Multifocal Balamuthia mandrillaris infection in a dog in Australia
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- Finnin, P.J., Visvesvara, G.S., Campbell, B.E. et al. Parasitol Res (2007) 100: 423. doi:10.1007/s00436-006-0302-0
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A 6-year-old male golden retriever, with an 8-month history of seizures and a clinical diagnosis of lymphoma in the central nervous system, was (at the owner’s request) euthanized after signs of respiratory distress and shock developed. Upon postmortem examination, the diagnoses of meningoencephalitis and pneumonia were made. A histological examination of selected tissues from both the lung and central nervous system revealed a severe, acute, multifocal, amoebic, embolic pneumonia and a severe, chronic, multifocal, nonsuppurative, amoebic meningoencephalitis. Indirect immunofluorescence analysis confirmed the presence of trophozoite and cyst stages of Balamuthia mandrillaris. This is the first report of B. mandrillaris (which is a free-living amoeba) causing fatal, multifocal granulomatous amoebiasis in a dog in Australia.
Balamuthia mandrillaris is a free-living amoeba (Acanthopodida, family Acanthamoebidae), capable of causing fatal granulomatous amoebic meningoencephalitis (GAE) in animals. While the route of transmission from the environment to an opportunistic host remains enigmatic (Schuster et al. 2003), invasion of the host via the skin and/or respiratory tract, followed by haematogenous dissemination, has been hypothesized (Martinez and Visvesvara 1997, 2001; Martinez et al. 2001). This amoeba was first isolated from Papio sphinx (mandrill; Visvesvara et al. 1990) and was subsequently detected in various nonhuman primates, including Gorilla gorilla gorilla (gorilla), Pongo pygmaeus (orangutan), Colobus guereza kikuyuensis (colobus monkey) and Hylobates concolor leucogenys (gibbon; Anderson et al. 1986; Canfield et al. 1997; Rideout et al. 1997), and has increasingly been found in humans affected by GAE (Martinez and Visvesvara 1997; Schuster and Visvesvara 2004). Also, cases of fatal B. mandrillaris infection have been reported for sheep (Fuentealba et al. 1992), horse (Kinde et al. 1998) and, more recently, dog (Foreman et al. 2004). While GAE cases in primates have been reported in Australia (Canfield et al. 1997; Reed et al. 1997), there has been no previous report in dogs. The present article describes the first canine case of multifocal balamuthiasis in Victoria, Australia.
A 6-year-old male, castrated golden retriever, with an 8-month history of seizures and treatment with phenobarbitone, was referred to the Department of Veterinary Clinic and Hospital of the School of Veterinary Science of the University of Melbourne. Two months before the referral, the dog developed a hearing loss and began showing other neurological signs, such as a circling to the left and a left-head tilt. An analysis of cerebrospinal fluid showed a lymphocytic pleocytosis, with some atypical lymphocytes being present. A clinical diagnosis of lymphoma in the central nervous system was made. The neurological signs appeared to resolve after the commencement of a course of prednisolone and lomustine chemotherapy at standard doses. Four weeks later, the animal presented with signs of respiratory distress and shock. The dog went into respiratory arrest and was then euthanized upon request by the owners.
This is the first record of balamuthiasis in a dog in Australia, although B. mandrillaris has been detected in fatal cases in primates in this country (Canfield et al. 1997; Reed et al. 1997). The progressive clinical signs, fatal outcome and granulomatous foci detected histologically in lung and brain tissues from this dog are consistent with a previous report in a dog from the USA (Foreman et al. 2004), with the exception of the nephritis in the latter case. Lesions associated with B. mandrillaris infection in animals and humans are usually restricted to the central nervous system and lymph node(s) (Fuentealba et al. 1992; Kinde et al. 1998; Martinez and Visvesvara 2001). However, granulomatous lesions and trophic and cyst stages of the amoeba were also detected in the lung in the present canine case, and in the kidney in a previous case (Foreman et al. 2004). As the lesions in the brain were more chronic in nature than those in the lung, it is possible that the involvement in the latter site was secondary to a haematogenous spread of the B. mandrillaris infection. Since it has been shown that B. mandrillaris (instilled intranasally in mice) can adhere to the nasal epithelium, migrate along the olfactory nerves, traverse the cribriform plate of the ethmoid bone and subsequently invade the brain (Kiderlen and Laube 2004), it is possible that the chronic brain lesions identified herein were the result of invasion via this route. While the source of infection was not proven, there was some indication, from a discussion with the owners, that the dog most likely had contracted the amoeba while swimming in stagnant freshwater (dam or pond). While invasion via the nasal cavity and olfactory nerve pathway is a plausible explanation, entry via the skin is also possible (Martinez and Visvesvara 2001), although skin lesions were not evident in the present case.
The dog initially presented with seizures consistent with epilepsy and had thus been treated with phenobarbitone. However, other neurological signs, such as a circling to the left, a head tilt (to the left) and a hearing loss, developed. The analysis of cerebrospinal fluid (revealing a lymphocytic pleocytosis) was consistent with a clinical diagnosis of lymphoma in the central nervous system. While the treatment with the anticancer drug, lomustine, and the anti-inflammatory corticosteroid compound, prednisolone, seemed to result in reduced neurological signs, the treatment course with the latter drug is likely to have predisposed the dog to the (probably secondary) B. mandrillaris infection in the lung and may have exacerbated the clinical disease. As a precise clinical diagnosis of B. mandrillaris infection is almost impossible and the treatment ineffective, such cases are usually fatal. The diagnosis of the first case of canine balamuthiasis in Australia, based on histopathological findings, represents an important learning experience and raises awareness of GAE. Thus, B. mandrillaris and other infections due to free-living amoeba, such as Acanthamoeba spp. or Naegleriafowleri (see Schuster and Visvesvara 2004), should be considered when animals are presented with neurological signs. Future studies should focus on the sources of B. mandrillaris infection, the route(s) and course of the infection, and the pathogenesis of the disease.
The authors thank Professor KVF Jubb for helpful comments and suggestions.