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).
Communication Channels: tactile ; chemical
Other Communication Modes: pheromones
Perception Channels: tactile ; chemical
The life cycle of S. vulgaris involves five juvenile stages and its equine host. Eggs are found in its host feces, where they hatch and the juveniles feed on the feces through the third larval stage. At this point, they crawl onto vegetation the equines feed on, where they are ingested by the host. Once in the small intestine, the third-stage juvenile penetrates through the intestinal wall and molts into its fourth larval stage. The larvae penetrate the surrounding arteries and make their way to the mesenteric arteries, where they develop into the fifth larval stage, immature adults. The immature adults make their way back to the intestines, where they encapsulate themselves and develop into adults. The adults hatch from the capsules and mate, producing eggs which are passed out in the feces.
Strongylus vulgaris has at times been a very common parasite in horses; it was estimated that it was present in 90% to 100% of horses in the U.S. The inflammation caused by the strongyle travelling throughout the arteries and intestines can cause blood clots to form. The clots can block oxygen passage to the intestines, causing parts of them to die. Ultimately, besides causing abdominal pain (colic) in equines, the complications from S. vulgaris infestation can lead to death.
S. vulgaris is no longer considered as much of a threat to horses, because it can be controlled by drugs such as benzimidazoles, ivermectin, and moxidectin, which kill both larvae and adult stages of the worm.
Negative Impacts: causes or carries domestic animal disease
Strongylus vulgaris is parasitic on horses.
Ecosystem Impact: parasite
Species Used as Host:
Through the first three larval stages of development S. vulgaris feeds upon the feces of its parent's host. The later larval stages are found in the circulatory system of equines, feeding on blood and tissue as it makes its way through different areas of the body. The adults are primarily found in the intestine and associated organs, where their feeding can cause major damage to the gastrointestinal organs.
Animal Foods: blood; body fluids
Other Foods: dung; microbes
Primary Diet: carnivore (Eats body fluids); coprophage
This parasite can be found worldwide; its dispersal is dependent on where its hosts (equines) are found.
Biogeographic Regions: nearctic ; palearctic ; oriental ; ethiopian ; neotropical ; australian
Other Geographic Terms: cosmopolitan
Strongylus vulgaris is found primarily in grasslands and pastures. They are essentially located where equine populations are concentrated.
Habitat Regions: temperate ; tropical ; terrestrial
Terrestrial Biomes: tundra ; taiga ; desert or dune ; savanna or grassland ; chaparral ; forest ; rainforest ; scrub forest ; mountains
Wetlands: marsh ; swamp
Other Habitat Features: urban ; suburban ; agricultural
These worms are cylindrical, dark red in color, with male adults approximately 2.5 to 4 cm in length, while females range from 4 to 6 cm. There are five larval stages before adulthood is reached. The buccal capsule, which adults use to feed, is relatively large and heavily sclerotized, with two lobed teeth. The anterior region is dorsally curved, giving the appearance characteristic of hookworms.
The cuticle has three or more main outer layers made of collagen and other compounds. The outer layers are non-cellular and are secreted by the epidermis. The cuticle layer protects the nematodes so they can invade the digestive tracts of animals.
Nematodes have longitudinal muscles along the body wall. The muscles are obliquely arranged in bands. Dorsal, ventral and longitudinal nerve cords are connected to the main body of the muscle.
Range length: 2.5 to 6 cm.
Other Physical Features: ectothermic ; heterothermic ; bilateral symmetry
Sexual Dimorphism: female larger; sexes shaped differently
These parasites are probably not preyed on directly, but are likely ingested by various animals. Larval mortality is high as most of the parasites do not reach appropriate hosts.
Females may produce a phermomone to attract males. The male coils around a female with his curved area over the female genital pore. The gubernaculum, made of cuticle tissue, guides spicules which extend through the cloaca and anus. Males use spicules to hold the female during copulation. Nematode sperm are amoeboid-like and lack flagella.
Key Reproductive Features: sexual ; fertilization (Internal ); oviparous
Parental Investment: pre-fertilization (Provisioning)
Strongylus vulgaris (large strongyles),[1] commonly known as the blood worm,[2] 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.[1] 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.[3]
During the infective stage of the S. vulgaris life cycle, the larvae that have matured in the intestinal tract of the horse will migrate into the surrounding blood vessels. Once in the blood vessels, the larvae will continue their migration throughout the body to various organs causing damage to the blood vessels along the way. This can cause anemia or blockage of blood flow caused by the detachment of blood clots from the vessel wall resulting in tissue death.[4] S. vulgaris are commonly found in pastures and stalls where feces are present. The larvae crawl up on the grass which is where they are then eaten by the horse. Harsh environments, such as freezing, do not kill S. vulgaris.[5]
Symptoms can range depending on how severe the infection is. In mild cases the most common clinical signs are weightloss, compromised performance, and a dull hair coat.[6] Other clinical signs can range from diarrhea, weakness, anorexia, anemia if there are significant blood loss and abdominal discomfort. Severe cases can show signs of having severe colic, rupture of the intestines, and death.[7] These signs may also be observed with other equine-related infections or illnesses and their presence alone should not be used to diagnose an infection of S. vulgaris. A veterinarian is required for further diagnosis when infection with S. vulgaris is suspected.
Large strongyle infections are commonly diagnosed through the observations of fecal samples. These fecal samples can be viewed under a microscope to identify the eggs of S. vulgaris. Diagnosis via egg identification is not enough to determine if the horse has a S. vulgaris infection as the fecal samples often contain a mixture of large and small strongyle eggs that are very similar in appearance. The best diagnostic method to determine if a horse has a S. vulgaris infection is through a fecal culture. Here the eggs grow and develop into the infective larval stage that is specific to the large strongyle parasite.[8]
The adults of S. vulgaris are primarily found in the cecum and colon of infected equids and it is here that the females will lay their eggs. These eggs will pass out of the horse's body in the feces. Once outside the body the eggs will hatch and develop into the infective larval stage L3. The larvae enter the host when the horse grazes a patch of grass containing the larval stage. Back inside the host the infective larval stage migrates to the small intestine where it can enter the intestinal mucosa and further develop into the L4 stage. It is this stage that can enter the blood vessels and migrate throughout the body for a period of up to six months. During this time the L4 stage matures into the L5 or immature adult stage before returning to the intestinal wall. The L5 stage resides primarily in the cecum and colon where the males and females copulate thus starting the cycle over again.[9]
Dewormers that have ivermectin or moxidectin are the most effective against these parasites.[10] Treating a horse with regular dewormer when they have the worms inside of them may cause the worms to migrate all at once, causing rupture of the intestines and lead to death.[11] Recommendations for deworming horses include performing fecal egg counts to determine what kind of protection each individual horse requires and alternating products in the fall and spring. An example would be using ivermectin based products (Equell or Zimectrin) in the spring and moxidectin based products in combination with praziquantel (Quest Plus) in the fall or vice versa.[12] A deworming schedule should be discussed with a veterinarian.
Horses are able to pick up this parasite from food and water contaminated by feces. This can be avoided by cleaning water tanks and picking out pastures often, avoidance of feeding on the ground, and avoidance of overstocking pastures.[13] As foals can be extremely susceptible to this parasite, it is best to treat broodmares before they give birth and move them to uninfected pastures to avoid transfer.
{{cite web}}: CS1 maint: archived copy as title (link) {{cite web}}: Missing or empty |title= (help) Strongylus vulgaris (large strongyles), 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.
