Paulo Arruda1, Kent Schwartz1, Albert Rovira 3, Jerome Nietfeld 2, Paul Sundberg4, Ben Hause2
1. Iowa State Veterinary Diagnostic Laboratory, Ames IA
2. Kansas State University, Manhattan KS
3. Minnesota Veterinary Diagnostic Laboratory, Saint Paul MN
4. Swine Health Information Center, Ames IA
An acute outbreak of atypical neurologic disease in 11-week-old pigs was recently investigated by the Iowa State University Veterinary Diagnostic laboratory (ISUVDL). The farm was located within region 5 according to the Swine Health Information Center emerging disease rapid response regions of the U.S. (https://www.swinehealth.org/ ). All affected animals originated from a single nursery and were placed in two different finishers at 9 weeks-of-age. Over the following 3 weeks, the clinical onset and progression of signs in affected pigs varied but included decrease of water and feed consumption, compromised ambulation with ataxia, incoordination, mental dullness, paresis, paralysis and decreased response to environmental stimuli. Clinical examination revealed that affected animals had discernible ataxia yet had deep pain perception and withdrawal reflexes in hind limbs. They were able to move their tail and had righting reflex intact. Despite mental dullness and aimless wandering, pigs generally had central awareness with no nystagmus or cranial nerve deficits observed. Overall morbidity of 20% and case fatality rate of 30% was reported by the field veterinarian.
The additional diagnostic fee support needed for this investigation was provided by the Swine Health Information Center (SHIC).
Histopathologic examination of brain revealed severe lymphoplasmacytic and necrotizing encephalomyelitis with multifocal areas of gliosis and neuron satelliosis, suggestive of a neurotropic viral infection. Cultures did not demonstrate bacterial pathogens in multiple tissues from affected pigs. Immunohistochemistry and PCR for PRRS and porcine circovirus were negative. Sections of spinal cord submitted for PCR for enterovirus, teschovirus and sapelovirus were found consistently positive for porcine sapelovirus.
Next Generation Sequencing of brain stem and spinal cord samples investigated the possible presence of other or novel pathogens as well as to confirm previous sapelovirus PCR results. Interestingly, a genetically (perhaps antigenically) novel sapelovirus was identified within CNS tissues of affected animals. The 2,323 amino acid polyprotein sequence has an overall 94% amino acid identity and 86% nucleotide identity to recent Korean sapelovirus (Kyu-Yeol Son, et al. 2014). No other viral agents were identified within examined samples.
The biologic relevance of this finding is not clear at this point as there is a significant gap of knowledge concerning the pathophysiology and the potential role of this particular virus in cases of encephalomyelitis in swine. Historically, similar cases have been sporadically associated with “enterovirus infection”; however, serotyping was not commonly performed and therefore true prevalence of cases associated with specific enterovirus serotypes are not known to this date.
Porcine sapelovirus is a single stranded, positive-sense genomic RNA virus in the family of Picornaviridae, formerly known as porcine enterovirus serotype 8. Porcine enteroviruses were historically serotyped by virus-neutralization and divided in 13 serotypes. Based on modern molecular techniques and physiochemical properties these 13 serotypes are now subdivided as follows:
To date, sapelovirus from other species have not been reported to be associated with nervous disease. In this case, novel sapelovirus was the only agent detected associated with a unique clinical presentation of CNS disease. At least one previous case report documents the neuroinvasive potential of porcine sapelovirus in swine (Alex Schock, et al. 2014). However, knowledge gaps remain in disease causation (i.e. Koch’s postulates as yet unfulfilled), epidemiology, pathogenesis and biologic relevance of this potential pathogen.