Hartz Exotic Health April 2003 Vol. 2, No. 2

Captive Management of the Green Iguana

Heidi L. Hoefer, DVM, Diplomat ABVP West Hills Animal Hospital Huntington, New York

The majority of problems seen in reptile pets are a result of improper caging, feeding, and lighting techniques. It is important for the veterinarian to understand the requirements of each species being treated and to advise owners as to their proper care. The green iguana (Iguana iguana) is one of the most popular reptile species kept as a pet and also, unfortunately, one of the least understood.
In its natural habitat, the green iguana is an arboreal, diurnal folivore (leaf-eater) naturally found in Mexico and Central and South America. The iguana is a basking lizard that thrives in daytime temperatures near 100°F. It is a strict herbivore from hatching through adulthood and does not eat insects or mice at any time during its development. Iguanas are strong swimmers and can remain submerged in water for up to 30 minutes.
Captive, farm-reared iguanas are readily available for the pet trade. In captivity, iguanas grow rapidly (30 to 60 cm/year) and reach adult size in 2 to 3 years if properly cared for. They need large tanks or enclosures to accommodate this growth, and it is suggested that the first purchased tank be as large as possible. Like all reptiles, iguanas are solitary species that should be housed as individuals. Dominance and aggression can result in severe injuries or poor growth for the subordinate lizard. Iguanas should not be allowed to roam free in the house because they will not receive adequate heat or UV light, and they are prone to ingesting foreign matter (e.g., hair, coins, etc.).

Cage Setup

Substrate
Substrate (cage floor covering) comes in a variety of materials. The ideal substrate should be inexpensive, easy to clean, digestible if eaten, and pleasant to look at. Newspaper works well, but synthetic indoor/outdoor carpeting (AstroTurf [SRI Sports, Leander, TX] or Repti Cage Carpet [Zoo Med Laboratories, San Luis Obispo, ]) is more aesthetic and is easy to clean and disinfect. Even these products can fray along the edges and can pose problems if not maintained or replaced periodically, however. Alfalfa pellets (rabbit food) can also be used but must be changed frequently. Avoid the use of sand, corncob, gravel, shavings, cat litter, and small wood chips, which can be eaten by the iguana resulting in mouth abrasions and gastrointestinal impactions. They are also difficult to keep clean and can harbor bacteria and fungal organisms. Avoid the use of so-called "digestible" substrates such as Calci-Sand (T-Rex, Chula Vista, CA); these products
are very slow to digest and can lead to intestinal impactions.

Lighting
Lighting is very important to basking lizards such as the iguana. The full spectrum of natural light provided by the sun plays an integral role in vitamin synthesis and calcium metabolism. Both UVA and UVB wavelengths are recommended. UVB of wavelength 290 to 320 nm is necessary for vitamin D activation in the skin. Unfiltered sunlight (not through glass or plastic) is always the best source of ultraviolet radiation; when outside temperatures are above 70°F, the iguana should be exposed to direct sunlight. Indoor ultraviolet lighting is important in colder months, although it is not known if these synthetic bulbs provide the correct amount of UV rays for vitamin metabolism. Black light (BL type) fluorescent bulbs (General Electric), Vita-lite fluorescent tubes (Durotest, Lyndhurst, NJ) and Reptisun 5.0 (Zoo Med) are some good choices. Plant grow lights or black light blue (BLB) tubes for psychedelic posters do not work. The UV lights must be within 18 inches of the lizard and should be left on 10 to 12 hours/day and turned off at night. These bulbs lose their UV radiation in time, even though they continue to give off light, and should be replaced every year.

Supplemental Heat
Supplemental heat is needed for captive iguanas. Iguanas must be in
their preferred optimal temperature zone (POTZ) for metabolic processes like digestion, growth, healing, and immune system function. Temperature ranges during the day should be 85 to 95°F and not less than 75°F at night. A temperature gradient within the enclosure is recommended, with a focal hot spot or basking area of 95 to 100 °F. An incandescent or infrared bulb or a nonilluminating ceramic bulb placed outside of the cage works well. Be careful not to burn the iguana; it should not be able to get too close to the heat source (Figure 1). Use thermometers to measure the temperature both on the substrate as well as on top of any climbing branches within the enclosure. Hot rocks do not work and are not recommended.

Humidity
Humidity is an important consideration in the reptile enclosure. Iguanas are subtropical species and inhabit rain forests surrounded by lush vegetation. This level of humidity is very difficult to duplicate in most pet iguana homes. Commercial humidifiers, potted plants, large water bowls, and daily misting can help raise the humidity. Environments that are too damp can promote fungal and bacterial overgrowth in the enclosure. Dry environments can lead to poor shedding with retained pieces of skin and chronic dehydration. Because iguanas like to swim, daily soaks in a large tub or pool should be considered. Many iguanas will defecate in the water during one of these baths; use strict hygiene if this occurs in the family bathtub!

