Toxocara cati

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Geographic Range

Toxocara cati are found in domestic as well as wild cats around the world. Because cats have become more domesticated, this species is also more concentrated in those areas where humans reside. However, the spread of T. cati is dependent on the ingestion of its eggs, which are excreted with the hosts feces. Climate is a major factor in not only maintaining the eggs, but the feces that surrounds it. Therefore it has been observed that areas with mild temperate climates are the most favorable environment for T. cati. (O'Lorcain, 1994)

Habitat

Toxocara cati hosts are predominantly within the genus Felis, the cats. Most research, however, has been focused on the house cat, Felis domesticus because of its close contact with humans. Studies excluding strays cited 8% of the cats with Toxocara cati while another study including strays found 42% of cats had the parasite (O'Lorcain, 1994).

There are also many other paratenic hosts. These include earthworms, cockroaches, birds, rodents, dogs and humans (Schierenberg, 1997). Within the paratenic hosts, T. cati remain juveniles and, depending on where they migrate, cause immune reactions throughout their host's body. Therefore during the other stages of its life, T. cati is found in limited areas of the cat. As J1s, they remain in the egg, in the environment outside of potential hosts. If ingested, as J2s they may be found in the stomach wall, or if they undergo further migration - in the liver, lungs, bronchi, trachea, pharynx, stomach, and small intestine. Finally, as J3s, J4s, and adults, T. cati is found in the lumen of the intestine of cats only. Eggs are produced within this area, and excreted with the cat's feces (Prociv, 1989).

Toxocara cati are mainly found in kittens because of the transmammary route of transmission. In female kittens, they are most prevalent from 24-48 weeks, while in male kittens they are mainly found in those aging 12-24 weeks. The reason for this sexual variation is possibly due to the different timing of their immune system development (O'Lorcain, 1994). (O'Lorcain, 1994; Prociv, December 1989)

Physical Description

Toxocaara cati, as well as most nematodes, do not have appendages, eyes, segments, or other features that would cause these small creatures to stand out. The hydroskeleton is a single chamber, similar to a balloon filled with water. Movement depends on the pressure exerted in the hydroskeleton over the parasite's body. By contracting its longitudinal muscles, which are separated into four quadrants, the worm squeezes its "balloon" and moves through the hosts body in "contractile waves" (Schierenberg, 1997). Adult T. cati also have a complete digestive system with a mouth at one end, made up of three fleshy lips, and an anus near the posterior end (Roberts and Janovy, 2000).

Toxocara cati are dioecious, and like most nematodes, the females in this species, at about 10 cm, are larger than the males which can be up to 6 cm (Uga et al., 2000). The posterior end of the males is curved with paired spicules, small pointy structures that help him to "feel" a female with which he can mate (Roberts and Janovy, 2000).

The rough, pitted eggs produced, on average, measure 75 X 65 µm and may survive for years in the environment (Uga et al., 2000). These appear very dark under the microscope because the one-celled zygote fills the entire interior of the egg, but due to their ovoid shape, the albuminous shell of the egg becomes visible as well.

Four larval instars precede the well-known "arrowhead" adult nematode. Both males and females have clear thickened cuticles, alae, along the sides of the anterior end of the worm, which end abruptly and give them the appearance of an arrow. These alae may provide stability and help in its movement through the host's body. (Roberts and Janovy, Jr., 2000; Schierenberg, 1997; Uga, et al., October 20, 2000)

  • Sexual Dimorphism
  • female larger
  • sexes shaped differently
  • Range length
    6 to 10 cm
    2.36 to 3.94 in

Development

Adult T. cati migrate to the intestine, and begin producing eggs after just a few weeks. The eggs are excreted with the host's feces, and require a variable amount of time in the environment to mature. Depending on temperature and weather conditions, maturation takes on average about 2-3 weeks during the summer (Prociv, 1989). During this time, the juvenile passes through its first stage (J1), and into its second infective stage (J2) (Roberts and Janovy, 2000). After this time, any organism (from worms and rodents to humans) that ingests these eggs is at risk of infection. Stimulated by the stomach acid, the eggs hatch and the J2 larvae begin their migration through the host's body. Many move from the stomach into the stomach wall, to the liver and lungs, and then back into the stomach wall again. After having passed through four juvenile stages, the mature T. cati migrate to the small intestine where they reproduce and begin shedding eggs (Prociv, 1989).

