Detection and disease diagnosis trends (2017-2022) for Streptococcus suis, Glaesserella parasuis, Mycoplasma hyorhinis, Actinobacillus suis and Mycoplasma hyosynoviae at Iowa State University Veterinary Diagnostic Laboratory

BACKGROUND

Accurate measurement of disease associated with endemic bacterial agents in pig populations is challenging due to their commensal ecology, the lack of disease-specific antemortem diagnostic tests, and the polymicrobial nature of swine diagnostic cases. The main objective of this retrospective study was to estimate temporal patterns of agent detection and disease diagnosis for five endemic bacteria that can cause systemic disease in porcine tissue specimens submitted to the Iowa State University Veterinary Diagnostic Laboratory (ISU VDL) from 2017 to 2022. The study also explored the diagnostic value of specific tissue specimens for disease diagnosis, estimated the frequency of polymicrobial diagnosis, and evaluated the association between phase of pig production and disease diagnosis.

RESULTS

S. suis and G. parasuis bronchopneumonia increased on average 6 and 4.3%, while S. suis endocarditis increased by 23% per year, respectively. M. hyorhinis and A. suis associated serositis increased yearly by 4.2 and 12.8%, respectively. A significant upward trend in M. hyorhinis arthritis cases was also observed. In contrast, M. hyosynoviae arthritis cases decreased by 33% average/year. Investigation into the diagnostic value of tissues showed that lungs were the most frequently submitted sample, However, the use of lung for systemic disease diagnosis requires caution due to the commensal nature of these agents in the respiratory system, compared to systemic sites that diagnosticians typically target. This study also explored associations between phase of production and specific diseases caused by each agent, showcasing the role of S. suis arthritis in suckling pigs, meningitis in early nursery and endocarditis in growing pigs, and the role of G. parasuis, A. suis, M. hyorhinis and M. hyosynoviae disease mainly in post-weaning phases. Finally, this study highlighted the high frequency of co-detection and -disease diagnosis with other infectious etiologies, such as PRRSV and IAV, demonstrating that to minimize the health impact of these endemic bacterial agents it is imperative to establish effective viral control programs.

CONCLUSIONS

Results from this retrospective study demonstrated significant increases in disease diagnosis for S. suis, G. parasuis, M. hyorhinis, and A. suis, and a significant decrease in detection and disease diagnosis of M. hyosynoviae. High frequencies of interactions between these endemic agents and with viral pathogens was also demonstrated. Consequently, improved control programs are needed to mitigate the adverse effect of these endemic bacterial agents on swine health and wellbeing. This includes improving diagnostic procedures, developing more effective vaccine products, fine-tuning antimicrobial approaches, and managing viral co-infections.

Diagnostic investigation of Mycoplasma hyorhinis as a potential pathogen associated with neurological clinical signs and central nervous system lesions in pigs

Mycoplasma hyorhinis (M. hyorhinis) is a commensal of the upper respiratory tract in swine with the typical clinical presentations of arthritis and polyserositis in postweaning pigs. However, it has also been associated with conjunctivitis and otitis media, and recently has been isolated from meningeal swabs and/or cerebrospinal fluid of piglets with neurological signs. The objective of this study is to evaluate the role of M. hyorhinis as a potential pathogen associated with neurological clinical signs and central nervous system lesions in pigs. The presence of M. hyorhinis was evaluated in a clinical outbreak and a six-year retrospective study by qPCR detection, bacteriological culture, in situ hybridization (RNAscope®), and phylogenetic analysis and with immunohistochemistry characterization of the inflammatory response associated with its infection. M. hyorhinis was confirmed by bacteriological culture and within central nervous system lesions by in situ hybridization on animals with neurological signs during the clinical outbreak. The isolates from the brain had close genetic similarities from those previously reported and isolated from eye, lung, or fibrin. Nevertheless, the retrospective study confirmed by qPCR the presence of M. hyorhinis in 9.9% of cases reported with neurological clinical signs and histological lesions of encephalitis or meningoencephalitis of unknown etiology. M. hyorhinis mRNA was confirmed within cerebrum, cerebellum, and choroid plexus lesions by in situ hybridization (RNAscope®) with a positive rate of 72.7%. Here we present strong evidence that M. hyorhinis should be included as a differential etiology in pigs with neurological signs and central nervous system inflammatory lesions.

Cough associated with the detection of Mycoplasma hyopneumoniae DNA in clinical and environmental specimens under controlled conditions

Background

The association of cough with Mycoplasma hyopneumoniae (MHP) DNA detection in specimens was evaluated under conditions in which the MHP status of inoculated and contact-infected pen mates was closely monitored for 59 days post-inoculation (DPI).

