Toxocara canis

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Toxocara canis
Canine roundworm 1.JPG
Adult worms of the dog roundworm (Toxocara canis) live in the gut of dogs, puppies and other canids
Scientific classification OOjs UI icon edit-ltr.svg
Domain: Eukaryota
Kingdom: Animalia
Phylum: Nematoda
Class: Chromadorea
Order: Ascaridida
Family: Toxocaridae
Genus: Toxocara
Species:
T. canis
Binomial name
Toxocara canis
(Werner, 1782)

Toxocara canis (T. canis, also known as dog roundworm) is a worldwide-distributed helminth parasite that primarily infects dogs and other canids, but can also infect other animals including humans. [1] [2] The name is derived from the Greek word "toxon," meaning bow or quiver, and the Latin word "caro," meaning flesh. [3] T. canis live in the small intestine of the definitive host. This parasite is very common in puppies and somewhat less common in adult dogs. [4] In adult dogs, infection is usually asymptomatic but may be characterized by diarrhea. By contrast, untreated infection with Toxocara canis can be fatal in puppies, causing diarrhea, vomiting, pneumonia, enlarged abdomen, flatulence, poor growth rate, and other complications. [1]

Contents

As paratenic hosts, a number of vertebrates, including humans, and some invertebrates can become infected. Humans are infected, like other paratenic hosts, by ingestion of embryonated T. canis eggs. [5] The disease (toxocariasis) caused by migrating T. canis larvae results in two syndromes: visceral larva migrans and ocular larva migrans. [6] Owing to transmission of the infection from the mother to her puppies, preventive anthelmintic treatment of newborn puppies is strongly recommended. Several anthelmintic drugs are effective against adult worms, for example fenbendazole, milbemycin, moxidectin, piperazine, pyrantel, and selamectin. [1]

Morphology

T. canis is dioecious, having morphology distinctly different between the male and female. Male worms measure 4 to 6 cm (1.5" to 2.3"), typically smaller than female worms who measure at 6.5 to 15 cm (2.6" to 5.9"). The male's posterior end is curved ventrally and the tail is bluntly pointed. The male has a single tubular testis. [7] They also have simple spicules, which allow for direct sperm transfer. In the female, the vulva is about one-third the body length from the anterior end. The ovaries are very large and extensive. The uteri contain up to 27 million eggs at a time. [7]

Both males and females have three prominent lips. Each lip has a dentigerous ridge. The lateral hypodermal chords are visible with the naked eye. No gubernaculum is present. In both sexes there are prominent cervical alae. The adult T. canis has a round body with spiky cranial and caudal parts, covered by yellow cuticula. Toxocara canis is gonochoristic. The cranial part of the body contains two lateral alae (length 2 to 3.5 mm, width 0.1 mm). The eggs are brownish and almost spherical.T. canis eggs have oval or spherical shapes with granulated surfaces, are thick-walled, and measure from 72 to 85 μm. The eggs are very resistant to various weather and chemical conditions typically found in soil.[ citation needed ]

Life cycle

The eggs of T. canis are shed in the scat of an infected dog or puppy; environmental contamination with the eggs is considered the main source of human toxocariasis Dog defecation 1.jpg
The eggs of T. canis are shed in the scat of an infected dog or puppy; environmental contamination with the eggs is considered the main source of human toxocariasis
Life Cycle (Toxocara canis) Toxocara canis LifeCycle.gif
Life Cycle (Toxocara canis)

Eggs are deposited in feces of dogs, becoming infectious after 2–4 weeks. [8] Dogs ingest infectious eggs, allowing the eggs to hatch and the larval form of the parasite to penetrate through the gut wall. In dogs under 3 months of age, the larvae hatch in the small intestine, get into the bloodstream, migrate through the liver, and enter the lungs. Once in the lungs, the larvae crawl up the trachea. The larvae are then coughed up and swallowed, leading back down to the small intestine, where they mature to adulthood. This process is called tracheal migration. In dogs older than 3 months of age, the larvae hatch in the small intestine and enter the bloodstream, where they are carried to somatic sites throughout the body (muscles, kidney, mammary glands, etc.) where they become encysted second stage larvae. This process is called somatic migration. At the height of pregnancy, the encysted eggs in an infected female dog will migrate from the mother to the developing fetus, where they will reside in the liver. After parturition, the larvae migrate from the pup's liver to the lungs to undergo tracheal migration. Alternatively, the migrating larvae in the mother may encyst within the mammary glands, becoming active during lactation and passing directly to the nursing puppy via the milk. Larvae transmitted in this manner do not migrate once they are within the small intestine of the puppy; they will develop directly into the adult stage in the small intestine. [3] Once infected, a female dog will usually harbor sufficient larvae to subsequently infect all of her litters, even if she never again encounters an infection. A certain amount of the female dog's dormant larvae penetrate into the intestinal lumen, where molting into adulthood takes place again, thus leading to a new release of eggs containing L1 larvae. [8]

Another possible route of infection is the ingestion of paratenic hosts that contain encysted larvae from egg consumption, allowing the parasite to escape from the paratenic host and grow to adulthood within the small intestine of its definitive host, the dog.

