Genetic and evolutionary analysis of emerging HoBi-like pestivirus

Highly pathogenic bovine viral diarrhea virus BJ-11 unveils genetic evolution related to virulence in calves

Bovine viral diarrhea virus (BVDV) is the causative agent of bovine viral diarrhea, which causes significant economic loss to the global livestock industry. Despite the widespread use of inactivated BVDV vaccines, highly pathogenic strains continue to emerge. In China, regional variations in BVDV subtypes, morbidities, and symptoms, however, only the BVDV 1a subtype vaccine is currently approved. Therefore, this study is to gain insight into the biological characteristics and genetic variation of BVDV strains prevalent in Beijing. Meanwhile, this will provide a theoretical foundation and technical support for the prevention and control of BVDV, as well as raise awareness of the potential for virulence enhancement caused by the unregulated use of BVDV vaccines. In this study, A BVDV strain, BJ-11, was isolated from calves that died of diarrhea and vaccinated of BVDV. To evaluate its virulence, newborn calves were experimentally infected with the BJ-11. Clinical signs included fever, diarrhea, bloody stools, anorexia, and death in some cases. A marked reduction in leukocyte and lymphocyte counts were observed, accompanied by an increase in neutrophil counts. Histopathological changes manifested as severe lung lesions. Phylogenetic analysis indicated that BJ-11 belongs to the BVDV 1b subtype, genetically closest to the JL-1 strain. Analysis of the E2 glycosylation site disappeared (298SYT) in one of the four common glycosylation sites in the BVDV-1, which has been reported to affect the ability of the virus to infect and an additional glycosylation site (122NGS). These results indicate that BJ-11 is a highly pathogenic strain evolved from a low-virulence ancestor and should be served as a challenge strain. Simultaneously, these results contribute to a broader understanding of BVDV and whether imperfect vaccination strategies lead to reversal of immunosuppressive virulence.

Genotypic analysis of a localised hotspot of Pestivirus A (BVDV-1) infections in Northern Ireland

BACKGROUND

Bovine viral diarrhoea (BVD) is caused by Pestivirus A and Pestivirus B. Northern Ireland (NI) embarked on a compulsory BVD eradication scheme in 2016, which continues to this day, so an understanding of the composition of the pestivirus genotypes in the cattle population of NI is required.

METHODS

This molecular epidemiology study employed 5' untranslated region (5'UTR) genetic sequencing to examine the pestivirus genotypes circulating in samples taken from a hotspot of BVD outbreaks in the Enniskillen area in 2019.

RESULTS

Bovine viral diarrhoea virus (BVDV)-1e (Pestivirus A) was detected for the first time in Northern Ireland, and at a high frequency, in an infection hotspot in Enniskillen in 2019. There was no evidence of infection with BVDV-2 (Pestivirus B), Border disease virus (pestivirus D) or HoBi-like virus/BVDV-3 (pestivirus H).

LIMITATIONS

Only 5'UTR sequencing was used, so supplementary sequencing, along with phylogenetic trees that include all BVDV-1 genotype reference strains, would improve accuracy. Examination of farm locations and animal movement/trade is also required.

CONCLUSIONS

Genotype BVDV-1e was found for the first time in Northern Ireland, indicating an increase in the genetic diversity of BVDV-1, which could have implications for vaccine design and highlights the need for continued pestivirus genotypic surveillance.

Analysis for codon usage bias in membrane anchor of nonstructural protein 5A from BVDV

The nonstructural protein 5A (NS5A) of the bovine viral diarrhea virus (BVDV) is a monotopic membrane protein. This protein can anchor to the cell membrane by an in-plane amphipathic ⍺-helix, which participates in the viral replication complex. In this study, the effects of synonymous codon usage pattern of NS5A and the overall transfer RNA (tRNA) abundance in cells on the formation of the in-plane membrane anchor of NS5A were analyzed, based on NS5A coding sequences of different BVDV genotypes. BVDV NS5A coding sequences represent the most potential for BVDV genotyping. Moreover, the nucleotide usage of BVDV NS5A dominates the genotype-specific pattern of synonymous codon usage. There is an obvious relationship between synonymous codon usage bias and the spatial conformation of the in-plane membrane anchor. Furthermore, the overall tRNA abundance profiling displays that codon positions with a high level of tRNA abundance are more than ones with a low level of tRNA abundance in the in-plane membrane anchor, implying that high translation speed probably acts on the spatial conformation of in-plane membrane anchor of BVDV NS5A. These results give a new opinion on the effect of codon usage bias in the formation of the in-plane membrane anchor of BVDV NS5A.

Whole-Genome-Sequence-Based Evolutionary Analyses of HoBi-like Pestiviruses Reveal Insights into Their Origin and Evolutionary History

HoBi-like pestivirus (HoBiPeV), classified under Pestivirus H species, is an emerging cattle pathogen of high economic impact. However, the origin and evolution of HoBiPeV are not very clear due to a lack of full genomic sequences from diverse clades. This study aimed to determine full-genome sequences of HoBiPeV strains of three novel clades (c, d and e) and perform full-genome-based genetic and evolutionary analyses. Bayesian phylogenetic analyses herein confirmed the existence and independent evolution of four main HoBiPeV clades (a, c, d and e) globally, with genetic divergence ranging from 13.0% to 18.2%. Our Bayesian molecular clock estimates revealed that HoBiPeV most likely originated in India, with a dated tMRCA of 1938 (1762–2000), evidencing a more recent origin of HoBiPeV. The evolution rate of HoBiPeV was estimated to be 2.133 × 10−3 subs/site/year at full-genome level but varied widely among individual genes. Selection pressure analyses identified most of the positively selected sites in E2. Additionally, 21.8% of the ORF codon sites were found under strong episodic diversifying selection, providing first evidence of negative selection in HoBiPeV evolution. No recombination event was evident for HoBiPeV-c, d and e strains. These findings provide new insights into HoBiPeV origin and evolutionary history for better understanding the epidemiology and host–pathogen interactions and stimulate vaccine research.

