Abstract Immune elimination of alphaviruses in immunized hamsters appears to involve formation of virus/antibody aggregates which are subsequently cleared from the circulation by cells of the reticuloendothelial system (RES). Virulent strains of Venezuelan (VEE) and Western equine encephalitis (WEE) viruses which were cleared slowly from the circulation of nonimmune hamsters, were cleared rapidly when inoculated into the blood of immunized hamsters. Likewise, when these viruses were mixed with specific hamster immune serum prior to inoculation, they were efficiently cleared from the circulation of nonimmune hamsters. Virus, mixed with specific immune serum, or inoculated into immunized hamsters, formed virus/antibody aggregates, as demonstrated by density gradient centrifugation, filtration through polycarbonate membranes, precipitation with Staphylococcus protein A, and electron microscopy. Cleared virus was concentrated primarily in liver and spleen, as confirmed by autoradiography. Immune clearance of virulent VEE was demonstrable within 5 to 6 days following immunization of hamsters with live attenuated VEE vaccine, strain TC‐83. In these hamsters, a close association was established between formation of virus/antibody aggregates, rapid clearance, and survival of challenged hamsters. Adsorption of virus to hamster macrophages in culture was enhanced by immune serum in the presence of complement. These results are compatible with the hypothesis that immune clearance of virus in the intact hamster involves a complement‐dependent interaction of virus/antibody complexes with cells which possess Fc and complement receptors. The clearance of immune complexes by the RES serves to amplify the protective effect of neutralizing antibody alone.
Five Bulldog pups, 4 weeks of age or younger, were presented over a 2-day period for postmortem examination and diagnostic evaluation. The pups originated from 2 different litters but had been cared for at a common facility since their birth. All 5 pups died after exhibiting symptoms consisting of lethargy, dyspnea, nasal discharge, anorexia, vomiting, diarrhea, and abdominal pain. Necropsy examination revealed locally extensive to diffusely red, firm, consolidated lungs in all pups. Histopathologically, the lungs were variably effaced by multifocal areas of necrosis. The alveolar lumens contained fibrin, edema fluid, macrophages, and neutrophils. Many of the bronchioles contained cellular debris and neutrophils admixed with sloughed bronchiolar epithelium, which often contained large intranuclear amphophilic inclusion bodies that peripherally displaced chromatin. Fluorescent antibody testing was positive for Canine adenovirus. An adenovirus isolated via cell culture was positive on direct fluorescent antibody test and was identified as Canine adenovirus serotype 2 via polymerase chain reaction. Electron microscopy revealed typical viral inclusions within bronchiolar epithelial cells. Hemolytic Escherichia coli was also isolated from the lungs in 3 of the 5 pups. The current case demonstrates a natural and rare fatal infection with a viral agent that is typically associated with immunosuppression in both animals and humans.
Porcine Epidemic Diarrhea Virus (PEDV) is a coronavirus that infects the intestinal tract and causes diarrhea and vomiting in older pigs or extreme dehydration and death that could reach 100% mortality in neonatal piglets. In the US, the first PEDV outbreaks occurred in 2013 and since then US PEDV strains have quickly spread throughout the US and worldwide, causing significant economic and public health concerns. Currently two conditionally approved vaccines exist in the US, but there is no live attenuated vaccine, which is considered the best option in controlling PEDV by inducing transferrable mucosal immunity to susceptible neonatal piglets. In this study, we passaged an US PEDV isolate under various conditions to generate three strains and characterized their growth and antigenicity in cell culture using various assays including Western blot analysis, serum neutralization assay, sequencing analysis and confocal microscopy. Finally, these strains were evaluated for pathogenicity in nursing piglets (1–4 days old). One of the PEDV strains generated in this study (designated as PEDV 8aa) is able to replicate in cells without any protease and grows to a high titer of >8 log10 TCID50/ml in cell culture. Interestingly, replication of PEDV 8aa was severely reduced by trypsin and this correlated with the inhibition of virus attachment and entry into the cells. In neonatal nursing piglets, PEDV 8aa (passage number 70 or 105) was found to be fully attenuated with limited virus shedding. These results suggest that applying selective pressure during viral passages can facilitate attainment of viral attenuation and that PEDV 8aa warrants further investigation as an attenuated vaccine.
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Pestiviruses are some of the most significant pathogens affecting ruminants and swine. Here, we assembled a 11 276 bp contig encoding a predicted 3635 aa polyprotein from porcine serum with 68 % pairwise identity to that of a recently partially characterized Rhinolophus affinis pestivirus (RaPV) and approximately 25-28 % pairwise identity to those of other pestiviruses. The virus was provisionally named atypical porcine pestivirus (APPV). Metagenomic sequencing of 182 serum samples identified four additional APPV-positive samples. Positive samples originated from five states and ELISAs using recombinant APPV Erns found cross-reactive antibodies in 94 % of a collection of porcine serum samples, suggesting widespread distribution of APPV in the US swine herd. The molecular and serological results suggest that APPV is a novel, highly divergent porcine pestivirus widely distributed in US pigs.
