Dermatobiasis is a parasitic human disease caused by a gadfly larva. Typical manifestations of the disease include single or multiple skin lesions in the form of tumor-like formations with infiltrates around them, sensations of a foreign body, symptoms of intoxication. Mucous membranes and internal organs are much less often involved. Diagnosis of parasitosis is based on the detection of the pathogen during visual examination or laboratory examination of the biopsy. Treatment of dermatobiasis is mainly surgical, aimed at removing the larva. If complications occur, symptomatic therapy is prescribed.
B87.9 Unspecified miasis
Dermatobiasis (South American miasis) is a transmissible pathology associated with the penetration of larval stages of gadfly under the skin. Most often, the disease occurs in the countries of Central and South America, mainly among residents and tourists staying in mountain moist forests, working on coffee plantations. Dermatobiasis is also common in regions engaged in animal husbandry. Only imported cases are registered in Europe and the USA. There are no significant differences in the sex and age composition of patients.
The causative agent of dermatobiasis is the larva of the human gadfly Dermatobia hominis. The female gadfly lays eggs with a sticky outer shell, attaches them to the bellies of mosquitoes, flies, ticks, and other blood-sucking insects. Upon contact with the body of a warm-blooded animal or human, the larva leaves the egg, painlessly penetrates into the thickness of the skin and begins to grow, causing clinical manifestations of parasitosis. The pathogen has no specific localization sites on the human torso.
The main risk factors for dermatobiasis are: work in conditions of high humidity, abundance of blood-sucking insects, neglect of repellents. Agricultural workers, veterinarians, residents and tourists of endemic areas are at risk. A complicated course of the disease with a probable fatal outcome is expected in young children, elderly people, people with decompensated somatic pathologies, pronounced immune deficits.
The larva, under the influence of the heat of the victim’s skin, gets out of the egg and penetrates under the skin. In the thickness of the dermis, the causative agent of dermatobiasis successively passes through three stages of its natural development, increasing in size. A focus of local inflammation is gradually formed around the larva, subcutaneous infiltrate turns into an abscess with the formation of a fistulous course necessary for the pathogen to breathe.
Serous-purulent exudate containing leukocytes, digestive products of the parasite, is released from the fistula. The larva feeds on both necrotic and healthy tissues, while it practically does not move, being within the affected area. The maturation period of an individual is 5-12 weeks, after this period the pathogen reaches a size of up to 25 mm, leaves the human body and pupates. The symptoms of multiple invasions are described.
Dermatobiasis is a parasitization of the larval stage of gadfly in the human body. Symptoms directly depend on the place of introduction of the larva. Since the carriers are blood-sucking insects and ticks, parasitosis is attributed to vector-borne diseases. In infectology , the disease is classified according to the localization of the pathogen invasion:
- Ophthalmomiasis. It is characterized by pain, visual impairment, swelling of the eyelids. It can lead to severe iridocyclitis.
- Genitourinary miasis. Typical itching, painful ulcer on the penis, vulva, vagina or uterine cavity, separation of purulent exudate.
- Labial miasis. There is an increase, swelling, sharp soreness, cyanosis of the upper or lower lip.
- Mammary miasis. The symptoms of painful compaction, bright hyperemia, and a feeling of stirring in the breast, both in men and women, are described.
The incubation period lasts up to a day, sometimes more. At the beginning of the disease, the wound practically does not cause subjective sensations. After a while, there is a feeling of movement under the skin at the site of the introduction of the pathogen. Well-being worsens: headaches occur, body temperature rises to 38 ° C with chills, weakness. The focus of the invasion can reach 1 cm in height and 3 cm in diameter. The skin above it becomes hot, red in hue, with a central hole above the infiltrate.
Purulent-serous fluid oozes from the center of the formation, over time the exudate dries into dense crusts. Patients with dermatobiasis can notice both the larva itself and its spiracles located outside, and see air bubbles forming on the surface. Regional lymph nodes are also often enlarged, bead-shaped dense paths of inflamed lymphatic vessels appear.
