Abstract

Plasmodium spp. affect a wide variety of zoo animal species and are common parasites of terrestrial chelonians. Parasitemia can result in fatal hemolytic anemia, although most hemoparasites are considered to be non-pathogenic. Four wild-caught, confiscated star tortoises (Geochelone elegans) presented with marked anemia and suspected Plasmodium infection. Administration of chloroquine (15 mg/kg PO) and primaquine (0.75 mg/kg PO) given every 7 days for 4 treatments, resulted in a marked improvement in red and white blood cell parameters.

Introduction

Plasmodium is a common parasite of terrestrial chelonians and can result in fatal hemolytic anemia.^1,9 The intra-erythrocytic gametocytes of Plasmodium and Haemoproteus have refractile pigment granules, resulting from the breakdown of hemoglobin. Plasmodium can be differentiated from Haemoproteus by the presence of schizogony in the peripheral blood since schizogony of Haemoproteus only occurs in the host tissues. Plasmodium is transmitted by an invertebrate vector.

Case Reports

Four wild-caught star tortoises (Geochelone elegans) were quarantined at the Edinburgh Zoo following confiscation by UK authorities and subsequent donation to the zoo. Plasma biochemistries, hematology, and fecal parasitology revealed no abnormalities.

Five months later, one tortoise presented with an aural abscess. The mucous membranes were noticeably pale. Surgery for abscess removal under general anesthesia using propofol (Rapinovet: Schering-Plough Animal Health Breakspear Road South, UB9 6LS, UK) at 10 mg/kg IV and isoflurane (IsoFlo Vet: Schering-Plough Animal Health Breakspear Road South, UB9 6LS, UK) in oxygen (2% via endotracheal tube) was uneventful. Blood was taken for blood biochemistry and hematology analysis and fresh blood smears were prepared. The results revealed anemia and a leucocytosis with relative lymphocytosis. The presence of plasmodium-like inclusions in erythrocytes was detected using a Wright-Giemsa stain of the blood smears.

Examination of the remaining three tortoises revealed pallor of the mucous membranes. Blood collected from these tortoises revealed similar degrees of anemia and erythrocyte inclusions morphologically similar to those seen in the first tortoise.

Primaquine (0.75 mg/kg; one 7.5-mg tablet, generic formulation, crushed and dissolved in 1 ml water) and chloroquine (15 mg/kg; Nivaquine syrup 10 mg/ml: Rhone-Poulenc Rorer, 50 Kings Hill Avenue, ME19 4AH, UK) were administered via orogastric feeding tube. The drugs were given weekly for 4 doses. All tortoises required ketamine (15 mg/kg IM; Ketaset, Fort Dodge Animal Health, Flanders Rd, SO30 4QH, UK) in order to extend the head and pass the feeding tube into the stomach.

After four treatments the mucous membranes were markedly pinker. Blood was again collected at the end of treatment (t=4 weeks) and at 12 weeks from initial diagnosis (t=12 weeks). The results showed a slight improvement at 4 weeks and a marked improvement at 12 weeks in red cell parameters (Table 1). No parasites were detected on examination of fresh blood smears stained with Wright-Giemsa. The white cell parameters showed an initial increase followed by a reduction to below pre-treatment levels.

Table 1

Hematologic parameters of one male (M) and one female (F) star tortoise (Geochelone elegans) with suspected Plasmodium spp. infection before and after treatment with primaquine and chloroquine

Discussion

Plasmodium schizonts and gametocytes occur in erythrocytes. Plasmodium and Haemoproteus are generally considered non-pathogenic in reptiles, however subtle signs of infection may occur (e.g., infected lizards may produce fewer eggs than non-infected lizards).⁶

Chloroquine treatment has been suggested in Chelonia at 125 mg/kg PO q 48 h for three doses for the treatment of blood parasites.⁷ The doses used here were taken from reported avian doses of 0.75 mg/kg primaquine and 15 mg/kg chloroquine administered weekly.⁵ The combination anti-plasmodium therapy described in the tortoises has previously been reported to prevent mortality and eliminate parasites from the blood in penguins.⁸ The treatment of parasitemic birds has reduced mortality in some outbreaks from 50% to 13.8%.³

The vector for transmission of plasmodium in chelonians is unknown. We believe that the star tortoises had acquired the disease in the wild.

Malarial organisms are not always found in circulating erythrocytes in infected animals, therefore negative findings on blood smears cannot be relied upon to indicate lack of infection.⁴ The use of blood smear diagnosis allows detection of the disease weeks before clinical signs may occur.⁸ Leukocytosis with a relative lymphocytosis was a characteristic finding of infected birds.⁸ However, other authors found no correlation between total white blood cell counts or relative lymphocytosis in parasitized or non-parasitemic African penguins.³ The results from the star tortoises in this study suggest a leucocytosis with a relative lymphocytosis when the animals were parasitemic.

The disease can recrudesce after a period of time,² therefore it is possible that at first sampling the tortoises were infected but were not parasitemic.

Acknowledgments

We thank Martin Gibbons (Assistant Curator, Edinburgh Zoo) and Edwin Blake (Head of Reptiles, Edinburgh Zoo) for their help and expertise.

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