Porcine Sapovirus Webinar Demonstrates Need for Diligence in Diagnostics

The Swine Health Information Center and American Association of Swine Veterinarians hosted a webinar on porcine sapovirus, a potentially emerging disease, on August 30 with 394 registrants from 22 countries. Speakers shared diagnostic and field experience with PSaV including clinical presentation, production impacts, control/response strategies, and other insights. Cumulatively, presenters offered advice on the risks of narrowly focusing on a single pathogen during a diagnostic investigation, which may result in missed detections of emerging or less common pathogens. A definitive lab diagnosis is necessary to know which pathogen or combination of pathogens are the cause of clinical disease in your swine herd.

The webinar can be viewed here.

Dr. Qiuhong Wang, The Ohio State University College of Veterinary Medicine, shared a historical perspective on PSaV. The Cowden strain was first detected in the US, together with rotavirus and astrovirus, by electron microscopy in the intestinal contents of a 27-day-old diarrheic pig from an Ohio swine farm in 1980. Dr. Wang said its genomic organization is that of a single-stranded, positive-sense RNA genome and shared illustrations of its structure. Dr. Wang discussed SaV’s classification which includes 19 genogroups of which eight infect pigs – GIII, GV-VXI. Further information in her presentation dove into details of PSaV etiology, prevalence at different farms and different ages of pigs, cell culture adaptation, and antibody assays.

Dr. Tom Petznick, practitioner with ArkCare in Omaha, Nebraska, shared his experience with discovery of PSaV on a client’s farm and the lessons learned in the process. Clinical signs on the farm included diarrhea and reduced average daily gain in pigs 7 days of age and older. Specifically, diarrhea was gravy to toothpaste-like in consistency and grey, yellow, yellowish-brown in color. Disease was self-limiting at or shortly after weaning with high morbidity/low mortality. The pigs didn’t respond to treatment. While there was low mortality, some pigs were too light at weaning and morbidity was variable. Affected pigs exhibited 1.5 pounds of lost wean weight.

Dr. Petznick pursued a definitive diagnosis in his client’s herd with planning, sample collection, and follow-up analysis. Initial results were negative for the usual causes – rotavirus, PEDV, PDCoV, and TGEV.  The pursuit of a diagnosis continued with collaboration from Iowa State University’s Veterinary Diagnostic Lab, Merck Animal Health’s Sequivity division, the producer, and the Swine Health Information Center Diagnostic Fee Support. Next generation sequencing unexpectedly found PSaV. Though identified in the US in 1980, PSaV had not been identified as a significant cause for diarrhea in US herds for decades.

After implementing environmental analysis, sanitation and controlled/timed exposure in an unsuccessful effort to control the PSaV, Dr. Petznick investigated vaccination. In a four-step process including review of previous data, identifying the sample subject, analyzing fecal shedding vs weaning weight, and performing a vaccine field trial, the proof of concept was completed. In the field trial, staff and Dr. Petznick observed almost complete disappearance of diarrhea and weaning weights increased.

While other farms Dr. Petznick serves had similar clinical signs in pigs, the causative agents differed. Four farms in a swine production system were diagnosed with coccidiosis, sapovirus, rotavirus, and a co-infection of sapovirus/rotavirus, respectively. Diligent pursuit of diagnosis led to appropriate treatment and care.

Dr. Will Fombelle, practitioner with Carthage Veterinary Service, LTD, shared another field perspective. His observation included mid- to late-lactation piglet diarrhea which presented as could be expected with multiple pathogens, especially coccidia. Pudding-like diarrhea, rough hair, weaning weight deficits, and low mortality were all seen. Dr. Fombelle reflected on the easy assumption that diarrhea and low weaning weight were the result of coccidiosis and was surprised to learn it wasn’t the cause. By ruling out coccidia, they needed to “rule something in.” The process included tissue submission, rectal swabs, and fecal flotations.

In their evaluation, economics was given consideration. Dr. Fombelle shared the cost of weaning weight loss of 1 pound would equate to $22 per sow per year. This guided decision-making for treatment. He said vaccines with favorable efficacy are available to manage PSaV and recommended other practical management strategies as well.

Dr. Marcelo Almeida, Iowa State University Veterinary Diagnostic Lab, shared PSaV characteristics and results of work done to identify the causative agent from Dr. Petznick’s client’s herd outbreak. He said the epidemiology of PSaV shows it can be detected in pigs both with and without diarrhea and as such, detection does not equal causation. He also stated that PSaV can infect pigs at any age, but that detection rates are higher during suckling and nursery phases. Transmission, per Dr. Almeida, is fecal-oral. Early detection of PSaV in piglets is common but questions remain surrounding sow-to-piglet transmission and environmental contamination. For disinfection, sodium hypochlorite at 2.5 mg per liter for 30 minutes is effective.

For diagnosis, Dr. Almeida said samples should come from acutely affected pigs. Fresh and fixed samples of small intestines and colon are needed as well as feces. Tests used for diagnosis include histopathology, PCR, and RNAscope. Differentials for PSaV diagnosis are enteric coronaviruses, rotavirus, Cystoisospora suis, and others.

The final presenter was Dr. Yanyun Huang, sharing a western Canadian perspective as chief executive officer and anatomic pathologist with Prairie Diagnostic Services Inc. in Saskatoon, Saskatchewan, Canada. He said veterinarians affiliated with the Canada West Swine Health Intelligence Network and Canadian Swine Health Intelligence Network first reported PSaV being detected in cases of piglet diarrhea in the first quarter of 2023. No Canadian labs offered testing for PSaV at that time.

Their pursuit of a diagnosis followed a similar process as their US counterparts with sampling and other diagnostics being pursued when more common causes were ruled out. In work with the Government of Saskatchewan, Dr. Huang says their next steps are to fully validate PCR assays, implement surveillance in the province, and conduct further genetic analysis of more Canadian strains. He is encouraged by recent advancements in diagnostic technology increasing the ease of implementing a comprehensive investigative approach.

Do you have a recommendation for a topic to be addressed in this format? SHIC and AASV would like your input! Reach out to SHIC Executive Director Dr. Paul Sundberg at [email protected], Associate Director Dr. Megan Niederwerder at [email protected], or AASV Director of Public Health and Communications Dr. Abbey Canon at [email protected] with your webinar recommendations. Access previous webinars here. Webinars are conducted by ISU’s Swine Medicine Education Center.

The Swine Health Information Center, launched in 2015 with Pork Checkoff funding, protects and enhances the health of the US swine herd by minimizing the impact of emerging disease threats through preparedness, coordinated communications, global disease monitoring, analysis of swine health data, and targeted research investments. As a conduit of information and research, SHIC encourages sharing of its publications and research. Forward, reprint, and quote SHIC material freely. For more information, visit http://www.swinehealth.org or contact Dr. Paul Sundberg at [email protected] or Dr. Megan Niederwerder at [email protected].