Unusual severe cases of type 1 porcine reproductive and respiratory syndrome virus (PRRSV) infection in conventionally reared pigs in South Korea

Recent Progress in Studies of Porcine Reproductive and Respiratory Syndrome Virus 1 in China

Due to the high incidence of PRRSV mutation and recombination, PRRSV infection is difficult to prevent and control in China and worldwide. Two species of PRRSV, Betaarterivirus suid 1 (PRRSV-1) and Betaarterivirus suid 2 (PRRSV-2), exist in China, and PRRSV-1 has always received less attention in China. However, the number of PRRSV-1 strains detected in China has increased recently. To date, PRRSV-1 has spread to more than 23 regions in China. Based on the phylogenetic analysis of ORF5 and the whole genome of PRRSV-1, Chinese PRRSV-1 can be divided into at least seven independent subgroups. Among them, BJEU06-1-like has become the mainstream subgroup in some regions of China. This subgroup of strains has a 5-aa (4 + 1) characteristic discontinuous deletion pattern at aa 357~aa 360 and aa 411 in Nsp2. Previous studies have indicated that the pathogenicity of PRRSV-1 in China is mild, but recent studies found that the pathogenicity of PRRSV-1 was enhanced in China. Therefore, the emergence of PRRSV-1 deserves attention, and the prevention and control of PRRSV-1 infection in China should be strengthened. PRRSV infection is usually prevented and controlled by a combination of virus monitoring, biosafety restrictions, herd management measures and vaccination. However, the use of PRRSV-1 vaccines is currently banned in China. Thus, we should strengthen the monitoring of PRRSV-1 and the biosafety management of pig herds in China. In this review, we summarize the prevalence of PRRSV-1 in China and clarify the genomic characteristics, pathogenicity, vaccine status, and prevention and control management system of PRRSV-1 in China. Consequently, the purpose of this review is to provide a basis for further development of prevention and control measures for PRRSV-1.

Genomic Characterization and Pathogenicity of BJEU06-1-Like PRRSV-1 ZD-1 Isolated in China

Porcine reproductive and respiratory syndrome virus (PRRSV)-1 and PRRSV-2 have long been cocirculating in China. To date, all PRRSV-1 strains in China have been classified as subtype 1. We investigated the prevalence of PRRSV-1 in several areas of China from 2016 to 2022 and found that BJEU06-1-like strains comprised the main epidemic branch of PRRSV-1. Pathogenicity data for this subgroup are currently lacking. In this study, the Chinese BJEU06-1-like PRRSV-1 strain ZD-1 was isolated from primary alveolar macrophages (PAMs). ZD-1 has undergone no recombination and has a 5-aa discontinuous deletion in the Nsp2 protein, similar to other BJEU06-1-like strains; additionally, ZD-1 has a 26 aa C-terminal truncation in the GP3 gene. Pathogenicity studies revealed that ZD-1 causes obvious clinical symptoms: prolonged fever; reduced body weight; alveolar epithelial proliferation and moderate alveolar diaphragm widening in the lungs; diffuse lymphocytic hyperplasia in the lymph nodes; high levels of viremia in the serum; and elevated viral loads in the lungs, lymph nodes, and tonsils. These results suggested that the BJEU06-1-like PRRSV-1 strain ZD-1 is moderately pathogenic to piglets. This is the first study to evaluate the pathogenicity of the BJEU06-1-like branch in China, enriching the understanding of PRRSV-1 in China.

Postweaning mortality in commercial swine production II: review of infectious contributing factors

Postweaning mortality is extremely complex with a multitude of noninfectious and infectious contributing factors. In the current review, our objective is to describe the current state of knowledge regarding infectious causes of postweaning mortality, focusing on estimates of frequency and magnitude of effect where available. While infectious mortality is often categorized by physiologic body system affected, we believe the complex multifactorial nature is better understood by an alternative stratification dependent on intervention type. This category method subjectively combines disease pathogenesis knowledge, epidemiology, and economic consequences. These intervention categories included depopulation of affected cohorts of animals, elimination protocols using knowledge of immunity and epidemiology, or less aggressive interventions. The most aggressive approach to control infectious etiologies is through herd depopulation and repopulation. Historically, these protocols were successful for Actinobacillus pleuropneumoniae and swine dysentery among others. Additionally, this aggressive measure likely would be used to minimize disease spread if either a foreign animal disease was introduced or pseudorabies virus was reintroduced into domestic swine populations. Elimination practices have been successful for Mycoplasma hyopneumoniae, porcine reproductive and respiratory syndrome virus, coronaviruses, including transmissible gastroenteritis virus, porcine epidemic diarrhea virus, and porcine deltacoronavirus, swine influenza virus, nondysentery Brachyspira spp., and others. Porcine circovirus type 2 can have a significant impact on morbidity and mortality; however, it is often adequately controlled through immunization. Many other infectious etiologies present in swine production have not elicited these aggressive control measures. This may be because less aggressive control measures, such as vaccination, management, and therapeutics, are effective, their impact on mortality or productivity is not great enough to warrant, or there is inadequate understanding to employ control procedures efficaciously and efficiently. Since there are many infectious agents and noninfectious contributors, emphasis should continue to be placed on those infectious agents with the greatest impact to minimize postweaning mortality.

