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OCW Zoological Medicine 2008
Amphibian Medicine (2008)
E. Baitchman, DVM
Cummings School of Veterinary Medicine at Tufts University

1. Learning Objectives and Review

1.1. Learning Objectives

This section on Amphibian Medicine will give you a good review of the major husbandry challenges, diseases, and clinical approaches to amphibian health issues. Color coded topics indicate learning objectives that the student should become familiar with. Cases will be presented in class to illustrate these topics. At a minimum, you will be expected to be familiar with the following:

  • Gain an appreciation for the physiological basis of many amphibian husbandry and health issues (skin permeablility, ectothermia, etc.)

  • Become familiar with the major amphibian health issues seen in a captive setting

  • Know what "redleg" is

  • Understand the implications of Chytridiomycosis as an emerging disease of free-ranging amphibians

1.2. Recommended anatomy review

It is recommended that you review your amphibian anatomy notes from
1st Year Comparative Anatomy .

For good overview visit: http://biog-101-104.bio.cornell.edu/Biog101_104/tutorials/frog.html

2. Introduction

2.1. Why learn about Amphibians?

  • Increasingly popular in research/science e.g. pregnancy testing, pain research

  • More and more people keep them as pets

2.2. Basic things to know about amphibians...

  • There are no marine amphibians

  • Amphibians are ectothermic

  • Go through metamorphosis

    • egg-larva-adult

    • sometimes prolonged stages (e.g. axolotl)

  • Skin is very specialized

The knobbly appearance typical of toad skin.
The knobbly appearance typical of toad skin.

Histopathology of amphibian skin.
Histopathology of amphibian skin.

  • Glands

  • No scales

  • Very delicate

  • Respiratory organ

  • 3 chambered heart - 2 atria, 1 ventricle

  • S.C. lymphsacs in frogs and toads - Can be used for phlebotomy

  • Excrete Urea or Ammonia

2.3. Taxonomy

White's tree frog, Litoria caerulea is native to Australia, New Guinea and Indonesia.
White's tree frog, Litoria caerulea is native to Australia, New Guinea and Indonesia.

  • Amphibians have been around for > 300 million years

  • amphibios means double life

    Three Orders of Amphibia

    Gymnophiona

    Limbless amphibians
    Caecilians, Fossorial and aquatic species

    150 species

    Caudata (Urodela)

    Tailed amphibians
    Sirens, Cryptobranchs, Salamanders, and Newts

    400 species

    Anura

    Frogs and Toads

    4000 species

2.4. Biology

2.4.1. Respiration

  • Cutaneous

  • Buccopharyngeal

  • Pulmonic

  • Branchial

2.4.2. Water homeostasis

  • Permeable skin

  • Especially inguinal

  • Water access / high humidity

2.4.3. Calcium homeostasis

  • Hormonal regulation

    • Calcitonin

    • Parathormone

    • Vitamin D

    • Prolactin

  • Ultraviolet radiation requirement is questionable

  • Storage

    • Bone

    • Skin

    • Endolymphatic sacs or paravertebral lime sacs

2.4.4. Toxins

  • Dendrobatidae

    • Alkaloid toxins

      • Batrachotoxin

      • Tetrodotoxin

    • Not toxic in captivity

      • Stored from alkaloids in arthropod prey

2.5. Husbandry

  • Inappropriate husbandry most common cause for morbidity and mortality

  • Natural history - Species identification critical

Chinese Fire Belly Newt (Cynops orientalis)
Chinese Fire Belly Newt (Cynops orientalis)

The poison arrow or poison dart frogs are all from Central and South America. Dendrobates auratus (green and black), Denrobates leucomelas (yellow and black), Denrobates azureus (blue).
The poison arrow or poison dart frogs are all from Central and South America. Dendrobates auratus (green and black), Denrobates leucomelas (yellow and black), Denrobates azureus (blue).

Chinese Fire Bellied Toad (Bombina orientalis).
Chinese Fire Bellied Toad (Bombina orientalis).

Tomato Frog (Dyscophus antongilii).
Tomato Frog (Dyscophus antongilii).

  • Attention to detail - monitor environmental parameters

    • Temperature

    • Humidity

    • Water quality

      • pH

      • NH3, NO2, NO3

      • Hardness (cations)

  • Shelter - exposure is stressful

Typical captive setting for keeping amphibians.
Typical captive setting for keeping amphibians.

