Myiasis

Myiasis is a parasitic infestation with fly larvae, commonly known as maggots, of humans or animals. Maggots can feed on bodily fluid and both dead or living tissue of mammals, which includes humans. It can cause a wide area of infestation depending on the location on the body. There are mainly three types of myiasis that are in cutaneous form; furuncular, wound and migratory myiasis. Other forms of myiasis include urogenital, ophthalmomyiasis, nasopharyngeal, cavitary, and hematophagous myiasis.

Main Cutaneous Types of Myiasis

Furuncular myiasis

Human botflies, particularly Dermatobia hominis, are the common causes of furuncular myiasis. Dermatobia hominis is commonly found in Central and South American area. Other species that can cause furuncular myiasis are species of Cuterebra, Wohlfahrtia, and Cordylobia anthropophaga. Many of these flies do not directly drop their eggs on the skin of humans. They will either transfer it to other insects, like mosquitoes or drop it on them. When the insects or items carrying the eggs get in contact with human skin, then the eggs are transferred and eventually turn into larvae. It then burrows in the skin until it reaches maturity. The size of mature larvae ranges from 1 – 2 cm. Symptoms of furuncular myiasis are piercing pain, itchiness and movement sensation. Initially, the bumps may appear like the bite of an arthropod and you may notice that it has serous fluid drainage on the center.

Wound myiasis

Wound myiasis is caused by infestation with larvae of a black or green blowfly. This type of myiasis is normally found in wounds of alcoholic or homeless people. This becomes more serious when the wound is untreated and neglected.

Migratory myiasis

With migratory myiasis, the case is a bit different for humans because the flies that lay eggs don’t intend to affect humans. Instead, humans get in contact with the fly larvae when they get in contact with animals that are infested. However, it’s rarely seen that eggs are laid directly on human skin. Some species of flies that brings this form of larvae are species of Hypoderma and horse botflies.

Causes of Myiasis

Cochliomyia hominivorax

The larvae of this fly have been found in wound myiasis and are considered as one of the major obligate parasites. t is also known as the New World Screwworm fly. The New World Screwworm fly can survive low temperatures and have been a huge factor in its spread of infestations. The female form of this species lays the eggs on the edge of a person/animal’s wound or on the mucous membranes.

Dermatobia hominis

The fly Dermatobia hominis is the main cause for furuncular myiasis. It is also known as the human botfly. Its larvae burrow in the skin which causes pain and lesions to drain. The adult male form of the D. hominis can live for a little over a week and appears to be like a bumblebee. The adult female form of the D. hominis that bears egg will catch an arthropod that sucks blood, like mosquitoes, and will then lay the eggs midflight on its abdomen. The arthropod with eggs laid on is meant to land on to a host with warm blood, particularly humans, to suck blood. The heat from the host will trigger the eggs to hatch and the larvae will then fall off on the human skin. The larvae will then enter inside the bitten area of the arthropod. The larvae can mature and grow up to 20 millimeters in size. When uninterrupted, it can stay for up to 5 to 10 weeks until it falls on the ground and turn in to D. hominis flies in a couple of weeks or more.

Oestrus ovis

Oestrus ovis, also known as the sheep botfly, mainly causes ophthalmomyiasis. This fly transfers its eggs by dropping it directly on the face of a human while on midair. Nevertheless, there is another way that it gets to humans and it is by accident. This happens when the hands of a human accidentally touch the eggs of the Oestrus ovis and place the fingers on any mucous membrane part of the body, then the life cycle of the fly begins.  

Cordylobia anthropophaga

The blowfly Cordylobia anthropophaga, commonly known as Mango fly, is one of the causes of furuncular myiasis. A person can be infested with its eggs not only through direct laying but also through an environment that’s contaminated. A mature fly is most likely to be in shady areas and is normally operating at dawn and afternoon. The female form of the fly prefers to place their eggs on damp clothes, like air-drying clothes, or dry soil and can thrive for 15 days. Within 1 to 3 days, the egg hatches and when it finds its host, it gets activated by body heat and penetrates the skin. It can grow as long as 15 millimeters.  

Chrysomya bezziana

Chrysomya bezziana, also known as Old World Screwworm fly, is considered as one of the flies that primarily produces myiasis. The female form lays its eggs directly on an open wound. They are very attracted to wounds and skin openings. Even a tick bite can be a way for the fly to lay its eggs.

Diagnosis

The diagnosis of myiasis varies on what species of larvae infested a person. There are also various methods in diagnosing myiasis as symptoms can occur in a lot of areas in the body. Hence, making it difficult to diagnose. The size of the larvae can be determined through the use of ultrasonography or commonly known as ultrasound. Magnetic Resonance Imaging (MRI) can help determine breast myiasis, furuncular myiasis, and cerebral myiasis.  Since myiasis can also cause eosinophilia and leukocytosis, Complete Blood Count (CBC) can be used to aid in diagnosing the illness.

Treatments and Home Remedies

 Suffocation Approach

Occlusion or suffocation approach is used to block the oxygen needed by the fly larvae to survive and forcing it to escape from the skin. For the larvae to escape, the material used in occlusion shouldn’t be confining as to not kill the fly larvae of suffocation while it’s inside the skin. If the larvae died without migrating, surgery is needed to remove it. This type of approach is mostly used in removing botflies.

To perform this method, you may use petroleum jelly, heavy oil, strips of bacon or beeswax as covering and place it on top of the tiny hole where the larvae entered. The larvae will then exit from the skin automatically. Once its head has started showing up, you may pull it out with tweezers. After applying the covering, the larvae will come out in 3 hours to a day.

Surgical Excision with local anesthetics

This method entails incision of skin bumps under local anesthesia and removal of the fly larvae. In most cases, Lidocaine is used as local anesthetics for the surgery. When applying local anesthetics, you may inject the local anesthesia directly inside the lesion to put pressure inside to force the larvae to move outwards. They are somehow attached tightly Inside the skin, so it is necessary that the whole of the larvae is intact after removal. Leaving some parts may cause some form of reaction in your body later on.

When forcibly removing the larvae, exercise caution as to not create deep cuts on it as to not allow other parts to be left behind inside the skin. When removal of fly larvae is successful, use antiseptic dressing to prevent infection, cleanse the area and debride. If there is some form of infection, antibiotics may be needed.

Oral/Topical Larvicides

This form of approach is applicable to all forms of myiasis but oral ivermectin works best with oral myiasis and topical ivermectin helps a lot in treating myiasis in the nasal area. Topical ivermectin in removing fly larvae manually.

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