Methods

Seven-week-old pigs (n = 39) were allocated to five rooms (with one pen). Rooms contained 9 pigs each, with 1, 3, 6, or 9 MHP-inoculated pigs, respectively, except Room 5 (three sham-inoculated pigs). Cough data (2 × week) and specimens, tracheal swabs (2 × week), oral fluids (daily), drinker wipes (~ 1 × week), and air samples (3 × week) were collected. At 59 DPI, pigs were euthanized, and lung and trachea were evaluated for gross and microscopic lesions. Predictive cough value to MHP DNA detection in drinker and oral fluid samples were estimated using mixed logistic regression.

Results

Following inoculation, MHP DNA was first detected in tracheal swabs from inoculated pigs (DPI 3), then oral fluids (DPI 8), air samples (DPI 10), and drinker wipes (21 DPI). MHP DNA was detected in oral fluids in 17 of 59 (Room 1) to 43 of 59 (Room 3) samples, drinker wipes in 4 of 8 (Rooms 2 and 3) to 5 of 8 (Rooms 1 and 4) samples, and air samples in 5 of 26 (Room 2) or 3 of 26 (Room 4) samples. Logistic regression showed that the frequency of coughing pigs in a pen was associated with the probability of MHP DNA detection in oral fluids (P < 0.01) and nearly associated with drinker wipes (P = 0.08). Pathology data revealed an association between the period when infection was first detected and the severity of gross lung lesions.

Conclusions

Dry, non-productive coughs suggest the presence of MHP, but laboratory testing and MHP DNA detection is required for confirmation. Based on the data from this study, oral fluids and drinker wipes may provide a convenient alternative for MHP DNA detection at the pen level when cough is present. This information may help practitioners in specimen selection for MHP surveillance.

Replication of Streptococcus equi subspecies zooepidemicus infection in swine

Streptococcus equi subspecies zooepidemicus (SEZ) is a commensal bacterium of horses and causes infections in mammalian species, including humans. Historically, virulent strains of SEZ caused high mortality in pigs in China and Indonesia, while disease in the U.S. was infrequent. More recently, high mortality events in sows were attributed to SEZ in North America. The SEZ isolates from these mortality events have high genetic similarity to an isolate from an outbreak in China. Taken together, this may indicate SEZ is an emerging threat to swine health. To generate a disease model and evaluate the susceptibility of healthy, conventionally raised pigs to SEZ, we challenged sows and five-month-old pigs with an isolate from a 2019 mortality event. Pigs were challenged with a genetically similar guinea pig isolate or genetically distinct horse isolate to evaluate comparative virulence. The swine isolate caused severe systemic disease in challenged pigs with 100 % mortality. Disease manifestation in sows was similar to field reports: lethargy/depression, fever, reluctance to rise, and high mortality. The guinea pig isolate also caused severe systemic disease; however, most five-month-old pigs recovered. In contrast, the horse isolate did not cause disease and was readily cleared from the respiratory tract. In conclusion, we were able to replicate disease reported in the field. The results indicate differences in virulence between isolates, with the highest virulence associated with the swine isolate. Additionally, we generated a challenge model that can be used in future research to evaluate virulence factors and disease prevention strategies.

MALDI-TOF mass spectrometry and high-resolution melting PCR for the identification of Mycoplasma bovis isolates

BACKGROUND

Mycoplasma bovis is an important pathogen of cattle worldwide. Many different clinical manifestations of infection can occur, including respiratory disease, arthritis, and mastitis, causing heavy losses to beef and dairy industries. Because Mycoplasma species are slow-growing and fastidious, traditional identification methods are not cost- or time-effective, and improved methods are sought to streamline laboratory processes. High-resolution melting PCR (HRM-PCR) and matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) are 2 relatively recent tools that are rapid and inexpensive to use; we tested 9 isolates of M. bovis using both assays. The HRM-PCR assay used universal mycoplasma primers for the 16S-23S intergenic spacer region (IGSR).

RESULTS

The resulting melting profiles of the field isolates were indistinguishable from the reference strain, indicating accurate identification. For the MALDI-TOF MS, each M. bovis isolate was accurately identified. Mycoplasma arginini and Mycoplasma alkalescens isolates did not identify as M. bovis when tested by either assay.

CONCLUSIONS

Our work shows that either assay could be used to identify unknown M. bovis isolates. For future work, the MALDI-TOF MS library should be expanded to include more mycoplasmas, and the HRM-PCR assay should be tested on additional mycoplasmas to ensure that the melting profiles are sufficiently distinctive.

Research Relevant Background Lesions and Conditions: Ferrets, Dogs, Swine, Sheep, and Goats

Animal models provide a valuable tool and resource for biomedical researchers as they investigate biological processes, disease pathogenesis, novel therapies, and toxicologic studies. Interpretation of animal model data requires knowledge not only of the processes/diseases being studied but also awareness of spontaneous conditions and background lesions in the model that can influence or even confound the study results. Species, breed/stock, sex, age, anatomy, physiology, diseases (noninfectious and infectious), and neoplastic processes are model features that can impact the results as well as study interpretation. Here, we review these features in several common laboratory animal species, including ferret, dog (beagle), pig, sheep, and goats.

