Assessing the Sick Frog or Toad

Introduction

Frogs and toads belong to order Anura of class Amphibia. Frogs and toads are widely used in labs as research or zoological specimens and their popularity as pets is also growing (Fig 1, Table 1).

African bullfrog

Figure 1. The African bullfrog (Pyxicephalus adspersus) is one of many anurans commonly seen in the pet trade. Click to enlarge.

Table 1. Anurans commonly seen in the pet trade
Common NameScientific name
African bullfrogPyxicephalus adspersus
African clawed frogXenopus laevis
BullfrogRana catesbeina
Colorado river toadBufo alvarius
Fire-bellied toadsBombina sp.
Green tree frogHyla cinerea
Leopard frogRana pipiens
Marine (cane) toadBufo marinus
Ornate horned frogCeratophyrs ornata
Poison dart frogDendrobates sp.
White’s tree frogPelodryas caerulea

Whenever possible, the client should present the pet in its normal enclosure. If the home cage is too large to easily carry, plastic containers, garbage cans, deli cups or cloth bags can be used to transport anurans.

 

Taking a history

A detailed history should include husbandry-related information:

Housing

    • What is the substrate material?Needs will vary with the species, however enclosures are frequently lined with moss, soil, peat moss, orchid bark or moistened paper towels. Substrate material is particularly important in toads, since inappropriate material is commonly ingested creating gastrointestinal foreign bodies in these species.
    • Is visual security available?Cage furniture or plant material should provide areas for the frog or toad to hide. Lack of visual security can increase stress while decreasing appetite, leading to a host of potential problems.
    • What is used to clean the cage, and how often is the cage cleaned?Water dishes should be cleaned daily.The frequency with which the entire setup is broken down and disinfected will vary with its size and the species involved. For instance, an enclosure housing small dart frogs may need to be reconstructed biannually, while larger (messier) bullfrogs require biweekly partial water changes. Dilute bleach, rinsed thoroughly, may be used to disinfect the enclosure.
    • What is the temperature gradient?When compared to reptiles, most amphibians are tolerant of cooler temperatures. Temperature gradients are frequently maintained between 72-80°F (22-27°C) during the day. Radiant heat sources should not be used, as they tend to dry amphibian environments.
    • What is cage humidity?Relative humidity should exceed 70% to 80% in most species.
    • How is water provided (Table 2) and what proportion of the cage is dedicated to a water source?Arboreal species do not require standing water, however all terrestrial anurans should have access to a large, shallow water dish, a shallow pool, or a bog-like area. Semi-aquatic species require larger pools that cover 40%-60% of cage space.
      Table 2. Potential amphibian water sources

      • Aged water: Chlorinated water is allowed to sit in an open container for 24-48 hours so that chlorine levels can dissipate.

      • Bottled spring water

      • Filtered tap water: Water should be run through a sediment and activated charcoal filter

      The enclosures of arboreal, terrestrial and semi-aquatic species should also be lightly misted on a regular basis. Between misting, the substrate should remain damp, but not water logged.Aquatic anurans require systems utilizing a water pump, similar to those for freshwater fish. Water quality should generally reflect a neutral pH with minimal salts (<2 ppt). Ammonia, other nitrogen compounds and chlorine should all be absent.

  • Is an ultraviolet light source provided?Very little is known about the amount of ultraviolet (UVB) light needed by amphibians. Exposure to intense UVB rays has been associated with a number of problems including corneal and skin lesions, however the use of low-intensity UVB light has also been anecdotally correlated with improved health and increased activity, particularly in diurnal species. Therefore amphibian veterinarians recommend a low intensity 2.0 UVB light. Plant cover should also be provided to vary exposure to light intensity.

Diet

Depending on the species involved, the amphibian may eat insects, small fish, and/or earthworms. All of these food items can be readily purchased from local bait shops or pet stores or mail-ordered.

Ensure that the owner is providing vitamin and mineral supplementation by gut loading and dusting insect prey.

 

Other

Also question the owner about any recent acquisitions as well as standard quarantine practices. It is important to consider population or “herd” health aspects of care.

Also ask if the owner has administered any over-the-counter medications.

 

Diseases commonly affecting the anuran

There are a host of potential problems that may be seen in the frog or toad patient—some are common (Table 3), some are not.

Table 3. Common disease conditions reported in anurans

  • Nutritional secondary hyperparathyroidism (metabolic bone disease)

  • Foreign body ingestion in toads

  • Obesity and subsequent corneal lipidosis (rodent-based diet)

  • Uveitis, panophthalmitis may be seen with infectious disease

  • Trauma, rostral abrasions (horned frogs, etc.)

Probably the most unique feature of amphibian pathology is the importance of skin disease. Although adult anurans have well-developed sac-like lungs, all amphibians breathe, to some degree, by cutaneous respiration. Evidence of dermatitis, skin erythema, open wounds or even abrasions are clinically significant in amphibians and in fact may often prove fatal.

 

Examination of the frog or toad

Amphibian skin is very sensitive, and relatively thin and delicate. Handle anurans as little as possible and avoid an examination room that is too warm or dry.

