Amphibians

Amphibians are a popular group of pets among herpetologists and some aquarists. Popular species include a number of Anura (frogs and toads) and some Urodeles (salamanders and newts).

Consultation and handling

Handle amphibians with damp hands and/or smooth latex gloves to protect the delicate skin and mucous covering.

Large frogs such as horned frogs (Ceratophrys spp.) and African giant frogs (Pyxicephalus adspersus) can inflict a painful bite and are likely to do so. Handle these by gently grasping them around the waist. Large marine toads (Bufo marinus) may eject toxins from their parotid glands if severely stressed. Wild-caught poison-arrow frogs can produce potentially very toxic skin secretions, which are manufactured from prey; captive-bred frogs usually do not produce such toxins, but caution is advised.

Most amphibia have very thin, moist skins, which allow significant absorption of topical medications. This should be borne in mind if using topical preparations designed for mam­malian species, but these can be used advantageously, as therapeutic levels of active medica­tions may be able to be achieved following topical application of injectable drugs (e.g., antibiotics). Drugs absorbed transcutaneously may be transported directly to the kidneys via the lymphatic fluid, so care must be taken with potentially nephrotoxic drugs.

Nursing care

Provide an appropriate environment, including provision of:

1. Optimal temperature (basking lights where appropriate, heat mats etc. to allow thermoregulation). Use of max-min thermometers will assist in monitoring temperature ranges to which incumbent amphibia are exposed.

2. Full-spectrum lighting appears to be relatively unimportant for the majority of amphibia; if in doubt, use a light with a minimal (2%) UV output.

3. Humidity is crucially important. A relative humidity of 80% or higher is generally recommended.

4. Ventilation: Important, but may need to be sacrificed somewhat to maintain high humidity levels

5.

6. Keep individually to minimize intraspecies stress and competition for resources.

Fluid therapy

Most amphibians can absorb fluids directly across the skin, with terrestrial anurans possessing a vascular ventral pelvic skin patch designed for transcutaneous water absorption. Dehydrated amphibians show increased tackiness of the skin mucous covering, tightening of the skin, sunken eyes, and weight loss. Dehydration can also affect cutaneous gaseous exchange, leading to hypercapnia and acidosis.

Oral fluids are of limited use in amphibians. Dehydrated terrestrial amphibians should be placed in a shallow bath of clean, dechlorinated, and well-oxygenated water.

Fluid therapy for amphibians

1. Intracoelomic fluids should be slightly hypotonic:

a. 1 : 2 sodium chloride 0.9%: glucose 5%

b. 1 : 2 Hartmann’s solution : glucose 5%

c. 9 : 1 saline : sterile water (Wright 1995)

2. Do not exceed 25 mL/kg as an initial dose.

Nutritional support

Offer commercially available live food if possible. If anorexic:

1. Place whole prey items into mouth.

2. Consider use of stomach tube; initially use commercially available “critical care” products for reptiles (usually containing amino acids, vitamins, and electrolytes) and graduate to available carnivore products or high-energy formulations available for domestic dogs and cats.

Analgesia

Morphine: Intracoelomic at 10 to 100 mg/kg in frogs. Given at 30 to 100 mg/kg IM, SC, or topically provides analgesia that peaks at 60 to 90 minutes in leopard frogs, Lithobates pipiens (Stevens 2011).

Meloxicam at 0.1 mg/kg IM s.i.d. in American bullfrogs, Rana catesbiana (Minter et al 2011)

Anesthesia

Terrestrial amphibians have several respiratory surfaces, which can complicate the control of anesthesia. These include the lungs, skin, and buccal lining. Aquatic amphibians respire largely through gills, although the skin is also an important respiratory organ, and many possess lungs too.

When inducing terrestrial amphibians in a water bath, always guard against the possibility of drowning. Once anesthetized, large amphibians can be intubated and maintained as for reptiles with isoflurane, but maintenance can be difficult due to alternative respiratory surfaces.

Transcutaneous anesthetic techniques in amphibians

1. Isoflurane at 4% to 5% bubbled into water and administered according to the amphibian’s response, or place animal in damp towels in induction chamber.

2. Mix 3.0 mL of liquid isoflurane + 1.5 mL of water + 3.5 mL KY jelly:

a. Apply this mixture to animal’s dorsum at roughly 0.025 to 0.035 mL^zg body weight depending on species. Use a lower dose for frogs and newts, higher for toads.

b. Once the solution has been applied, place the animal in a small sealed container until induction has occurred (around 5 to 15 minutes). When righting and withdrawal reflexes are lost, wipe the dermis free of anesthetic. Should give 45 to 80 minutes of surgical time.

3. Fish anesthetics can be used, such as MS222 (see Chapter 14).

Parenteral anesthesia for amphibians

Propofol at 10 mg/kg IV in all large species; for salamanders use ventral tail vein; for frogs and toads use abdominal vein or heart or at 25 to 35 mg/kg intracoelomically (tiger salamander).

Skin disorders

The amphibian skin is thin and covered with a layer of mucus, which acts as an antibacterial and antifungal barrier. It is highly porous to medications and toxins; many treatments can be administered topically to achieve systemic effects. Normal flora are -gram-negative, such as Aeromonas spp., Pseudomonas spp., Proteus spp., and Escherichia coli. However, these can also be pathogenic, and so results may require a degree of interpretation.