Disease diagnostic coding to facilitate evidence-based medicine: current and future perspectives

Technologic advances in information management have rapidly changed laboratory testing and the practice of veterinary medicine. Timely and strategic sampling, same-day assays, and 24-h access to laboratory results allow for rapid implementation of intervention and treatment protocols. Although agent detection and monitoring systems have progressed, and wider tracking of diseases across veterinary diagnostic laboratories exists, such as by the National Animal Health Laboratory Network (NAHLN), the distinction between detection of agent and manifestation of disease is critical to improved disease management. The implementation of a consistent, intuitive, and useful disease diagnosis coding system, specific for veterinary medicine and applicable to multiple animal species within and between veterinary diagnostic laboratories, is the first phase of disease data aggregation. Feedback loops for continuous improvement that could aggregate existing clinical and laboratory databases to improve the value and applications of diagnostic processes and clinical interventions, with interactive capabilities between clinicians and diagnosticians, and that differentiate disease causation from mere agent detection, remain incomplete. Creating an interface that allows aggregation of existing data from clinicians, including final diagnosis, interventions, or treatments applied, and measures of outcomes, is the second phase. Prototypes for stakeholder cooperation, collaboration, and beta testing of this vision are in development and becoming a reality. We focus here on how such a system is being developed and utilized at the Iowa State University Veterinary Diagnostic Laboratory to facilitate evidence-based medicine and utilize diagnostic coding for continuous improvement of animal health and welfare.

Visualization and application of disease diagnosis codes for population health management using porcine diseases as a model

Accurate and timely results of diagnostic investigations and laboratory testing guide clinical interventions for the continuous improvement of animal health and welfare. Infectious diseases can severely limit the health, welfare, and productivity of populations of animals. Livestock veterinarians submit thousands of samples daily to veterinary diagnostic laboratories (VDLs) for disease diagnosis, pathogen monitoring, and surveillance. Individual diagnostic laboratory reports are immediately useful; however, aggregated historical laboratory data are increasingly valued by clinicians and decision-makers to identify changes in the health status of various animal populations over time and geographical space. The value of this historical information is enhanced by visualization of trends of agent detection, disease diagnosis, or both, which helps focus time and resources on the most significant pathogens and fosters more effective communication between livestock producers, veterinarians, and VDL professionals. Advances in data visualization tools allow quick, efficient, and often real-time scanning and analysis of databases to inform, guide, and modify animal health intervention algorithms. Value is derived at the farm, production system, or regional level. Visualization tools allow client-specific analyses, benchmarking, formulation of research questions, and monitoring the effects of disease management and precision farming practices. We present here the approach taken to visualize trends of disease occurrence using porcine disease diagnostic code data for the period 2010 to 2019. Our semi-automatic standardized creation of a visualization platform allowed the transformation of diagnostic report data into aggregated information to visualize and monitor disease diagnosis.

Performance of Commercial Mycoplasma hyopneumoniae Serum Enzyme-Linked Immunosorbent Assays under Experimental and Field Conditions

Mycoplasma hyopneumoniae is an economically significant pathogen of swine. M. hyopneumoniae serum antibody detection via commercial enzyme-linked immunosorbent assays (ELISAs) is widely used for routine surveillance in commercial swine production systems. Samples from two studies were used to evaluate assay performance. In study 1, 6 commercial M. hyopneumoniae ELISAs were compared using serum samples from 8-week-old cesarean-derived, colostrum-deprived (CDCD) pigs allocated to the following 5 inoculation groups of 10 pigs each: (i) negative control, (ii) Mycoplasma flocculare (strain 27399), (iii) Mycoplasma hyorhinis (strain 38983), (iv) Mycoplasma hyosynoviae (strain 34428), and (v) M. hyopneumoniae (strain 232). Weekly serum and daily oral fluid samples were collected through 56 days postinoculation (dpi). The true status of pigs was established by PCR testing on oral fluids samples over the course of the observation period. Analysis of ELISA performance at various cutoffs found that the manufacturers' recommended cutoffs were diagnostically specific, i.e., produced no false positives, with the exceptions of 2 ELISAs. An analysis based on overall misclassification error rates found that 4 ELISAs performed similarly, although one assay produced more false positives. In study 2, the 3 best-performing ELISAs from study 1 were compared using serum samples generated under field conditions. Ten 8-week-old pigs were intratracheally inoculated with M. hyopneumoniae Matched serum and tracheal samples (to establish the true pig M. hyopneumoniae status) were collected at 7- to 14-day intervals through 98 dpi. Analyses of sensitivity and specificity showed similar performance among these 3 ELISAs. Overall, this study provides an assessment of the performance of current M. hyopneumoniae ELISAs and an understanding of their use in surveillance.

