Selection of Diagnostic Cutoffs for Murine Typhus IgM and IgG Immunofluorescence Assay: A Systematic Review

Murine typhus is a neglected but widespread infectious disease that results in acute fever. The immunofluorescence assay (IFA) is the "gold standard" to identify IgM or IgG antibodies, although there is a lack of standardization in methodologies. The objective of this review is to summarize 1) the differences in published methodologies, 2) the diagnostic cutoff titers, and 3) the justification of diagnostic cutoffs. Searches were performed by combining the following search terms: "murine typhus," "rickettsia typhi," "immunofluorescence," "IFA," and "serologic" with restrictions (i.e., "rickettsia typhi" or "murine typhus," and "IFA" or "immunofluorescence," or "serologic*"). The search identified 78 studies that used IFA or immunoperoxidase assay (IIP) antibody cutoffs to diagnose murine typhus, 39 of which were case series. Overall, 45 studies (57.7%) provided little to no rationale as to how the cutoff was derived. Variation was seen locally in the cutoff titers used, but a 4-fold or greater increase was often applied. The cutoffs varied depending on the antibody target. No consensus was observed in establishing a cutoff, or for a single-value diagnostic cutoff. In conclusion, there is a lack of consensus in the establishment of a single-value cutoff. Further studies will need to be executed at each distinct geographic location to identify region-specific cutoffs, while also considering background antibody levels to distinguish between healthy and infected patients.

Acute Febrile Illness and Complications Due to Murine Typhus, Texas, USA1,2

Murine typhus occurs relatively commonly in southern Texas, as well as in California. We reviewed records of 90 adults and children in whom murine typhus was diagnosed during a 3-year period in 2 hospitals in southern Texas, USA. Most patients lacked notable comorbidities; all were immunocompetent. Initial signs and symptoms included fever (99%), malaise (82%), headache (77%), fatigue (70%), myalgias (68%), and rash (39%). Complications, often severe, in 28% of patients included bronchiolitis, pneumonia, meningitis, septic shock, cholecystitis, pancreatitis, myositis, and rhabdomyolysis; the last 3 are previously unreported in murine typhus. Low serum albumin and elevated procalcitonin, consistent with bacterial sepsis, were observed in >70% of cases. Rash was more common in children; thrombocytopenia, hyponatremia, elevated hepatic transaminases, and complications were more frequent in adults. Murine typhus should be considered as a diagnostic possibility in cases of acute febrile illness in southern and even in more northern US states.

CD4+ T Cells Are as Protective as CD8+ T Cells against Rickettsia typhi Infection by Activating Macrophage Bactericidal Activity

Rickettsia typhi is an intracellular bacterium that causes endemic typhus, a febrile disease that can be fatal due to complications including pneumonia, hepatitis and meningoencephalitis, the latter being a regular outcome in T and B cell-deficient C57BL/6 RAG1^-/- mice upon Rickettsia typhi infection. Here, we show that CD4⁺ T_H1 cells that are generated in C57BL/6 mice upon R. typhi infection are as protective as cytotoxic CD8⁺ T cells. CD4⁺- as well as CD8⁺-deficient C57BL/6 survived the infection without showing symptoms of disease at any point in time. Moreover, adoptively transferred CD8⁺ and CD4⁺ immune T cells entered the CNS of C57BL/6 RAG1^-/- mice with advanced infection and both eradicated the bacteria. However, immune CD4⁺ T cells protected only approximately 60% of the animals from death. They induced the expression of iNOS in infiltrating macrophages as well as in resident microglia in the CNS which can contribute to bacterial killing but also accelerate pathology. In vitro immune CD4⁺ T cells inhibited bacterial growth in infected macrophages which was in part mediated by the release of IFNγ. Collectively, our data demonstrate that CD4⁺ T cells are as protective as CD8⁺ T cells against R. typhi, provided that CD4⁺ T_H1 effector cells are present in time to support bactericidal activity of phagocytes via the release of IFNγ and other factors. With regard to vaccination against TG Rickettsiae, our findings suggest that the induction of CD4⁺ T_H1 effector cells is sufficient for protection.

Endemic typhus caused by Rickettsia typhi usually is a relatively mild disease. However, CNS inflammation and neurological symptoms are complications that can occur in severe cases. This outcome of disease is regularly observed in T and B cell-deficient C57BL/6 RAG1^-/- mice upon infection with R. typhi. We show here that CD4⁺ T cells are as protective as cytotoxic CD8⁺ T cells against R. typhi as long as they are present in time. This is evidenced by the fact that neither CD8⁺ nor CD4⁺ T cell-deficient C57BL/6 mice develop disease which is also true for R. typhi-infected C57BL/6 RAG1^-/- mice that receive immune CD8⁺ or CD4⁺ at an early point in time. Moreover, adoptive transfer of immune CD4⁺ T cells still protects approximately 60% of C57BL/6 RAG1^-/- mice when applied later in advanced infection when the bacteria start to rise. Although CD8⁺ T cells are faster and more efficient in bacterial elimination, R. typhi is not detectable in CD4⁺ T cell recipients anymore. We further show that immune CD4⁺ T cells activate bactericidal functions of microglia and macrophages in the CNS in vivo and inhibit bacterial growth in infected macrophages in vitro which is in part mediated by the release of IFNγ. Collectively, we demonstrate for the first time that CD4⁺ T cells alone are sufficient to protect against R. typhi infection. With regard to vaccination our findings suggest that the induction of R. typhi-specific CD4⁺ T_H1 effector T cells may be as effective as the much more difficult targeting of cytotoxic CD8⁺ T cells.

