Seroprevalence for severe fever with thrombocytopenia syndrome virus among the residents of Miyazaki, Japan: An epidemiological study

INTRODUCTION

Severe fever with thrombocytopenia syndrome (SFTS) is a tick-borne infectious disease caused by the SFTS virus (SFTSV). The Miyazaki Prefecture has the highest number of SFTS cases in Japan and requires countermeasures for prevention. In this study, we aimed to conduct an epidemiological survey in Miyazaki Prefecture to determine the exposure conditions of SFTSV by measuring the seroprevalence among residents of Miyazaki and to evaluate the factors that influence the endemicity of SFTS.

METHODS

The survey was conducted between June 2014 and April 2019 in all 26 municipalities in Miyazaki Prefecture. SFTSV antibodies were detected using an enzyme-linked immunosorbent assay in the blood samples of 6013 residents (3184 men and 2829 women). A questionnaire-based survey of the living environment was also conducted.

RESULTS

Multiple logistic regression analysis revealed that age and occupation were significant factors related to the proportion of participants with an optical density (OD) value > 0.2 and a seroprevalence of 0.9 % (54/6013). Seven seropositive individuals (0.1 %) with an OD value of >0.4 were identified (three men and four women, aged 54-69 years), and all were asymptomatic. One participant had a higher OD than the positive control.

CONCLUSION

Although SFTS is endemic in Miyazaki Prefecture, Japan, its seroprevalence is relatively low. Since some risk areas in Miyazaki prefecture have been identified, it is important to enhance awareness of SFTS in residences and reduce contact with ticks, especially in high-risk areas.

Multiple mutations of SARS-CoV-2 Omicron BA.2 variant orchestrate its virological characteristics

IMPORTANCE

Most studies investigating the characteristics of emerging SARS-CoV-2 variants have been focusing on mutations in the spike proteins that affect viral infectivity, fusogenicity, and pathogenicity. However, few studies have addressed how naturally occurring mutations in the non-spike regions of the SARS-CoV-2 genome impact virological properties. In this study, we proved that multiple SARS-CoV-2 Omicron BA.2 mutations, one in the spike protein and another downstream of the spike gene, orchestrally characterize this variant, shedding light on the importance of Omicron BA.2 mutations out of the spike protein.

Clec4A4 Acts as a Negative Immune Checkpoint Regulator to Suppress Antitumor Immunity

Clec4A4 is a C-type lectin receptor (CLR) exclusively expressed on murine conventional dendritic cells (cDC) to regulate their activation status. However, the functional role of murine Clec4A4 (mClec4A4) in antitumor immunity remains unclear. Here, we show that mClec4A4 serves as a negative immune checkpoint regulator to impair antitumor immune responses. Deficiency of mClec4A4 lead to a reduction in tumor development, accompanied by enhanced antitumor immune responses and amelioration of the immunosuppressive tumor microenvironment (TME) mediated through the enforced activation of cDCs in tumor-bearing mice. Furthermore, antagonistic mAb to human CLEC4A (hCLEC4A), which is the functional orthologue of mClec4A4, exerted protection against established tumors without any apparent signs of immune-related adverse events in hCLEC4A-transgenic mice. Thus, our findings highlight the critical role of mClec4A4 expressed on cDCs as a negative immune checkpoint molecule in the control of tumor progression and provide support for hCLEC4A as a potential target for immune checkpoint blockade in tumor immunotherapy.

An inhaled ACE2 decoy confers protection against SARS-CoV-2 infection in preclinical models

