Haemonchus contortus

Taxonomy, Common Name, Disease

Scientific name - Haemonchus contortus

Common name - barber pole worm

Hosts

sheep, goats, cattle, wild ruminants

Distribution

More prevalent in warm moist regions than in cold, dry ones.

Life Cycle

No intermediate host is required. Adult male and female worms live in the abomasum (or true stomach) of ruminant animals. The female deposits 5,000 to 10,000 eggs per day which pass out of the host with the feces. First stage juveniles hatch from the eggs. First and second stage juveniles feed on bacteria. Third stage juveniles retain the second stage cuticle as a sheath. Third stage juveniles do not feed and are infective for the vertebrate host. The ruminant becomes infected while grazing by eating the third-stage juveniles. Exsheathment occurs in the rumen, anterior to the abomasum, and the young worms pass into the abomasum where they burrow into the mucosa. Here they undergo another molt, and the fourth-stage juveniles come back into the paramucosal lumen of the abomasum. They begin to feed and undergo another molt before reaching adulthood. Mating of adults occurs and egg production commences.The eggs hatch in soil or water and develop directly to infective third-stage juveniles. Some infections may also occur through the skin. Enormous numbers of juveniles may accumulate on heavily grazed pastures.

Symptoms-Pathogenicity

Anemia, emaciation, edema, intestinal disturbances resulting principally from loss of blood and injection of hemolytic proteins in the host's system. Heavy infections may be fatal.

Management

Application of a knowledge of the biology and ecology of these parasites to principles of sheep husbandry is important in keeping losses at a minimal level. Drenching sheep at prescrdibed periods based on the biology of the worms with phenothiazine kills the stages in the lumen of the abomasum. Administering the drug free-choice in feed or salt maintains a low level of infection in the animals. Residual phenothiazine in the feces interferes with development and hatching of the eggs as well as killing many first and second stage larvae. A phenomenon known as self-cure in which adult worms are spontaneously expelled occurs with this nematode. It results when the animal is reinfested at regular intervals. The process of exsheathment of the third-stage juveniles causes a change in the pH of the intestine which prevents adults from remaining attached.

Importance

The family contains many genera and species. They are parasites of the small intestine of all classes of vertebrates, causing great economic losses in domestic animals, especially ruminants. It is common for an animal to be infected with several species of trichostrongylids at the same time.

Characteristics

The males are 10 to 20 mm and the females 18 to 30 mm long. The white uteri and ovaries winding around the red blood-filled intestine give a twisted or barberpole appearance. The small buccal capsule bears a curved dorsal tooth. There are two prominent lateral spike-like cervical papillae near the junction of the first and second quarters of the esophagus. The male bursa has long lateral lobes and slender rays with a flap-like dorsal lobe located asymmetrically near the base of the left lateral lobe. The spicules are 450 to 500 um long, each with a terminal barb; the gubernaculum is navicular. Usually, the vulva is covered by an anterior thumb-like flap which may be reduced to a mere knob in some individuals. The oval eggs are 70 to 85 um long by 41 to 44 um wide and in the early stages of cleavage when laid. They are somewhat yellowish.

References

  1. Levine, N.D. 1968. Nematode Parasites of Domestic Animals and of Man. Burgess Publishing Company. Minneapolis. 600 pages.
  2. Georgi, J.R. and M.E. Georgi. 1990. Parasitology for Veterinarians. W.B. Saunders Company. Philadelphia. 411 pages.
  3. Read, C.P. 1972. Animal Parasitism. Prentice Hall. New Jersey. 182 pages.
  4. Olson, O.W. 1974. Animal Parasites Their Life Cycles and Ecology. Dover Publications Inc., New York. 562 pages.