Sylvatic is a scientific term referring to diseases or pathogens affecting only wild (sylvan means forest-dwelling) animals. In the context of animal

Animal

Animals are a major group of multicellular, eukaryotic organisms of the kingdom Animalia or Metazoa. Their body plan eventually becomes fixed as they develop, although some undergo a process of metamorphosis later on in their life. Most animals are motile, meaning they can move spontaneously and...

 research, its opposite is domestic, which refers to pets, farm animals or other animals which do not dwell in the wild.

• Examples: sylvatic rabies
  Rabies
  Rabies is a viral disease that causes acute encephalitis in warm-blooded animals. It is zoonotic , most commonly by a bite from an infected animal. For a human, rabies is almost invariably fatal if post-exposure prophylaxis is not administered prior to the onset of severe symptoms...
  
  ; sylvatic and domestic bacterial strains; sylvatic yellow fever
  Yellow fever
  Yellow fever is an acute viral hemorrhagic disease. The virus is a 40 to 50 nm enveloped RNA virus with positive sense of the Flaviviridae family....
  
  

The word "sylvatic" is also simply a synonym for "sylvan

Silvan

Silvan , or Sylvan, may be used as an adjective or as a given name .It may refer to:-People:*Richard Sylvan, Australian logician and environmentalist also known as Richard Routley...

" (or "silvan") = "of the forest".