Loiasis is a chronic infectious disease caused by roundworms. A characteristic clinical symptom is the formation of a limited edematous area, mainly on the extremities, as well as damage to the mucous membranes, more often conjunctiva. Visceral invasions are less common. Diagnosis of the disease consists in the detection of the pathogen in the blood and tissues, the determination of antibodies. Etiotropic therapy (diethylcarbamazine) and symptomatic, special attention is paid to the relief of the allergic component of the disease. Surgical treatment is used in the case of subconjunctival localization.
Loiasis (Calabar tumor) is a nematode, a distinctive feature of which is the migration of adult individuals in the tissues of the body. The pathogen was discovered in 1778 by the French scientist Guyot. The disease is common in humid tropical climates in the countries of West and Central Africa, it does not have a clear seasonality. The prevalence of the local population is 70-90%, visitors – up to 20%, while among the inhabitants of the endemic region, an asymptomatic course of pathology is usually registered. Risk groups are men, representatives of the Black race, persons aged 30-39 years, agricultural workers, loggers.
The causative agent of the disease is a helminth related to roundworms, Loa loa (African eye worm). The parasite is viviparous, bisexual. For its development, it needs a change of hosts: microfilariae larvae live in the body of the intermediate host, and mature individuals capable of migrating in tissues live in the final host. The source and reservoir of infection is a sick person and, probably, some primates. The transmission pathway is transmissible, infection occurs during an insect bite.
The larval stage of loa loa takes place in the muscular apparatus of the carrier of the disease – horsefly, this process takes 7-20 days, in the future microfilariae move into the salivary glands of the insect. It has been established that in endemic areas of Africa, the incidence of loa loa in the horsefly population reaches more than 5%. Attacks on people are usually observed during the day in the habitat of vectors – shaded riverbanks, thickets of shrubs, forests; insects can attract fire, smoke, moving objects.
The introduction of microfilariae into the human bloodstream begins during a horsefly attack. In the future, the larvae enter the capillaries of the lungs, where they reach puberty within 6-18 months, penetrate the subcutaneous adipose tissue, conjunctiva of the eyes and serous membranes, hatching live larvae, after which the cycle repeats. Migration of microfilariae and their greatest number in peripheral blood is usually detected during daytime hours (12:00-14:00). Together with the larvae, toxic products of their vital activity enter the bloodstream.
In the pathogenesis of clinical manifestations in loiasis, toxic-allergic reactions play an essential role, in which specific immunoglobulins (E, G3, G4 and others) produced by the immune system of infected people participate. Among HIV-infected patients with loiasis who do not receive antiretroviral drugs of VAART, the level of microfilariemia is directly proportional to the increase in the titer of HIV in the blood. This can lead to an aggravation of the course of both diseases, increase the risk of complications and death.
The incubation period for this helminthiasis is several years, in rare cases 4 months. The disease begins abruptly, against the background of full health, with an increase in body temperature of more than 38 ° C, chills, weakness, pain in joints and bones, rashes on the body in the form of large blisters, pain in the extremities, sensitivity disorders. When moving loa loa, both the movements themselves are felt, as well as burning pain, itching. At the same time, painless edematous areas form on the body (usually on the hands or feet), which disappear independently within three days.
When localized in the eye area, there is swelling of the eyelids, burning, a feeling of movement of the parasite, copious lacrimation, intense redness; symptoms pass immediately after the penetration of the helminth into the area of paraorbital fiber. Less often, loa loa enters the urethra, which is manifested by sharp pain even at rest, and damage to the membranes of the brain, in which the main symptoms are difficulty in contact with the patient, delirium, hallucinations, severe headaches, inability to bring the chin to the chest, etc.
The most common complications are considered to be various manifestations of edematous allergic syndrome, described testicular dropsy, blepharospasm, dilated cardiomyopathy, nephropathy, encephalopathy. Intramuscular abscesses and phlegmon of the extremities are often found due to the addition of a secondary infection; uveitis and panophthalmitis with ocular lesions, pyelonephritis, cystitis, urethritis, orchitis and prostatitis with the involvement of the genitourinary system are associated with the same cause.
Complications such as intestinal obstruction, mesenteric vascular thrombosis and hypogonadism are much less common. The latter condition is associated with a high level of gonadotropin and a low titer of serum testosterone in men with loiasis, which becomes a prerequisite for the formation of secondary infertility. Prolonged persistence of helminth inside the vitreous body and a high level of microfilariemia lead to retinal hemorrhages, edema of the optic nerve disc, its atrophy and blindness.
