A strain of type 2 human rotavirus (Wa) was grown to relatively high titer through 14 passages in primary cultures of African green monkey kidney (AGMK) cells. This passage series was initiated with virus that had been passaged 11 times serially in newborn gnotobiotic piglets. In contrast, virus present in the stool of patient Wa as well as virus from the first, second, or third passage in piglets could not be propagated successfully in African green monkey kidney cells. Prior to each passage in cell culture, the virus was treated with trypsin and the inoculated cultures were centrifuged at low speed. Cultivation of a type 2 human rotavirus should aid attempts to characterize this virus and to develop a means of immunoprophylaxis for a serious diarrheal disease of human infants.

Virus particles morphologically similar to caliciviruses and rotaviruses were detected by electron microscopy (EM) in the intestinal contents of a 27-day-old diarrheic nursing pig. A third small spherical 23-nm virus-like particle was also observed. Calicivirus-like particles averaged 33 nm in diameter. Similar to rotaviruses, rotavirus-like particles were present as single-capsid 55-nm forms or double-capsid 70-nm particles. Most gnotobiotic pigs orally exposed to samples containing these three viruses developed diarrhea and villous atrophy of the small intestine, and all shed the three viruses in their intestinal contents. Attempts to propagate these viruses in cell culture were unsuccessful. The antigenic relationship of the rotavirus-like particles to known rotaviruses was explored by immune EM and immunofluorescent staining. By these techniques, the rotavirus-like particles did not cross-react with antisera to porcine, bovine, or human rotaviruses or to reovirus type 3. Antisera from gnotobiotic pigs exposed to all three viruses had enzyme-linked immunosorbent assay and virus neutralization titers of <4 against porcine rotavirus. Previous infection of gnotobiotic pigs with the mixture containing rotavirus-like particles failed to protect them against a subsequent challenge with porcine rotavirus. The antigenic relationship of the calicivirus-like particles to known caliciviruses was investigated by immune EM and virus neutralization. By these tests, the calicivirus-like particles did not react with antisera against feline calicivirus strain 255 or M-8. In a study conducted at Plum Island Animal Disease Center, antiserum against the three combined agents did not specifically neutralize any serotype of swine vesicular exanthema virus.

Seven rotavirus strains were isolated in cell cultures from the intestinal contents of piglets with diarrhea. MA104 cells with pancreatin in the cell culture medium was the host system of choice for virus isolation and replication. A cell culture immunofluorescence test in which MA104 cells were used in microtiter plates was very effective for detecting and assaying rotaviruses. A plaque reduction neutralization test, cross-protection studies in gnotobiotic pigs, and electrophoresis of rotaviral double-stranded RNA were used for comparing viruses. Three strains produced plaques on initial isolation attempts, replicated well in cell cultures, and were antigenically very similar. We suggest that these three strains be considered porcine rotavirus serotype 1, with The Ohio State University (OSU) strain serving as the prototype. The OSU strain was distinct from bovine, simian, canine, and human (Wa and M) rotaviruses by plaque reduction neutralization. Four strains did not produce plaques on initial isolation attempts, were difficult to adapt to cell cultures, and were related to each other but were distinct from the serotype 1 strains. We suggest that the Gottfried (G) strain be tentatively considered as a prototype for porcine rotavirus serotype 2. The G strain was antigenically closely related to canine and simian rotaviruses and less so to human M rotavirus (human rotavirus serotype 3). Canine, simian, and human M rotaviruses were closely related. All seven porcine rotavirus strains caused diarrhea in gnotobiotic pigs. Cell-cultured vaccines of the OSU and G strains caused only mild or no diarrhea in gnotobiotic pigs, and protection occurred when such pigs were challenged with homologous, bur not heterologous, virulent viruses. A survey indicated that 94% of 274 porcine serum samples and 100% of 75 herds were serologically positive to the porcine OSU rotavirus.

The antibody response of pregnant swine to transmissible gastroenteritis (TGE) virus was studied, with special reference to the titers and the immunoglobulin (Ig) class of TGE neutralizing antibodies in colostrum and milk. Animals vaccinated twice intramuscularly or intramammarily with live attenuated TGE virus developed high levels of antibodies in serum and colostrum, but the levels in milk declined markedly within a few days post-farrowing. In contrast, animals naturally or experimentally infected with virulent virus generally developed lower levels of antibodies in serum and colostrum but maintained higher levels in milk, as compared to the vaccinated animals. Gel filtration studies indicated that antibodies in milk from vaccinated animals were primarily of the IgG class, whereas those

Some characteristics of a newly recognized porcine enteric virus are described. Tentatively, the virus was referred to as porcine pararotavirus (PaRV) because it resembled rotaviruses in respect to size, morphology, and tropism for villous enterocytes of the small intestine. However, it was antigenically distinct from porcine, human, and bovine rotaviruses and reoviruses 1, 2, and 3, and the electrophoretic migration pattern of PaRV double-stranded RNA was distinct from the electrophoretic migration patterns of the rotaviral and reoviral genomes. By passage in gnotobiotic pigs, PaRV was isolated from two suckling diarrheic pigs originating from two herds. After oral exposure of gnotobiotic pigs, villous enterocytes of the small intestines became infected as judged by immunofluorescence, resulting in villous atrophy and diarrhea. Mortality was high when gnotobiotic pigs less than 5 days old were infected. The C strain of this virus was serially passed 10 times in gnotobiotic pigs, and electron microscopy, immunofluorescence, and serological tests indicated no extraneous agents. The virus was serially passed five times in cell cultures which contained pancreatin in the medium, but replication was negligible or absent, as the number of immunofluorescent cells decreased with each passage. Since rotaviral infections are frequently diagnosed by direct electron microscopy of fecal specimens, the presence of other morphologically similar viruses, such as PaRV, should be considered. The use of immune electron microscopy is suggested as a means of helping recognize this situation.