Diet
Green iguanas are strict herbivores and in the wild eat a diet of leaves, flowers, and vines. Earlier recommendations included the feeding of a protein source to juveniles in an effort to prevent nutritional bone disease . Recent research suggests that this is not appropriate. Green iguanas can thrive and grow to
maturity without bone problems when fed a diet of carefully selected fibrous plant protein.
Captive iguanas should be fed a diet consisting of 80% vegetables and 20% fruit chopped into small pieces and mixed together. High protein supplements like tofu and dog, cat, or monkey chow can lead to metabolic problems and should not be given LA en to juveniles. Dark leafy greens high in calcium and low in phosphorus should make up the majority of the diet and include collard greens, bok choy, mustard dandelion leaves and flowers, Swiss chard, escarole. spinach, parsley, and watercress. Apples, grapes, melons, papaya, kiwi, and strawberries can be fed in small amounts. Bananas and iceberg lettuce are not recommended. The key to success is a wide variety of food, Juveniles less than 1 year of age can be fed daily, and adults can skip meals 1 days a week. Be careful with commercially prepared diets; not all of these have been properly tested and no one product should be relied on as a sole food. Water bowls large and heavy enough for the iguana to climb into should be provided.
Vitamins and minerals can be added to the diets of iguanas. Care must be taken not to overdose supplements, especially those containing phosphorus and vitamin D;. Use multivitamins sparingly; once or twice weekly is safe. Calcium should be provided as a separate supplement that does not contain vitamin D or phosphorus. It can be given in the form of powdered calcium carbonate, lactate, or gluconate Unfortunately, most store-bought reptile calcium products contain phosphorus and/or vitamin D. Human calcium tablets, Tums (GlaxoSmithKline), or pet bird cuttlebone shavings work well. Sprinkle calcium lightly on food two to three times weekly.

Nutritional Bone Disease
Also known as nutritional secondary hyperparathyroidism or metabolic bone disease, this is the most common diet-related problem of pet iguanas. Metabolic bone disease is a result of insufficient dietary calcium, excessive dietary phosphorus, and lack of vitamin D,. Young, growing lizards on poor diets are most commonly affected. Calcium and phosphorus imbalance results in poor bone mineralization with subsequent resorption of the bones and secondary fibrosis (fibrous osteodvstrophy, or FOD). Soft, flexible mandibles and swelling of the long bones are clinical manifestations of FOD). There may be pathologic fractures and scoliosis or kyphosis can occur . Often, these iguanas have posterior paresis and cannot lift themselves up off the ground. This is a chronic disease but may appear to be acute to some owners.
Treatment consists of client education, diet changes, UV light, calcium, and D, supplements. Parenteral calcium can be used initially (100 mg/kg IM, SQ, or IP) and then switched to oral administration at home. One or two doses of vitamin D^ is recommended (1000 IU/kg IM) at 2-week intervals. Vitamin D^ can be toxic in higher doses. Recovery is very slow but possible in most cases, even severely affected iguanas. There may be permanent bony changes such as scoliosis. Pathologic fractures are best managed with strict cage rest or light splints.

A Word About Salmonella
Because we are dealing with the handling of iguanas in the home environment, veterinarians must remember to discuss salmonellosis with the owners of these pets. Iguanas have been reported as an increasingly frequent cause of salmonellosis, particularly in homes with very voting children. According to the Centers for Disease Control and
Prevention, reptiles accounted for an estimated 2% to 5% of the over million cases in 1993. That is at least 20,000 cases, which is definitely cause for concern. Most of these cases would have been prevented with strict hygienic practices .
One of the greatest problems with Salmonella infections is that a reptile carrying the bacteria may not show any signs of the disease at all. Some iguanas shed Salmonella in their feces, with estimates ranging from 36% to 77% incidence. Other pet reptiles can also be a source of the bacteria. In the 1970s, turtles under 4 inches in length were banned sale by the FDA because many carried Salmonella and less than 4 inches meant kids could put them in their mouths. In the process ot handling reptiles, cleaning their food dishes, or cleaning then cages, fecal material may be transferred to human hands, become oral and result in human infection.
Symptoms of salmonellosis in humans vary widely. There may be mild abdominal pain, nausea or cramps, or more severe signs such diarrhea, vomiting, and fever. Occasionally the symptoms can be very serious, including meningitis, especially in very young children. It is much better to prevent infection in humans than to prevent and control infection in reptiles. Salmonella is difficult to culture, even with repeated fecal tests. It would be safest to just assume that most reptiles have Salmonella and to always practice good hygiene with all reptile species. Handlers and owners of reptiles should be given a handout describing basic guidelines for prevention of this very preventable disease.