In vitro neutralization of HoBi-like viruses by antibodies in serum of cattle immunized with inactivated or modified live vaccines of bovine viral diarrhea viruses 1 and 2

Multivariate Analysis as a Method to Evaluate Antigenic Relationships between Bovine Viral Diarrhea Virus 1b Isolates and Vaccine Strains

The antigenicity of bovine viral diarrhea virus (BVDV) has been evaluated using virus-neutralizing titer data analyzed by principal component analysis (PCA) and has demonstrated numerous isolates to be antigenically divergent from US vaccine strains. The lack of BVDV-1b strains in currently licensed vaccines has raised concerns regarding the lack of protection against BVDV-1b field strains. The aim of this study was to evaluate the antigenic diversity of BVDV-1b strains and better understand the breadth of antigenic relatedness using BVDV-1b antisera and antisera from vaccine strains. Results from this analysis demonstrate the antigenic diversity observed among BVDV-1b isolates and genetic assignment into the BVDV-1b subgenotype is not representative of antigenic relatedness. This is demonstrated by BVDV-1b isolates (2280N, SNc, Illc, MSU, and 2337) observed to be as antigenically dissimilar as BVDV-2a isolates when using BVDV-1b antisera. Additionally, when BVDV-1a vaccine antisera was used for comparisons, a greater percentage of BVDV-1b isolates clustered with BVDV-1a vaccine strains as part of PC1, suggesting antigenic relatedness and potentially partial protection. Collectively, data from this study would suggest that while most BVDV-1b isolates are antigenically similar, there are antigenically dissimilar BVDV-1b isolates as determined by the lack of cross-reactivity, which may contribute to the lack of protection.

Immune phenotype is differentially affected by changing the type of bovine respiratory disease vaccine administered at revaccination in beef heifers

During preconditioning, modified-live vaccines are frequently administered to beef calves before weaning. In this study, we began to characterize the immune phenotype of calves that received a modified-live vaccination at 3-4 months of age and then either received the same modified-live or an inactivated vaccine upon arrival at the feedlot (weaning) and 28 days post-arrival (booster). Innate and adaptive immune measures were assessed before revaccination and 14 and 28 days post. Heifers that received three doses of the modified-live vaccine exhibited a relatively balanced immune response based on increases in mean cytokine concentrations (IL-17, IL-21) and total immunoglobulin-G (IgG) and subsets IgG1 and IgG2, which are related to both arms of the adaptive immune system. Conversely, heifers that received one dose of modified live and two doses of the inactivated vaccine had a more robust neutrophil chemotactic response and greater serum-neutralizing antibody titers, resulting in an enhanced innate immune and a skewed proinflammatory response. These results indicate that the revaccination protocol used after initial vaccination with a modified-live vaccine differentially influences the immune phenotype of beef calves, with three doses of modified live inducing potentially immune homeostasis and a combination of modified live and inactivated vaccines inducing a skewed immune phenotype. However, more research is needed to determine the protective efficacy of these vaccination protocols against disease.

Abortion outbreak in pregnant goats and cows with coinfection of 'Candidatus Mycoplasma haemobos' and HoBi-like pestivirus

New emerging diseases, including 'Candidatus Mycoplasma haemobos' ('Ca. M. haemobos') and HoBi-like pestivirus in central China has been a huge challenge for ruminant production. From July to September 2022, an abortion outbreak affected 14 goat farms and 11 cattle farms in this area. To investigate whether the two pathogens are associated with the disease, samples were collected: Group 1 included 55 goat blood samples with foetal tissue samples and ticks on the skin; Group 2 included nine healthy goat blood samples; Group 3 included 36 cow blood samples with foetal tissue samples and ticks on the skin; and Group 4 included seven healthy cow blood samples. Then, these samples were analysed by serology, PCR, sequence analysis, and identification. A total of 339 Rhipicephalus (Boophilus) microplus and 61 Haemaphysalis longicornis ticks were identified in Group 1 and Group 3. By molecular detection, 32 'Ca. M. haemobos'-positive amplicons, and 27 HoBi-like pestivirus-positive amplicons were amplified from goats in Group 1; meanwhile, 20 'Ca. M. haemobos'-positive amplicons, and 18 HoBi-like pestivirus-positive amplicons were amplified from foetuses. Statistical significance (P = 0.002) and association (OR=7.556) between the 'Ca. M. haemobos' PCR results of foetus and goat samples were observed, and statistical significance (P = 0.017) and association (OR=4.271) between the HoBi-like pestivirus PCR results of foetus and goat samples were observed. These significances and associations were also observed in Group 3. In addition, coinfections were detected in Group 1 and Group 3. 'Ca. M. haemobos' was detected in both tick species. Further serological results revealed that the frequency of HoBi-like pestivirus was 20.0 % (11/55) in Group 1 % and 30.6 % (11/36) in Group 3 in central China. No ticks, pathogens, or neutralizing antibodies were observed in Group 2 or Group 4. This is the first molecular evidence of 'Ca. M. haemobos' and HoBi-like pestivirus natural coinfections in goats and cows with abortion in China. HoBi-like pestivirus and 'Ca. M. haemobos' can be transferred from goats/cows to their foetuses.

