What is the rarest illness you can get ??

Question: What is the rarest illness you can get ??
- Keywords:
  illness,
  rare
Asked by diddymus to Giovanna on 17 Nov 2014.
- Giovanna Bermano answered on 17 Nov 2014:
  
  Smallpox is classified as the top rarest disease….followed by polio…..maybe because vaccines have been discovered!!!!

Question: What is the rarest illness you can get ??