Undiagnosed respiratory disease: How to sample for success

This week, the Swine Health Information Center and the American Association of Swine Veterinarians hosted the webinar, “Undiagnosed Respiratory Disease: How to Sample for Success and What’s New,” which included viewpoints from practitioners, diagnosticians, and pathologists all seeking answers to contemporary respiratory problems . Diagnoses of porcine astrovirus 4 and porcine haemagglutinating encephalomyelitis virus resulted from pursuing a diagnosis that excluded more common viruses. While unlimited testing and diagnostic resources would be ideal for identifying the root causes of respiratory problems that have not been identified as common viruses, webinar attendees felt this was unrealistic. However, knowledge of unresolved respiratory problems could broaden the scope of diagnostic possibilities.

Evan Koep, Pipestone Veterinary Services, provided an overview of the challenge of endemic influenza on the farm, the system’s drive for health and a desire to identify the cause of the persistent cough. With the goal of eliminating influenza in sow herds within the Pipestone system, they hope to achieve the result of improved health and greater customer satisfaction.

After two years, their influenza elimination program has a success rate of about 70%. Despite this success, some farms continue to experience piglet cough. This nonproductive cough, with a prevalence of 20% to 60%, resembles influenza but is confirmed as not IAV by udder swab, nasal swab, and lung tissue tests.

Koep sought a definitive diagnosis, requesting tests for IAV, PPIV, PHEV, PRCV, MHR and other bacteria. He also submitted fixed and fresh lung, trachea, heart, spleen, liver, kidney and tonsil tissue. While these tests were all PCR negative for virus, histopathology said, “Lesions in the trachea and upper airways are suggestive of epitheliotropic virus.”

From that point forward, the next step was the sequencing of the next generation of lesioned lung specimens, where porcine astrovirus 4 was found and confirmed by follow-up PCR in previous cases. PAstV4, an uncommon virus, is unknown, nor is its association with the respiratory tract.

Ben Heimat, Cambridge Technologies, shared that there are five genotypes of the porcine astrovirus. Historically, they have been associated with gastrointestinal disease, although in 2015 PAstV4 was detected in multiple respiratory specimens submitted to the Kansas State VDL for metagenomic sequencing. In these cases, genome sequencing identified a new AstV in the PAstV4 lineage.

Tests at KSVDL compared Ct values ​​for positive samples between nasal and fecal material. Significantly lower Ct values ​​(higher concentrations of PAstV4 genome) were found in nasal swabs. It suggests that positive tests indicate respiratory tropism. The summary of Heim’s presentation indicated that astrovirus infections are common in pigs and extraintestinal infections in pigs involve the respiratory system.

Rachel Derscheid of the Iowa State University Veterinary Diagnostics Laboratory discussed the physiology of the trachea. While the trachea is a non-collapsible passageway for air, it contains rings of cartilage and a mucosal lining that regulate both temperature and moisture. The trachea protects and cleans columnar epithelium, goblet cells and mucociliary apparatus. Derschied shared typical VDL submissions for respiratory tissue and provided guidance for tracheal sampling for study purposes.

Presenting a case history, Derschied shared initial test results suggesting typical respiratory problems, including IAV. When the manufacturer submitted additional tissues due to the persistent cough, including comments on negative IAV, porcine parainfluenza virus 1 and porcine respiratory coronavirus results, further testing was initiated including NGS, PCR and in situ hybridization. These results indicate tracheitis with and without bronchitis not only for PAstV4. Porcine hemagglutinating encephalomyelitis virus and Mycoplasm hyopneumoniae, which cause persistent cilia damage, were other viruses identified.

“We don’t see what we’re not looking for,” Derscheid said, recommending an examination of the trachea, submitting a fixed trachea and/or leaving a portion attached to the fresh lung. And she emphasized communication.

In a retrospective evaluation of bronchitis and tracheitis of unknown etiology, Michael Rahe, ISU VDL, started with a case study. The clinical report concerned cough in three-week-old pigs with multifocal to coalescing atelectasis, all classic findings of influenza. However, the case was influenza PCR negative. The diagnosis code was respiratory – bronchitis, viral – unspecified. 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 identified a few cases of PAstV4-associated tracheitis/bronchitis. These are usually confined to the trachea and bronchi but do not appear to extend into the bronchioles, possibly due to a lack of receptors. Cts over 25 were negative by RNA scope in these cases.

SHIC, established in 2015 by the National Pork Board solely with funding from Pork Checkoff, remains focused on the prevention, preparedness and response to novel and emerging swine diseases for the benefit of swine health in the United States. SHIC is funded by American pork producers to fulfill its mission to protect and improve the health of the US swine herd.

Source: Swine Health Information Center, which is solely responsible for the information provided and is the sole property of the information. Informa Business Media and any of its affiliates are not responsible for the content of this information resource.