Toxocariasis (roundworms)
- 2. SCIENTIFIC CLASSIFICATION ļ” Kingdom:Animalia ļ” Phylum: Nematoda ļ” Order: Ascaridida ļ” Family: Toxocaridae ļ” Genus:Toxocara ļ” Species: T. canis (Dog roundworm), T. cati (Cat Roundworm)
- 3. WHAT IS TOXOCARIASIS? ļ” Toxocariasis is an infection transmitted from animals to humans (zoonosis) caused by the parasitic roundworms commonly found in the intestine of dogs (Toxocara canis) and cats (T. cati). ļ” The soil of parks and playgrounds is commonly contaminated with the eggs of T canis, and infection may cause human disease that involves the liver, heart, lung, muscle, eye, and brain.
- 4. WHO IS AT RISK FOR TOXOCARIASIS? ļ” Anyone can become infected with Toxocara. Young children and owners of dogs or cats have a higher chance of becoming infected.
- 5. EPIDEMIOLOGY ļ” Toxocariasis is a worldwide infection. ļ” Humans are accidental hosts of Toxocara ļ” Ways of Transmission: Fecal Oral. Dogs and cats that are infected with Toxocara can shed Toxocara eggs in their feces. You or your children can become infected by accidentally swallowing dirt that has been contaminated with dog or cat feces that contain infectious Toxocara eggs. Although it is rare, people can also become infected from eating undercooked meat containing Toxocara larvae.
- 6. MORTALITY/MORBIDITY ļ” Toxocariasis is almost always a benign, asymptomatic, and self- limiting disease, although brain involvement can cause severe morbidity. Brain involvement can evoke meningitis, encephalitis, or epilepsy. ļ” Ocular involvement may cause loss of visual acuity or unilateral blindness. ļ” Pulmonary and hepatic forms can cause protracted symptoms if the patient does not receive treatment.
- 7. AGE ļ” CDC studies have shown that transmission of Toxocara larvae is most common in young children and persons younger than 20 years. ļ” Toxocariasis is predominantly a disease of children, typically those aged 2-7 years. ļ” Ocular toxocariasis is most common in older children and young adults.
- 8. MORPHOLOGY ļ” Both species produce eggs that are brown and pitted. T. canis eggs measure 75-90 Āµm and are spherical in shape, whereas the eggs of T. cati are 65-70 Āµm in diameter and oblong. Second stage larvae hatch from these eggs and are approximately 0.5mm long and 0.02mm wide. Adults of both species have complete digestive systems and three lips, each composed of a dentigerous ridge. ļ” Adult T. canis are found only within dogs and foxes and the males are 4ā6 cm in length, with a curved posterior end. The males each have spicules and one ātubular testis.ā Females can be as long as 15 cm, with the vulva stretching one third of their bodylength. The females do not curve at the posterior end. ļ” T. cati adult females are approximately 10 cm long, while males are typically 6 cm or less. The T. cati adults only occur within cats, and male T. cati are curved at the posterior end.
- 9. PATHOPHYSIOLOGY ļ” Adult worms of the Toxocara species live in the small intestine of dogs and puppies and range from 4-12 cm in length. Almost all puppies are infected at or soon after birth. During the summer, in wet conditions, Toxocara eggs are embryonated in 2-5 weeks and become infective. They survive for years in the environment, and humans typically ingest the eggs via oral contact with contaminated hands. Once introduced into the human intestine, the eggs decorticate, releasing the larvae. The larval form is visible only under a microscope because it is less than 0.5 mm in length and 0.02 mm wide. The larvae penetrate the bowel wall and migrate through vessels to the muscles, liver, and lung and sometimes to the eye and brain.
- 11. ļ” Cats, dogs and foxes can become infected with Toxocara through the ingestion of eggs or by transmission of the larvae from a mother to her offspring.Transmission to cats and dogs can also occur by ingestion of infected accidental hosts, such as earthworms, cockroaches, rodents, rabbits, chickens, or sheep. ļ” Eggs hatch as second stage larvae in the intestines of the cat, dog or fox host (for consistency, this article will assume that second stage larvae emerge from Toxocara eggs, although there is debate as to whether larvae are truly in their second or third stage of development). Larvae enter the bloodstream and migrate to the lungs, where they are coughed up and swallowed. The larvae mature into adults within the small intestine of a cat, dog or fox, where mating and egg laying occurs. Eggs are passed in the feces and only become infective after several weeks outside of a host. During this incubation period, molting from first to second (and possibly third) stage larva takes place within the egg. In most adult dogs, cats and foxes, the full lifecycle does not occur, but instead second stage larvae encyst after a period of migration through the body. Reactivation of the larvae is common only in pregnant or lactating cats, dogs and foxes. The full lifecycle usually only occurs in these females and their offspring.
