In biology and medicine, a host is a larger organism that harbours a smaller organism; whether a parasitic, a mutualistic, or a commensalist guest (symbiont). The guest is typically provided with nourishment and shelter. Examples include animals playing host to parasitic worms, cells harbouring pathogenic (disease-causing) viruses, or a bean plant hosting mutualistic (helpful) nitrogen-fixing bacteria. More specifically in botany, a host plant supplies food resources to micropredators, which have an evolutionarily stable relationship with their hosts similar to ectoparasitism. The host range is the collection of hosts that an organism can use as a partner.
The European eel is a species of eel, a snake-like, catadromous fish. They are critically endangered due to overfishing by fisheries on coasts for human consumption and parasites.
Eels are any of several long, thin, bony fishes of the order Anguilliformes. They have a catadromous life cycle, that is: at different stages of development migrating between inland waterways and the deep ocean. Because fishermen never caught anything they recognized as young eels, the life cycle of the eel was a mystery for a very long period of scientific history that continues into the present day. Of significant interest is the search for the spawning grounds for the various species of eels and identifying impacts to population decline in each stage of the life cycle.
Dracunculus is a genus of spiruroid nematode parasites in the family Dracunculidae.
Gnathostomiasis, also known as larva migrans profundus, is the human infection caused by the nematode Gnathostoma spinigerum and/or Gnathostoma hispidum, which infects vertebrates.
The round goby is a euryhaline bottom-dwelling species of fish of the family Gobiidae. It is native to Central Eurasia, including the Black Sea and the Caspian Sea. Round gobies have established large non-native populations in the Baltic Sea, several major Eurasian rivers, and the North American Great Lakes.
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.
The Camallanida are an order of nematodes.
Like humans and other animals, fish suffer from diseases and parasites. Fish defences against disease are specific and non-specific. Non-specific defences include skin and scales, as well as the mucus layer secreted by the epidermis that traps microorganisms and inhibits their growth. If pathogens breach these defences, fish can develop inflammatory responses that increase the flow of blood to infected areas and deliver white blood cells that attempt to destroy the pathogens.
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.
Huffmanela is a genus of parasitic nematodes, belonging to the family Trichosomoididae.
Anguillicoloides novaezelandiae is a parasitic nematode worm that lives in the swimbladders of eels, particularly Anguilla australiensis, Anguilla anguilla and Anguilla dieffenbachii. Specimens have been located in Italy and New Zealand. The species is most similar to A. Australiensis. However, it differs from the latter species in the shape of the head end which is bulbously inflated, almost spherical, and followed by a marked neck constriction in A. Australiensis, whereas it is only slightly expanded in A. novaezelandiae. Also, the anterior ovary in A. australiensis females extends anteriorly to about the mid-length of the oesophagus, while it does not reach the end of the oesophagus in A. novaezelandiae. Both species differ in size and form. While the body of A. australiensis is long and relatively slender, that of A. novaezelandiae is much shorter and wider. The shape of the posterior end of the female body is different in these two species.
Anguillicoloides papernai is a parasitic nematode worm that lives in the swimbladders of eels, particularly Anguilla mossambica. Specimens have been located in Cape Province, South Africa. It is named after Dr. Ilan Paperna. What differentiates this species from its congeners is the presence of marked cuticular excrescences on the anterior and posterior ends of the body and the location of the buccal capsule deeply inside the head end. This species was the first Anguillicola member described from Africa.
Eustrongylidosis is a parasitic disease that mainly affects wading birds worldwide; however, the parasite's complex, indirect lifecycle involves other species, such as aquatic worms and fish. Moreover, this disease is zoonotic, which means the parasite can transmit disease from animals to humans. Eustrongylidosis is named after the causative agent Eustrongylides, and typically occurs in eutrophicated waters where concentrations of nutrients and minerals are high enough to provide ideal conditions for the parasite to thrive and persist. Because eutrophication has become a common issue due to agricultural runoff and urban development, cases of eustrongylidosis are becoming prevalent and hard to control. Eustrongylidosis can be diagnosed before or after death by observing behavior and clinical signs, and performing fecal flotations and necropsies. Methods to control it include preventing eutrophication and providing hosts with uninfected food sources in aquaculture farms. Parasites are known to be indicators of environmental health and stability, so should be studied further to better understand the parasite's lifecycle and how it affects predator-prey interactions and improve conservation efforts.
Skrjabingylus nasicola is a species of parasitic nematode in the family Metastrongylidae. Its lifecycle includes an intermediary mollusc host and a paratenic host, a shrew or small rodent. Adult worms are found in the nasal sinuses of mustelids.
Anisakis simplex, known as the herring worm, is a species of nematode in the genus Anisakis. Like other nematodes, it infects and settles in the organs of marine animals, such as salmon, mackerels and squids. It is commonly found in cold marine waters, such as the Pacific Ocean and Atlantic Ocean.
Bothriocephalus gregarius is a tapeworm that parasitises the turbot. It has a complex life cycle including two intermediate hosts, a copepod and a small fish.
Lernaeenicus sprattae is a species of copepod in the family Pennellidae. It is a parasite of the European sprat and certain other fish and is sometimes known as the sprat eye-maggot.
Contracaecum is a genus of parasitic nematodes from the family Anisakidae. These nematodes are parasites of warm-blooded, fish eating animals, i.e. mammals and birds, as sexually mature adults. The eggs and the successive stages of their larvae use invertebrates and increasing size classes of fishes as intermediate hosts. It is the only genus in the family Anisakidae which can infect terrestrial, marine and freshwater animals.
Pseudoterranova is a genus within the family Anisakidae of parasitic nematodes with an aquatic life cycle. The lifecycle of Pseudoterranova spp. involves marine mammals, pinnipeds as definitive hosts, planktonic or benthic crustaceans as intermediate hosts and fish which act as second intermediate or paratenic hosts. In some regions, the rise in seal numbers has prefaced a significant increase in fish infected with P. decipiens which is of concern for fish health. Infection with Pseudoterranova may affect the health and swimming ability of the fish host and is therefore of concern for the survival of wild caught and farmed species. Species belonging to this genus have been demonstrated to cause illness of varying exigency in humans if raw or under cooked infected fish is consumed. Cases of human infection have been reported from consuming partially cooked fish infected with Pseudoterranova decipiens, Pseudoterranova cattani and Pseudoterranova azarasi. The propensity of P. decipiens to encyst in the edible portion of fish musculature may make this parasite a considerable threat to human health in undercooked fish.
