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Toxocariasis

Toxocariasis

What Happens When People Have Toxocariasis?

How Can Toxocariasis Be Prevented?

Resource

Toxocariasis (TOK-so-ka-RY-a-sis) is an infection in people caused by parasitic roundworms found in the intestines of cats and dogs. It most commonly affects young children who come in contact with contaminated dirt.

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Infestation

Parasites

Roundworms

Toxocara canis

Toxocara catis

Many cats and dogs, especially kittens and puppies, have intestinal worms called Toxocara canis (in dogs) or Toxocara cati (in cats). Eggs from Toxocara pass with the stools from infected cats and dogs and then contaminate the soil.

When children play in contaminated areas, the eggs can stick to their hands or toys and then be swallowed. When the eggs enter the digestive system, they hatch. The larvae* burrow through the intestinal wall and move to the liver, lung, and sometimes to other sites, including the central nervous system, eye, kidney, and heart. The larvae may stay alive for many months and cause damage to tissues or organs. Because the larvae are cat or dog parasites, they do not complete their life cycle in humans.

* larvae
are worms at an intermediate stage of the life cycle between eggs and adulthood.

What Happens When People Have Toxocariasis?

Symptoms

Most people with toxocariasis have no symptoms. If symptoms occur, they may include fever, cough or wheezing, and seizures. Other symptoms may include abdominal pain, enlarged liver or spleen, loss of appetite, rash, and enlarged lymph nodes*. Toxocariasis can also affect the eyes and cause decreased vision, swelling around the eyes, and a cross-eyed appearance.

* lymph nodes
are round masses of tissue that contain immune cells whose job it is to filter out harmful microorganisms; lymph nodes can become enlarged during infection.

Diagnosis and Treatment

Toxocariasis is diagnosed through a blood test. For most cases, no treatment is necessary. Certain medications that are effective against toxocariasis may be used to eliminate the infection.

How Can Toxocariasis Be Prevented?

As with other infections, good hygiene and frequent handwashing are essential. Important safety measures include:

  • Keeping children from playing in areas contaminated by cats and dogs.
  • Teaching children not to put their hands and toys in their mouths after playing with cats and dogs.
  • Teaching children to wash their hands thoroughly after playing outside, after playing with pets, and before eating.
  • Keeping pets away from sandboxes, which should be covered when not in use.

Pets should be checked for parasites periodically by veterinarians and treated if they are found to be infected.

See also

Parasitic Diseases

Worms

Zoonoses

Resource

The U.S. Centers for Disease Control and Prevention (CDC), 100 Clifton Road N.E., Atlanta, GA 30333. CDC s Division of Parasitic Diseases posts a fact sheet about toxocariasis at its website. Telephone 404-639-3534 http://www.cdc.gov/ncidod/dpd/toxocar.htm

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trichuriasis

trichuriasis (trik-yoor-I-ă-sis) n. an infestation of the large intestine by the whipworm, Trichuris trichiura. Symptoms, including bloody diarrhoea, anaemia, weakness, and abdominal pain, are evident only in heavy infestations. Trichuriasis can be treated with various anthelmintics, including tiabendazole and piperazine salts.

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toxocariasis

toxocariasis (visceral larva migrans) (toks-oh-kair-I-ă-sis) n. an infestation with the larvae of the dog and cat roundworms, Toxocara canis and T. cati. It is characterized by enlargement of the liver, pneumonitis, fever, joint and muscle pains, vomiting, an irritating rash, and convulsions.

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roundworms

roundworms See Nematoda.

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roundworms

roundworms See NEMATODA.

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Roundworms

Roundworms

With more than 10,000 species described, roundworms (phylum Nematoda) are among the most numerous and widespread animals. They occur in all habitats, including freshwater, marine, and terrestrial ecosystems, from the tropics to the polar regions. They often occur in staggering numbers: 10.8 sq ft (1 sq m) of mud has been found to contain more than four million nematodes. Because of their distribution and ability to adapt to different situations, it is not surprising to find that nematodes have adapted to a wide range of living conditions. Many are free-living, but others are parasitic on both plants and animals.

All nematodes are characterized by their slender, elongate body, in which the two ends are slightly tapered to form a head and anal region. Many species measure less than 0.04 in (1 mm) in length; most are microscopic. The body is enclosed in a thin layer of collagen which represents the body wall, and is also supplied with a layer of muscle, enabling the worm to move in a sideways manner by contracting and expanding these muscles.

