Phlebotodermia (mosquito dermatosis) is an itchy parasitic entomosis characterized by the reaction of sensitized dermis to the bite of a mosquito of the genus Phlebotomus. It is clinically manifested by the development of inflammation within the first hour after a mosquito bite in the form of hyperemia, against which itchy blisters form. Over time, they turn into papules, then into dense knots, the itching becomes unbearable. Usually the general condition is not disturbed, sometimes prodroma phenomena are possible. In severe cases, Quincke’s edema occurs, which is preceded by bullous rashes that open with the addition of a secondary infection. Etiotropic therapy does not exist, hormones and antihistamines are used.
Phlebotodermia is a rare tropical allergodermatosis of an inflammatory nature, developing acutely as a result of a mosquito bite of the genus Phlebotomus. The pathological process is characterized by endemicity, occurs in the Middle East, in the countries of Central Asia, where the climate is hot and humid, which is a necessary condition for the vital activity of Phlebotomus. The disease has no age, gender, racial, seasonal differences. As an exception to the rule, phlebotodermia can sometimes be detected in a different climate, since mosquitoes are able to survive in harsher conditions than hot countries. In this case, the pathology will be characterized by seasonal summer-autumn bursts of morbidity. The first description of entomoses in dermatology dates back to the beginning of the XV century. The most dangerous complication of phlebotodermy – Quincke’s edema was described 150 years ago by the author whose name this syndrome bears. It is with this syndrome that the urgency of the problem at the present stage is connected.
The pathological process occurs only when a female Phlebotomus is bitten, preparing to lay eggs. Malaria, worm infestations, leishmaniasis contribute to phlebotodermia. The mechanism of pathology development, in fact, is the skin’s response to the toxins of the mosquito’s saliva, which for many is an allergen and causes toxic-allergic reactions in the body. The peculiarity of such manifestations of the immediate type in this case is the absence of any signs of skin damage after the first bite. Only repeated contact with saliva causes visual skin damage with the development of phlebotodermia.
When a female is bitten, the saliva-antigen partially enters the blood, partially into the skin, where it damages mast cells – specialized immune formations of connective tissue scattered in the dermis, but concentrated near blood and lymph vessels. Due to the toxic effect of saliva on the vascular wall of capillaries, their permeability increases, toxins from the bloodstream also enter the dermis. Mast cells take part in adaptive reactions of the immune system, probably due to the lack of skin response to the first contact with saliva. During the second contact, visual symptoms of phlebotodermia develop: histamine and prostaglandins are released from mast cells, the intercellular substance of the dermis changes. Inflammatory mediators provoke inflammation and an allergic antigen-antibody reaction, support the immune attack of T-lymphocytes on a foreign antigen.
In parallel, with the development of phlebotoderma in the dermis, proliferative processes are stimulated due to the action of a pathogenic toxin, aimed at restoring the integrity of the skin. The mitotic activity of epidermal cells is activated, papules are formed. An excess of free histamine permeates the collagen fibers, causing them to swell, which is manifested by the occurrence of local or widespread edema of the dermis, depending on the state of the body’s defenses, the state of the endocrine system, concomitant pathology. If we are talking exclusively about the toxic variant of phlebotodermy, then the saliva of mosquitoes stimulates the production of IgE, which degranulates mast cells, stimulates the production of eosinophils, which directly attack the foreign antigen, causing inflammation and associated proliferation of epidermal cells. However, the chronization of the pathological process and the appearance of primary elements in places located far from the bite site indicate the development of sensitization of the body by mast cells primarily damaged by toxins in this variant.
Modern dermatology divides the pathological process by the nature of its occurrence and course into three forms:
- Acute form of phlebotodermia, occurring within the first minutes after the bite, accompanied by manifest symptoms.
- A chronic form of phlebotodermia, developing for several hours, and sometimes days after the bite, characterized by erased clinical manifestations.
- A mixed form of phlebotodermia, occurring no later than an hour after the bite, developing slowly, having a long course with a tendency to polymorphism and resistance to therapy.
Symptoms and diagnosis
The primary clinical manifestation of the disease is the appearance of blisters or papules with a diameter of up to 1 cm of pale pink color with a pearly hue and a spot hemorrhage in the center. The elements occur against the background of edematous erythema. Localization is the place of penetration of mosquito saliva into the dermis. Rashes are accompanied by severe itching, burning of the skin. An acute rash that has arisen independently resolves after 2-5 days, a late reaction to a bite has the most pronounced resistance. The process extends to exposed areas of the skin. If the danger of bites is constant, then with each new attack the papules thicken, transform into nodes, the itching becomes obsessively continuous. The general state of health during phlebotodermy is not disturbed, there may be an increase in temperature, bruising.
Very rarely, phlebotoderma in allergy sufferers is complicated by the development of Quincke’s edema, when instead of blisters and papules on the skin, bulls the size of a pigeon egg and an inflammatory corolla on the periphery are acutely poured out. Bullae tend to spread, are opened, eroded, covered with crusts, they will be joined by a secondary, most often pyococcal infection. The swelling increases, the mucous membranes are involved in the process, the tongue becomes numb, tachycardia, nausea, vomiting occur, the patient needs hospitalization. In this case, the bubbles can self-resolve within a week. If the mosquito that bites the patient is a carrier of leishmaniasis and other parasitic or viral infections, not only phlebotodermia develops, but also concomitant pathology.
The clinical diagnosis is made by a dermatologist. Phlebotodermy does not cause great difficulties, since the anamnesis confirming the fact of a mosquito bite and clinical manifestations are sufficient for its staging. With phlebotodermy, it is customary to conduct a clinical minimum of examination, in difficult cases, histology results are used (hyperkeratosis of the upper layer of the epidermis, acanthosis, lymphocytic infiltration of the dermis, acute inflammation phenomena, dystrophic changes in collagen and elastic fibers with dystrophy of nerve bundles). Differentiate phlebotodermia with nodular pruritus, dermatitis of During, bites of other insects and arthropods, urticaria, prurigo.
Treatment and prevention
There is no etiotropic therapy. Dermatologists, if necessary (taking into account the self-resolution of phlebotodermia), stop the developed symptoms. Antihistamines, vitamins, corticosteroids, antipruritic drugs are used. Sometimes autohemotherapy is used in the treatment of phlebotomy. In case of complications, antibiotics are prescribed. A good effect is given by sea, hydrogen sulfide, radon baths, baths with starch and needles. Externally, ointments with naphthalene and tar containing sulfur and hormones are shown. Of the physiotherapy procedures for phlebotodermy, heliotherapy and ozokerite applications are used. In cases resistant to therapy, cryomassage and laser therapy are connected. Single nodes are electrocoagulated, injectable destruction is carried out with methylene blue in novocaine.
Patients are advised to exclude contact with a possible mosquito threat: use mosquito nets at home and in the country, use repellents and clothing that covers the skin as much as possible in nature. Preventive destruction of mosquitoes by chemicals is possible. The prognosis for phlebotodermia is favorable.