Four modes of infection are associated with this species. These modes of infection include direct transmission, prenatal transmission, paratenic transmission, and transmammary transmission. [9] [3]

Transmammary transmission occurs when the suckling pup becomes infected by the presence of L3 larvae in the milk during the first three weeks of lactation. There is no migration in the pup via this route. [9]

L2 larvae may also be ingested by a variety of animals like mice or rabbits, where they stay in a dormant stage inside the animals' tissue until the intermediate host has been eaten by a dog, where subsequent development is confined to the gastrointestinal tract. [10] [11]

Toxocara eggs- the surface contour is pitted due to the mammilation of the protein layer of the shell, and because of this the eggs are murky Toxocara embryonated eggs.jpg
Toxocara eggs- the surface contour is pitted due to the mammilation of the protein layer of the shell, and because of this the eggs are murky

Transmission to humans

Humans can be infected by T. canis, resulting in a condition called toxocariasis. Consumption of eggs from feces-contaminated items is the most common method of infection for humans, especially in children and young adults under the age of 20 years. [12] Although rare, being in close contact with an infected animal (e.g., stroking the fur of an infected animal) or with soil that contains infectious eggs can also cause human infection, especially handling soil with an open wound or accidentally swallowing contaminated soil, as well as eating undercooked or raw meat of an intermediate host of the parasite such as lamb or rabbit. [13] [10] [14] Although the risk of being infected by petting a dog is extremely limited, a single infected puppy can produce more than 100,000 roundworm eggs per gram of feces. [15]

Toxocariasis can result in complications such as hepatomegaly, myocarditis, respiratory failure and vision problems, depending on where the larvae are deposited in the body. [12] In humans, this parasite can infect organs including the lungs, liver, and the back of the eye (which can result in blindness). [16]

Treatment

Humans suffering from visceral infection of T. canis, the drugs albendazole, mebendazole and thiabendazole [ citation needed ] are highly effective. [16] [17] For other treatments, refer to the disease pages: visceralis larva migrans and ocularis larva migrans.

Anthelminthic drugs are used to treat infections in dogs and puppies for adult worms. Treatment protocol will vary based on the dog's age, production level and activity level. There are different treatment paths for puppies, pregnant bitches, lactating bitches, dogs with increased risk of infection, professional dogs, and dogs sharing homes with young children or immunocompromised individuals.[ citation needed ]

Puppies: from the age of two weeks, then every 14 days up to two weeks after weaning with fenbendazole/febantel, flubendazole, pyrantel, or nitroscanate, followed by monthly treatments for up to six months of age.

Pregnant bitches: to prevent transmission to the puppies, pregnant females can be given macrocyclic lactones on the 40th and 55th day of pregnancy or genbendazole daily from the 40th day of pregnancy continuing until the 14th day postpartum.

Lactating bitches: should be treated concurrently with the first treatment of puppies.

Dogs with increased risk of infection: i.e. those used in sports, competitions, shows, or those kept in kennels can be given two treatments 4 weeks before and 2–4 weeks after the event.

Professional dogs: i.e. therapy, rescue, or police dogs: 12 times a year, if excretion of worm eggs is to be excluded.

Dogs sharing homes with young children or immunocompromised individuals: 12 times a year, if excretion of worm eggs is to be excluded. [18]

Prevention

There are several ways to prevent a T. canis infection in both dogs and humans. Regular deworming by a veterinarian is important to stop canine re-infections, especially if the dog is frequently outdoors. [8] Removing dog feces from the yard using sealed disposable bags will help control the spread of T. canis. Good practices to prevent human infections include: washing hands before eating and after disposing of animal feces, teaching children not to eat soil, and cooking meat to a safe temperature in order to kill potentially infectious eggs. [10] [12]

See also

Related Research Articles

Toxocariasis is an illness of humans caused by the dog roundworm and, less frequently, the cat roundworm. These are the most common intestinal roundworms of dogs, coyotes, wolves and foxes and domestic cats, respectively. Humans are among the many "accidental" or paratenic hosts of these roundworms.

