Investigation of pseudorabies virus latency in nervous tissues of seropositive pigs exposed to field strain

Prevalence of viral agents causing swine reproductive failure in Korea and the development of multiplex real-time PCR and RT-PCR assays

This study aimed to investigate the prevalence of viral agents causing reproductive failure in pigs in Korea. In addition, two types of multiplex real-time PCR (mqPCR) were developed for the simultaneous detection of Aujeszky's disease virus (ADV) and porcine parvovirus (PPV) in mqPCR and encephalomyocarditis virus (EMCV) and Japanese encephalitis virus (JEV) in reverse transcription mqPCR (mRT-qPCR). A total of 150 aborted fetus samples collected from 2020 to 2022 were analyzed. Porcine reproductive and respiratory syndrome virus was the most prevalent (49/150 32.7%), followed by porcine circovirus type 2 (31/150, 20.7%), and PPV1 (7/150, 4.7%), whereas ADV, EMCV, and JEV were not detected. The newly developed mqPCR and mRT-qPCR could simultaneously detect and differentiate with high sensitivities and specificities. When applied to aborted fetuses, the newly developed mqPCR for PPV was 33.3% more sensitivities than the previously established diagnostic method. Amino acid analysis of the VP2 sequences of PPV isolates revealed considerable similarity to the highly pathogenic Kresse strain. This study successfully evaluated the prevalence of viral agents causing reproductive failure among swine in Korea, the developed mqPCR and mRT-qPCR methods could be utilized as effective and accurate diagnostic methods for the epidemiological surveillance of ADV, PPV, EMCV, and JEV.

A total infectome approach to understand the etiology of infectious disease in pigs

BACKGROUND

The global pork industry is continuously affected by infectious diseases that can result in large-scale mortality, trade restrictions, and major reductions in production. Nevertheless, the cause of many infectious diseases in pigs remains unclear, largely because commonly used diagnostic tools fail to capture the full diversity of potential pathogens and because pathogen co-infection is common.

RESULTS

We used a meta-transcriptomic approach to systematically characterize the pathogens in 136 clinical cases representing different disease syndromes in pigs, as well as in 12 non-diseased controls. This enabled us to simultaneously determine the diversity, abundance, genomic information, and detailed epidemiological history of a wide range of potential pathogens. We identified 34 species of RNA viruses, nine species of DNA viruses, seven species of bacteria, and three species of fungi, including two novel divergent members of the genus Pneumocystis. While most of these pathogens were only apparent in diseased animals or were at higher abundance in diseased animals than in healthy animals, others were present in healthy controls, suggesting opportunistic infections. Importantly, most of the cases examined here were characterized by co-infection with more than two species of viral, bacterial, or fungal pathogens, some with highly correlated occurrence and abundance levels. Examination of clinical signs and necropsy results in the context of relevant pathogens revealed that a multiple-pathogen model was better associated with the data than a single-pathogen model was.

CONCLUSIONS

Our data demonstrate that most of the pig diseases examined were better explained by the presence of multiple rather than single pathogens and that infection with one pathogen can facilitate infection or increase the prevalence/abundance of another. Consequently, it is generally preferable to consider the cause of a disease based on a panel of co-infecting pathogens rather than on individual infectious agents. Video abstract.

CRISPR/Cas9-mediated 2-sgRNA cleavage facilitates pseudorabies virus editing

Several groups have used CRISPR/Cas9 (clustered regularly interspaced short palindromic repeats/CRISPR-associated protein 9) for DNA virus editing. In most cases, one single-guide RNA (sgRNA) is used, which produces inconsistencies in gene editing. In this study, we used a swine herpesvirus, pseudorabies virus, as a model to systematically explore the application of CRISPR/Cas9 in DNA virus editing. In our current report, we demonstrated that cotransfection of 2 sgRNAs and a viral genome resulted in significantly better knockout efficiency than the transfection-infection-based approach. This method could result in 100% knockout of ≤3500 bp of viral nonessential large fragments. Furthermore, knockin efficiency was significantly improved by using 2 sgRNAs and was also correlated with the number of background viruses. We also demonstrated that the background viruses were all 2-sgRNA-mediated knockout mutants. Finally, this study demonstrated that the efficacy of gene knockin is determined by the replicative kinetics of background viruses. We propose that CRISPR/Cas9 coupled with 2 sgRNAs creates a powerful tool for DNA virus editing and offers great potential for future applications.-Tang, Y.-D., Guo, J.-C., Wang, T.-Y., Zhao, K., Liu, J.-T., Gao, J.-C., Tian, Z.-J., An, T.-Q., Cai, X.-H. CRISPR/Cas9-mediated 2-sgRNA cleavage facilitates pseudorabies virus editing.

An inactivated gE-deleted pseudorabies vaccine provides complete clinical protection and reduces virus shedding against challenge by a Chinese pseudorabies variant

Background

Since the end of 2011 an outbreak of pseudorabies affected Chinese pig herds that had been vaccinated with the commercial vaccine made of Bartha K61 strain. It is now clear that the outbreak was caused by an emergent PRV variant. Even though vaccines made of PRV Bartha K61 strain can confer certain cross protection against PRV variants based on experimental data, less than optimal clinical protection and virus shedding reduction were observed, making the control or eradication of this disease difficult.

