Haemonchus contortus has been found in Asia (Indonesia, India), Netherlands, Europe (Russia, Italy), South America (Brazil), Africa, as well as in the United States. This parasite has adapted to conditions ranging from tropical areas to cold, mountainous regions. (Dorny, et al., 1996; Eckert and Hertzberg, 1994; Newton, 1995)
Although this parasitic nematode has a great range, it is more prevalent in warm, moist regions rather than cold, dry ones. Haemonchus contortus inhabit the abomasum ("fourth stomach") of ruminent animals. H. contortus has been found in humans in Brazil and Australia. (Roberts and Janovy, 2000)
As a nematode, Haemunchus contortus is cylindrical, has a cuticle with three 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. The worms molt four times, the first two before hatching, and then before their adult stage.
Since it is a blood-sucker, Haemunchus contortus generally has a reddish appearance. The white ovaries that wind around the blood filled intestine, gives the nickname "barber pole", when referring to the females. While the females have a length ranging from 18-30 mm, the males are shorter, ranging from 10-20 mm. The male's distinct feature is its well-developed copulatory bursa, containing an asymmetrical dorsal lobe and y-shaped dorsal ray.
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.
The female deposits 5000-10,000 eggs in the abomasum per day, which eventually will pass out with feces of the host. In the first stage, the juveniles hatch from the eggs. During the first and second juvenile stages, they will feed on bacteria in the manure. In the third juvenile stage, that the ruminant becomes infected when eating the parasite. Physical changes to the environment that are specific to a determinate host signals the worms to develop into the next stage. Prior to further development, exsheathment, which is sheddding of the cuticle, must take place in the host's gut. Haemonchus contortus exsheath when they are stimulated by high pCO2 and elevated temperatures in the host. After exsheathment, the worm will pass into the abomasum where it will burrow into the mucosa. Here, it will molt and in the fourth stage finds its way back to the lumen of the abomasum, feeds and undergoes a final molt before reaching adulthood. (Chappell, 1979; Fetterer and Rhoads, 1996; Roberts and Janovy, 2000; White and Newton, 2001)
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. (Barnes, 1987; Roberts and Janovy, 2000)
The behavior of parasitic nematodes has evolved to have certain adaptations. For instance, during its infective stage, the third juvenile stage, Haemonchus contortus will migrate onto grass blades to make it more optimal for host ingestion. While adapting to extreme temperatures and conditions, the juvenile parasite will prefer to lay eggs in the "adapted" conditions even when given less harsh conditions. Further, although moist environments are optimal for laying eggs, the juvenile will prefer to reproduce in dry conditions when given the option between the two. (Li, et al., 1999)
Nematodes in general have papillae, setae and amphids as the main sense organs. Setae detect motion (mechanoreceptors), while amphids detect chemicals (chemoreceptors). (Roberts and Janovy, 2000)
During the first and second juvenile stages, Haemonchus contortus feeds on bacteria in manure. In the later stages, H. contortus parasitizes the abomasum, the "true stomach", in cattle, goats, other wild ruminants, but mainly sheep. In the abomasum, it will feed on blood using a single, dorsal tooth to cut into the host tissue.
Pharyngeal glands and intestinal epithelium produce digestive enzymes to feed on the hosts’ body fluids. Extracellular digestion begins within the lumen and is finished intracellularly. (Barnes, 1987; Fetterer and Rhoads, 1996; Newton and Munn, 1999; Roberts and Janovy, 2000)
These parasites are probably not preyed on directly, but are ingested from host to host. Larval mortality is high as most of the parasites do not reach appropriate hosts. (Barnes, 1987; Roberts and Janovy, 2000)
The major problem lies within the agricultural industry. These parasites cause great economic losses in domestic animals, specifically sheep, cattle and goat. Because Haemonchus contortus is a blood sucker, it can induce anemia and edema. Also, the hemolytic proteins that the parasite releases can lead to other intestinal disturbances. The host will often die with major infections.
Renee Sherman Mulcrone (editor).
Janelin Sendow (author), University of Michigan-Ann Arbor, Teresa Friedrich (editor), University of Michigan-Ann Arbor.
