The Synergistic Effect of Tanabesol and Calcium Hydroxide on Cryptosporidium parvum Oocyst Inactivation

Cryptosporidiosis is a major diarrheal disease with high mortality, primarily in young animals, and poses a zoonotic threat worldwide. Currently, no available drugs are fully effective against Cryptosporidium, and most commercial disinfectants show limited efficacy against its oocysts, underscoring the need for improved control strategies.

We aimed to investigate the ability of Tanabesol (an ortho-agent), calcium hydroxide solution, and their combination to inactivate Cryptosporidium parvum oocysts.

Oocyst morphology was examined using scanning electron microscopy (SEM) imaging. Vital dye staining combined with an in vitro excystation assay was applied to assess viability.

Ortho formulations induced oocyst wall disruption, rupture, and collapse, as revealed by SEM imaging. In addition, Tanabesol exhibited a dose-and time-dependent effect on Cryptosporidium oocysts, with higher concentrations and longer exposure times causing more significant inactivation. Hydrated lime has shown antimicrobial properties against enteric bacteria and viruses, but its impact on Cryptosporidium oocyst inactivation has yielded varying results. Limewater alone caused a significant decline in the total number of normal oocysts (i.e., >50%). Notably, no potentially viable oocysts were observed after sensitization with Tanabesol diluted in calcium hydroxide solution for 120 min, compared with using water as the diluent. Tanabesol with limewater reduced the viability percentage of oocysts to 30% and prevented sporozoite release by more than 84%.

Adding calcium hydroxide to the preparation of Tanabesol should help in the control and prevention of cryptosporidiosis in livestock farms.