The Omicron variant continuously evolves under the humoral immune pressure exerted by vaccination and severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection, and the resulting Omicron subvariants display further immune evasion and antibody escape. An engineered angiotensin-converting enzyme 2 (ACE2) decoy composed of high-affinity ACE2 and an IgG1 Fc domain could offer an alternative modality to neutralize SARS-CoV-2. We previously reported its broad spectrum and therapeutic potential in rodent models. Here, we demonstrate that the engineered ACE2 decoy retains neutralization activity against Omicron subvariants, including the currently emerging XBB and BQ.1 strains, which completely evade antibodies currently in clinical use. SARS-CoV-2, under the suboptimal concentration of neutralizing drugs, generated SARS-CoV-2 mutants escaping wild-type ACE2 decoy and monoclonal antibodies, whereas no escape mutant emerged against the engineered ACE2 decoy. Furthermore, inhalation of aerosolized decoys improved the outcomes of rodents infected with SARS-CoV-2 at a 20-fold lower dose than that of intravenous administration. Last, the engineered ACE2 decoy exhibited therapeutic efficacy for cynomolgus macaques infected with SARS-CoV-2. These results indicate that this engineered ACE2 decoy represents a promising therapeutic strategy to overcome immune-evading SARS-CoV-2 variants and that liquid aerosol inhalation could be considered as a noninvasive approach to enhance the efficacy of COVID-19 treatments.

Development of droplet digital PCR for quantification of bovine leukemia virus proviral load using unpurified genomic DNA

Bovine leukemia virus (BLV) is the causative agent of a B-cell tumor called enzootic bovine leukosis. Preventing BLV spreading is required to reduce economic loss related to BLV infection of livestock. To quantify proviral load (PVL) more easily and rapidly, we developed a quantification system of PVL using droplet digital PCR (ddPCR). This method uses a multiplex TaqMan assay of the BLV provirus and housekeeping gene RPP30 for the quantification of BLV in BLV-infected cells. Furthermore, we combined ddPCR with DNA purification-free sample preparation (unpurified genomic DNA). The percentage of BLV-infected cells based on unpurified genomic DNA was highly correlated with that based on purified genomic DNA (correlation coefficient: 0.906). Thus, this new technique is a suitable method to quantify PVL of BLV-infected cattle in a large sample number.

Gut dysbiosis promotes the breakdown of oral tolerance mediated through dysfunction of mucosal dendritic cells

While dysbiosis in the gut is implicated in the impaired induction of oral tolerance generated in mesenteric lymph nodes (MesLNs), how dysbiosis affects this process remains unclear. Here, we describe that antibiotic-driven gut dysbiosis causes the dysfunction of CD11c⁺CD103⁺ conventional dendritic cells (cDCs) in MesLNs, preventing the establishment of oral tolerance. Deficiency of CD11c⁺CD103⁺ cDCs abrogates the generation of regulatory T cells in MesLNs to establish oral tolerance. Antibiotic treatment triggers the intestinal dysbiosis linked to the impaired generation of colony-stimulating factor 2 (Csf2)-producing group 3 innate lymphoid cells (ILC3s) for regulating the tolerogenesis of CD11c⁺CD103⁺ cDCs and the reduced expression of tumor necrosis factor (TNF)-like ligand 1A (TL1A) on CD11c⁺CD103⁺ cDCs for generating Csf2-producing ILC3s. Thus, antibiotic-driven intestinal dysbiosis leads to the breakdown of crosstalk between CD11c⁺CD103⁺ cDCs and ILC3s for maintaining the tolerogenesis of CD11c⁺CD103⁺ cDCs in MesLNs, responsible for the failed establishment of oral tolerance.

Virological characteristics of the SARS-CoV-2 Omicron BA.2 subvariants, including BA.4 and BA.5

After the global spread of the SARS-CoV-2 Omicron BA.2, some BA.2 subvariants, including BA.2.9.1, BA.2.11, BA.2.12.1, BA.4, and BA.5, emerged in multiple countries. Our statistical analysis showed that the effective reproduction numbers of these BA.2 subvariants are greater than that of the original BA.2. Neutralization experiments revealed that the immunity induced by BA.1/2 infections is less effective against BA.4/5. Cell culture experiments showed that BA.2.12.1 and BA.4/5 replicate more efficiently in human alveolar epithelial cells than BA.2, and particularly, BA.4/5 is more fusogenic than BA.2. We further provided the structure of the BA.4/5 spike receptor-binding domain that binds to human ACE2 and considered how the substitutions in the BA.4/5 spike play roles in ACE2 binding and immune evasion. Moreover, experiments using hamsters suggested that BA.4/5 is more pathogenic than BA.2. Our multiscale investigations suggest that the risk of BA.2 subvariants, particularly BA.4/5, to global health is greater than that of original BA.2.

