''Toxascaris leonina'' is a common

parasitic Parasitism is a close relationship between species, where one organism, the parasite, lives on or inside another organism, the host, causing it some harm, and is adapted structurally to this way of life. The entomologist E. O. Wilson has ...

roundworm found in dogs, cats, foxes, and related host species. ''T. leonina'' is an

ascarid The Ascarididae are a family of the large intestinal roundworms. Members of the family are intestinal parasites, infecting all classes of vertebrates. It includes a number of genera,Anderson RC (2000)''Nematode Parasites of Vertebrates. Their De ...

nematode The nematodes ( or grc-gre, Νηματώδη; la, Nematoda) or roundworms constitute the phylum Nematoda (also called Nemathelminthes), with plant- parasitic nematodes also known as eelworms. They are a diverse animal phylum inhabiting a bro ...

, a worldwide distributed helminth parasite which is in a division of eukaryotic parasites that, unlike external parasites such as

lice Louse ( : lice) is the common name for any member of the clade Phthiraptera, which contains nearly 5,000 species of wingless parasitic insects. Phthiraptera has variously been recognized as an order, infraorder, or a parvorder, as a result o ...

and

fleas Flea, the common name for the order Siphonaptera, includes 2,500 species of small flightless insects that live as external parasites of mammals and birds. Fleas live by ingesting the blood of their hosts. Adult fleas grow to about long, a ...

, live inside their host. The definitive

hosts A host is a person responsible for guests at an event or for providing hospitality during it. Host may also refer to: Places * Host, Pennsylvania, a village in Berks County People *Jim Host (born 1937), American businessman *Michel Host ...

of ''T. leonina'' include

canids Canidae (; from Latin, ''canis'', " dog") is a biological family of dog-like carnivorans, colloquially referred to as dogs, and constitutes a clade. A member of this family is also called a canid (). There are three subfamilies found within th ...

(dogs, foxes, etc.) and felines (cats), while the intermediate hosts are usually rodents, such as mice or rats. Infection occurs in the definitive host when the animal eats an infected rodent. While ''T. leonina'' can occur in either dogs or cats, it is far more frequent in cats. A

coprolite A coprolite (also known as a coprolith) is fossilized feces. Coprolites are classified as trace fossils as opposed to body fossils, as they give evidence for the animal's behaviour (in this case, diet) rather than morphology. The name is ...

containing ''T. leonina'' eggs was excavated in Argentina's

Catamarca Province Catamarca () is a province of Argentina, located in the northwest of the country. The province had a population of 334,568 as per the , and covers an area of 102,602 km2. Its literacy rate is 95.5%. Neighbouring provinces are (clockwise, fr ...

and dated to 17002–16573 years old. This finding indicates that ''T. leonina'' has existed in South America since at least the Late Pleistocene.

Life cycle

The life cycle of ''T. leonina'' is fairly simple.

Eggs Humans and human ancestors have scavenged and eaten animal eggs for millions of years. Humans in Southeast Asia had domesticated chickens and harvested their eggs for food by 1,500 BCE. The most widely consumed eggs are those of fowl, especial ...

are ingested and hatch in the small intestine. The juveniles then penetrate the mucosal lining of the small intestine. After growth and molt, they return to the intestinal lumen and mature. The adult female worm lays eggs which are passed in the feces of the animal. The eggs become infective after 3–6 days in the environment. Cats can become infected by ingesting either the egg or rodents that contain the larvae. Rodents are usually the intermediate hosts of ''T. leonina''. The rodent ingests the eggs and, once the eggs are hatched, the larvae migrate through the tissues of the rodent. The definitive host is then infected with this parasite when it eats an infected rodent. The egg of the ''T. leonina'' is usually more oval than round. The prepatent period for ''T. leonina'' is two to three months. The adult worms are usually 3-4 inches long and can be seen in the feces and vomit of the animal. ''Toxascaris leonina'' differs from other

Toxocara The Toxocaridae are a zoonotic family of parasitic nematodes that infect canids and felids and which cause toxocariasis in humans ( visceral larva migrans and ocular larva migrans). The worms are unable to reproduce in humans. Notable species ...

in that the larvae do not migrate through the lungs; but rather, the entire developmental cycle occurs in the gut.

Symptoms of infection

Roundworms absorb the nutrients from the animal, which can interfere with digestion and can also damage the lining of the intestine. Animals may not show any outward symptoms of roundworms at all, or in other, usually more severe cases, animals may have diarrhea, vomiting, loss of appetite, experience thinning, dull coats, and in puppies or kittens, can develop distended abdomens, or "pot-belly" appearance. Infection symptoms are similar to infection by other ''Toxacara'' species ('' T. canis'', '' T. cati''). It is a common cause of diarrhea in young animals and can cause vomiting as well. Sometimes the worms themselves are vomited up, which can be alarming as they can be quite large with females reaching lengths of up to seven inches. The worms consume the host's food and can lead to lethargy and a classical pot-bellied appearance. Unlike T. canis and T. Cati, T. leonina is nonmigratory with its life cycle affecting only one organ.

Prevention and treatment

It is recommended to de-worm all puppies and kittens at 6 weeks and repeat treatment 2–4 weeks after the first treatment. ''T. leonina'' roundworm infections are treated with the same medication protocol as the ''T. canis'' or ''T. cati'' roundworm infections (see

Toxocariasis Toxocariasis is an illness of humans caused by the dog roundworm (''Toxocara canis'') and, less frequently, the cat roundworm ('' Toxocara cati'').https://academic.oup.com/ajcp/article/142/suppl_1/A104/1771175 Eosinophilic Pseudoleukemia Due to T ...

). Therefore, when eggs are seen on a fecal flotation exam, or fecal swab, it is not necessary to determine which species is present. Roundworm infections are treated with medication, called "de-wormers", and includes such drugs as fenbendazole,

pyrantel Pyrantel is a medication used to treat a number of parasitic worm infections. This includes ascariasis, hookworm infections, enterobiasis (pinworm infection), trichostrongyliasis, and trichinellosis. It is taken by mouth. Side effects include ...

milbemycin oxime Milbemycin oxime, sold under the brand name Interceptor among others, is a veterinary medication from the group of milbemycins, used as a broad spectrum antiparasitic. It is active against worms (anthelmintic) and mites (miticide). Mechanism of ...

, and piperazine. To prevent reinfection of parasitic roundworms, it is recommended that anything that the animal has been in contact with should be cleaned thoroughly or replaced, including bedding and kennels. It is also strongly recommended that outside areas where defecation may occur be cleaned, as well as all feces removed daily from outdoor pet runs, crates, and the yard.

Risk to humans

Humans are usually not infected with ''T. leonina''; however, this parasite has been found in humans in a few instances and is a cause of visceral larva migrans in children, though less frequently implicated than is '' Toxocara canis'', the most common roundworm parasite found in dogs.

References

* Schmidt, Gerald D & Roberts, Larry S. 2005. ''Foundations of Parasitology'' (7th Ed.). New York: McGraw-Hill pp 439. * Nash, Holly. 1997–2008. ''Pet education''. Foster & Smith, Inc.

External links