Coronavirus-like particles were detected by electron microscopy in the intestinal contents of pigs during a diarrhea outbreak on 4 swine breeding farms. Diarrhea was reproduced in experimental pigs with one of the isolates, designated CV777, which was found to be distinct from the 2 known porcine coronaviruses, transmissible gastroenteritis virus and hemagglutinating encephalomyelitis virus.

The close genetic and antigenic relatedness among the group 2 coronaviruses human coronavirus OC43 (HCoV-OC43), bovine coronavirus (BCoV), and porcine hemagglutinating encephalomyelitis virus (PHEV) suggests that these three viruses with different host specificities diverged fairly recently. In this study, we determined the complete genomic sequence of PHEV (strain PHEV-VW572), revealing the presence of a truncated group 2-specific ns2 gene in PHEV in comparison to other group 2 coronaviruses. Using a relaxed molecular clock approach, we reconstructed the evolutionary relationships between PHEV, BCoV, and HCoV-OC43 in real-time units, which indicated relatively recent common ancestors for these species-specific coronaviruses.Coronaviruses (family Coronaviridae, order Nidovirales) are large, enveloped, positive-stranded RNA viruses with a typical crown-like appearance. Their viral genomes (27 to 32 kb) are some of the largest known among all RNA viruses (12). Based on genetic and serological relationships, coronaviruses can be classified into three groups (8). Group 2 coronaviruses include murine hepatitis virus (MHV), bovine coronavirus (BCoV), human coronavirus OC43 (HCoV-OC43), rat sialodacryoadenitis virus, porcine hemagglutinating encephalomyelitis virus (PHEV), canine respiratory coronavirus, and equine coronavirus.PHEV was first isolated in 1962 in Canada from suckling piglets with encephalomyelitis (9, 18) and is now found to be widespread among swine worldwide, with frequent subclinical infections among swine. The virus has a strong tropism for epithelial cells of the upper respiratory tract and for the central nervous system (CNS) and is transmitted through nasal secretions (1). In addition to clinical signs of encephalomyelitis, vomiting and wasting disease can be another manifestation of PHEV infection in piglets (22). The clinical symptoms of vomiting and wasting are assumed to be centrally induced by infection of the vagus nerve, but a possible further dissemination of the virus into the CNS may lead to centrally induced motoric disorders.In this study, we determined the full-length genome sequence of the PHEV-VW572 strain and we reconstructed the common evolutionary history of PHEV and the closely related BCoV and HCoV-OC43. The PHEV-VW572 strain was isolated in Belgium in 1972 from the tonsils of two diseased pigs obtained from a litter in which an outbreak of vomiting and wasting disease occurred without further progression towards CNS motoric disorders (23). The isolate was propagated in a primary porcine kidney cell line. To determine the full-length genome sequence, primers developed for sequencing of group 2 coronaviruses, as described previously, were used (33).Multiple sequence alignments were prepared using ClustalX version 1.82 (30) and manually edited in GeneDoc (21). Maximum-likelihood phylogenetic analyses were conducted in Tree-Puzzle 5.1 using the VT (Mueller-Vingron 2000) model of amino acid substitution and a gamma distribution to model among-site rate heterogeneity (29). The SimPl...

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The acute stages of infection with swine influenza virus (SIV), porcine respiratory coronavirus (PRCV) and porcine reproductive-respiratory syndrome virus (PRRSV) were shown to differ in terms of clinical and lung inflammatory effects and proinflammatory cytokine profiles in bronchoalveolar lavage (BAL) fluids. Caesarian-derived colostrum-deprived pigs were inoculated intratracheally with one of the three viruses. SIV infection was followed within 1 day post inoculation (d PI) by characteristic respiratory and general signs, and excessive lung epithelial desquamation and neutrophil infiltration (38 to 56 per cent of BAL cells at 1 d PI vs 0 to 1 per cent in controls). High concentrations of bioactive interferon-alpha (IFN -alpha), tumour necrosis factor-alpha (TNF -alpha) and interleukin-1 (IL -1) coincided with peak symptoms and neutrophil infiltration. PRCV infection was asymptomatic and produced a mild bronchointerstitial pneumonitis and neutrophil infiltration (13 to 22 per cent of BAL cells at 4 d PI). IFN -alpha titres parallelled those found during SIV infection, TNF -alpha was negligible and IL -1 undetectable. PRRSV infection induced anorexia and lethargy between 3 and 5 d PI. There was marked infiltration with mononuclear cells in alveolar septa and BAL fluids between 7 and 10 d PI, while neutrophils remained at less than 11 per cent of BAL cells at any time. IL -1 was produced from three throughout 10 d PI, while IFN -alpha production was minimal and TNF -alpha undetectable. These data strongly suggest that proinflammatory cytokines can be important mediators of viral respiratory disease.