A survey of bovine leukemia virus resistant bovine leukocyte antigen (BoLA)-DRB3*009:02 allele-carrying Japanese Black cattle in two prefectures in Japan

The bovine leukocyte antigen (BoLA)-DRB3*009:02 allele is strongly associated with a low/undetectable bovine leukemia virus (BLV) proviral load. Understanding the status of cattle possessing DRB3*009:02 allele is key for BLV control by breeding. We performed a survey of DRB3*009:02-carrying cattle in two prefectures in Japan using a TaqMan assay developed previously. The allele was found in 3.8% (confidence interval (CI): 3.3-4.3) of 6,020 Japanese Black female cattle. A prefecture-level difference was found: the allele was observed in 8.6% CI: 3.3-4.3) of 2,242 cattle of the birth prefecture B in Kyushu/Okinawa region, and this percentage was significantly higher than those of prefecture C in Kyushu/Okinawa region (1.3% (CI: 0.4-3.4) of 319) and prefecture A in Chugoku region (0.9% (CI: 0.6-1.4) of 2,741), respectively. Consideration on the difference in possession of DRB3*009:02 allele is needed to establish the more efficient control strategy of BLV infection in Japanese Black cattle.

A pooled testing system to rapidly identify cattle carrying the elite controller BoLA-DRB3*009:02 haplotype against bovine leukemia virus infection

As genetically resistant individuals, the “elite controllers” (ECs) of human immunodeficiency virus infection have been focused on as the keys to developing further functional treatments in medicine. In the livestock production field, identifying the ECs of bovine leukemia virus (BLV) infection in cattle is desired to stop BLV transmission chains on farms. Cattle carrying the bovine leukocyte antigen (BoLA)‐DRB3*009:02 allele (DRB3*009:02) have a strong possibility of being BLV ECs. Most of cattle carrying this allele maintain undetectable BLV proviral loads and do not shed virus even when infected. BLV ECs can act as transmission barriers when placed between uninfected and infected cattle in a barn. To identify cattle carrying DRB3*009:02 in large populations more easily, we developed a pooled testing system. It employs a highly sensitive, specific real‐time PCR assay and TaqMan MGB probes (DRB3*009:02‐TaqMan assay). Using this system, we determined the percentage of DRB3*009:02‐carrying cattle on Kyushu Island, Japan. Our pooled testing system detected cattle carrying the DRB3*009:02 allele from a DNA pool containing one DRB3*009:02‐positive animal and 29 cattle with other alleles. Its capacity is sufficient for herd‐level screening for DRB3*009:02‐carrying cattle. The DRB3*009:02‐TaqMan assay showed high‐discriminative sensitivity and specificity toward DRB3*009:02, making it suitable for identifying DRB3*009:02‐carrying cattle in post‐screening tests on individuals. We determined that the percentage of DRB3*009:02‐carrying cattle in Kyushu Island was 10.56%. With its ease of use and reliable detection, this new method strengthens the laboratory typing for DRB3*009:02‐carrying cattle. Thus, our findings support the use of BLV ECs in the field.

The detection of long-lasting memory foot-and-mouth disease (FMD) virus serotype O-specific CD4+ T cells from FMD-vaccinated cattle by bovine major histocompatibility complex class II tetramer