Clinical presentations and antimicrobial susceptibilities of Corynebacterium cystitidis associated with renal disease in four beef cattle

Background

Renal disease caused by Corynebacterium cystitidis in beef cattle may be misclassified as Corynebacterium renale, and limited information about C. cystitidis infections in beef cattle currently is available.

Objective

To describe clinical presentation, diagnosis, minimum inhibitory concentrations (MICs), and outcome of renal disease caused by C. cystitidis in beef cattle.

Methods

Retrospective case series.

Animals

Four client‐owned beef cattle.

Results

All affected cattle had anorexia as a primary complaint. Of the 3 that had ante‐mortem diagnostic tests performed, all had pyelonephritis based on azotemia in combination with urinalysis and ultrasonographic findings. Cultures yielded C. cystitidis which was identified by biochemical testing, 16S RNA sequencing, and mass spectrometry. All affected cattle deteriorated despite aggressive treatment, indicating that C. cystitidis infections in beef cattle may carry a poor prognosis. Bacterial isolates collected from the 4 cattle showed similarities in MICs for ampicillin, florfenicol, gentamicin, neomycin, sulfadimethoxine, trimethoprim sulfonamide, and tylosin.

Conclusions and clinical importance

Corynebacterium cystitidis should be considered in the differential diagnosis of cattle with renal disease. Definitive diagnosis of C. cystitidis as compared to C. renale may be challenging.

Assessing the effects of medium-chain fatty acids and fat sources on PEDV infectivity

The overall objective of this study was to compare the efficacy of medium-chain fatty acids (MCFA) to other common fat sources to minimize the risk of porcine epidemic diarrhea virus (PEDV) cross-contamination in a pig bioassay. Treatments were feed with mitigants inoculated with PEDV after application and were: 1) positive control with no chemical treatment; 2) 0.325% commercially available formaldehyde-based product; 3) 1% blend of 1:1:1 caproic (C6), caprylic (C8), and capric acids (C10) and applied with an aerosolizing nozzle; 4) treatment 3 applied directly into the mixer without an aerosolizing nozzle; 5) 0.66% caproic acid; 6) 0.66% caprylic acid; 7) 0.66% capric acid; 8) 0.66% lauric acid; 9) 1% blend of 1:1 capric and lauric acids; 10) 0.3% commercially available dry C12 product; 11) 1% canola oil; 12) 1% choice white grease; 13) 2% coconut oil; 14) 1% coconut oil; 15) 2% palm kernel oil; 16) 1% palm kernel oil; 17) 1% soy oil and four analysis days (0, 1, 3, and 7 post inoculation) as well as 1 treatment of PEDV-negative feed without chemical treatment. There was a treatment × day interaction (P < 0.002) for detectable PEDV RNA. The magnitude of the increase in Ct value from d 0 to 7 was dependent upon the individual treatments. Feed treated with individual MCFA, 1% MCFA blend, or commercial-based formaldehyde had fewer (P < 0.05) detectable viral particles than all other treatments. Commercial-based formaldehyde, 1% MCFA, 0.66% caproic, 0.66% caprylic, and 0.66% capric acids had no evidence of infectivity 10-d old pig bioassay, while there was no evidence the C12 commercial product or longer chain fat sources inhibited PEDV infectivity. Interestingly, pigs given the coconut oil source with the highest composition of caprylic and capric only showed signs of infectivity on the last day of bioassay. These data suggest some MCFA have potential for reducing post feed manufacture PEDV contamination.

Early detection and differential serodiagnosis of Mycoplasma hyorhinis and Mycoplasma hyosynoviae infections under experimental conditions

Mycoplasma hyorhinis (MHR) and Mycoplasma hyosynoviae (MHS) are common opportunistic pathogens in the upper respiratory tract and tonsils of swine. The identification of the specific species involved in clinical cases using conventional diagnostic methods is challenging. Therefore, a recombinant chimeric polypeptide based on the seven known variable lipoproteins (A-G) specific of MHR and a cocktail of surface proteins detergent-extracted from MHS cultures were generated and their suitability as antemortem biomarkers for serodiagnosis of MHR- and MHS-infection were evaluated by ELISA. M. hyorhinis and MHS ELISA performance, evaluated using serum samples collected over a 56-day observation period from pigs inoculated with MHR, MHS, M. hyopneumoniae, M. flocculare, or Friis medium, varied by assay, targeted antibody isotype, and cutoffs. The progressions of MHR and MHS clinical diseases were evaluated in relation to the kinetics of the isotype-specific antibody response in serum and bacterial shedding in oral fluids during the observation period. In pigs inoculated with MHR, bacterial DNA was detected in one or more of the 5 pens at all sampling points throughout the study, IgA was first detected at DPI 7, one week before the first clinical signs, with both IgA and IgG detected in all samples collected after DPI 14. The peak of MHS shedding (DPI 8) coincided with the onset of the clinical signs, with both IgA and IgG detected in all serum samples collected ≥ DPI 14. This study demonstrated, under experimental conditions, that both ELISAs were suitable for early detection of specific antibodies against MHR or MHS. The diagnostic performance of the MHR and MHS ELISAs varied depending on the selected cutoff and the antibody isotype evaluated. The high diagnostic and analytical specificity of the ELISAs was particularly remarkable. This study also provides insights into the infection dynamics of MHR-associated disease and MHS-associated arthritis not previously described.

