Detection of Naegleria fowleri, Acanthamoeba spp, and Balamuthia mandrillaris in Formalin-Fixed, Paraffin-Embedded Tissues by Real-Time Multiplex Polymerase Chain Reaction

Genotyping and Molecular Identification of Acanthamoeba Genotype T4 and Naegleria fowleri from Cerebrospinal Fluid Samples of Patients in Turkey: Is it the Pathogens of Unknown Causes of Death?

PURPOSE

This study was aimed to investigate the presence of pathogenic free-living amoebae (FLA) in suspected cases of meningoencephalitis with unknown causes of death in Turkey.

METHOD

A total of 92 patients, who were diagnosed as meningoencephalitis, were enrolled. All cerebrospinal fluid (CSF) samples were directly microscopically examined and cultured. Acanthamoeba, N. fowleri and B. mandrillaris were further investigated using molecular diagnostic tools including real-time PCR, sequencing, and phylogenetic analyses.

RESULTS

The examined CSF samples were not found positive for the presence of FLA by microscopic examination and culture method. However, two CSF samples were detected positive by real-time PCR assay. Of the positive CSF samples, one was identified as Acanthamoeba genotype T4 and the second positive sample was identified as N. fowleri belonging to genotype II. Furthermore, the pathogens diagnoses was verified through Sanger sequencing.

CONCLUSION

This study was significant to report the presence of Acanthamoeba genotype T4 and N. fowleri genotype II in CSF samples by real-time PCR assay. The present study shows the significance of primary amoebic meningoencephalitis (PAM) and granulomatous amoebic encephalitis (GAE) as one of the differential diagnoses to be considered by clinicians during the evaluation of suspected meningoencephalitis or cases of unknown cause in Turkey. Using real-time PCR, this has made the rapid detection, in a short time-frame, of Acanthamoeba and N. fowleri in CSF samples from patients. The problems with qPCR is that it is not available in every laboratory, reagents are expensive, and it requires skilled and expert personnel to set up these assays.

Various brain-eating amoebae: the protozoa, the pathogenesis, and the disease

Among various genera of free-living amoebae prevalent in nature, some members are identified as causative agents of human encephalitis, in which Naegleria fowleri followed by Acanthamoeba spp. and Balamuthia mandrillaris have been successively discovered. As the three dominant genera responsible for infections, Acanthamoeba and Balamuthia work as opportunistic pathogens of granulomatous amoebic encephalitis in immunocompetent and immunocompromised individuals, whereas Naegleria induces primary amoebic meningoencephalitis mostly in healthy children and young adults as a more violent and deadly disease. Due to the lack of typical symptoms and laboratory findings, all these amoebic encephalitic diseases are difficult to diagnose. Considering that subsequent therapies are also affected, all these brain infections cause significant mortality worldwide, with more than 90% of the cases being fatal. Along with global warming and population explosion, expanding areas of human and amoebae activity in some regions lead to increased contact, resulting in more serious infections and drawing increased public attention. In this review, we summarize the present information of these pathogenic free-living amoebae, including their phylogeny, classification, biology, and ecology. The mechanisms of pathogenesis, immunology, pathophysiology, clinical manifestations, epidemiology, diagnosis, and therapies are also discussed.

Free Living Amoebic Infections: Review

Infections caused by Naegleria fowleri, Acanthamoeba spp., and Balamuthia mandrillaris result in a variety of clinical manifestations in humans. These amoebae are found in water and soil worldwide. Acanthamoeba spp. and B. mandrillaris cause granulomatous amoebic encephalitis, which usually presents as a mass, while N. fowleri causes primary amoebic meningoencephalitis. Acanthamoeba spp. can also cause keratitis, and both Acanthamoeba spp. and B. mandrillaris can cause lesions in skin and respiratory mucosa. These amoebae can be difficult to diagnose clinically as these infections are rare and, if not suspected, can be misdiagnosed with other more common diseases. Microscopy continues to be the key first step in diagnosis but the amoeba can be confused with macrophages or other infectious agents if an expert in infectious disease pathology or clinical microbiology is not consulted. Although molecular methods can be helpful in establishing the diagnosis, these are only available in referral centers. Treatment requires combination of antibiotics and antifungals and, even with prompt diagnosis and treatment, mortality for neurological disease is extremely high.

Molecular and Histologic Diagnosis of Central Nervous System Infections

Infections of the central nervous system cause significant morbidity and mortality in immunocompetent and immunocompromised individuals. A wide variety of microorganisms can cause infections, including bacteria, mycobacteria, fungi, viruses, and parasites. Although less invasive testing is preferred, surgical biopsy may be necessary to collect diagnostic tissue. Histologic findings, including special stains and immunohistochemistry, can provide a morphologic diagnosis in many cases, which can be further classified by molecular testing. Correlation of molecular, culture, and other laboratory results with histologic findings is essential for an accurate diagnosis, and to minimize false positives from microbial contamination.

Acanthamoeba and its pathogenic role in granulomatous amebic encephalitis

Acanthamoeba is a free-living amoeba that is widely distributed in the environment. It is an opportunist protist, which is known to cause rare yet fatal infection of the central nervous system (CNS), granulomatous amebic encephalitis (GAE) in humans. GAE cases are increasingly been reported among immunocompromised patients, with few cases in immunocompetent hosts. Diagnosis of GAE primarily includes neuroimaging, microscopy, cerebrospinal fluid (CSF) culture, histopathology, serology and molecular techniques. Early diagnosis is vital for proper management of infected patients. Combination therapeutic approach has been tried in various GAE cases reported worldwide. We tried to present a comprehensive review, which summarizes on the epidemiology of GAE caused by Acanthamoeba along with the associated clinical symptoms, risk factors, diagnosis and treatment of GAE among infected patients.