Astroviruses are non-enveloped, positive-sense, ssRNA viruses and often associated with gastrointestinal diseases. Murine astrovirus (MuAstV) was first confirmed in a laboratory mouse colony in 2011. Although infected mice do not present significant clinical symptoms, the virus might interfere with research results. A recent surveillance has shown that MuAstV is highly prevalent in laboratory mice. The aims of the present study were to identify and characterize MuAstV strains as well as to investigate the prevalence rate of viral RNA in laboratory mice in Taiwan, and to estimate the origin and past population demography of MuAstVs. Based on molecular surveillance, MuAstV RNA was detected in 45.7 % of laboratory mice (48/105) from seven of nine colonies. Three fully sequenced MuAstV strains, MuAstV TW1, TW2 and TW3, exhibited 89.1−94.4 % and 89.1–90.0 % nucleotide identities with the reference strains MuAstV STL1 and STL2, respectively. Phylogenetic analyses of the partial regions of the RNA-dependent RNA polymerase (RdRp) and capsid protein (CP) genes of 18 Taiwan strains along with other astroviruses revealed that there are three distinct lineages of mouse astrovirus, MuAstV1, MuAstV2 and mouse astrovirus JF755422. The mutation rates of MuAstV1 were 2.6×10−4 and 6.2×10−4 substitutions/site/year for the RdRp and CP regions, respectively. Based on the above molecular clock, the colonization of MuAstV1 in laboratory mice was between 1897 and 1912, in good agreement with the establishment of ‘modern’ laboratory mouse facilities. Since its initial infection, the population size of MuAstV1 has increased 15–60-fold, probably consistent with the increased use of laboratory mice. In conclusion, MuAstV1 has been associated with modern laboratory mice since the beginning, and its influence on research results may require further investigation.

Rodent fur mite infestation is a persistent and intractable problem in laboratory rodent colonies, due to insensitive diagnostics, unrepresentative samples for testing and improper sentinel system. Myocoptes musculinus (COP), Myobia musculi (MOB) and Radfordia affinis (RDA) have been reported in laboratory mouse colonies. To improve the sensitivity and efficiency of fur mite detection, COP-specific PCR and MOB/RDA-specific PCR assays were developed to detect and differentiate these fur mites, with the existence of a rodent housekeeping gene. The COP-specific PCR and the MOB/RDA-specific PCR could specifically detect COP and MOB/RDA at as low as 10 copies, respectively. In comparison of the specific PCRs with traditional methods (pluck test, tape test and pelt exam) for fur mite diagnosis, 31 rodents and 17 cage environment samples were evaluated. In screening for the infestation status of various fur mites on individual animals, the specific PCR assays showed distinctly higher sensitivity and accuracy (100% and 100%) than those of the traditional methods (sensitivity: 25–80%, accuracy: 83.9–96.8%). Interestingly, by using cage wipe environmental samples, the specific PCR assays exhibited 100% sensitivity and accuracy in the fur mite detection and differentiation. The COP-specific and MOB/RDA-specific PCR assays developed in this study could be reliable alternatives for routine pathogen monitoring of laboratory mice and environments of animal facilities without animal sacrifice. [Chou C-L, Cheng Y-C, Wang MH, Wan CH, Novel PCR assays for three fur mites in naturally infected mice without animal sacrifice, Taiwan Vet J XX(X):XX–XX, 2020.