#04-191

Complete

Date Full Report Received

12/01/2005

Date Abstract Report Received

12/01/2005

Investigation

Institution:
Primary Investigator:

In order to generate a protocol to sample lactating piglets to evaluate PRRSV chronically infected herds twelve PRRSV naïve pregnant sows were individually housed and assigned to three different groups. Sows in group A were injected with 3 mL of sterile MEM, group B with 101 TCID50 total dose of PRRSV isolate MN 30-100 and sows in group C were inoculated with 102 TCID50 total dose. All sows were intramuscularly injected at 90 days of gestation. Piglets were intensively observed and sampled during all lactation period. PRRSV real time PCR was used to identify and quantify the virus. Under the conditions of this study, where completely susceptible sows were inoculated at 90 days of gestation, dose of inoculated virus did not affect the proportion of viremic piglets at birth or the viral load in serum (RNAc/mL). Under this conditions 4 days of age seems to be best sampling age compared to birth (pre-colostrum intake) or weaning. Under the conditions of this trial there has not found evidence that sampling should be concentrated on early farrowings because the number and viral load of positive pigs is not different; however in a chronically infected farm, those sows that have not been exposed to the virus are more likely to early farrow compared to previously infected sows. In that case those early farrowing sows might have a higher probability of produce viremic piglets at birth. It could be suggested that stillbirths, mummies and “very sick” pigs are a better sample than all other pigs in order to catch potential positive pigs that means that the PRRS virus is still actively being transmitted in the sow herd. Under the conditions of this study there is no reason to sample lighter litters or piglets at birth but as expected affected litters will have a lower growing performance during lactation. Real time PCR on blood swab could be used as an alternative tool for herd monitoring in the case that a very often evaluation is recommended and when for some reason a veterinarian can not be present; however, clinical evaluation in order to select the best samples, given our results, is important to increase the chances to catch those potentially positive pigs. Real time PCR on blood swab could be used as an alternative tool for herd monitoring in the case that a very often evaluation is recommended and for when some reason a veterinarian can not be present; however, the clinical evaluation in order to select the best samples, given our results, is important to increase the chances to catch those potentially positive pigs. Under the conditions of this experiment, maybe because the sows were completely susceptible to the virus, most of the RNAc/mL values obtained were very high and pooling does not seem to affect much the ability of detecting at least one positive sample. However, in chronically infected farms, were a percentage of sows have been exposed the viral load of positive pigs might or might not be lower depending on the assumptions of partial or complete immunity.