This decade is being hailed as the Age of the Brain. Viruses can alter brain activity. A recent example is the discovery that cats carry a virus that can affect rats and make the rodents cat-tolerant. In an experiment, rats were placed in a pen that had the scent of cats in one corner. The rats with the virus went towards the corner, while those unaffected stayed away.
A cat-loving rat is destined for a short feline-rodent relationship!
The virus can also affect humans but is entirely harmless unless the person has HIV, in which case it is fatal.