Foot‐and‐mouth disease (FMD) is a highly contagious, economically devastating disease of cloven‐hooved animals. The development of long‐lasting effective FMD vaccines would greatly benefit the global FMD control programme. Deep analysis of adaptive immunity in cattle vaccinated against FMD is technically challenging due to the lack of species‐specific tools. In this study, we aimed to identify CD4⁺ T‐cell epitopes in the FMD virus (FMDV) capsid and to phenotype the CD4⁺ T cells that recognize them using bovine major histocompatibility complex (BoLA) class II tetramer. A BoLA class II tetramer based on the DRA/DRB3*020:02 allele and FMDV antigen‐stimulated PBMCs from bovine vaccinates were used to successfully identify four epitopes in the FMDV capsid, three of which have not been previously reported; two epitopes were identified in the structural protein VP1, one in VP3 and one in VP4. Specificity of the three novel epitopes was confirmed by proliferation assay. All epitope‐expanded T‐cell populations produced IFN‐γ in vitro, indicating a long‐lasting Th1 cell phenotype after FMD vaccination. VP3‐specific CD4⁺ T cells exhibited the highest frequency amongst the identified epitopes, comprising >0·004% of the CD4⁺ T‐cell population. CD45RO⁺CCR7⁺ defined central memory CD4⁺ T‐cell subpopulations were present in higher frequency in FMDV‐specific CD4⁺ T‐cell populations from FMD‐vaccinated cattle ex vivo. This indicates an important role in maintaining cell adaptive immunity after FMD vaccination. Notably, FMDV epitope‐loaded tetramers detected the presence of FMDV‐specific CD4⁺ T cells in bovine PBMC more than four years after vaccination. This work contributes to our understanding of vaccine efficacy.

Characterization of bovine interleukin-2 stably expressed in HEK-293 cells

Interleukin 2 (IL-2) is a pleotropic cytokine and well-known as a T cell growth factor in immunology. It is now known to exert both immunostimulatory and immunosuppressive effects, optimizing immunological microenvironments for effector and regulatory T cell responses. The immunomodulatory role of IL-2 is critical for deciding whether or not T cell responses against specific antigens result in protection. We have established a mammalian cell line (HEK-293) stably expressing bovine IL-2 (boIL-2) (designated as HEK-293/boIL-2), using the piggyBac transposon system. The concentration of recombinant bovine IL-2 (rboIL-2) in the culture supernatant of HEK-293/boIL-2 reached 100 ng/ml on day 7 and showed similar proliferative activity to recombinant human IL-2 (rhuIL-2) for bovine peripheral mononuclear blood cells. Although rhuIL-2 has been often used to activate bovine T cells, our results indicate that characteristics of the T cell activation through rboIL-2 and huIL-2 appear slightly but significantly different. Interestingly, the rboIL-2/anti-boIL-2 monoclonal antibody (C5) (rboIL-2/C5) complex strongly induced proliferation of bovine NKp46⁺cells, natural killer (NK) cells, in vitro. This indicates that the rboIL-2/C5 complex could function as an IL-2 agonist specifically to increase the NK cell population, which in turn could enhance the activity of NK cells leading to protective immunity.

Quantitative Risk Assessment for the Introduction of Bovine Leukemia Virus-Infected Cattle Using a Cattle Movement Network Analysis

The cattle industry is suffering economic losses caused by bovine leukemia virus (BLV) and enzootic bovine leukosis (EBL), the clinical condition associated with BLV infection. This pathogen spreads easily without detection by farmers and veterinarians due to the lack of obvious clinical signs. Cattle movement strongly contributes to the inter-farm transmission of BLV. This study quantified the farm-level risk of BLV introduction using a cattle movement analysis. A generalized linear mixed model predicting the proportion of BLV-infected cattle was constructed based on weighted in-degree centrality. Our results suggest a positive association between weighted in-degree centrality and the estimated number of introduced BLV-infected cattle. Remarkably, the introduction of approximately six cattle allowed at least one BLV-infected animal to be added to the farm in the worst-case scenario. These data suggest a high risk of BLV infection on farms with a high number of cattle being introduced. Our findings indicate the need to strengthen BLV control strategies, especially along the chain of cattle movement.