Hypovitaminosis A may contribute to secondary skin infections (e.g., chytridiomycosis), possibly by reducing cutaneous mucus production (see also “Hypovitaminosis A” in Gastro­intestinal Disorders).

Pruritus

• Trombiculid mites (terrestrial forms)

• Poor water quality, especially high ammonia levels, can cause skin irritation in both adults and tadpoles.

• Environmental tobacco smoke

Erosions and ulceration

• Traumatic wounds (e.g., bites)

• Bacterial (see also “Changes in Pigmentation,” below)

• Iridovirus (ranavirus, including frog virus 3—see Systemic Disorders)

• Mycobacteriosis

• Cutaneous capillariasis: Pseudocapillaroides xenopi (African clawed toads)

• Fungal infections include Batrachochytrium dendrobatidis (chytridiomycosis) and Basidiobolus ranarum

• Microsporidia

• Trombiculids in terrestrial amphibians (erythematous vesicles)

Nodules and nonhealing wounds

• Ichthyophonus hoferi

• Trematodes (Clinostomum attenuatum)

Changes in pigmentation

• Erythema and ulceration (“red leg”)

• Environmental pathogens (Aeromonas spp., Pseudomonas spp.)

• Environmental irritants

• Iridovirus (ranavirus)

• Chlamydophila in Xenopus laevis

• Chromomycosis

• Chytridiomycosis

• Saprolegnia (aquatic amphibians): Cotton wool-like growth on the skin

• Trombiculids in terrestrial amphibians (erythematous vesicles)

• Whitish patches on caecilians (fungal infection, water too hard, poor water quality)

• Environmental toxins (see also Systemic Disorders)

• Chlorhexidine

• Povidone-iodine

• Chlorine

• Quaternary ammonium compounds

• Ammonium

Ectoparasites

• Aquatic adult and larval amphibians

• Oodinium pillularis

• Ciliated protozoa

• Crustaceans

• Argulus (large, disc-shaped crustacean)

• Copepods

• Leeches

• Terrestrial amphibians

• Trombiculids

• Bufolucilia spp. (toadfly—see Respiratory Disorders)

Neoplasia

• Hemangioma

Findings on clinical examination

• Inflammation and ulceration (see “Erosions and Ulceration” and “Changes in Pigmentation,” above). Septicemic infections may be accompanied by systemic signs such as inappetence, lethargy, convulsions, swelling of the body (either with fluid or gas), and obvious eye abnormalities.

• Wasting (often despite an apparently good appetite), ulceration, swellings either at the skin or deeper (mycobacteriosis)

• Graying of the skin (excess mucus production) and gills, respiratory impairment, debilitation, and death (ectoparasites, including Oodinium pillularis)

• Dark, raised nodules in the skin, debilitation and weight loss (chromomycosis—see also Systemic Disorders)

• Skin sloughing, splayed leg (chytridiomycosis)

• Inactivity

• Anorexia

• Damage and deformity to the head, especially the nares, in toads (Bufolucilia)

• Raised mass (granuloma, neoplasia)

Investigations

1.

a. Oodinium: Can be quite large, up to 1.0-mm diameter, oval-shaped with a very dark appearance because of chloroplasts, not usually mobile

b. Pseudocapillaroides xenopi: Eggs and worms visible

c. Copepods

d. Trombiculid mites

2. PCR for chytridiomycosis

3. Radiography

4. Routine hematology and biochemistry

5. Culture and sensitivity

6. Endoscopy

7. Biopsy/necropsy

8. Ultrasonography

9. Water quality testing

Management

1. Fluid therapy—see Nursing Care

2. Wound management

a. Debride and clean by flushing with sterile saline solution.

b. Iodine compounds, chlorhexidine, isopropyl alcohol, and quaternary ammonium compounds are potentially toxic and should be used with care.

c. Wounds (and hemostasis achieved) should be sealed either by suturing or with cyanoacrylate.

TreatmentZspecific therapy

• Trauma—see “Management” above

• Aeromonas and Pseudomonas

• Appropriate antibiosis

• Often secondary to immunocompromise from poor environmental conditions (e.g., inappropriate temperature, poor nutrition)

• Chlamydophila

• Appropriate antibiosis (e.g., doxycycline at 10 to 50 mg/kg PO s.i.d.)

• Mycobacteriosis

• Treatment is rarely effective and so euthanasia should be considered.

• Saprolegnia

• Removing visible hyphae by swabbing the affected area with a 10% povidone-iodine solution s.i.d.

• Salt-water baths (10 to 25 mg sea salt per liter) s.i.d. for 10 to 30 minutes

• Often secondary to poor water quality and high biologic contamination of water

• Basidiobolus ranarum

• Benzalkonium chloride dips, at 0.25-2 mg/L water for 30 minutes every 48 hours for 3 treatments

• Chromomycosis

• No effective treatment. Consider euthanasia.

• Chytridiomycosis

• Larval stages lack keratinized skin so are less susceptible to infection, so heavy mortalities may follow metamorphosis (postmetamorphic death syndrome, PMDS). Can be carried on mouthparts of larvae

• Very virulent; consider euthanasia.

