Toxoplasma gondii oocysts persist and remain infectious in soil for about 1.5 years.  In water--including seawater--about 4.5 years.  The point in eradicating its vectors (70-80% of US free-roaming cats are infected) is that once they're killed and their carcasses are incinerated to a core temperature of at least 157 degrees F, they DON'T GET TO KEEP ADDING TO THE PATHOGEN PILE.  And after 4.5 years, those oocysts that didn't manage to embed themselves in Pacific sardines, anchovies, mussels, oysters and other filter-feeding organisms in the nearshore marine environment will--finally--dissipate.  Here's some research for you.  Ask if you need help sounding out the big words:

http://www.academicjournals.org/article/article1380205329_Ajmal%20et%20al.pdf