SUMMARY A porcine respiratory, non-enteric virus which is related to the coronavirus transmissible gastroenteritus virus (TGEV) has been isolated in pigs and in cell culture. The isolate was designated TLM 83. It has become very widespread and enzootic among the swine population in Belgium and in other swine raising countries. It causes an infection of the lungs and appears to spread by aerogenic route. It does not replicate in the enteric tract. The experimental infection in conventional and gnotobiotic pigs in isolation remains subclinical. The infection, either experimental or in the field, results in the formation of antibodies which neutralise the classical enteric TGEV. Based on this relationship, this virus is assumed to be a new TGEV-related porcine respiratory coronavirus or TGEV itself which has totally lost its tropism for the enteric tract.

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In this study, the susceptibility of porcine peripheral blood monocytes (BMo), peritoneal macrophages (PM phi) and alveolar macrophages (AM phi) to PRRSV was examined. To test the effect of differentiation and activation on their susceptibility, AM phi and BMo were aged, cultivated in either adhesion or suspension and treated with bacterial lipopolysaccharide (LPS) and phorbol myristate acetate (PMA). It was found that freshly isolated PM phi and BMo were non-permissive to PRRSV. PM phi remained refractory but a few BMo became susceptible after 1 day cultivation. AM phi were permissive with a significant increase of their susceptibility after one day cultivation. In a binding assay, it was demonstrated that the attachment of biotinylated PRRSV to AM phi is much more efficient than to PM phi and BMo. Two monoclonal antibodies (Mabs) 41D3 and 41D5 which block PRRSV infection of AM phi and are directed against a candidate receptor for PRRSV only reacted with the cell membrane of AM phi. PMA treatment of AM phi blocked PRRSV replication in the cells in a dose-dependent manner. The blocking effect of PMA decreased after 9 h continuous pre-treatment and diminished after 24 h continuous pre-treatment. PMA treatment did not affect the binding of PRRSV and MAb 41D3 and 41D5 to AM phi. Direct or indirect treatment of AM phi and BMo with LPS or cultivation in suspension did not significantly affect their susceptibility. These results provide clear evidence that PRRSV has a strongly restricted tropism for only some sub-populations of porcine monocytes/macrophages and that some specific states of differentiation and activation of monocytes/macrophages considerably affect their susceptibility.

Since it first appeared in 1992, white spot syndrome virus (WSSV) has become the most threatening infectious agent in shrimp aquaculture. Within a decade, this pathogen has spread to all the main shrimp farming areas and has caused enormous economic losses amounting to more than seven billion US dollars. At present, biosecurity methods used to exclude pathogens in shrimp farms include disinfecting ponds and water, preventing the entrance of animals that may carry infectious agents and stocking ponds with specific pathogen-free post-larvae. The combination of these practices increases biosecurity in shrimp farming facilities and may contribute to reduce the risk of a WSSV outbreak. Although several control methods have shown some efficacy against WSSV under experimental conditions, no therapeutic products or strategies are available to effectively control WSSV in the field. Furthermore, differences in virulence and clinical outcome of WSSV infections have been reported. The sequencing and characterization of different strains of WSSV has begun to determine aspects of its biology, virulence and pathogenesis. Knowledge on these aspects is critical for developing effective control methods. The aim of this review is to present an update of the knowledge generated so far on different aspects of WSSV organization, morphogenesis, pathology and pathogenesis.