 

Visual examination

The color of your anuran patient will vary with the species. Some amphibians are brilliantly hued, while other species have drab colors that blend with their muddy environment. Amphibian coloration arises from specialized pigment-containing cells or chromatophores. Many species are capable of slowly changing their skin color by concentrating or dispersing various pigments within the chromatophores.

Coax the frog into a small, fully transparent container to perform a visual examination. Look as carefully, completely and closely as possible since the physical exam must be brief:

  • As a rule, amphibians appear relatively quiet when compared to reptile patients.
  • The normal anuran should demonstrate carpal lift, resting with its head up and the legs flexed beside its body (Fig 2).
Normal frog in seated position

Figure 2. The normal frog or toad sits with its head elevated and the legs flexed beside its body. Click to enlarge.

  • Respiration can be observed as rapid movement within the intermandibular (gular) space.
  • The apex beat of the heart is found caudal to the xiphoid process. The “generic” anuran has a heart rate of approximately 25-30 beats per minute at 70°F (21°C).
  • The patient should appear well fleshed with little evidence of the underlying skeleton.
  • The eyes should be wide open.
  • Permeability to water paired with the presence of many mucous glands means that amphibian skin is normally smooth and moist. The exception to this rule of thumb is toads, which have prominent ridges or mounds.
  • A transparent container is particularly useful for checking the bottoms of the feet.

 

A variety of abnormalities can be observed in the sick anuran.

  • Accumulation of lymph sac fluid can appear as subcutaneous edema.
  • The dehydrated patient will exhibit tightening of skin over the skeleton.
  • Hypocalcemia may manifest as paresis, paralysis, muscle fasciculations or even seizures.
  • Abnormal movement is observed with metabolic bone disease.
  • Coelomic distension can be seen with bloat or hydrocoelom.
  • Prolapse of the cloaca, rectum or bladder is also not an uncommon finding

Manual restraint

To properly restrain an amphibian, moisten clean hands or powder-free gloves. Then grasp the patient using a firm, steady grip to prevent escape. Be sure to keep a spray bottle filled with fresh, chemical-free water handy to keep your patient moist. Be forewarned that some species like the ornate horned frog are capable of inflicting a forceful bite. Although there are no teeth, there are boney outgrowths of the jawbone called “vomerine teeth”. The critically ill or injured amphibian responds particularly poorly to stimuli and typically shows little resistance to handling.

Anurans often release a large amount of urine when first restrained so be prepared to catch a sample for testing.

 

Physical examination

Gather all equipment that may be needed beforehand (Table 4).

Table 4. Equipment for the anuran physical examination

  • Magnification (i.e. head loupe)

  • Bright light source (i.e. transilluminator)

  • Mouth speculum (i.e. business card or index card, plastic credit card, developed radiographic film, flat metal spatula, rubber spatula, rubber-coated baby spoon)

  • Ultrasound Doppler or ultrasound probe to measure heart rate (a stethoscope may be used in large anurans)

  • Gram scale

Be quick and efficient, systematically going from head to toe.

  1. Gently palpate the skin. The skin is normally thin, smooth, and moist except in toads and some species of frog. Toads have prominent ridges or mounds. Some arboreal species produce a waxy secretion that coats the skin and leaves it thickened. The dehydrated anuran may feel tacky due to an increased thickness or stickiness of the mucus layer that normally coats the skin. Severe dehydration is also associated with skin tenting and sunken eyes.
  2. Perform an ocular exam. A slit lamp, where available, is ideally suited for examination of the amphibian eye since it provides magnification and illumination. Keep in mind that aquatic frogs lack eyelids.
  3. Inspect the oral cavity. Palpate the jaw to look for evidence of metabolic bone disease. Be gentle! Even the normal anuran possesses relatively fragile mandibular and hyoid bones.Gently touch the rictus (the commissure of the mouth) to stimulate mouth opening, or gently use a mouth speculum to press into the filtrum (the small depression at the rostral edge of the mouth).
    • Many normal amphibians possess pale mucous membranes.
    • The eyes are separated from the buccal region by only a thin membrane, so make sure your oral exam is particularly detailed when eye problems are observed.
    • Make sure the tongue can move normally. Tongue paresis or paralysis may be observed with metabolic bone disease.
    • Also evaluate the lingual plexus (see No. 4 below) by gently pulling the tongue forward with a cotton-tipped applicator.
  4. Evaluate the cardiovascular system. When visualization of the apex beat is insufficient, use a Doppler or ultrasound probe to evaluate the heartbeat. A stethoscope can be used in a large anuran. Circulatory abnormalities may be associated with reduced prominence of the lingual plexus or the central abdominal vein.
  5. Examine the coelom.  Transillumination can be used to identify internal organs, coelomic fat pads and even egg masses in small species. Diagrams and figures illustrating frog anatomy are available at:

    Coelomic palpation can also be performed and may sometimes be useful in detecting egg masses, gastrointestinal obstructions or bladder stones. Unfortunately palpation is not always possible since some species will defensively inflate themselves with air when threatened or stressed.

  6. Perform the musculoskeletal exam, palpating the limbs for any abnormalities.
  7. Weigh the patient.Weigh the patient using a gram scale. Body weight can vary greatly with the presence of food in the stomach, changes in hydration status, or a full urinary bladder.

Quiz

Carefully read each question before clicking the link to see the correct answer.

References