2.5.1. Water

  • Tap water

    • Chlorine or flourides

    • Metals (copper)

  • Distilled / Deionized water

    • Hypoosmotic

    • Chronic exposure can be lethal

    • Need to add back solutes - NaHCO3 NaCl CaCL

2.6. Nutrition & Diet

This native green frog, Rana clamitans eyes a worm offered to him in the hospital. Both are kept on moist paper towel to maintain humidity. This frog is native to New England.
This native green frog, Rana clamitans eyes a worm offered to him in the hospital. Both are kept on moist paper towel to maintain humidity. This frog is native to New England.

  • Calcium Phosphorous ratio

    • 1.5:1 or better

    • Gut loading (8% Ca) / dusting

    • Crickets are all phosphorous!

  • Vitamins

  • Size

3. Examination of amphibians

Observation
Physical exam
Fecal sample
Blood sampling
Skin scrape

Transillumination
Radiographs
Ultrasound
Endoscopy

3.1. Physical exam

One should always wear gloves when examining amphibian patients.
One should always wear gloves when examining amphibian patients.

  • Skin

  • Eyes

  • Oral cavity

  • Palpation

  • Transillumination

  • Magnification

Wear moistened gloves !

This image shows the incorrect way to restrain an amphibian species. Gloves should always be worn!
This image shows the incorrect way to restrain an amphibian species. Gloves should always be worn!

No gloves !

Protective slime/mucous secretions on the skin of an amphibian easily comes off on the bare hands of a handler. Gloves should always be worn!
Protective slime/mucous secretions on the skin of an amphibian easily comes off on the bare hands of a handler. Gloves should always be worn!

3.2. Fecal exam

  • Wet mount

    • Protozoal trophozoites - Ciliates Flagellates

  • Floatation

3.3. Cloacal wash

  • Sterile saline flush of the cloaca

3.4. Blood sampling

  • Ventral abdominal vein

  • Small gauge needle

    • Heparinized syringe

Blood sampling in a frog.
Blood sampling in a frog.

3.5. Skin scrape

  • Dull scalpel edge

  • Wet mount

3.6. Imaging

  • Radiographs

  • Ultrasound

  • Endoscopy

A dorso-ventral radiograph of a frog.
A dorso-ventral radiograph of a frog.

Radiography in a frog.
Radiography in a frog.

4. Anesthesia

4.1. Tricaine methanesulfonate (MS-222)

  • Use buffered solution to 7.0 - 7.4 pH

  • 1 g/L (0.1%) induction solution

  • Removal to fresh water once induced

  • Titrate anesthetic plane with 0.5 g/L solution

Administration of MS222 in a horned frog.
Administration of MS222 in a horned frog.

4.2. Isoflurane

  • Different application techniques

    • 0.28% bath (0.35ml isoflurane liquid in 125ml H2O)

    • Topical gel - 3ml isoflurane liquid, 3ml water soluble jelly, 1ml water

    • 5% isoflurane gas bubbled into water bath

    • Intubation

  • Removal to fresh water once induced

  • Titrate anesthetic plane with topical application of induction solution

  • Effectiveness possibly limited to anurans

4.3. Ketamine

  • Wide dose ranges reported (20 - 200 mg/kg)

  • Long inductions and recovery

  • Limited effect on some species

4.4. Opioids and alpha-2 adrenergic agonists

Analgesia without anesthesia

4.5. Monitoring

Utilizing a doppler and a pulse oximeter to monitor anesthesia in a frog during surgery.
Utilizing a doppler and a pulse oximeter to monitor anesthesia in a frog during surgery.

  • Phases of induction

    • Excitement / escape behavior

    • Light anesthesia: loss of righting and corneal reflexes

    • Surgical anesthesia: loss of gular respiration, withdrawal reflex, heart beat remains visible

  • Doppler

  • Pulse oximeter

5. Diseases

5.1. Nutritional Disorders

5.1.1. Metabolic Bone Disease

  • Imbalance of calcium and phosphorous

  • Inadequate vitamin D3

  • Ultraviolet radiation requirements unknown

  • Hypervitaminosis A in large carnivorous species

  • Treatment

    • Injectable calcium and vitamin D if hypocalcemic tetany

    • Long term treatment with calcium and vitamin D3

    • Monitor bone density with radiographs

5.1.2. Corneal lipidosis

  • Corneal arcus

  • Lipid keratobpathy

  • Deposition of cholesterol in cornea

  • Lethal if animal can not see to feed

  • No effective treatment - Diet alteration

5.1.3. Hypovitaminosis A

  • Squamous metaplasia

  • Decreased mucous production

  • "Short tongue" syndrome in Wyoming toads

  • Conjunctival swelling

  • Vitamin A 2 IU/g q 72h until signs resolve

5.1.4. Gastric overload

  • Oversized prey items

  • Overfeeding

5.1.5. Obstruction / foreign bodies

  • Cricket ovipositors

  • Hair

  • Substrate

5.1.6. Spindly leg, Scoliosis, Paralysis

  • Not confirmed nutritional disorders

  • Some suspect vitamin B deficiency

    • Or hypocalcemia?