Polioencephalomyelitis in Domestic Swine Associated With Porcine Astrovirus Type 3

In the past decade, different members of the genus Mamastrovirus have been associated with outbreaks of neurologic disease in humans, cattle, sheep, mink, and, most recently, porcine astrovirus 3 (PoAstV3) in swine. We performed a retrospective analysis of 50 cases of porcine neurologic disease of undetermined cause but with microscopic lesions compatible with a viral encephalomyelitis to better understand the role and pathogenesis of PoAstV3 infection. Nucleic acid was extracted from formalin-fixed paraffin-embedded (FFPE) tissue for reverse transcription quantitative polymerase chain reaction (RT-qPCR) testing for PoAstV3. In addition, 3 cases with confirmed PoAstV3-associated disease were assayed by RT-qPCR to investigate PoAstV3 tissue distribution. PoAstV3 was detected in central nervous system (CNS) tissue via RT-qPCR and in situ hybridization in 13 of 50 (26%) FFPE cases assayed. PoAstV3 was rarely detected in any tissues outside the CNS. Positive cases from the retrospective study included pigs in various production categories beginning in 2010, the earliest year samples were available. Based on these results, PoAstV3 appears to be a recurring putative cause of viral encephalomyelitis in swine that is rarely detected outside of the CNS at the time of clinical neurologic disease, unlike other common viral causes of neurologic disease in swine.

Comparison of multilocus sequence types found among North American isolates of Mycoplasma bovis from cattle, bison, and deer, 2007-2017

A prior multilocus sequence typing (MLST) study reported that Mycoplasma bovis isolates from North American bison possess sequence types (STs) different from those found among cattle. The 42 bison isolates evaluated were obtained in 2007 or later, whereas only 19 of 94 (~20%) of the available cattle isolates, with only 1 from North America, were from that same time. We compared STs of additional, contemporary, North American cattle isolates with those from bison, as well as isolates from 2 North American deer, all originating during the same timeframe, to more definitively assess potential strain-related host specificity and expand our understanding of the genetic diversity of M. bovis. From 307 isolates obtained between 2007 and 2017 (209 from cattle, 96 from bison, 2 from deer), we identified 49 STs, with 39 found exclusively in cattle and 5 exclusively in bison. Four STs were shared between bison and cattle isolates; one ST was found in cattle and in a deer. There was no clear association between ST and the health status of the animal of origin. An MLST-based phylogeny including 41 novel STs identified in our study reveals that STs found in bison fall within several divergent lineages that include STs found exclusively in cattle.

Characterizing the rapid spread of porcine epidemic diarrhea virus (PEDV) through an animal food manufacturing facility

New regulatory and consumer demands highlight the importance of animal feed as a part of our national food safety system. Porcine epidemic diarrhea virus (PEDV) is the first viral pathogen confirmed to be widely transmissible in animal food. Because the potential for viral contamination in animal food is not well characterized, the objectives of this study were to 1) observe the magnitude of virus contamination in an animal food manufacturing facility, and 2) investigate a proposed method, feed sequencing, to decrease virus decontamination on animal food-contact surfaces. A U.S. virulent PEDV isolate was used to inoculate 50 kg swine feed, which was mixed, conveyed, and discharged into bags using pilot-scale feed manufacturing equipment. Surfaces were swabbed and analyzed for the presence of PEDV RNA by quantitative real-time polymerase chain reaction (qPCR). Environmental swabs indicated complete contamination of animal food-contact surfaces (0/40 vs. 48/48, positive baseline samples/total baseline samples, positive subsequent samples/total subsequent samples, respectively; P < 0.05) and near complete contamination of non-animal food-contact surfaces (0/24 vs. 16/18, positive baseline samples/total baseline samples, positive subsequent samples/total subsequent samples, respectively; P < 0.05). Flushing animal food-contact surfaces with low-risk feed is commonly used to reduce cross-contamination in animal feed manufacturing. Thus, four subsequent 50 kg batches of virus-free swine feed were manufactured using the same system to test its impact on decontaminating animal food-contact surfaces. Even after 4 subsequent sequences, animal food-contact surfaces retained viral RNA (28/33 positive samples/total samples), with conveying system being more contaminated than the mixer. A bioassay to test infectivity of dust from animal food-contact surfaces failed to produce infectivity. This study demonstrates the potential widespread viral contamination of surfaces in an animal food manufacturing facility and the difficulty of removing contamination using conventional feed sequencing, which underscores the importance for preventing viruses from entering and contaminating such facilities.

