Gina, remember that we lost our two oldest cats to feline anemia last year - the whole region got infested with fleas, and they came indoors and feasted on anything with fur and four legs. You might want to hint about it to your vet.
Viking, the first thing they did was all the blood tests for those kinds of viruses and diseases. His blood work was normal. Something else is wrong. Hopefully they’ll know more today.