Among the free-living species, many roundworms are carnivorous, feeding on a wide range of protozoans as well as other nematodes; aquatic species feed largely on bacteria, algae, and microscopic diatoms. Some terrestrial species attack the roots of plants, extracting nutrients and essential fluids.

Most nematodes are dioecious (either male or female), with males commonly being smaller than females. When ready to breed, females of some species are thought to give off a pheromone that serves to attract potential suitors. During copulation, the male inserts its sperm into the female and fertilization takes place. The egg then develops a toughened outer coating and may either be held within the body for a short period or released to the outside. In hermaphrodite species, the sperm develop ahead of the eggs and are stored in special chambers until the eggs are ready for fertilization to take place. The young larvae that emerge progress through a series of body molts until they develop adult characteristics.

Many species of parasitic nematodes are unable to complete their life cycle without the presence of another animal. Commonly eggs are deposited on plants, which are then ingested or absorbed into the body in some manner. Once within the host animal, the eggs hatch and burrow their way into the flesh (often the intestine or lungs), where they attach firmly to the lining of the chamber and begin to mature. From there the nematodes absorb nutrients from the host animal and release additional eggs, which pass out of the body in the feces.

Although some nematodes are beneficial in the manner in which they break down dead or decaying matter, many are of considerable economic importance: a great number are pests of animals and plant crops, while others are the cause of serious illnesses in humans. The tiny hookworms, for example, are believed to affect millions of people worldwide, causing serious bleeding and tissue damage. Larvae of the guinea worm (Dracunculus medinensis), which lives in freshwater streams in parts of Africa and Asia, seek an open wound in the body through which they pass and become installed in the connective tissue. Females of this species may develop to a length exceeding 3.3 ft (1 m), causing considerable discomfort.

See also Parasites.

David Stone

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Roundworms

Roundworms

With more than 10,000 species described, roundworms (phylum Nematoda) are among the most numerous and widespread animals. They occur in all habitats, including freshwater , marine, and terrestrial ecosystems, from the tropics to the polar regions. They often occur in staggering numbers: 10.8 sq ft (1 sq m) of mud has been found to contain more than four million nematodes. Because of their distribution and ability to adapt to different situations, it is not surprising to find that nematodes have adapted to a wide range of living conditions. Many are free-living, but others are parasitic on both plants and animals.

All nematodes are characterized by their slender, elongate body, in which the two ends are slightly tapered to form a head and anal region. Many species measure less than 0.04 in (1 mm) in length; most are microscopic. The body is enclosed in a thin layer of collagen which represents the body wall, and is also supplied with a layer of muscle, enabling the worm to move in a sideways manner by contracting and expanding these muscles.

Among the free-living species, many roundworms are carnivorous, feeding on a wide range of protozoans as well as other nematodes; aquatic species feed largely on bacteria , algae , and microscopic diatoms . Some terrestrial species attack the roots of plants, extracting nutrients and essential fluids.

Most nematodes are dioecious (either male or female), with males commonly being smaller than females. When ready to breed, females of some species are thought to give off a pheromone that serves to attract potential suitors. During copulation, the male inserts its sperm into the female and fertilization takes place. The egg then develops a toughened outer coating and may either be held within the body for a short period or released to the outside. In hermaphrodite species, the sperm develop ahead of the eggs and are stored in special chambers until the eggs are ready for fertilization to take place. The young larvae that emerge progress through a series of body molts until they develop adult characteristics.

Many species of parasitic nematodes are unable to complete their life cycle without the presence of another animal . Commonly eggs are deposited on plants, which are then ingested or absorbed into the body in some other manner. Once within the host animal, the eggs hatch and burrow their way into the flesh (often the intestine or lungs), where they attach firmly to the lining of the chamber and begin to mature. From there the nematodes absorb nutrients from the host animal and release additional eggs, which pass out of the body in the feces.

Although some nematodes are beneficial in the manner in which they break down dead or decaying matter , many are of considerable economic importance: a great number are pests of animals and plant crops , while others are the cause of serious illnesses in humans. The tiny hookworms, for example, are believed to affect millions of people worldwide, causing serious bleeding and tissue damage. Larvae of the guinea worm (Dracunculus medinensis), which lives in freshwater streams in parts of Africa and Asia , seek an open wound in the body through which they pass and become installed in the connective tissue . Females of this species may develop to a length exceeding 3.3 ft (1 m), causing considerable discomfort.

See also Parasites.

David Stone

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