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.

MicroRNA profiles for different tissues from calves challenged with Mycoplasma bovis or challenged with Mycoplasma bovis and bovine viral diarrhea virus

The objective was to determine differences in microRNAs (miRNAs) counts in several tissues of calves challenged with Mycoplasma bovis (M. bovis) or with M. bovis and bovine viral diarrhea virus (BVDV). Eight calves approximately 2 months of age were randomly assigned to three groups: Control (CT; n = 2), M. bovis (MB; n = 3), and Coinfection (CO; n = 3). On day 0, calves in CO were intranasally challenged with BVDV and calves in MB with M. bovis. On day 6, CO calves were challenged with M. bovis. Calves were euthanized 17 days post-challenge and serum (SER), white blood cells (WBC), liver (LIV), mesenteric (MLN) and tracheal-bronchial (TBLN) lymph nodes, spleen (SPL), and thymus (THY), were collected at necropsy. MiRNAs were extracted from each tissue from each calf. Significant (P< 0.01) differences in miRNAs expression were observed in SER, LIV, MLN, TBLN, SPL, and THY. There were no significant (P> 0.05) miRNAs in WBC. In SER, the CO group had levels of miR-1343-3p significantly higher than the CT and MB groups (P = 0.0071). In LIV and SPL, the CO group had the lowest counts for all significant miRNAs compared to CT and MB. In TBLN, the CT group had the highest counts of miRNAs, compared to MB and CO, in 14 of the 21 significant miRNAs. In THY, the CO group had the highest counts, in 4 of the 6 significant miRNAs compared to CT and MB. BVDV was associated with reduction of miRNAs in LIV, SPL, MLN, and TBLN, and M. bovis reduced counts of miRNAs in only TBLN. Measuring circulating miRNAs to assess disease condition or to develop intervention strategies to minimize respiratory diseases in cattle caused by BVDV or M. bovis will be of limited use unless an alternative approach is developed to use them as indicators of disease.

Congenital Neurological Disease Associated With HoBi-like Pestivirus Infection in a Newborn Dairy Calf From Brazil

HoBi-like pestivirus (HoBiPeV) has been reported in several biological samples from cattle worldwide, but there are no descriptions of this virus associated with neurological symptoms. This report described the first occurrence of neurological disease associated with HoBiPeV in a newborn dairy calf. A mixed-breed Holstein calf had severe neurological symptoms at birth and died at 21 days old. The tissue fragments (central nervous system (CNS), myocardium, liver, kidney, lung, intestine, and spleen) were submitted to reverse transcription (RT)–PCR assay for the partial 5'-untranslated region (5'UTR) and N-terminal autoprotease (Npro) gene of the pestivirus genome, and the CNS tissue fragments were submitted to histopathological and immunohistochemical evaluation. The RT–PCR assay indicated that the kidney, CNS, and intestinal tissue fragments were positive for the pestivirus 5'UTR, and the CNS and intestinal tissue fragments were positive for the pestivirus Npro gene. Amplicons with high DNA quantification in the 5'UTR (CNS—cerebral cortex) and Npro (CNS—cerebral cortex and intestine) RT–PCR assays were sequenced. The nucleotide (nt) sequence and phylogenetic analysis of the 5'UTR strain exhibited 93.6 to 99.4%, 85%, 89.4 to 89.9%, 85.1%, and 90.5 to 91.5% nt identity with HoBiPeV strains from clades a, b, c, d, and e, respectively. The Npro amplicons showed 99.7% nt identity to each other and 90.4 to 96.5%, 85.1 to 85.3%, 79.2 to 79.7%, and 85.8 to 86.5% nt identity with HoBiPeV strains from clades a, c, d, and e, respectively. A histopathology revealed neuronal necrosis at the cerebrum, cerebellum, and brain stem. An immunohistochemical assay designed to identify antigens of bovine viral diarrhea virus revealed positive intracytoplasmic immunoreactivity within neurons at the cerebral cortex, cerebrum, cerebellum, and spinal cord. Thus, this report provides information about the first identification of HoBiPeV in tissues of the CNS in a newborn dairy calf with neurological symptoms.

