In 1980 virus was ''proven'' to be the reason of disease. We can replace the word ''proven'' in this sentence with the word ''considered'' or ''shown''.
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I would suggest, to identify; (was identified to be)– CardinalCommented Dec 5, 2017 at 15:40
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1@Cardinal identify doesn't take infinitival complements -- we say "identified as the cause of the disease"– StoneyB on hiatusCommented Dec 5, 2017 at 15:56
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@StoneyB Thanks stoney for the correction. You know I checked google books and thought it's correct. I learner something new. Thanks.– CardinalCommented Dec 5, 2017 at 16:49
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1@Cardinal You find this occasionally in bureaucratic and scientific use, but it is rare and jarring: see this Google Ngram. Bureaucratic and scientific texts are not notable for clarity or idiomaticity.– StoneyB on hiatusCommented Dec 5, 2017 at 17:00
3 Answers
I believe that the word "confirm" is what you are looking for.
In 1980 virus was confirmed to be the reason of disease.
Neither "considered" nor "shown" has the same meaning with "proven", which means that something has been put into a test or has been verified.
"Proven" means that we are now certain that this is true. "Considered" means that we thought about it as one of many possibilities, or think that it is the most likely possibility. "Shown" means essentially the same thing as proven in this context but has weaker connotations. If you said that something is "shown" I'd understand that to mean a high probability, but not the certainty that "proven" implies.
Used in the context of your sentence, demonstrated is an exact synonym, meaning logically proven. In addition to the words Jay has given, other synonyms are confirmed and found. These also have a bit weaker connotation than demonstrated or proven, both of which mean a conclusion arrived at through a rigorous logical process.
However, demonstrated has similar but different meanings in other contexts. See this dictionary entry.