Sinefungin, a natural nucleoside isolated from cultures of Streptomyces incarnatus and S. griseolus, is structurally related to S-adenosylhomocysteine and S-adenosylmethionine. Sinefungin is a DNA methyltransferase (DNMT) inhibitor (IC₅₀ = 0.1 - 20 uM). Sinefungin has been shown to inhibit the development of various fungi and viruses, but its major attraction to date resides in its potent antiparasitic activity. This compound has been reported to display antiparasitic activity against malarial, trypanosomal, and leishmanial species. Sinefungin inhibits pneumococcal biofilm growth in vitro and colonization in vivo, decreases AI-2 production, and downregulates luxS, pfs, and speE gene expressions. Sinefungin was significantly suppressive against both L. donovani and L. braziliensis panamensis infections in hamsters when compared with meglumine antimonate. An immunosuppressed rat model was used to investigate the anti-Cryptosporidium parvum activity of sinefungin. In infected animals, oral sinefungin therapy resulted in a dose-related suppression of oocyst shedding, which correlated with oocyst disappearance from ileal sections. When administered prior to or on the day of oocyst challenge, sinefungin successfully prevented infection. These data suggest that sinefungin could be considered as a candidate molecule in the treatment of human cryptosporidiosis, considered to be the most significant enteric opportunistic infection in AIDS.