King Cobra Plague

I'm in the process of building a new world that has a Plague that has the entire continent of Equatorial South America quarantined by the rest of the world, and I'm currently trying to build the start of the plague. <br><br>&#x200B;<br><br>I also have a snake in my world called the Shadowstalker, a hybrid between a King Cobra and a Kraitsnake (a venomous snakes in Asia which is nocturnal). In my world, the Shadowstalker is found in the upper half of South America and has been slowly creeping towards the middle. <br><br>&#x200B;<br><br>Here is my question; Do you think it would be believable to have the Shadowstalker be the place where this plague started from? If humans get bitten by a human who has the plague, what is the chance of people contracting the plague as a result of a bite from a snake who has it?<br><br>&#x200B;<br><br>If this is believable, what are some interesting traits of the plague that I could have. I want the plague to have a new symptom every couple of years, that will be a percentage of all new people who contract the plague. <br><br>&#x200B;<br><br>Thank you for all the help, I am a beginner and am really excited for this project!