Green tree frog
Amphibian vitamin A deficiency, or hypovitaminosis A, refers to low levels of vitamin A (retinol) in the liver. Low levels of it lead to changes in some types of cells (squamous and mucus-secreting epithelial cells) of the tongue, bladder, kidney, reproductive organs, and the conjunctiva around the eyes.
Signs and Risk Factors
An amphibian with vitamin A deficiency may have these cellular changes in one or, more commonly, multiple organs. If these changes affect the tongue, the condition is known as short-tongue syndrome. The tongue’s mucus-secreting glands cannot produce the viscous coating that adheres to prey so the amphibian has difficulty eating; an anuran may be unable to draw prey into its mouth even though the tongue hits the prey.
When changes occur to the reproductive system, the amphibians will experience low fertility rates, and produce low numbers of eggs, and tadpoles will often die early in life or fail to be able to complete metamorphosis.
Changes to kidney cells can result in impaired kidney function, which often causes fluid retention. In these cases, you can see a fluid-filled stomach, like a pot belly, or large amounts retained under the skin (edema). Changes to bladder cells can result in retained urine and a ruptured bladder or bladder stones.
When the eyes and the conjunctiva are affected, the amphibian will have swelling and bulging of the skin around the eyes; commonly, white, raised bumps will be seen surrounding the eyes. Amphibians with hypovitaminosis A are more susceptible to disease due to the cellular changes in multiple organs and overall immune suppression.
The risk factors for developing vitamin A deficiency include:
- Diets with absolute low levels of vitamin A.
- Diets with high levels of vitamin D and vitamin E.
- Aged or inappropriately stored vitamin products (e.g., high heat or humidity).
Young, rapidly growing juvenile amphibians and those that are going through (tadpoles) or have just completed metamorphosis. Metamorphs, which are froglets that still have legs and a tail, are most commonly affected, but it may occur at any age. Vitamin A deficiency has been seen in frogs, toads, and salamanders.
Your veterinarian will take a complete history including husbandry questions, especially concerning diet, temperature, and lighting details as well as a complete physical examination.
Examination of the tongue may suggest short-tongue syndrome by decreased mucus production and an opaque appearance, but without a normal animal for comparison, this is often difficult to interpret. However, a presumptive diagnosis of hypovitaminosis A may be based on the history of an inability to catch and eat prey.
White, semicircular swollen areas may be noticed in the lower eyelid, beneath or surrounding one or both eyes (i.e., conjunctival swelling), and nonspecific signs of low vitamin A, such as weight loss and skin discoloration may be noted.
A history of using supplements that claim to provide vitamin A through beta-carotene (precursors of vitamin A) is often associated with hypovitaminosis A because many or most amphibians cannot convert beta-carotene to usable vitamin A.
Your veterinarian may run some diagnostic tests to look for vitamin A deficiency. Tongue swabs may reveal increased numbers of keratinized squamous epithelia suggestive of the disorder. A fine needle aspirate of the swellings around the eyes may show large numbers of keratinized squamous epithelia.
For amphibians that die or are euthanized, your veterinarian may want to submit the entire amphibian for histopathologic (microscopic) examination. A diagnosis this way for hypovitaminosis A will show squamous metaplasia of the tongue, bladder, kidney, reproductive organs, and skin. In addition, your veterinarian may want to submit the whole liver of the euthanized amphibian to test the levels of vitamin A in the liver. Low levels are supportive of hypovitaminosis A.
This condition is extremely common in captive amphibians. Owing to its prevalence, any ill amphibian should receive vitamin A supplementation as part of the initial treatment.
The main goal of treatment is to restore vitamin A levels to the point that cellular changes causing disease are reversed. In addition, any infections occurring due to immune dysfunction or organ dysfunction from the vitamin A deficiency will be treated by your veterinarian.
Once your veterinarian diagnoses a vitamin A deficiency, treatment will start with either a pill or a topical supplementation of pre-formed vitamin A. Both fat-soluble and water-soluble forms of pre-formed vitamin A have been used with equal effectiveness.
As soon as clinical signs resolve, your reptile will switch to a maintenance stage using vitamin supplementation that contains pre-formed vitamin A and not beta-carotene for the reasons mentioned above. This means dusting (putting the supplement on the prey item) prey items with a balanced multivitamin supplement at least once weekly, more often (two to three times per week) with growing or reproductively active adult amphibians. Some amphibians develop the disease despite being fed items dusted with supplements rich in vitamin A, likely because of inappropriate storage of the product with concomitant degradation of the vitamins; your veterinarian will discuss the proper methods of vitamin storage so that they maintain their effectiveness.
Too Much Vitamin A?
Provide vitamin A supplementation according to your veterinarian's directions. Too much vitamin A will interfere with the absorption and utilization of vitamins D, E, and K.
Signs of too much vitamin A in the diet include ulcers of the eye, rough-thickened skin, long bone deformities, and signs of metabolic bone disease (see metabolic bone disease). If these signs are noticed, stop the vitamin supplementation and bring your amphibian to your veterinarian.
Prevention and Prognosis
Provide proper husbandry of and appropriate supplementation with a multivitamin containing pre-formed vitamin A; avoid the use of supplements that contain beta-carotene. Remember that more is not better and too much vitamin A can cause as many problems as too little.
The prognosis for uncomplicated (no current infections) vitamin A deficiency is guarded to fair; most amphibians receiving treatment will improve within one to two weeks. If there are other infections or severe organ dysfunction the prognosis worsens; so, the earlier the amphibian is brought to the veterinarian and gets treatment the better chance for a cure.