Your best bet is probably to go with a religious reason why this aspect of science is ignored. 

If your civilization fervently believes in Creationism, their Church may well discourage the study of medicine as it might threaten their teachings. 

Furthermore, this religion might place a very high emphasis on being reborn, so maybe trying to cure people who are too ill is actually seen as keeping them from reaching Heaven, and being reborn. 

If they are devout/fanatical enough about their beliefs this will guarantee that biology will be seen as a sort of necessary evil, and few people will want to know much about this aspect of science. 

Of course, some suspension of disbelief is required, as a civilization that is interested in scientific pursuit is unlikely to embrace this kind of blind obedience, but you can make it work.