The Iowa State University Veterinary Diagnostic Laboratory identified a new virus in the genus Morbillivirus (porcine morbillivirus or PoMV) from the fetal tissues of 22 pig fetuses from six litters originating in Mexico in the spring of 2020.
Currently known members in the genus Morbillivirus include highly contagious pathogens such as measles virus, rinderpest virus, peste des petits ruminants virus, canine distemper virus, phocine distemper virus, cetacean morbillivirus, and feline morbillivirus. These viruses can cause serious human and animal diseases, the Swine Health Information Center (SHIC) reports.
Although PoMV was identified from porcine cases with fetal death, encephalitis and placentitis, the etiological role of PoMV had not been determined. Because it was unknown if PoMV was present in the U.S. swine population, Iowa State University (ISU) and USDA Agricultural Research Service researchers investigated these knowledge gaps with SHIC funding.
A Look at the Results
To determine if PoMV was present in the U.S. swine herd, various tissues from neonatal mortalities and mummified fetus banked samples submitted to the ISU Veterinary Diagnostic Laboratory were subjected to PoMV rRT-PCR. Researchers tested 450 clinical samples from across the country (brains, lungs and spleens from neonatal mortalities, stillbirths and mummified fetuses). Testing to date has not detected PoMV in U.S. swine samples, SHIC reports.
Researchers attempted to isolate PoMV in various cell lines using four available PoMV PCR-positive tissue homogenates. Because no cytopathic effect was observed and no PoMV-specific antibody for immunofluorescence staining was available, researchers tested the cell culture lysates at different passages by PoMV rRT-PCR to determine virus isolation outcomes.
Based on PCR results, no PoMV isolate was identified that is capable of efficient replication in cell culture. As no additional PoMV PCR-positive clinical samples from Mexico could be obtained, efforts to optimize conditions for further VI attempts are limited. However, if more PoMV PCR-positive samples become available in the future, further VI attempts would be warranted, SHIC says.
Paramyxoviruses that are known to naturally infect swine include porcine rubulavirus, Menangle virus, Nipah virus and porcine parainfluenza virus. Although there are reports of less well-characterized paramyxoviruses associated with central nervous and respiratory disease in pigs, none of these viruses are classified in the genus Morbillivirus.
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