No single breed of cat has the worst health. It really depends
on what diseases that the certain breed is likely to get that you
consider the worst. However, purebreds usually have the most
problems.
Could a black cat be a Tiffany?
As long as it had the certain characteristics of the Tiffany
breed, than, yes, a black cat could be a Tiffany.
Is the Burmese cat breed closely related to the Burmilla cat breed?
Yes, the Burmese cat breed is closely related to the Burmilla
cat breed.