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: An extremely rare case of delusional parasitosis in a chronic hepatitis C patient during pegylated interferon alpha - 2b and ribavirin treatment .
### Output Text:
An extremely rare case of delusional parasitosis in a chronic hepatitis C patient during <span class="chemical">pegylated interferon alpha - 2b</span> and <span class="chemical">ribavirin</span> treatment . 