Reproduction

Adult T. cati migrate to the intestine, and begin producing eggs after just a few weeks. The eggs are excreted with the host's feces, and require a variable amount of time in the environment to mature. Depending on temperature and weather conditions, maturation takes on average about 2-3 weeks during the summer (Prociv, 1989). During this time, the juvenile passes through its first stage (J1), and into its second infective stage (J2) (Roberts and Janovy, 2000). After this time, any organism (from worms and rodents to humans) that ingests these eggs is at risk of infection. Stimulated by the stomach acid, the eggs hatch and the J2 larvae begin their migration through the host's body. Many move from the stomach into the stomach wall, to the liver and lungs, and then back into the stomach wall again. After having passed through four juvenile stages, the mature T. cati migrate to the small intestine where they reproduce and begin shedding eggs (Prociv, 1989).

Paratenic hosts (those hosts that carry the worm, but the worm will not further develop) are especially important in T. cati infection of cats because of their predatory nature. If a mouse, for example, ingests a T. cati egg - the egg hatches, but the J2 larvae does not undergo further development. When this mouse is eaten by the cat, the J2 enters the wall of the stomach, and molts (by shedding its external cuticle and replacing it with the new one formed underneath) into J3 (Schrierenberg, 1997). When the juvenile procedes to migrate into the intestine lumen, it undergoes its last molt, into J4. These juveniles then molt into immature adults, and finally mature into adults capable of reproducing (Prociv, 1989).

Another important method of transmission is through the mammary glands of a pregnant female cat. Because T. cati do not migrate through the bloodstream and into the placenta, kittens are born free of worms, even if their mother was infected. However, after about 3-4 weeks, the newly hatched J2s migrate to the mother's mammary glands, where they are ingested by the feeding kittens (O'Lorcain, 1994). These enter the stomach, and then intestine of the kitten where they undergo the rest of their development into mature adults (Prociv, 1989). (O'Lorcain, 1994; Prociv, December 1989; Roberts and Janovy, Jr., 2000; Schierenberg, 1997)

  • Parental Investment
  • pre-fertilization
    • provisioning

Behavior

Paratenic hosts (those hosts that carry the worm, but the worm will not further develop) are especially important in T. cati infection of cats because of their predatory nature. If a mouse, for example, ingests a T. cati egg - the egg hatches, but the J2 larvae does not undergo further development. When this mouse is eaten by the cat, the J2 enters the wall of the stomach, and molts (by shedding its external cuticle and replacing it with the new one formed underneath) into J3 (Schrierenberg, 1997). When the juvenile procedes to migrate into the intestine lumen, it undergoes its last molt, into J4. These juveniles then molt into immature adults, and finally mature into adults capable of reproducing (Prociv, 1989).

Another important method of transmission is through the mammary glands of a pregnant female cat. Because T. cati do not migrate through the bloodstream and into the placenta, kittens are born free of worms, even if their mother was infected. However, after about 3-4 weeks, the newly hatched J2s migrate to the mother's mammary glands, where they are ingested by the feeding kittens (O'Lorcain, 1994). These enter the stomach, and then intestine of the kitten where they undergo the rest of their development into mature adults (Prociv, 1989). (O'Lorcain, 1994; Prociv, December 1989; Schierenberg, 1997)

Communication and Perception

Nematodes within the Secernentea have phasmids, which are unicellular glands. Phasmids likely function as chemoreceptors. Females may produce pheromones to attract males.

Nematodes in general have papillae, setae and amphids as the main sense organs. Setae detect motion (mechanoreceptors), while amphids detect chemicals (chemoreceptors). (Barnes, 1987; Roberts and Janovy, Jr., 2000)

Food Habits

Toxocara cati reside in the lumen of the small intestines. However, because they do not attach to the wall of its host's gut, it becomes apparent that these worms do not suck blood. Instead they feed primarily off of the liquid contents in the intestine (Roberts and Janovy, 2000), often resulting in malnutrition for the host.

