Studies on Heterologous Protection Between Japanese PRRSV-1 and PRRSV-2

. 2020 May 22.

 doi: 10.1292/jvms.20-0122. Online ahead of print.

Studies on Heterologous Protection Between Japanese Type 1 and Type 2 Porcine Reproductive and Respiratory Syndrome Virus Isolates

Hiroshi Iseki 1, Kenji Kawashima 1, Michihiro Takagi 1, Tomoyuki Shibahara 2 3, Masaji Mase 1 4

Affiliations

• 1Division of Viral Disease and Epidemiology, National Institute of Animal Health, National Agriculture and Food Research Organization.
• 2Division of Pathology and Pathophysiology, National Institute of Animal Health, National Agriculture and Food Research Organization.
• 3Department of Veterinary Science, Graduate School of Life and Environmental Sciences, Osaka Prefecture University.
• 4United Graduate School of Veterinary Sciences, Gifu University.

• PMID: 32448816
 
• DOI: 10.1292/jvms.20-0122

Abstract

The objective of the present study was to evaluate the cross-protective immunity between type 1 and type 2 porcine reproductive and respiratory syndrome virus (PRRSV) isolates in growing pigs. Japanese type 1 PRRSV, first isolated from a pig with respiratory disorders in a farm in 2009, exhibits unique genetic characteristics. The pathogenicity of a Japanese standard strain of type 2 PRRSV, EDRD1, in pigs immunized by the type 1 PRRSV isolate, Jpn EU 4-37 was determined by evaluating clinical signs, viremia, antibody response, and pathological lesions. Similarly, we evaluated the pathogenicity of Jpn EU 4-37 in pigs immunized by EDRD1 and compared the cross-protective immunity between these isolates. The EDRD1 challenge after Jpn EU 4-37 inoculation reduced viral clearance and shedding in pigs, compared to those treated with the EDRD1 single infection. On the other hand, the pathogenicity of Jpn EU 4-37 after EDRD1 infection did not differ significantly compared to non-immunized pigs treated with Jpn EU 4-37. Therefore, exposure to Jpn EU 4-37 could not induce enough immunity to reduce the viremia against subsequent infection by type 2 PRRSV. However, the immunity induced by Jpn EU 4-37 infection may play a role in reducing viremia caused by type 2 PRRSV. Moreover, the immunity induced by the EDRD1 and other genetically related viruses, which are broadly distributed in Japan, may not contribute to cross-protection against Jpn EU 4-37 as an emerging virus.

Keywords: immunity; pig; porcine reproductive and respiratory syndrome virus.

Practical Aspects of PRRSV Detection in Processing Fluids

. 2020 May 4;180:105021. doi: 10.1016/j.prevetmed.2020.105021.Online ahead of print. Practical Aspects of PRRSV RNA Detection in Processing Fluids Collected in Commercial Swine Farms
Will A López 1, Jeffrey J Zimmerman 2, Phillip C Gauger 2, Karen M Harmon 2, Laura Bradner 2, Min Zhang 3, Luis Giménez-Lirola 2, Alejandro Ramirez 2, Jean Paul Cano 1, Daniel C L Linhares 4

• 1

• Veterinary Diagnostic and Production Animal Medicine Department, College of Veterinary Medicine, Iowa State University, Lloyd Veterinary Medical Center, 1809 S Riverside Dr., Ames, IA 50011-3619, United States; PIC North America, 100 Bluegrass Commons Blvd #2200, Hendersonville, TN 37075, United States.

• 2

• Veterinary Diagnostic and Production Animal Medicine Department, College of Veterinary Medicine, Iowa State University, Lloyd Veterinary Medical Center, 1809 S Riverside Dr., Ames, IA 50011-3619, United States.

• 3

• Department of Statistics, College of Liberal Arts and Sciences, Iowa State University, Ames, Iowa 50011, United States.

• 4

• Veterinary Diagnostic and Production Animal Medicine Department, College of Veterinary Medicine, Iowa State University, Lloyd Veterinary Medical Center, 1809 S Riverside Dr., Ames, IA 50011-3619, United States. Electronic address: linhares@iastate.edu.

• PMID: 32428814
 
• DOI: 10.1016/j.prevetmed.2020.105021

Abstract

Processing fluid samples are easily collected under field conditions and provide the means to test more piglets more frequently in a practical way, thereby improving PRRSV surveillance. However, a deeper understanding of the diagnostic characteristics of this newly described sample type is still required. Therefore, the objective of this field-based study was to determine the relationship between viremic piglets and the detection of PRRSV RNA in processing fluid samples. In two PRRSV-positive breeding herds, processing fluids (n = 77) and individual piglet serum samples (n = 834) were collected from 77 litters in three sampling events and tested for PRRSV RNA. Among the 77 litters in the study, 55 litters (71.4%) contained no viremic piglets and processing fluids tested negative for PRRSV RNA. Among the 22 (28.6%) litters with ≥1 viremic piglets, 10 litters contained a single viremic piglet and 5 of the 10 processing fluids from this group tested positive for PRRSV RNA. Based on a fitted mixed effects logistic regression model, the probability of detecting PRRSV RNA in processing fluids was highly dependent on the number of viremic piglets contributing to the sample. When the within-litter prevalence was ≥39%, the probability of detecting PRRSV RNA in processing fluids was ≥95%. By extension, the results suggest that pooling processing fluids from several litters increases the probability of PRRSV RNA detection because of the greater likelihood of including multiple litters each with ≥1 viremic piglets. In contemporary breeding herds that use processing fluid samples for PRRSV surveillance, the diagnostic costs associated with testing 100% of the processing-age piglet population can be estimated at €0.077 ($0.086 USD) per pig weaned. In contrast, to achieve an equivalent testing coverage with the use of individual piglet serum samples, the diagnostic costs associated would be €4.48 ($5.00 USD) per pig weaned. Processing fluid represents a practical, reliable and efficient method to surveil breeding herds for PRRSV because it allows for continuous surveillance at a low cost.

Keywords: Monitoring; PRRS virus; Processing fluids; Surveillance; Swine.

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