Never Be a Vet for Bats, They Don't Need One

By: Chang Shu

Bats are extraordinary because they constantly carry various diseases but do not development many apparent symptoms. In mammals, whenever a harmful organism such as bacteria is introduced into the body, reactive oxygen species (ROS) is produced by immune cells. These ROS can destabilize and destroy bacterial cells. However, too much ROS can lead to oxidative stress which causes damage to important biomolecules like protein, fat, and DNA, consequently damaging the animals’ own cells. Bat’s body is very interesting. Despite of the numerous viruses and bacteria bats carry inside their body, they do not show any clinical symptoms. By discovering how bats respond to induced infection, it can potentially tell us more about how their bodies works. In this paper, David Costantini and his team from Tuscia University injected Egyptian fruit bats (Rousettus aegyptiacus) with bacterial E. coli to determine whether an infection would trigger an inflammatory response and cause oxidative stress in these bats.

At the beginning of the study, the researchers captured 26 adult male bats and treated them with medications to remove any kind of parasites on them. After these bats are settled in, the experimenters injected some of the bats with E. coli cell walls to induce an infection and others with non-infectious injections. Then after 24 and 48 hours, the researchers measured the body weight of all bats and collected blood samples for analysis. All the data collected from the bats were tested in a lab and statistically analysed. What the researchers tested for in the blood was the presence of indicators of immunological response like haptoglobin and lysozyme, or indicators of oxidative damage like ROS.

The researchers discovered that the group of bats that got the bacterial wall injection had higher haptoglobins, which are cheap and fast chemicals bat’s body can produce when initially encountering an infection. Not only that, they also had significantly more lysozyme in the blood which are natural chemicals produced by the body to destroy bacterial cell walls and induce bacterial cell death. Most interestingly, the E. coli injection did not trigger and produce any of the oxidative agents like reactive oxygen species in the bat’s body that got the bacterial injections.

What the researchers concluded was that the induced bacterial injections triggered only inflammation response, but not oxidative stress in these bats. This suggests that these bats have a way to promote the balance of the level of oxidative stress during an infection and prevent oxidative stress and damage to the animals’ own cells. The exact mechanism is unclear right now, but several hypotheses have been stated in the paper. Some researchers have hypothesised that it could be due to the strong reduction in activities which the bats exhibit and how it can lead to lower production of ROS during an infection. Other researchers have hypothesised that it could be due to the fruity diet that these bats are eating, where they can get and store the chemical agents that can help them to fight diseases.

This study is especially interesting because it highlights the importance of haptoglobin and lysozyme following an infection, and in order to further understand the underlying mechanism, we need to further test these chemicals and other potentially important chemicals in bat’s body during an infection. Apart from the real scientific findings, I think this paper can better convince my professors that I need fruits and sleep when I am sick, not assignments!

Costantini, D., Weinberg, M., Jordán, L., Moreno, K. R., Yovel, Y., Czirják, G. Á. (2022). Induced bacterial sickness causes inflammation but not blood oxidative stress in Egyptian fruit bats (Rousettus aegyptiacus). Conservation Physiology. 10, coac028.