• Some cases respond to itraconazole baths. Create 0.01% itraconazole solution (dilute a 10 mg/mL itraconazole suspension in 0.6% saline solution), and give 5-minute baths in this solution daily for 11 days. Note: Chlorhexidine is potentially toxic to amphibians.

• B. dendrobatidis is susceptible to temperatures above 23° C, but beware that amphibians with chytridiomycosis will have reduced heat tolerance, so use hyperthermia with caution.

• Oodinium and ciliated protozoa

• Try a proprietary Oodinium (velvet) treatment formulated for aquarium fish.

• Metronidazole at 10 to 14 mg/L for up to 24 hours daily for 10 days

• Quinine hydrochloride at 10 to 20 mg/L indefinitely. Some amphibians may be sensitive to this.

• The encysted stage is relatively resistant to chemical attack.

• Antibiotic cover should be considered, as secondary infections are common at the areas where the skin is damaged.

• Eliminate the parasite from a show aquarium by removing all amphibians (and fish), reducing or cutting out the light levels, and raising the temperature to 30 to 32° C for 3 weeks.

• Microsporidia

• Chloramphenicol sodium succinate (5 to 10 mg/kg intracoelomic) plus topical oxytetracycline and polymyxin B s.i.d.

• Pseudocapillaroides xenopi

• Fenbendazole at 50 to 100 mg/kg PO repeat after 2 weeks

• Thiabendazole at 50 to 100 mg/kg PO once only. Repeat after 2 weeks.

• Levamisole (100 to 300 mg/L) bath for up to 24 hours once weekly for up to 12 weeks

• Leeches

• Individual removal

• Copepods

• Hypertonic bath (10 to 25 g NaCl—not table salt) for 5 to 30 minutes

• Treat with lufenuron at 0.088 mg/L as a single dose.

• Argulus (fish louse)

• Individual removal of parasites

• Treat with lufenuron at 0.088 mg/L as a single dose.

• A potassium permanganate bath at 10 ppm (mg/L) for 5 to 60 minutes can be used to rid both individual amphibians and plants of this parasite.

• Trombiculids

• Physical removal of mites with damp cotton bud

• Topical ivermectin: Dilute 1:50 in Hartmann's solution and apply topically to dorsal surface.

• Selamectin topically at 6 mg/kg (D'Agostino et al 2007)

• Bufolucilia (toadfly)

• Physical removal of parasites if possible

• Flush the nares and oropharynx with ivermectin or levamisole.

• Covering antibiosis

Respiratory tract disorders

Amphibians respire through a variety of organs—namely, the lungs, buccopharyngeal lining, skin, and gills (larval amphibia). In terrestrial amphibians dehydration may affect gaseous exchange at the skin, leading to hypercapnia and acidosis.

Bacterial

• Pneumonia

Fungal

• Pneumonia

Protozoal

• Oodinium and other aquatic protozoa (larval amphibian; see Respiratory Disorders in Chapter 15)

Parasitic

• Rhabdias spp.

• Trematodes (wide variety—see Systemic Disorders)

Neoplasia

Other noninfectious problems

• Acute pulmonary emphysema

• Poor water quality, especially larval amphibians. High ammonia and nitrite levels may predispose to gill damage and secondary bacterial and fungal infections.

Findings on clinical examination

• Increased respiratory rate (especially larval amphibians)

• Open-mouthed breathing

• “Wet” or unusual respiratory noises

• Discharge around the glottis or inside the proximal trachea

• Occluded nostrils

• Sudden death

Investigations

1. Microscopy

2. Fecal examination

3. Embryonated eggs or rhabditiform larvae (Rhabdias spp.)

4. Transillumination of very small or transparent amphibian a. May see large adult worms in lungs

5. Radiography

6. Routine hematology and biochemistry

7. Culture and sensitivity

8. Endoscopy

9. Biopsy

10. Ultrasonography

11. Water quality testing

Management

1. For aquatic amphibians, transfer to a shallow container and increase aeration to maximally oxygenate water.

2. For terrestrial amphibians, transfer to a high-oxygen environment. Note: High air flow rates may increase the risk of dehydration from moisture loss across the skin.

TreatmentZspecific therapy

• Pneumonia

• Appropriate antimicrobials

• Oodinium

• Proprietary fish treatments

• Metronidazole at 50 mg/L for up to 24 hours daily for 10 days

• Quinine hydrochloride at 10 to 20 mg/L indefinitely. Some amphibians may be sensitive.

• The encysted stage is relatively resistant to chemical attack.

• Can colonize the intestines of fish and possibly larval amphibians, where again it can be protected from medications

• Antibiotic cover should be considered, because secondary infections are common at the areas where the skin is damaged.

• Eliminate the parasite from a show vivaria/aquaria by removing all amphibians, reducing or cutting out the light levels and raising the temperature to 30 to 32° C for 3 weeks.

• Rhabdias

• Ivermectin

- Dilute 1:50 in Hartmann's solution and apply topically to dorsal surface.

