EXPERIMENTAL REPRODUCTION OF PORCINE EPIDEMIC ABORTION AND RESPIRATORY SYNDROME (MYSTERY SWINE DISEASE) BY INFECTION WITH LELYSTAD VIRUS - KOCH POSTULATES FULFILLED (REPRINTED FROM THE VETERINARY QUARTERLY, VOL 13, PG 131-136, 1991)

Aerosol exposure of eight pregnant sows to cell-culture-propagated Lel ystad virus resulted in clinical signs characteristic of so-called mys tery swine disease. After an incubation of four to seven days, all sow s were inappetent and listless for six to nine days. Two sows develope d a transient red-blue discolouration of the ears ('abortus blauw' or blue ear disease) accompanied by abdominal respiration, and two had a fever for one day only. One sow aborted at 109 days of gestation. The other seven sows, farrowing between 113 and 117 days of gestation, gav e birth to numerous mummified dead, and weak piglets. Of these seven, the mean number of piglets born dead to each sow was 4.6 and the mean number born alive was 7.7 of which 3.1 piglets per sow (40%) died with in the first week. Lelystad virus was isolated from 31 piglets, which were born dead or died shortly after birth. Antibody was detected in p recolostral blood samples or ascitic fluids of 23 piglets, a finding w hich demonstrated transplacental passage of the virus in six out of ei ght litters. We conclude that Lelystad virus is the causal agent of my stery swine disease. Since its aetiology is no longer a mystery, we pr opose the more appropriate name 'porcine epidemic abortion and respira tory syndrome' (PEARS).