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 HBV viral loads for mono - infected and co - infected patients ranged from 3 . 32 x 10 ( 2 ) to 3 . 82 x 10 ( 7 ) and < 200 to 4 . 40 x 10 ( 3 ) copies / ml , respectively .
### Output Text:
The HBV viral loads for mono - infected and co - infected patients ranged from 3 . 32 x 10 ( 2 ) to 3 . 82 x 10 ( 7 ) and < 200 to 4 . 40 x 10 ( 3 ) copies / ml , respectively . 