Liver Necrosis and Lethal Systemic Inflammation in a Murine Model of Rickettsia typhi Infection: Role of Neutrophils, Macrophages and NK Cells

Rickettsia (R.) typhi is the causative agent of endemic typhus, an emerging febrile disease that is associated with complications such as pneumonia, encephalitis and liver dysfunction. To elucidate how innate immune mechanisms contribute to defense and pathology we here analyzed R. typhi infection of CB17 SCID mice that are congenic to BALB/c mice but lack adaptive immunity. CB17 SCID mice succumbed to R. typhi infection within 21 days and showed high bacterial load in spleen, brain, lung, and liver. Most evident pathological changes in R. typhi-infected CB17 SCID mice were massive liver necrosis and splenomegaly due to the disproportionate accumulation of neutrophils and macrophages (MΦ). Both neutrophils and MΦ infiltrated the liver and harbored R. typhi. Both cell populations expressed iNOS and produced reactive oxygen species (ROS) and, thus, exhibited an inflammatory and bactericidal phenotype. Surprisingly, depletion of neutrophils completely prevented liver necrosis but neither altered bacterial load nor protected CB17 SCID mice from death. Furthermore, the absence of neutrophils had no impact on the overwhelming systemic inflammatory response in these mice. This response was predominantly driven by activated MΦ and NK cells both of which expressed IFNγ and is considered as the reason of death. Finally, we observed that iNOS expression by MΦ and neutrophils did not correlate with R. typhi uptake in vivo. Moreover, we demonstrate that MΦ hardly respond to R. typhi in vitro. These findings indicate that R. typhi enters MΦ and also neutrophils unrecognized and that activation of these cells is mediated by other mechanisms in the context of tissue damage in vivo.

Evaluation of a new serological test for the detection of anti-Coxiella and anti-Rickettsia antibodies

Coxiella burnetii and members of the genus Rickettsia are obligate intracellular bacteria. Since cultivation of these organisms requires dedicated techniques, their diagnosis usually relies on serological or molecular biology methods. Immunofluorescence is considered the gold standard to detect antibody-reactivity towards these organisms. Here, we assessed the performance of a new automated epifluorescence immunoassay (InoDiag) to detect IgM and IgG against C. burnetii, Rickettsia typhi and Rickettsia conorii. Samples were tested with the InoDiag assay. A total of 213 sera were tested, of which 63 samples from Q fever, 20 from spotted fever rickettsiosis, 6 from murine typhus and 124 controls. InoDiag results were compared to micro-immunofluorescence. For acute Q fever, the sensitivity of phase 2 IgG was only of 30% with a cutoff of 1 arbitrary unit (AU). In patients with acute Q fever with positive IF IgM, sensitivity reached 83% with the same cutoff. Sensitivity for chronic Q fever was 100% whereas sensitivity for past Q fever was 65%. Sensitivity for spotted Mediterranean fever and murine typhus were 91% and 100%, respectively. Both assays exhibited a good specificity in control groups, ranging from 79% in sera from patients with unrelated diseases or EBV positivity to 100% in sera from healthy patients. In conclusion, the InoDiag assay exhibits an excellent performance for the diagnosis of chronic Q fever but a very low IgG sensitivity for acute Q fever likely due to low reactivity of phase 2 antigens present on the glass slide. This defect is partially compensated by the detection of IgM. Because it exhibits a good negative predictive value, the InoDiag assay is valuable to rule out a chronic Q fever. For the diagnosis of rickettsial diseases, the sensitivity of the InoDiag method is similar to conventional immunofluorescence.

[Macrophage activation syndrome: rare complication of murine typhus]

INTRODUCTION

Typhi is one of the rickettsial species endemic in the Mediterranean countries and is associated with the zoonotic infection of murine typhus, which may have a complicated course especially in adult patients. The association with macrophage activation syndrome (MAS) has rarely been reported in the medical literature.

CASE REPORT

We describe a case of murine typhus in a diabetic woman complicated with MAS, who was effectively treated with cyclin and parenteral immunoglobulin.

CONCLUSION

The murine typhus can be exceptionally complicated with SAM. This infection should be suspected in front of the discovery of SAM.

Rapid and Simple Identification ofOrientia tsutsugamushifrom Other Group Rickettsiae by Duplex PCR Assay UsinggroELGene

In this study, two new duplex PCR methods based on the groEL gene were developed and investigated for the diagnosis of rickettsiae. The first duplex PCR assay amplified the 229-bp and the 366-bp DNAs of 6 strains including typhus group (TG) and spotted fever group (SFG) rickettsiae, and 5 scrub typhus group (STG) rickettsiae, respectively. The second duplex PCR assay amplified the 397-bp and the 213-bp DNAs of 6 Rickettsia strains and 5 STG strains. These duplex PCR methods could simultaneously perform the rapid identification of rickettsiae and the differential diagnosis of STG and other group rickettsiae in a single reaction.

