Surface temperature changes indicate disease onset after pulmonary murine corona virus infection, but do not constitute a humane endpoint

Abstract

Mouse models are important contributors for understanding the immune system during infections. Objective parameters help to assess the course of infection and guarantee animal welfare. In this study we analyzed if surface temperature measured via thermal imaging of the dorsal area is a suitable marker to evaluate animal wellbeing during murine coronavirus (MCoV) infection. Infected BALB/c mice displayed severe symptoms whereas C57BL/6 mice were less affected. In BALB/c animals, temperature increased from 27.1 °C to 28.4 °C within 24 h with levels remaining slightly elevated over the observation period. In contrast, a decrease in body weight was consistent through the period with 60% of the animals reaching the previously set termination point of 20% weight loss (n = 6). Also, C57BL/6J animals showed a significant temperature increase from 27.1 °C to 28.4 °C within 24 h and a significant weight loss over time with two out of ten reached weight loss end point. However, temperature and weight changes were not related in individual animals. In contrast to temperature values, body weight clearly set a trajectory towards early termination. Taken together, our data indicate that superficial temperature did not serve as a predictive parameter for defining humane end points, but indicate disease onset after pulmonary virus infection.

Keywords: Humane endpoint; Murine coronavirus; Surface temperature; Viral infections.

Fig. 1

Technical setup of surface temperature measurement (a) Example of surface temperature measurement via thermal imaging of the dorsal area and (b) camera setting. (c) Representative images depicting the region of interest of a selected C57BL/6J (left) and a BALB/c (right) mouse. (d) Picture of a mouse that cannot be included due to animal positioning

Fig. 2

Temperature measurements in BALB/c mice during Murine Corona Virus infection (MCoV). BALB/c mice were infected with MCoV at day 0 and monitored over 10 days. Temperature and weight were measured twice a day. During MCoV infection, (a) more than 50% of the animals were lost during the observation period. (b) Surface temperature increased initially but was not statistically significant at later time points. (c) Weight loss started at day 2 and continued over the whole observation period. One-way ANOVA with Dunnett post hoc test was used to determine significance. n = 6. p < 0.05 is considered significant. **p < 0.01,***p < 0.005, ****p < 0.001

Fig. 3

Temperature measurement in C57BL/6J mice during Murine Corona Virus infection (MCoV). C57BL/6J mice were infected with MCoV at day 0 and monitored over 3 (a-b) or 9 (c-f) days. During the short-term experiment, we observed minimal changes in weight (a) and a slight increase in body temperature (Temp.) (b). During a longer observation period, 80% of the animals survived the virus infection (c). We found weight loss towards the later time points with elevated temperatures for the first day (d). (e-f) Percentage values of individual mice of body weight (e) and surface temperature (f). Red symbols indicate mice, which reached the humane endpoint (HEP) criteria of 20% body weight loss before the end of the experiment and blue symbols indicate mice, which reached 20% weight loss on the harvest day. We observed that body weight in contrast to the surface temperature already declined before the threshold of HEP was met. One-way ANOVA with Dunnett post hoc test or Kruskal-Wallis with Dunn’s post hoc test was used to determine significance. n = 10. p < 0.05 is considered significant. *p < 0.05, **p < 0.01,***p < 0.005, ****p < 0.001