Amphibians

Chapter 10 Amphibians

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

Table 10.1 Popular species of amphibians: Key facts

Species	Notes	Common disorders
Horned frogs (Ceratophrys spp)	From South America, these sit-and-wait predatory frogs grow large and have a strong bite	Aeromonas infections, gout, corneal lipidosis
Poison-arrow frogs (Dendrobates spp)	South American. Skin toxins are based on plant alkaloids ingested by native prey insects. Captive bred and long-term captives usually safe to handle with appropriate precautions	Bacterial and fungal infections
White’s tree frogs Littoria caerulea	A large Australian tree frog requiring high temperatures (26–32°C daytime; 20–24°C nighttime) and a comparatively low humidity (50–60%)	Bacterial and fungal infections
African clawed toad Xenopus laevis (in both wild and albino forms)	Totally aquatic. Extremely popular	Bacterial and fungal infections. Poor water quality
Axolotl Ambystoma mexicanum	A neotenous salamander originating from Mexico. Keep cool (15–20°C)	Poor water quality, ingestion of foreign bodies, bite injuries from other axolotls
Caecilians, such as Typhlonectes compressicauda	These aquatic and moist subterranean worm-like amphibia are occasionally available in aquarium outlets	Fungal skin infections, poor water quality

Consultation and handling

Handle amphibians with damp hands and/or smooth latex gloves to protect the delicate skin and mucous covering. Amphibia can be very unpredictable and are excellent at leaping from the unsuspecting grasp of the veterinarian, therefore beware of potentially traumatic falls to the floor. Wrapping them in very damp, thin paper towels enables some control; areas of interest are accessed by gently tearing through the paper.

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.

Nursing care

Provide 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 Easily cleaned accommodation; use paper substrate and disposable/sterilizable hides and other vivarium furniture

6 Keep individually to minimize intra-specific stress and competition for resources.

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 high-energy formulations available for domestic dogs and cats.

Analgesia

Morphine. Intracoelomic at 10–100 mg/kg in frogs.

Anaesthesia

Terrestrial amphibians have several respiratory surfaces, which can complicate the control of anaesthesia. These include the lungs, skin and buccal lining. Aquatic amphibia respire largely through gills.

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

Parenteral anaesthesia for amphibians

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

Skin disorders

The amphibian skin is thin and covered with a layer of mucous, 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 G −ve, such as Aeromonas spp, Pseudomonas spp, Proteus spp and E. 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 mucous 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.

Nodules and non-healing wounds

• Trematodes (Clinostomum attenuatum).

Neoplasia

• Haemangioma.

Findings on clinical examination

• Inflammation and ulceration (see ‘Erosions and ulceration’ and ‘Changes in pigmentation’, above). Septicaemic 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).

• Greying of the skin (excess mucous production) over the skin 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)

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

• Raised mass (granuloma, neoplasia).

Treatment/specific therapy

• Trauma – see ‘Wound 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 10–50 mg/kg p.o. 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 (10–25 mg sea salt per litre) s.i.d. for 10–30 min

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

• Basidiobolus ranarum

• Benkalkonium chloride dips, at 2 mg/100 mL water for 30 min every 48 h for 3 treatments

• Chromomycosis

• No effective treatment. Consider euthanasia

• Chytridiomycosis

• Larval stages lack keratinized skin so less susceptible to infection, so heavy mortalities may follow metamorphosis (post metamorphic 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) and undertake 5 min baths in this solution daily for 11 days

Note that chlorhexidine is potentially toxic to amphibia

• Microsporidia

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

• Pseudocapillaroides xenopi

• Fenbendazole at 50–100 mg/kg p.o.

• Thiabendazole at 50–100 mg/kg p.o.

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

• Individual removal

• Hypertonic bath (10–25 g NaCl (not table salt)) for 5–30 min

• 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 p.p.m. (mg/L) for 5–60 min can be used to rid both individual amphibia and plants of this parasite

• Trombiculids

• Physical removal of mites with damp cotton-bud

• Topical ivermectin: Dilute 1:50 in Hartman’s solution and apply topically to dorsal surface

• 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 amphibia dehydration may affect gaseous exchange at the skin leading to hypercapnia and acidosis.

Management

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

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

Treatment/specific therapy

• Appropriate antimicrobials

• Proprietary fish treatments

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

• Quinine hydrochloride at 10–20 mg/L indefinitely. Some amphibia may be sensitive

• The encysted stage is relatively resistant to chemical attack

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

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

• Eliminate the parasite from a show vivaria/aquaria by removing all amphibia, reducing or cutting out the light levels and raising the temperature to 30–32^oC for 3 weeks

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