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

### Input Text: For improvement over previous studies , a new set of primers has been designed , which allow for amplification of the coding and splicing sequences only .
### Output Text:
For improvement over previous studies , a new set of primers has been designed , which allow for amplification of the coding and splicing sequences only . 