More and more evidence points to the fact that bats are ancient natural hosts of many viruses, including coronaviruses. Furthermore, research has shown bats being reservoir hosts for zoonotic viruses such as betacoronaviruses, e.g., the SARS-CoV-2 (Covid-19). It has also been established that the Rousettus aegyptiacus (Egyptian fruit bat) is susceptible to the intranasal infection of Covid-19, however, they do not show signs of disease nor effectively transmit the virus to other bats. In a recent study, the infection routes were compared and which effect each had on virus replication and on the immune system, and which effect the SARS-CoV-2 viral infection has on body temperature and activity of challenged bats.

Activity and core body temperature measured for 14 days
Scientists from the Friedrich-Loeffler-Institute in Germany implanted a group of Egyptian fruit bats (Rousettus aegyptiacus) with Star-Oddi DST micro-ACT loggers and DST nano-T loggers. The experiment was divided into experiments 1 (low dose) and 2 (high dose), and further into groups of inoculation routes and control groups. Two bats from each group received implants. The DST micro-ACT was used alone in the first experiment, and both logger types were used in the second experiment. The activity loggers were set to measure activity and temperature every 5 minutes from midnight to noon, and every 10 minutes from noon to midnight. The experiments lasted 14 days each.

All challenged bats show lower locomotor activity during nighttime
There was a clear nocturnal circadian rhythm seen, where activity and temperature were highest during nighttime. This was seen in both experiments. Disturbances in the circadian rhythm were seen in the orally challenged groups. All challenged bats in both experiments showed decreased activity during nighttime. Large temperature ranges were seen in orotracheally and orally challenged bats in the first experiment.

Wide temperature range seen in orotracheally and orally challenged bats
Interestingly, in the low-dose experiment, the orotracheally and orally challenged groups showed the largest variability in body temperature ranges or 33.5-40.6°C and 32.6-40.7°C, respectively.

Remarkably, in the high-dose experiment, the orally challenged group showed higher locomotor activity during the day compared to the night. The same group displayed a higher temperature during the nighttime, showing lower locomotor activity at the same time.

Below is fig. 3 from the article showing the circadian rhythms and distribution of activity and temperature measurements in the second experiment.

Further results can be found in the article published in the MDPI Special Issue Antiviral Immune Responses of Bat.