    • Or parental nutritional state?

    • Or genetics?

    • Or toxicosis?

5.2. Bacterial infections

5.2.1. "Red leg"

  • Bacterial dermatosepticemia

  • Gram negative bacteria

  • Aeromonas hydrophila

Redleg (erythema) and full thickness ulcer in a tree frog.
Redleg (erythema) and full thickness ulcer in a tree frog.

5.2.2. Mycobacteria

  • Granulomatous lesions

  • Integument, musculoskeletal, or internal dissemination

  • Immunosuppression

This animal (Ambystoma tigrinum was diagnosed with a systemic mycobacterial infection. See next file for gross necropsy images.
This animal (Ambystoma tigrinum was diagnosed with a systemic mycobacterial infection. See next file for gross necropsy images.

Mycobacterium was found on necropsy of this Tiger salamander (Ambystoma tigrinum).
Mycobacterium was found on necropsy of this Tiger salamander (Ambystoma tigrinum).

5.2.3. Chlamydiosis

  • Chlamydophila psittaci

  • African clawed frogs (Xenopus spp.)

  • Signs similar to red-leg

  • Treat with doxycycline

African Clawed Frog (Xenopus laevis)
African Clawed Frog (Xenopus laevis)

5.3. Mycotic infections

5.3.1. Watermolds

  • Saprolegnia

  • Opportunistic pathogens

  • Tx: Malachite green or copper sulfate baths

5.3.2. Chromomycosis

  • Pigmented fungi

  • Systemic infection

  • Treatment usually unsuccessful

Fungal dermatitis in a White's Tree Frog (Litoria caerulea) seen grossly, on an impression smear, and grown up in culture media.
Fungal dermatitis in a White's Tree Frog (Litoria caerulea) seen grossly, on an impression smear, and grown up in culture media.

5.3.3. Chytridiomycosis

  • Batrachochytrium dendrobatidis

  • Excessive shedding of skin

  • Digits often affected first

  • Avoidance of ventral surface contact

  • Death without prior clinical signs

  • Tx: Itraconazole bath

  • Infects keratinized epithelial cells

  • Diagnosed by cytology, histopathology, or PCR

5.4. Parasitic infections

  • Protozoa

    • Ciliates and flagellates

    • Commensal organisms

    • Trichomonad flagellates can overgrow in debilitated animals

    • Amoeba

  • Trematodes

  • Nematodes

    • Rhabdias spp.

    • Lungworm

    • Fenbendazole

5.5. Viral infections

  • Iridovirus

    • Ranavirus-Frog virus III

  • Tadpole edema syndrome

    • Edema, SQ hemorrhage

    • Adults non-clinical carriers

  • Mass mortality of Ambystoma spp.

  • Also causing morbidity and mortality in reptiles

    • Stomatitis death in Terrapene carolina

5.6. Toxicosis

  • Chlorine

    • Tap water

    • Allow chlorine to evaporate

  • Household bleach - Thoroughly rinse

  • Paper towels - Use unbleached paper

  • Organophosphates

    • Insecticides

    • Acetylcholinesterase inhibitors

    • Tetany

5.6.1. Metals

  • Tap water - Copper pipes

  • Enclosures - Metal screen tops

5.6.2. Ammonia

  • "New tank syndrome"

  • NH3 more toxic than NH4+

    • Higher pH promotes unionized form

  • Levels should be undetectable

  • Escape behavior, avoiding contact

5.7. Edema syndrome

  • Hydrocelom, hydrops

  • Common presentation

  • Many possible etiologies

    • Dermatosepticemia

    • Osmotic imbalance

    • Renal failure

    • Reproductive

    • Lymph heart dysfunction - Hypocalcemia?