- 10 g/L bath for 1 hour weekly for up to 12 weeks

• Selamectin topically at 6 mg/kg once only (D'Agostino et al 2007)

• Levamisole (100 to 300 mg/L) bath for up to 24 hrs once weekly for up to 12 weeks

• Fenbendazole at 50 to 100 mg/kg PO. Repeat after 2 weeks

• Acute pulmonary emphysema

• Repetitive aspiration of coelomic air until pulmonary lesion seals

• Covering antibiosis

Gastrointestinal tract disorders

Bacterial

• Enteritis (rarely encountered)

Fungal

• Enteritis (rarely encountered)

Protozoal

• Entamoeba ranarum

• Ciliates

Parasitic

• Strongyloides spp.

• A variety of nematode species may be detected.

• Acanthocephalans

• Cestodes (wide variety—see Systemic Disorders)

• Trematodes (wide variety—see Systemic Disorders)

Nutritional

• Short-tongue syndrome of frogs (suspected hypovitaminosis A)

Neoplasia

• Myxoma (especially tree frogs)

Other noninfectious problems

• Gastric impaction (especially large frogs, such as horned frogs, Ceratophrys spp.): May be the result of gastric overload (i.e., offered too large food item)

• Gastric prolapse

• Intestinal foreign body

• Cloacal prolapse (especially tree frogs)

Findings on clinical examination

• Diarrhea, blood in feces, wasting, loss of appetite (Entamoeba)

• Firm swelling from lining of oral cavity; if large, can affect frog's ability to feed (myxoma)

• Inability to catch prey

• Weight loss

• Swollen, often gassy coelom (gastric impaction)

• Anorexia

• Inactivity

• Cloacal prolapse (intestinal parasitism, enteritis, toxins)

Investigations

1. Fecal examination

a. Entamoeba: Multinucleate cysts; nuclear endosomes measure up to nucleus diameter

b. Ciliated protozoa

2. Radiography

3. Routine hematology and biochemistry

4. Culture and sensitivity

5. Endoscopy

6. Biopsy/necropsy

a. Squamous metaplasia of the mucus-secreting glands of the tongue (short-tongue syndrome)

b. Hepatic retinol levels in suspected hypovitaminosis A (Table 13-2)

7. Ultrasonography

8. Water quality testing

Management

• See Nursing Care.

TreatmentZspecific therapy

• Entamoeba ranarum

• Metronidazole at 10 to 14 mg/L bath for 1 hour unless showing signs of distress.

• Ciliated protozoa

• These are usually considered normal gut commensals.

• If high numbers and amphibians showing consistent clinical signs, treat as for Entamoeba

• Strongyloides spp.

• Ivermectin

- Dilute 1:50 in Hartmann's solution and apply topically to dorsal surface.

- 10 g/L bath for 1 hour weekly for up to 12 weeks

• Selamectin topically at 6 mg/kg once only. (D'Agostino et al 2007)

• Levamisole (100 to 300 mg/L) bath for 1 hour once weekly for up to 12 weeks

• Nematodes and acanthocephalans

• As for Strongyloides spp. above

• Fenbendazole 50 to 100 mg/kg PO. Repeat after 2 weeks as necessary.

• Acanthocephalans require intermediate arthropod host so can be self-limiting.

• Myxoma

• Surgical resection

• Radiosurgery

• Likely to recur but grow very slowly

• Short-tongue syndrome

• Supplement with vitamin A. Note: Commercial injectable vitamin A preparations are too concentrated for amphibians.

• 2 lU/g IM every 72 hours or 1 lU/g PO or topically s.i.d.

• May require hand-feeding as prey-capturing adhesive qualities of the tongue are significantly reduced.

• Gastric impaction

• Removal of impaction contents by gastric lavage, endoscopic retrieval, or gastroenterotomy

• Broad-spectrum covering antibiotics

• Gastric prolapse

• Appears as a fleshy structure above the tongue

• Can be a normal activity in some frogs

• Can be pathologic—often linked to starvation or increased intracoleomic pressure

• Gently replace stomach and fill with liquid food to maintain position.

• Often fatal

• Intestinal foreign body

• Laxatives often beneficial due to short GI tract.

• May require enterotomy

• Cloacal prolapse

• Investigate possible underlying etiologies (e.g., endoparasites).

• Surgical replacement often poorly tolerated

• Prognosis is guarded.

Nutritional disorders

• Hypocalcemia (metabolic bone disease—see Musculoskeletal Disorders)

• Hypervitaminosis D₃ accompanied by hypercalcemia (see Systemic Disorders)

• Hypovitaminosis A (see also Gastrointestinal Disorders and Ophthalmic Disorders)

• Obesity (especially horned frogs Ceratophrys spp.)

• Manage by switching to a low-energy diet (e.g., substituting more invertebrate prey for mammalian) plus supplement with vitamin E especially.

• Lipid keratopathy (see Ophthalmic Disorders)

Hepatic disorders

Bacterial

• Aeromonas spp., Pseudomonas spp.

