Barbers pole worm

Haemonchus contortus

ORDER Strongylida

FAMILY

Trichostrongylidae TAXONOMY

Strongylus contours (Rudolphi, 1803), originally Strongylus ovis-aries (?), Europe.

OTHER COMMON NAMES

English: Barber pole worm, sheep stomach worm, wire worm. PHYSICAL CHARACTERISTICS

A stomach parasitic roundworm found inside ruminants such as sheep, goats, cattle, and wild ruminants. Males have a length of 0.7-0.8 in (18-21 mm); females 0.7-1.2 in (18-30 mm). Females possess white uteri and ovaries that spiral around their red blood-filled intestine, which gives a twisted ("barber pole") appearance. The small buccal capsule contains a curved dorsal tooth. There are two distinctive lateral spike-like cervical papillae near the connection 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, which is located asymmetrically near the bases of the left lateral lobe. Spicules are 0.018-0.020 in (450-500 pm) in length, each with a terminal barb, and the gubernaculums is navicular (that is, its structure is considered to be shaped like a small boat). Usually, an anterior thumb-like flap covers the vulva, and may be reduced to a mere knob in some worms. The oval eggs are 0.00276-0.00335 in (70-85 pm) in length by 0.0016-0.00173 in (41-44 pm) in width.

DISTRIBUTION

Distributed in the Arctic and immediately adjacent temperate regions of Europe, North Africa, and Asia, north of the tropics. (Specific distribution map not available.)

HABITAT

Found in coastal and high rainfall areas, especially in areas where hosts such as goats and sheep are plentiful. They are found in many terrestrial habitats, including tundra, taiga, temperate forest, and rainforest, temperate grassland, chaparral, tropical deciduous and scrub forests, tropical savanna and grasslands, and mountains. They live inside the abomasums (fourth stomach) of ruminants. Egg development is limited to areas and seasons where pastures are moist during warm months. (They are more prevalent in warm, moist regions than in cold, dry ones.) However, juveniles can survive for some time, particularly during cool conditions, and can infect hosts even without favorable periods of development. Pastures that remain green over the summer, perennial pastures (especially with kikuyu grass), irrigated pastures, and areas near creeks, troughs, and seepage points are preferred.

BEHAVIOR

Do not require an intermediate host. The first three juvenile stages are free-living. After the infective stage is reached, the organisms move to an area that will optimize its chances of being eaten by a host. The organisms have a short lifecycle (90 days) and must find a host quickly after it has completed its first stages of growth.

FEEDING ECOLOGY AND DIET

As a parasitic species, they feed on their hosts. They parasitize the abdomen or stomach of its host, using a single dorsal tooth to make cutting movements in the host tissues. A secreted anticoagulant allows them to feed on blood, but cell contents and other fluids are also consumed. Adults in the fourth stage of life are able to form a clot and feed from it.

REPRODUCTIVE BIOLOGY

Following internal fertilization, females lay eggs that pass out in the feces of the host. Each female can deposit 5,000-10,000 eggs per day. The first microscopic larvae hatch 14-17 hours after being passed through the feces; in 3-5 days the organism will have the ability to infect a host. First- and second-stage ju veniles feed on bacteria. Third stage juveniles retain the second stage cuticle as a sheath; they do not feed and are infective for the vertebrate host. In a sheep's gut, larvae develop to adults in about three weeks. Mating of adults occurs and egg production commences. The eggs hatch in soil or water. Infections by third stage juveniles may also occur through the skin. Enormous numbers of juveniles may accumulate on heavily grazed pastures. However, many die during low temperatures.

CONSERVATION STATUS Not listed by the IUCN.

SIGNIFICANCE TO HUMANS

Cause haemonchosis, which is related to the degree of blood loss. Large numbers of worms can accumulate very rapidly, causing host deaths often without warning, especially in young animals. Vaccination of sheep and goats (de-worming) is used for control. When the worms move through the soil, they help to aerate the soil, which helps to control erosion and keeps the soil from clumping and hardening. ♦

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