The diagnosis of loiasis is confirmed by an infectious disease specialist; it is important to carefully collect an epidemiological history, in particular, to clarify the stay in countries endemic to loiasis over the past decade. An ophthalmologist’s examination is mandatory, according to the indications, consultations of other specialists are appointed. Diagnostic methods necessary for the verification of a loaotic lesion include the following techniques:
- Physical examination. An objective examination reveals skin urticary rashes, swelling of the extremities, genitals, face and eyelids. In the area of localized edematous formations, hyperemia is observed, or (more often) pallor of the skin, itching. Percussion may be marked by expansion of the boundaries of the heart, palpation – hepatosplenomegaly. With the involvement of the central nervous system, cerebral, focal and meningeal symptoms are determined.
- Examination by an ophthalmologist. The most frequent is the lesion of the eyelids. During ophthalmoscopy, the mucosa is swollen, hyperemic, with copious lacrimation. A moving roundworm and exudate can be detected in the submucosa and anterior chamber, possible overgrowth of the pupil; signs of keratitis, retinitis, cataracts, optic nerve atrophy are characteristic. Visual acuity with a prolonged course of loiasis progressively decreases.
- Laboratory tests. In general clinical blood test – leukocytosis, pronounced eosinophilia up to 50-70%, secondary anemia of varying degrees, slight acceleration of ESR. There is an increase in the activity of ALT, AST, creatinine and urea, hypergammaglobulinemia, hypoalbuminemia. The immunogram is characterized by an increase in class E immunoglobulins. In the general analysis of urine, hematuria, proteinuria is possible.
- Identification of infectious agents. Microscopy of blood taken during the daytime allows you to detect loa loa larvae. Serological diagnostics is carried out with the help of ELISA. Rapid tests for the determination of antibodies to loa loa by immunochromatographic method have been developed. A test with diethylcarbamazine (Masotti test) becomes positive for any filariasis, therefore it is not considered either proof or refutation of loiasis.
- Instrumental techniques. Chest X-ray is performed to exclude other worm infestations; the use of MRI, CT of the soft tissues of the visual apparatus helps to visualize the helminth in retrobulbar tissue. Ultrasound of the eyeballs and orbit allows you to detect the parasite in soft tissues that are inaccessible during examination. Ultrasound examination of subcutaneous tissue, abdominal organs is recommended for the purpose of differential diagnosis.
Differentiation is carried out with ascariasis, in which the rash appears together with intestinal and lung lesions, trichinosis, which is characterized by facial edema and severe muscle pain, vuhereriosis with typical lymphangitis, lymphadenitis and rash, brugiosis (rashes, elephantiasis of the limbs). In addition to infectious pathology, loiasis should be distinguished from insect bites, alimentary and drug allergies, serum sickness that occurs 7-14 days after the introduction of heterogeneous serums and immunoglobulins.
Inpatient treatment is indicated for patients with ocular symptoms, moderate and severe course of the disease. Bed rest is prescribed to a stable normal body temperature for 3-4 days. Dietary recommendations have not been developed; alcohol, nicotine, highly allergenic and indigestible foods should be excluded, and protein-rich foods should be included. It is important to observe a normal drinking regime. It is allowed to use local antipruritic ointments and gels, in order to avoid contamination of combs, you need to cut your nails short, wash your hands with soap more often.
Etiotropic anthelmintic treatment traditionally consists of oral administration of diethylcarbamazine, the therapeutic course should be at least three weeks. Some foreign studies have suggested the use of albendazole and ivermectin, but the lowest frequency of repeated courses of therapy was recorded among patients receiving diethylcarbamazepine. The use of hormonal drugs in order to reduce the side effects of anthelmintic agents had no proven effectiveness.
Pronounced allergization of the patient’s body is a direct indication for the administration of desensitizing and detoxifying solutions, antihistamines. In the case of severe edema, the appointment of glucocorticosteroids, diuretics and albumin preparations is allowed. The addition of purulent complications requires antibiotic therapy, sometimes surgical intervention. Ocular loiasis is an indication for surgical treatment, the volume of which is determined individually – from the removal of the worm to the evisceration of the organ of vision.
Prognosis and prevention
The prognosis for loiasis is favorable, except in cases of complicated course of the disease. No fatal cases were recorded. Specific prevention (vaccine) has not been developed at this stage of medical development. The main preventive measures are early detection and isolation of patients, the use of mosquito nets in homes and hospitals, drainage of swamps, disinsection, the use of repellents, sprays and clothing made of dense fabrics when working in the usual habitats of horseflies. When staying in an endemic area for a long time, it is recommended to take preventive doses of diethylcarbamazine.