Cross-reactivity of Rickettsia japonica and Rickettsia typhi demonstrated by immunofluorescence and Western immunoblotting

Nonnegligible Seroprevalence and Predictors of Murine Typhus, Japan

To elucidate the epidemiology of murine typhus, which is infrequently reported in Japan, we conducted a cross-sectional study involving 2,382 residents of rickettsiosis-endemic areas in Honshu Island during August-November 2020. Rickettsia typhi seroprevalence rate was higher than that of Orientia tsutsugamushi, indicating that murine typhus is a neglected disease.

Orientia and Rickettsia: different flowers from the same garden

Recent discoveries of basal extracellular Rickettsiales have illuminated divergent evolutionary paths to host dependency in later-evolving lineages. Family Rickettsiaceae, primarily comprised of numerous protist- and invertebrate-associated species, also includes human pathogens from two genera, Orientia and Rickettsia. Once considered sister taxa, these bacteria form distinct lineages with newly appreciated lifestyles and morphological traits. Contrasting other rickettsial human pathogens in Family Anaplasmataceae, Orientia and Rickettsia species do not reside in host-derived vacuoles and lack glycolytic potential. With only a few described mechanisms, strategies for commandeering host glycolysis to support cytosolic growth remain to be discovered. While regulatory systems for this unique mode of intracellular parasitism are unclear, conjugative transposons unique to Orientia and Rickettsia species provide insights that are critical for determining how these obligate intracellular pathogens overtake eukaryotic cytosol.

Co-infection with Severe Fever with Thrombocytopenia Syndrome Virus and Rickettsia japonica after Tick Bite, Japan

Severe fever with thrombocytopenia syndrome was diagnosed in a febrile woman in Japan after a tick bite. However, Rickettsia japonica DNA was retrospectively detected in the eschar specimen, suggesting co-infection from the bite. Establishment of the severe fever with thrombocytopenia syndrome virus infection might have overpowered the R. japonica infection.

The presence of Tularemia infection in patients with Japanese spotted fever

In our previous study, by measuring serum cytokine levels in the acute and recovery stage of Japanese spotted fever (JSF), IFN-ɤ and IL-6 were proved to be the critical immunological cytokines against Rickettsia japonica (R. japonica) infection. Tularemia is an infectious disorder caused by tick biting or contact with infected animals, and is also known as rabbit fever. There have been no confirmed cases in the recent two decades in Japan. We measured serum anti Francisella tularensis (F. tularensis) IgG titer using indirect enzyme-linked immunosorbent assay (ELISA) kit in the acute and recovery stage of three patients with JSF. The result of the IgG titer was compared with the cytokine concentrations of IFN-ɤ, IL-6, IL-4, IL-5, IL-9, and IL-33, eosinophil count, and CRP quoted from our previous report. Two of three cases have anti F. tularensis IgG, and the IgG levels between acute and recovery stage were unchanged. These two cases showed low IFN-ɤ concentration and CRP, but IL-4, IL-5, IL-9, IL-33 levels and eosinophils were high compared to those in the F. tularensis IgG-negative patient. IL-6 concentration was unchanged between the three patients. Residents living in the endemic area of JSF in Mie prefecture, Japan, may have antibodies against F. tularensis, although tularemia has never been reported. The cases of having the F. tularensis antibody showed a mild inflammatory response of JSF and might skew to type 2 immunological condition even in the acute phase of JSF.

Diagnosis of spotted fever group Rickettsia infections: the Asian perspective

Spotted fever group rickettsiae (SFG) are a neglected group of bacteria, belonging to the genus Rickettsia, that represent a large number of new and emerging infectious diseases with a worldwide distribution. The diseases are zoonotic and are transmitted by arthropod vectors, mainly ticks, fleas and mites, to hosts such as wild animals. Domesticated animals and humans are accidental hosts. In Asia, local people in endemic areas as well as travellers to these regions are at high risk of infection. In this review we compare SFG molecular and serological diagnostic methods and discuss their limitations. While there is a large range of molecular diagnostics and serological assays, both approaches have limitations and a positive result is dependent on the timing of sample collection. There is an increasing need for less expensive and easy-to-use diagnostic tests. However, despite many tests being available, their lack of suitability for use in resource-limited regions is of concern, as many require technical expertise, expensive equipment and reagents. In addition, many existing diagnostic tests still require rigorous validation in the regions and populations where these tests may be used, in particular to establish coherent and worthwhile cut-offs. It is likely that the best strategy is to use a real-time quantitative polymerase chain reaction (qPCR) and immunofluorescence assay in tandem. If the specimen is collected early enough in the infection there will be no antibodies but there will be a greater chance of a PCR positive result. Conversely, when there are detectable antibodies it is less likely that there will be a positive PCR result. It is therefore extremely important that a complete medical history is provided especially the number of days of fever prior to sample collection. More effort is required to develop and validate SFG diagnostics and those of other rickettsial infections.

