Vitamin A is an essential nutrient, necessary for vision, immunity, red blood cell production, and the health of epithelial cells such as the skin, lung, and intestinal lining. It is primarily stored in the liver and in adipose tissue. (Donoghue and Langenberg, 1996; Nutrition.org, 2005; Linus Pauling Institute, [n/d]) Deficiency in reptiles is characterized by blepharoedema (not necessarily bilateral), lethargy, anorexia, cachexia, and nasal or ocular discharge. (Boyer, 1996a; Donoghue and Langenberg, 1996; Mader, 2001) Like other fat-soluble vitamins, vitamin A has been shown to have toxic effects if overdosed.

Source:
Iatrogenic toxicity in captive reptiles and amphibians occurs mainly in chelonians because they are well-known for their tendency to develop hypovitaminosis A due to inadequate diets. (Boyer, 1996a and 1996b; Kaplan, 2002) When a chelonian is presented with blepharitis and ocular or nasal discharge, it has been many veterinarians' misassumption that it is caused by hypovitaminosis A. Without proper investigation, parenteral or oral vitamin A supplementation is administered, and hypervitaminosis may occur. (Boyer, 1996a; Frye, 1991; Kaplan, 2002; Tabaka, 2003) Additionally, suggested doses of vitamin A vary in veterinary literature, and most commercially prepared forms are designed for large animals, so dosage errors occur, even when the diagnosis is correct. (Boyer, 1996a; Merck and Co., Inc., 2003)

Clinical Signs:
Reptiles afflicted with hypervitaminosis A display depression, anorexia, vomiting, blepharitis/blepharoedema, conjunctivitis, bone lesions, localized erythema, hepatomegaly, xeroderma and skin sloughing. Secondary infections are also common due to an increase in susceptibility to infection and because the dermis is exposed without protection. (Donoghue and Langenberg, 1996; Boyer, 1996a and 1996b; Mader, 2001; Rossi, 1996)

Pathophysiology:
The most obvious symptom of vitamin A toxicity in chelonians is the gradual sloughing of the skin. Vitamin A is necessary for the health and maintenance of epithelial cells, however it seems that an excess irritates them. Localized xeroderma and erythema occur, followed by the epidermis detaching from the dermis. Blisters form and further separate the two layers, and then the epidermis sloughs off to expose the dermis, and eventually the underlying muscle. (Frye, 1991) Dehydration and secondary infections follow because of the exposed tissue. (Boyer, 1996a; Frye, 1991) Blepharitis and conjunctivitis seem to be related due to vitamin A's involvement in maintenance of epithelial cells. (Case et al, 2000)

Vitamin A also promotes the proper function of osteoblasts and osteoclasts in bone maintenance. It has been suggested that an excess of vitamin A provokes excessive osteoclastic activity, which results in bone lesions. (Case et al, 2000)

It also seems that hypervitaminosis A-induced hepatomegaly is linked to the fact that most vitamin A in the body is stored in the liver. (Case et al, 2000; Linus Pauling Institute, [n/d])

Treatment:
Cessation of supplemental vitamin A is absolutely necessary, and symptoms are to be treated accordingly. (Boyer, 1996a and 1996b; Donoghue and Langenberg, 1996; Frye, 1991; Merck and Co., Inc., 2003) Supportive care for generalized epidermal sloughing includes a topical ointment to prevent secondary bacterial infections, either bacitracin-neomycin-polymixin (Boyer, 1996a) or silver sulfadiazine (Tabaka, 2003) on the exposed dermis. Systemic antibiotics have also been suggested. (Tabaka, 2003) Shallow warm water baths (24-27°C) for several hours a day and parenteral Lactated Ringer's solution administered at 20 mL/kg epicoelemically every twenty-four hours are suggested to prevent dehydration. Recovery is expected to take between four to six months. (Boyer, 1996a)

Prevention
Supplemental or therapeutic vitamin A should not be administered unless both dietary history and clinical signs suggest a deficiency. (Boyer, 1996a; Merck and Co., Inc., 2003) Careful dosage is essential, and parenteral vitamin A should only be used in severe cases, once every two weeks at no more than 200 IU/kg for no more than two injections (Merck and Co., Inc., 2003) Oral vitamin A is safer and recommended (Boyer, 1996a; Merck and Co., Inc., 2003), in a commercial preparation or through cod liver oil, given with the animal's regular diet as a couple of drops a few times a week (Merck and Co., Inc., 2003). Ultimately, providing a well-balanced, suitable diet with careful usage of vitamin and mineral supplements is the best way to prevent nutritionally-derived illnesses. (Boyer, 1996a and 1996b; Donoghue and Langenberg, 1996; Frye, 1991; Mader, 2001; Rossi, 1996)

References

Boyer, T.H. 1996a. "Hypovitaminosis A and Hypervitaminosis A" in Mader, D.M. (ed): Reptile Medicine and Surgery. W.B. Saunders Co., Philadelphia, PA. 382-385.

Boyer, T.H. 1996b. "Turtles, Tortoises, and Terrapins" in Mader, D.M. (ed): Reptile Medicine and Surgery. W.B. Saunders Co., Philadelphia, PA. 61-78.

Case, L.P., D.P. Carey, D.A. Hirakawa and L. Daristotle. 2000. Canine and Feline Nutrition. Mosby, Inc., St. Louis, MS.

Donoghue, S., and J. Langenberg. 1996. "Nutrition" in Mader, D.M. (ed): Reptile Medicine and Surgery. W.B. Saunders Co., Philadelphia, PA. 148-174.

Erdman, J. and H.C. Furr. 2005. "Vitamin A - Nutrient Information." Nutrition.org. <http://www.nutrition.org/nutinfo/content/via.shtml> (April 6, 2005).

Frye, F. L. 1991. Reptile Care: An Atlas of Diseases and Treatments, Volume 1. T.F.H. Publications, Inc., New Jersey.

Kaplan, M. 2002. "Bulging, Drooping, Distended Eyes in Reptiles." Anapsid.org. <http://www.anapsid.org/eyebulge.html> (April 6, 2005).

Linus Pauling Institute's Micronutrient Information Centre, The. (No date) "Vitamin A." Oregon State University. <http://lpi.oregonstate.edu/infocenter/vitamins/vitaminA/> (April 6, 2005).

Mader, D. 2001. "Veterinarian Q&A: Vitamin A Myths." REPTILES. 9 [11] (November 2001): 82-83.

Merck and Co., Inc. 2003. "Reptiles: Nutrient Requirements." The Merck Veterinary Manual. <http://www.merckvetmanual.com/mvm/index.jsp?cfile=htm/bc/171207.htm> (April 6, 2005).

Rossi, J.V. 1996. "Dermatology" in Mader, D.M. (ed): Reptile Medicine and Surgery. W.B. Saunders Co., Philadelphia, PA. 104-117.

Tabaka, C. 2003. "Hypervitaminosis A in an Indotestudo elongata." World Chelonian Trust. <http://www.chelonia.org/Articles/hypervitaminosisA.htm> (April 6, 2005)