Abstract

Entamoeba invadens is the etiologic agent of amoebiasis in reptiles. This parasite has a direct life cycle (fecal-oral) and is very pathogenic with high morbidity and mortality, although this may vary according to the reptilian species involved.⁵ The present report describes the successful prophylactic use of a particular dosage regimen of metronidazole in order to control reptile amoebiasis in the Zoo of Antwerp.

Materials and Methods

For many years, the Royal Zoological Society of Antwerp (RZSA) has been housing reptiles with a significant number of deaths by amoebiasis (Table 1). In all cases, a standardized necropsy protocol has been carried out. Macroscopically, lesions consisted of necrotizing enteritis and/or liver abscesses, and in wet or histopathologic preparations of these lesions, the amoebal vegetative form or cysts could be observed. Data in 1994 demonstrated that the problem of amoebiasis was increasing. Therefore, prophylactic treatment of snakes started on 8 February 1994 and similar observations 4 years later led to the start of medical prophylaxis in the other reptiles (tortoises, varans, other lizards) on 1 April 1998.

Table 1. Number of snakes and other reptiles and the respective number of deaths due to amoebiasis at the Royal Zoological Society of Antwerp

For practical reasons, a system with two different capsules (A and B) was used. Capsule A contains 100 mg metronidazole (Flagyl—Aventis Pharma, Brussels, Belgium) and 67 mg CaCO₃, and capsule B contains 20 mg metronidazole and 83 mg CaCO₃. Capsules A are administered to big snakes and capsules B to all other reptiles. The dosage regimen is given in Table 2.

Table 2. Prophylactic regimen of metronidazole in reptiles at the Royal Zoological Society of Antwerp

For statistical analysis, a generalized linear model with binomially distributed error term is fitted to the yearly number of deaths given the number at risk, including as covariate a binary variable expressing whether the year appeared before or after treatment commenced. The year when treatment started is not included in the analysis.

Discussion and Conclusion

Amoebae can be found in fecal material of reptiles without any clinical or pathologic symptoms (e.g., Entamoeba invadens is only occasionally pathogenic in turtles⁵). However, the patients described in this study showed gross necropsy lesions in which amoebae were demonstrated.

For the treatment of clinical amoebiasis, many authors describe metronidazole dosages ranging from 25–275 mg/kg body weight once or for 1 to 7 days, with repetitive intervals of 1–3 weeks for 2–3 treatments.^1-4,7 On the other hand, data on chemoprophylaxis are scanty. According to Soulsby,⁶ tetracycline at 400–800 mg/m body length has prophylactic activity.

Since metronidazole has proven activity against amoebae, we decided to develop a practical regimen that could be effective in the long run. The calculated dosages per kg body weight lie in the range of the therapeutic ones described by the different authors; only the prophylactic treatment intervals differ (Table 2). The death rate by amoebiasis decreased markedly 1 year after the prophylactic treatment started and remains very low after 10 and 6 years of chemoprophylaxis in snakes and other reptiles, respectively.

The ratio of the odds of deaths before and after treatment equals 10.45 (95% CI: 4.11–26.53) for the snakes and 10.76 (95% CI: 2.55–45.44) for the other reptiles. Both odds ratios are significantly higher than 1 and indicate that for both groups, animals were more likely to die from amoebiasis before prophylactic treatment started.

Obviously, chemoprophylaxis has to be strengthened by strict hygiene. Since the same hygienic measures had been implemented during the entire duration of the present study, it can be concluded that the metronidazole prophylactic treatment played a key role in the control of clinical and lethal amoebiasis.

Literature Cited

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