GMAT Sentence Correction (SC) | Re: While industry insiders insist that fish farming takes a burden off

C. harm rather than help, increasing the spread of diseases and that of parasites such as sea lice, and astronomically increasing the level of pollution in wild ecosystems

For a discussion on C, the OA, how many factors are there in the modifying clause "increasing the spread of diseases and that of parasites such as sea lice, and astronomically increasing the level of pollution in wild ecosystems"? In other words, is "the spread of diseases and that of parasites such as sea lice"