• Mycobacteria

Fungal

Protozoal

• Amebiasis

Parasitic

Neoplasia

• Cholangiocellular carcinoma

Findings on clinical examination

• Ascites (see Systemic Disorders)

• Anasarca

Investigations

1. Radiography

2. Routine hematology and biochemistry

3. Culture and sensitivity

4. Endoscopy

a. Multifocal abscessation (mycobacteriosis)

5. Biopsy/necropsy

6. Ultrasonography

7. Water quality testing

Management

• Milk thistle (Silybum marianum) is hepatoprotectant. Dose at 4 to 15 mg/kg PO b.i.d. or t.i.d.

• Aspirate excess fluid from the coelom if ascitic.

• Furosemide at 2.5 mg/kg IM b.i.d.

• For aquatic and semi-aquatic amphibia attempt to correct osmotic imbalance by keeping in either salt solution (0.55 to 1.0%) or magnesium sulfate solution.

TreatmentZspecific therapy

• Bacterial hepatitis

• Appropriate antibiosis

• Mycobacteriosis

• Potential zoonosis

• Considering euthanasia as treatment is often unrewarding (but see Systemic Disorders in Chapter 15).

• Hepatic amebiasis

• Metronidazole at 100 mg/kg PO every 14 days (Wright 1995)

Cardiovascular and hematologic disorders

Amphibians have a well-developed lymphatic system with a significant exchange rate with the vascular system (up to 10 mL/hr in the frog). Lymph is circulated with a varying number of lymph hearts. Cardiac and/or lymph heart disease and insufficiency is likely to lead to fluid accumulation in the coelom and lymphatics, presenting as an ascites or anasarca-like condition.

Bacterial

• Endocarditis

Fungal

Protozoal

• Trypanosomes

• Haemogregarina spp.

• Hepatozoon spp.

Parasitic

• Microfilaria (see Systemic Disorders)

Dietary

Neoplasia

Other noninfectious problems

• Cardiomyopathy

• Lymph heart insufficiency

Findings on clinical examination

• Edema, ascites (may be gross and present with swollen coelom or confined to one or more limbs)

• Anorexia

• Mortalities

Investigations

1. Radiography

2. Routine hematology and biochemistry

3. Culture and sensitivity

4. Endoscopy

5. Biopsy

6. Ultrasonography

7. Electrocardiogram

8. Water quality testing

Management

1. Fluid accumulation causes a reduction in circulating fluid volume, tissue hypoxia, and lung compression.

2. Aspirate excess fluid from the coelom.

3. Furosemide at 2.5 mg/kg IM b.i.d.

4. For aquatic and semi-aquatic amphibians, attempt to correct osmotic imbalance by keeping in either salt solution (0.55% to 1.0%) or magnesium sulfate solution.

5. Treat any underlying specific causes.

TreatmentZspecific therapy

• Bacterial and fungal disorders

• Appropriate antimicrobials

• Trypanosomes

• Bathe in quinine sulfate (30 mg/L) for 1 hour daily.

• Haemogregarina spp. and Hepatozoon spp.

• Potentiated sulfonamides may relieve symptoms; chloroquine and primaquine regimens as outlined for treating hemoparasites in snakes (see Chapter 11) may be modified.

• May be self-limiting as an invertebrate vector such as mosquito or leech is usually required

Systemic disorders

Viral

• Frog virus 3 (iridovirus; tadpole edema disease—see also Renal and Urinary Disorders)

• Bohle iridovirus (in Australian amphibians)

Bacterial

• Aeromonas spp., Pseudomonas spp.

• Flavobacterium spp.

• Mycobacteriosis, especially M. marinum, M. chelonae, M. ranae, M. xenopi, M. fortuitum, and rarely M. avium complex (M. intracellulare and M. avium avium)

Fungal

• Chromomycosis (see also Skin Disorders), such as Veronaea botryosa (Mayer et al 2000)

• Batrachochytrium dendrobatidis (chytridiomycosis)

• Mucor amphibiorum

Protozoal

• Microsporidia (e.g., Pleistophora, Microsporidium)

Parasitic

• Microfilaria

• Cestodes (wide variety—see Systemic Disorders)

• Trematodes (wide variety—see Systemic Disorders)

Nutritional

• Hypervitaminosis D₃/hypercalcemia (see Nutritional Disorders)

• Hypocalcemia (see Musculoskeletal Disorders)

Neoplasia

• Fibrosarcoma

• Thymoma (Jacobson et al 2004)

• Gonadal neoplasia

Other noninfectious problems

• Acute pulmonary emphysema (see Respiratory Disorders)

• Renal disease

• Cardiovascular disease

• Failure of lymph hearts

• Intestinal disease (gaseous bloating—see Gastrointestinal Disorders)

• Keeping in very soft water (inducing osmotic imbalance)

• Thermal shock (Green et al 2003)

• Environmental toxins

• Chlorhexidine

• Povidone-iodine

• Chlorine toxicity (tadpoles, aquatic amphibians)

• Quaternary ammonium compounds

• Ammonium

• Heavy metal, especially zinc, lead, or copper (see also Neurologic Disorders)

Findings on clinical examination

• Weight loss

• Anorexia (consider brumation)

• Unwilling/unable to move

• Splayed legs, skin sloughing (chytridiomycosis); high mortality following metamorphosis (PMDS)

• Swollen coelom (ascites, anasarca, lymphedema, septicemia, renal disease, acute pulmonary emphysema, hypervitaminosis D₃)

• Septicemic infections may be indicated by signs typical of “red leg” (see Skin Disorders), such as inflammation, ulceration, inappetence, lethargy, convulsions, coelomic swelling, and obvious eye abnormalities.

