If you’re looking for a quick way to boost realism in your story or explore a new means of explaining Smarty Syndrome/Hellgremlinism or how it spreads among a population, maybe a bad seed infecting a community be it Feral or Domestic, maybe create some tragic irony between breeder/shop myths and the reality or maybe some good Samaritan/Abuser activist influencing population behavior by manipulating infection rate one way or the other, new research on wolves indicates pack-forming, aggression and territoriality, and loner traits are influenced by bacterial infection (which affects many animals in different ways, including humans).
Per the article:
Toxoplasma gondii is a ubiquitous protozoan parasite that can infect any warm-blooded species. In lab studies, infection with T. gondii has been shown to increase dopamine and testosterone levels along with risk-taking behaviors in hosts including rodents, chimps, and hyenas. Oh, and humans.
They found that “the odds that a seropositive [infected] wolf becomes a pack leader is more than 46 times higher than a seronegative wolf becoming a pack leader.”
Wolves with antibodies against the parasite were significantly more likely to disperse (leave their packs and set out on their own) and to become pack leaders. Pursuing both of these courses of action constitutes aggressive and risky wolf behavior, and they represent the two biggest decisions in a wolf’s life.
An infected leader may increase the overall number of infected wolves, both because pack leaders have a reproductive advantage and because risk-taking leaders might be less hesitant to lead their packs into cougar territory, where they can pick up their own infections.
Plus, wolves are social creatures who learn from and emulate their leader’s behaviors. So T. gondii-infected, aggressive, risk-taking pack leaders can yield “a more assertive, risk-embracing pack culture even though only a few key individuals are actually infected.”
Of course, increased engagement in risky behaviors is dangerous, so some of these hyper-aggressive wolf leaders and the packs that copy them are more likely to get themselves killed. Regardless, the selfish genes dictating their behaviors and their fates aren’t even their own genes. Parasites are the puppeteers.
You could say there is an organism unique to infecting Fluffies, play with how various real diseases/parasites/infections affect them different, or just namedrop it to handwave any logical leaps in your story.