SDAV, the Rat Coronavirus-How Much Do We Know about It in the Light of Potential Zoonoses.

Sialodacryoadenitis virus (SDAV) is known to be an etiological agent, causing infections in laboratory rats. Until now, its role has only been considered in studies on respiratory and salivary gland infections. The scant literature data, consisting mainly of papers from the last century, do not sufficiently address the topic of SDAV infections. The ongoing pandemic has demonstrated, once again, the role of the Coronaviridae family as extremely dangerous etiological agents of human zoonoses. The ability of coronaviruses to cross the species barrier and change to hosts commonly found in close proximity to humans highlights the need to characterize SDAV infections. The main host of the infection is the rat, as mentioned above. Rats inhabit large urban agglomerations, carrying a vast epidemic threat. Of the 2277 existing rodent species, 217 are reservoirs for 66 zoonotic diseases caused by viruses, bacteria, fungi, and protozoa. This review provides insight into the current state of knowledge of SDAV characteristics and its likely zoonotic potential.

Discovery, diversity and evolution of novel coronaviruses sampled from rodents in China.

Although rodents are important reservoirs for RNA viruses, to date only one species of rodent coronavirus (CoV) has been identified. Herein, we describe a new CoV, denoted Lucheng Rn rat coronavirus (LRNV), and novel variants of two Betacoronavirus species termed Longquan Aa mouse coronavirus (LAMV) and Longquan Rl rat coronavirus (LRLV), that were identified in a survey of 1465 rodents sampled in China during 2011-2013. Phylogenetic analysis revealed that LAMV and LRLV fell into lineage A of the genus Betacoronavirus, which included CoVs discovered in humans and domestic and wild animals. In contrast, LRNV harbored by Rattus norvegicus formed a distinct lineage within the genus Alphacoronavirus in the 3CL(pro), RdRp, and Hel gene trees, but formed a more divergent lineage in the N and S gene trees, indicative of a recombinant origin. Additional recombination events were identified in LRLV. Together, these data suggest that rodents may carry additional unrecognized CoVs.

Detection of rodent coronaviruses by use of fluorogenic reverse transcriptase-polymerase chain reaction analysis.

Reverse transcriptase-polymerase chain reaction (RT-PCR) assays have proved useful for the detection of mouse hepatitis virus (MHV) and rat coronavirus (RCV) in acutely infected animals and contaminated biomaterials. Fluorogenic nuclease RT-PCR assays combine RT-PCR with an internal fluorogenic hybridization probe, thereby eliminating post-PCR processing and potentially enhancing specificity. Consequently, a fluorogenic nuclease RT-PCR assay specific for rodent coronaviruses was developed. Primer and probe sequences were selected from the viral genome segment that encodes the membrane (M) protein that is highly conserved among rodent coronaviruses. Use of the fluorogenic nuclease RT-PCR detected all strains of MHV and RCV that were evaluated, but did not detect other RNA viruses that naturally infect rodents. Use of the assay detected as little as two femtograms of in vitro transcribed RNA generated from cloned amplicon, and when compared directly with mouse antibody production tests, had similar sensitivity at detecting MHV-A59 in infected cell culture lysates. Finally, use of the assay detected coronavirus RNA in tissues, cage swipes, and feces obtained from mice experimentally infected with MHV, and in tissues and cage swipes obtained from rats naturally infected with RCV. These results indicate that the fluorogenic nuclease RT-PCR assay should provide a potentially high-throughput, PCR-based method to detect rodent coronaviruses in infected rodents and contaminated biological materials.

Reverse transcriptase polymerase chain reaction-based diagnosis and molecular characterization of a new rat coronavirus strain.

