- 4 minutes, 31 seconds
- Expertise article
- A. Patterson*, G. Haiwick, J. Victoria, J. Hermann, R. Philips
Introduction:in 2014 in North Carolina, anecdotal reports of a particularly virulent PRRSV isolate (RFLP cut pattern 1-7-4) were reported by practicing veterinarians. Reports indicated that the isolate was more transmissible, had higher levels of viremia for longer time periods and was more virulent in comparison to other circulating PRRSV strains. The objective of this study was to evaluate PRRS 1-7-4 isolates under experimental challenge conditions.
Materials and Methods: sixty, PRRSV negative convencional, three week old pigs were randomized into four tretment groups (n=15/group). On D0, animals in Group 1 and 2 were inoculated intranasally with 2ml of one of two viral harvests derived from clinical samples collected in 2014 (RFLP pattern 1-7-4; lineage 1); animals in Group 3 were challenged with a positive control isolate (RFLP pattern 1-18-2; lineage 1); animals in Group 4 were inoculated with 1X PBS. Serum was collected on D0, 1, 3, 5, 7, 14, 28 and 35. On D14, 10 animals from each group were necropsied; remaining animals were necropsied on D35. At the time of necropsy, lungs were scored for macroscopic lesions and bronchalveolar lavage was collected. Serum samples and BAL were tested by RT-PCR for the presence of PRRSV RNA and by ELISA for the presence of anti-PRRSV antibodies. BAL was cultured for the presence of bacteria.
Results: least sqaure mean lung lesion scores (with 95% confidence intervals) at D14 for groups 1-3 were 3.1% (0.0-10.7%), 12.4% (5.6-21.3%) and 15.2% (7.3-25.3%), respectively. At D35, lung socres for Group 1-3 were 2.8% (0.1%-13.1%), 28.4 (3.9%-63.8%) and 34.5% (1.3%-82.6%), respectively. Viremia ocurred in 13/15 animals in Group 2 and 3 by D1; all animals became viremic by D3. In Group 1, 13/15 animals were viremic by D3; all animals were viremic by D7. Viremia was detectable in all remaining challenged animals at D35. There was no significant difference in cycle quantification values among challenged animals. All challenged animals had detectable PRRSV antibodies by D14; animals challenged with placebo material remained seronegative througout the tral. By D35, PRRSV antibodies were only detected in 0/5 and 1/5 pigs in Group 1 and 2 respectively. Conversely, in Group 3, 4/5 animals had detectable PRRSV antibodies at D35. No vremia or seroconversion was detected in Group 4, nor were any lung lesions present. Additional results were compiled but not reported.
Conclusion: two PRRSV isolates recovered in 2014 from farms experiencing severe clinical signs associated with PRRSV were compared to a virulent PRRSV isolate recovered in 2008. Based on lung lesions and viremia, the 2014 isolates were not more virulent in comparison to a 2008 within the same lineage.
Disclosure of Interest: none declared.
Keywords: isolate, PRRSV, Virulence
Viral and Viral Diseases
PRRS
PO-PW1-142
Effect of piglet vaccination against PRRS in Belgian farrow-to-finish heards
E. de Jong1*, T. Vandersmissen1, H.Nauwynk2
1Animal Health Care Flanders, Drongen, 2Virology, Parasitology and Immunology, University of Ghent, Merelbeke, Belgiu
Introduction: Porcine Reproductive and Respiratory Syndrome virus (PRRSv) may cause significant in pig herds due to pre-weaning mortality and reduced performance in growing pigs. In Belgium, the virus is widespread and endemic in most herds. An earlier trial showed that infection of PRRSv mainly occurs near the end of nursery (8-12 wekks of age (w)). PRRSv vaccines are effective under experimental conditions but sometimes fail to cover the field expectations. Sow vaccination against PRRS is common practice in Belgian herds. recently, also piglet vaccination strongly increased. The aim of this trial was to evaluate the serological response after vaccination and to investigate the effect of piglet vaccination on the timing of infection with PRRSv.
Materials and Methods: in 5 farrow-to-finish herds, with a PRRSv infection at the end of the nursery as shown by previous analyses, 1 batch of piglets was vaccinated with an attenuated EU PRRSv vaccine strain (Porcilis® PRRS, MSD, The Neatherlands). Piglets were vaccinated by the farmer at 19-20 days of age, except for 1 herd in which piglets were 23-24 days old. In each herd, 60 piglets were randomly selected individually earmarked (20 piglets from sows of parity 1, parity 2-4 and parity >5 resp). A horitzontal serological screening was perofrmaced at 4, 7, 10, 13, 18, and 23w. Serum was examined for antibodies (ab) against PRRSv by IPMA and virus isolation was done on serum during seroconversion.
Results: in 3 herds, 62, 57 and 57% of piglets with a maternal ab (mab) tire of > 160 at 4w seroconverted at 10w. In contrast, in 1 herd interference with mab awas observed: 83% of piglets with a mab titre > 160 did not seroconvert at 10w. Seroconversion indicated a PRRSv infection between 18 and 23w in those 4 herds, which was confirmed by insolation of wild type virus in 2 herds at 18w. The percentage of serological non-responding piglets to vaccination in the 4 herds was 50, 43, 47 and 33%, resp. In the 5th herd, viraemic piglets were found. Extremely high ab titres (>2560) were detected at 4w and wild type virus was alredy isolated in piglets of 7w, indicating an early infection. Biosecurity was poor in the latter herd.
Conclusion: the results demostrate that a substantial number of piglets do not seroconvert after vaccination. Piglet vaccination could not eliminate the virus from the herd, but seems to delay the timing of PRRSv infection towards the second half of the finishing period. Results undelrine that biosecurity measures play an important role in an effective control program. Further research is needed to investigate the clinical protection induced by vaccination, especially in the seriologycal non-responders.
Disclosure of Interest: none declared
Keywords: piglet vaccination, PRRSV, Serological evaluation