Inter- and intra-operator variability in the reading of indirect immunofluorescence assays for the serological diagnosis of scrub typhus and murine typhus

Inter- and intra-observer variation was examined among six microscopists who read 50 scrub typhus (ST) and murine typhus (MT) indirect immunofluorescence assay (IFA) immunoglobulin M (IgM) slides. Inter-observer agreement was moderate (κ = 0.45) for MT and fair (κ = 0.32) for ST, and was significantly correlated with experience (P = 0.03 and P = 0.004, respectively); κ-scores for intra-observer agreement between morning and afternoon readings (range = 0.35–0.86) were not correlated between years of experience for ST and MT IFAs (Spearman's ρ = 0.31, P = 0.54 and P = 0.14, respectively; P = 0.78). Storage at 4°C for 2 days showed a change from positive to negative in 20–32% of slides. Although the titers did not dramatically change after 14 days of storage, the final interpretation (positive to negative) did change in 36–50% of samples, and it, therefore, recommended that slides should be read as soon as possible after processing.

Murine typhus in the homeless

Homeless populations are particularly exposed to many vector-borne diseases because of their poor living conditions. We tested sera from 299 homeless people recruited in 2010 and 2011 in Marseilles, France for antibodies to Rickettsia typhi by microimmunofluorescence using a titer of 1:25 as a cut-off titer, and we confirmed the results by Western blot and cross-adsorption studies. Sixty-three persons (22%) had antibodies against R. typhi. The murine typhus seroprevalence rates have significantly increased in homeless populations between the 2000-2003 and 2010-2011 periods. These findings indicate that the homeless are increasingly exposed to flea-borne murine typhus in Marseilles. One might suggest that multiple strikes of sanitation workers resulting in the increase of waste and construction sites combined with the poor living conditions of the homeless expose this population to rodents and their fleas. Further annual studies are necessary to follow rodent-associated diseases among homeless people in Marseille.

Murine typhus in Caldas, Colombia

In the north of Caldas, Colombia, febrile syndromes with positive Weil-Felix reactions have been reported as Murine typhus to the national health authorities. We used indirect immunofluorescence assay (IFA) of serial paired samples to confirm the diagnosis of murine typhus in 14 of 120 patients with a compatible febrile syndrome.

Murine typhus in children, South Texas

Children from South Texas were evaluated for immunoglobulin G to Rickettsia typhi, the causative agent of murine typhus. Of 513 children, 8.6% of those 1-5 years of age, 13.3% of those 6-11 years of age, and 13.8% of those 12-17 years of age had positive results.

Study on serum transcobalamin II in patients with murine typhus

We measured the serum transcobalamin II in murine typhus- infected patients (n = 16) admitted to the Hospital for Tropical Diseases in 1996-1997, compared with healthy controls (n = 60). The results showed that the transcobalamin II (TCII) and total serum unsaturated vitaminB12 binding capacity (UBBC) in patients with murine typhus (2,126.5 pg/ml, range 1,262-4,568 and 3,771.5 pg/ml, range 1,576-6,763 pg/ml) were statistically significantly higher than normal subjects (987.5 pg/ml, range 678-2,000 pg/ml and 1,402 pg/ml, range 932-2,470 ml) (p<0.001). Serum TCII levels in patients (63%) were elevated during the febrile period and returned to normal post-treatment. These findings suggest that patients with murine typhus had stimulation of reticulo-endothelial system, spleen, mesenteric lymph nodes, liver and skin and then released TCII into the blood circulation. The elevation in TCII may be used for confirming a diagnosis of murine typhus.

Serological evidence of infection with Rickettsia typhi and Rickettsia felis among the human population of Catalonia, in the northeast of Spain

Murine typhus (MT) is a cause of fever of intermediate duration in the south of Spain. Rickettsia typhi has been described as the MT etiological agent. Rickettsia felis produces an infection similar to MT. The aim of the study is to determine their seroprevalence in humans in Catalonia. Antibodies to Rickettsia typhi and Rickettsia felis from 217 serum samples were examined by indirect immunofluorescence assay (IFA). Age, gender, residence area, contact with animals, and occupation were surveyed. Rickettsia typhi and Rickettsia felis seroprevalences were 8.8% and 3.2%, respectively. Rickettsia typhi was present in 7.6% of the samples in urban, 8.5% in semirural, and in 21.4% in rural areas, whereas Rickettsia felis was present in 3.5% in urban, 1.7% in semirural, and 7.1% in rural area. The only statistically significant association observed was that between Rickettsia felis seropositivity and age. Our data seem to indicate the presence of Rickettsia typhi and Rickettsia felis in humans in Catalonia.

A sero-epidemiological study of Rickettsia typhi infection in dogs from Soria province, central Spain

Data relating to Rickettsia typhi infection in Spain are scarce. The seroprevalence of canine infection with this species has now been investigated, in dogs from the central province of Soria. The results of indirect immunofluorescence assays indicated that nine (12.3%) of the 73 dogs checked were carrying antibodies against R. typhi. The gender, age and breed of the dog, and whether it was used for hunting, shepherding, guarding or simply as a pet, apparently had no significant affect on the probability of it being seropositive. Being infested with fleas or having a history of such infestation was, however, significantly associated with seropositivity. The present results confirm that dogs may be infected with R. typhi and indicate their potential usefulness as sentinels in epidemiological studies of the pathogen. The results of wide-scale, serological studies of dogs may allow the geographical distribution of R. typhi to be mapped relatively simply.

Emerging rickettsial infections in Sri Lanka: the pattern in the hilly Central Province

OBJECTIVES

To identify different rickettsial infections using a specific immunofluorescent technique in patients clinically diagnosed as 'typhus fever' in the Central Province of Sri Lanka, and to define the clinical picture, assess the severity of infection and to determine the pattern of geographical distribution of the infections of the hospital-based patients.

