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: Mutations associated with lamivudine - resistance in therapy - na ve hepatitis B virus ( HBV ) infected patients with and without HIV co - infection : implications for antiretroviral therapy in HBV and HIV co - infected South African patients .
### Output Text:
Mutations associated with <span class="chemical">lamivudine</span> - resistance in therapy - <span class="chemical">na</span> ve hepatitis B virus ( HBV ) infected patients with and without HIV co - infection : implications for antiretroviral therapy in HBV and HIV co - infected South African patients . 