Epidemiology of Pestivirus H in Brazil and Its Control Implications

Along with viruses in the Pestivirus A (Bovine Viral Diarrhea Virus 1, BVDV1) and B species (Bovine Viral Diarrhea Virus 2, BVDV2), members of the Pestivirus H are mainly cattle pathogens. Viruses belonging to the Pestivirus H group are known as HoBi-like pestiviruses (HoBiPev). Genetic and antigenic characterization suggest that HoBiPev are the most divergent pestiviruses identified in cattle to date. The phylogenetic analysis of HoBiPev results in at least five subgroups (a–e). Under natural or experimental conditions, calves infected with HoBiPev strains typically display mild upper respiratory signs, including nasal discharge and cough. Although BVDV1 and BVDV2 are widely distributed and reported in many South American countries, reports of HoBiPev in South America are mostly restricted to Brazil. Despite the endemicity and high prevalence of HoBiPev in Brazil, only HoBiPev-a was identified to date in Brazil. Unquestionably, HoBiPev strains in BVDV vaccine formulations are required to help curb HoBiPev spread in endemic regions. The current situation in Brazil, where at this point only HoBiPev-a seems present, provides a more significant opportunity to control these viruses with the use of a vaccine with a single HoBiPev subtype. Despite the lack of differentiation among bovine pestiviruses by current BVDV tests, the reduced genetic variability of HoBiPev in Brazil may allow reliable identification of cases within the region. On the other hand, introducing foreign ruminants, biologicals, and genetic material to South America, especially if it originated from other HoBiPev-endemic countries, should consider the risk of introducing divergent HoBiPev subtypes.

Vaccination Failure in Eradication and Control Programs for Bovine Viral Diarrhea Infection

Vaccination against bovine viral diarrhea (BVD) is one of the key elements to protect cattle herds from this economically important disorder. Bovine viral diarrhea virus (BVDV) is a pestivirus infecting animals at all ages with significant impact on reproductive, digestive, and respiratory systems. Financial burden caused by this pathogen prompts many farmers to introduce vaccination as the control and prophylactic measure especially when persistently infected (PI) individuals, being the main source of the virus in the herd, are removed after test-and-cull approach. The aim of the study was to compare the serological response in cattle herds where new PI calves were identified without prior removal of PI animals or despite their removal and after the introduction of whole herd vaccination against BVDV infection. Overall seroprevalence in 5 vaccinated herds was 91.7 and 83.3% using ELISA and virus neutralization test, respectively. Despite high titers for both vaccine and field strains of BVDV in analyzed herds the analysis of comparative strength of neutralization indicated that 41.4% of positive samples did not have a predominant titer against one specific subtype of BVDV. In 3 herds BVDV-1b subtype was identified while in 2 others it was BVDV-1d, while the vaccine used was based on BVDV-1a which was never identified in Poland so far. To increase the success of the BVDV eradication program, a careful approach is suggested when planning herd vaccination. Comparison of existing field strains and their similarity with vaccine strains at antigenic and genetic levels can be a useful approach to increase the effectiveness of vaccination and efficient protection of fetuses from persistent infection.

Sequence analysis of the DA domain of glycoprotein E2 of pestiviruses isolated from beef cattle in Southern Brazil

The envelope glycoprotein E2 of pestiviruses is a major target for neutralizing antibodies. In this study, we analyzed the E2 DA domain of 43 pestiviruses from Southern Brazil. The isolates were identified as Bovine viral diarrhea virus (BVDV) subtypes 1a and 1b or BVDV-2b. Compared to reference strains, the BVDV-1 and -2 isolates had four and two mutations in the DA domain, respectively. All BVDV-2 isolates had a deletion of residues 724 and 725. All mutated amino acids in the BVDV isolates had the same aa substitution, and all were in previously identified antibody binding sites. It is possible that an immunity-mediated selection is acting on the pestiviruses circulating in Southern Brazil.

Multivariate analysis as a method to evaluate antigenic relationships between BVDV vaccine and field strains

Bovine viral diarrhea virus (BVDV) is comprised of two species, BVDV-1 and BVDV-2, but given the genetic diversity among pestiviruses, at least 21 subgenotypes are described for BVDV-1 and 4 for BVDV-2. Genetic characterization can be achieved through complete or partial sequencing and phylogeny, but antigenic characterization can be difficult to determine due to the antigenic diversity and cross-neutralization that exists among isolates. The traditional method for evaluating antigenic relationships between pestivirus isolates is the virus neutralization (VN) assay, but interpretation of the data to determine antigenic difference can be unclear. Data from this study utilized a multivariate analysis for visualization of VN results to analyze the antigenic relationships between vaccine strains and multiple field isolates. Polyclonal sera were generated against 6 BVDV strains currently contained in vaccine formulations, and each serum was used in VN's to measure the neutralizing antibody titers against 15 BVDV field isolates characterized as prevalent and divergent subgenotypes in the USA. Principal component analysis (PCA) were performed on the VN assay datasets, and results were interpreted from PCA clustering within the PCA dendrogram and scatter plot. The results demonstrated clustering patterns among isolates suggestive of antigenic differences. While expected, the BVDV-1 and BVDV-2 isolates did not cluster together and had the greatest spatial distribution. In addition, other BVDV isolates had distinct spatial patterns suggesting antigenically divergent isolates. This analysis provides an alternative and more efficient means to analyze large VN datasets to visualize antigenic relationships between pestivirus isolates. This analysis could be beneficial for vaccine development and evaluation of efficacy, since most vaccines cannot fully protect animals from the broad range diversity of BVDV viruses.