METHODS

A specific indirect immunofluorescent antibody technique was used on the sera of two groups of patients in laboratories in Japan and Thailand.

RESULTS

We serodiagnosed infections with Orientia tsutsugamushi, Rickettsia typhi and spotted fever group in 56 of 118 clinically investigated patients. There were eight infections with O. tsutsugamushi, two with R. typhi and 10 spotted fever group patients with IgM antibodies suggestive of acute infection. Nineteen patients had antibodies against these three rickettsial species, suggestive of past exposure, co-infection or cross-reactivity of antigens. Discrete, erythematous maculopapular rash was common to all three types of infection except for five patients who had no rash. Five patients positive for spotted fever antibodies developed fern-leaf type skin necrosis with severe illness. Duration of the febrile period ranged from 4 to 23 days with defervescence occurring after specific antibiotic treatment.

CONCLUSIONS

The study has shown the presence of different types of rickettsial infections in the Central Province of Sri Lanka. The characterization of the clinical picture and the severity of infection provide useful information for the proper management of the patients in the future.

Rickettsial infection in murine models activates an early anti-rickettsial effect mediated by NK cells and associated with production of gamma interferon

Natural killer (NK) cell activity was significantly increased on days 2-6 of infection in the Rickettsia conorii-infected C3H/HeN mice and on day 2 in the Rickettsia typhi-infected C57BL/6 mice. Depletion of NK cell activity utilizing anti-NK1.1 monoclonal antibody enhanced the susceptibility of normally resistant C57BL/6 mice to infection with R. typhi, and depletion of NK cell activity with antibody to asialo GM1 enhanced the susceptibility of C3H/HeN mice to infection with R. conorii. Serum gamma interferon was increased in R. conorii-infected C3H/HeN mice compared with NK cell-depleted, infected mice during the early course of infection. Additionally, the NK cell activating cytokine IL-12 was elevated in the sera of infected mice during the time period representing enhanced NK cell activity compared with uninfected mice. Thus, it appears that NK cells contribute to the early anti-rickettsial immune response, likely via a mechanism involving gamma interferon.

Cloning and sequencing of the gene encoding the candidate HtrA of Rickettsia typhi

We screened a phage library of Rickettsia typhi with a polyclonal antiserum to clone genes which encode immunogenic proteins of R. typhi. Among several clones obtained, one clone codes for a 466-amino-acid protein similar to the heat-shock protein, HtrA. The deduced rickettsial HtrA contains a putative signal peptide sequence at the N-terminus, a serine protease-like domain, and two PDZ domains. The recombinant protein of rickettsial HtrA reacted with sera from patients with murine typhus and tsutsugamushi disease. We suggest that this gene and its recombinant protein would be valuable for the immunologic diagnosis of rickettsial diseases.

Serological differentiation of murine typhus and epidemic typhus using cross-adsorption and Western blotting

Differentiation of murine typhus due to Rickettsia typhi and epidemic typhus due to Rickettsia prowazekii is critical epidemiologically but difficult serologically. Using serological, epidemiological, and clinical criteria, we selected sera from 264 patients with epidemic typhus and from 44 patients with murine typhus among the 29,188 tested sera in our bank. These sera cross-reacted extensively in indirect fluorescent antibody assays (IFAs) against R. typhi and R. prowazekii, as 42% of the sera from patients with epidemic typhus and 34% of the sera from patients with murine typhus exhibited immunoglobulin M (IgM) and/or IgG titers against the homologous antigen (R. prowazekii and R. typhi, respectively) that were more than one dilution higher than those against the heterologous antigen. Serum cross-adsorption studies and Western blotting were performed on sera from 12 selected patients, 5 with murine typhus, 5 with epidemic typhus, and 2 suffering from typhus of undetermined etiology. Differences in IFA titers against R. typhi and R. prowazekii allowed the identification of the etiological agent in 8 of 12 patients. Western blot studies enabled the identification of the etiological agent in six patients. When the results of IFA and Western blot studies were considered in combination, identification of the etiological agent was possible for 10 of 12 patients. Serum cross-adsorption studies enabled the differentiation of the etiological agent in all patients. Our study indicates that when used together, Western blotting and IFA are useful serological tools to differentiate between R. prowazekii and R. typhi exposures. While a cross-adsorption study is the definitive technique to differentiate between infections with these agents, it was necessary in only 2 of 12 cases (16.7%), and the high costs of such a study limit its use.

Short report: prevalence of antibodies against spotted fever, murine typhus, and Q fever rickettsiae in humans living in Zambia

The causative agents of rickettsial diseases (Rickettsia conorii, R. typhi, and Coxiella burnetii) have been reported throughout the African continent. However, there have been no reports on epidemiologic surveys of these infections in Zambia. This study was designed to clarify the prevalence of three rickettsioses in 377 humans in Zambia. The seroprevalence of antibodies against R. conorii, R. typhi, and C. burnetii was 16.7%, 5.0%, and 8.2%, respectively. The rates of antibody positivity against R. conorii and C. burnetii were higher in the eastern (23.1% and 11.8%) and western (16.8% and 7.4%) areas of Zambia than in the northern (3.0% and 3.0%) area of this country. There was little difference among the three areas in the distribution of antibodies against R. typhi. Since cattle breeding is more extensive in the western and eastern areas than in the northern area, it is thought that cattle-breeding areas are foci of R. conorii and C. burnetii infections in Zambia.

