You can't "get" AIDS. It's a symptom of infection by HIV along with other diseases.
You can get HIV, however AFAIK a cow or a worm can't get HIV. There may be a cow equivelant to HIV, but if it exists the odds that it would affect humans in the same way as HIV is pretty slim.
In general HIV is pretty hard to catch w/out a blood-to-blood route.
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