Undiagnosed respiratory disease is frustrating and difficult to fight. It’s expensive, time-consuming and draining for everyone involved.
Although unlimited resources for testing and diagnosis would be ideal for identifying root causes of respiratory issues not identified as common viruses, participants in a recent webinar hosted by the Swine Health Information Center (SHIC) and the American Association of Swine Veterinarians, say it’s unrealistic.
In “Undiagnosed Respiratory Disease: How to Sample for Success and What’s New,” viewpoints of the practitioner, diagnostician and pathologists were presented and how they each seek answers to ongoing respiratory issues.
Diagnoses of porcine astrovirus 4 (PAstV4) and porcine hemagglutinating encephalomyelitis virus (PHEV) resulted from the pursuit of a diagnosis when more common viruses were ruled out. Excluding possible foreign animal diseases, as well as ongoing concern for herd health, drove the production systems to press diagnosticians to expand their investigations, leading to the confirmation of PAstV4 and PHEV and implementation of corresponding response and control measures on the farm.
An overview of the challenge of endemic influenza on the farm was presented by Evan Koep, DVM, with Pipestone Veterinary Services. He discussed the system’s push for higher health and desire to identify the cause of ongoing coughing. The Pipestone system has a goal of eliminating influenza in sow herds and hope to achieve a result of improved health and improved client satisfaction.
After two years, Koep explained, Pipestone’s influenza elimination program has a roughly 70% elimination success rate. Despite this success, some farms continue to have piglets coughing. This non-productive cough, at 20% to 60% prevalence, resembles influenza yet is confirmed not to be IAV via udder wipes, nasal swabs and lung tissue testing.
Koep said he sought a definitive diagnosis, with tests for Influenza A virus, porcine parainfluenza virus, PHEV, porcine respiratory coronavirus, Mycoplasma hyorhinis and other bacteria requested. He submitted fixed and fresh lung, trachea, heart, spleen, liver, kidney and tonsil tissues. Although these tests were all PCR negative for viruses, histopathology said, “Lesions in the trachea and upper airways are suggestive of an epitheliotropic virus.”
This was followed up with next generation sequencing on lung samples with lesions with porcine astrovirus 4 found and confirmed by follow-up PCR on past cases. PAstV4, an uncommon virus, is not well known nor is its association with the respiratory tract, SHIC reports.
Ben Hause, vice president for research and development at Cambridge Technologies shared the five genotypes of porcine astrovirus (AstV). Historically, they are associated with gastroenteric disease. However, Hause said in 2015, PAstV4 was detected in multiple respiratory samples submitted for metagenomic sequencing at the Kansas State Veterinary Diagnostic Lab (KSVDL). Genome sequencing identified a novel AstV in the PAstV4 lineage in those cases, SHIC reports.
Testing at KSVDL compared Ct values for positive samples between nasal and fecal material. There were significantly lower Ct values (higher levels of PAstV4 genetic material) in nasal swabs. This suggests positive tests are indicative of a respiratory tropism. Hause’s summary revealed AstV infections are common in pigs and extraintestinal infection in pigs includes the respiratory system.
Rachel Derscheid, DVM, with the Iowa State University Veterinary Diagnostic Lab (ISU VDL), reviewed trachea physiology. While a non-collapsible passageway for air, the trachea includes cartilage rings and mucosal lining, regulating both temperature and humidity, SHIC reports. The trachea protects and cleans columnar epithelium, goblet cells and mucociliary apparatus. Derschied shared typical respiratory tissue VDL submissions and provided guidance for sampling the trachea for study.
In presenting a case history, Derschied shared initial results of testing which indicated typical respiratory issues, including IAV. When the producer submitted additional tissues due to ongoing coughing, including notes on negative IAV, porcine parainfluenza virus 1, and porcine respiratory coronavirus results, further tests were initiated, including NGS, PCR, and in situ hybridization. These results indicated tracheitis with and without bronchitis, not just for PAstV4. Porcine hemagglutinating encephalomyelitis virus and Mycoplasma hyopneumoniae causing persistent cilia damage were other viruses identified.
“We don’t see what we don’t look for,” Derscheid said. She recommended examination of the trachea, submitting fixed trachea and/or leaving a portion attached to fresh lung. She also emphasized communication.
In a retrospective evaluation of bronchitis and tracheitis of unknown etiology, Michael Rahe, DVM with the ISU VDL, discussed a case observation. The clinical report was of coughing in three-week-old pigs with multifocal to coalescing atelectasis, all of which are classic findings for influenza. However, the case was influenza PCR negative. The diagnostic code was respiratory – bronchitis, viral – non-specified. PAstV4 was identified via NGS.
Rahe then addressed the question, “How many cases of non-specific tracheitis/bronchitis are caused by non-influenza viral infections?” The review did identify some cases of PAstV4 associated tracheitis/bronchitis. SHIC reports those tend to be limited to the trachea and bronchi but do not seem to extend into bronchioles, perhaps due to a lack of receptors. Cts over 25 in these cases were negative via RNA scope.