Seroepidemiologic survey of Orientia tsutsugamushi, Rickettsia typhi, and TT118 spotted fever group rickettsiae in rubber estate workers in Malaysia

The seroprevalence of Orientia tsutsugamushi, Rickettsia typhi, and TT118 spotted fever group (SFG) rickettsiae in 300 rubber estate workers in Slim River, Malaysia was determined in December 1996 and March 1997. In December, which was the wet season, 23.3%, 3.0%, and 57.3% of the population had antibodies detected against the three rickettsiae, respectively. The highest seropositive rate of 40% was detected for single infection with SFG rickettsiae, followed by a rate of 15.3% for both O. tsutsugamushi and SFG rickettsiae among the rubber estate workers. Subjects less than 21 years old had a lower seroprevalence of SFG rickettsiae compared with the other age groups. Indians had a higher seroprevalence of O. tsutsugamushi compared with other ethnic groups. Rubber tappers had a higher seroprevalence of SFG rickettsiae compared with other occupational groups. During the dry season in March 1997, there was a significant increase in the seroprevalence of R. typhi. The seroconversion rates for IgM against O. tsutsugamushi, R. typhi, and SFG rickettsiae were 5.7%, 12.3%, and 15.1%, respectively, during the four-month period. Significant variations of antibody titers towards the three rickettsiae was noted among subjects who were bled twice. This suggests a significant and continual exposure of rubber estate workers to the three rickettsiae.

Serosurvey of wild rodents for Rickettsioses (spotted fever, murine typhus and Q fever) in Java Island, Indonesia

The prevalence of antibodies against spotted fever group rickettsia (SFGR), murine typhus and Q fever were investigated in wild rats captured in Indonesia. Sera of 327 rats were collected from Jakarta and Boyolali on Java Island. The prevalences of antibodies against SFGR and murine typhus were 128 (39.1%) and 48 (14.7%), respectively. Antibodies against Q fever were not detected in these serum samples. Antibodies against SFGR were found in all species of rats (20.8-51.9%). The antibody positive rate against murine typhus in Rattus norvegicus (38.0%) was significantly higher than that in other rat species (0-4.8%, p<0.01). The antibody positive rates against SFGR and murine typhus in rats captured in Jakarta were significantly higher than those in rats captured in Boyolali (p<0.01). In this survey, all species of rats had antibodies against SFGR, indicating that the 4 species of tested rats (R. norvegicus, R. rattus, R. exulans, R. tiomanicus) were infected with SFGR and that SFGR may infest the whole of Java Island. Most of the rats that were antibody-positive against murine typhus were captured in Jakarta. Therefore, R. norvegicus and R. rattus are likely to be important hosts of murine typhus in Jakarta. The antibody-positive rates against SFGR and murine typhus in rats captured in the dry season were significantly higher than those in rats captured in the rainy season. This may coincide with the active periods of ticks and fleas in Indonesia.

Murine typhus in travelers returning from Indonesia

We report the first three documented cases of murine typhus imported into Europe from Indonesia, discuss clues for the diagnosis of the disease, and urge that murine fever be considered in the diagnosis of febrile disease in travelers.

Seroepidemiology of Rickettsia typhi, spotted fever group rickettsiae, and Coxiella burnetti infection in pregnant women from urban Tanzania

Immunofluorescent antibody (IFA) testing was performed on sera drawn from 150 pregnant women in the port city of Dar es Salaam, Tanzania. Prevalence of antibodies to Rickettsia typhi was 28%, higher than in any of the 12 other African countries in which serosurveys using IFA testing have been performed. Seroprevalence of antibodies to spotted fever group rickettsiae antigens was 25.3%, comparable with that found in other sub-Saharan countries endemic for Amblyomma ticks. Only 4.7% of women were seropositive for Coxiella burnetii.

Prevalence of antibodies to Coxiella burnetti, Rickettsia conorii, and Rickettsia typhi in seven African countries

The prevalences of antibodies reactive with Coxiella burnetti, Rickettsia conorii, and Rickettsia typhi were determined by indirect fluorescent antibody testing of sera from seven African countries. The seroprevalences of antibodies reactive with C. burnetti and R. conorii in countries from North Africa were similar to those reported from southern Europe. In countries of sub-Saharan Africa, the seroprevalence of antibodies reactive with C. burnetti varied greatly; the generally higher figures for West Africa, where stock breeding is prominent, suggested that domestic animals might be the main reservoirs of infection. The prevalence of antibodies to the recently described species Rickettsia africae was higher than that reported for spotted fever-group rickettsiae from elsewhere in the world and paralleled the distribution of Amblyomma species. Western blot results suggested that the antibodies detected were more likely to be reactive with R. africae than with R. conorii, the main vector of which (Rhipicephalus species) rarely feeds on humans. The seroprevalences of antibodies reactive with R. typhi were higher in coastal regions, where Rattus norvegicus--the natural host of the vector Xenopsylla--is more prevalent, than in inland areas.

Serological studies of the antigenic similarity between typhus group rickettsiae and Weil-Felix test antigens

The sera from two patients with murine typhus reacted with whole cells of Rickettsia prowazekii, R. typhi, and Proteus vulgaris OX19, and with lipopolysaccharides (LPS) from the spotted fever group rickettsia strain TT-118 and P. vulgaris OX19 in the enzyme-linked immunosorbent assay. Sera from these patients reacted with ladder-like bands of LPS from R. prowazekii and R. typhi in the immunoblot, whereas the reactivity of these sera with LPS from P. vulgaris OX19 differed from each other. These results indicate that LPS from the typhus group rickettsiae and P. vulgaris OX19 contain similar epitopes.

