Roundworm Parasites of the Digestive Tract of Cattle

DALE A. PORTER, HARRY HERLICH, AND HALSEY H. VEGORS.

APPROXIMATELY 25 species of roundworms can live in the digestive tract of cattle. About 10 of them are of economic importance. Natural parasitism usually is a mixture of several or all of them in one animal, and each type of worm produces a specific effect on the infected animal.

Three species of roundworms are commonly to be found in the stomach (abomasum) of cattle.

THE COMMON STOMACH WORM, Haemonchus contortus, occurs throughout the United States in cattle and sheep. It is three-fourths inch to one and one-half inches long and about as thick as a common pin. The adult females are larger than the males. The red spiral effect often seen in the living worms gives rise to such common names as wireworm, barberpole worm, and the twisted stomach worm.

The free-living part of its life cycle is much the same as that of all the roundworm species in cattle (except two species of intestinal worms). Eggs are passed with the feces of the infected animal. In 5 to 8 days, depending on temperature and humidity, the eggs have produced infective larvae (immature worms), which are capable of further development if swallowed by susceptible grazing stock.

The larvae do not feed and are enclosed within the cuticle (skin) of the preceding stage of development. They also have an inner cuticle. The two cuticles make the larvae able to survive unfavorable conditions.

The infective larvae are eaten with the grass. They pass down to the stomach, where they cast off their sheaths and undergo further growth until they become mature males and females. Fertilization occurs, and 18 to 23 days after the larvae have been swallowed, eggs from the female are passed with the droppings of the host.

We used to think that a bovine and an ovine strain of the common stomach worm existed, but F. H. S. Roberts in Australia stated in 1954 that the common stomach worms from sheep and cattle were two distinct species. He proposed that the name H. contortus be continued for the sheep species. He proposed the name H. placei for the cattle species. Cattle are more susceptible to H. placei than are sheep, and sheep acquire greater numbers of H. contortus than cattle do.

THE COMMON STOMACH WORM appears to affect sheep and cattle in the same way and is one of the most harmful species to both.

The most common symptoms are anemia, which is shown in paleness of the mouth and eyes, and emaciation despite continued good appetite. Infected cattle may have a rough hair coat and "bottle-jaw," a fluid accumulation in the lower jaw. They may be stunted. Diarrhea is rare. The most acute stage of infection is usually during the first 2 to 3 weeks after larvae have been swallowed. Symptoms often disappear when the worms have reached maturity. Severe cases may result in death.

THE MEDIUM STOMACH WORM, Ostertagia ostertagi, is hard to detect with the naked eye. In clear water against a black background, however, it can be seen readily as a worm slightly less than one-half inch long and about half as thick as a pin. Living worms are often reddish.

Its infective larvae are susceptible to heat and resistant to cold, so that they often become a problem during the colder months. The larvae shed their sheaths 3 days after they have been swallowed and penetrate the lining of the stomach. There they undergo further development for about 7 days. The worms then return to the stomach lumen (cavity) and develop to maturity. Many worms remain in the stomach lining for months. Eggs are passed with the feces about 25 days after cattle swallow the larvae.

The worms damage the stomach lining severely as they bore into it. This action stimulates a host reaction, which produces small nodules raised, hemorrhagic (bleeding) spots in an attempt to overcome the invading larvae. Eventually the worms leave the nodules, or die within them. Thereupon the nodules degenerate and leave patchy, eroded areas.

Animals infected with the medium stomach worm show general symptoms of parasitism, including scouring, weakness, stunted growth, and anemia. Severe infections cause death.

Postmortem examination often reveals a highly edematous or swollen stomach wall, in which there are many hemorrhagic or eroded spots. In the West and Southwest, the losses that are directly attributed to roundworm parasites are due mostly to the medium stomach worm.

THE SMALL HAIRWORM, Trichostrongylus axei, is the smallest of the roundworms affecting cattle. It is less than one-fourth inch long and about as thick as a hair. Laboratory equipment is needed to detect it. The small hair-worm can establish itself readily in sheep, goats, and horses. In horses it causes an extremely severe gastritis (a stomach inflammation). Rabbits, hamsters, and guinea pigs have been experimentally infected with it.

The life history of the small hairworm generally is like that of the common stomach worm and the medium stomach worm. The worms spend part of their developmental cycle within the stomach lining of cattle and produce ringworm-like lesions similar to those produced by this parasite in horses. About 4 weeks after cattle have swallowed infective larvae, eggs are passed in their feces.

