Comparison of the survival of different isolates of SARS-CoV-2 in evaporating aerosols.

Numerous variants of SARS-CoV-2 with increased transmissibility have emerged over the course of the pandemic. Potential explanations for the increased transmissibility of these variants include increased shedding from infected individuals, increased environmental stability, and/or a lower infectious dose. Upon exhalation of a respiratory particle into the environment, water present in the particle is rapidly lost through evaporation, resulting in a decrease in particle size. The aim of the present study was to compare the losses of infectivity of different isolates of SARS-CoV-2 during the rapid evaporation of aerosol particles that occurs immediately post-generation to assess if there are differences suggestive of increased survival, and ultimately greater transmissibility, for more recent variants. Losses of infectivity of several isolates of SARS-CoV-2 suspended in viral culture media were assessed following aerosolization and evaporation in a flowing chamber. The results demonstrate that losses of infectivity measured post-evaporation were similar for three different isolates of SARS-CoV-2, including isolates from the more recent Delta and Omicron lineages. The average loss in infectivity across all three isolates was 61 ± 15% (-0.46 ± 0.17 log10 TCID50/L-air) at a relative humidity <30%. These results, together with those from several previous studies, suggest that it is unlikely that an increase in environmental stability contributes to the observed increases in transmissibility observed with more recent variants of SARS-CoV-2.

Evidence for co-infection of ovine prion strains in classical scrapie isolates.

The diversity of strains of ovine prions within classical scrapie isolates was investigated by transmission studies in wild type mice. To determine the maximum diversity of prion strains present in each ovine scrapie isolate examined, isolates from mice having the shortest and longest incubation times for terminal disease after primary inoculation were passaged serially. Serial passage of ARQ/ARQ scrapie isolates in RIII mice revealed the ME7 prion strain in mice with short incubation times for terminal prion disease and the 87A strain in those mice with long incubation times. Serial passage of VRQ/VRQ scrapie isolates in RIII mice led to emergence of the 221C prion strain in mice with short incubation times and a variant of the 221C strain in those mice with long incubation times. RIII mice with short incubation times had higher levels of total and proteinase K-resistant PrP(Sc) compared with those RIII mice with long incubation times, while mice with long incubation times had large aggregates and plaques of PrP(Sc). ME7 PrP(Sc) differed in stability compared with the 87A prion strain, while PrP(Sc) associated with 221C had similar stability to that of the 221C variant. Serial passage in VM mice led to identification of ME7 and 87V in the same scrapie isolate. The data show that different prion strains can emerge from the same ovine scrapie isolate following serial passage in wild type mice and that the transmission properties of these strains correlate with distinct patterns of PrP(Sc) deposition.

Transmission of classical scrapie to wild-type mice: the influence of the ovine PrP sequence on lesion profiles.

Susceptibility of sheep to classical scrapie is determined by polymorphisms in the coding region of the prion protein gene (PRNP), mainly at codons 136, 154 and 171. It has recently been shown that lesion profiles from classical field scrapie isolates that transmitted to RIII mice can be classified into different groups. There was also strong, but not absolute, association between the different groups and codon 136. Here, we examine the hypothesis that additional polymorphisms in the open reading frame sequence of the ovine PRNP may account for the different groups of lesion profiles observed following transmission to mice.

UV stimulation of chromosomal marker exchange in Sulfolobus acidocaldarius: implications for DNA repair, conjugation and homologous recombination at extremely high temperatures.

The hyperthermophilic archaeon Sulfolobus acidocaldarius exchanges and recombines chromosomal markers by a conjugational mechanism, and the overall yield of recombinants is greatly increased by previous exposure to UV light. This stimulation was studied in an effort to clarify its mechanism and that of marker exchange itself. A variety of experiments failed to identify a significant effect of UV irradiation on the frequency of cell pairing, indicating that subsequent steps are primarily affected, i.e., transfer of DNA between cells or homologous recombination. The UV-induced stimulation decayed rather quickly in parental cells during preincubation at 75 degrees, and the rate of decay depended on the incubation temperature. Preincubation at 75 degrees decreased the yield of recombinants neither from unirradiated parental cells nor from parental suspensions subsequently irradiated. We interpret these results as evidence that marker exchange is stimulated by recombinogenic DNA lesions formed as intermediates in the process of repairing UV photoproducts in the S. acidocaldarius chromosome.

Detection of astrovirus in the faeces of cats with diarrhoea.

Examination by electron microscopy of faeces from two separate cases of young cats with diarrhoea revealed the presence of 28 nm viral particles morphologically consistent with an astrovirus. No visible cytopathic effect was observed when the virus was inoculated into a feline kidney cell culture.