Ocular dirofilariasis is a disease of the visual organ caused by parasites of the genus Dirofilaria. It is accompanied by the formation of granulomas or nodules containing helminths in the subcutaneous tissue of the eyelids or structures of the eyeball. The clinic depends on the location of the pathogen. Common manifestations characteristic of all forms: pain, itching, a feeling of stirring in the eye. Diagnosis is based on the data of anamnesis, examination, laboratory (general blood test, ELISA, PCR), instrumental and parasitological methods of research. Surgical treatment is reduced to the removal of granulomas. In parallel with anthelmintic therapy, NSAIDs, glucocorticoids and antihistamines are indicated.
General information
Ocular dirofilariasis is a helminthiasis that develops when the larva of a filamentous nematode invades the structures of the eyeball and is characterized mainly by a chronic course. The first dirofilariasis was described by the Portuguese Lusitano Amato in 1566 after the isolation of dirofilariae from the eye of a three-year-old child. The disease is usually diagnosed in people of the middle age category. Dirofilaria immitis is 2 times more often detected in males, Dirofilaria repens, on the contrary, is more prone to infect women, which leads to their greater infection in the population due to the wide prevalence of the pathogen. Epidemiologically significant foci of infection are Sri Lanka, the territories of Southern and Eastern Europe, Asia Minor. Subcutaneous forms of the disease are often found in the post-Soviet countries.
Causes
Ocular dirofilariasis develops when infected with parasites of the genus Dirofilaria, belonging to the class of roundworms. Usually the lesion is caused by D. repens and D. immitis. The average length of the female D. repens is 145 mm, width – 0.4 mm. The longitudinal size of the male is about 55 mm, transverse – 0.4. The body of the female D. immitis reaches 300 mm, the male – 110 mm. A person acts as the final (dead-end) host of worms, most parasites die in the human body before reaching puberty. Only one case of microfilariae entering the bloodstream has been described in the literature.
Human infection is carried out transmissively by the bite of a mosquito affected by the larval stage of dirofilariae. Sources of infection for mosquitoes are stray dogs, rarely cats. Infection of a person usually occurs during work in the garden and in the garden, while resting near a pond or while traveling. The risk of infection increases from May to September when staying in places where there are a large number of carriers of dirofilariasis.
Symptoms of ocular dirofilariasis
The causative agents of dirofilariasis are most often localized in the subcutaneous tissue of the eyelids and conjunctiva, in rare cases – in the structures of the eyeball (anterior chamber, sclera). Dirofilariae can spread to the surrounding tissues (the cellulose of the eye socket, eyebrows). When a mosquito bite forms a limited area of inflammation, which eventually acquires a dense consistency. The seal is filled with serous or purulent contents, macrophages, leukocytes and neutrophils, there is a parasite inside the seal. A fibrous capsule forms outside the granuloma.
The lesion of the eyelids is accompanied by edema, decreased mobility, severe itching and lacrimation. Patients complain of pain when touching and at rest. Later, hyperemia, progressive ptosis and blepharospasm develop. Seals under the skin of the eyelids can increase in size and change shape. Patients detect granulomas during self-examination, applying makeup, etc. Externally, the manifestations of the disease resemble angioedema.
When pathogens are located under the conjunctiva or in the eyeball, specific symptoms are a sensation of a foreign body, protrusion of the eye, pathological stirring under the eyelid, in the orbit or structures of the eyeball. With an intra-conjunctival arrangement, the parasites are visible to the naked eye, resemble twisted threads or nodules. Their sudden disappearance in combination with a change in symptoms indicates penetration into the eyeball. There is an attachment of the clinical picture of conjunctivitis. The movements of worms provoke burning, severe pain and itching. The mucous membrane of the eyes becomes edematous, hyperemic. With ocular dirofilariasis or conjunctiva, visual acuity does not decrease. There may be a slight increase in intraocular pressure.