HoBi-like Pestivirus Is Highly Prevalent in Cattle Herds in the Amazon Region (Northern Brazil)

Pestiviruses are globally distributed and cause substantial economic losses to the cattle industry. In Brazil, the country with the world's largest cattle population, pestivirus infections are well described in some regions, such as in the south, where a high frequency of BVDV-2 is described and contrasts with the high prevalence of HoBi-like pestivirus (HoBiPeV) in the northeast. However, there is a lack of information about pestiviruses in the Amazon Region, in northern Brazil, with a cattle population estimated at 55.7 million head, which has a significant impact on the international livestock market. Therefore, this study investigated the seroprevalence and genetic variability of ruminant pestiviruses in 944 bovine serum samples from four states in northern Brazil: Pará (PA), Amapá (AP), Roraima (RR), and Amazonas (AM). Our results showed that 45.4% of the samples were seropositive (19.8% for BVDV-1, 14.1% for BVDV-2, and 20.9% for HoBiPeV). All samples were tested by RT-qPCR, and three were positive and classified as HoBiPeV in a phylogenetic analysis. These serological and molecular results contrast with those from other regions of the world, suggesting that the northern Brazilian states have a high prevalence of all bovine pestiviruses including HoBiPeV.

Temporal and geographic dynamics of bovine viral diarrhea virus in American countries

Bovine viral diarrhea virus (BVDV) is a worldwide distributed pathogen of livestock classified into three species, BVDV-1 (Pestivirus A), BVDV-2 (Pestivirus B), and HoBi-like pestivirus (HoBiPeV; Pestivirus H). Despite being considered endemic in several regions of the Americas, the spatiotemporal distribution of BVDV is scarcely known. This study aimed to reconstruct the population dynamics of BVDV in American countries. The analyses performed with the partial 5´UTR gene showed that BVDV-1 and -2 would have started their diversification in the 1670s and 1790s in the United States, whereas HoBiPeV probably emerged in the 1980s in Brazil. No evident geographic clustering was observed in the Bayesian trees, which may indicate that multiple introductions events would have occurred following the first introduction. This study provides new insights into BVDV dynamics, although further analyses including sequences from other American countries and continents will help to expand the knowledge of BVDV evolution and transmission.

Non-structural proteins of bovine viral diarrhea virus

Bovine viral diarrhea virus (BVDV) belongs to the family Flaviviridae genus pestivirus. The viral genome is a single-stranded, positive-sense RNA that encodes four structural proteins (i.e., C, Erns, E1, and E2) and eight non-structural proteins (NSPs) (i.e., Npro, p7, NS2, NS3, NS4A, NS4B, NS5A, and NS5B). Cattle infected with BVDV exhibit a number of different clinical signs including diarrhea, abortion, and other reproductive disorders which have a serious impact on the cattle industry worldwide. Research on BVDV mainly focuses on its structural protein, however, progress in understanding the functions of the NSPs of BVDV has also been made in recent decades. The knowledge gained on the BVDV non-structural proteins is helpful to more fully understand the viral replication process and the molecular mechanism of viral persistent infection. This review focuses on the functions of BVDV NSPs and provides references for the identification of BVDV, the diagnosis and prevention of Bovine viral diarrhea mucosal disease (BVD-MD), and the development of vaccines.

A Serosurvey for Ruminant Pestivirus Exposure Conducted Using Sera From Stray Mexico Origin Cattle Captured Crossing Into Southern Texas

The US Department of Agriculture (USDA), Animal Plant Health Inspection Service (APHIS), Cattle Fever Tick Eradication Program (CFTEP) monitor a quarantine zone along the Texas border to prevent the introduction of stray livestock carrying cattle fever ticks entering the United States from Mexico. Stray cattle collected by CFTEP are checked for ticks and several infectious disease-causing pathogens, but not for bovine viral diarrhea virus (BVDV). BVDV is one of the most economically impactful viruses affecting US cattle producers. BVDV is present in all parts of the world, but it has been demonstrated that another distantly related pestivirus, HoBi-like pestivirus (HoBiPev), can also cause BVD. To date, HoBiPev has not been detected in the United States, but is commonly found in Brazil, and sporadically in Europe and Asia. The objective of the current study was to evaluate the seroprevalence of pestiviruses, with a specific focus on HoBiPev, in stray cattle. Virus neutralization (VN) assay was used to determine seroprevalence (or antibody titers) of BVDV-1, BVDV-2, and HoBiPev. Approximately 50% (67 of 134) of the samples were seropositive for pestiviruses; all 67 positive samples were positive (50%) for BVDV-1, 66 samples of the 67 were positive (49.3%) for BVDV-2, and the same 66 samples of the 67 were also positive (49.3%) for HoBiPev. Due to the antigenic cross-reactivity among Pestiviruses, the comparative antibody against each pestivirus was calculated from all VN-positive samples. Titers were clearly higher against BVDV-1, and only one sample had a titer clearly higher against BVDV-2. No sample had an antibody titer higher for HoBiPev, and while this does not prove the absence of HoBiPev, it does provide evidence that the prevalence of HoBiPev is less predominant than BVDV-1. Additionally, data from these samples provide evidence on the susceptibility of animals that may enter into the United States, with ~50% of the animals seronegative for bovine pestiviruses. This cattle population provides a unique opportunity to evaluate and monitor changes in seroprevalence of economically important cattle diseases affecting the cattle industry.