BACKGROUND AND PURPOSE: Rat coronaviruses (RCV) are highly infectious and spread rapidly through laboratory rat colonies, causing sneezing, nasal and ocular discharges, photophobia, and cervical swelling. Current diagnostic methods include serologic testing and histologic examination. During a recent rat coronavirus outbreak, we tested a rapid, noninvasive method of RCV diagnosis that involved use of reverse transcriptase-polymerase chain reaction (RT-PCR) analysis to detect RCV RNA on cages housing infected rats. METHODS: The RT-PCR was used to detect RCV RNA in tissues from infected rats and on cages housing infected rats and to amplify portions of the RCV N, M, and S genes for molecular characterization. RESULTS: The RT-PCR detected RCV RNA on cages and in tissues from infected rats. The RCV-NJ N gene is most closely related to the MHV-Y N gene. The M proteins of RCV-NJ and RCV-SDA are 99% homologous, and the six RCV S protein fragments are 97 to 100% homologous. CONCLUSIONS: Use of RT-PCR with cage-swab specimens was capable of diagnosing RCV infection in and viral excretion from rats. Additionally, molecular characterization of the N, M, and S genes of RCV-NJ provided baseline information that can be used in performing further epidemiologic studies.

Comparison of the pathogenicity in rats of rat coronaviruses of different neutralization groups.

BACKGROUND AND PURPOSE: Rat coronaviruses (RCVs) are common natural pathogens of rats that cause clinical illness, necrosis, and inflammation of respiratory, salivary, and lacrimal organs. The aim of the study was to determine whether antigenically different strains of RCV vary in their pathogenic potential in rats. METHODS: Neutralization groups were identified by use of RCV strain-specific antisera. Sprague Dawley rats were inoculated oronasally with RCV-SDA, RCV-BCMM, or RCV-W. Histologic examination, immunohistochemical analysis, and reverse transcriptase-polymerase chain reaction analysis were performed on tissues from infected rats. RESULTS: Clinical illness was not evident in any of the inoculated rats. The RCV-SDA strain caused mild lesions in the exorbital gland of one rat. The RCV-BCMM strain caused severe lesions in the Harderian and parotid glands and mild lesions in the exorbital glands, lungs, and nasal mucosa. The RCV-W strain caused severe lesions in the Harderian, exorbital, and parotid glands and mild lesions in the submandibular glands, lungs, and nasal mucosa. The RNA concentration was highest in the Harderian, parotid, and exorbital glands of RCV-BCMM- and RCV-W-infected rats at postinoculation day 7. CONCLUSIONS: Although RCV-SDA, RCV-BCMM, and RCV-W caused different degrees and patterns of lesions, neutralization groups are not useful for predicting the pathogenic potential of a new RCV isolate.

Attachment glycoproteins and receptor specificity of rat coronaviruses.

Murine coronavirus (MHV) and rat coronavirus (RCV) are antigenically related viruses that have different natural rodent hosts. Both MHV and RCV can be propagated in the L2(Percy) and CMT-93 mouse cell lines. In these cell lines MHV uses the MHV receptor (MHVR or Bgp1a) and several related murine Bgp glycoproteins in the immunoglobulin superfamily as receptors. To determine whether RCV also uses these murine glycoproteins as receptors, we characterized the envelope glycoproteins of two strains of RCV and compared the effects of anti-MHVR monoclonal antibody on susceptibility of the mouse cells to MHV and RCV. The Parker (RCV-P) and sialodacryoadenitis (RCV-SDAV) strains of RCV expressed the spike glycoprotein S, but only RCV-P expressed a hemagglutinin-esterase glycoprotein that had acetylesterase activity. Therefore RCV-SDAV must bind to cellular receptors by the viral S glycoprotein, whereas RCV-P might bind to cells by its hemagglutinin-esterase glycoprotein as well as by S. Pretreatment of L2(Percy) 41.a or CMT-93 cells with anti-MHVR monoclonal antibody blocked infection with MHV-A59 but did not prevent infection of these murine cells with RCV-P or RCV-SDAV. Baby hamster kidney cells transfected with cDNAs encoding MHVR (Bgp1a) or Bgp2 were susceptible to MHV-A59 but not to RCV-P or RCV-SDAV. Thus the RCV strains cannot use these murine coronavirus receptors and must be infecting murine cells by another, as yet unknown, receptor.