Haemonchus contortus is an aggressive blood feeding worm (Figure 4).
This worm gets its name from the barberpole appearance,
consisting of the white ovaries that twist around the red blood-
filled gut. It is rather large compared to other
stomach and intestinal worms of goats, measuring up to three-fourths of an
inch. When large numbers are present, worms can readily be
seen as thin, red, hair-like worms
on the stomach surface. Female worms are prolific egg-
laying machines, and large numbers with favorable conditions can contaminate the environment with a very large number of eggs. These worms thrive under hot, moist environmental conditions, which are conducive for survival and development of the free-living stages and are found predominantly in tropical
and subtropical regions of the world. In the United States, these conditions
prevail in the Southeast. However, in the rest of the country, where
similar environmental conditions are encountered during the
summer, H. contortus transmission also frequently occurs. Generally, H. contortus transmission and infection is at the lowest level during the winter. Transmission and infection increases with the warmer temperatures and increasing moisture during the spring and peaks during the summer. As temperatures and moisture dissipate during the fall, transmission and infection decreases. Hypobiosis has not been observed to any great extent in the southeast United States because the life cycle can be maintained year around. But it does occur in more northern/western temperate regions of the United States.
Animals infected with H. contortus show symptoms associated with blood loss, or anemia. These include pale mucous membranes that are most visible by viewing inside the lower eyelid, and bottle jaw, an accumulation of fluid under the chin (Figure 5).
The greater the infection level, the more blood is lost, and eventually the animal may die.
The other abomasal worm of importance is Telodorsagia circumcincta, which is smaller than H. contortus and is not readily visible because it is about as big as an eyelash. These worms feed mostly on nutrients in mucous and do not feed on blood, per se, but can ingest some blood if present. Female worms do not produce as many eggs as H. contortus. Infection causes direct damage to the stomach lining, thereby interfering with digestion and appetite. Infection is usually considered a production disease as animals do not grow very well. However, under very high infection conditions, death can result. When infections reach levels that cause disease to be manifested, the primary symptom is diarrhea. This worm thrives in cooler, wet environmental conditions which are encountered in the more temperate regions of the United States, excluding most of the Southeast. Hypobiosis occurs when environmental conditions are too cold or too dry.