This paper describes the isolation of porcine epidemic diarrhea (PED) virus in Vero and porcine cell cultures, and the influence of age on disease in experimental infection. PED virus was isolated from the small intestine of piglets inoculated with PED samples and cultured in Vero, porcine bladder and kidney cells propagated in collagen-coated tissue culture plates in maintenance medium (MM) containing trypsin. In porcine bladder and kidney cell cultures inoculated with isolated PED virus, cytopathic effects (CPE) including cell fusion were detected. Specific brilliant fluorescence was observed in the cytoplasm of these cells. Two- and 7-day old, and 2-, 4-, 8- and 12-week old specific pathogen-free (SPF) pigs were orally inoculated with PED virus isolated from an outbreak. All 2- and 7-day old pigs inoculated developed severe watery diarrhea from post-inoculation day (PID) 1 and died between PID 3 and 4. Although three of five 2-week old pigs developed diarrhea on PID 1-4, they eventually recovered. In the 4-week old group, three of five pigs had mild diarrhea for 1-2 days. None of the 8- and 12-week old pigs showed any clinical signs. Antibodies against PED virus were detected in all surviving pigs by virus neutralization (VN) test and immunofluorescence assay (IFA). Therefore, there is an age-dependent resistance to pathogenic PED virus infection in pigs.

A sudden outbreak of epidemic diarrhoea of piglets occurred in Japan, the principal features being watery diarrhoea, dehydration and high mortality in newborn animals. The microscopical lesions were villous atrophy in the small intestine, the villous enterocytes being vacuolated and cuboidal in shape. The villus-crypt ratio was severely reduced, varying from 1:1 to 3:1. Transmission electron microscopy showed numerous coronaviruses within the cytoplasm of enterocytes and among microvilli. Specific antigens of porcine epidemic diarrhoea (PED) virus were detected in the cytoplasm of enterocytes by the streptavidin-biotin (SAB) technique. Infected cells, which were most abundant in the villous epithelia of the jejunum and ileum, were present in small numbers in the large intestine, the crypt epithelia, the lamina propria and Peyer's patches. The study suggests that the SAB technique is useful for the diagnosis of PED.

ABSTRACT. Replication of porcine reproductive and respiratory syndrome (PRRS) virus in swine alveolar macrophages (AM) and cell population in broncho-alveolar lavage fluid (BALF) obtained from PRRS virus-infected pigs were investigated. BALF samples were periodically collected from 6 pigs infected with PRRS virus and 3 non-inoculated control pigs by means of fiber-optic bronchoscope between post-inoculation day (PID) 0 and 56. The mean ratio of macrophages in BALF collected from infected group was 92.7 ± 3.2% before inoculation and gradually decreased from PID 14. On the other hand, the ratio of lymphocytes was 4.8 ± 3.2% before inoculation and increased from PID 21 and indicated 41.8 ± 9.1% on PID 28. After that, they decreased gradually and that of macrophages correspondingly increased. The ratio of neutrophils maintained between 0.7% and 5.1%. The ratios of macrophages, lymphocytes and neutrophils collected from control group were almost stable through the examination. Intracellular PRRS virus antigens in AM were detected from PID 2 by indirect immunofluorescence assay (IIFA). PRRS virus was first isolated from BALF samples collected from inoculated group between PID 2 and 49. From serum, virus was isolated between PID 2 and 21. Antibodies in sera measured by IIFA to PRRS virus were first detected on PID 14 and the antibody titer rose to 1:640 or 1: 1,280. The results suggested that PRRS virus replicates in swine AM for a relatively long period. -KEY WORDS: alveolar macrophage, broncho-alveolar lavage, PRRS virus, swine.

ABSTRACT. The effects of hyperimmune cow colostrum (HCC) on experimentally induced porcine epidemic diarrhea (PED) were investigated in piglets. In experiment 1, four 2-day-old piglets fed HCC containing an antibody titer of 1:512 and another four piglets fed unimmune cow colostrum (UCC) were orally inoculated with 10LD 50 of PED virus. The piglets were given colostrum three times a day at 4 hr intervals. Half of the piglets fed HCC showed diarrhea and recovered, and all piglets survived. In contrast, all piglets fed UCC developed diarrhea and three of them died. In experiment 2, 2-day-old piglets fed HCC containing antibody titers of 1:512, 1:128 and 1:32, and UCC were inoculated with PED virus, and survival rates after challenge were 100, 75, 50 and 0 %, respectively. In experiment 3, 1-day-old piglets fed HCC with 1:512 antibody titer or UCC were inoculated and necropsied at 24, 48 and 72 hr after the inoculation for pathological examination. Piglets fed HCC remained healthy and PED virus antigen was not detected in the epithelial cells of the small intestine, and the length of the villi in small intestine was normal. On the other hand, in piglets fed UCC, villous atrophy and PED virus antigen were observed in epithelial cells of the jejunum and ileum from 24 hr. It was concluded that oral administration of HCC to piglets was effective in preventing PED virus infection and reduced their mortality. KEY WORDS: cow colostrum, passive protection, porcine epidemic diarrhea virus, swine.