Growth of rat sialodacryoadenitis viruses in LBC cell culture

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.

Viral Disease

This chapter discusses the infections caused by DNA viruses and also RNA viruses. The chapter focuses on the detection, diagnosis, risk assessment, and decision-making regarding viral infections. Several infections caused by DNA viruses are parvoviruses, rat cytomegalovirus, poxviruses, adenovirus, and papovavirus. Several RNA viruses and infections caused by these viruses are coronaviruses, paramyxoviruses, rotavirus and reovirus, and picornaviruses. Monitoring for viral infections should cover at least three venues: animals in established breeding and experimental colonies, animals held in entry quarantine, and animal tissues and products destined for in vivo use. For established colonies, monitoring should be tailored to local conditions. Effective monitoring should encompass sampling on a pre-arranged schedule, which can be intensified if evidence or suspicion of viral infection emerges. Because viral infections of rats can spread insidiously, early detection and epidemiologic “staging” should employ a detection matrix that includes clinical observation, appropriate sampling, and sensitive and specific diagnostic testing.

Isolation and characterization of sialodacryoadenitis virus (coronavirus) from rats by established cell line LBC

The outbreak of sialoadenitis occurred in a laboratory rat colony and the causative agent was isolated from the affected salivary glands of diseased rats using the established cell line LBC. The isolate readily multiplied, producing clear cytopathic effects with syncytium formation, and it was identified virologically and serologically as rat sialodacryoadenitis virus. In attempts to isolate the virus by primary rat kidney (PRK) cells and suckling mice as well as LBC cells, the LBC cells showed higher susceptibility for the virus growth as compared with PRK cells or the brain of suckling mice. The isolation rate of virus was 100% (5/5) in LBC, 40% (2/5) in PRK cells and 60% (3/5) in suckling mice. After four passages in the LBC cells, the virus did not produce disease in adult rats, while the mouse brain-passaged virus did.

Plaque assay and propagation in rat cell line LBC cells of rat coronavirus and 5 strains of sialodacryoadenitis virus

Various factors influencing the plaque formation of rat coronavirus (RCV) and sialodacryoadenitis virus (SDAV) in LBC cell monolayers were studied to develop the practical method for plaque assay. By this method, 4 Japanese isolates of SDAV also produced clear plaques. In one-step growth experiments of these viruses, newly formed virus was first recognized within 7.5 h postinfection and showed subsequently a rapid exponential increase. The virus was released rapidly from the infected cells. By indirect immunofluorescence virus specific antigen was detected as perinuclear granules in the cytoplasm of the cells at 5-6 h postinfection, and all the cells revealed fluorescence at 12 h postinfection.

Replication of sialodacryoadenitis virus in mouse L-2 cells

Sialodacryoadenitis (SDA) is a naturally-occurring infection of the laboratory rat raused by the coronavirus, sialodacryoadenitis virus (SDAV). The study of SDAV has been limited because there is no widely available continuous cell line for the propagation of high titers of the virus. The purpose of this study, therefore, was to compare the ability of SDAV to replicate in the permanent cell lines, LBC, of rat origin, and the mouse cell lines. L-929 and L-2. Following 2 to 6 repeated passages of SDAV in LBC cells, the virus could be readily propagated in LBC and L-2 cells, but not in L-929 cells. Similarly, SDAV adapted to replicate directly in L-2 cells could be readily propagated in LBC, but not L-929 cells. In LBC and L-2 cells, cytopathic effect (CPE), viral antigen, viral particles, and virus infectivity could be demonstrated. Titers of up to 10(8.0) infectious viral particles/0.25 ml of culture fluid were obtained at 48 hours in L-2 cells. Titers in LBC cells were one to two logs lower. When susceptible rats were inoculated with eighth passage L-2 cell-adapted virus, they developed typical lesions of SDA. Virus could be recovered from infected tissues and propagated in L-2 cells on first passage. The ability to propagate SDAV to high titers in the widely available L-2 cell line should promote the study of this virus and facilitate its comparison with other murine coronaviruses.