Reptile infectious disease

Sharon Redrobe BSc (Hons) BVetMed CertZooMed MRCVS

Bristol Zoo Gardens, Bristol, BS83HA UK

sredrobe@bristolzoo.org.uk

Reptiles often presented to the veterinarian with advanced disease. Septicaemia, noted by petechiation of mucus membranes, toxic heterophillia, is therefore a common presenting sign. This is due in part to the few signs of illness demonstrated by reptiles and the tolerance of long-term anorexia or lethargy of their pet by some reptile owners. Any change in behaviour in reptiles e.g. increased/decreased basking, anorexia, lethargy, poor skin shedding (ecdysis) should therefore be acted upon as a sign of disease. Treatment of the reptile patient therefore usually requires attention to correction of septicaemia, dehydration and hepatic lipidosis and well as addressing the underlying disease.

Reptiles are ectothermic animals and therefore many physiology systems are inexorably linked to the husbandry of the animal. Reptiles must be maintained within the Preferred Optimum Temperature Zone (POTZ) in order for the immune system to work effectively. Both a range of temperatures as well as access to the optimal temperature must be provided to enable the reptile to thermoregulate by behavioural means.

Whether reptiles are able to mount a febrile response to infection has long been controversial but recent reports support the view that reptile do indeed mount such a response. Studies in the common Agama lizard (1) found that the average duration of the fever response is related to the level of infection; however, the magnitude of the fever is relatively independent of the level of infection. Early studies indicated that the Sudan plated lizard, Gerrhosaurus major, did not exhibit a febrile response when challenged with bacterial pyrogen. More recent results indicated that a 14-day antibiotic treatment regime produced a significant decrease (0.5 +/- 0.1 degree C) in the mean selected body temperature (MSBT) for this species (31.3 +/- 0.2-30.8 +/- 0.2 degrees C). The antibiotic treatment results suggested that G. major already had a fever caused by a pre-existing bacterial infection. This study demonstrated that the previously reported a febrile state for G. major was the result of animals having pre-existing bacterial infections. G. major does exhibit a febrile response similar to other lizard species (2).

Common infectious diseases include pneumonia, osteomyelitis, stomatitis, and enteritis. Parasitic diseases may occur even in long term or second-generation captive animals, especially if infected with parasites that pursue a direct life cycle. All reptiles should therefore be subject to biannual faecal parasitology counts and appropriate anthelmintic therapy.

Microbial diseases may be caused by virus, bacteria or fungal organisms. All three types may be involved in pneumonia of reptiles. A common presentation in snakes is a diagnosis of fungal pneumonia with a Gram negative bacterial component, however the underlying factor may be a Paramyxovirus (PMV). Inclusion Body Disease virus (IBDV) is another viral infection of snakes that may present as pneumonia or CNS disease. Both PMV and IBDV are incurable disease that may lead to a 90-100% mortality in snake collections. Control is therefore based upon serology testing and culling of positive animals (3,4,5). The relatively high incidence of pneumonia is captive snakes may be related to the relatively small space afforded these animals in captivity leading to stress related immunosuppression and/or insufficient expansion of the lungs as it is not uncommon for these animals to be kept in enclosures which do not permit them to fully stretch out.

Stomatitis studies have noted an association between Pseudomonas sp. and periodontal disease and that Gram negative bacteria tended to predominate in diseased lizards (6). A wider range of bacteria, including yeasts, are isolated from healthy animals, compared with only one or two gram negative bacteria and no yeasts isolated from diseased animals (7). Yeasts are considered part of the normal oral flora of herbivorous reptiles (8). Conversely, it is interesting to note that the ‘normal’ animals had Salmonella sp. identified in the oral flora and that this organism has been associated with osteomyelitis in snakes (9). Although disease has been suggested to be caused by organisms that form part of normal flora (6). Treatment, including removal of dental calculus, lavage of subgingival pockets, excision of abscesses and osteomyelitic lesions, and prolonged parental antibiosis, has been recommended for this condition.

Osteomyelitis has been associated with celomitis, hepatitis, and oophoritis in snakes (10), and to the ‘stick’ phenomenon where the spinal vertebrae fuse to form a rigid spine. Salmonella sp. are often implicated in such osteoarthritides. Bone infection in lizards and tortoises carries a similar poor prognosis and may be associated with systemic disease (11). Infection of the distal limb may be treated aggressively by surgical curettage and the placement of antibiotic impregnated beads. A more radical, and often more successful approach, is to amputate the affected limb.

Subcutaneous abscesses in reptiles are common in pet species and may be caused by (aberrant) parasite migration, bacterial or fungal disease. Reptile heterophils are unable to form liquid purulent material as in most mammals therefore reptile abscesses tend to be firm caseated\masses requiring surgical removal. Attention should be paid to investigating the underling cause as most cases of subcutaneous abscessation are associated\with episodes of septicaemia and may also have caused infection of internal organs. Recent publications have suggested that in many cases the mass formed is a Fibriscess and not a true abscess (12)

Salmonella infection of reptiles is a much discussed issue surrounding the pet reptile trade. Many authors have concluded that as Salmonella sp. are so commonly isolated from overtly healthy reptiles that it is a normal part of reptile enteric flora. However, recent studies have found that Salmonella infection is a disease of captivity in green iguanas (13). Although Salmonella has been isolated from wild tortoises (14). It is difficult, if not impossible, to ‘cure’ animals of this infection therefore, from a zoonotic point of view, it is more practical to view all reptiles and carriers of Salmonella and exercise appropriate hygiene precautions (15)

LITERATURE CITED

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2. Muchlinski AE, Gramajo R, Garcia C. Pre-existing bacterial infections, not stress fever, influenced previous studies that labeled Gerrhosaurus major an afebrile lizard species. Comp Biochem Physiol A Mol Integr Physiol 1999 Nov;124(3):353-7
3. Manvell RJ, Drury SE, Geach M, Lewis JC. Isolation of ophidian paramyxovirus type 7 from a reticulated python in the UK. Vet Rec. 2000 Dec 9;147(24):696.
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9. Ramsay EC, Daniels GB, Bemis DA, Tryon BW. 1996. Salmonella Arizona osteomyelitis in a colony of Arizona ridge nosed rattlesnakes (Crotalus w. willardi). Proc Am Assoc Zoo Vet; 218
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13. Mitchell MA, Shane SM.Preliminary findings of Salmonella spp. in captive green iguanas (Iguana iguana) and their environment. Prev Vet Med. 2000 Jun 12;45(3-4):297-304
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15. Bradley T, Angulo FJ. ARAV/ CDC Salmonella and Reptiles: Veterinary Guidelines 1999. Association of Reptilian and Amphibian Veterinarians (ARAV), PO Box 1897, Lawrence, Kansas, 66044-8897, USA