Living in Australia, New Zealand, Tasmania, New Guinea and associated islands.
living in sub-Saharan Africa (south of 30 degrees north) and Madagascar.
living in the Nearctic biogeographic province, the northern part of the New World. This includes Greenland, the Canadian Arctic islands, and all of the North American as far south as the highlands of central Mexico.
living in the southern part of the New World. In other words, Central and South America.
living in the northern part of the Old World. In otherwords, Europe and Asia and northern Africa.
living in landscapes dominated by human agriculture.
having body symmetry such that the animal can be divided in one plane into two mirror-image halves. Animals with bilateral symmetry have dorsal and ventral sides, as well as anterior and posterior ends. Synapomorphy of the Bilateria.
an animal that mainly eats meat
either directly causes, or indirectly transmits, a disease to a domestic animal
Found in coastal areas between 30 and 40 degrees latitude, in areas with a Mediterranean climate. Vegetation is dominated by stands of dense, spiny shrubs with tough (hard or waxy) evergreen leaves. May be maintained by periodic fire. In South America it includes the scrub ecotone between forest and paramo.
uses smells or other chemicals to communicate
an animal that mainly eats the dung of other animals
having a worldwide distribution. Found on all continents (except maybe Antarctica) and in all biogeographic provinces; or in all the major oceans (Atlantic, Indian, and Pacific.
in deserts low (less than 30 cm per year) and unpredictable rainfall results in landscapes dominated by plants and animals adapted to aridity. Vegetation is typically sparse, though spectacular blooms may occur following rain. Deserts can be cold or warm and daily temperates typically fluctuate. In dune areas vegetation is also sparse and conditions are dry. This is because sand does not hold water well so little is available to plants. In dunes near seas and oceans this is compounded by the influence of salt in the air and soil. Salt limits the ability of plants to take up water through their roots.
animals which must use heat acquired from the environment and behavioral adaptations to regulate body temperature
union of egg and spermatozoan
forest biomes are dominated by trees, otherwise forest biomes can vary widely in amount of precipitation and seasonality.
having a body temperature that fluctuates with that of the immediate environment; having no mechanism or a poorly developed mechanism for regulating internal body temperature.
fertilization takes place within the female's body
marshes are wetland areas often dominated by grasses and reeds.
having the capacity to move from one place to another.
This terrestrial biome includes summits of high mountains, either without vegetation or covered by low, tundra-like vegetation.
found in the oriental region of the world. In other words, India and southeast Asia.
reproduction in which eggs are released by the female; development of offspring occurs outside the mother's body.
an organism that obtains nutrients from other organisms in a harmful way that doesn't cause immediate death
chemicals released into air or water that are detected by and responded to by other animals of the same species
rainforests, both temperate and tropical, are dominated by trees often forming a closed canopy with little light reaching the ground. Epiphytes and climbing plants are also abundant. Precipitation is typically not limiting, but may be somewhat seasonal.
an animal that mainly eats blood
scrub forests develop in areas that experience dry seasons.
remains in the same area
reproduction that includes combining the genetic contribution of two individuals, a male and a female
living in residential areas on the outskirts of large cities or towns.
a wetland area that may be permanently or intermittently covered in water, often dominated by woody vegetation.
uses touch to communicate
that region of the Earth between 23.5 degrees North and 60 degrees North (between the Tropic of Cancer and the Arctic Circle) and between 23.5 degrees South and 60 degrees South (between the Tropic of Capricorn and the Antarctic Circle).
Living on the ground.
the region of the earth that surrounds the equator, from 23.5 degrees north to 23.5 degrees south.
A terrestrial biome. Savannas are grasslands with scattered individual trees that do not form a closed canopy. Extensive savannas are found in parts of subtropical and tropical Africa and South America, and in Australia.
A grassland with scattered trees or scattered clumps of trees, a type of community intermediate between grassland and forest. See also Tropical savanna and grassland biome.
A terrestrial biome found in temperate latitudes (>23.5° N or S latitude). Vegetation is made up mostly of grasses, the height and species diversity of which depend largely on the amount of moisture available. Fire and grazing are important in the long-term maintenance of grasslands.
living in cities and large towns, landscapes dominated by human structures and activity.
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