I think if TB is on the go it is more airborn from people coughing, it drying up and the disease becoming airborn is the least probably way of it spreading. Generally if you dont eat the spit or put it on on y open wounds you should be ok. If you walk around licking spit off the ground and rubbing it into your wounds you got bigger problems.

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"Diplomacy is the art of saying 'Nice doggie' until you can find a rock - Will Rogers"