Results

An infectious clone of PRV AH02LA strain was constructed to generate a gE deletion mutant PRV(LA-A^B) strain. PRV(LA-A^B) strain can reach a titer of 10^8.43 TCID₅₀ /mL (50% tissue culture infectious dose) on BHK-21 cells. To evaluate the efficiency of the inactivated vaccine made of PRV(LA-A^B) strain, thirty 3-week-old PRV-negative piglets were divided randomly into six groups for vaccination and challenge test. All five piglets in the challenge control showed typical clinical symptoms of pseudorabies post challenge. Sneezing and nasal discharge were observed in four and three piglets in groups C(vaccinated with inactivated PRV Bartha K61 strain vaccine) and D(vaccinated with live PRV Bartha K61 strain vaccine) respectively. In contrast, piglets in both groups A(vaccinated with inactivated PRV LA-AB strain vaccine) and B(vaccinated with inactivated PRV LA-A^B strain vaccine with adjuvant) presented mild or no clinical symptoms. Moreover, viral titers detected via nasal swabs were approximately 100 times lower in group B than in the challenge control, and the duration of virus shedding (3–4 days) was shorter than in either the challenge control (5–10 days) or groups C and D (5–6 days).

Conclusions

The infectious clone constructed in this study harbors the whole genome of the PRV variant AH02LA strain. The gE deletion mutant PRV(LA-A^B)strain generated from PRV AH02LA strain can reach a high titer on BHK-21 cells. An inactivated vaccine of PRV LA-A^B provides clinical protection and significantly reduces virus shedding post challenge, especially if accompanied by the adjuvant CVC1302. While Inactivated or live vaccines made of PRV Barth K61 strain can provide only partial protection in this test.

Aujeszky's disease in red fox (Vulpes vulpes): phylogenetic analysis unravels an unexpected epidemiologic link

We describe Aujeszky's disease in a female of red fox (Vulpes vulpes). Although wild boar (Sus scrofa) would be the expected source of infection, phylogenetic analysis suggested a domestic rather than a wild source of virus, underscoring the importance of biosecurity measures in pig farms to prevent contact with wild animals.

Neuroinflammation resulting from covert brain invasion by common viruses - a potential role in local and global neurodegeneration

Neurodegenerative diseases are a horrendous burden for their victims, their families, and society as a whole. For half a century scientists have pursued the hypothesis that these diseases involve a chronic viral infection in the brain. However, efforts to consistently detect a specific virus in brains of patients with such diseases as Alzheimer's or multiple sclerosis have generally failed. Neuropathologists have become increasingly aware that most patients with neurodegenerative diseases demonstrate marked deterioration of the brain olfactory bulb in addition to brain targets that define the specific disease. In fact, the loss of the sense of smell may precede overt neurological symptoms by many years. This realization that the olfactory bulb is a common target in neurodegenerative diseases suggests the possibility that microbes and/or toxins in inhaled air may play a role in their pathogenesis. With regard to inhaled viruses, neuropathologists have focused on those viruses that infect and kill neurons. However, a recent study shows that a respiratory virus with no neurotropic properties can rapidly invade the mouse olfactory bulb from the nasal cavity. Available data suggest that this strain of influenza is passively transported to the bulb via the olfactory nerves (mechanism unknown), and is taken up by glial cells in the outer layers of the bulb. The infected glial cells appear to be activated by the virus, secrete proinflammatory cytokines, and block further spread of virus within the brain. At the time that influenza symptoms become apparent (15 h post-infection), but not prior to symptom onset (10 h post-infection), proinflammatory cytokine-expressing neurons are increased in olfactory cortical pathways and hypothalamus as well as in the olfactory bulb. The mice go on to die of pneumonitis with severe acute phase and respiratory disease symptoms but no classical neurological symptoms. While much remains to be learned about this intranasal influenza-brain invasion model, it suggests the hypothesis that common viruses encountered in our daily life may initiate neuroinflammation via olfactory neural networks. The numerous viruses that we inhale during a lifetime might cause the death of only a few neurons per infection, but this minor damage would accumulate over time and contribute to age-related brain shrinkage and/or neurodegenerative diseases. Elderly individuals with a strong innate inflammatory system, or ongoing systemic inflammation (or both), might be most susceptible to these outcomes. The evidence for the hypothesis that common respiratory viruses may contribute to neurodegenerative processes is developed in the accompanying article.

The cytotoxicity to leukemia cells and antiviral effects of Isatis indigotica extracts on pseudorabies virus

AIM OF THE STUDY

Isatis indigotica (I. indigotica), Cruciferae, has been used in Chinese medicine for anti-leukemia and anti-severe acute respiratory syndrome (SARS). The aim of this study was to evaluate the cytotoxicity of Isatis indigotica extracts on human leukemia cell line (HL-60) and the antiviral activity on swine pseudorabies virus (PrV) in in vitro assays.

MATERIALS AND METHODS

Extracts and derived fractions of Isatis indigotica were prepared from root (R) and leaf (L) using methanol (M), ethyl acetate (E) and distilled water (D). The cytotoxic effect of extracts on swine peripheral blood mononuclear cells (PBMCs) and HL-60 was assessed by MTT method. The cytopathic effect (CPE) reduction, plaque reduction and inhibition assays on viral replication, and virucidal activity were further conducted to investigate the anti-PrV activity.

RESULTS

Indirubin, one of the biological active compounds of Isatis indigotica, had the most significant cytotoxicity on HL-60 cells and inhibitory effect on PrV replication. Extracts from roots and leaves of Isatis indigotica also presented CPE inhibition either before or after infection of PrV on porcine kidney (PK-15) cells. Leaf extracts had better virucidal activity than roots, and ethyl acetate extracts exhibited the highest efficacy among extracts tested.

CONCLUSION

Isatis indigotica posses a valuable virucidal effect in disease control of pseudorabies virus infection in swine.