Introduction:
In 1950, toxocariasis infection by Toxocara species was first described by Wilder. Toxocariasis is caused by ascarids (nematode species) that infect dogs and cats worldwide. The ascarid eggs contaminate the human environment as dogs and cats are kept as pets in various households and are also present throughout the streets. These eggs are generally found in the feces of cats and dogs and deposited in local parks and public beaches. Infection is caused in humans by ingesting eggs accidentally. The symptoms are usually seen during the migrating larval stages. In the United States (U.S.), five percent of the population has antibodies against the infection.
What Are the Clinical Features of Toxocariasis?
Two clinical forms that manifest the infection are:
1. Visceral Larva Migrans: Visceral toxocariasis is seen when the larvae migrate to different organs of the body, like the central nervous system or the liver. Symptoms include fever, cough, or abdominal pain.
2. Ocular Larva Migrans: Ocular toxocariasis is seen when the larvae migrate to the eye. Symptoms include loss of vision, inflammation of the eye, or damage to the retina. It can also lead to diffuse endophthalmitis and secondary glaucoma. Toxocariasis majorly affects young children below the age of five years. The common symptoms include:
-
Fever.
-
Enlargement.
-
Necrosis of the liver.
-
Enlargement of the spleen.
-
Lower respiratory symptoms like bronchospasm.
-
Eosinophilia (increase in the number of eosinophils in the blood).
-
Hypergammaglobulinemia of immunoglobulin M (IgM), IgG, and IgE classes.
In severe cases, it causes myocarditis (an increase in the number of eosinophils in the blood), nephritis (inflammation of kidney tissues), and involvement of the central nervous system that may lead to seizures or neuropsychiatric symptoms.
What Is the Causative Agent of Toxocariasis?
Toxocariasis is caused by ascarid nematodes Toxocara canis or Toxocara cati. They belong to the order Ascaridida, superfamily Ascaridiodea, and family Toxocariase. T. canis and T. cati are widely distributed due to the global presence of the human population along with domestic animals like cats and dogs.
How Is Toxocariasis Transmitted?
Generally, toxocariasis does not cause any severe infection, especially in adults where the infection occurs through small immature worms. However, in rare cases, the infection becomes serious, particularly in children who acquire the infection by playing in dirt contaminated with the feces of dogs and cats. The infection is transmitted to the host by ingesting contaminated substances. The infective larvae develop into eggs in around two to four weeks. If humans consume these eggs, they become infected with toxocariasis. This infection does not spread by contact from one person to another.
After the ingestion of the egg, the larvae hatch. However, these young larvae do not mature into adult worms and continue to wander throughout the body for months or several years, destroying the tissues or organs they enter.
How to Prevent Toxocariasis?
Toxocariasis can be prevented by taking the following measures:
-
Pets should be taken regularly to the veterinarian to avoid infection with Toxocara species. Deworming should be performed if necessary.
-
After touching pets or other animals, hands should be washed properly with soap and water.
-
Children should also be taught the importance of washing hands to prevent infection.
-
Children should avoid playing in areas contaminated with animal feces.
-
Hands should be washed after handling pet waste.
-
Children should be taught the danger of eating dirt or soil.
How Is Toxocariasis Diagnosed?
Eosinophilia and unexplained febrile illness in children are suspected of having toxocariasis. Hepatosplenomegaly and symptoms of the multisystem disease may also indicate this infection. Similarly, in ocular toxocariasis, the child complains of unilateral loss of vision and strabismus (crossed eyes or a condition where the eyes do not line up with one another). Immunological diagnostic tests are usually performed for visceral toxocariasis.
The precipitin test is done by cross-reaction between blood group substance A and common antigens of the larvae. The enzyme-linked immunosorbent assay (ELISA) is one of the best indirect tests for diagnosing this infection that utilizes antigens secreted by the second-stage larva.
Recombinant antigens produced from the second-stage larvae of T. canis show a greater specificity to an already reliable test (around 92 percent). The enzyme-linked immunosorbent assay (ELISA) has a high degree of specificity (around 78 percent) and a titer greater than 1:32.
The infection is also indicated by hypergammaglobulinemia and an elevated isohemagglutinin titer. Ocular toxocariasis is generally diagnosed based on an ophthalmic examination. However, the immunological tests used for visceral toxocariasis are unreliable for ocular toxocariasis, and in only 45 percent of the cases with ocular toxocariasis, the titers were higher than 1:32.
How Is Toxocariasis Treated?
The treatment of choice for toxocariasis is Albendazole. It is administered as a five-day course of 10 milligrams/kilogram body weight per day divided into two doses. The recommended therapy is administering 400 milligrams of albendazole twice daily for five days.
The second line of treatment involves drugs like Benzimidazole and Mebendazole. Unfortunately, these drugs show poor absorption outside the gastrointestinal tract. However, it can be beneficial if 1 gram or more is administered for 21 days. Finally, corticosteroids are administered for symptomatic treatment to suppress allergic reactions caused by the infection.
Ocular toxocariasis can be treated by:
-
Vitrectomy (a type of eye surgery to treat problems of the retina and vitreous).
-
Anthelmintic chemotherapy (curative cancer treatment that involves anti-cancer drugs as part of a standardized chemotherapy schedule).
Conclusion:
Toxocariasis is a serious infection throughout the world, leading to multisystem disease in young individuals. Moreover, in many regions of the world, the spread of the infection portrays a depressing situation due to overcrowding and cohabitation with cats and dogs. Therefore, various control programs are organized to reduce the number of domestic animals or limit their entry to areas accessed by young children.
Treating pets regularly with Benzimidazoles helps limit worms and the number of eggs deposited in the soil. Further, to prevent the infection, radical new approaches like vaccine development should be encouraged. Finally, safer drugs for pediatric patients and effective single-dose treatment can help limit the duration of the disease.
