by Boehringer Ingelheim Animal Health USA Inc./May 5, 2019
Porcine reproductive and respiratory syndrome (PRRS) is a complex and costly disease, due in part to the high degree of genetic variation among PRRS field isolates.
Know the Facts
• The protection provided by all commercially available modified-live virus PRRS vaccines is heterologous, due to the high degree of variation among porcine reproductive and respiratory syndrome virus (PRRSV) field isolates.
• PRRSV protection can’t be predicted by a vaccine’s lineage origin.
• PRRSV protection can’t be predicted by a vaccine’s sequence similarities to field strains.
The Basics
Porcine reproductive and respiratory syndrome (PRRS) is a complex and costly disease, due in part to the high degree of genetic variation among PRRS field isolates. Throughout its 25-year history, Ingelvac PRRS® MLV, the No. 1 PRRS vaccine on the market, has demonstrated its ability to provide heterologous protection against numerous wild-type PRRSV strains that differ from the vaccine strains in terms of nucleotide sequence and lineage.2–3
Key Terms
PRRSV PHYLOGENETIC CLASSIFICATION
Diverse PRRSV strains are classified by the nucleotide sequences in the open reading frame 5 (ORF5) of viral DNA. Advanced software is used to further identify phylogenetic similarities between strains and provide a reference for future studies.
LINEAGE
Lineage is the cluster of strains that appear to descend from a common genetic ancestor. The North American PRRSV strains are generally divided into nine lineages.
HOMOLOGOUS
When the nucleotide sequences between two strains vary by less than 2–3%.4–7
HETEROLOGOUS
When the nucleotide sequences between two strains vary by more than 2–3%.4–7
Commercial vaccines provide heterologous protection
The protection provided by all commercially available modified-live virus PRRS vaccines is heterologous, due to the high degree of variation among PRRSV field isolates.
A recent analysis of commercial PRRS vaccines found that none falls within the scientifically agreed-upon window to be considered homologous to lineage 1 field strains.1
See Table 1 below for more information.
Studies suggest that when there is a difference of more than 2–3% between two ORF5 sequences, they may not be closely related.4–7 Homology tables, based on percent similarity of open reading frame 5 (ORF5) sequences, are commonly used to determine the relatedness of one virus to another.
None of the current commercial modified-live virus vaccines is close enough to the 2–3% threshold to be considered homologous to the recently isolated wild-type PRRSV lineage 1 strains shown in Table 1; therefore, they would be considered as heterologous to these wild-type PRRSV strains.1
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Cross-protection across lineages
PRRSV protection can’t be predicted by a vaccine’s lineage origin.
Although it is sometimes assumed that vaccines with similar sequence or lineage origin to current field strains may provide more effective protection, studies have shown this isn’t the case.2–4 INGELVAC PRRS MLV is classified as lineage 5.1, and challenge studies have shown that it provides heterologous protection against multiple lineage 1 PRRSV strains, including the common field strains 1-7-42 and 1-3-4,2 in addition to 1-8-4 and 1-4-4.3
See Tables 2 and 3 below for more information.
INGELVAC PRRS MLV is classified as lineage 5.1. To confirm the vaccine provides effective cross-protection against current and virulent PRRSV strains of a different lineage, two challenge studies were conducted with PRRS 1-7-4 and 1-3-4 field isolates, both strains within lineage 1.2 In both studies, pigs vaccinated with INGELVAC PRRS MLV showed significantly reduced lung lesions and significantly increased average daily weight gain (ADWG) compared with the placebo group.2
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Cross-protection across sequences
PRRSV protection can’t be predicted by a vaccine’s sequence similarities to field strains.
Another paper summarized 21 independent studies conducted by Boehringer Ingelheim that evaluated the efficacy of INGELVAC PRRS MLV and INGELVAC PRRS ATP, following challenge with eight genetically diverse PRRSV isolates that varied by sequence.3 The paper found that INGELVAC PRRS MLV and INGELVAC PRRS ATP significantly reduced lung lesions in vaccinated pigs when compared to non-vaccinates.3
See Table 4 and Table 5 below for more information.
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The publication included 21 different challenge studies, using genetically diverse heterologous PRRS isolates, and found that pigs vaccinated with INGELVAC PRRS MLV and INGELVAC PRRS ATP had significantly reduced incidence of lung lesions when compared to non-vaccinates (Table 5).3 These findings further demonstrate that sequence similarity between virus isolates is an unreliable way to predict cross-protective immunity.8,9 In addition, the pig challenge model used in these studies is still the gold standard for evaluating the expected level of a vaccine’s heterologous protection.
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References
1 Bates, T. Use of bioportal to characterize recently isolated wild-type PRRSV strains from the field. BIAH-HMC Ames, Iowa.
2 Patterson A, Haiwick G, Hermann J, et al. Efficacy of Ingelvac PRRS® modified-live virus vaccine against heterologous porcine reproductive and respiratory syndrome virus challenges. J Vaccines Vaccin 2019.10:407. Doi: 10. 35248/2157-7560.19.10.407.
3 Patterson A, Victoria J, Jordan D, et al. Modified-live PRRSV vaccination is efficacious following challenge with eight genetically diverse PRRSV isolates, in Proceedings. Allen D. Leman Swine Conf. 2013;194.
4 Stricker A, Polson D, Murtaugh M, et al. Variation in porcine reproductive and respiratory syndrome virus open reading frame 5 diagnostic sequencing. J Swine Health Prod 2015:23(1):18–27.
5 Polson D, Baker R, Philips R, et al. Distribution characteristics of PRRS virus ORF5 sequences in large production system applying intensive vaccination, in Proceedings. IPVS Cong 2008;2:134.
6 Murtaugh M, Faaberg K. How to interpret and use PRRSV sequence information, in Proceedings. Allen D. Leman Swine Conf. 2001;60-66.
7 Christopher-Hennings J, Faaberg K, Murtaugh M, et al. Porcine reproductive and respiratory syndrome (PRRS) diagnostics: interpretation and limitations. J Swine Health Prod 2002;10(5):213–218.
8 Murtaugh M. Use and interpretation of sequencing in PRRSV control programs, in Proceedings. Allen D. Leman Swine Conf. 2012;49–55. Available at: https://conservancy.umn.edu/bitstream/handle/11299/139321/1/Murtaugh.pdf. Accessed February 4, 2019.
9 Yeager M. NPB-funded research study. Iowa State University. 2014.
INGELVAC PRRS® is a registered trademark of Boehringer Ingelheim Vetmedica GmbH, used under license. ©2022 Boehringer Ingelheim Animal Health USA Inc., Duluth, GA. All Rights Reserved. US-POR-0129-2022