Torovirus - Replication, Pathogenesis
Replication of Torovirus
Attachment of Torovirus protein (maybe also HE is present) to host receptors mediates endocytosis of the virus into the host cell
synthesis and proteolytic cleavage of the replicase polyprotein
Fusion of Torovirus membrane with the endosomal membrane (probably mediated by E2), ssRNA (+) genome is released into the cytoplasm
synthesis and proteolytic cleavage of the replicase polyprotein
replication occurs in viral factories
A Torovirus dsRNA genome is synthesized from the genomic ssRNA(+)
The dsRNA genome is replicated thereby providing viral mRNAs/new ssRNA (+) genomes
Synthesis of structural proteins encoded by subgenomic mRNAs
Assembly and budding at membranes of the endoplasmic reticulum (ER), the intermediate compartments, and/or the Golgi complex
Release of new virus by exocytosis
Pathogenesis of Torovirus
Little is known of the disease potential of the Bern virus in horses, as only a single case has been described- this in a horse with diarrhea.
Breda virus causes diarrhea in calves and can be a serious problem in some herds
In swine, torovirus infection has been associated with neonatal diarrhea, but infection is apparently often subclinical
Torovirus infection of turkeys causes diarrhea, poor feed conversion, reduced weight gain (stunting), listlessness, and litter eating
Epidemiological surveys have indicated that torovirus infections are involved in two disease entities in cattle:
diarrhea in calves up to 2 months of age
winter dysentery of adult cattle in the Netherlands and Costa Rica
Human Torovirus has been detected in stool samples, most commonly from diarrheic children; with prevalence rates of 22-35%.
Respiratory problems viz, laryngitis, tracheitis, and pneumonia have also been documented with these viruses.