THE SMALL HAIRWORM does not seem to affect the health of calves very much unless the level of exposure is high. Experimental findings, however, have borne out clinical evidence that the small hairworm has been the main cause of many cases of severe illness and death.

The detrimental effect of the small hairworms on calves is notably marked in cases of parasitism involving both the small hairworms and the medium stomach worms. Postmortem examination of stomachs of these cases shows a diffuse reddish-gray or slate-gray color, with evidence of edema. As many as 400,000 small hairworms have been recovered after death the animal must have swallowed enormous numbers of larvae, because not all the larvae become adults.

A CLOSELY RELATED form, T. colubriformis, primarily a parasite of sheep and goats, occurs in the small intestines of cattle. It has been found in great numbers in New York in calves suffering from parasitism. It might become a serious menace to cattle as the practice of raising sheep and cattle together becomes more prevalent.

SEVERAL SPECIES OF ROUNDWORMS exist in the small intestines of cattle. Three species of small worms are referred to as cooperids. One of them, Cooperia punctata, occurs in all parts of the United States. C. oncophora and C. pectinata are more often found in the Northern and Southern States, respectively. (A fourth species, C. curticei, primarily a parasite of sheep, is found occasionally in cattle.)

The cooperids are as thick as a hair and less than one-third inch long. The live worms are yellowish or pinkish brown. They occur most often on (and occasionally embedded in) the lining of the intestines, principally along the upper half of the small intestines.

All three species are similar in the essential details of their development, which resembles that of the common stomach worm. The main difference is the rapidity with which the cooperids complete their development within the animal. Eggs of C. punctata are in the feces of infected animals 11 days after infective larvae have been swallowed.

The cooperids have been implicated in field cases of severe parasitism in cattle, but other parasites usually were present and it was hard to determine the extent of the detrimental effects directly traceable to the cooperids.

C. punctata is potentially harmful to cattle: It can cause scouring, loss of appetite, weakness, and death. Anemia was not evident in any experimentally infected animals. The lesions consist chiefly of hemorrhages, which are usually no bigger than a pinhead. The intestinal wall is thickened. The surface of the intestinal lining has an unusual grayish-white appearance. The entire length of the small intestine may have an accumulation of white or yellowish, cheesy material, indicating irritation of the intestinal lining.

The hookworm, Bunostomum phlebotomum, occurs in cattle all over the world. It is most prevalent in regions of high rainfall and warm climate, as in the Southeastern States. Normally it is found in the upper half of the small intestine, chiefly in the first 8 or 10 feet. The male worms are about one-half inch long. The females are about three-fourths inch long. Both sexes are much stouter than the common stomach worm.

Cattle become infected when they swallow infective larvae. Larvae might also penetrate their skin when they are lying on contaminated bedding or ground. The larvae that enter through the skin migrate to the lungs, probably through the blood stream, and penetrate the lung. Then they are coughed up and swallowed and complete their development in the intestine. The time required for this migration and development is 52 to 79 days.

The head end of the hookworm has a large, cup-shaped mouth cavity armed with teeth, or cutting plates. With them it attaches itself to the intestinal wall. It sucks a part of the intestinal lining into its mouth and cuts the finer blood vessels with the teeth, and so gets its food from the blood of the animal. When many worms are present, the many small hemorrhages cause anemia.

Other symptoms are like those seen in infections of stomach worms. The calf may go off feed and eventually die. Diarrhea, weakness, and unthriftiness are apparent about a month after infection while the worms are still immature. Thus severe symptoms of a hookworm infection often are present during a period in which the infection cannot be detected by finding eggs in the droppings.

Adult hookworms may live in cattle as long as 10 months. Infected cattle acquire an immunity to further infection with this parasite.

THE INTESTINAL THREADWORM, the Strongyloides papillosus, is another skin-penetrating worm. It reaches maturity in the small intestine. It is very widely distributed and is common in young calves, especially in dairy calves and in the beef calves that are dropped in barnyards.

These roundworms are so tiny that they often are overlooked at postmortem examination. The adult females, about one-eighth of an inch long, usually are buried in the lining of the upper two-thirds of the small intestine. Parasitic males have not been found. The eggs contain fully developed larvae at the time they are passed in the feces. Intestinal threadworms have a cycle in which there are free-living males and females.

The worms may enter through the skin, or the infective larvae may be swallowed. Immature females are found in the small intestine as early as 7 days after infection. Eggs are usually in the feces 10 days after the animal is exposed.