In vitro method to evaluate virus competition between BVDV-1 and BVDV-2 strains using the PrimeFlow RNA assay

Bovine viral diarrhea viruses (BVDV), segregated in BVDV-1 and BVDV-2 species, lead to substantial economic losses to the cattle industry worldwide. It has been hypothesized that there could be differences in level of replication, pathogenesis and tissue tropism between BVDV-1 and BVDV-2 strains. Thus, this study developed an in vitro method to evaluate virus competition between BVDV-1 and BVDV-2 strains. To this end the competitive dynamics of BVDV-1a, BVDV-1b, and BVDV-2a strains in cell cultures was evaluated by a PrimeFlow RNA assay. Similar results were observed in this study, as was observed in an earlier in vivo transmission study. Competitive exclusion was observed as the BVDV-2a strains dominated and excluded the BVDV-1a and BVDV-1b strains. The in vitro model developed can be used to identify viral variations that result in differences in frequency of subgenotypes detected in the field, vaccine failure, pathogenesis, and strain dependent variation in immune responses.

Serological survey for antibodies against pestiviruses in Wyoming domestic sheep

Pestiviruses including Bovine viral diarrhea virus type 1 (BVDV-1), BVDV-2 and Border disease virus (BDV) have been reported in both sheep and cattle populations, together with the HoBi-like, an emerging group of pestiviruses. Pestivirus control programs in the United States have focused on the control of BVDV-1 and 2. The incidence of pestivirus infection in sheep in the United States and the risk of transmission between cattle and sheep populations are unknown. The aim of this study was to perform serological surveillance for pestivirus exposure in sheep from an important sheep producing state in the Unites States, Wyoming. For this, sera from 500 sheep, collected across the state of Wyoming (US) in 2015-2016, were examined by comparative virus neutralization assay against four species/proposed species of pestiviruses: BVDV-1, BVDV-2, BDV and HoBi-like virus. Rates of exposure varied between geographic regions within the state. The overall pestivirus prevalence of antibodies was 5.6%. Antibodies were most frequently detected against BVDV-1 (4%), and the highest antibody titers were also against BVDV-1. Data from this study highlights understanding of the dynamics of sheep pestivirus exposure, consideration of reference strains used for VN assays, transmission patterns, and potential vaccination history should be taken into account in implementation of control measures against pestiviruses in sheep and for successful BVDV control programs in cattle.

Pestivirus infection in cattle dairy farms: E2 glycoprotein ELISA reveals the presence of bovine viral diarrhea virus type 2 in northwestern Italy

Background

Bovine viral diarrhea virus (BVDV) types 1 and 2 are members of the Pestivirus genus of the Flaviviridae family. This genus also includes the HoBi-like virus, tentatively classified as BVDV type 3. BVDV-1 is widely distributed in Italy despite the extensive use of BVDV-1-based vaccines, while BVDV-2 and HoBi-like Pestivirus have been detected occasionally. Monitoring the occurrence of sporadic or atypical pestiviruses is a useful approach to evaluate the need for additional vaccine strains that can be used in BVDV control programs.

Results

In this study we developed a multiwell antibody ELISA based on the recombinant E2 protein of the three bovine pestiviruses. We evaluated the assay’s applicability for surveillance purposes using pooled milk samples, each prepared from a maximum of 35 lactating cows and collected from 176 dairy herds. As expected, the majority of the pooled samples reacted to a greater extent against the BVDV-1 E2 antigen. All three milk pools from a single farm reacted to the BVDV-2 antigen, however. Further analysis using spot tests, antigen detection, and sequence analysis of the 5′-UTR region confirmed the presence of five persistently infected calves carrying a BVDV-2a strain.

Conclusions

This study highlights for the first time that sporadic circulation of BVDV-2 can be predicted by immunoenzymatic methods in the absence of specific vaccination.

Electronic supplementary material

The online version of this article (10.1186/s12917-017-1305-z) contains supplementary material, which is available to authorized users.

