Porcine epidemic diarrhea virus (PEDV) was identified in the United States (U.S.) swine population for the first time in April 2013 and rapidly spread nationwide. However, no information has been ...published regarding the minimum infectious dose (MID) of PEDV in different pig models. The main objective of this study was to determine the oral minimum infectious dose of PEDV in naïve conventional neonatal piglets and weaned pigs. A U.S. virulent PEDV prototype isolate (USA/IN19338/2013) with known infectious titer was serially ten-fold diluted in virus-negative cell culture medium. Dilutions with theoretical infectious titers from 560 to 0.0056 TCID50/ml together with a medium control were orogastrically inoculated (10ml/pig) into 7 groups of 5-day-old neonatal pigs (n = 4 per group) and 7 groups of 21-day-old weaned pigs (n = 6 per group). In 5-day-old pigs, 10ml of inoculum having titers 560-0.056 TCID50/ml, corresponding to polymerase chain reaction (PCR) cycle threshold (Ct) values 24.2-37.6, resulted in 100% infection in each group; 10ml of inoculum with titer 0.0056 TCID50/ml (Ct>45) caused infection in 25% of the inoculated pigs. In 21-day-old pigs, 10ml of inoculum with titers 560-5.6 TCID50/ml (Ct 24.2-31.4) resulted in 100% infection in each group while 10ml of inoculum with titers 0.56-0.0056 TCID50/ml (Ct values 35.3 ->45) did not establish infection in any pigs under study conditions as determined by clinical signs, PCR, histopathology, immunohistochemistry, and antibody response. These data reveal that PEDV infectious dose is age-dependent with a significantly lower MID for neonatal pigs compared to weaned pigs. This information should be taken into consideration when interpreting clinical relevance of PEDV PCR results and when designing a PEDV bioassay model. The observation of such a low MID in neonates also emphasizes the importance of strict biosecurity and thorough cleaning/disinfection on sow farms.
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Congenital tremors is a sporadic disease of neonatal pigs characterized by action-related repetitive myoclonus. A majority of outbreaks of congenital tremors have been attributed to an unidentified ...virus. The objectives of this project were to 1) detect potential pathogen(s) in samples from piglets with congenital tremors and 2) develop an infection model to reproduce disease. Using next-generation sequencing, a divergent lineage pestivirus was detected in piglets with congenital tremors. The virus was originally most closely related to a bat pestivirus but is now more closely related to a recently published novel porcine pestivirus provisionally named atypical porcine pestivirus. A quantitative real-time PCR detected the virus in samples from neonatal piglets with congenital tremors from two separate farms, but not in samples from unaffected piglets from the same farm. To fulfill the second objective, pregnant sows were inoculated with either serum containing the pestivirus or PBS (control) by intravenous and intranasal routes simultaneously with direct inoculation of fetal amniotic vesicles by ultrasound-guided surgical technique. Inoculations were performed at either 45 or 62 days of gestation. All sows inoculated with the novel pestivirus farrowed piglets affected with congenital tremors while PBS-inoculated control piglets were unaffected. Tremor severity for each piglet was scored from videos taken 0, 1 and 2 days post-farrowing. Tremor severity remained relatively constant from 0 to 2 days post-farrowing for a majority of piglets. The prevalence of congenital tremors in pestivirus-inoculated litters ranged from 57% (4 out of 7 affected piglets) to 100% (10 out of 10 affected piglets). The virus was consistently detected by PCR in tissues from piglets with congenital tremors but was not detected in control piglets. Samples positive by PCR in greater than 90% of piglets sampled included brainstem (37 out of 41), mesenteric lymph node (37 out of 41), tracheobronchial lymph node (37 out of 41), and whole blood (19 out of 20). Although the first description of congenital tremors was in 1922, this is the first reported reproduction of congenital tremors following experimental inoculation with a divergent lineage porcine pestivirus. Studies investigating disease mechanism, epidemiology, and diagnostic assay development are needed to better understand the pathophysiology of congenital tremors due to this pestivirus.
