Loiasis: causes, symptoms, diagnosis, treatment

Loalosis is a transmissible biohelminthiasis. Mature individuals parasitize in the skin, subcutaneous tissue, under the conjunctiva of the eye and under the serous membranes of various human organs. Larvae (microfilariae) circulate in the blood.

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Loalosis development cycle

Human infection with loalosis occurs through the bite of horseflies of the genus Chrysops. Loalosis is a biohelminthiasis, in the cycle of its development there are definitive hosts - humans, monkeys, and intermediate ones - blood-sucking horseflies of the genus Chrysops.

Horseflies live in areas of densely shaded, slow-moving bodies of water. Females lay eggs on the leaves of aquatic plants. The larvae develop in water, coastal silt, and damp soil. Horsefly bites are painful. When sucking blood, they absorb up to 300 mg of blood, which may contain several hundred larvae. Microfilariae undergo a development cycle in the thoracic muscles of the horsefly in the same way as Wuchereria larvae in mosquitoes, and after 10-12 days they reach the invasive stage. Infective larvae migrate to the oral apparatus of the horsefly. When a horsefly bites a person, the invasive larvae migrate to the surface of the skin and after the bite enter the blood. Horseflies are able to transmit larvae to the final host for 5 days.

After 1.5-3 years, the microfilariae reach sexual maturity and begin to produce live larvae. Sexually mature individuals migrate through the subcutaneous connective tissue. Microfilariae born by the female penetrate the lungs through the lymphatic and blood vessels and accumulate there. Periodically, they migrate to the peripheral blood vessels. Microfilariae circulate in the blood only during the day, and therefore they are called Microfilaria diurna (daytime microfilariae). The greatest number of larvae in the peripheral blood is observed between 8 and 17 o'clock.

In the process of evolution, mutual adaptations occurred in the development cycle of helminths associated with the vital activity of carriers.

The carriers (horseflies) are intermediate hosts. They are active during the day, so the peripheral blood of the final host contains the largest number of larvae at this time.

The lifespan of adult helminths ranges from 4 to 17 years.

Epidemiology of loalosis

Endemic foci are found in forest zones of West and Central Africa from 80° N to 50° S. Loiasis is common in Angola, Benin, Gambia, Gabon, Ghana, Zaire, Cameroon, Kenya, Congo, Liberia, Nigeria, Senegal, Sudan, Tanzania, Togo, Uganda, Chad, etc.

The source of loalosis is sick people. The specific carrier of loalosis is horseflies, which are capable of transmitting the pathogen by biting.

The incubation period of loalosis lasts several years, but sometimes is reduced to 4 months. Microfilariae can be detected in the peripheral blood 5-6 months after invasion.

The pathogenic effect is caused by the sensitization of the human body to the products of metabolism and decay of helminths. Active movement of filariae (at a speed of 1 cm per minute) causes mechanical damage to tissues, itching

What causes loalosis?

Loalosis is caused by the "African eye worm" - Loa loa, which has a white translucent thread-like body. The cuticle of the helminths is covered with numerous rounded protrusions. Females are 50-70 mm long, 0.5 mm wide, males 30-34 mm and 0.35 mm respectively. The tail end of the male is bent to the ventral side and has two unequal spicules. Adult helminths are able to actively migrate through the subcutaneous connective tissue, penetrating, in particular, into the conjunctiva.

Microfilariae have a barely noticeable sheath; their length is 0.25-0.30 mm, width - 0.006-0.008 mm. The nuclei reach the top of the pointed tail end.

Symptoms of loalosis

Loalosis begins with allergic manifestations. The initial symptoms of loalosis are: pain in the limbs, urticaria, subfebrile temperature. The course of the disease may be asymptomatic until the helminth penetrates under the conjunctiva, into the eyeball. Edema of the eyelids, retina, optic nerve, pain, hyperemia of the conjunctiva, deterioration of vision may occur. Due to the damage to the eyes, this helminth is called the "African eye worm".

An important symptom of loalosis is the development of "Calabar edema". It appears on limited areas of the body, slowly increases in size and slowly resolves, the skin above it is of normal color. When pressing on the edematous area, no pit remains. Edema occurs in places where filariae are localized in the skin and subcutaneous tissue, most often they appear in the areas of the wrists and elbow joints. The localization of edema is inconsistent. The appearance of edema can last for several years. Edema can cause pain, disrupt organ function, be accompanied by skin itching, subfebrile temperature, skin rashes.

From the blood side, eosinophilia and anemia are observed; an increase in and fibrosis of the spleen is also observed.

Migration of helminths in the urethra causes severe pain, especially during urination. Due to the disruption of lymph outflow, hydrocele may develop in men.

Penetration of larvae into the brain capillaries causes focal lesions, development of meningitis and meningoencephalitis. Damage to the central nervous system can lead to death.

The course of the disease is long, with alternating exacerbations and remissions. The prognosis for uncomplicated loalosis is favorable.

Complications of loalosis

Neuritis, meningoencephalitis, retinal detachment, development of abscesses, laryngeal edema, endocardial fibrosis are frequently encountered complications in residents of endemic regions for loalosis.

Diagnosis of loalosis

Differential diagnosis of loalosis with other filariases is necessary.

Laboratory diagnostics of loalosis is associated with the detection of larvae in smears and thick blood drops. Blood for testing is taken at any time of the day. In endemic areas, the diagnosis is often made based on clinical symptoms (the presence of "Calabar edema", eosinophilia). Helminths are visible to the naked eye under the conjunctiva. In loalosis encephalitis, microfilariae can be detected in the cerebrospinal fluid. Immunodiagnostics are sometimes used.

Treatment of loalosis

Treatment of loalosis is carried out in a hospital. Diethylcarbamazine is used according to the same scheme as for wuchereriasis. Given the pronounced allergization of the body by the decay products of helminths, antihistamines or glucocorticoids are also prescribed at the same time.

Helminths are removed from under the conjunctiva of the eye surgically.

How to prevent loalosis?

Personal prevention of loalosis consists of protection from attacks by horseflies: wearing thick clothing, using repellents. Public prevention of loalosis - identifying and treating patients, fighting carriers, clearing river banks of bushes in which horseflies live, draining and treating wetlands with insecticides to destroy horsefly larvae.