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

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 support colony health and reliable research outcomes, clear guidance on parasite detection, molecular characterization, and control is required. We describe the detection of a Cystoisospora sp. showing high sequence similarity to Cystoisospora ohioensis and Pentatrichomonas hominis in a laboratory colony and evaluate an integrated control strategy. 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, regardless of the presence or absence of oocysts or trophozoites, were analyzed by 18S rRNA gene (18S rRNA) and/or mitochondrial cytochrome c oxidase subunit 1 (COI) polymerase chain reaction (PCR) and sequencing for molecular identification. The entire colony was then screened at the cage level and received colony-wide treatment 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 colony-wide treatment, positive animals were re-tested and treated with MET or TS until negative. Body weights were compared across the study period. 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. Parasite 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 samples were identified as Cystoisospora sp. closely related to C. ohioensis , showing 99.15–99.80% and 99.65–99.75% sequence identity based on 18S rRNA and COI gene sequencing, respectively. Four samples were identified as P. hominis , showing 98.33–100.00% sequence identity based on 18S rRNA gene sequencing. Colony-wide screening included all 233 animals housed in 93 cages; 216 animals received two antiprotozoal doses of TOL and TIN at two-week intervals. After colony-wide treatment, 12 cages remained positive for P. hominis . Thirty-seven animals from these cages were treated with MET for 7 days, and three animals required an additional 15-day course of MET before testing negative. Body weight increased significantly during the study period ( P < 0.001). Fecal parasite screening should be considered when sporadic and persistent diarrhea is observed in a colony. In the present colony, Cystoisospora sp. was no longer detected following two administrations of TOL at a two-week interval, combined with environmental sanitation. Although P. hominis is generally considered non-pathogenic in common marmosets, its clinical significance in the present colony remains uncertain. Persistent detection of P. hominis following TIN administration was subsequently managed with individual MET treatment. These findings suggest that an integrated approach combining parasite screening, colony-wide and targeted antiprotozoal treatment, and environmental sanitation may be useful for the management of protozoal infections in common marmoset colonies.