- 12. ļ” Second stage larvae will also hatch in the small intestine of an accidental host, such as a human, after ingestion of infective eggs. The larvae will then migrate through the organs and tissues of the accidental host, most commonly the lungs, liver, eyes, and brain. Since L2 larvae cannot mature in accidental hosts, after this period of migration, Toxocara larvae will encyst as second stage larvae.
- 13. SYMPTOMS : ļ” Ocular toxocariasis: Ocular toxocariasis occurs when Toxocara larvae migrate to the eye. Symptoms and signs of ocular toxocariasis include vision loss, eye inflammation or damage to the retina. Decreased visual acuity, seeing floaters or bubblelike images . Typically, only one eye is affected. ļ” Visceral toxocariasis: Visceral toxocariasis occurs when Toxocara larvae migrate to various body organs, such as the liver or central nervous system. Symptoms of visceral toxocariasis include fever, fatigue, decreased appetite, restlessness, hives, history of seizures, coughing, wheezing, or abdominal pain.
- 14. PHYSICAL ļ” Tenderness in the right upper quadrant or hepatomegaly may be present in patients with liver involvement. ļ” With pulmonary involvement, wheezing may be heard. Breath sounds may be decreased if a pleural effusion is present. ļ” Patients with ocular involvement may present with the following: ļ” Retinal detachment due to traction caused by retinal fibrosis ļ” Peripapillary inflammation ļ” Peripheral retinal exudates ļ” Gliotic mass in peripheral retina ļ” Vitreoretinal traction band in peripheral retina
- 15. FUNDUSCOPIC EXAMINATION OF THE RIGHT EYE OF A PATIENT WITH OCULAR TOXOCARIASIS SHOWING RHEGMATOGENOUS RETINAL DETACHMENT.
- 16. THREE SYNDROMES OF TOXOCARA INFECTION ARE GENERALLY RECOGNIZED, AS FOLLOWS: ļ” In children, covert toxocariasis is a mild, subclinical, febrile illness. Symptoms can include cough, difficulty sleeping, abdominal pain, headaches, and behavioral problems. Examination may reveal hepatomegaly, lymphadenitis, and/or wheezing. ļ” Visceral larva migrans is caused by the migration of larvae through the internal organs of humans and the resulting inflammatory reaction. A constellation of symptoms develops, including fatigue, anorexia, weight loss, pneumonia, fever, cough, bronchospasm, abdominal pain, headaches, rashes, and, occasionally, seizures. Examination may reveal hepatomegaly, lymphadenitis, and/or wheezing. Occasionally, pleural effusions develop. Chronic urticaria has been described. Severe cases can lead to myocarditis or respiratory failure.
- 17. ļ” Ocular larva migrans, which is caused by migration of larva into the posterior segment of the eye, tends to occur in older children and young adults. Patients may present with decreased vision, red eye, or leukokoria (white appearance of the pupil). Granulomas and chorioretinitis can be observed in the retina, especially at the macula. Unilateral visual loss, retinal fibrosis, retinoblastoma, and retinal detachment occur. Serum antibodies to Toxocara are often absent or present in low titers.
- 18. RISK FACTORS OF TOXOCARIASIS INCLUDE THE FOLLOWING: ļ” Living with or raising dogs and cats ļ” Eating without handwashing ļ” Infection via contact with soil from a yard, sandbox, park, or playground
- 19. DIAGNOSIS Laboratory Studies ļ” The diagnosis of toxocariasis requires a high index of suspicion and depends on serologic testing (eg, ELISA, immunoblot). ļ” Peripheral blood eosinophilia is the most important finding; however, it may be absent in patients with ocular or covert toxocariasis. ļ” Serum total IgE: Patients with toxocariasis often have a marked increase in total IgE levels. ļ” ELISA with Toxocara excretory-secretory antigen (TES-Ag) may show the following: ļ” An elevated antiāTES-Ag IgE level indicates acute infection or progressive inflammation caused by toxocariasis. ļ” An increase in the immunoglobulin G (IgG) level confirms a past or present infection with minimum inflammation. ļ” In ocular toxocariasis, an IgG or IgE titer is lower because the worm burden is smaller. ļ” ELISA with aqueous fluid is therefore useful when ocular toxocariasis is suspected.
- 20. IMAGING STUDIES ļ” Chest radiography ļ” In a patient with pulmonary involvement, chest radiography may show multiple pulmonary nodules with surrounding ground-glass opacities, or possibly pleural effusion. ļ” Ultrasonography ļ” Ultrasonography reveals multiple hypoechoic areas in the liver. ļ” CT scan ļ” Hepatic lesions are of low density. ļ” Pulmonary involvement manifests as multiple pulmonary nodules and surrounding ground-glass opacities or, rarely, pleural effusion. ļ” In the CNS, granulomas appear cortically or subcortically, showing a hyperintense appearance on proton density and T2-weighted images.
