Figure 1. Green tree frog (Litoria caerulea).
This adult L. caerulea was found on a farm at Biloela,
Queensland, Australia.
The frog's behaviour and appearance were abnormal. It was reluctant to hop, and had an abnormal snout (shown above). You can see a solid, cream coloured mass 5 x 6 mm protruding from the snout with spread into adjacent skin.
When the snout was opened up, we could see that the mass had spread through the mucosa and submucosa of the nasal passages, obstructing them. Multiple cream coloured nodules, 2-3 mm in diameter, were present in the lung, liver and spleen. In the spleen these nodules had coalesced.
Figure 2. Histopathology of the nasal lesion (low power H&E).
The cross section at low power (Fig. 2) shows that the nasal mucosa is thickened by granulomatous inflammatory tissue. The nodules at other sites were also due to granulomatous inflammation. Foreign body giant cells were occasionally seen in the granulomas.
The causative agent, M. amphibiorum, is shown in the histological sections below (Figures 3 and 4).
Figure 3. High power view of sphaerules of M. amphibiorum. Diameters of sphaerules are approximately 5-8 microns. PAS.
Figure 4. High power view of sphaerule containing daughter sphaerules. Diameter
approximately 15 microns. PAS.
These are spherules of Mucor amphibiorum. In Figure 4 you can see a mother sphaerule with at least 8 daughter sphaerules developed internally. The sphaerules and particularly the presence of daughter sphaerules are the main diagnostic clue that the fungus is M. amphibiorum. The sphaerules stain strongly with PAS, a common stain used to demonstrate fungi in tissues.
This case was reported in:
Berger L, Speare R,
Humphrey J. Mucormycosis in a free-ranging green tree frog from Australia.
Journal of Wildlife Diseases 1997;33(4):903-907.