Parascaris equorum

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Parascaris equorum
Ascarid1 (5842674095).jpg
Male (top) and female (bottom) P. equorum
Scientific classification Red Pencil Icon.png
Kingdom: Animalia
Phylum: Nematoda
Class: Chromadorea
Order: Ascaridida
Family: Ascarididae
Genus: Parascaris
Species:
P. equorum
Binomial name
Parascaris equorum

Parascaris equorum is a species of ascarid that is the equine roundworm. Amongst horse owners, the parasites are colloquially called "Ascarids". This is a host-specifichelminth intestinal parasite that can infect horses, donkeys, and zebras. Horses up to six months of age are the most susceptible to infection. After this time, infection rates begin to decline and is extremely uncommon in horses over twelve months of age. [1] It cannot infect humans or other animals. [2] It is yellow-white in color, and females can become as large as 15 inches (38 cm) in length. [3] Found worldwide, P. equorum is one of the most difficult equine parasites to kill, requiring larger doses of more powerful anthelmintic medications than are needed for other equine parasites. [2]

Contents

Life cycle

P. equorum is sexually dimorphic, the females are significantly larger than males. While males only grow up to 15–28 cm in length, the females can grow up to 50 cm in length. They are a white colored, cylindrical worm and have three very large lips. [4] Mating occurs in the small intestine of the equid. The female is able to lay over 170,000 eggs in a day, and 60,000,000 eggs in a year. [5] Eggs have a thick, multilayered shell for protection and the ability to adhere to any surface they touch once expelled. [2] Eggs are expelled in feces, which are then consumed by a horse while eating contaminated grass or drinking contaminated water. In a three-month life cycle, the swallowed eggs become larva and migrate from the small intestines into blood vessels and from there travel to the liver, where they molt into another larval stage. From there, they migrate to the lungs, where they emerge from blood vessels into the alveoli. [2] They spend between 14 and 17 days migrating through the liver and lungs. [5] At this point, they are coughed up and re-swallowed, where the larvae mature into adult roundworms that produce eggs. [3] The worms take from 79 to 110 days to reach adulthood. P. equorum lives by sucking up the liquid contents of the intestine and may occasionally also suck blood from the intestinal wall. [5]

Clinical signs of infestation

Horses may develop a cough and a nasal discharge during the lung migration stage. Scarring of internal organs, particularly the lungs and liver, can occur during parasite migration. Severe infestations of adult P. equorum can also cause colic, intestinal blockage and potential intestinal rupture. Feed absorption is often reduced, and other clinical signs may include unthriftiness, potbelly, rough hair coat, and slow growth. [3]

Severe infestations of P. equorum are able to create a mechanical blockage in the intestines. In some cases, deworming treatment may actually trigger an intestinal blockage of dead and dying parasites; for this reason, severe cases may require multiple treatments of milder drugs. [2]

Diagnosis of infestation can be found by looking for eggs in feces via a microscopic examination. The limitation of this method is that only mature worms can be detected via their eggs; immature larval forms are difficult to detect, and blood tests are unreliable. [2]

Treatment

Mature horses appear to develop a certain degree of resistance to this parasite, but it is a concern for younger horses up to about two years old. [3] P. equorum is one of the few parasites where a natural immunity develops in the host. [2] However, when an infection is found in an adult horse, both the worm and egg counts are substantially low. [1]

Deworming can begin with foals at four to eight weeks of age and is repeated about every 60 days. Treatment is with anthelmintic medication, and rotating between different classes of anthelmintics is recommended. [6] Effective treatments include the macrocyclic lactones, notably ivermectin or moxidectin, which can kill the early larval stages before they migrate into the liver and lungs. Another class of effective medication are the benzimidazoles, such as fenbendazole. Pyrantel pamoate is also used, and a closely related variant, pyrantel tartrate, can be fed as a daily dose that is effective at killing larvae. Prior to development of these drugs, during the 1950s and 1960s, treatment with piperazine, dichlorvos and trichlorfon was used. [2]

Keeping pastures and stables free of manure has been shown to be effective in reducing parasite infestations in horses. Rotation of pastures, particularly by putting animals of other species into the rotation, can also reduce the amount of parasite infestation. [6]

Related Research Articles

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

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<i>Ascaris</i> Genus of roundworms

Ascaris is a genus of parasitic nematode worms known as the "small intestinal roundworms", which is a type of parasitic worm. One species, Ascaris lumbricoides, affects humans and causes the disease ascariasis. Another species, Ascaris suum, typically infects pigs. Parascaris equorum, the equine roundworm, is also commonly called an "ascarid".

