Haemonchus contortus

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.

As a Secernentea, Haemonchus contortus has a specialized tubular excretory system with three canals. The canals are arranged to form an “H”. (Barnes, 1987; Mieczyslaw, 1955; Roberts and Janovy, 2000)

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 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). (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)

Haemonchus contortus inhabit the abomasum ("fourth stomach") of ruminent animals. H. contortus has been found in humans in Brazil and Australia.

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.

Haemonchus contortus is known to adapt well to even harsh conditions, which makes it more difficult to eliminate this parasite. (Jacquiet, et al., 1998; White and Newton, 2001)