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: We present a 49 - year - old woman who developed a delusional parasitosis during treatment with pegylated interferon alpha - 2b weekly and ribavirin .
### Output Text:
We present a 49 - year - old woman who developed a delusional parasitosis during treatment with <span class="chemical">pegylated interferon alpha - 2b</span> weekly and <span class="chemical">ribavirin</span> . 