Serological Cross-Reactivity among Orientia tsutsugamushi Serotypes but Not with Rickettsia japonica in Japan

The rickettsial diseases Japanese spotted fever (JSF) and scrub typhus (ST) are caused by Rickettsia japonica and Orientia tsutsugamushi, respectively. The diseases share clinical symptoms, such as fever, rash, and eschar. However, there are no systematical investigations of the serological cross-reactivity between R. japonica and O. tsutsugamushi. Also, the serological cross-reactivity among O. tsutsugamushi serotypes is still unclear. We analyzed 1406 cases tested by indirect immunoperoxidase assay using seven rickettsial antigens—one R. japonica and six O. tsutsugamushi serotypes—between 2003 and 2016 at two reference centers in Japan. Of these, 167 JSF and 190 ST cases were serologically diagnosed. None of the ST cases had a significant increase in IgM titers against R. japonica. Six JSF cases showed IgG titers of ≥40 against O. tsutsugamushi, but no IgG titer showed a significant elevation in the convalescent phase sample. We observed a substantial degree of cross-reactivity between O. tsutsugamushi serotypes. Cross-reactivity was significant among Karp, Hirano/Kuroki, and Kato types and between Gilliam and Irie/Kawasaki types in IgM, while the Shimokoshi type was less cross-reactive than the others. In conclusion, there is no serological cross-reaction between R. japonica and O. tsutsugamushi. The cross-reactivity among O.tsutsugamushi varies depending on serotypes.

A case of scrub typhus requiring maintenance hemodialysis

Renal failure caused by scrub typhus is known to be reversible. In most cases, renal function is almost fully restored after appropriate antibiotic treatment. A 71-year-old man was diagnosed with scrub typhus complicated by renal failure. A renal biopsy revealed histopathologic findings consistent with acute tubulointerstitial nephritis. Renal function did not improve 18 months after discharge and the patient required continuous hemodialysis. Although severe renal failure requiring dialysis is a rare complication of scrub typhus, we describe a case of scrub typhus requiring maintenance hemodialysis. To the best of our knowledge, this is the first such report.

Spotted fever group and typhus group rickettsioses in humans, South Korea

Multiplex-nested PCR and sequencing analysis indicated rickettsialike agents in serum specimens from febrile patients.

The presence of the nucleic acid of the spotted fever group (SPG) and typhus group (TG) rickettsiae was investigated in 200 serum specimens seropositive for SFG rickettsiae by multiplex-nested polymerase chain reaction with primers derived from the rickettsial outer membrane protein B gene. The DNA of SFG, TG, or both rickettsiae was amplified in the 24 serum specimens, and sequence analysis showed Rickettsia conorii, R. japonica, and R. felis in the specimens. R. conorii and R. typhi were found in 7 serum specimens, which indicated the possibility of dual infection in these patients. These findings suggest that several kinds of rickettsial diseases, including boutonneuse fever, rickettsialpox, R. felis infection, and Japanese spotted fever, as well as scrub typhus and murine typhus, are occurring in Korea.

Sequence analysis of the gene encoding the major outer membrane protein rOmp B of Rickettsia japonica

The complete nucleotide sequence of the gene encoding rOmp B (ompB), one of the two major outer membrane antigen proteins, of Rickettsia japonica was determined and compared to those of the other spotted fever group and typhus group rickettsiae. Open reading frame of the ompB gene of R. japonica consisted of 4,968 nucleotides coding for a putative precursor protein with 1,656 amino acids (aa) in which the N-terminal 1,363 aa and the C-terminal 293 aa encode 135-kilodalton rOmp B and 32-kilodalton beta-peptide, respectively. Putative promoter and terminator sequences for transcription were present in the upstream region of the ATG start codon and downstream of the TAA stop codon. Overall sequences of the ompB genes were well conserved beyond the group, especially in the beta-peptide regions.

Intracytoplasmic localization of antigenic heat-stable 120- to 130-kilodalton proteins (PS120) common to spotted fever group rickettsiae demonstrated by immunoelectron microscopy

Immunoelectron microscopy demonstrated antigenic heat-stable 120- to 130-kilodalton proteins (PS120) of spotted fever group (SFG) rickettsiae with antiserum against recombinant PS120 of Rickettsia japonica. In the case of R. japonica, a major part of the protein was shown to be localized outside the electron-lucent nucleoid-like region in the cytoplasm of the organisms. The other SFG rickettsiae represented a similar localization of the PS120 antigens cross-reactive to that of R. japonica. On the other hand, a typhus group rickettsia demonstrated no antigens cross-reactive to the PS120 of SFG rickettsiae.

Demonstration of a heat-stable 120-kilodalton protein of Rickettsia japonica as a spotted fever group-common antigen

Genomic libraries of Rickettsia japonica were cloned into an expression vector lambda gt11. A clone expressing a protein reactive with antiserum against 120-kilodalton (kDa) proteins, a mixture of heat-modifiable and heat-stable polypeptides, was selected and designated as lambda Rj120-1. The expressed protein has a molecular mass of 180 kDa. Western immunoblotting demonstrated that the expressed protein was a fusion protein with beta-galactosidase. The antiserum against 120-kDa proteins was absorbed by the induced lysogen, resulting in the removal of reactivity to the heat-stable 120-kDa polypeptide. The antiserum against the expressed protein reacted with heat-stable 120- to 130-kDa polypeptides of spotted fever group (SFG) rickettsiae in addition to R. japonica. The findings indicated that the protein expressed from the cloned gene of R. japonica possessed the antigenicity group-common to SFG rickettsiae. Primers designed from the gene coding for R. conorii heat-stable 120-kDa protein (Schuenke, K.W., and Walker, D.H., Infect. Immun. 62: 904-909, 1994) and lambda gt11 lacZ gene amplified the lambda Rj120-1 DNA by the polymerase chain reaction (PCR). Analysis of restriction fragment length polymorphism (RFLP) of the PCR-amplified products revealed that the cloned DNA corresponds to a portion of the gene coding for the heat-stable 120-kDa protein of R. conorii with 2,519 nucleotides beginning at nucleotide 190 of the open reading frame. RFLP demonstrated that the cloned gene was highly homologous to the corresponding gene of R. conorii.