Potential swine disease emerge

A potential emerging disease, porcine sapovirus (PSaV), was addressed at the 2023 Nebraska Pork Expo held in Lincoln, Neb. in July and during the Swine Disease Reporting System’s July monthly podcast.

More recently, the Swine Health Information Center (SHIC) and American Association of Swine Veterinarians (AASV) held a webinar on Aug. 30 regarding PSaV. 

Sapovirus is an up-and-coming topic among producers, veterinarians and researchers, but PSaV is not new. The virus was initially detected in U.S. swine herds over 40 years ago but drew little to no attention.

Speakers at each event shared their field experience with PSaV, including diagnosing, clinical research, production impacts, strategies and other insights into the virus.

PSaV History

During the August webinar, Qiuhong Wang, PhD and professor in the College of Veterinary Medicine at Ohio State University in Wooster, Ohio, shared a historical perspective on PSaV. 

Wang states, “The Cowden strain was first detected in the U.S., 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.”

“PSaV is a genomic organization of a single-stranded, positive-sense RNA genome and shares illustrations of its structure,” Wang continues. “PSaV’s classification includes 19 genogroups, of which eight infect pigs.” 

According to SHIC, “Current testing to diagnose PSaV includes histopathology, PCR and RNAscope. However, there is no treatment for PSaV.”

Symptoms

SHIC explains, “PSaV, a calicivirus, has been detected in swine with or without diarrhea and co-infection is common. However, PSaV has been identified as the sole cause of diarrhea in some outbreaks and infection but is often subclinical, occurring most frequently during the post-weaning period.” 

Diarrhea can be mild to severe and is usually self-limiting, although it may result in productivity and efficiency setbacks.

“Swine of all growing stages can be infected with PSaV, but young and post-weaning pigs have a higher infection rate than other age groups,” SHIC continues.

AASV advises, “A definitive lab diagnosis is necessary to know which pathogen or combination of pathogens cause clinical disease in a swine herd.”

Marcelo Almeida, DVM, PhD and assistant professor at Iowa State University’s College of Veterinary Medicine explains, “The epidemiology of PSaV shows it can be detected in pigs both with and without diarrhea, and detection does not equal causation.”

He continues, “PSaV detection rates are higher during suckling and nursery phases and transmission is fecal-oral.” 

“Early detection of PSaV in piglets is common, but questions remain on surrounding sow-to-piglet transmission and environmental contamination,” he concludes. 

Raising awareness

A Nebraska-based swine veterinarian at ArkCare, Dr. Tom Petznick, fielded questions from pork producers regarding PSaV at the July Nebraska Pork Expo and participated in the August webinar with SHIC and AASV.

“It is indistinguishable in my eyes to identify it in the crate,” Petznick states. “Looking at it from weaning to day seven, it can look like coccidia, rotavirus or a combination of them, but if a producer is still fighting it from day seven to 21, signs point to it being PSaV.”

“In my experience with PSaV, the disease was self-limiting at or shortly after weaning with high morbidity and low mortality, and the pigs didn’t respond to treatment,” he shares. “While there was low mortality, affected pigs exhibited 1.5 pounds of lost weaning weight, and for some pigs who were too light at weaning, morbidity was a variable.”

Petznick continues, “The pursuit of a diagnosis continues with collaboration from Iowa State University’s Veterinary Diagnostic Lab, Sequivity, the producer and SHIC, as the next generation sequencing unexpectedly found PSaV, which has not been identified in U.S. herds for decades.”

Prevention and awareness

SHIC notes, “Cleaning and disinfection are important to prevent PSaV outbreak, and sick pigs should be isolated to minimize disease spread as PSaV is stable in environments and can survive at high temperatures and in acidic conditions. But, PSaV is inactivated by using a solution of sodium hypochlorite at 2.5 milligrams per liter and leaving it on for 30 minutes.”

Petznick continues discussing PSaV on the SDRS webinar and describes a PSaV outbreak he has been involved in. 

“What prompted us to do an investigation is we had done previous diagnostic work which would commonly show minimal amount of rotavirus or we couldn’t find coccidiosis, and we kept getting lesions similar to what one would see with rotavirus,” Petznick says.

“It was put to the challenge by the owner to fix this,” he states. “It was a very clean herd at the time – triple negative pigs – but it just wasn’t acceptable where we were at with weaning weights.” 

“After implementing environmental sanitation and controlled or timed exposure in an unsuccessful effort to control the PSaV outbreak, further investigation led to vaccination efforts,” Petznick notes.

Petznick recalls, “It was costing the producer one to two pounds of growth per pig at weaning, so we used next-generation sequencing to isolate the pathogen’s genetic code and we were able to develop an initial vaccine.” 

In this field trial, Petznick observed almost complete disappearance of diarrhea and increased weaning weights when a four-step process included reviewing previous data, identifying the sample subject, analyzing fecal shedding versus weaning weight and performing a vaccine field trial. 

He concludes, “Prescription vaccine platforms have favorable efficacy and are available to manage PSaV, but other practical management strategies should be utilized as well.”

He notes  he intends to survey producers to learn more about the incidence of PSaV infections and also to raise awareness of their impact on production.

For over 25 years, Petznick has successfully met client needs through a balance of science-based and practical approaches to livestock health and is respected as a leader in PSaV research and will receive the 2023 Science in Practice Award at the Allen D. Leman Swine Conference in September.

Melissa Anderson is the editor of the Wyoming Livestock Roundup. Send comments on this article to roundup@wylr.net.