Toxocariasis: causes, symptoms, diagnosis, and treatment

Toxocariasis is a parasitic disease caused by the larvae of Toxocara canis and Toxocara cati.


Causes

Fertilized eggs of Toxocara canis and Toxocara cati are excreted through feces and develop into infective eggs under optimal conditions. When the infective eggs are ingested by humans, the eggs are hatched in the small intestine, and the larvae enter the lymphatic system or portal circulation through the intestinal wall. Subsequently, the larvae migrate to the various organs, such as liver, lungs, brain, kidney, heart, muscles, and eyeballs. In the human body, the larvae are often enveloped by inflammatory granulomas composed of eosinophils, and the larvae no longer develop, but the larvae can still survive for many years.


Signs and Symptoms

Visceral larva migrans usually occurs in children aged 6 months to 4 years, averagely 2 years. Fever, irritability, paleness, anorexia, and malaise are common clinical manifestations in children. In mild patients, there are only mild to moderate eosinophilia, but no other clinical symptoms. In severe patients, the disease can be fulminant and life-threatening, and is manifested by pneumonia, congestive heart failure or convulsions.

Ocular toxocariasis, also known as ocular larva migrans, is more common in children over 4 years of age, averagely 8 years old, mostly monocular and solitary. There is often a history of contact with puppies, but there are usually not visceral larva migrans and eosinophilia.

According to clinical manifestations, ocular toxocariasis can be divided into endophthalmitis, posterior pole granuloma, and peripheral granulomas.

Figure 1 ocular toxocariasis

Endophthalmitis is more common in children aged 2 - 9 years, and is manifested by chronic and diffuse hyalitis. There may be granulomatous inflammation or empyesis in the anterior chamber. Due to the dense inflammatory reaction of the vitreous body, it is difficult to observe the fundus, and sometimes the lumpy lesions of the fundus can be vaguely seen. Extensive vitreous proliferation, cyclitic membrane formation, and tractional or rhegmatogenous retinal detachment may be secondary to inflammation.

Posterior pole granulomas are often in the macula or optic disc, and are yellowish white, subrounded, subretinal or intraretinal, slightly raised lesions. Localized hyalitis or chorioretinitis may be present.

Peripheral granulomas occur in the equatorial region, and there may be hyalitis and vitreous traction bands connected to the posterior pole.


Diagnosis

If there are clinical manifestations and Toxocara antigens or antibodies detected in enzyme immunoassay, the disease can be diagnosed.


Treatment

Patients with mild or no symptoms do not need treatment, because the infection is usually self-limiting.

Moderate to severe patients should be treated with albendazole 400 mg po bid for 5 days or mebendazole 100 - 200 mg po bid for 5 days.

The treatment of ocular toxocariasis is mainly to reduce inflammation with steroid hormones. If vitreous proliferations lead to tractional retinal detachment and severe visual impairment, vitreoretinal surgery should be considered.

If there are live larvae in the eye, laser photocoagulation can be used to eliminate the larvae in the retina.