Rickets in a Crab-eating Fox (Cerdocyon thous)

Abstract

Background : Calcium is essential for the healthy development of animals, especially regarding bone formation. Diverse factors influence calcium metabolism, and failure in any of these points may result in metabolic bone diseases. Rickets is an uncommon disease of growing bones occurring exclusively in young animals, it is a characterized by the failure of osteoid to calcify and can be a result of lack of vitamin D, imbalance of calcium and phosphorus or hereditary conditions. Nutritional origin is more frequent in veterinary medicine, but it has become rarer after the availability of balanced commercial rations. This report describes the diagnosis and treatment of rickets in a crab-eating fox puppy. Case : A 3-month-old male crab-eating fox was presented with ataxia and angular deviation of the tibia and radius/ulna with suspected osteometabolic disease. It was part of a group of three orphan siblings hand-raised. The other two siblings did not present any clinical signs. All three animals presented pale mucous membranes and were infected by ancylostoma, coccidia, toxocara, and sarcocystis. Radiographic findings of the affected animal showed generalized osteopenia of the entire skeleton associated with widening radiolucent distal physeal plates and cupping of the metaphysis, changes classical of rickets. The other two siblings presented no skeletal alterations and complete blood count and biochemistry of all three animals were taken for comparison, including serum vitamin D and PTH. All three animals presented lymphopenia (5.4-9.3 x 10³/uL, reference range 10.3-16.5 x 10³/uL), hypoproteinemia (5.1-5.3 g/dL, reference range 5.9-8.2 g/dL), low levels of creatinine (0.4-0.6 mg/dL, reference range 0.7-1.2 mg/dL), increased ALP (181-285 U/L, reference range 209.7-267 U/L) and CK (421-500 U/L, reference range for domestic dogs 16-140 U/L). The affected fox presented ionized calcium (10.9 mg/dL, reference range for domestic dogs 9.3-11.5 mg/dL) and vitamin D (26.4 ng/mL, reference range for domestic dogs 9.5-129 ng/mL) close to the inferior limits associated with elevated phosphorus (8.8 mg/dL, reference range for domestic dogs 2.5-5.6 mg/dL) and PTH (4.3 pg/mL, reference range for domestic dogs < 2.82 pg/dL). Besides that, the affected animal presented the quickest development (weight gain) among the offspring. Discussion : Recent reports of rickets in veterinary medicine are not common. The advent of balanced commercial rations and improvement in animal husbandry reduced the frequency of this condition. Wild species are more frequently reported to present metabolic bone disease due to inadequate nutrition management of the different species. Bone formation and growth are result of the deposition of hydroxyapatite crystals and it depends on calcium intake or absorption, adequate serum vitamin D levels and proper calcium and phosphorus balance. All these three situations were breached in this case report, resulting in a multifactorial scenario for development of rickets in this crab-eating-fox. Radiographic exam, complete blood count, biochemistry, and clinical response to dietary correction confirmed the diagnosis of rickets with nutritional origin. Hereditary rickets had been described in people and a domestic dog, but not in wildlife species. The animal responded well to clinical and nutritional management, presenting clinical response within a couple of weeks. This is the first report of rickets in this species as well as dosage of serum vitamin D and PTH in crab-eating foxes.