Pharyngeal glands and intestinal epithelium produce digestive enzymes to feed on the hosts’ body fluids. Extracellular digestion begins within the lumen and is finished intracellularly (Barnes, 1987). (Barnes, 1987; Roberts and Janovy, Jr., 2000)

  • Animal Foods
  • body fluids

Predation

These parasites are usually not preyed on directly, but are ingested from host to host.

Ecosystem Roles

Toxocara cati are found in domestic as well as wild cats around the world.

Species Used as Host

Economic Importance for Humans: Negative

Anywhere from 8-42% of cats may be infected with T. cati (O'Lorcain, 1994). Routes of transmission are either transmammary (directly to the newborn kittens), or by accidental ingestion of eggs found within paratenic hosts, or within the environment.

Cats are not the only source of infection. Every year 3,000-4,000 cases of human infection are also reported to the Centers for Disease Control and Prevention and state public health departments (CDC, 2000). Children are most often the recipient of these worms by accidently swallowing the eggs when they lick their fingers, or orally clean out the dirt underneath their fingernails. As with other paratenic hosts, the J2 larvae hatch and migrate throughout the human's body. The tissues they migrate to determine the symptoms of the child's infection.

Infection with the worm, T. cati, is called Toxocariasis. The two forms of this disease are ocular larva migrans (OLM) and visceral larva migrans (VLM). OLM is an eye disease caused when the worm enters the eye causing inflammation and scaring of the retina. This may lead to blindness. VLM, on the other hand, is due to repeated infections of T. cati, and effects of its continual movement throughout the body. The organs and tissues swell from the immune response to this foreign invader, and the central immune system may be affected. Symptoms of VLM include fever, coughing, ashma, or pneumonia. VLM is easily treated with antiparasitic drugs and anti-inflammatory medications. OLM, on the other hand is more difficult to treat, and the focus is usually on prevention versus cure (CDC, 2000). (Centers for Disease Control and Prevention (CDC) and National Center for Infectious Diseases, March, 2002; O'Lorcain, 1994)

Contributors

Renee Sherman Mulcrone (editor).

Gayle Soskolne (author), University of Michigan-Ann Arbor, Barry OConnor (editor), University of Michigan-Ann Arbor.

Glossary

Australian

Living in Australia, New Zealand, Tasmania, New Guinea and associated islands.

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Ethiopian

living in sub-Saharan Africa (south of 30 degrees north) and Madagascar.

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Nearctic

living in the Nearctic biogeographic province, the northern part of the New World. This includes Greenland, the Canadian Arctic islands, and all of the North American as far south as the highlands of central Mexico.

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Neotropical

living in the southern part of the New World. In other words, Central and South America.

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Palearctic

living in the northern part of the Old World. In otherwords, Europe and Asia and northern Africa.

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agricultural

living in landscapes dominated by human agriculture.

bilateral symmetry

having body symmetry such that the animal can be divided in one plane into two mirror-image halves. Animals with bilateral symmetry have dorsal and ventral sides, as well as anterior and posterior ends. Synapomorphy of the Bilateria.

carnivore

an animal that mainly eats meat

causes disease in humans

an animal which directly causes disease in humans. For example, diseases caused by infection of filarial nematodes (elephantiasis and river blindness).

causes or carries domestic animal disease

either directly causes, or indirectly transmits, a disease to a domestic animal

chaparral

Found in coastal areas between 30 and 40 degrees latitude, in areas with a Mediterranean climate. Vegetation is dominated by stands of dense, spiny shrubs with tough (hard or waxy) evergreen leaves. May be maintained by periodic fire. In South America it includes the scrub ecotone between forest and paramo.

chemical

uses smells or other chemicals to communicate

cosmopolitan

having a worldwide distribution. Found on all continents (except maybe Antarctica) and in all biogeographic provinces; or in all the major oceans (Atlantic, Indian, and Pacific.

desert or dunes

in deserts low (less than 30 cm per year) and unpredictable rainfall results in landscapes dominated by plants and animals adapted to aridity. Vegetation is typically sparse, though spectacular blooms may occur following rain. Deserts can be cold or warm and daily temperates typically fluctuate. In dune areas vegetation is also sparse and conditions are dry. This is because sand does not hold water well so little is available to plants. In dunes near seas and oceans this is compounded by the influence of salt in the air and soil. Salt limits the ability of plants to take up water through their roots.

