Practically all such claims are hoaxes.
Viruses can only work in executable code.
They cannot function in text documents or data files. Viruses could execute through email only if email software had the ability to recognize and execute directives embedded within text messages. Our research has not produced a single instance of an email program having such capabilities. It is possible that one could send an infected executable program as an attachment to an email message. Such programs could infect a system only after being executed.