DISEASES AND PARASITES AFFECTING--sheep and goats

Coccidiosis of Sheep and Goats

JOHN C. LOTZE.

COCCIDIOSIS is caused by microscopic, one-celled parasites (Protozoa), known as coccidia. It is a common but generally overlooked disease of lambs and kids throughout the United States.

The developing stages of the parasites live in the lining. of the intestine and destroy parts of it. This causes diarrhea, or scours, which may or may not be bloody. Severely affected animals become unthrifty, fail to grow, and may die.

Sheep and goats acquire coccidiosis by swallowing feed and water contaminated with the droppings of infected animals.

THE LIFE CYCLE of coccidia has two main phases a free-living phase outside the body of the animal and a parasitic phase in its intestine.

The free-living phase, known as oocysts, is the one by which the parasites spread to new hosts. The oocysts are discharged in the manure of infected animals. In moist places with temperatures above freezing, eight tiny, wormlike bodies sporozoites form inside each one in about a week. They are then known as sporulated oocysts and are infective.

0ocysts have thick shells and are resistant to drying and most chemical disinfectants. The parasites in this phase may live for several months on soil. Generally they occur in large numbers on pastures and in pens and other places where infected animals are kept. The parasites are readily killed by ammonia produced by fermenting manure.

The parasitic phase begins when the sporulated oocysts, are swallowed.

When the oocysts; reach the upper part of the small intestine, the sporozoites inside them become active and escape. Each sporozoite then enters one of the cells that line the small intestine and divides a number of times. It is then known as a schizont.

As the schizont grows, the host's cell grows also, sometimes to a tremendous size. It finally dies. Enormous numbers of tiny, cigar-shaped bodies, known as merozoites, develop within each schizont. The merozoites escape from the schizont, and each invades a separate, different cell. Millions of cells may be affected at one time.

Some of the merozoites develop into eggs. Others divide into numerous wormlike forms, which migrate to the eggs and fertilize them. A thick shell develops around each egg and it is now called an oocyst. The oocysts are released into the cavity of the intestine and pass to the outside with the droppings. The first oocysts are produced about 16 to 21 days after inoculation. An infected animal may void enormous numbers of oocysts in 10 or 15 days.

Destruction of large areas of the lining of the intestine may begin 5 to 7 days after infection, but severely affected animals usually do not appear to be sick until about the 11th day of the infection when the young stages or merozoites in the schizonts are reaching maturity.

TEN SPECIES of coccidia, all of the genus Eimeria, have been reported in sheep and goats. It is generally assumed but not proved that the same species affect both sheep and goats. It has been assumed also that the different species are equally harmful.

The three species that occur oftenest in sheep may differ in their ability to damage the animal. Lambs, raised free of parasites until they were 3 to 5 months old and maintained on a good diet, were studied in a research project at the Parasite Station of the Beltsville Research Center.

Some of the lambs were given one-half million sporulated oocysts of one of the most common species, Eimeria ninae-kohl-yakimova. About half of these lambs died from severe coccidiosis. Some lambs were fed one-half million oocysts of either E. arloingi or E. faurei, but did not seem to be affected seriously. Others got 5 million oocysts of E. arloingi; none died. Still others were fed 50 million oocysts of E. faurei a tremendous dose but none died.

SYMPTOMS OF COCCIDIOSIS depend on the amount of damage the parasites do to the intestine. That in turn depends on the number of oocysts swallowed at one time and the species involved. At birth or shortly thereafter, most or all sheep and goats acquire light infections of one or more species of coccidia, apparently without bad effects.

The development of large numbers of the parasites in the intestine at one time may injure extensive areas of the intestine and thereby interfere with digestion and cause diarrhea, loss of weight, and death. Breaks in the wool may occur about a month after the sheep acquires a heavy infection.

TO DIAGNOSE COCCIDIOSIS of sheep and goats one needs a microscope to detect the parasites, either the oocysts in the droppings or the parasites in their various stages of development in the intestines. One needs experience to recognize the parasites and to judge whether the infections were severe enough to produce the symptoms and deaths encountered, because other disorders may be present and produce like symptoms.

When animals become heavily infested, symptoms may occur and the animal may die before oocysts are formed. Furthermore, the number of oocysts in the droppings may not always reflect the severity of the infection because of resistance or some factor that tends to check the formation of oocysts.

In general, however, coccidiosis should be suspected when lambs have diarrhea.

No specific chemical treatment of proved reliability is available for coccidiosis of sheep and goats.

Sulfonamides, especially sulfaguanidine, sulfamethazine, and sulfasuxadine, have been used advantageously in several instances. At the proper time and in proper amounts, they may destroy some of the intestinal stages, reduce the production of oocysts, and help the animal withstand the injurious effects of the parasites. Since the developing stages of coccidia injure the lining of the intestine and make it easier for bacteria to invade the intestinal wall, these drugs may be of help in stopping invasions by certain bacteria.

Fly strike is favored by the watery feces of coccidial scours, which keeps the wool on the hind parts moist. The odor of the feces attracts blowflies, and they lay tremendous numbers of eggs on the soiled wool. The larva, or maggots, that hatch from the eggs live close to the skin and attack the tissues of the living animal. Severe infestations of the larva may cause death unless they are detected early and proper treatment is given.

Treatment consists in removing the soiled wool and applying a medicated smear or ointment to destroy the maggots and to promote the healing of lesions. Commercial screwworm remedies are recommended for this purpose.

Control of coccidiosis of sheep and goats rests largely on the use of management practices that help to keep the animals from contaminating their feed and water with droppings, which may contain oocysts. That, in turn, helps keep the animals from swallowing large numbers of oocysts at one time and thus prevent severe cases.

Some suggestions:

Clean pens often and keep them dry. Ordinary disinfectants have little or no effect on oocysts. Washing pens with disinfectants may be of little value against coccidiosis, but may help to control bacterial diseases.

Crowding animals together in close quarters favors coccidiosis. With increased use of improved pastures and more intensive farming, there is an increasing tendency to keep larger numbers of sheep and goats in small areas. Pastures should not be overstocked. A plan of pasture rotation should be followed.

Feed good diets and use prescribed medicines in recommended ways to help prevent severe infections, especially when animals are crowded. Sulfur mixed in the feed of lambs kept in feed lots is reported to have given good results against coccidiosis.

JOHN C. LOTZE, a parasitologist in the Animal Disease and Parasite Research Branch, has done research on protozoan diseases of livestock at the Agricultural Research Center since 1938.