LLOYD A. SPINDLER.
INTESTINAL threadworms (Strongyloides) cause pigs to suffer from diarrhea, have a poor appetite, be unthrifty, lose weight, and die. Suckling pigs kept under crowded conditions in unclean pens are the ones most apt to be affected.
The cost of intestinal threadworms to hog raisers in the United States has been estimated at about 25 million dollars a year. Good husbandry practices help to avoid losses from thread-worms as well as from other parasites.
Intestinal threadworms are slender, whitish, and about one-sixth inch long when fully grown. The adults, all of which are females, live in the small intestine. They lay microscopic eggs, which already are partially developed. The eggs pass from the intestine of the pig with its droppings and may hatch within a few hours.
The young worms (larvae) that emerge from the eggs follow one of two courses of development. Some develop directly to a stage that is infective to swine. Others develop into tiny males and females. These mate, and the females produce eggs, which hatch within a day or two. The larvae that issue from these eggs quickly become infective.
Intestinal threadworms are the only roundworm parasites of swine that multiply thus on soil.
Pigs acquire threadworms by swallowing the infective larvae or when the larvae burrow through the skin. In general, the larvae then travel by way of the blood stream to the liver, the lungs, up the windpipe, down the esophagus, or gullet, to the stomach, and through it to the small intestine, where they quickly mature and begin producing eggs.
Some of the larvae wander more extensively in the pig's body. They even enter the brain and spinal cord, the muscles of the body and heart, the tongue, the voice box, the kidneys, and other places. Eventually, however, most of them make their way to the lungs and then to the small intestine.
Only about a week is required for threadworms to make this journey through the pig's body, grow to maturity in the intestine, and begin laying eggs.
The pigs are injured severely by both adult and young threadworms. The adults burrow into the wall of the intestine, where they may be overlooked, except by trained observers. The damage they do may cause severe scouring. As a result, the pig becomes weak and unthrifty and may lose weight. When large numbers of the worms are present, the damage they do to the wall of the intestine often causes it to bleed. When the bleeding is severe, the pig soon dies.
Threadworm larvae that enter the body muscles cause the pig to be stiff and sore. When they invade the heart muscle or the brain and spinal cord, the pig may die suddenly. Sows in a weakened condition from suckling their litters may die as a result of damage inflicted on the heart, brain, and spinal cord by wandering threadworm larvae.
A few threadworms may have little noticeable effect on pigs fed adequate amounts of a well-balanced diet. The adult worms have been found, generally in small numbers, in a fair proportion of the apparently healthy swine that have been especially examined. Even a few threadworms in the intestine of a sow may be a source of possible danger to her pigs, however. The pigs sometimes become infected with threadworms before they are born. Threadworm larvae wandering through the body of a pregnant sow invade the unborn pigs, but it is not known whether any die from this cause.
No treatments based on thorough tests have been devised for removing intestinal threadworms from swine. Consequently sanitation must be used to combat the parasite.
The best way to fight threadworms is by cleanliness: Keeping the farrowing pens and other premises occupied by little pigs clean and dry, and providing the pigs with plenty of fresh, dry bedding. Eggs and larvae of threadworms are killed by dryness, but they live well in manure and damp bedding.
It is important to clean and wash the pens frequently and destroy the old bedding. Young pigs should be kept away from the droppings of older animals and from bedding that has been used by older animals.
Pigs that are farrowed and raised on temporary pastures generally are troubled less with intestinal thread-worms than are those raised indoors.
LLOYD A. SPINDLER joined the Department of Agriculture in 1929.
KENNETH C. KATES.
THE THORN-HEADED worm, Macracanthorhynchus hirudinaceus, has a big hooked snout by which it attaches itself firmly to the wall of the small intestine of pigs. It belongs to an unusual group of parasites, the Acanthocephala, which look somewhat like roundworms but are unlike them in body structure.
This parasite is found in swine throughout the United States.
It is a giant of its kind. The adult female is more than a foot long and has a maximum diameter of one-third inch. The male, smaller than the female, attains a length of 4 inches and width of about one-fourth inch. It is milk white and somewhat flat when alive, but it becomes more or less cylindrical when it is kept in water or preserving fluid.
The muscular snout, which protrudes from the front end, is about one twenty-fifth inch long and has hooks arranged in six spiral rows of six hooks each.
The thorn-headed worm has no digestive system or mouth. It absorbs predigested food materials through the body wall in the intestine of the host. Female worms are essentially elongated, tubular sacs, which contain large numbers of eggs, or embryos in shells, in various stages of development. A complicated organ at the hind end rejects eggs that have not completed their development and ejects the fully developed eggs.
The male reproductive system consists of two small organs, or testes, arranged in tandem and connected with the exterior by a tube or duct.
A female worm can produce more than 10 million eggs during a normal lifetime of several months in the host. Fully developed eggs contain small larvae (acanthors), which are encased in a thick shell. After the eggs are eliminated from the host, the larvae remain in the shell and undergo no further development until they are swallowed by the white grubs of many species of beetles particularly June-beetles--as they burrow through the soil and manure.
Larvae hatch in the midgut of the grubs, penetrate to the body cavity, and develop into another larval stage (acanthella). Eventually juvenile worms (cystacanths), about one-eighth inch long, and with the snout inverted into the body, develop from the acanthellas. Larval development in white grubs takes 2 to 3 months at average summer temperature. The worms reach maturity in swine in about 2 months.
Pigs become infected by eating infected grubs while rooting in the soil. Young worms, which are freed from the grubs in the host animal's digestive tract, attach themselves to the small intestine with their thorny snouts.
That is how the parasite does most of its damage. A pea-sized nodule forms at each place of attachment. Worms move about in the small intestine and form a new nodule each time the snout bores into the wall. At first the nodules may be surrounded by a red, inflamed border. Later they become filled with cheeselike material. The snouts may perforate the intestinal wall. Then the escape of bacteria into the body cavity may cause an inflammation of its lining (peritonitis).
No specific symptoms are associated with these infections in pigs, but the worms contribute to general unthriftiness. The nodules formed by the worms lower the value of the casings that are prepared from pig intestines in abattoirs for use as skins for sausages and other meat products.
It is difficult to control thorn-headed worms. No effective drug is available to remove them from swine; it is uneconomical to employ control measures for white grubs in the soil of hog-lots and pastures. Furthermore, eggs in soil will remain infective to white grubs for several years.
Some control measures have value. The noses of pigs may be ringed to keep them from rooting and eating infected grubs. The use of old hog lots and permanent pastures should be avoided. The elimination of old straw piles and other debris from places where hogs are kept will help to reduce the number of white grubs and thereby the chances of infection.
KENNETH C. KATES is parasitologist in charge of investigations on helminth parasites of sheep and goats in the Helminth Parasite Section, Animal Disease and Parasite Research Branch, Beltsville, Md.