Complete Genome Sequence of a Hobi-Like Virus Isolated from a Nelore Cow with Gastroenteric Disease in the State of São Paulo, Brazil

The Hobi-like virus presents antigenic and molecular differences in relation to bovine virus diarrhea virus 1 and 2. The description of the complete genome of the Hobi-like virus SV757/15, isolated from a Nelore cow with gastroenteric disease in Brazil, will help in understanding the evolution and diversity of pestiviruses.

Genomic and antigenic relationships between two 'HoBi'-like strains and other members of the Pestivirus genus

'HoBi'-like viruses comprise a putative new species within the genus Pestivirus of the family Flaviviridae. 'HoBi'-like viruses have been detected worldwide in batches of fetal calf serum, in surveillance programs for bovine pestiviruses and from animals presenting clinical signs resembling bovine viral diarrhea virus (BVDV)-associated diseases. To date, few complete genome sequences of 'HoBi'-like viruses are available in public databases. Moreover, detailed analyses of such genomes are still scarce. In an attempt to expand data on the genetic diversity and biology of pestiviruses, two genomes of 'HoBi'-like viruses recovered from Brazilian cattle were described and characterized in this study. Analysis of the whole genome and antigenic properties of these two new 'HoBi'-like isolates suggest that these viruses are genetically close to recognized pestiviruses. The present data provide evidence that 'HoBi'-like viruses are members of the genus Pestivirus and should be formally recognized as a novel species.

A serosurvey for ruminant pestivirus exposure conducted using cattle sera collected for brucellosis surveillance in the United States

Four species of ruminant pestivirus are currently circulating in the United States: Bovine viral diarrhea virus 1 and 2 (BVDV-1, -2; predominant host: cattle), Border disease virus (BDV; predominant host: sheep), and pronghorn virus (sporadically detected in wild ruminants). A third bovine pestivirus called HoBi-like virus has been detected in cattle and water buffalo in South America, Asia, and Europe. To date, no isolations of HoBi-like viruses from U.S. cattle have been reported. To assess exposure, 2,000 cattle sera, collected between 2014 and 2015 as part of the U.S. brucellosis surveillance program, were tested for antibodies against BVDV-1, BVDV-2, and HoBi-like viruses. In addition, RNA was extracted and tested by reverse transcription-polymerase chain reaction for the presence of pestiviruses; all samples tested negative. The percent of VN-positive samples was 91.3% for BVDV-1, 89.3% for BVDV-2, and 84.9% for HoBi-like viruses. Because the 3 bovine pestiviruses are antigenically cross-reactive, the comparative level of antibody against each pestivirus species was determined. Based on comparative titers, samples were segregated into 6 categories: no titers (7.6%), titers clearly higher against BVDV-1 (22.2%), titers substantially higher against BVDV-2 (9.1%), BVDV-1 and BVDV-2 titers equivalent but substantially higher than HoBi titers (25.7%), titers substantially higher against HoBi-like viruses (0%), and equivocal (35.4%). Titers tended to be higher against BVDV-1 than BVDV-2. However, the overall percentage of animals with titers below levels considered protective against acute bovine pestivirus infection were ~11% for BVDV-1, 12% BVDV-2, and 18% for HoBi-like virus.

Detecção do virus ‘HoBi’-like (BVDV-3) em bovino no semiárido do Estado da Paraíba

RESUMO: Objetivou-se descrever os aspectos clínicos e anatomopatológicos, e a identificação viral de um caso de infecção pelo vírus ‘Hobi’-like (BVDV-3) em bovino do semiárido paraibano, Nordeste do Brasil. Um bovino, fêmea, três meses de idade, foi levado ao Hospital Veterinário da UFCG apresentando salivação, dificuldade de apreensão do teto, falta de apetite, fezes escuras e em pouca quantidade. Diante da piora do quadro clínico optou-se por sua eutanásia in extremis, seguida da realização da necropsia e coleta de material para histopatologia. Histologicamente, nas mucosas do trato digestivo, havia edema, degeneração balonosa, necrose e infiltrado inflamatório, que foi observado na face dorsal da língua e no seu epitélio mais profundo. A imunohistoquímica de amostras de extremidade de pavilhão auricular demonstrou marcação antigênica positiva e pela RT-PCR foi possível detectar RNA viral do BVDV no soro sanguíneo, cujo efeito citopático em células epiteliais de rim bovino da linhagem “Madin Darby bovine kidney” (MDBK) não foi observado. O sequenciamento do gene 5’NCR demonstrou que o vírus isolado estaria mais relacionado ao ‘Hobi’-like (BVDV-3). Após a confirmação do diagnóstico foram coletadas amostras de soro dos 23 animais do rebanho para sorologia por ELISA indireto, sendo constatada 69,6% (16/23) de soropositividade. A identificação deste novo caso de infecção por ‘Hobi’-like na Paraíba reafirma a necessidade de um monitoramento regular para BVDV na região para detecção precoce da infecção dos rebanhos e adoção de medidas eficazes de prevenção e controle.

