasionally involved are:
Flesh flies, or sarcophagids, members of the family Sarcophagidae, can cause Intestine myiasis in humans if the females deposit larvae on meat or fruit.
The adult flies are not parasitic, but when they lay their eggs in open and these hatch into their stage (also known as or Larva), the larvae feed on live or necrotic tissue, causing myiasis to develop. They may also be ingested or enter through other body apertures.
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. Serologic testing has also been used to diagnose the presence of botfly larvae in human ophthalmomyiasis.
Currently, myiasis commonly is classified according to aspects relevant to the case in question:
The principal control method of adult populations of myiasis-inducing flies involves insecticide applications in the environment where the target livestock is kept. Insecticide or Insecticide 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 to copulate and thus cause females to lay batches of unfertilized eggs that cannot develop into the larval stage.
One prevention method involves removing the environment most favourable to the flies, such as by removal of the tail. 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 that is used in some countries is mulesing, where the skin is removed from young animals to tighten remaining skinleaving it less prone to fly attack.
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.
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 sheep dip, a process that involves drenching the animals in persistent insecticide to poison the larvae before they develop into a problem.
In addition to blowfly strike in sheep, myiasis from Cochliomyia ( Cochliomyia hominivorax in particular) regularly cause upwards of US$100 million in annual damages to domestic and . Screwworm-related myiasis is primarily mitigated through the sterile insect technique.
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.
Fly larvae that feed on dead tissue can clean wounds and may reduce bacterial activity and the chance of a secondary infection. They dissolve dead tissue by secreting digestive enzymes onto the wound as well as actively eating the dead tissue with mouth hooks, two hard, probing appendages protruding on either side of the "mouth". Maggot therapyalso known as maggot debridement therapy (MDT), larval therapy, larva therapy, or larvae therapyis the intentional introduction by a health care practitioner of live, disinfected green bottle fly maggots into the non-healing skin and soft tissue wounds of a human or other animal for the purpose of selectively cleaning out only the necrotic tissue within a wound to promote healing.
Although maggot therapy has been used in the US for the past 80 years, it was approved by the FDA as a medical device only in 2004 (along with leeches). Maggots were the first live organism to be marketed in the US according to FDA regulations, and are approved for treating neuropathic (diabetic) foot ulcers, pressure ulcers, venous stasis ulcers, and traumatic and post-surgical wounds that are unresponsive to conventional therapies. Maggots were used in medicine before this time, but were not federally regulated. In 1990, California internist Ronald Sherman began treating patients with maggots produced at his lab at the UC Irvine School of Medicine. Sherman went on to co-found Monarch Labs in 2005, which UC Irvine contracted to produce maggots for Sherman's own continuing clinical research on myiasis at the university. Monarch Labs also sells maggots to hospitals and other medical practices, the first US commercial supplier to do so since the last one closed in 1935.
In the US, demand for these fly larvae doubled after the FDA ruling. Maggot therapy is now used in more than 300 sites across the country. The American Medical Association and Centers for Medicare and Medicaid Services recently clarified the reimbursement guidelines to the wound care community for medicinal maggots, and this therapy may soon be covered by insurance. The larvae of the green bottle fly (Lucilia fly) are now used exclusively for this purpose, since they preferentially devour only necrotic tissue, leaving healthy tissue intact. This is an important distinction, as most other major varieties of myiasitic fly larvae attack both live and dead wound tissue indiscriminately, effectively negating their benefit in non-harmful wound debridement. Medicinal maggots are placed on the wound and covered with a sterile dressing of gauze and nylon mesh. However, too many larvae placed on the wound could result in healthy tissue being eaten, efficiently creating a new wound, and rendering it a type of myiasis.
William Baer, an orthopedic surgeon at Johns Hopkins during the late 1920s, used maggot therapy to treat a series of patients with osteomyelitis, an infection of bone or bone marrow. The idea was based on an experience in World War I in which two soldiers presented to him with broken femurs after having lain on the ground for seven days without food. Baer could not figure out why neither man had a fever or signs of sepsis. He observed: "On removing the clothing from the wounded part, much was my surprise to see the wound filled with thousands and thousands of maggots, apparently those of the blow fly. The sight was very disgusting and measures were taken hurriedly to wash out these abominable looking creatures." However, he then saw that the wounds were filled with "beautiful pink granulation tissue" and were healing well.
Maggot therapy was common in the United States during the 1930s. However, during the second half of the twentieth century, after the introduction of antibiotics, maggot therapy was used only as a last resort for very serious wounds. Lately maggots have been making a comeback due to the increased resistance of bacteria to antibiotics.
Classifications
Germany Entomology 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 Cheese fly attack stored food such as cheese or preserved meats; such activity suggests saprophagy rather than parasitism; it even may be medically beneficial in Maggot therapy.
Accidental myiasis commonly is enteric, resulting from swallowing eggs or larvae with one's food. The effect is called pseudomyiasis. One traditional cause of pseudomyiasis was the eating of maggots of Piophilidae in cheeses such as Stilton cheese. Depending on the species present in the gut, pseudomyiasis may cause significant medical symptoms, but it is likely that most cases pass unnoticed.
(1996). 9780697260710, Wm. C. Brown. ISBN 9780697260710
Prevention
The first control method is preventive and aims to eradicate the adult flies before they can cause any damage and is called. The second control method is treatment once the infestation is present, and concerns the infected animals (including humans).
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.
Epidemiology
Myiasis is prevalent in livestock, and especially in sheep. Myiasis in sheep is often caused by Calliphoridae ( Lucilia sericata and Lucilia cuprina in particular) and is commonly referred to as blowfly strike. Blowfly strike, and other flystrike, occurs worldwide but is most common in regions where hot and wet conditions are sustained, such as Sub-Saharan Africa, Southeast Asia, Latin America, Australia, and New Zealand. As of 2021, blowfly strike accounts for over A$280 million a year in losses for the Australian Sheep farming. As mitigation, Australian sheep farmers may engage in mulesing, a procedure designed to remove strips of wool-producing skin that are the most common targets for flies. Farmers may also dock lambs' tails to reduce the likelihood of infestation. However, both mulesing and tail-docking have received criticism from animal welfare groups, who say the mitigative procedures are excessive and can have other negative effects.
History
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.
Maggot therapy
Throughout recorded history, maggots have been used Therapy to clean out necrotic , an application known as maggot therapy.
History
Maggot therapy has a long history and prehistory. The indigenous people of Australia used maggot therapy, and so do the Hill Peoples of Northern Burma, and possibly the Mayans of Central America. Surgeons in Napoleon's armies recognized that wounded soldiers with myiasis were more likely to survive than those without the infestation. In the American Civil War, army surgeons treated wounds by allowing blowfly maggots to clean away the decayed tissue.
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