Broadly Reactive Polymerase Chain Reaction for Pathogen Detection in Canine Granulomatous Meningoencephalomyelitis and Necrotizing Meningoencephalitis

Abstract

Background: Granulomatous meningoencephalomyelitis (GME) and necrotizing meningoencephalitis (NME) are common inflammatory conditions of the central nervous system of dogs. Infectious pathogens, particularly viruses, are suspected to contribute to the etiopathogenesis of GME and NME.Hypothesis: Broadly reactive PCR might aid in the identification of infectious agents in GME and NME. Animals: Sixty-eight client-owned dogs evaluated by necropsy at 1 university referral hospital. Methods: A mixed prospective/retrospective case-control study was performed. Brain tissue prospectively collected at necropsy from GME, NME, and control cases was evaluated by broadly reactive polymerase chain reaction (PCR) for adenoviruses, bunyaviruses, coronaviruses, enteroviruses, flaviviruses, herpesviruses, paramyxoviruses, and parechoviruses. In addition, these tissues were retrospectively evaluated for the presence of mycoplasmas by PCR, culture, and immunohistochemistry (IHC).Results: Brain tissue was collected from 11 GME and 27 NME cases and 30 controls. Viral nucleic acids were not identified in the 6 GME cases, 25 NME cases, and 2 controls evaluated by viral PCR. Mycoplasma canis was identified by Mycoplasma genus PCR in 1/5 GME and 4/25 NME cases and subsequently was cultured from 4/5 GME and 4/8 NME cases as well as 2/9 controls. The IHC did not detect M. canis in any of the 11 GME and 27 NME cases or 14 controls evaluated with strain PG14 polyclonal antiserum.Conclusions and Clinical Importance: The negative results suggest that viral pathogens are not common in the brain tissue of dogs with GME and NME. Further investigation is warranted to determine the importance of M. canis in cases of GME and NME.

Perspectives on Meningoencephalomyelitis of Unknown Origin

“…Infection by Cryptococcus spp is usually detected by antigen testing, and other microbial DNA or RNA can also be detected by polymerase chain reaction (PCR) assays, which have high sensitivity and specificity. [8][9][10]99 Results should still be interpreted carefully to avoid false positives, and rigorous negative controls must be evaluated in parallel with the clinical sample. A negative PCR result needs to take into account that the nucleic acid may be present but at undetectable levels, the agent may be in the neural tissue but not in CSF, and the disorder may have been triggered by an agent that is no longer present.…”

“…99 Nonetheless, specific pathogens in CSF and diseased tissues have not been identified as being associated with the MUOs. 4,[8][9][10] Genetic Testing…”

“…[5][6][7][8] Suspected agents include environmental or infectious antigenic triggers that might activate autoreactive cells in the CNS, although no such agent has yet been incriminated in the development of MUO. [9][10][11][12] Susceptibility genes may confer susceptibility or protection for autoimmunity by influencing the maintenance of self-tolerance. Data from inbred rodent studies have identified a strong influence of genetic background as a competing influence in the variability of lymphocyte responses in clearing pathogens from the CNS and promoting neuroprotection.…”

Cellular Microbiology of Mycoplasma canis

“…Although it did not occur frequently or consistently among cases of GME or NME, deposition of oxidized DAB throughout some vascular cuffs probed with anti-M. canis antibody (Fig. 7B and C) was evidence that the presence of M. canis in canine brains cannot be attributed solely to contamination during nonaseptic tissue collection (2). Because brain tissue specimens are typically not available for examination until long after clinical signs of chronic progressive neurological disease have developed, the abundance of intact M. canis cells remaining to be visualized at necropsy may be very low.…”

“…We found unexpectedly that M. canis was also detectable by culture or PCR in a majority of brain tissue specimens in a retrospective case-control study of canine granulomatous meningoencephalitis (ME) (GME) and necrotizing ME (NME) (2). The presence of M. canis in brain tissue was associated with both GME and NME (both P Ͻ 0.05, as determined by a 2 test).…”