Hemorrhagic Tracheitis Standardized Submissions to Help Find Etiology Supported by SHIC

July 14, 2020 — 

Hemorrhagic tracheitis syndrome (HTS) has been diagnosed in Canada for years, and recently increasingly recognized in the US. To date, no etiologic agent(s) has been definitively or consistently associated with the syndrome in the cases examined or reported. To investigate etiology, a joint project of the Iowa State University Veterinary Diagnostic Lab (ISU VDL), Animal Health Laboratory, University of Guelph (AHL-UG), and the Laboratoire de santé animale, MAPAQ,Québec has begun with support from SHIC. Diagnostic investigations at both ISU VDL and AHL-UG to date for tracheitis cases have been hampered by dependence on the submitter's tissue sampling and diagnostic test selection. A standardized diagnostic test plan for swine tracheitis cases has been developed. This joint VDL project will facilitate thorough, consistent testing of these cases, allow staff to exclude common respiratory pathogens as the cause of tracheitis in individual animals and herds, and establish a tissue bank for future NGS to search for novel or emerging pathogens in those cases with no confirmed etiologic diagnosis.

This spring, the Swine Health Information Center (SHIC) and America Association of Swine Veterinarians co-hosted a webinar providing information on the syndrome, its signalments, tissues for postmortem assessment, and management. The webinar is available to view here.

Severe necrohemorrhagic tracheitis syndrome observed in finishing pigs and replacement breeding stock is characterized by severe erosive or ulcerative lesions. Transient outbreaks are reported, with herd resolution over a period of two to three weeks. Opportunistic bacterial infection is common among the tracheal lesions at the time of necropsy and evaluation. The temporal pattern, clinical signs, and gross and histologic lesions of severe necrohemorrhagic tracheitis, together with the failure to consistently identify any known respiratory pathogen in many of the cases, raises concern of either a novel infectious agent or a novel strain of a known infectious agent. Alternatively, the lesion may represent a stereotypic sequel to a variety of primary cause. Contribution of anatomic features (e.g. tracheal diameter, length) compressive effects of cervical lymphadenopathy, genetic factors, and environmental/air quality conditions to the development and severity of tracheitis must be considered.

Morbidity ranges from <1% to 10 to 50%, depending on the herd, with consistently low mortality (<1-3%). Clinical signs resolve over seven to 10 days, sometimes in response to antibiotic and/or anti-inflammatory therapy; however, resolution was noted in some herds with no or minimal treatment or interventions.

The following represents desired submissions for the HTS study at participating VDLs to develop a diagnostic investigation protocol and establishment of a tissue bank. Samples should be sent using each facility's particular submission forms.

Clinical history: Percent morbidity/mortality, approximate weight of hogs, herd genetics
Gross images: Cervical region and pluck at time of necropsy
Intact plucks: Trachea from larynx to bifurcation, both lungs, from affected pigs; Tracheas should be partially opened during the field necropsy to confirm lesions compatible with necrohemorrhagic tracheitis; Further dissection and sampling of trachea and lung for diagnostic testing and lesion documentation will be done at the VDLs
Lymph nodes: Bilateral caudal deep cervical and costo-axillary lymph nodes; Intact, fresh, and labelled (right and left, anatomic site)
Control animals: Plucks and lymph nodes as above from two or three unaffected herdmates dying or euthanized during the same timeframe, potentially due to other causes, and without gross lesions of necrohemorrhagic tracheitis
Systemic samples: Fresh AND formalin-fixed: spleen, stomach, ileum, and heart
Oral fluids: From all affected pens, two unaffected pens in affected barn, and two pens in unaffected barns
Serum: From five animals in each of one representative affected pen, one unaffected pen, and one pen in an unaffected barn.

Additionally, environmental control records for affected barns for two weeks prior to outbreak, targeting sudden fluctuations in temperature or humidity are requested, including comments regarding barn air quality.

Tissues submitted towards this study should be clearly labeled with "SHIC Hemorrhagic Tracheitis Project," or similar verbiage, and directed towards the attention of the diagnostician associated with this project at the respective institution (see below).

VDL	Address	Submission form link	Attending diagnostician
Iowa State University	Veterinary Diagnostic Laboratory Iowa State University 1850 Christensen Dr Ames, IA 50011-1134	Please use "Pathology Request Form" under "Cases WITH tissue" ISU Form	Alyona Michael (515-294-9019)
University of Guelph	Animal Health Laboratory, University of Guelph Address: Building 89, 419 Gordon St., Guelph, Ontario Canada N1G 2W1	UG Form	Josepha DeLay (519-824-4120 ext 54576)
MAPAQ	Laboratoire de santé animale : 2650, rue Einstein Québec (Québec) G1P 4S8	MAPAQ Form	Isabelle St-Pierre 418-643-6140 ext. 2626 isabelle.st-pierre@mapaq.gouv.qc.ca

As the world deals with the COVID-19 pandemic, SHIC continues to focus efforts on prevention, preparedness, and response to novel and emerging swine disease for the benefit of US swine health. As a conduit of information and research, SHIC encourages sharing of its publications and research. Forward, reprint, and quote SHIC material freely. SHIC is funded by America's pork producers to fulfill its mission to protect and enhance the health of the US swine herd. For more information, visit http://www.swinehealth.org or contact Dr. Sundberg at psundberg@swinehealth.org.