Evaluating the Risk Factors for Porcine Epidemic Diarrhea Virus Infection in an Endemic Area of Vietnam

Porcine epidemic diarrhea virus (PEDV) causes enteritis, vomiting, watery diarrhea, and high mortality in suckling pigs, threatening the swine industry. Porcine epidemic diarrhea (PED) re-emerged globally in 2013 in many important swine-producing countries in Asia and the Americas. Several studies have identified the risk factors for the spread of PEDV in acute outbreaks. However, limited information is available on the risk factors for the transmission of PEDV in endemic regions. We hypothesized that poor biosecurity, location, and some social or cultural practices are the main risk factors for PEDV transmission in the Vietnamese pig population. The aim of this study was to evaluate the potential risk factors for the transmission of PEDV in an endemic area in Vietnam. In this case–control study, questionnaires containing 51 questions were completed for 92 PEDV-positive and 95 PEDV-negative farms. A logistic regression analysis was performed to assess the risk factors associated with PEDV infection. Province and the total number of pigs were included as random effects to determine their influence on the risk of PEDV infection. Twenty-nine variables of interest that have been associated with PEDV status were analyzed in a univariate analysis (P <0.20), with backward stepwise selection. Only three of these 29 variables in four models remained significant PEDV risk factors in the final model: farrow-to-wean production type, distance from the farm to the slaughterhouse (<1,000 m), and the presence of chickens on site (P <0.05). This is the first study to identify the main risk factors for PEDV infection in an endemic area. Our findings suggest that hygiene measures should be strictly implemented on farms for the effective control and prevention of PEDV infection.

Establishment of a novel diagnostic test for Bovine leukaemia virus infection using direct filter PCR

Enzootic bovine leucosis (EBL) is a neoplastic disease of cattle caused by Bovine leukaemia virus (BLV). EBL causes great economic losses, so a fast and reliable diagnostic method is critical for understanding the status of BLV. This will allow us to control BLV infections efficiently and mitigate economic losses. In this study, we established a direct diagnostic test for BLV using dried blood-spotted filter papers without sample pre-treatment. The study was based on 159 clinical blood specimens collected in EDTA from one farm in Kyushu, Japan. The blood-spotted filter papers were used as the template for direct filter PCR. When an ELISA was used as the diagnostic gold standard, the sensitivity and specificity of the direct filter PCR were 90.1% and 97.5%, respectively. The kappa value for the direct filter PCR and real-time PCR methods was 0.97. The dried blood samples spotted onto filter papers were stable for at least 10 days at room temperature, even when the samples were from cattle with a low BLV proviral load. Direct filter PCR is a rapid, easy, reliable and cost-effective diagnostic test that directly detects the BLV proviral genome in clinical blood specimens without DNA extraction. Moreover, it simplifies the collection, transportation and storage procedures for clinical blood specimens.

IncI1 Plasmid Associated with blaCTX-M-2 Transmission in ESBL-Producing Escherichia coli Isolated from Healthy Thoroughbred Racehorse, Japan

In our previous study, extended spectrum β-lactamase (ESBL)-producing Escherichia coli (ESBLEC) were isolated from healthy Thoroughbred racehorse feces samples in Japan. Some ESBL genes were predicted to be located on the conjugative plasmid. PCR-based replicon typing (PBRT) is a useful method to monitor and detect the association of replicons with specific plasmid-borne resistant genes. This study aimed to evaluate the plasmid replicon associated with ESBLEC isolated from healthy Thoroughbred racehorses at Japan Racing Association Training Centers in Japan. A total of 24 ESBLECs isolated from 23 (10.8%) individual Thoroughbred racehorse feces samples were used in this study. ESBL gene transfer was performed using a conjugation assay. Then, replicon types of ESBLEC isolates and their transconjugants were determined using PBRT. Pulsed-field gel electrophoresis (PFGE) was performed to look at the clonality of the ESBLECs isolates. ESBLECs were detected from 10.8% of healthy Thoroughbred racehorses. The bla_CTX-M-2 was identified as the dominant type of ESBL gene, followed by bla_CTX-M-1 and bla_TEM-116. In this study, only the bla_CTX-M-2 and the IncI1 plasmid were transferred to transconjugants. The PFGE results showed that ESBL genes were distributed in diversity of ESBLECs. This finding suggested that the IncI1 plasmid was associated with the dissemination of bla_CTX-M-2 in Thoroughbred racehorses in Japan.