<i>Baylisascaris</i> Genus of worms

Baylisascaris is a genus of roundworms that infect more than fifty animal species.

Spirometra is a genus of pseudophyllid cestodes that reproduce in canines and felines, but can also cause pathology in humans if infected. As an adult, this tapeworm lives in the small intestine of its definitive host and produces eggs that pass with the animal's feces. When the eggs reach water, the eggs hatch into coracidia which are eaten by copepods. The copepods are eaten by a second intermediate host to continue the life cycle. Humans can become infected if they accidentally eat frog legs or fish with the plerocercoid stage encysted in the muscle. In humans, an infection of Spirometra is termed sparganosis.

<i>Echinococcus granulosus</i> Species of flatworm

Echinococcus granulosus, also called the hydatid worm, hyper tape-worm or dog tapeworm, is a cyclophyllid cestode that dwells in the small intestine of canids as an adult, but which has important intermediate hosts such as livestock and humans, where it causes cystic echinococcosis, also known as hydatid disease. The adult tapeworm ranges in length from 3 mm to 6 mm and has three proglottids ("segments") when intact—an immature proglottid, mature proglottid and a gravid proglottid. The average number of eggs per gravid proglottid is 823. Like all cyclophyllideans, E. granulosus has four suckers on its scolex ("head"), and E. granulosus also has a rostellum with hooks. Several strains of E. granulosus have been identified, and all but two are noted to be infective in humans.

<span class="mw-page-title-main">Toxocaridae</span> Family of roundworms

The Toxocaridae are a zoonotic family of parasitic nematodes that infect canids and felids and which cause toxocariasis in humans. The worms are unable to reproduce in humans.

Visceral larva migrans (VLM) is a condition in humans caused by the migratory larvae of certain nematodes, humans being a dead-end host, and was first reported in 1952. Nematodes causing such zoonotic infections are Baylisascaris procyonis, Toxocara canis, Toxocara cati, and Ascaris suum. These nematodes can infect but not mature in humans and after migrating through the intestinal wall, travel with the blood stream to various organs where they cause inflammation and damage. Affected organs can include the liver, heart and the CNS. A special variant is ocular larva migrans where usually T. canis larvae travel to the eye.

<span class="mw-page-title-main">Pooper-scooper</span> Device used to pick up animal feces

A pooper-scooper, or poop scoop, is a device used to pick up animal feces from public places and yards, particularly those of dogs. Pooper-scooper devices often have a bag or bag attachment. 'Poop bags' are alternatives to pooper scoopers, and are simply a bag, usually turned inside out, to carry the feces to a proper disposal area. Sometimes, the person performing the cleanup is also known as the pooper-scooper.

Spirometra erinaceieuropaei is a parasitic tapeworm that infects domestic animals and humans. The medical term for this infection in humans and other animals is sparganosis. Morphologically, these worms are similar to other worms in the genus Spirometra. They have a long body consisting of three sections: the scolex, the neck, and the strobilia. They have a complex life cycle that consists of three hosts, and can live in varying environments and bodily tissues. Humans can contract this parasite in three main ways. Historically, humans are considered a paratenic host; however, the first case of an adult S. erinaceieuropaei infection in humans was reported in 2017. Spirometra tapeworms exist worldwide and infection is common in animals, but S. erinaceieuropaei infections are rare in humans. Treatment for infection typically includes surgical removal and anti-worm medication.

Uncinaria stenocephala is a nematode that parasitizes dogs, cats, and foxes as well as humans. It is rare to find in cats in the United States. Uncinaria stenocephala is the most common canine hookworm in cooler regions, such as Canada and the northern regions of the US, where it can be found primarily in foxes (40%). U. stenocephala is also one of the most common hookworms in the UK, called the northern hookworm, however it has a rather low prevalence. U. stenocephala is also considered to be zoonotic hookworms because they live in animals but can be transmitted to humans.

<i>Toxocara cati</i> Species of worm

Toxocara cati, also known as the feline roundworm, is a parasite of cats and other felids. It is one of the most common nematodes of cats, infecting both wild and domestic felids worldwide. Adult worms are localised in the gut of the host. In adult cats, the infection – which is called toxocariasis – is usually asymptomatic. However, massive infection in juvenile cats can be fatal.