- 21. The image on the left is a posteroanterior chest radiograph in a patient with toxocariasis. The image on the right is a CT scan of the patient with toxocariasis showing multiple pulmonary nodules with surrounding ground-glass opacities at first visit.
- 22. OTHER TESTS ļ” An immunoblot is more specific than ELISA when bands from 24- 35 kD are considered out of typical 7-band patterns (24, 28, 30, 35, 132, 147, 200 kD). ļ” Funduscopic examination should be performed in patients suspected of having acute toxocariasis.
- 23. PROCEDURES ļ” Biopsy is rarely performed to confirm the presence of Toxocara larvae. ļ” A needle biopsy of the liver is required for histologic diagnosis in cases of liver involvement; however, some results are false-negative because lesions in the liver are very small.
- 24. HISTOLOGIC FINDINGS ļ” The encapsulated larvae can be found in the liver, lung, brain, and/or enucleated eye. The larvae occur in a matrix of epithelioid cells surrounded by a fibrous capsule with weak inflammatory reactions. In ocular toxocariasis, a mobile larva can be directly observed under the retina.
- 25. ļ” Diagnostic Considerations ļ” Eosinophilic lung infiltrates may be due to other helminths, to fungi, or to allergic reactions to ļ” Differential Diagnoses ļ” Hepatitis A
- 26. TREATMENT (ANTHELMINTIC DRUGS ) ļ” Mebendazole (Vermox) ļ” Emverm: 100 mg PO q12hr for 3 days; if cure is not achieved 3 wk after treatment, a second course of treatment is advised ļ” Vermox: 500 mg PO as a single dose ļ” DOC. Adverse effects are negligible, except headaches during early therapy. These symptoms are from metabolites secreted from nematodes that are killed by the drug. Causes worm death by selectively and irreversibly blocking uptake of glucose and other nutrients in susceptible adult intestines where helminths dwell.
- 27. ļ” Albendazole (Albenza) ļ” 400 mg PO once ļ” Second DOC if mebendazole is difficult to obtain. Decreases ATP production in the worm, causing energy depletion, immobilization, and, finally, death. ļ” Diethylcarbamazine citrate (Hetrazan) 100mg ļ” Synthetic organic compound highly specific for several common parasites. Does not contain any toxic metallic elements. Not recommended as the DOC because of more severe adverse effects. Recommended if therapy with mebendazole fails or mebendazole is not available.
- 28. ļ” Chemotherapy: the treatment of choice in most patients with liver, lung, or eye involvement. Occasionally, ocular involvement requires ocular surgery. ļ” Corticosteroids, are prescribed in severe cases of VLM or if the patient is diagnosed with OLM. ļ” Surgical Care ļ” For liver or lung involvement, no surgical care is required. ļ” For ocular involvement with retinal detachment, laser treatment may be considered.
- 29. CONSULTATIONS ļ” A consultation with an ophthalmologist is indicated in cases of ocular larva migrans. ļ” Consultation with a neurologist is indicated in cases of brain involvement with neurologic symptoms or seizures. ļ” Consultation with an infectious disease specialist may be indicated when questions exist regarding the indications for and selection of treatment for visceral larva migrans.
- 30. PREVENTION OF TOXOCARIASIS? ļ” Take your pets to the veterinarian to prevent infection with Toxocara. Your veterinarian can recommend a testing and treatment plan for deworming. ļ” Wash your hands with soap and water after playing with your pets or other animals, after outdoor activities, and before handling food. ļ” Teach children the importance of washing hands to prevent infection. ļ” Do not allow children to play in areas that are soiled with pet or other animal feces. ļ” Clean your petās living area at least once a week. Feces should be either buried or bagged and disposed of in the trash. Wash your hands after handling pet waste. ļ” Teach children that it is dangerous to eat dirt or soil.
- 31. COMPLICATIONS ļ” Decreased visual acuity may occur if ocular toxocariasis is not identified and treated. ļ” Retinal detachment due to ocular involvement may cause unilateral visual loss. ļ” Seizures may result from cerebral involvement.
- 32. PROGNOSIS ļ” Toxocariasis is generally a self-limited disease. The prognosis is good when adequately treated, except in some patients with ocular or cerebral involvement.
- 33. PATIENT EDUCATION ļ” Properly de-worm kittens and puppies. ļ” Pets should undergo periodic stool examinations by a veterinarian, and they should be treated if examination findings are positive for Toxocara eggs. ļ” Do not bring stray dogs or cats home. If such animals are brought home, they should be examined by a veterinarian for toxocariasis. ļ” Focus on personal hygiene. If dogs or cats have been in the yard, consider it contaminated. Wash hands after lawn work or gardening.
- 34. REFERENCE ļ” www.Medscape.com ļ” www.Wikipedia.com ļ” www.cdc.gov