Extended-spectrum β-lactamase-producing Escherichia coli isolated from healthy Thoroughbred racehorses in Japan

Extended-spectrum β-lactamase-producing Escherichia coli (ESBLEC) have become a major health concern in both human and veterinary medicine. These bacteria could become a critical problem in equine medicine due to the limited number of antimicrobial drugs available. However, there are no previous reports of ESBLEC isolated from horses in Japan. The objectives of this study were to investigate the occurrence of ESBLEC isolated from feces in healthy Thoroughbred racehorses in Japan. Feces samples were collected from 147 healthy Thoroughbred racehorses by equine veterinarians at the Japan Racing Association (103 from Miho Training Center and 44 from Ritto Training Center) between March 2017 and April 2018. Samples were screened for ESBLECs using MacConkey agar supplemented with 1 µg/ml cefotaxime. Detection of ESBL genes was performed by PCR and confirmed by DNA sequencing. Horizontal transmission was demonstrated by conjugation assay. In this study, 24 ESBLECs were isolated from twelve horse feces samples (8.2%). All ESBLECs harbored bla_CTX-M-2, and both bla_TEM-1 and bla_CTX-M-2 were detected in nine isolates (37.5%). ESBLECs showed resistance to all β-lactam antibiotics (100%) tested, followed by trimethoprim (66.7%), streptomycin (62.5%), tetracycline (25.0%), and oxytetracycline (25.0%). Horizontal transmission was successfully demonstrated by conjugation assay in eight of 13 isolates, and bla_CTX-M-2 was detected by PCR in all transconjugants. This study showed that racehorses in Japan are potential reservoirs of ESBLECs.

Meteorological factors affecting the risk of transmission of HPAI in Miyazaki, Japan

Highly pathogenic avian influenza (HPAI) outbreaks engender a severe economic impact on the poultry industry and public health. Migratory waterfowl are considered the natural hosts of HPAI virus, and HPAI viruses are known to be transmitted over long distances during seasonal bird migration. Bird migration is greatly affected by the weather. Many studies have shown the relationship between either autumn or spring bird migration and climate. However, few studies have shown the relationship between annual bird migration and annual weather. This study aimed to establish a model for the number of migratory waterfowl involved in HPAI virus transmission based on meteorological data. From 136 species of waterfowl that were observed at Futatsudate in Miyazaki, Japan, from 2008 to 2016, we selected potential high-risk species that could introduce the HPAI virus into Miyazaki and defined them as 'risky birds'. We also performed cluster analysis to select meteorological factors. We then analysed the meteorological data and the total number of risky birds using a generalised linear mixed model. We selected 10 species as risky birds: Mallard (Anas platyrhynchos), Northern pintail (Anas acuta), Eurasian wigeon (Anas penelope), Eurasian teal (Anas crecca), Common pochard (Aythya ferina), Eurasian coot (Fulica atra), Northern shoveler (Anas clypeata), Common shelduck (Tadorna tadorna), Tufted duck (Aythya fuligula) and Herring gull (Larus argentatus). We succeeded in clustering 35 meteorological factors into four clusters and identified three meteorological factors associated with their migration: (1) the average daily maximum temperature; (2) the mean value of global solar radiation and (3) the maximum daily precipitation. We thus demonstrated the relationship between the number of risky birds and meteorological data. The dynamics of migratory waterfowl was relevant to the risk of an HPAI outbreak, and our data could contribute to cost and time savings in strengthening preventive measures against epidemics.

Slaughterhouse survey for detection of bovine viral diarrhea infection among beef cattle in Kyushu, Japan