<span class="mw-page-title-main">Deworming</span> Use of anthelmintic drugs

Deworming is the giving of an anthelmintic drug to a human or animals to rid them of helminths parasites, such as roundworm, flukes and tapeworm. Purge dewormers for use in livestock can be formulated as a feed supplement that is eaten, a paste or gel that is deposited at the back of the animal's mouth, a liquid drench given orally, an injectable, or as a pour-on which can be applied to the animal's topline. In dogs and cats, purge dewormers come in many forms including a granular form to be added to food, pill form, chew tablets, and liquid suspensions.

<i>Toxascaris leonina</i> Species of roundworm

Toxascaris leonina is a common parasitic roundworm found in dogs, cats, foxes, and related host species. T. leonina is an ascarid nematode, a worldwide distributed helminth parasite which is in a division of eukaryotic parasites that, unlike external parasites such as lice and fleas, live inside their host. The definitive hosts of T. leonina include canids 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.

<i>Ancylostoma braziliense</i> Species of worm

Ancylostoma braziliense is a species of hookworm belonging to the genus Ancylostoma. It is an intestinal parasite of domestic cats and dogs. Severe infection is often fatal to these pets, especially in puppies and kittens. The infection is particularly endemic in the southern United States. It is most often confused with the zoonotic hookworm species Ancylostoma ceylanicum because of their uncanny resemblance.

<i>Ancylostoma caninum</i> Species of roundworm

Ancylostoma caninum is a species of nematode known as a hookworm, which principally infects the small intestine of dogs. The result of A. caninum infection ranges from asymptomatic cases to death of the dog; better nourishment, increasing age, prior A. caninum exposure, or vaccination are all linked to improved survival. Other hosts include carnivores such as wolves, foxes, and cats, with a small number of cases having been reported in humans.

Trichuris vulpis is a whipworm that lives in the large intestine of canines in its adult stages. Out of different types of worms, Trichuris vulpis is one of the smaller worms with a size ranging from 30–50 mm in length. As the name suggests, the worm has a whip-like shape with distinct features including a small, narrow anterior head, which is the digestive part of the worm, and a larger posterior tail, which is the reproductive part of the worm. Eggs from T. vulpis are oval shaped with bipolar plugs and contain a thick outer shell. Their sizes range from 72–90 μm in length and 32–40 μm in width. Because of their thick outer shell, T. vulpis eggs are very resistant to environmental extremes such as freezing or hot temperatures, thus allowing for their long viability in the outside world.

<i>Baylisascaris procyonis</i> Species of roundworm

Baylisascaris procyonis, also known by the common name raccoon roundworm, is a roundworm nematode, found ubiquitously in raccoons, the definitive hosts. It is named after H. A. Baylis, who studied them in the 1920s–30s, and Greek askaris. Baylisascaris larvae in paratenic hosts can migrate, causing larva migrans. Baylisascariasis as the zoonotic infection of humans is rare, though extremely dangerous due to the ability of the parasite's larvae to migrate into brain tissue and cause damage. Concern for human infection has been increasing over the years due to urbanization of rural areas resulting in the increase in proximity and potential human interaction with raccoons.

Gnathostoma hispidum is a nematode (roundworm) that infects many vertebrate animals including humans. Infection of Gnathostoma hispidum, like many species of Gnathostoma causes the disease gnathostomiasis due to the migration of immature worms in the tissues.

<span class="mw-page-title-main">Hookworm</span> Intestinal, blood-feeding, parasitic roundworms that cause types of infection known as helminthiases

Hookworms are intestinal, blood-feeding, parasitic roundworms that cause types of infection known as helminthiases. Hookworm infection is found in many parts of the world, and is common in areas with poor access to adequate water, sanitation, and hygiene. In humans, infections are caused by two main species of roundworm, belonging to the genera Ancylostoma and Necator. In other animals the main parasites are species of Ancylostoma. Hookworm is closely associated with poverty because it is most often found in impoverished areas, and its symptoms promote poverty through the educational and health effects it has on children. It is the leading cause of anemia and undernutrition in developing countries, while being one of the most commonly occurring diseases among poor people. Hookworm thrives in areas where rainfall is sufficient and keeps the soil from drying out, and where temperatures are higher, making rural, coastal areas prime conditions for the parasite to breed.

<span class="mw-page-title-main">Cat worm infections</span> Worm infections in cats

Cat worm infections, the infection of cats (Felidae) with parasitic worms, occur frequently. Most worm species occur worldwide in both domestic and other cats, but there are regional, species and lifestyle differences in the frequency of infestation. According to the classification of the corresponding parasites in the zoological system, infections can be divided into those caused by nematode and flatworms - in the case of the latter, mainly cestoda and trematoda - while other strains are of no veterinary significance. While threadworms usually do not require an intermediate host for their reproduction, the development cycle of flatworms always proceeds via alternate hosts.