[Cloning and expression in Escherichia coli of three Rickettsia prowazekii genes, coding outer membrane proteins]

Rickettsia prowazekii (virulent Breinl strain) random genomic DNA fragments were cloned in the lambda gt11 expression vector by using non-palindromic adaptors. Several immunoreactive clones were selected after screening 20,000 individual recombinant plaques with human convalescent serum. Some recombinants synthesized the complete 60 K protein, and others synthesized beta-galactosidase fusion polypeptides containing epitopes of 134 K protein of the R. prowazekii outer membrane. The amplified genomic library was screened with monospecific antibodies directed against abundant 31 K and 29.5 K outer membrane proteins. Several recombinant clones expressing full or part of 29.5 K polypeptide, and none expressing 31 K polypeptide were revealed. The serum of a patient convalescing from epidemic typhus did not react in western blot with recombinant 29.5 K protein.

Murine typhus identified as a major cause of febrile illness in a camp for displaced Khmers in Thailand

Scrub and murine typhus have been identified as causes of illness among the 238,000 displaced Khmer people residing in temporary settlements on the Thai side of the Thai-Cambodian border. Still, the true extent of the problem and the relative frequency of infection with scrub typhus as compared to murine typhus are unknown. We evaluated consecutive patients with unexplained pyrexia (documented fever, no exclusionary diagnosis, and constitutional symptoms) in 1 temporary settlement over 1 month. Laboratory studies included culture of blood and assay of paired sera for rickettsial IgM and IgG antibody, for dengue IgM and IgG antibody, and for leptospiral IgM and IgG antibody. Among 37 patients (27 adults and 10 children), 28 (75%) had a rickettsiosis (26 cases of murine typhus and 2 cases of scrub typhus). No case of enteric fever, dengue, or leptospirosis was diagnosed. The illnesses of 9 patients were not identified. Signs and symptoms did not distinguish confirmed rickettsial infections from undiagnosed illnesses. The 1 month attack rate of rickettsial infection was 29/100,000 for children and 185/100,000 for adults. Murine typhus was a major cause of febrile illness in this settlement.

Serological study of louse borne and flea borne typhus in Addis Ababa

A total of 500 subjects (288 males and 212 females) were tested in Addis Ababa, Ethiopia, in Virology and Rickettsiology Division of the National Research Institute of Health, in 1987, for anti R. prowazekii using Complement Fixation Test (CFT). Out of these 58 subjects (41 males and 17 females) were also tested for anti R. typhi using the same test. The study population included three groups. Group I included 200 patients referred to the National Research Institute of Health (NRIH) for the Weil-Felix test for the diagnosis of typhus. Group II consisted of 200 patients with febrile illness visiting the Outpatient Department (OPD) of St. Paul's Hospital. Group III included 100 blood donors' serum samples included from previous collections. The blood donors had no sign of febrile illness during the collection of the blood samples. The results showed that anti R. prowazekii was detected in 38 subjects (7.6%). The sex ratio among the positive subjects indicated that there were 32 males (22%) and 6 females (2.8%). From the 58 subjects who were also tested for anti R-typhi only 7 (5 males and 2 females) (12%) were found to be positive. Only one person was found to be positive both for anti R. prowazekii and anti R-typhi. From 200 samples (Group-I) tested both by the Weil-Felix test and by Complement Fixation Test for anti R. prowazekii only 4 samples were positive by both test, thus showing very low percent agreement.(ABSTRACT TRUNCATED AT 250 WORDS)

Newborn rats in the murine typhus enzootic infection cycle: studies on transplacental infection and passively acquired maternal antirickettsial antibodies

This study focused attention on the newborn rat as a possible significant participant in the highly successful enzootic cycle of murine typhus. We examined the influence of maternal Rickettsia typhi (R. mooseri) infection in rats on the offspring with respect to the possible vertical transmission of R. typhi and the passive transfer of maternal antirickettsial antibodies. Transmission of R. typhi by rickettsemic pregnant rats did not occur either transplacentally during gestation to their fetuses or postnatally through colostrum and milk to their newborn. The rickettsial burden of the placenta was sometimes greater than 10(6) plaque forming units per g tissue and undetectable in colostrum or milk. However, newborn rats were highly susceptible to infection per os. Transplacental passage of antirickettsial antibody to offspring was detectable only when the mother's antibody titer was high. Passive postpartum acquisition of antirickettsial antibodies by newborn rats from colostrum and milk of immune mothers occurred regardless of the height of the maternal antibody titer, rose to a maximum at about 3 weeks of age, and then declined rapidly, becoming undetectable 4 weeks after birth.

Suppression of Rickettsia typhi transmission in fleas maintained on murine typhus-immune rats

The presence of host antibodies against Rickettsia typhi in the hemolymph of Xenopsylla cheopis fed on immune rats was studied using an indirect immunofluorescent antibody (IFA) test and enzyme-linked immunosorbent assay (ELISA). The time course experiment revealed that antibody to R. typhi appears in the flea hemolymph after 18 hr exposure to host and persists for 24 hr. IFA tests utilizing specific antisera to rat IgG (Fc) and rat IgG (Fab) fragments, indicate that some unaltered rat IgG to R. typhi were present in the hemolymph of immune fed fleas. Host antibody to R. typhi was detected on the surface of the rickettsiae in the flea hemolymph and gut contents by IFA. Maintenance of infected fleas on immune host had no significant effect on the establishment and subsequent growth of rickettsiae within the fleas. However, 19-22 day infected fleas maintained on immune hosts failed to transmit R. typhi to baby rats.

