Dynamics of virus excretion via different routes in pigs experimentally infected with classical swine fever virus strains of high, moderate or low virulence

Classical swine fever virus (CSFV) is transmitted via secretions and excretions of infected pigs. The efficiency and speed of the transmission depends on a multitude of parameters, like quantities of virus excreted by infected pigs. This study provides quantitative data on excretion of CSFV over time from pigs infected with a highly, moderately or low virulent strain. For each strain, five individually housed pigs were infected. Virus excretion was quantified in oropharyngeal fluid, saliva, nasal fluid, lacrimal fluid, faeces, urine and skin scraping by virus titration and quantitative Real-Time Reverse Transcription Polymerase Chain Reaction (qRRT-PCR). Infectious virus was excreted in all secretions and excretions of pigs infected with the highly and moderately virulent strain, while excretion from pigs infected with the low virulent strain was mostly restricted to the oronasal route. Pigs infected with the highly virulent strain excreted significantly more virus in all their secretions and excretions over the entire infectious period than pigs infected with the moderately or low virulent strains. An exception were the pigs that developed the chronic form of infection after inoculation with the moderately virulent strain. During the entire infectious period, they excreted the largest amounts of virus via most secretions and excretions, as they excreted virus continuously and for a long duration. This study highlights the crucial role chronically infected pigs may play in the transmission of CSFV. Furthermore, it demonstrates the importance of discriminating between strains and the clinical appearance of infection when using excretion data for modelling.