<span class="mw-page-title-main">Nematode infection in dogs</span> Threadworm infections of dogs are frequent

Nematode infection in dogs - the infection of dogs with parasitic nemamotodes - are, along with tapeworm infections and infections with protozoa, frequent parasitoses in veterinary practice. Nematodes, as so-called endoparasites, colonize various internal organs - most of them the digestive tract - and the skin. To date, about 30 different species of nematode have been identified in domestic dogs; they are essentially also found in wild dog species. However, the majority of them often cause no or only minor symptoms of disease in adult animals. The infection therefore does not necessarily have to manifest itself in a worm disease (helminthosis). For most nematodes, an infection can be detected by examining the feces for eggs or larvae. Roundworm infection in dogs and the hookworm in dogs is of particular health significance in Central Europe, as they can also be transmitted to humans (zoonosis). Regular deworming can significantly reduce the frequency of infection and thus the risk of infection for humans and dogs.

References

  1. 1 2 3 "Roundworms in Small Animals - Digestive System". Merck Veterinary Manual. Retrieved 2023-08-31.
  2. ↑ "CDC - Toxocariasis". www.cdc.gov. 2023-06-08. Retrieved 2023-08-31.
  3. 1 2 3 Bassert , J., & Thomas, J. (2014). McCurnin's Clinical Textbook for Veterinary Technicians. (8th ed.). St. Louis , MO: Elsevier
  4. ↑ CVPM, Sandy Walsh, RVT (2019-08-27). "Roundworms in Dogs". Today's Veterinary Practice. Retrieved 2023-08-31.{{cite web}}: CS1 maint: multiple names: authors list (link)
  5. ↑ Gillespie SH (1988). "The epidemiology of Toxocara canis". Parasitol Today. 4 (6): 180–182. doi:10.1016/0169-4758(88)90156-1. PMID   15463080.
  6. ↑ Despommier D (2003). "Toxocariasis: clinical aspects, epidemiology, medical ecology, and molecular aspects". Clin Microbiol Rev. 16 (2): 265–272. doi:10.1128/CMR.16.2.265-272.2003. PMC   153144 . PMID   12692098.
  7. 1 2 Harris-Linton, Megan. "Toxocara canis". Animal Diversity Web. Retrieved 2019-12-09.
  8. 1 2 3 "Ascarid (Also Roundworm, Also Toxocara)". Companion Animal Parasite Control. CAPC. Oct 2015. Archived from the original on 7 March 2016. Retrieved 22 Apr 2016.{{cite web}}: CS1 maint: bot: original URL status unknown (link)
  9. 1 2 Johnstone, Colin Dr. "Parasites and Parasitic Diseases of Domestic Animals." University of Pennsylvania, 24 Jan. 2000. http://cal.vet.upenn.edu/projects/merial/ascarids/asc_05a.html Archived 2014-02-26 at the Wayback Machine . 22 Apr. 2014.
  10. 1 2 3 "Toxocariasis." Parasites. Centers for Disease Control and Prevention, 10 Jan. 2013. https://www.cdc.gov/parasites/toxocariasis/treatment.html. 22 Apr. 2016.
  11. ↑ Veterinary parasitology 2nd edition G M Urqhart, J Armour, J L Duncen, A M Dunn F W Jennings Blackwell Science publishing 1996.[ page needed ]
  12. 1 2 3 Toxocariasis at eMedicine. Updated 16 Feb. 2016.
  13. ↑ "Dog stroking can transmit debilitating parasite". [New Scientist]. Andy Coghlan. Published 4-23-2003. Accessed 6-01-2012.
  14. ↑ "Toxocariasis: Symptoms & Causes". Cleveland Clinic. Retrieved 2023-08-31.
  15. ↑ "Round Worms from an infected puppy" "TheDoctorsTv". Published 3-19-2012. Accessed 6-01-2012.
  16. 1 2 "CDC - Toxocariasis - Resources for Health Professionals". www.cdc.gov. 2020-05-26. Retrieved 2023-08-31.
  17. ↑ "Toxocariasis: Symptoms & Causes". Cleveland Clinic. Retrieved 2023-08-31.
  18. ↑ ESCCAP. (2017). “Worm Control in Dogs and Cats”. European Scientific Counsel Companion Animal Parasites. https://www.esccap.org/uploads/docs/0x0o7jda_ESCCAP_Guideline_01_Third_Edition_July_2017.pdf Archived 2020-02-15 at the Wayback Machine   
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