Foreign Diseases

By Edwin I. Pilchard.

More than 14 foreign diseases and arthropod pests are important threats to the $615 million sheep and $375 million goat enterprises of the United States.

Three of these diseases were once present, but were eliminated through industry and State cooperation in Federally organized eradication programs. The last outbreak of foot-and-mouth disease was eradicated in 1929, screw-worms in 1966, and sheep scabies (Psoroptes ovis) in 1973.

Both sheep and goats are susceptible to some of the foreign diseases for example, foot-and-mouth disease, heart-water, screwworm myiasis, babesiosis (Babesia motasi and B. ovis), contagious agalactia, Borna, melioidosis, Nairobi sheep disease, peste des petits ruminants, tick-borne fever (Rhipicephalus phagocytophilia), and exotic types of blue-tongue disease. Foot-and-mouth disease, screwworms, and heartwater are discussed under Section II on cattle.

Exotic types of bluetongue and Rift Valley fever deserve special attention because of their potential to become established if they should emerge in the United States. Also, although five types of bluetongue virus have been reported in the United States, 15 others are foreign and therefore subject to regulatory efforts to keep them out.

Bluetongue disease in sheep usually produces fever accompanied by difficult breathing; purplish-red discoloration of the muzzle, lips, ears and tongue; and many deaths in infected flocks.

In cattle, signs may resemble those seen in sheep, with the development of raw areas on the muzzle in some individuals. However, many may show little or no outward sign of sickness. Lowered fertility may be seen in some affected breeding herds.

Rift Valley fever causes high rates of abortion and death of lambs in infected flocks. It is described more fully under Section III.

Pox Viruses

Certain foreign diseases of sheep do not affect goats. These include sheep pox, louping ill, and nematodiasis.

Sheep pox is caused by a virus that differs in its immunizing characteristics from the virus of goat pox. It produces a high fever, and many sheep in affected flocks die showing typical pox lesions on unwooled areas of skin. Conversely, goat pox virus causes a disease in goats similar to that described in sheep with sheep pox.

Louping ill, a nonfatal tick-borne viral disease of sheep, is seen as a peculiar leaping gait, difficulty in coordinating the legs and body while walking or standing, and exaggerated movements when touched or frightened. This disease also has been reported in cattle and other animal species and humans.

Nematodiasis, caused by Nematodirus battus in Great Britain and parts of Europe, is an intestinal parasitism that produces profuse diarrhea, severe dehydration, and deaths of lambs 6- to 12-weeks old.

Babesiosis destroys red blood cells in animals on which carrier ticks have fed, producing severe anemia, yellowish discoloration of the white parts of the eyes and other tissues (jaundice), and sometimes death.

Agalactia

Contagious agalactia of sheep and goats, caused by the bacteria-like microbe Mycoplasma agalactia, produces sudden and profound swelling of the udder, swollen leg joints, abortion, and sensitivity to bright light which causes affected sheep to seek shade or darkened shelters.

Contagious caprine pleuropneumonia in goats closely resembles contagious bovine pleuropneumonia in cattle as described in Section III. However, cattle are not susceptible to the virus of caprine pleuropneumonia.

Borna disease, caused by an unclassified virus, has a prolonged course in which affected sheep and goats progressively lose control of their muscles and sense of balance. The loss of muscular control often allows the tongue to protrude from the mouth.

Melioidosis can affect sheep, goats, cattle, horses, and certain wildlife. The bacteria causing this disease, Pseudomonas pseudomallei, can produce a variety of signs ranging from an acute, fatal pneumonia, to arthritis, loss of muscular control, and death. Many affected animals have lumps or swellings under the skin caused by swollen lymph nodes.

Peste des petits ruminants (French), or plague of small ruminants (English), resembles rinderpest, described under Section III on cattle. However, the virus causing it does not produce disease when injected into cattle.

Tick-borne fever of sheep, goats, and cattle, caused by a microbe called Rickettsia phagocytophilia, is seen as a fever with stiffness of the body, neck, and limbs, and lameness accompanied by weight loss, with abortion in pregnant ewes or does. Few deaths are caused by this disease in fully developed animals.

Prevention of foreign diseases of sheep and goats requires compliance with Federal import laws by all who import animals or unsterilized animal products from affected countries. Prevention also requires that no one brings or sends prohibited animal products or souvenirs into the United States.

Section I gives more details on the prevention of foreign animal diseases, and a brief description of the way foreign diseases are found and eradicated.

Edwin I. Pilchard is a Principal Staff Officer, Veterinary Services, Animal and Plant Health Inspection Service.