Cutaneous myiasis is a skin infestation caused by the larvae of certain fly species.
There are mainly three types of skin infestations by larvae of flies:
- Furuncular myiasis
- Wound myiasis
- Migratory myiasis
It is to note here that all these disorders vary greatly depending on the species of fly involved. These infestations usually occur in tropical countries.
These are in the form of open wounds and are found typically in homeless people, alcoholics, and others in poor social circumstances. Improper sanitation and hygiene leads them to get infested with fly larvae. Tissues at the mouth lining, nose, or eyes may also become infested. The most common carriers are green or black blowflies. Most larvae that cause wound myiasis attack both healthy and dead tissue. As a treatment, doctors remove the larvae by flushing the wounds and pulling the larvae out. Doctors can also cut away any dead tissue, if required.
Many of the flies causing Furuncular myiasis are commonly known as bot flies. The most well-known species of flies that cause Furuncular myiasis come from South and Central America and sub-Saharan and tropical Africa. North America, Europe, and Pakistan are the site of origin for other species. Many of the flies do not lay eggs on humans. Rather, the flies lay their eggs on other insects such as mosquitoes or on objects such as drying laundry that are likely to come into contact with people’s skin.
Eggs hatch into larvae that burrow into the skin and develop into mature larvae. If people are not cured on time, the larvae ultimately emerge from the skin and drop to the ground to continue their life cycle.
Typical symptoms of Furuncular myiasis are itching, a sensation of movement, and sharp, stabbing pain. Initially, people have a small red bump that may resemble a common insect bite or the beginning of a pimple. The bump grows later and a small opening may be visible at the center. The opening may drain yellowish fluid, and sometimes a small portion of the end of the larva is visible.
The need of oxygen for the larvae to survive forces them to leave or at least come closer to the surface when the skin is blocked. And, when they are closer to the surface, it is easier to pull them out.
In order to block the skin opening, people usually apply petroleum jelly, or even bacon or a paste of tobacco. Larvae that die before being removed are harder to pull out and usually cause an intense inflammatory reaction. Sometimes doctors inject an anesthetic into the skin, make a small incision, and pull the larva out with forceps. To kill the larvae or cause them to leave, doctors also recommend drug ivermectin, given by mouth or applied to the skin.
The most common sources are flies that usually infest horses and cattle. People can become infested if they have contact with the infected animals. It is very less often that the flies lay eggs directly on people. Larvae do not stay in one spot; rather they burrow under the skin and causes itchy lesions that may be mistaken for cutaneous larva migrants.
How is cutaneous myiasis diagnosed?
- Diagnosis of cutaneous myiasis is made primarily on the clinical appearance of the lesions, associated symptoms, and travel history.
- Dermoscopy and ultrasound may be significant.
- Submerging the scratches under water may confirm the diagnosis. If the larva is alive, bubbling will occur.
- G. intestinalis larva can be diagnosed by massaging a thin layer of mineral oil over the red abrasion. Black transverse bands can be visible representing spines on the larva’s body segments under magnification.