Just wondering, why does the rabies virus go airborne when it infects humans and not animals like dogs?

Actually, it's always transmitted by saliva, but in some cases, there's sufficient aerosolized saliva to transmit it. It's not unique to humans.

The Rabies Virus is transmitted by saliva. It passes from one animal to another when the first animal bites the second animal. Once the Rabies Virus is in the blood, it attacks cells.

 

Once the virus is in the brain, it spreads quickly to the rest of the body. Then the host (infected animal) shows signs of the disease. An animal with Rabies first gets flu-like symptoms, including fever and headaches. Then, as the disease spreads, the animal's brain will not work properly. It will get confused, anxious, agitated, and delirious. It will not behave normally. The animal will hallucinate and it will not be able to sleep.

 

Animals, such as foxes and raccoons, which normally come out at night, may be out during the day if they have Rabies.