This is a theory that stretches back as far as the ancient Egyptians. There are two parts to this theory. The mythological part, and the scientific part. We all know of the cat scratch disease. Due to the frequency of cats scratching people, that disease is well known. However this one, is well hidden. Usually when a family member dies from a cause like that one, you document it as something else while trying to preserve your loved one's image. You wouldn't want the world to know that your husband had a secret fetish of having his testicles licked by your feline pet. Then when it happens you hide it so that your children keep the image they had of their father.
So let's travel back in time, to the ancient Egyptians. As we all know the cats were considered holy. But how did they reach that level of holiness? In the beginning they were considered simple Gods, they were still worshiped but mostly they were considered as small time divine beings. However as people were trying to reach divine levels for them selves, they would try different ways to bond with these divine beasts. This had escalated as people began performing sexual acts with these cats. Then a plague hit. A lot of holy-men, priests and others had started dying one after the other. They had observed that after having a cat lick their testicles, they would, after a period of time, get sick and die. This took their holiness up in ranks. Then when the Pharaohs tried it, to some it would seem ineffective. Those Pharaohs were then considered advanced gods. Their bloodline would then be worshiped as gods. When a male boy was born in the royal bloodline it would be tested against a cat. If it would survive the licking he would be the next heir of the throne. Else, he was considered a mortal and was left to die. But how does this work?
Believe it or not, there is science behind this. Did you know that a cat's tongue has a spike like surface? Yes it is a DNA trait left from their ancestors who had to lick the flesh off the bones of their pray. That means it had to be able to pierce and tear it away from where it was glued.
You are now going to tell me "But Tsinik, my cat licks me all the time and I'm fine". While that might be the case, a cat usually licks as in places which are in constant exposure to the environment. That kind of skin has hardened due to the circumstances around it and can now withstand a cat's soft tongue. However a man's testicles are always covered and protected. That leaves them weak and vulnerable when uncovered. So if a cat tries to lick them the spikes can enter through the pores of the testicle's skin. This is easier done in hotter places where the skin is loose and soft, with expanded pores that are trying to receive as much air and water as possible. That is why there was such a huge phenomenon in Egypt. If you live in a northern country with lot's of cold, and your testicles are cuddled up in a corner, then it is harder for the penetration to happen. If however, you live in a more warm environment then the exposure is possible.
So why do we die? Well, when your testicle is penetrated by their spikes, saliva passes through and enters the bloodstream through the testicles. Due to the fact that they need to clean their selves constantly, cats and felines in general evolved into having toxic saliva. Now the toxic is in your blood and you might die. Thankfully nowadays science has provided cures, but it is a fast acting poison and if you are not fast enough, even though you might survive due to medicine, you might need to lose your infected testicle.
On the other hand, some people are by birth immune to this due to highly adaptive blood flow. Those were also the ones considered divine by ancient Egyptians since they didn't have the science to explain the fact that they wouldn't die after receiving God's wrath. It is also considered that Pharaoh Pepi the Second had his testicles licked by multiple cats and survived. So if a cat licks your testicles and you live, then congratulations, you might just have a Pharaoh's DNA passing through you.
That is it for this theory, you may now sleep more soundly knowing about this hidden disease. Please be careful around your cat, and don't give in to your weird fetishes. I am Tsinik, and goodbye!