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Metarhizium granulomatis infection

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Synonym(s): Metarhizium (Chameleomyces) granulomatis

Introduction

  • Cause: infection with the fungus Metarhizium (Chameleomyces) granulomatis. This is an emerging, aggressive, primary fungal infection in veiled chameleons (Chamaeleo calyptratus). More research on diagnosis and treatment is needed.
  • Signs: infection has been associated with dermatitis, glossitis and disseminated granulomatous mycosis in reptiles. Veiled chameleons are the most affected species, although infection has also been reported in an Inland Bearded dragon (Pogona vitticeps) and two Panther chameleons (Furcifer pardalis).
  • Diagnosis: fungal culture and histopathological examination of a biopsy of affected tissue. Definitive diagnosis requires molecular identification. The main differential diagnosis is infection with Metarhizium viride, a closely related fungus, although this has a wider host species range.
  • Treatment: surgical excision of infected tissue where feasible. Medical anti-fungal treatment appears to be ineffective.
  • Prognosis: poor – infection is often fatal.

Presenting signs

  • Glossitis, glossal hemorrhage, pharyngitis, dermatitis, anorexia and emaciation in veiled chameleons. Some chameleons will show only some of the clinical signs.
  • Infection in an Inland Bearded dragon and one panther chameleon was asymptomatic.
  • Some veiled chameleons have been found to carry M. granulomatis but be asymptomatic.

Geographic incidence

  • Not yet clear.
  • Has been found in pet chameleons and those in zoological collections in Europe.

Age predisposition

  • Only adult chameleons appear to be affected.

Gender predisposition

  • None apparent.

Breed/species predisposition

  • Primarily seen in veiled chameleons.
  • One survey isolated M. granulomatis in one Inland Bearded dragon and two Panther chameleons (although infection was asymptomatic). This was part of a survey to see if M. granulomatis would be isolated from species other than veiled chameleons.

Public health considerations

  • None apparent.

Cost considerations

  • The keeper should be counselled as to potential costs associated with diagnosis (particularly specialized molecular techniques) and with attempted surgical treatment, particularly in view of the guarded prognosis.

Pathogenesis

Etiology

  • Infection with Metarhizium (Chamaeleomyces) granulomatis – a primary fungal pathogen.
  • Metarhizium spp, in the order Hypocreales,family Clavicipitaceae, are best known as insect pathogens. They are ascomycetous, filamentous fungi.
  • There are distinct genotypes of M. granulomatis:
    • Genotype A appears to be  associated with dermatitis.
    • GGenotypes B-E more associated with glossitis.
    • Infection with more than one genotype can occur.
  • M. granulomatis has been found in environmental soil samples, and infection is presumed to be via ingestion or direct contact from the environment.

Predisposing factors

General

  • Veiled chameleons appear to be predisposed to this infection, both pets and those in zoological collections.

Pathophysiology

  • As yet unclear but presumed to be overwhelming fungal infection.
  • Chameleons with glossitis will struggle to eat, and therefore anorexia and emaciation will ensue.
  • The survival time is longer in those with solely dermatitic lesions.

Timecourse

  • Survival time in veiled chameleons appears to be 8-10 months.
  • Survival time is reduced in chameleons with glossitis but increased in those showing only dermatitis.

Epidemiology

  • As yet unclear.

Diagnosis

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Treatment

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Prevention

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Outcomes

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Further Reading

Publications

Refereed papers

  • Schmidt V, Klasen L, Schneider J et al (2017) Characterization of Metarhizium viride mycosis in Veiled chameleons (Chamaeleo calyptratus), Panther chameleons (Furcifer pardalis), and Inland Bearded dragons (Pogona vitticeps). J Clin Microbiol 55 (3), 832-843 PubMed.
  • Schmidt V, Klasen L, Schneider J et al (2017) Fungal dermatitis, glossitis and disseminated visceral mycosis caused by different Metarhizium granulomatis genotypes in veiled chameleons (Chamaeleo calyptratus) and first isolation in healthy lizards. Vet Microbiol 207, 74-82 PubMed.
  • Pfaff M, Schmidt V, Plenz B & Pees M (2015) Examination on the occurrence, clinical appearance and the detection of Chamaeleomyces sp. in clinically diseased chameleons. Berliner und Munchener Tierarztliche Wochenschrift 128 (1-2), 39-45 PubMed.
  • Schmidt V (2015) Fungal infections in reptiles – An emerging problem. J Exotic Pet Med 24 (3), 267-275 SciDirect.
  • Schmidt V, Plenz B, Pfaff M & Pees M (2012) Disseminated systemic mycosis in Veiled chameleons (Chamaeleo calyptratus) caused by Chamaeleomyces granulomatis. Vet Microbiol 161 (1-2), 145-152 PubMed.
  • Sigler L, Gibas C F C,  Kokotovic B & Bertelsen M F (2010) Disseminated m mycosis in Veiled chameleons (Chamaeleo calyptratus) caused by Chamaeleomyces granulomatis, a new fungus related to Paecilomyces viridis. J Clin Microbiol 48 (9), 3182-3192 PubMed.

Other sources of information

  • Wellehan J F X & Divers S J (2019) Mycology. In: Mader’s Reptile and Amphibian Medicine and Surgery. 3rd edn. Eds: Divers S J & Stahl S J. Elsevier, USA. pp 270-280.