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Although 90% of BRD relapses are reported to receive retreatment with a different class of antimicrobial, studies examining the impact of antimicrobial selection (i.e. bactericidal or bacteriostatic) ...on retreatment outcomes and the emergence of antimicrobial resistance (AMR) are deficient in the published literature. This survey was conducted to determine the association between antimicrobial class selection for treatment and retreatment of BRD relapses on antimicrobial susceptibility of Mannheimia haemolytica, Pasteurella multocida, and Histophilus somni. Pathogens were isolated from samples submitted to the Iowa State University Veterinary Diagnostic Laboratory from January 2013 to December 2015. A total of 781 isolates with corresponding animal case histories, including treatment protocols, were included in the analysis. Original susceptibility testing of these isolates for ceftiofur, danofloxacin, enrofloxacin, florfenicol, oxytetracycline, spectinomycin, tilmicosin, and tulathromycin was performed using Clinical and Laboratory Standards Institute guidelines. Data were analyzed using a Bayesian approach to evaluate whether retreatment with antimicrobials of different mechanistic classes (bactericidal or bacteriostatic) increased the probability of resistant BRD pathogen isolation in calves. The posterior distribution we calculated suggests that an increased number of treatments is associated with a greater probability of isolates resistant to at least one antimicrobial. Furthermore, the frequency of resistant BRD bacterial isolates was greater with retreatment using antimicrobials of different mechanistic classes than retreatment with the same class. Specifically, treatment protocols using a bacteriostatic drug first followed by retreatment with a bactericidal drug were associated with a higher frequency of resistant BRD pathogen isolation. In particular, first treatment with tulathromycin (bacteriostatic) followed by ceftiofur (bactericidal) was associated with the highest probability of resistant M. haemolytica among all antimicrobial combinations. These observations suggest that consideration should be given to antimicrobial pharmacodynamics when selecting drugs for retreatment of BRD. However, prospective studies are needed to determine the clinical relevance to antimicrobial stewardship programs in livestock production systems.
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We report highly pathogenic avian influenza A(H5N1) virus in dairy cattle and cats in Kansas and Texas, United States, which reflects the continued spread of clade 2.3.4.4b viruses that entered the ...country in late 2021. Infected cattle experienced nonspecific illness, reduced feed intake and rumination, and an abrupt drop in milk production, but fatal systemic influenza infection developed in domestic cats fed raw (unpasteurized) colostrum and milk from affected cows. Cow-to-cow transmission appears to have occurred because infections were observed in cattle on Michigan, Idaho, and Ohio farms where avian influenza virus-infected cows were transported. Although the US Food and Drug Administration has indicated the commercial milk supply remains safe, the detection of influenza virus in unpasteurized bovine milk is a concern because of potential cross-species transmission. Continued surveillance of highly pathogenic avian influenza viruses in domestic production animals is needed to prevent cross-species and mammal-to-mammal transmission.
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To evaluate trends in bacterial causes of valvular endocarditis in swine, we retrospectively analyzed 321 cases diagnosed at Iowa State University Veterinary Diagnostic Laboratory (Ames, IA, USA) ...during May 2015--April 2020. Streptococcus gallolyticus was the causative agent for 7.59% of cases. This emerging infection in swine could aid study of endocarditis in humans.
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Porcine astrovirus type 3 (PoAstV3) has been previously identified as a cause of polioencephalomyelitis in swine and continues to cause disease in the US swine industry. Herein, we describe the ...characterization of both untranslated regions, frameshifting signal, putative genome-linked virus protein (VPg) and conserved antigenic epitopes of several novel PoAstV3 genomes. Twenty complete coding sequences (CDS) were obtained from 32 diagnostic cases originating from 11 individual farms/systems sharing a nucleotide (amino acid) percent identity of 89.74-100% (94.79-100%), 91.9-100% (96.3-100%) and 90.71-100% (93.51-100%) for ORF1a, ORF1ab and ORF2, respectively. Our results indicate that the 5'UTR of PoAstV3 is highly conserved highlighting the importance of this region in translation initiation while their 3'UTR is moderately conserved among strains, presenting alternative configurations including multiple putative protein binding sites and pseudoknots. Moreover, two predicted conserved antigenic epitopes were identified matching the 3' termini of VP27 of PoAstV3 USA strains. These epitopes may aid in the design and development of vaccine components and diagnostic assays useful to control outbreaks of PoAstV3-associated CNS disease. In conclusion, this is the first analysis predicting the structure of important regulatory motifs of neurotropic mamastroviruses, which differ from those previously described in human astroviruses.
