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PSEUDORABIES
- Page 1 (AUJESKY'S DISEASE, MAD ITCH) BY: DAVID G. THAWLEY, UNIVERSITY OF MISSOURI; DON P. GUSTAFSON, PURDUE UNIVERSITY; C. JOHN MARE, UNIVERSITY OF ARIZONA; L.W. SCHNURRENBERGER, USDA , WASHINGTON, D.C. PORK INDUSTRY HANDBOOK |
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Introduction and History: Pseudorabies is an acute, frequently fatal disease affecting most species of domestic and wild animals; however, man and the higher apes are resistant to it. The disease is caused by a herpes virus and is characterized by a variety of clinical signs; the most prominent involve the nervous and respiratory systems. Severe itching and self-mutilation are seen in most species, but rarely in swine. Aujesky first recognized pseudorabies as a disease of cattle and dogs in Hungary in 1902. It soon became evident, however, that swine were the natural hosts of the virus and pigs also could die as a result of the disease. In Europe, pseudorabies has been recognized for years as an important cause of death in swine of all ages and as a cause of abortion. In the United States, until recently the disease was considered important only as a cause of death in baby pigs and occasionally in cattle, sheep, dogs and cats. However, pseudorabies is more prevalent in the U.S. than was formerly believed and the present viruses are capable of causing a variety of clinical manifestations, including death in newborn and adult swine and fetal death with abortion in pregnant swine. The disease is widespread and of considerable economic importance in several Midwestern states. A slaughter serum survey conducted in 1983 revealed a nationwide prevalence of 18.8% in breeding swine and state rates ranging from 0% to 34.4%. Clinical Signs: Pigs less than 3 weeks old: In baby pigs, the disease may be characterized by sudden death with few, if any clinical signs. Death frequently is preceded by fever which may exceed 105 degrees, fullness, loss of appetite, vomiting, weakness, incoordination, and convulsions if vomiting and diarrhea occur, the disease in baby pigs closely resembles transmissible gastroenteritis (TGE). In pigs less than 2 weeks old: Death losses frequently approach 100%. Baby pigs may have become infected before birth and die within 2 days after birth, occasionally after showing violent shaking and shivering. Piglets infected immediately after birth may show clinical signs within the first 2 days of life and usually die before they are 5 days old. Pigs 3 weeks to 5 months old: After 3 weeks of age, pigs usually develop a degree of resistance to the disease, and death losses may decrease from 50% in pigs exposed when 3 weeks old to less than 5% in pigs exposed when 5 months old. Death losses vary with different strains of the virus, and even in grown pigs severe death losses occasionally occur. |
Fever is a prominent clinical sign in these growing pigs and usually is followed by loss of appetite, listlessness, labored breathing, excessive salivation, vomiting, trembling, and eventually marked incoordination, especially of the hind legs. Death is usually preceded by convulsions. Involvement of the respiratory tract with sneezing, rubbing of the nose, and coughing may occur. Clear to yellowish nasal discharges may be seen. Infected pigs which recover will usually have lost condition and will be slow to gain weight. Mature pigs: The disease in adult pigs is usually not severe, but with some strains of pseudorabies virus deaths may occur. The disease in adult pigs often is characterized by fever and respiratory signs such as nasal discharges, sneezing, nose rubbing and coughing. Nervous signs such as trembling, incoordination, and itching occasionally occur, and blindness may rarely follow pseudorabies infection. Vomiting and diarrhea or constipation may be seen. Since 1980, an acute, often fatal pneumonia caused by pseudorabies virus has increased in prevalence. This condition is most often seen in herds which have a prolonged history of the pseudorabies infection. Animals often die from a fatal secondary bacterial pneumonia. Sows infected in the early stages of pregnancy may return to heat because of death and resorption of their fetuses. Sows infected in middle pregnancy may eventually abort mummified fetuses, whereas sows infected late in pregnancy often abort or give birth to weak, shaker or stillborn pigs. Postmortem Lesions: No gross lesions characteristic of pseudorabies are consistently found. Small grayish-white spots of focal necrosis may occur in the liver or spleen of pseudorabies-infected young pigs. Congested pneumonic lungs are commonly seen. Virus isolation and fluorescent antibody examination of these and other tissues will reveal if these lesions are related to the disease. Immunity: Recovery by swine from pseudorabies confers resistance for at least 12 months. Re-exposure may result in re-infection, but it is usually asymptomatic. The passive immunity passed on from an immune sow to her offspring through the colostrum may protect the piglets for 5 to 10 weeks, after which they gradually become fully susceptible. However, the passive immunity may be too low to protect the piglets so the off spring of immune sows also may die of pseudorabies.
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