• Dark, raised nodules in the skin, debilitation, and weight loss (chromomycosis)

• Increased mucus production, erythema, agitation, lethargy, dyspnea, convulsions, paralysis, diarrhea, and death following exposure to chlorhexidine (chlorhexidine toxicity)

• Mortalities

Investigations

1. Radiography

2. Routine hematology and biochemistry

a. Cold-adapted amphibians show an increased RBC count, hemoglobin concentration, heterophilia, lymphopenia, and eosinopenia

3. Culture and sensitivity

4. Endoscopy

a. Microfilaria free in coelomic cavity

5. Biopsy/necropsy

a. Microfilaria in vasculature or encysted in a variety of tissues and organs

b. A wide variety of trematodes and cestodes at different developmental stages may be encountered in a variety of tissues.

6. Ultrasonography

7. Water quality testing

Management

1. Ascites and anasarca

a. Fluid accumulation causes a reduction in circulating fluid volume, tissue hypoxia, and lung compression.

b. Aspirate excess fluid from the coelom.

c. Furosemide at 2.5 mg/kg IM b.i.d.

d. For aquatic and semi-aquatic amphibians, attempt to correct osmotic imbalance by keeping in either salt solution (0.55% to 1.0%) or magnesium sulfate solution.

e. Treat any underlying specific causes.

TreatmentZspecific therapy

• Bacterial infections (Aeromonas, Pseudomonas, Flavobacterium)

• Appropriate antibiosis

• Mycobacteriosis

• Potential zoonosis, so consider euthanasia

• Hypervitaminosis D₃∕hypercalcemia

• Metastatic calcification in many organs (e.g., heart, liver, kidneys) leads to marked ascites.

• Treat symptomatically.

• Investigate possible causes of dietary imbalance.

• Chromomycosis

• Treatment often ineffective

• Some apparent success with fluconazole (Mayer et al 2000)

• Consider euthanasia.

• Chytridiomycosis

• Larval stages lack keratinized skin so are less susceptible to infection, so heavy mortalities may follow metamorphosis (PMDS). Can be carried on mouthparts of larvae

• Very virulent; consider euthanasia.

• Microsporidia

• No effective treatment. Consider:

- Toltrazuril at 30 mg/L bath for 60 minutes repeated every other day for 3 treatments

- Feeding a diet of 0.1% fumagillin

• Microfilaria

• Ivermectin

- Dilute 1:50 in Hartmann's solution and apply topically to dorsal surface.

- 10 g/L bath for 1 hour weekly for up to 12 weeks

• Mortality may occur following treatment.

• Trematodes and cestodes

• Praziquantel at 10 mg/L bath for 3 hours as a single dose or 8 to 24 mg/kg PO or SC daily for 14 days

• Thermal shock

• Usually diagnosed postmortem

• History of sudden temperature change—either to a markedly low or high temperature

• If identified soon enough, return to clean, well-oxygenated water close to previous temperature.

• Supportive treatment

• Environmental toxins

• Bathe amphibian in clean water.

• Supportive therapy (e.g., parenteral fluids)

• Ammonia toxicity

• If due to poor water quality, undertake partial water changes to dilute the ammonia levels.

• Adding zeolite will absorb large quantities of ammonia.

• Longer-term control may include addition of commercially available Nitrosomonas bacterial cultures or equivalent.

• Chlorine toxicity

• Place in aged water.

• Avoid either by use of aged water or commercial dechlorinators as used for aquarium fish.

• Brumation

• A period of inactivity characterized by anorexia, withdrawal from the environment, and immobility and reduced responsiveness.

• Typically can be associated with periods of adverse environmental conditions in the wild (e.g., low temperatures or arid conditions).

• Most likely seen in Chacoan horned frogs (Ceratophrys cranwelli), but other species may present.

• If unsure whether brumating or not, monitor weight: Weight loss is negligible, of the order of 1% to 2% body weight per month, in brumation, whereas it can be very pronounced in the presence of disease.

• Assess exposure to possible brumation triggers such as low temperatures, shortened day lengths, reduced light intensity, and reduced humidity.

Musculoskeletal disorders

Bacterial

• Bacterial osteomyelitis

• Mycobacteriosis

Fungal

• Mycotic osteomyelitis

• Chromomycosis

Protozoal

• Pleistophora (Microsporidia)

Parasitic

• Ribeiroia ondatrae (trematode)

Nutritional

• Metabolic bone disease (especially at time of metamorphosis)

• Fluorosis (Shaw et al 2012)

Neoplasia

Other noninfectious problems

• Gout (articular and periarticular), especially in horned frogs (Ceratophrys spp.)

• Trauma (fractures)

Findings on clinical examination

• Swellings (abscess, gout, fracture)

• Any limb or spinal swelling, fracture, or paralysis should be considered as a possible sign of a pathologic fracture.