Serologic evidence of acute murine typhus infection in a patient with culture-negative endocarditis

A patient with culture-negative infective endocarditis is presented in whom detailed serological studies were indicative of acute infection with murine typhus. The patient had aortic and mitral regurgitation with congestive heart failure and typical peripheral manifestations of subacute endocarditis, but no documented fever. Aortic and mitral valve replacement surgery and a 6-week course of doxycycline therapy produced a clinical cure in this patient, as well as a diagnostic fall in markedly elevated preoperative typhus indirect fluorescent antibody (IFA) and complement fixation (CF) titers. Serological studies were consistently negative for Q fever.

Human T helper cells specific for antigens of typhus group rickettsiae enhance natural killer cell activity in vitro

The peripheral blood mononuclear cells (PBMC) from 5 individuals immune to typhus group rickettsiae and from 13 nonimmune individuals were stimulated in vitro for 7 days with typhus group rickettsial antigen (TGRA). At the end of day 7, lysis of the natural killer (NK)-susceptible target K562 by these PBMC was determined. As controls, PBMC from both groups of donors were cultured in vitro for 7 days without antigen or were freshly isolated, and lysis of the K562 target was determined. There was no significant difference between the level of NK activity in freshly isolated PBMC from immune and nonimmune donors. PBMC from immune donors which were stimulated with antigen for 7 days exhibited significantly greater NK activity than did the control population, which was cultured for 7 days without antigen. PBMC from immune donors which were stimulated with TGRA demonstrated significantly higher NK activity than the same PBMC stimulated with antigen derived from an antigenically unrelated rickettsia, Coxiella burnetii. There was no significant difference, however, in the level of NK activity of nonimmune antigen-stimulated PBMC compared with that of the same PBMC population cultured without antigen. Most of the antigen-stimulated NK activity was mediated by Leu-11-positive cells as determined by electronic cell sorting. The ability of TGRA to sustain the NK activity of PBMC from immune donors was abolished when the T4/Leu-3-positive population of lymphocytes was eliminated by positive or negative selection prior to antigen stimulation. The ability of TGRA to sustain the NK activity of PBMC from immune donors was also significantly decreased in the presence of antibodies against human interleukin-2. The results suggest that the activity of human NK cells can be sustained in vitro by antigen-specific T helper cells and that the effect of the T helper cell is mediated, at least in part, by interleukin-2.

Characterization of human cytotoxic lymphocytes directed against cells infected with typhus group rickettsiae: evidence for lymphokine activation of effectors

An in vitro culture and assay system was used to determine whether cytotoxic lymphocytes are generated in humans after rickettsial infection. Peripheral blood mononuclear cells (PBMC) were obtained from six individuals with serologic evidence of prior infection with typhus group rickettsiae and from six nonimmune individuals. After PBMC from immune individuals were stimulated in vitro for 7 days with rickettsial antigen, they were capable of lysing typhus group rickettsia-infected, autologous phytohemagglutinin (PHA)-induced blasts, but not uninfected PHA-blasts. No cytotoxic effector cells were generated when either PBMC from immune individuals were placed in culture for 7 days without antigenic stimulation, or when PBMC from nonimmune individuals were stimulated in vitro with antigen for 7 days. Freshly isolated PBMC from immune donors were also unable to lyse typhus group rickettsia-infected autologous PHA-blasts or an autologous rickettsia-infected lymphoblastoid cell line (LCL). Neither supernatants from antigen-stimulated cultures of PBMC from immune donors nor recombinant human interferon-gamma were capable of significantly lysing typhus group rickettsia-infected PHA blasts by this assay. Populations of cytotoxic effector cells depleted of OKT3, OKT4, or OKT8-positive cells by treatment with the respective monoclonal antibodies and complement were assayed for their cytotoxic capacity. The results suggest that the cytotoxic effector cell population is predominantly OKT3 and OKT8-positive, but OKT4-negative. Positive selection with the use of a fluorescence-activated cell sorter also suggested that most of the cytotoxic effector cells are OKT8-positive. PBMC from immune donors after in vitro stimulation with rickettsial antigen were capable of significantly lysing infected autologous LCL or infected HLA-mismatched LCL as compared with the respective uninfected controls. In addition, PBMC from either immune donors or nonimmune donors after stimulation in vitro for 7 days with media containing purified lymphokines were capable of significantly lysing autologous infected LCL as compared with the uninfected autologous control. We conclude that lysis of cells infected with typhus group rickettsiae is mediated by a lymphokine-activated killer.

Mechanisms of immunity to rickettsial infection: characterization of a cytotoxic effector cell

Rickettsiae, as other intracellular bacteria, are relatively sequestered from the effects of antibody and local antibody-independent responses. Considering the obligate intracellular nature of rickettsia, the exact mechanisms by which lymphocytes and macrophages encounter rickettsial antigens and eliminate the infection depends upon the appropriate presentation of antigen to the immune system. We demonstrate here that cells taken from the spleens of Rickettsia typhi- or R. tsutsugamushi-infected mice are able to lyse specifically tissue culture targets infected with the homologous organism. This effect was eliminated upon treatment of the spleen cells with anti-Thy-1.2 + complement. Furthermore such T cells exhibit H-2-restricted killing when tested on infected targets of different genetic backgrounds. We propose that a T cell-mediated cytotoxic immune mechanism exists that may play an important role in the elimination of rickettsial organisms during infection.

