Clinical history

An Australian green tree frog (Litoria caerulea) was presented with the following clinical signs for one day:

The frog was acquired from a pet shop 2 years previously and it was unknown whether it was captive bred or wild caught. It was kept in a 60 cm × 40 cm × 60 cm sized aquaterrarium (1/4 water, 3/4 soil, pebbles and moss) together with a second Australian green tree frog of the same origin. The air humidity in the aquaterrarium was on average 60–80%, the air temperature about 26°C and the water temperature about 22°C. During the night the temperature decreased about 2°C. Illumination and UV radiation were achieved by two 50 watt floodlit emitters over 12 hours daily. The food consisted of commercially-available larvae from darkling beetles (Zophobas morio), house crickets (Acheta domesticus), mealworms (Tenebrio molitor) and cockroaches (Periplaneta americana).

Clinical examination

On presentation, the frog had a good nutritional status (bodyweight 38 g). The animal was calm but alert and responsive. The general health and the animal’s behaviour seemed to be unimpaired. The skin surface was smooth, moist and shiny. The mucous membrane in the mouth appeared pale pink-coloured and shiny. On the upper and lower surface of the right thigh were two 0.2 cm to 1.5 cm sized, whitish, round to oval, soft and elastic visible swellings. Similar distensions occurred on the frog’s right foot and on its right body wall (Fig. 4.1).

Fig. 4.1 Australian green tree frog (Litoria caerulea) with several boil-like distensions (yellow arrows) on its right body wall.

Faecal examination and ultrasonographic examination (Fig. 4.2) were performed, followed by incision of the distensions.

Fig. 4.2 Ultrasonographic examination of the frog’s right thigh. A 1.39 cm × 0.92 cm sized vesicle is focused. An examination glove filled with water is used as aqueous standoff.

Diagnostic lancing and laboratory examination

Incision of distensions

One vesicle at the frog’s right foot and one on its abdominal wall were incised using a 23-G-needle. Several white objects were removed (Fig. 4.3) and microscopically evaluated.

Fig. 4.3 Left side: using a 23 G needle, one distension on the frog’s right foot was incised and several white objects were removed. Right side: in the procedure approximately 50 0.1–0.8 cm sized, irregularly shaped, white, partly transparent and tough objects were removed. Single objects were up to 3 cm long. The brown particles are soil from the aquaterrarium.

A swab was taken out of one vesicle and subjected to a microbiological examination.

2. What is your interpretation of the removed structures (see Fig. 4.3)?

Results

Please evaluate the clinical history, Figs 4.1– 4.3, the results of the physical examination, diagnostic lancing and laboratory tests.

3. List your differential diagnoses.

4. List your further diagnostic strategy.

5. List your therapeutic strategy.

Differential diagnoses for subcutaneous swellings in frogs

Further diagnostics

Therapy (Table 4.1)

Table 4.1 Therapy

Discussion

Amphibians act as definitive hosts but more often as intermediate hosts of cestodes worldwide. In the two-phase life cycle of Spirometra erinaceieuropaei, amphibians, reptiles and rodents are common intermediate hosts. Litoria cerulea is also regularly reported as host of this tapeworm. The first larval stages of the cestode, the procercoids, develop in copepods as first intermediate hosts. If amphibians act as second intermediate host, the copepods may be already eaten by the tadpoles. Later, the plerocercoids develop inside the amphibians also during the metamorphosis. Cats, as preferred definitive host and other vertebrates get infected by eating the plerocercoid-containing intermediate host. As Spirometra erinaceieuropaei has no specific definitive host, humans may get infected too. However, the parasite infects humans not only by ingestion. In fact, the sparganosis is frequently transmitted to humans by applying raw meat on wounds and inflammatory processes, which is a routine treatment in Asia. Therefore, sparganosis is a common zoonosis in East Asia. The larval stages of the parasite are able to move from the raw meat and from contaminated water actively into the human.

In the tadpoles, an infection with plerocercoids results in prolonged growth. In the adult amphibian, they affect peritoneum, liver and other tissues. In the intermediate host, they cause boil-like distensions of skeletal muscles and skin by settling down in these tissues. If a frog is a definitive host, an infection may be clinically unapparent or unspecific. Symptoms like ileus, obstipation, cachexia, blood loss, necrosis and atrophy of the intestinal mucosa are described in immunosuppressed animals, after suffering transport or stress.

The faecal examination revealed negative results for endoparasites because only larval stages but no egg-producing adult cestodes were present in the frog. In general, tapeworm eggs can be demonstrated by using sedimentation techniques. The thorough examination of the removed structures was important to plan further steps of diagnosis and therapy. While the exact species diagnosis was done out of scientific interest, the identification and classification of the parasite was necessary to choose the right medication.

As therapy of a subcutaneous sparganosis, the surgical removal of plerocercoids is indicated. This should be performed under general anaesthesia to reduce potential pain and stress for the animal. As the larvae may also lie in deeper tissues and organs, praziquantel should be administered in parallel to treat cestodes. The literature provides a high dosage range (5–24 mg/kg) and different application intervals (once or twice every second week). Oral, subcutaneous, intracoelomical or topical administrations are described as application routes in amphibians. However, the dosage of 15 mg/kg SC twice every second week used in the present case did not lead to any side effects in the animal and was able to cure the disease in conjunction with surgical intervention.

In this case, the green tree frog probably was imported to Europe. It is most likely that the frog was infected for a long time before he came into the pet shop, especially as the second frog was without symptoms and should have been also affected if the aquaterrarium were contaminated. However, a later infection cannot be excluded but seems unlikely because the obligatory intermediate hosts in the parasitic life cycle must be present. The patient responded well on removal of the plerocercoids and two injections of praziquantel. No new distensions or swellings on the frog’s body surface appeared and the animal recovered well from treatment.