Toxocara, also known as visceral larva migrans, are a group of nematodes. The larvae of these nematodes are pathogenic to humans. The term ‘Toxocara’ is derived from two words: ‘Toxo’ meaning arrow, and ‘kara’ meaning head. Two species of Toxocara, namely Toxocara canis and Toxocara cati, are known to cause disease in humans.
What is Toxocara? [Morphological features]
The Toxocara nematodes have distinct morphological features. Their heads resemble an arrow or a spear, similar to the Indian cobra. They are essentially the roundworms of dogs and cats. These worms measure between 5 to 15 centimeters in length. A distinguishing feature of these worms is their two clear cephalic alae, which are broadened like the head of an Indian cobra.
Humans can become infected with Toxocara when they accidentally ingest the eggs of these nematodes, which may be present in dog or cat feces. Once ingested, the larvae migrate to various organs in the body, causing severe inflammatory responses. In some cases, if the larvae migrate to the eye, it can result in blindness. Children aged between 2 to 6 years are most commonly infected due to lack of awareness and hygiene.
In addition to Toxocara canis and Toxocara cati, there is another roundworm species called ‘Baylisascaris procyonis’, which is found in raccoons and is also a cause of visceral larva migrans.
The life cycle of Toxocara
The life cycle of Toxocara begins when the final host excretes the eggs with feces. These eggs are immature, similar to Ascaris eggs, and need to stay outside for 1 to 3 weeks to mature and form L2 larvae. When children play in areas frequented by dogs and cats or come into contact with these animals, they may accidentally ingest these eggs, leading to infection.
After the Toxocara eggs enter the human digestive system, the larvae emerge from the eggs in the intestine and start migrating through the bloodstream. The larvae attempt to complete their cardiac-pulmonary circulation to complete their life cycle. However, since humans are not their primary host, the larvae lose their way and start migrating to various organs, causing severe inflammatory responses. Humans are considered a biological dead end for Toxocara because the larvae cannot complete their life cycle in the human body.
Note: The life cycle of Toxocara involves dogs or cats shedding eggs in their feces, which can then contaminate soil. These eggs mature into a form that can infect humans. When ingested, the eggs hatch in the human intestine, releasing larvae that penetrate the gut wall and migrate to various tissues, including the liver, lungs, brain, muscles, and eyes.
Symptoms of Infection
General symptoms of infection with visceral larva migrans include fever, headache, and malaise. A key characteristic of Visceral Larva Migrans (VLM) is severe and long-term eosinophilia, which is present in about 20 to 90 percent of patients. Other symptoms of this disease include pneumonia, hepatosplenomegaly (enlargement of the spleen and liver), and myocardial inflammation (myocarditis).
Another manifestation of this disorder is Ocular Larva Migrans (OLM), which can lead to blindness. In such cases, the patient typically suffers from corneal inflammation (keratitis). In this form of the disease, retinal detachment and granulomatous reactions can be observed in tissues, especially in the brain and liver, surrounding the larvae.
| Type of Toxocariasis | Symptoms |
|---|---|
| Visceral Toxocariasis |
|
| Ocular Toxocariasis |
|
Prevention Strategies
Preventing toxocariasis centers around minimizing contact with contaminated soil and practicing good hygiene:
- Environmental Hygiene: Regularly clean areas where pets defecate to prevent soil contamination.
- Personal Hygiene: Wash hands thoroughly after contact with soil or pets, especially before eating.
- Pet Care: Deworm pets regularly and take them for routine veterinary check-ups to prevent Toxocara infections.
- Public Awareness: Educate communities about the risks of toxocariasis, especially in areas where stray dogs and cats are common.
- Prevention can be achieved by avoiding contact with dogs and cats, maintaining hygiene, fencing off children’s play areas, and preventing dogs and cats from entering these areas.
Who is Most at Risk for Toxocariasis?
- Children and Adolescents: Young individuals, particularly those under the age of 20, are more susceptible due to habits such as playing in dirt and sandboxes where pet feces may be present.
- Pet Owners: Those who own dogs or cats, especially if the pets are not regularly dewormed or are allowed to roam outdoors, have a higher chance of encountering Toxocara eggs.
- People Living in Poverty: Socio-economic deprivation is associated with a higher risk of Toxocariasis, possibly due to closer contact with contaminated environments.
- Residents of Rural Areas: Living in rural settings can increase exposure to contaminated soil, especially in regions with stray animals.
- Individuals in Warm, Humid Regions: Geographic location affects the prevalence of Toxocara, with higher rates in climates where eggs survive better in soil
Diagnosis and Treatment of Toxocara
To diagnose Toxocara, one can consider the patient’s history, their contact history with dogs and cats, the symptoms presented by the patient, and the use of serological tests such as ELISA. However, a definitive diagnosis is made by observing the larvae in the tissue. Severe and persistent eosinophilia is another diagnostic indicator. Imaging techniques such as MRI and ultrasound can also assist in diagnosis. Stool testing is not helpful in diagnosing visceral larva migrans because humans are not the primary hosts.
In the treatment of Toxocara, corticosteroids like Prednisone are suitable for reducing inflammation in response to the larvae. Also, Diethylcarbamazine (DEC) at a dose of 1 milligram per kilogram, twice a day for three weeks, and Albendazole at a dose of 400 milligrams, twice a day for three days, is used to kill the larvae. These medications must be used under the supervision of a doctor.
Conclusion
Toxocara parasites pose a hidden risk to human health, particularly for children and pet owners. Understanding the transmission, symptoms, and prevention of toxocariasis is crucial for reducing the incidence of this parasitic infection. Implementing effective hygiene practices and pet care can significantly lower the risk of Toxocara transmission and protect public health.
Reference:
- Toxocara and Toxocariasis, Volume 109 – 1st Edition | Elsevier Shop
- CDC
- Red Book Atlas of Pediatric Infectious Diseases
