Serum Cobalamin (Vitamin B12) Concentrations in Rhesus Macaques (Macaca mulatta) and Pigtailed Macaques (Macaca nemestrina) with Chronic Idiopathic Diarrhea

Abstract

Chronic diarrhea poses a significant threat to the health of NHP research colonies, and its primary etiology remains unclear. In macaques, the clinical presentation of intractable diarrhea and weight loss that are accompanied by inflammatory infiltrates within the gastrointestinal tract closely resembles inflammatory bowel disease of humans, dogs, and cats, in which low serum and tissue cobalamin (vitamin B12) levels are due to intestinal malabsorption. We therefore hypothesized that macaques with chronic idiopathic diarrhea (CID) have lower serum cobalamin concentrations than do healthy macaques. Here we measured serum cobalamin concentrations in both rhesus and pigtailed macaques with CID and compared them with those of healthy controls. Serum cobalamin levels were 2.5-fold lower in pigtailed macaques with CID than control animals but did not differ between rhesus macaques with CID and their controls. This finding supports the use of serum cobalamin concentration as an adjunct diagnostic tool in pigtailed macaques that present with clinical symptoms of chronic gastrointestinal disease. This use of serum vitamin B12 levels has implications for the future use of parenteral cobalamin supplementation to improve clinical outcomes in this species.

Figure 1.

Distribution of serum cobalamin levels in healthy populations of pigtailed and rhesus macaques (n = 25 each group).

Figure 2.

Serum cobalamin concentrations (bar, median) in pigtailed macaques with chronic idiopathic diarrhea (CID) compared with healthy controls. Serum cobalamin levels were significantly (Mann–Whitney test, P = 0.0043, 2-tailed) lower in pigtailed macaques with CID than in control animals.

Figure 3.

Platelet counts (bar, median) in pigtailed macaques with chronic idiopathic diarrhea (CID) compared with healthy controls. Platelet counts were significantly (Mann–Whitney test, P = 0.0022, 2-tailed) higher in pigtailed macaques with CID compared with control animals.