Bearded Dragon Biology and Medicine
Bearded dragons (Pogona vitticeps) are omnivorous lizards that are native to Central Australia. These squamates have been raised in captivity with great success, with (estimates of) over 250,000 being produced in captivity per year. As the popularity of these reptiles continues to rise, veterinarians can expect to encounter them more frequently in their practices. The purpose of this presentation is to provide attendees an overview of bearded dragon biology and common disease presentations.
Bearded dragons are a species of lizard that inhabit arid to semi-arid environments. These “sun-loving” species prefer to bask in the morning and late afternoon hours in temperatures that approach and exceed 100oF. Because dragons are ectotherms, it is important to provide them an appropriate environmental temperature range. In general, a diurnal range from 85-100°F is appropriate, while a nighttime drop to 70-80°F will suffice. Dragon not provided an appropriate environmental temperature may have a decreased metabolic rate and immune response, resulting in limited growth and chronic infections.
For years there has been very little research focused at identifying the specific nutritional requirements of reptiles. Omnivorous reptiles, such as the dragon, should be provided a diet comprised of both animal and plant materials. As juveniles, dragons tend to prefer animal proteins, while adult dragons tend to consume more plant protein in their diet. The author has found that romaine lettuce and other dark leafy lettuces are generally well received by the dragons. In the wild, these dragons have the opportunity to select their diet from a diverse number of insect prey items. These insects are nutritionally balanced because they can select from a variety of natural plant and animal food sources. In the United States, there are six invertebrates sold commercially, including the commercial cricket (Acheta domesticus), mealworm (Tenebrio molitor), superworm (Zoophobias morio), waxworm larva (Galleria mellonella), fruit fly (Drosophila spp.), and earthworm (Lumbricus terrestris). The primary advantage to using these invertebrates is that they are readily available through most pet distributors year round. Unfortunately, these prey items do not provide a complete and balanced diet for an insectivore. Most of these invertebrates are deficient in calcium, the exception being earthworms maintained in high calcium soils. Feeding or “gut-loading” commercial invertebrates prior to offering them to a dragon can help to increase the mineral content of the prey items. Dusting the prey item with a calcium carbonate powder may also help to increase the calcium content of the prey items.
Some pet owners elect to capture wild invertebrates to feed their dragons. It is important to only use invertebrates from areas where insecticides are not used. There are a number of invertebrates that produce toxins that can prove fatal to a reptile. Bearded dragons, and likely other reptiles and amphibians, are very susceptible to the toxins produced by lightning bugs. Dragons may die within minutes to hours of eating a single lightning bug. I strongly recommend against feeding wild caught invertebrates because of our limited understanding of the toxins produced by these organisms.
Dragons not provided a balanced diet might develop secondary nutritional hyperparathyroidism (SNHP) (metabolic bone disease). Secondary nutritional hyperparathyroidism is most commonly diagnosed in animals offered a calcium deficient diet, phosphorus rich diet, and/or vitamin D deficient diet. Affected dragons are often depressed, anorectic, develop muscle tremors, have soft pliable bones and seizures. In severe cases, affected animals can die from SNHP. Fast-growing juveniles and reproductively active females are most commonly affected. Treatment should include correcting dietary and environmental deficiencies. Supplemental oral calcium and exposure to ultraviolet B radiation (e.g., sun or full spectrum lighting) should be provided.
Obesity is a common problem identified in captive dragons. Commercially available larval insects have a very high fat content. Because these prey items routinely comprise the majority of the dragon’s diet in captivity, they are susceptible to an over-accumulation of fat. Obesity can lead to other health issues, including dystocia and hepatic disease, and clients should be provided dietary recommendations to reduce the weight of their dragons.
Historically, veterinarians have attributed most reptile disease processes to bacterial infections. Although bacteria are frequently isolated from dragons with clinical disease, we often have difficulty in differentiating primary and opportunistic infections. It is possible that some of the diseases characterized as bacterial in origin were actually caused by viruses or other pathogens. The advent of new and improved diagnostic methods has enhanced our ability to characterize new pathogens in reptiles and amphibians. Many of these new and emerging pathogens are viruses and can only be isolated or identified using molecular diagnostic techniques.
Bearded dragon adenovirus was first reported in Australia in the early 1980’s. The virus was not characterized in the United States until more than a decade later. Since that time, the virus has spread through the bearded dragon population in the USA and should be considered endemic. Transmission of the virus is primarily by the direct route (fecal-oral), although vertical transmission may also be possible. Affected animals may present with anorexia, weight loss, limb paresis, diarrhea and opisthotonous. Concurrent dependovirus and coccidial infections have also been observed in neonatal bearded dragons. Biopsies of the liver, stomach, esophagus, and kidney may be collected to confirm diagnosis (ante-mortem). On histopathology, basophilic intranuclear inclusion bodies are strongly suggestive of adenoviral infection. Currently, there is no non-invasive ante mortem diagnostic test to confirm adenovirus in the reptile; however, the author is currently working on a polymerase chain reaction (PCR) assay to detect adenovirus in the feces of affected animals. There is no effective treatment for adenoviral infections, although supportive care (e.g., fluids, enterals, antibiotics) may be useful in stemming the secondary effects of the disease. Again, very little is known regarding the epidemiology of this virus, therefore, special precautions should be taken when working with affected animals. Because there is no effective treatment, affected bearded dragons should be culled from breeding populations.
Coccidiosis is a major cause of morbidity and mortality in bearded dragons. These endoparasites are especially problematic in neonatal dragons, often resulting in stunting, diarrhea, and death. Whereas most coccidial infections in higher vertebrates are self-limiting, these infections often persist in bearded dragon colonies. Eliminating coccidia from bearded dragons is difficult. Most of the therapeutics used to eliminate coccidia are coccidiostatic and produce inconsistent results in reptile patients. The author has found that treatment regimens recommended in the veterinary literature (3-5 days) are far too short. A combination of extended treatment (14-30 days) with a coccidiostat, quarantine, and environmental disinfection/sanitation are required to eliminate coccidia from dragon colonies.
Orlando Diaz-Figueroa, DVM, MS, Dipl. ABVP (Avian Specialty)
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