Dendritic cell-targeted porcine reproductive and respiratory syndrome virus (PRRSV) antigens adjuvanted with polyinosinic-polycytidylic acid (poly (I:C)) induced non-protective immune responses against heterologous type 2 PRRSV challenge in pigs

Porcine Reproductive and Respiratory Syndrome (PRRS) is an economically important swine viral disease worldwide. Current modified live-attenuated vaccines are ineffective against heterologous strains of PRRS virus (PRRSV) circulating in the field. In this study, we evaluated three dendritic cell (DC)-targeted vaccine candidates for their protective efficacy against heterologous PRRSV challenge. Ectodomain regions of DNA-shuffled structural proteins GP3, GP4, GP5 and M of PRRSV were fused together to form the vaccine antigen which was in turn fused with one of three recombinant antibodies each specific to a DC receptor: DC-SIGN, Langerin, and DEC205. The recombinant antibody-fused vaccine antigens were co-administered with polyinosinic-polycytidylic acid (poly (I:C)) adjuvant and subsequently challenged with a heterologous type 2 PRRSV strain (NADC20) in pigs. Our results demonstrate that pigs in DC-SIGN- and DEC205-targeted, but not Langerin- and non-targeted, vaccine groups showed significant IFN-γ- and IL-4-specific CD4T cell immune responses against the vaccine antigen in 7days post-challenge. Pigs in DC-SIGN- and Langerin-targeted vaccine groups showed greatly reduced IgG responses as compared to the DEC205- and non-targeted vaccine groups. The immune responses induced by DC-targeted vaccines did not reduce viremia and lung pathological lesions in type 2 PRRSV-challenged pigs. In contrast, pigs in Langerin-targeted vaccine group showed significantly increased serum viral titers and viral antigen in lung tissues at 7 and 14days post-challenge respectively. In conclusion, specific targeting of PRRSV antigen through DC-SIGN or DEC205 or Langerin-specific antibodies in the presence of poly (I:C) adjuvant induced immune responses that failed to protect pigs against heterologous type 2 PRRSV challenge.

Validation of a portable pneumatic captive bolt device as a one-step method of euthanasia for use in depopulation of feedlot cattle

OBJECTIVE

To validate the effectiveness of a penetrating captive bolt device with a built-in low-pressure air channel pithing mechanism (PCBD) as a 1-step method for euthanasia of cattle.

DESIGN

Clinical trial.

ANIMALS

66 feedlot steers and heifers (weight, 227 to 500 kg [500 to 1,100 lb]) that were not expected to survive or finish the feeding period with their cohorts.

PROCEDURES

Cattle were transported to a university facility and euthanized with the PCBD. For each calf, clinical variables were monitored and recorded immediately before and for at least 10 minutes after application of the PCBD. Following euthanasia, the head of each calf was removed and trauma to the brain and skull was assessed and scored.

RESULTS

Death was successfully achieved with the PCBD without application of an ancillary technique in all 66 cattle; however, 4 (6%) cattle required a second or third shot from the PCBD because of technical errors in its placement. All shots from the PCBD that entered the cranial vault successfully rendered cattle unconscious without a return to sensibility.

CONCLUSIONS AND CLINICAL RELEVANCE

Results indicated that the PCBD was an effective 1-step method of euthanasia for use in mass depopulation of feedlot cattle.

Outbreak of H5N2 highly pathogenic avian Influenza A virus infection in two commercial layer facilities: lesions and viral antigen distribution

The largest outbreak of highly pathogenic avian Influenza A virus (HPAIV) infection in U.S. history began in December 2014 resulting in the euthanasia of millions of birds and collateral economic consequences to the U.S. poultry industry. We describe 2 cases of H5N2 HPAIV infection in laying hens in Iowa. Following a sharp increase in mortality with minimal clinical signs, 15 dead birds, from 2 unrelated farms, were submitted to the Iowa State University Veterinary Diagnostic Laboratory. Common lesions included diffuse edema and multifocal hemorrhage of the comb, catarrhal exudate in the oropharynx, and multifocal tracheal hemorrhage. Less common lesions included epicardial petechiae, splenic hemorrhage, and pancreatic necrosis. Influenza A virus nucleoprotein was detected by immunohistochemistry in multiple cell types including ependymal cells, the choroid plexus, neurons, respiratory epithelium and macrophages in the lung, cardiac myocytes, endothelial cells, necrotic foci in the spleen, Kupffer cells in the liver, and necrotic acinar cells in the pancreas. Real-time polymerase chain reaction and sequencing confirmed H5N2 HPAIV with molecular characteristics similar to other contemporary U.S. H5N2 HPAIVs in both cases.

