Invasive Species Compendium

Detailed coverage of invasive species threatening livelihoods and the environment worldwide

Abstract

Is there evidence of Sarcocystis calchasi involvement in meningoencephalitis of unknown origin in mammals? A retrospective study.

Abstract

Sarcocystis calchasi is a novel intracellular protozoan parasite belonging to the phylum Apicomplexa with an obligatory two-host, predator-prey life cycle. The northern goshawk (Accipiter gentilis) is its definitive host and the domestic pigeon (Columba livia f. domestica) its intermediate host. It has been identified as the causative agent of Pigeon Protozoal Encephalitis (PPE) during an outbreak in Berlin in the period between 2006 and 2008. PPE is an ongoing threat as new cases are continuously diagnosed in pigeons in the Berlin area. Since many Sarcocystis spp. are polyxenous, being capable of infecting more than one species, and birds as well as mammals may usually serve as their intermediate hosts, a retrospective study was conducted to determine whether Sarcocystis calchasi may be involved in cases of meningoencephalitis of unknown origin (MUO) in mammals. Formalin fixed paraffin embedded (FFPE) samples of 143 brains with MUO of different mammalian species (dog, cat, pig, cattle, sheep, guinea pig, horse, goat, mouse, raccoon, ferret, hamster, mink, mane wolf) from the time period between 1989 and 2012 were reexamined histologically using H&E stain. DNA was isolated from FFPE material and screened by polymerase chain reaction (PCR) with primers specific for the 18S rRNA and the Internal Transcribed Spacer region 1 (ITS1) to detect Sarcocystis calchasi or other apicomplexan parasites, respectively. In all samples the diagnosis of non-suppurative (lymphoplasmacytic and/or granulomatous) meningoencephalitis was histologically confirmed but no parasitic structures were found in the histopathological investigation. DNA of Sarcocystis calchasi or other apicomplexan parasites could not be detected in any of the samples. However due to formalin fixation the DNA quality of the samples might not have been optimal in all cases, which is why the results should be interpreted carefully. Even though the prevalence of PPE in pigeons remains constant and Sarcocystis calchasi constitutes a persistent threat to pigeons in the Berlin area, no evidence was found here for a role of this parasite in MUO in mammalian species. Nevertheless, taking into consideration the methodical drawbacks of analyzing FFPE retrospective cases, a prospective study using new emerging cases with optimal DNA quality and/or immunohistochemical studies with specific antibodies would be advisable.