Bovine viral diarrhea virus (BVDV) footprint has spread across the globe and is responsible for one of the most economically important diseases in cattle. In Japan, some regional surveillance and preventive measures to control bovine viral diarrhea (BVD) have been implemented. However, BVDV infection is poorly understood in cattle industries, and there is no systematic BVD surveillance system and control program. Kyushu is the center for raising beef cattle in Japan. Therefore, this study aimed to determine the BVDV infection using a slaughterhouse survey among beef cattle in Kyushu, Japan. A total of 1,075 blood samples were collected at two regional slaughterhouses in Miyazaki prefecture from December 2015 to June 2016. Antigen ELISA was used for detection of BVDV antigen in blood samples. Two samples showed positive results (2/1,075; 0.18%). BVDV RNA was extracted from positive blood samples; the sequence was determined and analyzed by the neighbor-joining method for construction of the phylogenetic tree. Phylogenetic analysis based on the 5’-UTR revealed that the two positive samples were grouped into the same subtype BVDV-1b in the BVDV-1 genotype, but the infected cattle belonged to two different farms. In conclusion, this is the first study to identify the presence of BVDV in a slaughterhouse survey in Kyushu. These findings suggest that a slaughterhouse survey is a useful tool for developing a surveillance system for monitoring infectious diseases in cattle.

Detection of neutralizing antibody against porcine epidemic diarrhea virus in subclinically infected finishing pigs

The purpose of this study was to detect porcine epidemic diarrhea virus (PEDV) subclinically infected pigs shipped from non-case farms to slaughterhouses. Systematic sampling was conducted at two slaughterhouses. A total of 1,556 blood samples were collected from 80 case and non-case farms from pigs over 6 months old. Blood samples were centrifuged to obtain sera. Serial serum dilutions were subjected to serological examination for PEDV presence using Neutralization test (NT). The cut-off titer was set at titer of 1:2 dilution and farms with at least one positive sample in duplicate were classified as PED-positive farms. Several non-case farms (9.4%, 6/64) and 100% (16/16) of the case farms were indeed positive for PEDV. The proportion of seropositive animals from case farms was 63.7%, significantly different from that of non-case farms (4.3%, P<0.05). In both case and non-case farms, the proportion of seropositive animals in farrow-to-finish farms was significantly higher than in wean-to-finish farms (P<0.05). Seropositive animals in non-case farms were detected by NT in a sero-survey by sampling at slaughterhouses. Therefore, subclinically infected pigs should be considered prior to shipment.

Development of pooled testing system for porcine epidemic diarrhoea using real-time fluorescent reverse-transcription loop-mediated isothermal amplification assay

Background

Porcine epidemic diarrhoea (PED) is an emerging disease in pigs that causes massive economic losses in the swine industry, with high mortality in suckling piglets. Early identification of PED virus (PEDV)-infected herd through surveillance or monitoring strategies is necessary for mass control of PED. However, a common working diagnosis system involves identifying PEDV-infected animals individually, which is a costly and time-consuming approach. Given the above information, the thrusts of this study were to develop a real-time fluorescent reverse transcription loop-mediated isothermal amplification (RtF-RT-LAMP) assay and establish a pooled testing system using faecal sample to identify PEDV-infected herd.

Results

In this study, we developed an accurate, rapid, cost-effective, and simple RtF- RT-LAMP assay for detecting the PEDV genome targeting M gene. The pooled testing system using the RtF-RT-LAMP assay was optimized such that a pool of at least 15 individual faecal samples could be analysed.

Conclusions

The developed RtF-RT-LAMP assay in our study could support the design and implementation of large-scaled epidemiological surveys as well as active surveillance and monitoring programs for effective control of PED.

Electronic supplementary material

The online version of this article (10.1186/s12917-018-1498-9) contains supplementary material, which is available to authorized users.

Cattle with the BoLA class II DRB3*0902 allele have significantly lower bovine leukemia proviral loads

The bovine MHC (BoLA) class II DRB3 alleles are associated with polyclonal expansion of lymphocytes caused by bovine leukemia virus (BLV) infection in cattle. To examine whether the DRB3*0902 allele, one of the resistance-associated alleles, is associated with the proviral load, we measured BLV proviral load of BLV-infected cattle and clarified their DRB3 alleles. Fifty-seven animals with DRB3*0902 were identified out of 835 BLV-infected cattle and had significantly lower proviral load (P<0.000001) compared with the rest of the infected animals, in both Japanese Black and Holstein cattle. This result strongly indicates that the BoLA class II DRA/DRB3*0902 molecule plays an important immunological role in suppressing viral replication, resulting in resistance to the disease progression.