Effects of Three Types of Inactivation Agents on the Antibody Response and Immune Protection of Inactivated IHNV Vaccine in Rainbow Trout

Infectious hematopoietic necrosis virus (IHNV) infects salmonid fish, resulting in high mortality and serious economic losses to salmonid aquaculture. Therefore, an effective IHNV vaccine is urgently needed. To select an inactivation agent for the preparation of an effective IHNV vaccine, rainbow trout were immunized with mineral oil emulsions of IHNV vaccines inactivated by formaldehyde, binary ethylenimine (BEI), or β-propiolactone (BPL). The fish were challenged 8 weeks after vaccination, and their IgM antibody response and relative percent survival (RPS) were evaluated. The results show that formaldehyde, BEI, and BPL abolished IHNV HLJ-09 infectivity within 24, 48, and 24 h at final concentrations of 0.2%, 0.02%, and 0.01%, respectively. The mean levels of specific IgM, both in serum and mucus (collected from the skin surface and gills), for the three immunized groups (from high to low) ranked as follows: the BPL group, BEI group, and formaldehyde group. From weeks 5 to 9, the mean log2 serum titers of IgM in the BPL group were significantly higher compared with those of the other groups (p < 0.05) during the 9 weeks of observation after vaccination (immunized at weeks 0 and6). Mucus OD490 values of the BPL group were significantly higher compared with those of the other groups (p < 0.05) when reaching their peak at weeks 5 and 8, but the difference between the formaldehyde and BEI groups was not significant (p > 0.05). The BPL-inactivated whole-virus vaccine had the greatest protective effect on the rainbow trout after challenge by an intraperitoneal injection of live IHNV, with an RPS rate of 91.67%, which was significantly higher compared with the BEI (83.33%) and formaldehyde (79.17%) groups. These results indicate that the BPL-inactivated IHNV oil-adjuvant vaccine was more effective than the formaldehyde- or BEI-inactivated vaccines. The results of this study provide an important foundation for further studies on inactivated IHNV vaccines.

Comparison of 'HoBi'-like viral populations among persistent infected calves generated under experimental conditions and to inoculum virus

Like other members from the Pestivirus genus, 'HoBi'-like pestiviruses cause economic losses for cattle producers due to both acute and persistent infections. The present study analyzed for the first time PI animals derived from a controlled infection with two different 'HoBi'-like strains where the animals were maintained under conditions where superinfection by other pestiviruses could be excluded. The sequence of the region coding for viral glycoproteins E1/E2 of variants within the swarms of viruses present in the PI calves and two viral inoculums used to generate them were compared. Differences in genetic composition of the viral swarms were observed suggesting that host factors can play a role in genetic variations among PIs. Moreover, PIs generated with the same inoculum showed amino acid substitutions in similar sites of the polyprotein, even in serum from PIs with different quasispecies composition, reinforcing that some specific sites in E2 are important for host adaptation.

Difficulties arising from the variety of testing schemes used for bovine viral diarrhoea virus (BVDV)

Globally, the eradication of bovine viral diarrhoea virus (BVDV) is still in its infancy, but eradication has been, or is being, adopted by several countries or regions. Comparisons between countries' schemes allow others to assess best practice, and aggregating published results from eradication schemes provides greater statistical power when analysing data. Aggregating data requires that results derived from different testing schemes be calibrated against one another. The authors aimed to evaluate whether relationships between published BVDV test results could be created and present the outcome of a systematic literature review following the Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines. The results are tabulated, providing a summary of papers where there is potential cross-calibration and a summary of the obstacles preventing such data aggregation. Although differences in measuring BVDV present barriers to academic progress, they may also affect progress within individual eradication schemes. The authors examined the time taken to retest following an initial antibody BVDV test in the Scottish eradication scheme. The authors demonstrate that retesting occurred quicker if the initial not negative test was from blood rather than milk samples. Such differences in the response of farmers/veterinarians to tests may be of interest to the design of future schemes.

