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: Apopain , a human counterpart of the nematode cysteine protease death - gene product , CED - 3 , has a key role in proteolytic events leading to apoptosis .
### Output Text:
Apopain , a human counterpart of the nematode cysteine protease death - gene product , CED - 3 , has a key role in proteolytic events leading to apoptosis . 