Sam Young

CHLORAMPHENICOL WITH FLUID AND ELECTROLYTE THERAPY CURES TERMINALLY ILL GREEN TREE FROGS (LITORIA CAERULEA) WITH CHYTRIDIOMYCOSIS

Abstract:  Terminal changes in frogs infected with the amphibian fungal pathogen Batrachochytrium dendrobatidis (Bd) include epidermal degeneration leading to inhibited epidermal electrolyte transport, systemic electrolyte disturbances, and asystolic cardiac arrest. There are few reports of successful treatment of chytridiomycosis and none that include curing amphibians with severe disease. Three terminally ill green tree frogs (Litoria caerulea) with heavy Bd infections were cured using a combination of continuous shallow immersion in 20 mg/L chloramphenicol solution for 14 days, parenteral isotonic electrolyte fluid therapy for 6 days, and increased ambient temperature to 28°C for 14 days. All terminally ill frogs recovered rapidly to normal activity levels and appetite within 5 days of commencing treatment. In contrast, five untreated terminally ill L. caerulea with heavy Bd infections died within 24–48 hr of becoming moribund. Subclinical infections in 15 experimentally infected L. caerulea were cured within 28 days by continuous shallow immersion in 20 mg/L chloramphenicol solution without adverse effects. This is the first known report of a clinical treatment protocol for curing terminally ill Bd-infected frogs.

Defects in Host Immune Function in Tree Frogs with Chronic Chytridiomycosis

The amphibian chytrid fungus Batrachochytrium dendrobatidis (Bd) has caused mass mortality leading to population declines and extinctions in many frog species worldwide. The lack of host resistance may be due to fungal immunosuppressive effects that have been observed when Bd is incubated with cultured lymphocytes, but whether in vivo host immunosuppression occurs is unknown. We used a broad range of hematologic and protein electrophoresis biomarkers, along with various functional tests, to assess immune competence in common green (Litoria caerulea) and white-lipped (L. infrafrenata) tree frogs experimentally infected with Bd. Compared with uninfected frogs, Bd infection in L. caerulea caused a reduction in immunoglobulin and splenic lymphocyte responses to antigenic stimulation with sheep red blood cells, along with decreased white blood cell and serum protein concentrations, indicating possible impaired immune response capability of Bd-infected frogs. This is the first in vivo study suggesting that infection with Bd causes multiple defects in systemic host immune function, and this may contribute to disease development in susceptible host species. Although L. infrafrenata failed to maintain Bd infection after exposure, white blood cell and serum globulin concentrations were lower in recovered frogs compared with unexposed frogs, but antigen-specific serum and splenic antibody, and splenic cellular, responses were similar in both recovered and unexposed frogs. This may indicate potential systemic costs associated with infection clearance and/or redirection of host resources towards more effective mechanisms to overcome infection. No clear mechanism for resistance was identified in L. infrafrenata, suggesting that localized and/or innate immune defense mechanisms may be important factors involved in disease resistance in this species.

SEVERE SPARGANOSIS IN AUSTRALIAN TREE FROGS

Spargana of Spirometra erinacei infect many vertebrate species, but severe disease from sparganosis has been reported from few host species. Information on the effects of this common, introduced tapeworm of cats on Australian frogs is lacking. Our survey to detect significant diseases in free-ranging amphibians in eastern Australia between 1993 and 2000 revealed that infection with spargana (plerocercoids) of S. erinacei occurred in 12/243 (4.9%) sick frogs. Infections occurred in skeletal muscle and subcutis, especially the thighs, of large adults of Litoria caerulea, Litoria aurea, Litoria gracilenta, and Litoria peronii. Three frogs were also infected in the coelomic cavity. Heavy burdens in seven frogs were associated with poor body condition and debilitating lesions, whereas lighter infections in five sick frogs were considered likely to be incidental to other diseases. In severe infections, a large proportion of thigh muscle was replaced with spargana and various amounts of fibrosis, and some frogs also had myonecrosis, granulomatous inflammation, hemorrhage, and skin ulceration. Concurrent infections were common. Our findings suggest sparganosis is one of a few currently recognized serious diseases affecting free-ranging frogs in Australia.

Hematologic and plasma biochemical reference intervals for health monitoring of wild Australian tree frogs

BACKGROUND Few hematologic and biochemical reference intervals for wild amphibians have been established. Reference values would aid in early detection of emerging infectious diseases, which are a significant problem for amphibian conservation efforts. OBJECTIVE We aimed to establish reference intervals for a wide range of hematologic and plasma biochemistry variables for 2 species of Australian tree frogs, describe morphologic features of leukocytes, and analyze the effects of season, year, and parasite status on blood values. METHODS Blood specimens were collected from reference populations of wild adult Australian tree frogs, Litoria caerulea and L infrafrenata, for analysis of hematologic (manual) variables, plasma biochemical (automated) analytes, and plasma and serum proteins using automated methods, refractometry, and electrophoresis. RESULTS Inter- and intraspecies differences were found in L caerulea (n = 80) and L infrafrenata (n = 66) frogs for hematologic and biochemical variables. Intraspecies differences were largely associated with seasonal variations. In the dry season, both species had higher WBC counts, with higher lymphocyte counts in L caerulea and higher neutrophil counts in L infrafrenata, and uric acid concentrations. In the wet season, both species had higher glucose and potassium concentrations, L caerulea frogs had higher neutrophil counts, and L infrafrenata frogs had higher total protein, phosphorus, and sodium concentrations, AST activity, PCV, hemoglobin concentration, and RBC, thrombocyte, and basophil counts. Hemogregarines were identified in 19% of blood samples from L infrafrenata frogs; multiple hematologic and biochemical variables were altered in infected frogs. CONCLUSIONS Wide interspecies and seasonal variations highlight the need to establish species- and season-specific reference intervals for amphibians. Hematologic and plasma biochemical reference values should be useful in assessing the health status and in detecting emerging diseases in wild amphibians.

Occurrence of cloacal prolapse in wild hylids in the Wet Tropics, Australia

The idiopathic syndrome of cloacal prolapse was observed in the frog Litoria rheocola at 2 sites in the Wet Tropics of Australia; 1 of 365 individuals (0.3%) at Tully Gorge National Park and 5 of 92 individuals (5.4%) at Murray Upper National Park. The condition appeared to have resolved spontaneously with no clinical complications in 2 individuals at successive captures 14 and 155 d later. It was not observed in the sympatric frogs L. genimaculata (n = 206), L. nannotis (n = 357) or Nyctimystes dayi (n = 304) at either location. The underlying cause was not conclusively determined.