Emerging pestiviruses infecting domestic and wildlife hosts

Until the early 1990 s there were just three recognized species in the pestivirus genus, bovine viral diarrhea virus (BVDV), border disease virus (BDV) and classical swine fever virus (CSFV). Subsequently BVDV were divided into two different species, BVDV1 and BVDV2 and four additional putative pestivirus species have been identified, based on phylogenetic analysis. The four putative pestivirus specices, listed in chronological order of published reports, are Giraffe (isolated from one of several giraffes in the Nanyuki District of Kenya suffering from mucosal disease-like symptoms), HoBi (first isolated from fetal bovine serum originating in Brazil and later from samples originating in Southeast Asia), Pronghorn (isolated from an emaciated blind pronghorn antelope in the USA), and Bungowannah (isolated following an outbreak in pigs, resulting in still birth and neonatal death, in Australia). In addition to the emergence of putative new species of pestivirus, changes in host and virulence of recognized or 'classic' pestiviruses have led to reevaluation of disease control programs and management of domestic and wildlife populations.

Impact of species and subgenotypes of bovine viral diarrhea virus on control by vaccination

Bovine viral diarrhea viruses (BVDV) are diverse genetically and antigenically. This diversity impacts both diagnostic testing and vaccination. In North America, there are two BVDV species, 1 and 2 with 3 subgentoypes, BVDV1a, BVDV1b and BVDV2a. Initially, US vaccines contained BVDV1a cytopathic strains. With the reporting of BVDV2 severe disease in Canada and the USA there was focus on protection by BVDV1a vaccines on BVDV2 disease. There was also emphasis of controlling persistently infected (PI) cattle resulted in studies for fetal protection afforded by BVDV1a vaccines. Initially, studies indicated that some BVDV1a vaccines gave less than 100% protection against BVDV2 challenge for fetal infection. Eventually vaccines in North America added BVDV2a to modified live virus (MLV) and killed BVDV1a vaccines. Ideally, vaccines should stimulate complete immunity providing 100% protection against disease, viremias, shedding, and 100% fetal protection in vaccinates when challenged with a range of diverse antigenic viruses (subgenotypes). There should be a long duration of immunity stimulated by vaccines, especially for fetal protection. MLV vaccines should be safe when given according to the label and free of other pathogens. While vaccines have now included BVDV1a and BVDV2a, with the discovery of the predominate subgenotype of BVDV in the USA to be BVDV1b, approximately 75% or greater in prevalence, protection in acute challenge and fetal protection studies became more apparent for BVDV1b. Thus many published studies examined protection by BVDV1a and BVDV2a vaccines against BVDV1b in acute challenge and fetal protection studies. There are no current BVDV1b vaccines in the USA. There are now more regulations on BVDV reproductive effects by the USDA Center for Veterinary Biologics (CVB) regarding label claims for protection against abortion, PI calves, and fetal infections, including expectations for studies regarding those claims. Also, the USDA CVB has a memorandum providing the guidance for exemption of the warning label statement against the use of the MLV BVDV in pregnant cows and calves nursing pregnant cows. In reviews of published studies in the USA, the results of acute challenge and fetal protection studies are described, including subgenotypes in vaccines and challenge strains and the results in vaccinates and the vaccinates' fetuses/newborns. In general, vaccines provide protection against heterologous strains, ranging from 100% to partial but statistically significant protection. In recent studies, the duration of immunity afforded by vaccines was investigated and reported. Issues of contamination remain, especially since fetal bovine serums may be contaminated with noncytopathic BVDV. In addition, the potential for immunosuppression by MLV vaccines exists, and new vaccines will be assessed in the future to prove those MLV components are not immunosuppressive by experimental studies. As new subgenotypes are found, the efficacy of the current vaccines should be evaluated for these new strains.

Generation of calves persistently infected with HoBi-like pestivirus and comparison of methods for detection of these persistent infections

The identification and elimination of persistently infected (PI) cattle are the most effective measures for controlling bovine pestiviruses, including bovine viral diarrhea virus (BVDV) and the emerging HoBi-like viruses. Here, colostrum-deprived calves persistently infected with HoBi-like pestivirus (HoBi-like PI calves) were generated and sampled (serum, buffy coat, and ear notches) on the day of birth (DOB) and weekly for 5 consecutive weeks. The samples were subjected to diagnostic tests for BVDV--two reverse transcriptase PCR (RT-PCR) assays, two commercial real-time RT quantitative PCR (RT-qPCR), two antigen capture enzyme-linked immunosorbent assays (ACE), and immunohistochemistry (IHC)--and to HoBi-like virus-specific RT-PCR and RT-qPCR assays. The rate of false negatives varied among the calves. The HoBi-like virus-specific RT-PCR detected HoBi-like virus in 83%, 75%, and 87% of the serum, buffy coat, and ear notch samples, respectively, while the HoBi-like RT-qPCR detected the virus in 83%, 96%, and 62%, respectively. In comparison, the BVDV RT-PCR test had a higher rate of false negatives in all tissue types, especially for the ear notch samples (missing detection in at least 68% of the samples). The commercial BVDV RT-qPCRs and IHC detected 100% of the ear notch samples as positive. While ACE based on the BVDV glycoprotein E(rns) detected infection in at least 87% of ear notches, no infections were detected using NS3-based ACE. The BVDV RT-qPCR, ACE, and IHC yielded higher levels of detection than the HoBi-like virus-specific assays, although the lack of differentiation between BVDV and HoBi-like viruses would make these tests of limited use for the control and/or surveillance of persistent HoBi-like virus infection. An improvement in HoBi-like virus tests is required before a reliable HoBi-like PI surveillance program can be designed.