Comparison of four commercial PRRSV MLV vaccines in herds with co-circulation of PRRSV-1 and PRRSV-2

The efficacy of four commercial porcine reproductive and respiratory syndrome virus (PRRSV) modified-live virus (MLV) vaccines against respiratory disease was evaluated and compared in pig farms suffering from co-infection with PRRSV-1 and PRRSV-2. All vaccinated groups on average exhibited improved growth rate compared to the unvaccinated pigs. Interestingly, the two groups vaccinated with either of the PRRSV-2 MLV vaccines had a better overall growth rate compared to the pigs vaccinated with either of the PRRSV-1 MLV vaccines. Vaccination of pigs with either of the PRRSV-1 MLV vaccines did not result in reduction of PRRSV-1 or PRRSV-2 viremia whereas vaccination of pigs with either of the PRRSV-2 MLV vaccines resulted in the reduction of PRRSV-2 viremia only. Taken together, the results of this field study demonstrate that a PRRSV-2 MLV vaccine can be efficacious against respiratory disease caused by co-infection with PRRSV-1 and PRRSV-2.

Phylogeographic analysis of porcine reproductive and respiratory syndrome virus 1 in Guangdong province, Southern China

Porcine reproductive and respiratory syndrome virus (PRRSV) is considered an important economic pathogen for the international swine industry. At present, both PRRSV-1 and PRRSV-2 have been confirmed to be co-circulating in China. However, there is little available information about the prevalence or distribution of PRRSV-1 in Guangdong province, southern China. In this study, we performed molecular detection of PRRSV-1 in 750 samples collected from 50 farms in 15 major pig farming regions in this province. After RT-PCR testing, 64% (32/50) of farms were confirmed as PRRSV-1-positive. Surprisingly, PRRSV-1 was circulating on at least one pig farm in all 15 regions; of the 750 samples, 186 samples (24.8%) were positive for PRRSV-1. Furthermore, 15 representative PRRSV-1 ORF5 sequences (606 bp) (n = 1 per region) were obtained from those PRRSV-1-positive regions. Sequence alignment analysis indicated that they shared 81.8% ~ 100% nucleotide and 81.2% ~ 100% amino acid similarity with each other. Although all current PRRSV-1 sequences were divided into pandemic subtype 1, most of them had unique glycoprotein-5 amino acid sequences that are significantly different from other known PRRSV-1 isolates. To conclude, the present findings revealed wide geographical distribution of PRRSV-1 in Guangdong province, southern China. This study further extends the epidemiological significance of PRRSV-1 in China.

Pathogenic Characterization of European Genotype Porcine Reproductive and Respiratory Syndrome Virus Recently Isolated in Mainland China

BACKGROUND

Porcine reproductive and respiratory syndrome virus (PRRSV) is an important pathogen in pig that causes tremendous economic loss in the global swine industry. PRRSV is divided into the European and North American genotypes, with virulence ranging from apathogenic-moderately virulent to highly pathogenic. The emergence of new highly virulent type 1 strains and coexistence of the two genotypes complicate the differential diagnosis, disease prevention, and control of PRRSV. Although the emergence of a novel type 1 PRRSV strain in mainland China was first confirmed in 2011, there is no information available concerning the pathogenesis of this strain.

OBJECTIVES

We sought to determine the pathogenesis of a newly emerged Chinese type 1 PRRSV strain HLJB1.

METHODS

Pigs were infected with HLJB1 and characterized using serological and histopathological tests.

RESULTS

HLJB1 infection induced transient chemosis, reddened conjunctiva, skin cyanosis, mild transient pyrexia, dyspnea, and tachypnea between 7 and 13 days post-infection. Gross pneumonic lesions were characterized by multifocal, tan-mottled areas. Lymph nodes and spleen were enlarged. Characteristic microscopic lesions consisted of pulmonary consolidation and alveolar septal thickening with red blood cell infiltration, depletion of splenic lymphocytes, and hyperplasia and activation of macrophage. No pigs infected with HLJB1 died during the experiment.

CONCLUSION

Our findings indicate that Chinese type I PRRSV strain HLJB1 caused classic PRRSV-specific lesions. As it caused lower viremia in pigs compared with other classic type 1 isolates, HLJB1 is less virulent than other type I strains.