Nematomorpha are a phylum of parasitoid animals superficially similar to nematode worms in morphology, hence the name. Most species range in size from 50 to 100 millimetres, reaching 2 metres (79 in) in extreme cases, and 1 to 3 millimetres in diameter. Horsehair worms can be discovered in damp areas, such as watering troughs, swimming pools, streams, puddles, and cisterns. The adult worms are free-living, but the larvae are parasitic on arthropods, such as beetles, cockroaches, mantises, orthopterans, and crustaceans. About 351 freshwater species are known and a conservative estimate suggests that there may be about 2000 freshwater species worldwide. The name "Gordian" stems from the legendary Gordian knot. This relates to the fact that nematomorphs often coil themselves in tight balls that resemble knots.
Gnathostomiasis, also known as larva migrans profundus, is the human infection caused by the nematode Gnathostoma spinigerum and/or Gnathostoma hispidum, which infects vertebrates.
Taenia pisiformis, commonly called the rabbit tapeworm, is an endoparasitic tapeworm which causes infection in lagomorphs, rodents, and carnivores. Adult T. pisiformis typically occur within the small intestines of the definitive hosts, the carnivores. Lagomorphs, the intermediate hosts, are infected by fecal contamination of grasses and other food sources by the definitive hosts. The larval stage is often referred to as Cysticercus pisiformis and is found on the livers and peritoneal cavities of the intermediate hosts. T. pisiformis can be found worldwide.
Spinochordodes tellinii is a parasitic nematomorph hairworm whose larvae develop in grasshoppers and crickets. This parasite is able to influence its host's behavior: once the parasite is grown, it causes its grasshopper host to jump into water, where the grasshopper will likely drown. The parasite then leaves its host; the adult worm lives and reproduces in water. S. tellinii does not influence its host to actively seek water over large distances, but only when it is already close to water.
Eucestoda, commonly referred to as tapeworms, is the larger of the two subclasses of flatworms in the class Cestoda. Larvae have six posterior hooks on the scolex (head), in contrast to the ten-hooked Cestodaria. All tapeworms are endoparasites of vertebrates, living in the digestive tract or related ducts. Examples are the pork tapeworm with a human definitive host, and pigs as the secondary host, and Moniezia expansa, the definitive hosts of which are ruminants.
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.
Sparganosis is a parasitic infection caused by the plerocercoid larvae of the genus Spirometra including S. mansoni, S. ranarum, S. mansonoides and S. erinacei. It was first described by Patrick Manson in 1882, and the first human case was reported by Charles Wardell Stiles from Florida in 1908. The infection is transmitted by ingestion of contaminated water, ingestion of a second intermediate host such as a frog or snake, or contact between a second intermediate host and an open wound or mucous membrane. Humans are the accidental hosts in the life cycle, while dogs, cats, and other mammals are definitive hosts. Copepods are the first intermediate hosts, and various amphibians and reptiles are second intermediate hosts.
Gnathostoma spinigerum is a parasitic nematode that causes gnathostomiasis in humans, also known as its clinical manifestations are creeping eruption, larva migrans, Yangtze edema, Choko-Fuschu Tua chid and wandering swelling. Gnathostomiasis in animals can be serious, and even fatal. The first described case of gnathostomiasis was in a young tiger that died in the London Zoo in 1835. The larval nematode is acquired by eating raw or undercooked fish and meat.
Toxocara canis is a worldwide-distributed helminth parasite that primarily infects dogs and other canids, but can also infect other animals including humans. The name is derived from the Greek word "toxon," meaning bow or quiver, and the Latin word "caro," meaning flesh. 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. 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.
Gongylonema pulchrum is the only parasite of the genus Gongylonema capable of infecting humans.
Cestoda is a class of parasitic worms in the flatworm phylum (Platyhelminthes). Most of the species—and the best-known—are those in the subclass Eucestoda; they are ribbon-like worms as adults, known as tapeworms. Their bodies consist of many similar units known as proglottids—essentially packages of eggs which are regularly shed into the environment to infect other organisms. Species of the other subclass, Cestodaria, are mainly fish infecting parasites.
Paragordius tricuspidatus belongs to the phylum Nematomorpha, and is known for manipulating the behavior of its host, the cricket Nemobius sylvestris. In its larval stage, the worm is microscopic, but grows into a large worm inside its host after accidental ingestion since their eggs are laid at the edge of the water by rivers where crickets frequently reside. Upon ingestion, the worm nourishes upon its host and fills the entire body cavity of the cricket, until maturation, when the parasitic worm is ready to exit into water to complete its life cycle, maximizing its reproductive success. The worm induces a peculiar behavior in its cricket host which causes the cricket to leap into water whereby the parasitic worm can slither out and find its mate, while the cricket often perishes. Should the cricket be preyed upon by a predator, such as a fish or frog, the worm has the ability to not only escape from the host's body but also the predator's digestive system. The worm emerges from the predator unharmed and proceeds to live its life normally.
Moniliformis moniliformis is a parasite of the Acanthocephala phylum in the family Moniliformidae. The adult worms are usually found in intestines of rodents or carnivores such as cats and dogs. The species can also infest humans, though this is rare.
Taenia serialis, also known as a canid tapeworm, is found within canines such as foxes and dogs. Adult T. serialis are parasites of carnivores, particularly dogs, with herbivorous lagomorph mammals such as rabbits and hares, serving as intermediate hosts. In definitive hosts, T. serialis is acquired by eating tissues from a variety of intermediate hosts. Accidental infection of humans though, can occur when eggs are ingested from food or water contaminated with dog feces and the human then becomes the T. serialis intermediate host.
Behavior-altering parasites are parasites capable of causing changes in the behavior of their hosts species to enhance their transmission, sometimes directly affecting the hosts' decision-making and behavior control mechanisms. By way of example, a parasite that reproduces in an intermediate host may require, as part of their life cycle, that the intermediate host be eaten by a predator at a higher trophic level, and some parasites are capable of altering the behavior of the intermediate host to make such predation more likely; a mechanism that has been called parasite increased trophic facilitation or parasite increased trophic transmission. Examples can be found in bacteria, protozoa, viruses, and animals. Parasites may also alter the host behavior to increase protection of the parasites or their offspring; the term bodyguard manipulation is used for such mechanisms.
Gordius is a genus of worms in the phylum Nematomorpha, the horsehair worms. It was formerly treated as the only genus in the family Gordiidae, but the genus Acutogordius is now considered as distinct. The genus is distributed worldwide except for Antarctica, where no Nematomorpha have been recorded.
Dirofilaria tenuis is a species of nematode, a parasitic roundworm that infects the subcutaneous tissue of vertebrates. D. tenuis most commonly infects raccoons, but some human cases have been reported. They are vectored by mosquitoes and follow similar development and transmission patterns as other Dirofilaria.
Pterygodermatites peromysci is an intestinal parasitic nematode in the genus Pterygodermatites of the family Rictulariidae.
Chordodes formosanus is a horsehair worm that has the praying mantis as its definitive host. Horsehair worms are obligate parasites that pass through different hosts at various stages. These worms can grow up to 90 centimetres (35 in) long and can be extremely dangerous for their host, especially the praying mantis.
Nectonema is a genus of marine horsehair worms first described by Addison E. Verrill in 1879. It is the only genus in the family Nectonematidae described by Henry B. Ward in 1892, in the order Nectonematoidea, and in the class Nectonematoida. The genus contains five species; all species have a parasitic larval stage inhabiting crustacean hosts and a free-living adult stage that swims in open water.
