Sudden change in cats behavior

[Anonymous]

I urgently need help.
My boy cat and girl cat are siblings, 3.5 years old, always together, very bonded, sometimes chase each other but they get along in no time.
2 days ago, girl cat had a skin biopsy for her recurrent rashes. She went to the clinic at 8 am and came home at 6 pm. She probably smelled of other animals. My boy cat hissed at her when she came home. She was and is struggling with walking due to biopsy. But when she sees the boy cat, both hiss at each other and she chases him and fights. We are keeping them separate when that happens but it's becoming difficult to manage them. Why are they suddenly being intolerant of each other? Please help. We have tried opening the door slightly and letting them sniff each other, petting one cat and giving our hand to the other cat to sniff.

[Anonymous]

Animals react badly to sick animals - even animals they previously liked. Self-preservation, perhaps. They perceive sickness. They dislike the sick animal. The other cat, the biopsied one is lashing out feeling vulnerable.

It'll pass.

[Anonymous]

Thanks.. that's very helpful