Human respiratory syncytial virus memphis 37 causes acute respiratory disease in perinatal lamb lung

Respiratory syncytial virus (RSV) is the leading cause of hospitalization due to respiratory illness among infants and young children of industrialized countries. There is a lack of understanding of the severe disease mechanisms as well as limited treatment options, none of which are fully satisfactory. This is partly due to lack of a relevant animal model of perinatal RSV infection that mimics moderate to severe disease in infants. We and others have shown mild disease in perinatal lambs with either a bovine or a human A2 strain of RSV. The Memphis 37 clinical strain of human RSV has been used to produce mild to moderate upper respiratory disease in healthy adult volunteers. We hypothesized that the Memphis 37 strain of RSV would infect perinatal lambs and produce clinical disease similar to that in human infants. Perinatal (3- to 5-day-old) lambs were inoculated intranasally with 2 mL/nostril of 1×10⁵ focus-forming units (FFU)/mL (n=2) or 2.1×10⁸ FFU/mL (n=3) of RSV Memphis 37. Clinical signs, gross and histological lesions, and immune and inflammatory responses were assessed. Memphis 37 caused moderate to severe gross and histologic lesions along with increased mRNA expression of macrophage inflammatory protein. Clinically, four of the five infected lambs had a mild to severe increase in expiratory effort. Intranasally administered RSV strain Memphis 37 infects neonatal lambs with gross, histologic, and immune responses similar to those observed in human infants.

Increased concentration of iodide in airway secretions is associated with reduced respiratory syncytial virus disease severity

Recent studies have revealed that the human and nonrodent mammalian airway mucosa contains an oxidative host defense system. This three-component system consists of the hydrogen peroxide (H2O2)-producing enzymes dual oxidase (Duox)1 and Duox2, thiocyanate (SCN(-)), and secreted lactoperoxidase (LPO). The LPO-catalyzed reaction between H2O2 and SCN(-) yields the bactericidal hypothiocyanite (OSCN(-)) in airway surface liquid (ASL). Although SCN(-) is the physiological substrate of LPO, the Duox/LPO/halide system can generate hypoiodous acid when the iodide (I(-)) concentration is elevated in ASL. Because hypoiodous acid, but not OSCN(-), inactivates respiratory syncytial virus (RSV) in cell culture, we used a lamb model of RSV to test whether potassium iodide (KI) could enhance this system in vivo. Newborn lambs received KI by intragastric gavage or were left untreated before intratracheal inoculation of RSV. KI treatment led to a 10-fold increase in ASL I(-) concentration, and this I(-) concentration was approximately 30-fold higher than that measured in the serum. Also, expiratory effort, gross lung lesions, and pulmonary expression of an RSV antigen and IL-8 were reduced in the KI-treated lambs as compared with nontreated control lambs. Inhibition of LPO activity significantly increased lesions, RSV mRNA, and antigen. Similar experiments in 3-week-old lambs demonstrated that KI administration was associated with reduced gross lesions, decreased RSV titers in bronchoalveolar lavage fluid, and reduced RSV antigen expression. Overall, these data indicate that high-dose KI supplementation can be used in vivo to lessen the severity of RSV infections, potentially through the augmentation of mucosal oxidative defenses.

Sucrose stabilization of Respiratory Syncytial Virus (RSV) during nebulization and experimental infection

BACKGROUND

Respiratory syncytial virus (RSV) is a common respiratory pathogen that can cause severe pneumonia. In vivo studies of RSV can be difficult due to variation in viral infection and disease severity in some animal models. Factors that may contribute to the variation are decreases in viral titer due to preparation and storage and method of virus administration. Nebulization is one method of RSV administration that provides even distribution of virus to all lung lobes; however, the exact quantity of the virus killed by nebulization is not defined. To test the hypothesis that sucrose enhances RSV stability and infectivity, a series of in vitro experiments were conducted with RSV strain Memphis 37 stored at varying concentrations (0%, 3%, 5%, 8%, 10%, 15%, and 20%) of sucrose as a possible cryo- and nebulization protectant. The optimal in vitro concentration was then assessed in vivo in a lamb model.

METHODS

Prior to titering the virus on HEp-2 cells, the various virus solutions were subjected to one freeze-thaw cycle and one nebulization cycle. Forty-eight hours after viral plating, infectious foci were detected and counted using immunofluorescent imaging. Titers were determined after freeze-thaw and after freeze-thaw followed by nebulization, then compared to the stock titers (before freezing) as well as to one another to determine the loss of infectivity. To further test this in vivo, lambs 2 to 3-days-old were infected via nebulization with RSV using inoculate containing either 20% sucrose or no sucrose followed by assessments of infection severity.