Penetrating into the fluid of the anterior chamber of the eye, the helminth becomes more mobile. Over time, a granuloma forms around it. The expansion of the pathological neoplasm leads to exophthalmos and diplopia. The location of worms inside the eyeball causes a decrease in visual acuity and the sensation of “pathological movements of worms”, which are often mistaken for visual hallucinations. Regardless of the location of the dirofilariae, patients present nonspecific complaints of general weakness, irritability, insomnia, headache and dizziness.
Depending on the localization of the pathogen, inflammatory processes may develop against the background of the underlying disease (blepharitis, conjunctivitis, keratitis, endophthalmitis, etc.). The most dangerous complication of dirofilariasis is retinal detachment. The chronic course of the disease leads to sensitization of the body, the disintegration of granuloma with the death of helminth or suppuration can cause severe intoxication and the occurrence of an allergic reaction. Hypersensitivity manifests itself in the form of papular rashes on the skin and swelling of the mucous membranes.
Diagnosis
Diagnosis of dirofilariasis is based on anamnesis data, the results of laboratory and instrumental research methods. Anamnestic data indicate a stay in the endemic region during the period of high mosquito activity (from May to September). With an objective examination of the eyelids and conjunctiva of the eye, it is often possible to visualize the pathogen in the form of convoluted threads located subcutaneously or in the thickness of the mucous membrane. The helminth can retain mobility. With palpation, the pain increases. Specific diagnostics consists of enzyme immunoassay (ELISA) and polymerase chain reaction (PCR). The diagnosis can be confirmed by the ELISA method when the IgM titer increases by more than 4 times, which indicates an acute or IgG – chronic course. PCR allows you to identify the DNA of the pathogen, which allows you to identify the type of dirofilariae.
In the general blood test, a slight increase in eosinophils is possible. The complex of parasitological research includes measuring the longitudinal and transverse size and assessing the maturity of the genitals of dirofilariae. In the absence of microfilariemia in the patient, it is necessary to study in detail the sexual system of the female for the detection of microfilariae in it. Microscopic diagnostics allows you to detect a specific granuloma, inside which the helminth is located. A feature of histological sections of dirofilariae is the presence of small “spikes” on the cuticle of the helminth. Diagnosis of the disease is often difficult, it is possible to identify the pathogen only after its extraction from the eye.
Optical coherence tomography is performed to diagnose dirofilariasis when helminths are located inside the structures of the eyeball. In case of internal localization, ultrasound examination in the B-scan mode is also indicated. Gonioscopy is informative only when the dirofilariae are located in the anterior chamber of the eye, this method is able to identify mobile parasites of filamentous shape. When examined by an ophthalmologist, visometry and tonometry are required, which allow you to measure visual acuity and intraocular pressure. The values of intraocular pressure and visual acuity depend on the location of the worms. With external localization, the indicators are within the normal range, with the internal location of the parasites, visual acuity is reduced, intraocular pressure is increased. Dirofilariasis should be differentiated with eye damage in loaosis, opisthorchiasis and ascariasis.
Treatment of ocular dirofilariasis
Treatment of dirofilariasis should be combined. In the chorus of surgical intervention, the removal of granulomas and other pathological formations containing helminth is carried out. On the eve of the operation, the use of ditrazine is recommended in order to reduce the mobility of worms. In the postoperative period, disinfectants and anti-inflammatory agents are prescribed in drops and ointments.
Drug therapy is reduced to taking anthelmintic drugs. The use of anthelmintic drugs and the decay of parasites in the body can provoke the development of allergic reactions and intoxication. Therefore, symptomatic treatment includes taking nonsteroidal anti-inflammatory drugs, glucocorticoids and antihistamines.
Prognosis and prevention
Prevention of ocular dirofilariasis consists in the treatment of mosquito breeding foci and delarvation of reservoirs with insecticides. When living in an endemic region, it is recommended to use repellents with a prolonged effect in the form of a spray, lotion or powder. If necessary, protective clothing and eye glasses should be worn. It is necessary to examine pets in a timely manner, carry out deworming. No specific preventive measures have been developed in ophthalmology.
The prognosis for life and working capacity in ocular dirofilariasis is favorable. Timely diagnosis and treatment ensure complete recovery without concomitant decrease in visual acuity and the development of other complications (retinal detachment, increased intraocular pressure).
