What exactly does this study shows?

1 - The first description of the inhibition of behavioral fever by a pathogen. These results indicate that this behavior has been acting as a selection pressure on pathogens throughout evolution. Importantly, this study is also the first report of a vertebrate virus capable of altering the behavior of its host through the expression of a single gene: To date, there are only two known examples of viral genes that are capable of affecting the behavior of the infected host, and both examples are genes from baculoviruses (2) that infect invertebrates.

2 – This research extends the knowledge of the evolutionary and functional relationship between behavioral fever in ectotherms and fever in endotherms to cytokine mediators that originated more than 400 million years ago. While a few previous studies have demonstrated that behavioral fever in ectotherms and fever in endotherms are evolutionarily related based on their regulation at the level of the central nervous system (prostaglandins), no study has yet demonstrated whether this evolutionary relationship extends to the cytokine mediators that inform the brain of infections detected in the body by immune cells. The discovery that Tnfα induces behavioral fever in teleost fish, in addition to its well-known mediation of fever in mammals (including humans), is truly fascinating. These results further suggest that the ancestral signaling pathway of behavioral fever regulation in ectotherms evolved in endotherms to regulate the expression of fever.

3 - A new mechanism through which environmental temperature changes can contribute to disease emergence. This study demonstrates that while an infection can be benign in conditions where the environment is compatible with the expression of behavioral fever, it can cause a high mortality rate when the environment does not allow for the expression of this behavior. This finding has important ecological implications and should be taken into account when considering for example modifications of natural habitats, introduction of ectotherms in new biotopes and environmental conditions in aquaculture systems. 

4 - A new dimension to environmental enrichment for laboratory animals. The study reports the first viral gene of a vertebrate virus that is capable of altering the behavior of its host. Remarkably, phenotypic expression of this gene was only observed in conditions that mimicked the temperature gradients of a natural environment, and no phenotypic expression of this gene was observed under standard laboratory conditions. This study strongly supports the concept that environment enrichment for laboratory animals may be essential for clarifying the function of numerous viral and cellular genes that do not show a phenotype under standard laboratory conditions.

5 - A striking example of the effect of the immune system on the central nervous system. An emerging scientific field is the study of the interactions between the immune system and the central nervous system (3). This work provides an outstanding example in support of this concept and demonstrates that pathogens can target these interactions.

6 - A robust example of the beneficial effect of (behavioral) fever on the control of infection. This study is a remarkable example, in a relevant host-pathogen model, that increased body temperature induced by infection must be tolerated to allow for control of the pathogen.

In conclusion, this research provides major findings related to host-pathogen interactions and is of interest for several scientific fields, including virology, immunology, animal behavior, evolution, ecology and even animal welfare. 

(2) Science 2011, 333: 1401; PNAS 2005 102: 2584-2589
(3) Nature Reviews Immunology 2011, 9: 625-632