How did the virus in the Walking Dead start?

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Tags

1. #virus
2. #departure
3. #learned
4. #human
5. #infected
6. #marked
7. #first
8. #death
9. #zombie
10. #walker
11. #every
12. #holds
13. #natural
14. #would
15. #traditional
16. #after
17. #season
18. #causes
19. #whether
20. #ensured