Veterinary Microbiology, 31 (1992) 11-18 11 Elsevier Science Publishers B.V., Amsterdam Experimental infection of pigs with the porcine respiratory coronavirus (PRCV) measure of viral excretion E. Bourgueil, E. Hutet, R. Cariolet and P. Vannier Ministre de lAgriculture et de la Fort, CNEVA Laboratoire de Recherches Avicole et Porcine, Station de Pathologie Porcine, BP 53, 22440 Ploufragan, France (Accepted 30 August 1991 ) ABSTRACT Bourgueil, E., Hutet, E., Cariolet, R. and Vannier, P., 1992. Experimental infection of pigs with the porcine respiratory coronavirus (PRCV): measure of viral excretion. Vet. Microbiol., 31: 11-18. Twelve pigs were experimentally infected with a porcine respiratory coronavirus (PRCV) by the oronasal route. Viral excretion was measured daily by two means-deep nasal swabs and air samples obtained in a cyclone sampler. Clinical signs were very slight on infected pigs. Airborne virus could be recovered from day 1 to day 6 post-infection in the cyclone sampler as well as in petri dishes placed in the same loose-box. Viral titres obtained from nasal swabs were significantly correlated with those obtained from air samples. Different collection media were compared. The most efficient media for the collection of infectious viral particles contained a protective agent such as foetal calf serum. INTRODUCTION Respiratory disorders due to viruses are the main problems recorded in areas of intensive porcine production. Common causes of the disease in- cludes pseudorabies virus (PRV), influenza viruses and the porcine respira- tory coronavirus (PRCV), the latter being first detected in different Euro- pean countries in 1983-1984 (Brown et al., 1986; Duret et al., 1988; Pensaert et al., 1986). Serological studies have demonstrated a close relationship be- tween PRCV and transmissible gastroenteritis virus (TGEV) with the vi- ruses being distinguished from each other only by the use of monoclonal an- tibodies (Laude et al., 1988; Garwes et al., 1988). Recently, Rasschaert et al. (1990) compared the genomic organization of each virus and showed that PRCV had various nucleotide deletions when compared to TGEV. No con- clusion could be made concerning the genomic modification (s) controlling the phenotypic difference observed between the viruses, namely the impaired multiplication of PRCV in the digestive tract. Until now, great attention has 0378-1135/92/$05.00 1992 Elsevier Science Publishers B.V. All rights reserved. 12 E. BOURGUEIL ET AL. been given to clinical disorders induced by PRCV in the field (Jestin et al., 1987; Brown and Cartwright, 1986) and under experimental conditions (Vannier, 1990; Pensaert et al., 1986; OToole et al., 1989), but nothing is known about excretion and airborne transmission of the virus. In order to better understand that aspect of the epidemiology of PRCV, we studied excre- tion of the virus in pigs experimentally infected with the virus. MATERIALS AND METHODS Animals Twenty one pigs from hysterectomy-derived sows were used. They were divided into two groups. One of twelve pigs was kept for experimental infec- tion, and the other of nine pigs was used as control. The pigs were infected at 12 weeks old and an average weight of 41 kg. Each group was kept totally isolated from the other. Virulent challenge The strain isolated in France was used (Duret et al., 1988 ) as described by Vannier (1990). This strain was derived from nasal swab liquid, amplified by three passages in swine testis (ST) cell line, kindly provided by Dr. Brun from Rh6ne-M6rieux-Lyon. The cytopathic effect (CPE), induced by the vi- rus, was neutralized by hyperimmune sera, specific for TGE virus and PRCV. The viral suspension was adjusted to an infectious titre of 106 TCIDso/ml. Each pig received 5 ml of the preparation by nasal (2 ml in each nostril ) and oral routes ( 1 ml). The day of administration of virus was considered as day zero (D0). Air sampling procedure From day 1 to day 8 post-infection, air samples were obtained with a stain- less-steel cyclone sampler, constructed according to the model described by Errington and Powell ( 1969 ). The air-flow rate of the apparatus was 3001 per minute. The airborne particles collected were eluted from the walls of the apparatus by addition of a collection medium with a peristaltic pump, ad- justed to a flow-rate of 2 ml per minute. The cyclone sampler was placed about 1 m above floor level, between the two fiat-decks each of which contained six pigs. Four collection media were tested: Medium 1 contained phosphate buff- ered saline (pH 7.2 ) and buffer HEPES (20 mM); Medium 2 was medium 1 plus 10% foetal calf serum (FCS); Medium 3 was medium 1 plus 0.5% gela- tine and Medium 4 was medium 3 plus 10% FCS. Each medium was supplemented with penicillin 100 IU/ml, streptomycin 0.1 mg/ml and neomycin 50 IU/ml. Petri dishes, containing 10 ml of each collecting fluid, were placed daily in each isolation unit at about 20 cm above INFECTION O