ectothermic

animals which must use heat acquired from the environment and behavioral adaptations to regulate body temperature

fertilization

union of egg and spermatozoan

forest

forest biomes are dominated by trees, otherwise forest biomes can vary widely in amount of precipitation and seasonality.

heterothermic

having a body temperature that fluctuates with that of the immediate environment; having no mechanism or a poorly developed mechanism for regulating internal body temperature.

internal fertilization

fertilization takes place within the female's body

motile

having the capacity to move from one place to another.

mountains

This terrestrial biome includes summits of high mountains, either without vegetation or covered by low, tundra-like vegetation.

oriental

found in the oriental region of the world. In other words, India and southeast Asia.

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oviparous

reproduction in which eggs are released by the female; development of offspring occurs outside the mother's body.

parasite

an organism that obtains nutrients from other organisms in a harmful way that doesn't cause immediate death

pheromones

chemicals released into air or water that are detected by and responded to by other animals of the same species

rainforest

rainforests, both temperate and tropical, are dominated by trees often forming a closed canopy with little light reaching the ground. Epiphytes and climbing plants are also abundant. Precipitation is typically not limiting, but may be somewhat seasonal.

scrub forest

scrub forests develop in areas that experience dry seasons.

sedentary

remains in the same area

sexual

reproduction that includes combining the genetic contribution of two individuals, a male and a female

suburban

living in residential areas on the outskirts of large cities or towns.

tactile

uses touch to communicate

temperate

that region of the Earth between 23.5 degrees North and 60 degrees North (between the Tropic of Cancer and the Arctic Circle) and between 23.5 degrees South and 60 degrees South (between the Tropic of Capricorn and the Antarctic Circle).

terrestrial

Living on the ground.

tropical

the region of the earth that surrounds the equator, from 23.5 degrees north to 23.5 degrees south.

tropical savanna and grassland

A terrestrial biome. Savannas are grasslands with scattered individual trees that do not form a closed canopy. Extensive savannas are found in parts of subtropical and tropical Africa and South America, and in Australia.

savanna

A grassland with scattered trees or scattered clumps of trees, a type of community intermediate between grassland and forest. See also Tropical savanna and grassland biome.

temperate grassland

A terrestrial biome found in temperate latitudes (>23.5° N or S latitude). Vegetation is made up mostly of grasses, the height and species diversity of which depend largely on the amount of moisture available. Fire and grazing are important in the long-term maintenance of grasslands.

urban

living in cities and large towns, landscapes dominated by human structures and activity.

References

Barnes, R. 1987. Invertebrate Zoology. Orlando, Florida: Dryden Press.

Centers for Disease Control and Prevention (CDC), , National Center for Infectious Diseases. March, 2002. "Parasitic Disease Information: Toxocariasis" (On-line). Division of Parasitic Diseases, Parasite Disease Information. Accessed 10/01/04 at www.cdc.gov/ncidod/dpd/parasites/toxocara/factsht_toxocara.htm.

Milstein, T., J. Goldsmid. March 1997. Parasites of feral cats from southern Tasmania and their potential significiance. Australian Veterinary Journal, 75(3): 218-219.

O'Lorcain, P. 1994. Epidemiology of Toxocara spp. in stray dogs and cats in Dublin, Ireland.. Journal of Helminthology, 68: 331-336.

Prociv, P. December 1989. Observations on the post-mortem migration of nematode larvae and its role in tissue digestion techniques. Journal of Helminthology, 63(4): 281-286.

Roberts, L., J. Janovy, Jr.. 2000. Foundations of Parasitology 6th ed.. McGraw-Hill Higher Education.

Schierenberg, E. 1997. Embryology:constructing the organism. Sunderland, MA.: Smauer Associates Inc..

Uga, S., J. Matsuo, D. Kimura, S. Rai, Y. Koshino. October 20, 2000. Differentiation of Toxocara canis and T. cati eggs by light and scanning electron microscopy. Veterinary Parasitology, 92(4): 287-294.