To the Editor.
—The article by Drs Nussenblatt and Belfort1 contains two errors of fact. First of all, oocysts are the form of Toxoplasma excreted in cat feces that can remain viable in humid soil for extended periods of time,2 not tissue cysts as stated.3Second, while Sibley and Boothroyd4 indeed have reported 10 mouse-virulent Toxoplasma isolates with the same genotype, no evidence was provided that these "strains" were "particularly virulent for humans."1 Sibley and Boothroyd state that "the mechanisms by which this clonality has arisen and is maintained cannot be determined from our study"4; hence, the meaning of virulence for mice remains a mystery, especially if one considers the frequency of transmission by cats in nature, with the possibility of genetic recombination, interposed between asexual transmission events from ingestion of raw or rare meat. However, it would be of interest to determine whether
Frenkel JK. Ocular Toxoplasmosis. JAMA. 1994;272(5):356. doi:10.1001/jama.1994.03520050034024