Faculty of Veterinary Medicine, G h ent University

1. Department of Reproduction, Obstetrics, and Herd Health Faculty of Veterinary Medicine, Ghent University 10 h No cleaning nor desinfection An experimental infection (II) to investigate the indirect transmission of classical swine fever by excretions and secretions. S. Ribbens1, J. Dewulf1, F. Koenen2, H. Laevens2, K. Mintiens2, A. de Kruif1 1 Department of Obstetrics, Reproduction and Herd Health, Veterinary Epidemiology Unit, Faculty of Veterinary Medicine, Ghent University, Salisburylaan 133, 9820 Merelbeke, Belgium 2 Department of Virology, Unit for modelisation of epidemiological diseases, and coordination center for veterinary diagnostics, Veterinary and Agrochemical Research Centre (CODA/CERVA/VAR), Groeselenberg 99, 1180 Brussels, Belgium MATERIALS AND METHODS INTRODUCTION The indirect transmission of classical swine fever virus (CSFV) via mechanical vectors is prone to discussion. It is believed that excretions and secretions of infected swine can contaminate mechanical vectors (e.g. vehicles for pig transport). When these contaminated vectors are brought into contact with susceptible pigs, they could transmit the virus. In a previous experiment, no virus transmission could be demonstrated if susceptible pigs were housed in pens previously contaminated by infected pigs. It was concluded that excretions and secretions do not cause virus transmission during the early stages of an infection (Dewulf et al., 2002). The purpose of the current experiment was to investigate if pigs infected with CSF virus and kept until late stage of disease with obvious clinical symptoms, can cause indirect transmission of CSF through excretions and secretions. Day 0: INOCULATION Day 15 (7h): DEPOPULATION No cleaning nor desinfection Day 15 (17h) RESTOCKING RESULTS Infection period (0-15 days post inoculation (dpi)) Observation period (15dpi-…) • 3 pigs became first viraemic 4 days post repopulation (dpr), followed by one other pig 2 days later (see Table). • Between the 14th dpr and the end of the experiment all remaining pigs became infected. • Exp. inoculation succeeded in all 10 pigs. • At the time of depopulation (15 dpi) all pigs were viraemic and clearly clinically ill (high fever, anorexia, apathy, conjunctivitis, constipation, diarrhea, ataxia and hemorrhages of the ears). • Virus could be isolated in saliva and faeces (see Table). DISCUSSION CONCLUSION • In this experiment, a WORST CASE SCENARIO (pig transport) was mimicked: • severe clinically ill animals (seeders) are transported (15 dpi) • livestock truck is not cleaned nor disinfected • same livestock truck is used for transport of susceptible pigs 10 hours later • Four contact pigs became infected through indirect transmission by excretions and secretions. Infection route of remaining pigs unknown but likely through between pen spread (time interval of ±8 days). • Differences with previous experiment (Dewulf et al., 2002): • current experiment: infected pigs euthanised 15 dpi (clearly clinically ill) • previous experiment: infected pigs euthanised 8 dpi (no clinical symptoms) • current experiment: 10 hours between depopulation and repopulation • previous experiment: 20 hours between depopulation and repopulation Based upon the results of this and the previous experiment, it is concluded that virus transmission via excretions and secretions is important only when seeder pigs are clinically diseased. This research was supported by the Belgian Ministry of Public Health, Research Foundation and the Fund for Health and Quality of Animals and Derived Products