Spontaneous pathology of the common marmoset (Callithrix jacchus) and tamarins (Saguinus oedipus, Saguinus mystax)

The new world primate family Callitrichidae , including marmosets ( Callithrix sp ) and tamarins ( Saguinus sp ), are the smallest NHP. This family is arboreal with claws, and possesses the highest fertility rate of any primate with average litters of two to three offspring [ 34 ]. The common marmoset ( Callithrix jacchus ) has become a popular research model in virology, viral oncology, reproductive physiology, bacterial infectious disease, transplantation immunology, pharmacology, endocrinology, teratology, metabolism, behavior, osteology, autoimmune encephalomyelitis models of multiple sclerosis, stroke, and toxicology [ 2 , 9 , 17 , 20 , 21 , 25 , 28 , 36 , 38 ]. This increase usage is reflected in the literature as there were over 40 times the number of publications involving marmosets in the 1990's than in the 1960's 1 . In part, their increased use has been attributed to well-established breeding colonies, small size, relatively rapid generational turnover, abundance in the wild (compared to other species of Callitrichidae) [ 1 ], and low zoonotic risk [ 34 ]. The common marmoset has been suggested for genome mapping [ 15 ]. Marmosets reach maturity at approximately 18 months of age [ 1 , 40 ]. In contrast, tamarins are not used as commonly as marmosets, partially due to the presence of less-established breeding colonies and declining wild populations. However, tamarins have played key research roles in vaccine trails, colon cancer, ulcerative colitis, inflammatory bowel disease, and Crohn's disease [ 18 , 19 , 23 , 33 ]. Tamarins reach maturity at approximately 16 months of age [ 3 ]. The spontaneous pathology of these species, which can impact study results, remains poorly defined in comparison to old world primates. There are two reviews of marmoset pathology [ 8 , 35 ] from the early 1980s and one recent review of marmoset pathology performed in animals utilized in viral studies [ 18 ]. Understanding the spontaneous pathology of these species can aid in interpreting pathological findings in research and in their husbandry. We documented the spontaneous pathology seen at necropsy for 129 common marmosets ( Callithrix jacchus ) and 52 cotton-top ( Saguinus oedipus , SOT) and moustached tamarins ( Saguinus mystax , SMT) from 1987 to 2008 housed at the Southwest National Primate Center at the Southwest Foundation for Biomedical Research (SFBR).

The morphologic lesions, body systems affected, and cause of death for the 129 common marmosets are summarized in Tables 1 , 2 and 3 . The most common marmoset lesions were dehydration, emaciation, nephritis, colitis, and inanition. The average age of all, mature, and immature common marmosets at necropsy was 3.9 +/- SD 3.1, 5.32 +/- SD 2.66, and 0.45 +/- SD 0.46 years. Three cases of colitis were cultured, yielding one isolate each of Escherichia coli ( E. coli ), Klebsiella pneumoniae , and Psuedomonas aeruginosa ( P. aeruoginosa ). The case of nematodisis was caused by the parasite Trichospirura leptostoma ( T. leptostoma ). Three cases of pneumonia were cultured: two yielded Bordetella bronchiseptica and one E. coli . Three cases of hepatitis were cultured: all yielded P. aeruoginosa . The morphologic lesions, body systems affected, and cause of death for the 52 tamarins are summarized in Tables 4 , 5 and 6 . The most common tamarin lesions were dehydration, ascites, emaciation, congestive heart failure, cardiomegaly, and colitis. The average age of all, mature, and immature tamarins at necropsy was 3.09 +/- SD 3.50, 5.21 +/- SD 3.39 and 0.01 +/- SD .00 years. Four cases of nematodiasis were caused by T. leptostoma and two were suspected to be caused by filaroides. One case of pneumonia was cultured, yielding E. coli . Klebsiella pneumoniae was cultured from a case of peritonitis.

