In the sentence extracted from biomedical literature, identify all the chemical entities. The required answer format is the same sentence with HTML <span> tags to mark up specific entities. 
### Entity Markup Guides:
Use <span class="chemical"> to denote a chemical.

### Input Text: The current best treatment for HCV infection is combination therapy with pegylated interferon and ribavirin .
### Output Text:
The current best treatment for HCV infection is combination therapy with pegylated <span class="chemical">interferon</span> and <span class="chemical">ribavirin</span> . 