6. Therapeutics

6.1. Stabilization

  • Fluid therapy most important

  • Osmotic balance (200 - 250 mOsm)

  • Amphibian Ringer's Solution

    • NaCl

    • KCl

    • CaCl2

    • NaHCO3

  • May use hypertonic solution if edema syndrome

6.2. Antibiotics

  • Often empirical treatment

    • Gram negative spectrum

    • Enrofloxacin 5-10 mg.kg PO, TO – may need to dilute with 0.9% NaCl

    • Bath solution

6.3. Moribund presentation

  • "Shotgun" treatment

    • Fluids, osmotic stabilization

    • Enrofloxacin

    • Calcium gluconate

    • Vitamin B complex

    • +/- Dexamethasone SP

  • Cool temperatures

  • +/- metronidazole or itraconazole

  • Work up once stabilized

6.4. Nutritional support

  • Assist-feeding crushed prey items

  • Tube feeding

  • Carnivore metabolic requirements

    • CliniCare Feline Liquid®

7. Conservation

Global Amphibian Decline

  • One-third of the world's species are threatened

  • Greater than 40% of species are declining

  • Habitat loss

  • Environmental contaminants

7.1. Chytridiomycosis

  • Global distribution

  • Believed spread by Xenopus trade

  • High mortality, up to 90% of population

  • Skin peptides give innate defense in some species

7.2. Crisis in Panama - El Valle Amphibian Conservation Center

  • Chytrid spreading

  • Rescue and triage

  • Itraconazole baths 10 min/day x 10 days

  • Establishment of survival assurance populations

White's Tree Frog (Litoria caerulea)
White's Tree Frog (Litoria caerulea)

8. References and Resources

8.1. Professional Organizations

Association of Reptile and Amphibian Veterinarians http://www.arav.org

8.2. Websites

North American Reporting Center for Amphibian Malformations [URL | http://frogweb.nbii.gov/

Society for the Study of Amphibians and Reptiles http://www.ssarherps.org/

Frog Morphology & Physiology Tutorials, Cornell University's introductory biology sequence, BioG 101-104 course online
http://biog-101-104.bio.cornell.edu/Biog101_104/tutorials/frog.html

8.3. Texts and Articles

Cloudsley-Thompson, Jl. The diversity of amphibians and reptiles . Springer Verlag, 1999.

Daszak, Peter, Lee Berger, Andrew A. Cunningham, Alex D. Hyatt, D. Earl Green, and Rick Speare. Emerging Infectious Diseases and Amphibian Population Declines. Emerging Infectious Diseases , v.5 (6), 1999.

Davies, Robert and Valerie. The Reptile & Amphibian Problem Solver . Tetra Press, 1997.

DeGraaf, R.U.M. and Audis, D.U.D. Amphibians and reptiles of New England . University of Masssachusetts Press, 1983.

Duellman, W.E. and L. Trueb. Biology of amphibians . Johns Hopkins University Press, 1994.

Feder, M.E. and W.W. Burggren. Environmental physiology of the amphibians . University of Chicago Press, 1992.

Fowler, Murray E. and Miller, R. Eric. Zoo and Wild Animal Medicine , 5th ed. Saunders, 2003. Chapters: 2-4.

Fridell, R. Amphibians in danger: a worldwide warning . Franklin Watts Publications, 1999.

Hoff, G.L. Diseases of reptiles and amphibians . Plenum Press, 1984.

Lafortune, Maud, Mitchell, Mark A. and Julie A. Smith. Evaluation of medetomidine, clove oil and propofol for anesthesia of leopard frogs, Rana pipiens. Journal of Herpetological Medicine and Surgery , 11 (4), 2001: 13-18.

Machin, Karen L. Amphibian pain and analgesia. Journal of Zoo and Wildlife Medicine , 30 (1), 1999, pp. 2-10.

Mattison, Chris. Keeping and Breeding Amphibians . Blandford, 1993.

Raphael, B. Amphibians. In: Quesenberry, K.E. and E.V. Hillyer. Vet. Clin. N. Amer . 23(6), 1993: 1271-1287.

Royal, Lillian W., Michael S. Grafinger, B. Duncan X, Lascelles, Gregory A., Lewbart, Larry S. Christian. Internal fixation of a femur fracture in an American bullfrog. JAVMA . April 15, 2007. Vol. 230, No. 8, pp. 1201-1204.

Staniszewski, Marc. Amphibians in Captivity . TFH Publications. 1995.

Stetter, M. Noninfectious medical disorders of amphibians. Seminars in Avian & Exotic Pet Medicine . 4(1), 1995 : 49-55.

Wright, Kevin M., Brent R. Whitaker. Amphibian Medicine and Captive Husbandry , Krieger Publishing Company; 2001.