In both species, dehydration and emaciation were generally considered secondary to other chronic diseases processes, such as colitis, heart failure, lymphosarcoma, and amyloidosis. This explains their high frequency as a morphological diagnosis and their infrequent listing as a cause of death. We identified two prior surveys of marmoset pathology conducted approximately 25 years ago. A survey of marmosets from a breeding colony [ 8 ] identified Heinz body haemolytic anemia, skeletal muscle myopathy, inflammatory disease of the intestinal tract and chronic colitis, and bacterial infections as the most frequent findings. A similar survey of marmosets used in experimental studies [ 35 ] identified chronic colitis, chronic thyroiditis and interstitial mononuclear infiltrates in the kidney as the most frequent findings. Similar to those surveys, nephritis, colitis and enteritis were commonly observed in our colony. Heinz body haemolytic anemia and skeletal muscle myopathy were uncommon in our animals. This may reflect improvements in diet and husbandry practices over the last 25 years, as these lesions were thought to be a result of a nutritional deficiency involving vitamin E, selenium, and protein [ 8 ]. Interestingly, hemosiderosis was still commonly encountered in our marmosets suggesting further dietary modifications are still required. It is likely that the decreased frequency of bacterial infections in our animals is also related to changes in housing and husbandry procedures over the last 25 years. Amyloidosis only accounted for 3% of marmoset diagnoses, however it was diagnosed in 15 of the 128 animals (12%). This is consistent with a prior study reporting a 17% incidence [ 26 ]. As in that study, affected animals in our colony included both immature and mature marmosets. Extramedullary hematopoiesis (EMH) in marmosets has been reported in the liver, adrenal glands, liver, kidney, spleen and mesenteric lymph nodes [ 17 , 24 , 28 ]. Although we did not find EMH in the mesenteric lymph nodes, we believe this is the first report of EMH in the lungs. Although endometriosis has been experimentally induced in marmosets [ 16 ], to the best of our knowledge, no spontaneous case has ever been reported in a marmoset. Colitis was the most common cause of death in marmosets, accounting for 22% and 23% of overall and mature marmoset deaths, respectively. Our results were significantly less than the 96% incidence rate reported in a 1998 study [ 13 ]. Environmental and dietary changes have been shown to radically alter the rates of colitis in marmoset colonies [ 23 ]. Although genetic differences between the colonies can not be excluded, it is possible that marmoset husbandry changes over the last 20 years could account for this difference. Lymphosarcoma has been previously reported in marmosets [ 30 ] and was the most common neoplasm and the second most common cause of death in mature marmosets in our colony. Inanition, stillbirths and colitis were the most common reasons for death in immature marmosets in our study, accounting for 61% of immature marmoset deaths. Forty percent of immature marmoset deaths occurred at under one month of age. Our results confirm a prior report that most deaths occur during the first month of life and the most common causes of death are reproductive failures (e.g. abortion, stillbirth) and rearing failure (inanition/starvation) [ 21 ]. Heart failure was by far the most common cause of death, accounting for 29% and 36% of overall and mature tamarin deaths, respectively. A high incidence of cardiac disease was reported in tamarins exposed to hepatitis A and GB viruses [ 7 , 9 , 18 ]. The authors in those studies believed the lesions were unrelated to the experimental study. Our findings of a high incidence of heart failure in naive tamarins supports their hypothesis. However the characteristic of the heart lesion was different; instead of myocardial fibrosis, we typically encountered a dilated heart (Cardiomegaly) with minimal histologic changes. Interestingly, heart failure in our colony was restricted to SMT, the same species used in these studies. Although fewer numbers of SOT were evaluated in our colony, the only cardiac lesion identified in these animals was one case of hemorrhage. Colitis only accounted for 5% of tamarin diagnoses, however it was diagnosed in 11 of the 52 animals (21%). This was still significantly less than the 73% incidence of colitis cystica profunda reported in a previous survey [ 18 ]. Additionally, while there were occasional lesions consistent with colitis cystica profunda, the majority of the colitis diagnoses we observed lacked the herniation through the basement membrane and the mucus-filled cysts characteristic of thet condition. Atelectasis, stillbirth, heart failure and colitis were the most common reasons for death in immature tamarins in our study, accounting for 64% of immature tamarin deaths. Forty five percent of immature tamarin deaths occurred at under one month of age. Tamarin infant pathology is poorly documented, leaving little published data for comparison.

The marmosets and tamarins were housed in indoor, conventional wire caging, fed a commercial diet (Mazuri Calltrichid diet, Richmond, Indiana, USA) supplemented with grains, vegetables, and fruits and provided water ad libitum . All animals in this report were part of a breeding colony and were not used experimentally. The marmosets and tamarins were cared for in compliance with the Guide for the Care and Use of Laboratory Animals. All procedures were approved by the SFBR Institutional Animal Care and Use Committee. The SFBR is accredited by the Association for Assessment and Accreditation of Laboratory Animal Care, International. A full necropsy with histological evaluation was performed for each Callitrichidae primate. Tissues were fixed in 10% neutral buffered formalin, processed conventionally, embedded in paraffin, cut at 5 μm, stained with hematoxylin and eosin, and reviewed by light microscopy. Necropsies were performed and histopathologic diagnoses were made by two board-certified veterinary pathologists (EJD and GBH). Special stains, cultures or other specialized tests or consultations were utilized as needed. All results were stored in an internal anatomic pathology database program (apath). We performed a search of apath for all pathology diagnoses from Callitrichidae primates from 1987 to 2008; NHP used experimentally were excluded. We identified 129 marmosets (56 male, 69 female, and 4 fetuses of undetermined gender) and 52 tamarins (18 male, 29 female, and 5 fetuses of undetermined gender). A definitive cause of death was identified for 122 of the marmosets and 42 of the tamarins. Individual records were assembled into a Microsoft Office Excel 2003 (Microsoft, 2003) spreadsheet to be sorted to generate tables organized by species, morphological diagnosis, organ systems, and cause of death, to include indications for euthanasia. The, number of male, female mature, immature (<18 months old, marmosets [ 1 ]; <16 months old, tamarins [ 3 ]) and total NHP was identified for each morphologic diagnosis; the tamarin results were also counted by species (SMT, SOT).