<i>Ascaridia galli</i> Species of roundworm

Ascaridia galli is a parasitic roundworm belonging to the phylum Nematoda. Nematodes of the genus Ascaridia are essentially intestinal parasites of birds. A. galli is the most prevalent and pathogenic species, especially in domestic fowl, Gallus domesticus. It causes ascaridiasis, a disease of poultry due to heavy worm infection, particularly in chickens and turkeys. It inhabits the small intestine, and can be occasionally seen in commercial eggs.

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<i>Strongylus vulgaris</i> Species of roundworm

Strongylus vulgaris, commonly known as the blood worm, is a common horse parasite in the phylum Nematoda. It looks like a long worm with a large biting mouth. They are usually reddish in color because of all the blood they take from the equine host. This nematode is considered to be one of the "most pathogenic" of the large strongyles subphylum and is distributed worldwide, wherever there are grassland and temperate environments.

<i>Toxocara canis</i> Species of roundworm

Toxocara canis is a worldwide-distributed helminth parasite of dogs and other canids. The name is derived from the Greek word "toxon," meaning bow or quiver, and the Latin word "caro," meaning flesh. They live in the small intestine of the definitive host. In adult dogs, the infection is usually asymptomatic but may be characterized by diarrhea. By contrast, massive infection with Toxocara canis can be fatal in puppies, causing diarrhea, vomiting, an enlarged abdomen, flatulence, and poor growth rate.

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

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Deworming Giving of an anthelmintic drug to a human or animals to rid them of helminths parasites

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. Toxascaris leonina, or 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.

Anthelmintics or antihelminthics are a group of antiparasitic drugs that expel parasitic worms (helminths) and other internal parasites from the body by either stunning or killing them and without causing significant damage to the host. They may also be called vermifuges or vermicides. Anthelmintics are used to treat people who are infected by helminths, a condition called helminthiasis. These drugs are also used to treat infected animals.

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Anoplocephala perfoliata is the most common intestinal tapeworm of horses, and an agent responsible for some cases of equine colic.

Parascaris univalens is a parasitic ascaridoid nematode that infects the gastrointestinal tracts of equines.

Strongyloides westeri, commonly referred to as intestinal threadworm, is a species of small nematode parasite in the family Strongylidae. Strongyloides are commonly found in the small intestine of mammals, that are characterized by an unusual lifecycle that involves one generations of free-living adult worms.

References

  1. 1 2 Johnstone, Dr.Colin (24 January 2000). "Parascaris equorum". University of Pennsylvania. Archived from the original on 26 August 2017. Retrieved 21 April 2017.
  2. 1 2 3 4 5 6 7 8 Briggs, Karen (March 1, 2004). "Ascarids: A Growing Problem". The Horse. Retrieved 9 November 2014.
  3. 1 2 3 4 Wood, Craig (October 30, 2014). "Ascarids in horses". eXtension. Archived from the original on 9 November 2014. Retrieved 9 November 2014.
  4. Cooper, Zachary (2003). "Parascaris equorum". Animal Diversity Web. Retrieved 21 April 2017.
  5. 1 2 3 Cooper, Zachary (2003). "Parascaris equorum". Animal Diversity Web. University of Michigan Museum of Zoology. Retrieved 11 November 2014.
  6. 1 2 Wood, Craig (October 29, 2014). "Management and control of internal parasites in horses". eXtension. Archived from the original on 9 November 2014. Retrieved 9 November 2014.