Halo teman! I think, not necessarily. In this example (if a context exists), the disease "has (already) reached" a more severe point, or stage, and then "it is (already) very severe", or "it has (already) become very severe". In other hand, the disease could be disappeared, perhaps after several consequences in a community or families, peoples, animals, and then the translation would use the past tense. This is just my humble opinion.
Selamat belajar! :)