Role of Rickettsial Outer Membrane Protein A in the Pathogenesis of Rickettsial Diseases

Diseases caused by Rickettsiales are often overlooked, although they pose important public health concerns. The Rickettsiales family comprises a broad range of intracellular bacteria with distinct evolutionary adaptations, making the development of treatment measures to combat infections, such as vaccines or antibiotics, a challenge. Interestingly, the outer membrane protein A (OmpA) was found to exist in the cell surface of most human pathogenic bacteria in the order Rickettsiales. However, knowledge about OmpA in each species and strain is scattered and ambiguous. In this study, we systematically compiled the existing information on OmpA and its relationship with human pathogenic rickettsiae to serve as a reference for future research. A comprehensive literature search was conducted using specific keywords across five databases. According to the literature, OmpA of spotted fever group rickettsia plays a crucial role as an adhesin and invasin that directly interacts with the surface of mammalian host cells to mediate bacterial localization in host cells. The presence of a premature stop codon in the amino acid sequence resulted in the secretion of non-functional OmpA, which is one of the main reasons for rickettsial strains or species to become avirulent. Similarly, OmpA also functions as an important adhesin in the Anaplasma family when it interacts with the sLex and sLex-like glycan of myeloid and endothelial cells, respectively. However, the OmpA of Anaplasma must be co-functional with the other two adhesins to promote bacterial internalization. Interestingly, certain sites in the amino acid residues of Ehrlichia and Orientia OmpA are predicted to be homologous to the binding domain region of Anaplasma OmpA. It is therefore suggested that OmpA is an important adhesin for bacteria to bind to their specific mammalian host cells

Rickettsial infections are neglected causes of acute febrile illness in Teluk Intan, Peninsular Malaysia

Rickettsial infections are among the leading etiologies of acute febrile illness in Southeast Asia. However, recent data from Malaysia are limited. This prospective study was conducted in Teluk Intan, Peninsular Malaysia, during January to December 2016. We recruited 309 hospitalized adult patients with acute febrile illness. Clinical and biochemistry data were obtained, and patients were stratified into mild and severe infections based on the sepsis-related organ failure (qSOFA) scoring system. Diagnostic assays including blood cultures, real-time PCR, and serology (IFA and MAT) were performed. In this study, pathogens were identified in 214 (69%) patients, of which 199 (93%) patients had a single etiology, and 15 (5%) patients had >1 etiologies. The top three causes of febrile illness requiring hospitalization in this Malaysian study were leptospirosis (68 (32%)), dengue (58 (27%)), and rickettsioses (42 (19%)). Fifty-five (18%) patients presented with severe disease with a qSOFA score of >/=2. Mortality was documented in 38 (12%) patients, with the highest seen in leptospirosis (16 (42%)) followed by rickettsiosis (4 (11%)). While the significance of leptospirosis and dengue are recognized, the impact of rickettsial infections in Peninsular Malaysia remains under appreciated. Management guidelines for in-patient care with acute febrile illness in Peninsular Malaysia are needed

Rickettsial infections are neglected causes of acute febrile illness in Teluk Intan, Peninsular Malaysia

Rickettsial infections are among the leading etiologies of acute febrile illness in Southeast Asia. However, recent data from Malaysia are limited. This prospective study was conducted in Teluk Intan, Peninsular Malaysia, during January to December 2016. We recruited 309 hospitalized adult patients with acute febrile illness. Clinical and biochemistry data were obtained, and patients were stratified into mild and severe infections based on the sepsis-related organ failure (qSOFA) scoring system. Diagnostic assays including blood cultures, real-time PCR, and serology (IFA and MAT) were performed. In this study, pathogens were identified in 214 (69%) patients, of which 199 (93%) patients had a single etiology, and 15 (5%) patients had >1 etiologies. The top three causes of febrile illness requiring hospitalization in this Malaysian study were leptospirosis (68 (32%)), dengue (58 (27%)), and rickettsioses (42 (19%)). Fifty-five (18%) patients presented with severe disease with a qSOFA score of ≥2. Mortality was documented in 38 (12%) patients, with the highest seen in leptospirosis (16 (42%)) followed by rickettsiosis (4 (11%)). While the significance of leptospirosis and dengue are recognized, the impact of rickettsial infections in Peninsular Malaysia remains under appreciated. Management guidelines for in-patient care with acute febrile illness in Peninsular Malaysia are needed

Combined PCR and MAT improves the early diagnosis of the biphasic illness leptospirosis.

The diagnosis of leptospirosis remains a challenge due to its non-specific symptoms and the biphasic nature of the illness. A comprehensive diagnosis that includes both molecular (polymerase chain reaction (PCR)) and serology is vital for early detection of leptospirosis and to avoid misdiagnosis. However, not all samples could be subjected to both tests (serology and molecular) due to budget limitation, infrastructure, and technical expertise at least in resource-limited countries. We evaluated the usefulness of testing the clinically suspected leptospirosis cases with both techniques on all samples collected from the patients on the day of admission. Among the 165 patient's blood/serum samples tested (from three hospitals in Central Malaysia), 43 (26%) showed positivity by microscopic agglutination test (MAT), 63 (38%) by PCR, while 14 (8%) were positive by both MAT and PCR. For PCR, we tested two molecular targets (lipL32 by qPCR and 16S rDNA or rrs by nested PCR) and detected lipL32 in 47 (29%) and rrs gene in 63 (38%) patients. The use of more than one target gene for PCR increased the detection rates. Hence, a highly sensitive multiplex PCR targeting more than one diagnostic marker is recommended for the early detection of Leptospira in suspected patients. When the frequencies for positivity detected either by MAT or PCR combined, leptospirosis was diagnosed in a total of 92 (56%) patients, a higher frequency compared to when samples were only tested by a single method (MAT or PCR). The results from this study suggest the inclusion of both serology and molecular methods for every first sample irrespective of the days post-onset of symptoms (DPO) collected from patients for early diagnosis of leptospirosis

Leptospira interrogans and Leptospira kirschneri are the dominant Leptospira species causing human leptospirosis in Central Malaysia

Background: Leptospirosis, commonly known as rat-urine disease, is a global but endemic zoonotic disease in the tropics. Despite the historical report of leptospirosis in Malaysia, the information on human-infecting species is limited. Determining the circulating species is important to understand its epidemiology, thereby to strategize appropriate control measures through public health interventions, diagnostics, therapeutics and vaccine development. Methodology/Principle findings: We investigated the human-infecting Leptospira species in blood and serum samples collected from clinically suspected leptospirosis patients admitted to three tertiary care hospitals in Malaysia. From a total of 165 patients, 92 (56%) were confirmed cases of leptospirosis through Microscopic Agglutination Test (MAT) (n = 43; 47%), Polymerase Chain Reaction (PCR) (n = 63; 68%) or both MAT and PCR (n = 14; 15%). The infecting Leptospira spp., determined by partial 16S rDNA (rrs) gene sequencing revealed two pathogenic species namely Leptospira interrogans (n = 44, 70%) and Leptospira kirschneri (n = 17, 27%) and one intermediate species Leptospira wolffii (n = 2, 3%). Multilocus sequence typing (MLST) identified an isolate of L. interrogans as a novel sequence type (ST 265), suggesting that this human-infecting strain has a unique genetic profile different from similar species isolated from rodents so far. Conclusions/Significance: Leptospira interrogans and Leptospira kirschneri were identified as the dominant Leptospira species causing human leptospirosis in Central Malaysia. The existence of novel clinically important ST 265 (infecting human), that is different from rodent L. interrogans strains cautions reservoir(s) of these Leptospira lineages are yet to be identified