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Diet has been implicated as a major factor impacting clinical disease expression of swine dysentery and Brachyspira hyodysenteriae colonization. However, the impact of diet on novel pathogenic ...strongly beta-hemolytic Brachyspira spp. including "B. hampsonii" has yet to be investigated. In recent years, distillers dried grains with solubles (DDGS), a source of insoluble dietary fiber, has been increasingly included in diets of swine. A randomized complete block experiment was used to examine the effect of increased dietary fiber through the feeding of DDGS on the incidence of Brachyspira-associated colitis in pigs. One hundred 4-week-old pigs were divided into five groups based upon inocula (negative control, Brachyspira intermedia, Brachyspira pilosicoli, B. hyodysenteriae or "B. hampsonii") and fed one of two diets containing no (diet 1) or 30% (diet 2) DDGS. The average days to first positive culture and days post inoculation to the onset of clinical dysentery in the B. hyodysenteriae groups was significantly shorter for diet 2 when compared to diet 1 (P = 0.04 and P = 0.0009, respectively). A similar difference in the average days to first positive culture and days post inoculation to the onset of clinical dysentery was found when comparing the "B. hampsonii" groups. In this study, pigs receiving 30% DDGS shed on average one day prior to and developed swine dysentery nearly twice as fast as pigs receiving 0% DDGS. Accordingly, these data suggest a reduction in insoluble fiber through reducing or eliminating DDGS in swine rations should be considered an integral part of any effective disease elimination strategy for swine dysentery.
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In March 2024, the emergence of highly pathogenic avian influenza (HPAI) A (H5N1) infections in dairy cattle was detected in the United Sates for the first time. We genetically characterize HPAI ...viruses from dairy cattle showing an abrupt drop in milk production, as well as from two cats, six wild birds, and one skunk. They share nearly identical genome sequences, forming a new genotype B3.13 within the 2.3.4.4b clade. B3.13 viruses underwent two reassortment events since 2023 and exhibit critical mutations in HA, M1, and NS genes but lack critical mutations in PB2 and PB1 genes, which enhance virulence or adaptation to mammals. The PB2 E627 K mutation in a human case associated with cattle underscores the potential for rapid evolution post infection, highlighting the need for continued surveillance to monitor public health threats.In March 2024, the emergence of highly pathogenic avian influenza (HPAI) A (H5N1) infections in dairy cattle was detected in the United Sates for the first time. We genetically characterize HPAI viruses from dairy cattle showing an abrupt drop in milk production, as well as from two cats, six wild birds, and one skunk. They share nearly identical genome sequences, forming a new genotype B3.13 within the 2.3.4.4b clade. B3.13 viruses underwent two reassortment events since 2023 and exhibit critical mutations in HA, M1, and NS genes but lack critical mutations in PB2 and PB1 genes, which enhance virulence or adaptation to mammals. The PB2 E627 K mutation in a human case associated with cattle underscores the potential for rapid evolution post infection, highlighting the need for continued surveillance to monitor public health threats.
Bovine respiratory disease is the most costly disease facing the cattle industry. Increasing resistance to antimicrobial treatment has been presented as a significant contributing factor, often ...through summarized susceptibility testing data. We assessed the relationship between previous antimicrobial treatment and antimicrobial susceptibility results from isolates of Mannheimia haemolytica, Pasteurella multocida, and Histophilus somni cultured from bovine respiratory cases submitted to the Iowa State University Veterinary Diagnostic Laboratory from 2013 to 2015. Antimicrobial susceptibility data from 1,251 bacterial isolates were included for analysis. More bacterial isolates from cattle that received antimicrobial treatment showed resistance compared to isolates from untreated cattle, and the percentage of resistant isolates increased as the number of antimicrobial treatments increased. Resistance to enrofloxacin, spectinomycin, tilmicosin, and tulathromycin was present in >75% of M. haemolytica isolates from cattle that had received 3 or more antimicrobial treatments; resistance to each of those 4 antimicrobials was present in ≤10% of M. haemolytica isolates from untreated cattle. Similar but less dramatic trends were apparent for isolates of P. multocida and H. somni. The percentage of multi-drug resistant bacterial isolates also increased with the number of treatments. Results of our study suggest that previous antimicrobial treatment may have a profound effect on antimicrobial susceptibility testing. Summarized susceptibility results from diagnostic laboratories should not be used to make generalized statements regarding trends in antimicrobial resistance without providing context regarding antimicrobial treatment history.
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Bovine coronavirus (BCoV) is a known cause of enteric disease in cattle; however, its role in bovine respiratory disease (BRD) is poorly understood, with a dearth of evidence of the detection of the ...virus in respiratory tract lesions. We coupled histologic evaluation of tracheal and lower airway tissues from 104 calves with BRD in which BCoV was detected in the lungs via PCR followed by direct detection of BCoV by immunohistochemistry and an RNA in situ hybridization assay (ISH; RNAscope technology). RNAscope ISH detected BCoV in respiratory epithelium in more cases than did IHC. Using both methods of direct detection, tracheal epithelial attenuation and identification of the virus within lesions were observed commonly. Our results confirm a role of BCoV in respiratory tract infection and pathology, and show that the virus likely plays a role in the development of BRD.
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