1. Mary Mallon, the first known healthy carrier of typhoid fever
, who spread it by working as a cook (typhoid fever is spread through water and food). When health officials tracked her down, she refused to believe she was a carrier, because a. since she was the first known case, she'd never before heard of healthy carriers and b. she did not understand a lot about typhoid fever. She was forcibly quarantined, released after two years on the condition that she wouldn't seek work as a cook again and quarantined again for life after another outbreak was tracked to her working as a cook under a pseudonym. It seems she had taken the job because other household jobs (like doing laundry) she got didn't pay as well and she still didn't believe she could spread the disease.
2. A carrier of any contagious disease who, through ignorance and recalcitrance or callousness, proceeds to take exactly those actions which are likely to cause the highest possible amount of infections in other people.
3. Someone who, analogous to 2, doesn't bother with anti-virus software or firewalls and so quickly gets their computer infected with all manner of computer viruses which then proceed to spread themselves from that computer. Especially if they persist in opening all attachments and not installing anti-virus software even after having been told they should.
1. (no example, real person after which 2 and 3 are named)
2. Mao seems to have been a typhoid Mary, according to accounts by his physician stating he had an STD which caused him little discomfort but which he spread at a rate of one young female follower infected per week.
3. If someone alerts you to a virus mail you sent them, and you do nothing about it, that makes you a typhoid Mary.