Lack of evidence for the presence of emerging HoBi-like viruses in North American fetal bovine serum lots

The detection of an emerging pestivirus species, "HoBi-like virus," in fetal bovine serum (FBS) labeled as U.S. origin, but packaged in Europe, raised concerns that HoBi-like virus may have entered the United States. In the current study, 90 lots of FBS originating in North America (NA) were screened for pestivirus antigen and antibodies. Lots in group 1 (G1, 72 samples) and group 2 (G2, 9 samples) originated in NA and were packaged in the United States. Group 3 (G3) was composed of 9 lots collected in NA and processed in Europe. Lots in G1 were claimed negative for Bovine viral diarrhea virus (BVDV), while lots in G2 and G3 were claimed positive by the commercial processor. All lots in G1 and G2 tested negative by reverse transcription polymerase chain reaction (RT-PCR) using HoBi-like-specific primers. Two G1 lots tested positive by BVDV RT-PCR. One of these was also positive by virus isolation. All G2 lots were positive by BVDV RT-PCR. In addition, four G2 lots were VI positive while 1 lot was antigen-capture enzyme-linked immunosorbent assay (ELISA) positive. Two G3 lots were positive by HoBi-like-specific RT-PCR tests. All lots were negative for HoBi_D32/00 neutralizing antibodies. Seven lots (4 G1; 1 G2; 2 G3) had antibodies against BVDV by virus neutralization and/or antigen-capture ELISA. While there is no evidence of HoBi-like viruses in NA based on tested samples, further studies are required to validate HoBi-like virus-free status and develop means to prevent the spread of HoBi-like virus into NA.

Emerging animal viruses: real threats or simple bystanders?

The list of animal viruses has been frequently added of new members raising permanent concerns to virologists and veterinarians. The pathogenic potential and association with disease have been clearly demonstrated for some, but not for all of these emerging viruses. This review describes recent discoveries of animal viruses and their potential relevance for veterinary practice. Dogs were considered refractory to influenza viruses until 2004, when an influenza A virus subtype H3N8 was transmitted from horses and produced severe respiratory disease in racing greyhounds in Florida/USA. The novel virus, named canine influenza virus (CIV), is considered now a separate virus lineage and has spread among urban canine population in the USA. A new pestivirus (Flaviviridae), tentatively called HoBi-like pestivirus, was identified in 2004 in commercial fetal bovine serum from Brazil. Hobi-like viruses are genetically and antigenically related to bovine viral diarrhea virus (BVDV) and induce similar clinical manifestations. These novel viruses seem to be widespread in Brazilian herds and have also been detected in Southeast Asia and Europe. In 2011, a novel mosquito-borne orthobunyavirus, named Schmallenberg virus (SBV), was associated with fever, drop in milk production, abortion and newborn malformation in cattle and sheep in Germany. Subsequently, the virus disseminated over several European countries and currently represents a real treat for animal health. The origin of SBV is still a matter of debate but it may be a reassortant from previous known bunyaviruses Shamonda and Satuperi. Hepatitis E virus (HEV, family Hepeviridae) is a long known agent of human acute hepatitis and in 1997 was first identified in pigs. Current data indicates that swine HEV is spread worldwide, mainly associated with subclinical infection. Two of the four HEV genotypes are zoonotic and may be transmitted between swine and human by contaminated water and undercooked pork meat. The current distribution and impact of HEV infection in swine production are largely unknown. Avian gyrovirus type 2 (AGV2) is a newly described Gyrovirus, family Circoviridae, which was unexpectedly found in sera of poultry suspected to be infected with chicken anemia virus (CAV). AGV2 is closely related to CAV but displays sufficient genomic differences to be classified as a distinct species. AGV2 seems to be distributed in Brazil and also in other countries but its pathogenic role for chickens is still under investigation. Finally, the long time and intensive search for animal relatives of human hepatitis C virus (HCV) has led to the identification of novel hepaciviruses in dogs (canine hepacivirus [CHV]), horses (non-primate hepaciviruses [NPHV] or Theiler's disease associated virus [TDAV]) and rodents. For these, a clear and definitive association with disease is still lacking and only time and investigation will tell whether they are real disease agents or simple spectators.