• Soft mandibles, foreshortening of the maxillae, swollen midshaft of long bones, kyphosis/scoliosis, weakness, inability to support own body weight (metabolic bone disease)

• Signs consistent with metabolic bone disease but increased cortical density and bone volume; water fluoride levels >0.2 mg/L (fluorosis/osteofluorosis)

• Muscle weakness, inability to support body or hunt/locate food

• Muscle fasciculations and other neurologic signs

• Kyphosis (microsporidial myositis)

• Supernumerary limbs, limb abnormalities (Ribeiroia ondatrae, trematode)

Investigations

1. Radiography

2. Cytology

a. Fine-needle aspirate

b. Gout tophi

3. Routine hematology and biochemistry

4. Culture and sensitivity

5. Endoscopy

6. Biopsy

7. Ultrasonography

TreatmentZspecific therapy

• Gout

• In large amphibians (e.g., horned frogs), may be linked to excessive mammalian prey intake; these are often fed on small mice, whereas their natural diet would be mostly insectivorous.

• Allopurinol at 10 mg/kg PO s.i.d.

• Metabolic bone disease

• Classically a nutritional secondary hyperparathyroidism due to relative lack of calcium

• May be especially pronounced at time of metamorphosis

• Postmetamorphic amphibians may exhibit signs of metabolic bone disease even on a good diet, as a result of a larval calcium deficit. Note: In many adult Urodeles and larval anurans, prolactin is an important hypercalcemic hormone as well as parathormone and 1,25-hydroxy vitamin D₃.

• Daily baths in a high calcium and vitamin D₃ solution (2 to 3 IU/mL)

• Oral or injectable calcium and vitamin D₃ supplementation (may be absorbed transcutaneously, so try applying to skin of back of terrestrial amphibians).

• Supplement with dietary calcium.

• Provide appropriate levels of UVB lighting.

• Some species endemic to hard water areas may have a higher calcium requirement.

• Fluorosis/osteofluorosis

• Exacerbated by hypocalcemia

• Use water filter through chemical media to remove fluorine.

• Increase calcium intake in diet (see “Metabolic Bone Disease” above).

• Provide UVB.

• Abscessation and osteomyelitis, myositis

• Appropriate antibiosis

• Consider amputation if damage is extensive.

• Fracture

• Differentiate between pathological fracture (chromomycosis, neoplasia) and traumatic fracture with radiography.

• For compound fractures, deal with skin lesions, as described under Skin Disorders.

• Extensive trauma to limbs is often best dealt with by amputation. Many Urodeles are able to regenerate lost limbs and tails.

Neurologic disorders

Bacterial

• Septicemia

• CNS granuloma

Fungal

• CNS granuloma

Neoplasia

Other noninfectious problems

• Hypoglycemia (weakness)

• Environmental toxins (see also Systemic Disorders)

• Chlorhexidine

• Povidone-iodine

• Chlorine toxicity (tadpoles, aquatic amphibians)

• Quaternary ammonium compounds

• Ammonium

• Poor water quality

• Cleaning agents

• Heavy metal, especially zinc, lead, or copper (see also Systemic Disorders)

Findings on clinical examination

• Abnormal behavioral signs, especially in larval amphibia (poor water quality)

• Flaccid paralysis

• Disorientation

• Seizures

• Loss of righting reflex

• Mortality

Investigations

1. Radiography

2. Routine hematology and biochemistry

a. Blood glucose levels: In the North American bullfrog (Rana catesbeiana) normal resting glucose levels around 0.4 mmol/L; 1.3 mmol/L when stressed (Crawshaw 1998)

3. Culture and sensitivity

4. Endoscopy

5. Biopsy

6. Ultrasonography

7. Water quality testing

Management

See Nursing Care.

TreatmentZspecific therapy

• Bacterial and fungal diseases

• Appropriate antimicrobials

• Supportive care

• Hypoglycemia

• Oral glucose, but see “Cataracts” under Ophthalmic Disorders

• Environmental toxins (see Systemic Disorders)

• Heavy metal poisoning

• Remove suspected source.

• Remove to unaffected water.

• Oxygenate or aerate water well.

Ophthalmic disorders

The amphibian eye changes during metamorphosis. At hatching, each larva has a duplex cornea with an inner cornea and a second, outer, cornea. At metamorphosis, these fuse into a single, mammalian-like cornea. Pupillary dilation is best achieved under general anesthesia with tricaine methanesulfonate (MS222). Otherwise, intracameral muscle relaxants such as vecuronium, succinylcholine, or D-tubocurarine are required.