The most common complications of dermatobiasis include a variety of purulent lesions of the skin and subcutaneous fat: abscess, purulent lymphadenitis, phlegmon. Treatment in such cases should be started immediately, the development of a secondary infection can lead to sepsis. In addition, depressive symptoms associated with changes in appearance (cosmetic defects after removal of the parasite), panic attacks, psychological problems may persist for a long time.
Diagnosis of dermatobiasis is carried out by doctors of various specialties – more often dermatologists, infectious diseases specialists. Treatment is carried out mainly by surgeons. A thorough collection of epidemiological anamnesis is important, especially regarding visits to areas endemic for parasitosis. Clinical and laboratory-instrumental studies are carried out to make a diagnosis:
- Physical examination. On the skin of the exposed parts of the body (scalp, face, limbs), an itchy erythematous papule is found, painful on palpation with a hole in the center, purulent-serous discharge or crust. The terminal part of the larva may be visible. Regional lymphadenitis, lymphangiitis is characteristic.
- Laboratory tests. When examining the hemogram, leukocytosis, moderate eosinophilia, and a slight acceleration of ESR are detected. In biochemical analyses, it is possible to increase the activity of acute-phase proteins.
- Identification of infectious agents. The detection of the desired parasite is performed by surgical opening of the lesion. Identification of the species of the pathogen is carried out in the laboratory.
- Instrumental methods. In severe cases, if there are suspected lesions of the orbit, chest tissues, and face, an MRI is performed. With small foci, soft tissue ultrasound with Dopplerography is recommended to assess the size, depth of invasion, and number of larvae.
Differential diagnosis of dermatobiasis is carried out with other myiases, while the final diagnosis is possible after visualization of the pathogen at the opening of the focus. It is also necessary to exclude a foreign body, as well as abscess, furunculosis and cellulite caused by non-specific flora. Dermatological symptoms of onchocerciasis are combined with severe eye lesions up to blindness, expressed by lymphedema.
Hospitalization is necessary in case of multiple lesions, severe course of concomitant somatic nosologies, suspicion of visceral dermatobiasis. Treatment is carried out more often on an outpatient basis. The patient may not agree to remove the larva, because after a few weeks the parasite leaves the body on its own. There are no restrictions on nutrition and the amount of liquid. Bed rest, semi-bed rest is prescribed according to indications.
A non-invasive approach to dermatobiasis therapy is implemented by stopping air access to the larva. To disrupt the breathing of the parasite, you can use vaseline, liquid paraffin, beeswax, also fatty dense oils and even strips of bacon. After 3-24 hours after applying the substances to the fistulous course, the larva completely crawls out of the wound, this process can be accelerated by capturing the parasite with tweezers.
The pathogen cannot be removed by forcible extrusion due to the threat of rupture and allergic reactions, as well as increased inflammation at the location. It is not recommended to use nail polish, because the larva will suffocate, unable to crawl out. An alternative treatment for dermatobiasis is oral tableted or topical ivermectin (1% solution), which has proven its effectiveness in orbital myiasis.
After removing the larva, careful treatment of the wound with antiseptic solutions, the imposition of a sterile dressing is necessary. With severe inflammation, symptoms of purulent complications, antibiotics are prescribed, mainly of a wide spectrum of action. Other treatment – antihistamines, sedatives, etc. ‒ it is prescribed according to the recommendations of the attending physician.
After anesthesia with lidocaine, the skin at the site of the lesion is excised, followed by primary closure of the wound. Alternatively, lidocaine can be injected into the base of the pathological focus in an attempt to create sufficient fluid pressure to passively squeeze out the larvae. Another surgical approach: performing perforation excision of the surrounding skin up to 4-5 mm to get better access to the parasite and its visualization, careful removal of the larva with tweezers or a clamp.
Prognosis and prevention
With timely diagnosis and treatment, the prognosis for dermatobiasis is favorable. The only fatal outcome in a sick child is described. There are no specific means of prevention. Non-specific measures: avoiding mosquito bites, gadflies, flies by putting on clothes with long sleeves and trousers, treating the body and things with repellents, especially in the evening, using mosquito nets.