[Frontiers in Bioscience 2, d471-481, September 15, 1997]|
THE COLOSTRUM-DEPRIVED, ARTIFICIALLY-REARED, NEONATAL PIG AS A MODEL ANIMAL FOR STUDYING ROTAVIRUS GASTROENTERITIS
Department of Animal Science, North Carolina State University, Raleigh, NC 27695-7626 and Center for Gastrointestinal Biology and Diseases, Chapel Hill and Raleigh, NC
Received 9/5/97 Accepted 9/10/97
6. ROTAVIRUS INOCULATION
In studies of experimentally-induced rotaviral gastroenteritis, the age of pigs at infection varied from 12 to 14 hours (11) to 28 days of age (7); in the majority of studies, pigs were infected between 2 and 8 days of age (8, 10, 14, 15, 17, 20 - 22). In our most recent studies, pigs have been inoculated with rotavirus at 5 or 6 days of age.
Human rotavirus isolates obtained from human infants with acute gastroenteritis (7, 8, 10, 11, 13, 15, 17), porcine rotavirus isolates (12, 14, 17, 19 - 22) as well as calf and foal rotaviruses (15) have been used as inocula to infect pigs. The source of rotavirus inocula that we have been using is a stock of bacteria-free fecal supernatant which was obtained from intestinal contents collected from rotavirus infected pigs as described by Lecce et al. (29), and belongs to rotaviruses of group A which have been established as the cause of significant diarrheal disease in both the human and animal young.
In several of the reports mentioned above, the concentration of rotavirus in the inocula was not always given but in those in which concentration was mentioned (8, 13, 17, 19 - 22), it varied between 106 and 108 rotavirus particles per pig. In a couple of studies in which rotaviruses were propagated by cell culture, the titer of the inocula used was 3.2 x 104 TCID50/mL (tisssue culture infective dose)(12) or 107 PFU/mL (plaque-forming units)(16). The minimal infective dose of rotavirus to induce clinical illness in colostrum-deprived, cesarean-derived, newborn pigs (inoculated at approximately 2 hours after birth) was 1 PFU (64). In our most recent experiments, we have been using inocula supplying between 104 and 105 rotavirus particles per pig and all pigs have shown the characteristic clinical manifestations of rotaviral-induced gastroenteritis (Gomez, unpublished results).
Oral administration has been the most common route of rotavirus inoculation but in a few studies, intranasal (7, 17) or nasogastric (13) administration has been used. In order to ensure total consumption of the rotavirus-containing preparation, particularly when neonatal pigs have been either fed throughout the day and/or allocated into the experimental groups the same day of infection, pigs have been inoculated, per os, after a 4- to 5-hour fasting period with 10 mL of the diet containing the specified rotavirus concentration followed by ~15 mL of regular diet. When pigs are not fed overnight and are distributed into the experimental groups 1 or 2 days before infection, rotavirus inoculation is carried out before the first feeding of the day.