He is blind and has diabetes - he thinks he can get away with anything.

Fast forward to last summer (2014) I got sick again, same symptoms as in 2009 and I'm pretty sure I had Mono (or Epstein-Barr Virus) again, even though I was never officially diagnosed with anything.  

It is an animal that works, provides assistance, or performs tasks for the benefit of a person with a disability, or provides emotional support that alleviates one or more identified symptoms or effects of a person’s disability.

If an 79 individual’s disability or disability-related need is not 80 readily apparent to a housing accommodation, the housing 81 accommodation may request written documentation prepared by a 82 health care practitioner, as defined in s. 456.001, which 83 verifies that the individual has a disability or a disability 84 related need and has been under the practitioner’s care or 85 treatment for such disability or need, and the animal provides 86 support to alleviate one or more identified symptoms or effects 87 of the individual’s disability or disability-related need. 88 b. 

As others have stated, check your lease and quote useful clauses from it regarding not disturbing neighbors.Best to you... this is likely a symptom of a larger issues so nip it...

The house is usually just a symptom of the problem.

Examples are seeing eye dogs, diabetes dogs, dogs who can sense seizures, and the list goes on. 

Your analogy is like telling a diabetic, "Well, you could of lost an arm and a leg with your diabetes but, it looks like we're only gonna have to amputate a leg".

Not having it is a symptom of much larger issues.  

There is no animals to test a vaccine on because there are 34 different coronavirus and the test animals develop no symptoms.