Submissions to the Iowa State University Veterinary Diagnostic Laboratory have recently included a growing number of pig cases with a severe lung lesion pattern called diffuse alveolar damage (DAD), a syndrome historically rare in swine. To understand what may be driving this change, the Swine Health Information Center funded a study led by Dr. Marcelo Almeida to investigate the etiology of this emergent swine respiratory disease syndrome. A total of 42 DAD cases were reviewed by veterinarians and tested by PCR for common respiratory viruses, including PRRSV, IAV, and PCV2, and next generation sequencing to detect other viruses. While many pigs were infected with common respiratory pathogens, no single virus consistently explained the DAD lesions, suggesting that controlling PRRSV, IAV, and PCV2 through vaccination and sound herd management remains the best strategy available today to help reduce the risk of this severe lung damage in pigs.
Find the industry summary for SHIC project #24-043 here.
In veterinary medicine, DAD is most frequently observed as a syndrome in cattle, referred to as atypical interstitial pneumonia, which is associated with ingested pneumotoxins, epitheliotropic viral agents, and noxious gas inhalation (Doster et al., 2010; Carvello et al., 2022; Chien et al., 2022; Haydock et al., 2022). Unlike cattle, diffuse alveolar damage is poorly documented or characterized in pigs, with only rare reports of compatible lesions associated with porcine respiratory coronavirus infection and a historical association with PCV2 (Carvallo et al., 2022; Jung et al., 2007).
In pigs with respiratory disease complex, expiratory dyspnea – often referred to as “thumping” – is caused by decreased oxygenation and lung compliance due to fluid or cellular expansion of the interstitium. This pattern of interstitial pneumonia occurs as a sequela of systemic insult due to endotoxemia and bacterial or viral infections and is most often associated with PRRSV and PCV2 infections in swine. In contrast, DAD, the focus of this study, is a lesion characterized by synchronous necrosis of respiratory pneumocytes and/or capillary endothelium that compromises diffusion of gases between the alveolar space and circulating red blood cells (Carvallo et al., 2022).
In the absence of intensive supportive care, DAD progresses to respiratory failure and/or cardiovascular collapse and death in pigs. Surviving pigs typically face a prolonged recovery and sustained clinical signs with adverse production impacts due to the severe and often irreversible damage to lung architecture, leading to interstitial fibrosis and permanently diminished oxygenation capacity.
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