parasitic (mostly) nematodes from stools of
Old World monkeys Nematodes that commonly parasitise humans include
ascarids (
Ascaris),
filarias,
hookworms,
pinworms (
Enterobius), and
whipworms (
Trichuris trichiura). The species
Trichinella spiralis, commonly known as the trichina worm, occurs in rats, pigs, bears, and humans, and is responsible for the disease
trichinosis.
Baylisascaris usually infests wild animals, but can be deadly to humans, as well.
Dirofilaria immitis is known for causing heartworm disease by inhabiting the hearts, arteries, and lungs of dogs and some cats.
Haemonchus contortus is one of the most abundant infectious agents in sheep around the world, causing great economic damage to sheep. In contrast,
entomopathogenic nematodes parasitize insects and are mostly considered beneficial by humans, but some attack beneficial insects. One form of nematode is entirely dependent upon
fig wasps, which are the sole source of
fig fertilization. They prey upon the wasps, riding them from the ripe fig of the wasp's birth to the fig flower of its death, where they kill the wasp, and their offspring await the birth of the next generation of wasps as the fig ripens. of
soybean cyst nematode (
Heterodera glycines) and egg A parasitic
tetradonematid nematode discovered in 2005,
Myrmeconema neotropicum, induces fruit mimicry in the tropical ant
Cephalotes atratus. Infected ants develop bright red
gasters (abdomens), tend to be more sluggish, and walk with their gasters in a conspicuous elevated position. These changes likely cause
frugivorous birds to confuse the infected ants for berries, and eat them. Parasite eggs passed in the bird's
feces are subsequently collected by foraging
C. atratus and are fed to their
larvae, thus completing the lifecycle of
M. neotropicum. Similarly, multiple varieties of nematodes have been found in the abdominal cavities of the primitively social sweat bee,
Lasioglossum zephyrus. Inside the female body, the nematode hinders ovarian development and renders the bee less active, thus less effective in pollen collection.
Agriculture and horticulture Depending on its species, a nematode may be beneficial or detrimental to plant health. From agricultural and
horticulture perspectives, the two categories of nematodes are the predatory ones, which kill garden pests; and the pest nematodes, which attack plants, or act as
vectors spreading
plant viruses between crop plants. Predatory nematodes include
Phasmarhabditis hermaphrodita which is a lethal parasite of gastropods such as
slugs and
snails. Some members of the genus
Steinernema such as
Steinernema carpocapsae and
Steinernema riobrave are generalist parasites of
webworms,
cutworms, armyworms,
girdlers, some
weevils,
wood-borers and
corn earworm moths. These organisms are grown commercially as
biological pest control agents which can be used as an alternative to
pesticides; their use is considered very safe. Plant-parasitic nematodes include several groups causing severe crop losses, taking 10% of crops worldwide every year. The most common genera are
Aphelenchoides (
foliar nematodes),
Ditylenchus,
Globodera (potato cyst nematodes),
Heterodera (soybean cyst nematodes),
Longidorus,
Meloidogyne (
root-knot nematodes),
Nacobbus,
Pratylenchus (lesion nematodes),
Trichodorus, and
Xiphinema (dagger nematodes). Several phytoparasitic nematode species cause histological damages to roots, including the formation of visible galls (e.g. by root-knot nematodes), which are useful characters for their diagnostic in the field. Some nematode species transmit plant viruses through their feeding activity on roots. One of them is
Xiphinema index, vector of
grapevine fanleaf virus, an important disease of grapes, another one is
Xiphinema diversicaudatum, vector of
arabis mosaic virus. Other nematodes attack bark and forest trees. The most important representative of this group is
Bursaphelenchus xylophilus, the pine wood nematode, present in Asia and America and recently discovered in Europe. This nematode is transmitted from tree to tree by sawyer beetles (
Monochamus). Greenhouse growers use
entomopathogenic nematodes as beneficial agents to control
fungus gnats. The nematodes enter the larvae of the gnats by way of their anus, mouth, and
spiracles (breathing pores) and then release
bacteria which kills the gnat larvae. Commonly used nematode species to control pests on greenhouse crops include
Steinernema feltiae for fungus gnats and
western flower thrips,
Steinernema carpocapsae used to control shore flies,
Steinernema kraussei for control of
black vine weevils, and
Heterorhabditis bacteriophora to control beetle larvae. Rotations of plants with nematode-resistant species or varieties is one means of managing parasitic nematode infestations. For example, planting
Tagetes marigolds as a cover crop just prior to planting a nematode-susceptible plant, has been shown to suppress nematodes. Another approach involves using natural antagonists, particularly bacteria and fungi, which have proven effective in suppressing plant-parasitic nematodes, such as the fungus
Gliocladium roseum.
Chitosan, a natural
biocontrol, elicits plant defense responses to destroy parasitic
cyst nematodes on roots of
soybean,
maize,
sugar beet,
potato, and
tomato crops without harming beneficial nematodes in the soil.
Soil steaming is an efficient method to kill nematodes before planting a crop, but indiscriminately eliminates both harmful and beneficial soil fauna. The golden nematode
Globodera rostochiensis is a particularly harmful pest that has resulted in quarantines and crop failures worldwide. It can be controlled, however.
CSIRO, the scientific research body of the Australian government, found a 13- to 14-fold reduction of nematode population densities in plots having
Chinese mustard Brassica juncea green manure or seed meal in the soil.
Disease in humans for intestinal nematode infections per 100,000 in 2002. effect of
papain on
Heligmosomoides bakeri A number of pathogenic intestinal nematodes cause diseases in humans, including
ascariasis,
trichuriasis, and
hookworm disease.
Anisakis species parasitise fish and
marine mammals and when consumed by humans can cause
anisakiasis, a
gastric or gastroallergic disease. Gastrointestinal nematode infections in humans are common, with approximately 50% of the global population being affected. Developing countries are most heavily impacted, in part due to lack of access to medical care.
Trichinosis starts in the intestines but larvae can migrate to muscle.
Filarial nematodes cause
filariases.
Toxocariasis is a
zoonotic infection caused by roundworms passed from dogs, and sometimes cats. It can give rise to different types of
larva migrans, such as
visceral larva migrans and
ocular larva migrans. Studies have shown that parasitic nematodes infect
American eels, causing damage to the eel's swim bladder, dairy animals like cattle and buffalo, and all species of sheep. == Soil ecosystems==