Bacterial

• Subspectacular abscess (larval amphibians)

• Keratitis and ulceration

• Uveitis

Fungal

• Keratitis and ulceration

• Uveitis

Protozoal

Parasitic

Nutritional

• Calcium lesions in the cornea

• Cholesterol lesions (lipid keratopathy)

• Hypovitaminosis A

Neoplasia

Other noninfectious problems

• Corneal trauma

• Crickets and other prey insects

• Collision with environmental objects, including transparent barriers

Findings on clinical examination

• Keratitis

• Calcium and cholesterol lesions in the cornea

• Bilateral conjunctival swellings (hypovitaminosis A)

• Fluorescein-positive corneal lesions (corneal ulceration)

• Buphthalmos

• Cataracts

Investigations

1. Ophthalmic examination

2. Radiography

3. Routine hematology and biochemistry

4. Culture and sensitivity

5. Endoscopy

6. Biopsy

7. Ultrasonography

8. Water quality testing, especially for aquatic amphibians

TreatmentZspecific therapy

• Hypovitaminosis A (see Gastrointestinal Disorders)

• Lipid and calcium keratopathies

• If only small part of cornea affected, then monitor

• Partial keratectomy if cornea largely affected plus topical antibiosis

• Lipid keratopathy may be linked with:

- Fat mobilization during oogenesis in females

- Failure to achieve (high) preferred body temperatures

- Diets high in mammalian fat (e.g., rodents)

• Corneal ulcers and secondarily infected corneal traumas

• Under anesthesia, swab for culture and sensitivity, clean, and debride lesion.

• Apply appropriate antibiosis and allow time for absorption.

• Seal with cyanoacrylate (Bicknese & Cranfield 1995).

• Uveitis

• Topical and systemic antibiosis

• Enucleation. Note: Many frogs and toads use the eyes during swallowing, so enucleation may affect feeding ability.

• In cases of buphthalmus, if enucleation is decided against, consider tarsorrhaphy to protect cornea from desiccation.

• Cataracts

• Various etiologies, including nutritional, toxic, and infectious, should be considered.

• Temporary cataracts in poison-arrow frogs linked with provision of 5% dextrose as part of supportive therapy (Williams & Whitaker 1994)

Endocrine disorders

Despite extensive studies into the amphibian endocrine system, especially with regard to metamorphosis, pathology of the endocrine system is little documented. Supplementation with thyroxine is known to trigger metamorphosis in the axolotl; prolonged larval stages may reflect a hypothalamic-pituitary-thyroidal dysfunction.

Neoplasia

• Thymoma (see Systemic Disorders and Renal and Urinary Disorders)

Renal and urinary disorders

Viral

• Frog virus 3 (iridovirus; tadpole edema disease—see also Systemic Disorders)

• Lucke tumor herpesvirus (induces renal adenocarcinoma in leopard frogs, Lithobates pipiens)

Bacterial

• Nephritis

Fungal

• Nephritis

Protozoal

• Entamoeba ranarum (renal amebiasis)

• Myxosporea

Parasitic

• Trematodes (wide variety—see Systemic Disorders)

Neoplasia

• Renal adenocarcinoma (in the leopard frog Lithobates pipiens, likely to be induced by a herpesvirus)

• Thymoma (see also Systemic Disorders)

Other noninfectious problems

• Prolapse of the urinary bladder (differentiate from cloacal or oviductal prolapse)

• Cystic calculi (tree frogs)

Findings on clinical examination

• Ascites (see also Systemic Disorders)

• Ascites in tadpoles (frog virus 3, but see also Systemic Disorders)

• Loss of appetite, anorexia

• Weight loss

• Inactivity

Investigations

1. Urinalysis of terrestrial amphibian

a. Renal casts

b. Inflammatory cells

c. Bacteria

2. Radiography

3. Routine hematology and biochemistry

a. Inverse calcium: phosphorus ratio, hypoproteinemia, and hypoalbuminemia suggest renal disease (or hepatic disease).

b. Nephrotic syndrome (may be linked with thymoma—Jacobson et al 2004)

4. Culture and sensitivity

5. Endoscopy

6. Biopsy/necropsy

a. Hemorrhage into Bowman's capsule, necrosis of glomerular endothelial cells, and tubular necrosis (frog virus 3)

7. Ultrasonography

8. Water quality testing

Management

• See Nursing Care.

TreatmentZspecific therapy

• Ranavirus (frog virus 3)

• No effective treatment. Potentially very infectious, so consider euthanasia.

• Bacterial and fungal nephritis

• Appropriate antimicrobials

• Myxosporea

• No effective treatment available. Try fumagillin as for fish at 1 g/kg food for 10 to 14 days for prevention.

• Renal amebiasis

• Metronidazole at 100 mg/kg PO every 14 days

• Renal neoplasia

• Partial or unilateral nephrectomy

• Lucke tumor herpesvirus

• Lethal in tadpoles, but adults relatively resistant

• Virus production associated with low temperatures (e.g., during hibernation)

• Urinary bladder prolapse

• Clean and aspirate out any urine.

• Gently replace.

• Consider cystopexy following a coeliotomy.

• Percutaneous cystopexy: Achieved by inserting a small probe into the bladder per cloaca as a guide to identify the position of the bladder. Hold the probe against the coelomic wall while transcutaneous sutures are positioned.

Reproductive disorders

Neoplasia

Other noninfectious problems

• Oviductal prolapse

• Ovarian prolapse

Findings on clinical examination

• Ovary or oviduct partially protruding from cloaca, usually following egg-laying

Investigations

1. Radiography

2. Routine hematology and biochemistry

3. Culture and sensitivity

4. Endoscopy

5. Biopsy

6. Ultrasonography

7. Water quality testing

Management

See Nursing Care.

TreatmentZspecific therapy

• Oviductal and ovarian prolapse

• Attempt surgical resection.

• Very guarded prognosis

• Gonadal neoplasia

• Surgical resection