RESULTS

Nebulization of virus in 0% sucrose resulted in a 0.580 log reduction in infectivity while virus in 20% sucrose exhibited a 0.297 log reduction. In vivo studies demonstrated that 20% sucrose enhanced RSV lesions and antigen distribution.

CONCLUSIONS

The data suggests that both nebulization and freeze-thawing of RSV in the absence of sucrose cause unacceptable losses in viral infectivity and that sucrose acts as a RSV protectant in both regards.

Effects of formalin-inactivated respiratory syncytial virus (FI-RSV) in the perinatal lamb model of RSV

Respiratory syncytial virus (RSV) is the most frequent cause of bronchiolitis in infants and children worldwide. There are currently no licensed vaccines or effective antivirals. The lack of a vaccine is partly due to increased caution following the aftermath of a failed clinical trial of a formalin-inactivated RSV vaccine (FI-RSV) conducted in the 1960’s that led to enhanced disease, necessitating hospitalization of 80% of vaccine recipients and resulting in two fatalities. Perinatal lamb lungs are similar in size, structure and physiology to those of human infants and are susceptible to human strains of RSV that induce similar lesions as those observed in infected human infants. We sought to determine if perinatal lambs immunized with FI-RSV would develop key features of vaccine-enhanced disease. This was tested in colostrum-deprived lambs immunized at 3–5 days of age with FI-RSV followed two weeks later by RSV infection. The FI-RSV-vaccinated lambs exhibited several key features of RSV vaccine-enhanced disease, including reduced RSV titers in bronchoalveolar lavage fluid and lung, and increased infiltration of peribronchiolar and perivascular lymphocytes compared to lambs either undergoing an acute RSV infection or naïve controls; all features of RSV vaccine-enhanced disease. These results represent a first step proof-of-principle demonstration that the lamb can develop altered responses to RSV following FI-RSV vaccination. The lamb model may be useful for future mechanistic studies as well as the assessment of RSV vaccines designed for infants.

Perinatal lamb model of respiratory syncytial virus (RSV) infection

Respiratory syncytial virus (RSV) is the most frequent cause of bronchiolitis in infants and children worldwide. Many animal models are used to study RSV, but most studies investigate disease in adult animals which does not address the unique physiology and immunology that makes infants more susceptible. The perinatal (preterm and term) lamb is a useful model of infant RSV disease as lambs have similar pulmonary structure including airway branching, Clara and type II cells, submucosal glands and Duox/lactoperoxidase (LPO) oxidative system, and prenatal alveologenesis. Lambs can be born preterm (90% gestation) and survive for experimentation although both preterm and term lambs are susceptible to ovine, bovine and human strains of RSV and develop clinical symptoms including fever, tachypnea, and malaise as well as mild to moderate gross and histologic lesions including bronchiolitis with epithelial injury, neutrophil infiltration and syncytial cell formation. RSV disease in preterm lambs is more severe than in term lambs; disease is progressively less in adults and age-dependent susceptibility is a feature similar to humans. Innate and adaptive immune responses by perinatal lambs closely parallel those of infants. The model is used to test therapeutic regimens, risk factors such as maternal ethanol consumption, and formalin inactivated RSV vaccines.

Regulation of surfactant protein and defensin mRNA expression in cultured ovine type II pneumocytes by all-trans retinoic acid and VEGF

Beta-defensins and surfactant proteins are components of the pulmonary innate immune system. Their gene expression is regulated by development, hormones, growth and immunoregulatory factors. It was our hypothesis that growth and differentiation factors such as all-trans retinoic acid (RA) and vascular endothelial growth factor (VEGF) may affect expression of selected innate immune genes by respiratory epithelial cells. Ovine JS7 cells (alveolar type II pneumocytes) were incubated in serum-free Dulbecco's modified Eagle's medium (DMEM) complete media that contained: no treatment (negative control), RA (500 nM), or VEGF (100 ng/ml) for 6, 12 or 24 h incubation. Total RNA was isolated, cDNA synthesized, and relative mRNA levels of surfactant protein A (SP-A) and SP-D, and sheep beta-defensin-1 (SBD-1) were determined by real-time reverse transcriptase-polymerase chain reaction (RT-PCR). Cells had significantly increased expression of SP-D mRNA at 6 h and 24 h, decreased expression of SP-A mRNA at 12 h, and unchanged levels of SBD-1 mRNA after the treatment with RA compared with their respective negative controls. VEGF did not alter the expression of the three innate immune genes. These findings suggest that SP-A and SP-D have different transcription regulation pathways, and that expression of SBD-1 is not inducible by RA similar to its human homolog HBD-1. The lack of changes induced by VEGF treatment suggests that VEGF does not have a direct effect on epithelial cells, but may affect gene expression indirectly.