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The common marmoset, Callithrix jacchus, is increasingly being used as the preferred nonhuman primate (NHP) model in biomedical research. Marmosets share several physiological and biological similarities with humans, as a Simiiformes species, and their use in research programs advances knowledge of several fields. Their unique characteristics, such as small size, high fecundity, and rapid growth, offer additional advances in laboratory settings. This article reviews the developments in experimental disease models using marmosets based on our experience at the Central Institute for Experimental Animals (CIEA) in Japan. The development of genetically modified marmoset models using advanced genome editing technology attracts researchers, particularly in neuroscience-related fields. In parallel, various marmoset models of human diseases induced by surgery or drug administration have contributed to preclinical and translational studies. Among these are models for Parkinson's disease, induced by 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine; spinal cord injury models; a model for type 1 diabetes, induced by the combination of partial pancreatectomy and streptozotocin administration; and a hepatic fibrosis model induced by thioacetamides. The development of these models has been supported by refinements in veterinary care, such as the careful design of anesthetic protocols and better understanding of pathogenic microorganisms. In the second part of this review, we present a compilation of practices currently in use at CIEA that provide optimal animal care and enable safe experimentation.

The common marmoset (Callithrix jacchus) is a nonhuman primate that is used for preclinical research on stem cell transplantation therapies due to its similarity to human beings as well as its small size, enabling researchers to perform experiments without preparing a large number of cells. In this study, we developed a marmoset hepatic fibrosis model for regenerative medicine research. Six female marmosets aged 4-6 years were administered thioacetamide (TAA) at a dose of 2.5-40 mg/kg two or three times a week. Hepatic fibrosis was assessed by liver biopsy when blood chemistry indicated liver damage. Administration of TAA increased total bile acid, aspartate aminotransferase, and total bilirubin and decreased serum albumin levels. Following more than 11 weeks of continuous injection of TAA, histological analyses detected hepatic fibrosis in all animals. Type IV collagen 7S serum levels in animals with hepatic fibrosis were significantly higher than in normal animals as a possible marker of hepatic fibrosis in marmosets. Serial liver biopsies following the last administration of TAA revealed that induced fibrosis remained up to 11 weeks. The results suggest that continuous TAA administration induces persistent hepatic fibrosis in the common marmoset and this nonhuman primate hepatic fibrosis model have the possibility to evaluate the therapeutic effects of test samples to ameliorate hepatic fibrosis.

Trichomonadid protozoa have been found in the intestinal tracts of common marmosets (Callithrix jacchus). However, there is little information available on species identification and the pathogenicity of these trichomonads. In this study, we conducted a fecal survey of a common marmoset colony maintained as laboratory animals in Japan and identified the trichomonad species. Screening using a fecal smear examination revealed that 66% (58/88) of the marmosets had trichomonadid trophozoites in their feces. The trichomonads were found in both normal feces (31/49, 63%) and diarrhea (27/39, 69%), with no significant difference in frequency. The protozoa were identified as Pentatrichomonas hominis using morphological characters and the 100% identity of the nucleotide sequence of the partial 18S rRNA gene (297 bp). The intraspecific genetic variability between P. hominis from the marmosets in this study and P. hominis from other reported mammal hosts was ≤1% in the nucleotide sequence, including the internal transcribed spacer (ITS)-1, 5.8S rRNA gene, and ITS-2 (293 bp). P. hominis inhabits the large intestine of various mammalian hosts, including primates, and is considered nonpathogenic. These results suggest that P. hominis is transmitted among marmosets and other mammals but is not a primary cause of bowel disease in marmosets.