Balamuthia spp

From Dog
Granulomatous lesions throughout the renal cortex of a dog due to Balamuthia mandrillaris infection[1]
Immunohistochemical staining of Balamuthia cysts in the kidney of the above dog[1]

Balamuthia is a free-living opportunistic leptomyxid amoeba found worldwide, causing granulomatous meningoencephalomyelitis in humans, horses and dogs[2].

The ameba is present in soil and is probably transmitted by inhalation of airborne cysts or by direct contamination of a skin lesion[3]. Dogs become infected usually by swimming in stagnant creeks or waterways.

Although this parasite mainly affects immunocompromised patients or those on long-term prednisolone therapy, it can cause multifocal nephritis, pneumonia and encephalitis in healthy, mature, apparently immunocompetent dogs[4].

Species pathogenic to dogs include:

  • Balamuthia mandrillaris

Clinically affected dogs usually present with dyspnea (due to pneumonia) and neurological disease characterized by ataxia, circling, head-pressing, seizures and blindness[5].

Diagnosis can be difficult as blood, imaging and CSF analysis is often unrewarding.

Histological samples of brain tissue postmortem usually reveal localised lytic lesion in the deep cerebellar white matter, with cavitation of the white matter and communication of the lesion with the fourth ventricle. Affected areas frequently contain structures consistent with amoebae and infiltrations of leucocytes.

Definitive diagnosis requires PCR analysis of brain tissue[6].

A differential diagnosis would include other causes of granulomatous meningoencephalomyelitis as well as other amoebas such as Acanthamoeba spp.

Empirical treatment with metronidazole and amoxycillin/clavulanate have been ineffective at controlling this disease.

References

  1. 1.0 1.1 Foreman O et al (2004) Disseminated infection with Balamuthia mandrillaris in a dog. Vet Pathol 41(5):506-510
  2. Centers for Disease Control and Prevention (CDC) (2008) Balamuthia amebic encephalitis - California, 1999-2007. MMWR Morb Mortal Wkly Rep 57(28):768-771
  3. Martinez AJ et al (2001) Balamuthia mandrillaris: its pathogenic potential. J Eukaryot Microbiol pp:6S–9S
  4. Hodge PJ et al (2011) Another case of canine amoebic meningoencephalitis--the challenges of reaching a rapid diagnosis. Parasitol Res 108(4):1069-1073
  5. Finnin PJ et al (2007) Multifocal Balamuthia mandrillaris infection in a dog in Australia. Parasitol Res 100(2):423-426
  6. Yagi S et al (2008) Demonstration of Balamuthia and Acanthamoeba mitochondrial DNA in sectioned archival brain and other tissues by the polymerase chain reaction. Parasitol Res 102(2):211-217