FIV and FeLV
Unlike the other three, these are not inherited — they are infectious viruses. No amount of DNA testing prevents them. What prevents them is knowing the status of every cat in the house and controlling what comes through the door.
What they are
Two unrelated retroviruses that happen to be screened together. FeLV, feline leukaemia virus, can cause anaemia, suppress the immune system and lead to lymphoma. FIV, feline immunodeficiency virus, gradually erodes immune function so that ordinary infections become serious ones.
Both spread between cats rather than down a pedigree — through bite wounds, prolonged close contact and mutual grooming, and from an infected queen to her kittens.
Why it matters
Neither virus can be cured. FeLV in particular is serious in young cats, and an infected kitten may be facing a shortened life from the day it is born.
For a cattery the risk is structural rather than genetic. One untested cat brought into a household of cats that share space, bowls and grooming can expose every animal in it. The failure mode is not bad luck; it is a missing test.
How it affects Maine Coons
There is nothing breed-specific here — a Maine Coon is no more susceptible than any other cat. The risk attaches to husbandry, not to genetics.
But it interacts directly with how we choose to raise our cats. Ours live loose together as a household group rather than in separate cages, which is better for temperament in every way we care about — and it also means the group's viral status has to be certain. Keeping the household clear is a precondition of raising cats this way, not an afterthought.
How we prevent it
Our cats are screened for both viruses, and are kept as an indoor household with no free-roaming outdoors, which removes the commonest route of infection — fighting with unknown cats.
If you would like to see current results for the specific cat or kitten you are considering, ask us and we will show you. We would rather answer that question than have you assume the answer.