Control of two protozoal infections (Cystoisospora ohioensis and Pentatrichomonas hominis) in laboratory-bred common marmoset (Callithrix jacchus) colony

Background As the use of the common marmoset ( Callithrix jacchus ) expands in biomedical research, knowledge gaps persist in the management of parasitic gastrointestinal disease that can cause diarrhea and weight loss. To enable healthy husbandry and robust research outcomes, clear guidance on parasite identification and control is required. We document infections by Cystoisospora ohioensis and Pentatrichomonas hominis in a laboratory colony and evaluate an integrated control strategy. Methods Marmosets with sporadic, persistent diarrhea underwent coproparasitological examination. Diarrheic animals were treated with metronidazole (MET, 25 mg/kg) and trimethoprim–sulfamethoxazole (TS, 48 mg/kg). Fecal samples with or without oocysts or trophozoites were analyzed by 18S rRNA gene (18S rRNA) and/or mitochondrial cytochrome c oxidase subunit 1 (COI) PCR and sequencing for species identification. The entire colony was then screened by cage unit and received metaphylaxis with toltrazuril (TOL, 20 mg/kg) and tinidazole (TIN, 150 mg/kg), accompanied by environmental sanitation (cages, water-delivery systems, feeding bottles, and rooms) using water washing and sodium hypochlorite disinfection. After metaphylaxis, positive animals were re-tested and treated with MET or TS until negative. Body weights were compared before and after metaphylaxis. Results Persistent watery or hemorrhagic diarrhea sporadically occurred in 34 marmosets, and symptomatic animals were treated with MET and TS for 5–12 days. Oocysts and trophozoites were detected in 10 fecal samples from symptomatic animals. Parasites identification was performed on 14 fecal samples (10 from symptomatic and coproparasitologically positive animals, 1 from symptomatic but coproparasitologically negative, and 3 from asymptomatic animals). Two sample were identified as C. ohioensis , showing 99.1–99.8% or 99.6–99.7% sequence identity based on 18S rRNA or COI PCR and sequencing, respectively. Four samples were identified as P. hominis with 98.33–100% identity based on 18S rRNA PCR and sequencing. Colony-wide screening included all 233 animals housed in 93 cages; 216 animals received two metaphylactic doses of TOL and TIN at two-week intervals. After metaphylaxis, 12 cages remained positive for P. hominis . Thiry-seven animals from these cages were treated with MET for 7 days, and three animals required an additional 15-day MET treatments before testing negative. Body weight increased significantly after metaphylaxis ( P  < 0.001). Conclusions Fecal parasite screening and deworming should be prioritized when sporadic and persistent diarrhea observed in a colony. C. ohioensis may be eliminated with a single dose of TOL administered as metaphylaxis. Although P. hominis is considered non-pathogenic, its control is recommended for maintaining colony health. It can be effectively managed through a combined approach: a single metaphylactic dose of TIN followed by individual treatment with MET for more than 5 days.