[Immunogenicity of a chemical typhus vaccine and of a corpuscular radioantigen obtained from Rickettsia prowazekii]

The protective activity of chemical typhus vaccine and R. prowazekii corpuscular radioantigen (CRA) was studied. Guinea pigs were immunized with doses of 32 and 48 antigenic units. Antibody production was assayed in the complement fixation test. On days 7, 15, 21, 30 and 60 after immunization the animals were challenged with R. prowazekii introduced in an amount of 10(5) minimum embryonal infective doses (MEID). On day 30 some of the animals were challenged with 10(3) MEID of R. typhi. The results demonstrated that both preparations were highly immunogenic and capable of protecting most of the animals from 10(5) MEID of R. prowazekii. Immunity developed earlier after immunization with CRA. The guinea pigs immunized with CRA, purified in percoll density gradient, and challenged with 10(3) MEID of R. typhi on day 30 showed a high level of cross immunity. In all control animals high fever and periorchitis were observed.

Experimental infection with Rickettsia mooseri and antibody response of adult and newborn laboratory rats

Quantitative studies of selected features of peripherally induced Rickettsia mooseri (= R. typhi) infection in Rattus norvegicus-derived white laboratory rats revealed a unique association between microbe and amplifying vertebrate host which appears to be especially conducive to maintenance of the enzootic cycle. Both adult and newborn (1-3 days old) rats were highly susceptible to percutaneous infection (ID50 = approximately 1 organism), but neither showed signs of disease or died even when inoculated with 10(4)-10(5) plaque-forming units. Gain in body weight of infected newborn rats was indistinguishable from that of uninfected newborn rats over the first 3 weeks of life. The course of the systemic infection, as measured by the rise and fall of R. mooseri titers in blood, brain and kidney and the serum antibody response, was almost identical in adult and newborn rats. Thus, despite their immaturity in certain immunological processes, newborn rats controlled postnatal R. mooseri infection about as well as did adult rats. The rickettsemic period of about 10 days corresponds to the period of infectivity of inoculated rats for fleas. Rickettsiae were not isolated from blood, brain or kidneys by methods employed for more than 4-5 weeks after infection. Serum antirickettsial antibodies persisted for at least 60 weeks postinfection, i.e., longer than the usual life span of rats in nature and, hence, are a valid measure of the cumulative experience of rat populations with R. mooseri infection.

Sensitization of mice to rickettsial toxin by Coxiella burnetii

Intraperitoneal (ip.) inoculation with live or killed Coxiella burnetii (C.b.) rendered mice more sensitive to intravenous (iv.) administration of a toxic live suspension of Rickettsia typhi. Sensitization of mice by live and killed C.b. was time-and dose-dependent. Killed phase I and phase II C.b. cells possessed a similar degree of sensitization, which was increased slightly by their preincubation with corresponding immune sera. Lipopolysaccharide (LPS)-protein complex extracted from phase I C.b. cells exerted lower sensitization than whole phase I C.b. cells, and chloroform-methanol (CM) treatment of phase I C.b. cells reduced markedly their sensitizing effect. No toxic effect was observed either in C.b.-inoculated or in control mice upon i.v. administration of a heated R. typhi suspension. Specificity of rickettsial toxicity was demonstrated by its distinct reduction both in control and C.b.-inoculated mice after preincubation of R. typhi suspension with immune anti-R. typhi mouse serum.

Characteristics of lymphoid cells that adoptively transfer immunity to Rickettsia mooseri infection in mice

The capacity of adoptively transferred immune lymphoid cells or passively transferred immune serum to alter the course of an established Rickettsia mooseri (R. typhi) infection in the spleen was evaluated in BALB/c mice. Immune cells, but not immune serum, controlled the established infection. An effective lymphocyte was a T-cell which had to possess a capacity to divide.

Murine and epidemic typhus rickettsiae: how close is their relationship?

Typhus fever has occurred globally as epidemic and endemic disorders. In 1910, Brill reported a typhus-like illness which Zinsser and others determined to be recurrent epidemic typhus fever. Maxcy, in 1926, proposed rodents and fleas as reservoir and vector, respectively, of endemic typhus, which Dyer confirmed in 1930. Animals experimentally infected with epidemic typhus (Rickettsia prowazeki) are immune to murine typhus (Rickettsia typhi) and vice versa. Similar solid cross-immunity exists for humans. The two diseases are clinically similar in pathologic and serologic reactions. Human epidemic typhus presumably involved a man-louse-man cycle without an animal reservoir. This concept is now questioned. Antibodies to R. prowazeki have been reported in livestock in Africa, rats in Manila, and from flying squirrels and humans in the United States. R. prowazeki was recovered from blood specimens of goats, sheep, from ixodid ticks, louse, and flea-ectoparasites of flying squirrels, and tissues of flying squirrels. More than 20 cases of squirrel-related acute epidemic typhus have been reported in the United States. R. prowazeki has not been recovered from human cases. Chemical studies of R. prowazeki and R. typhi show genetic similarities but differences in genome size and degree of hybridization suggest that interconversions between the two agents do not occur rapidly in nature. It is proposed that, with time, their relatedness will become even closer.

Mechanisms of immunity in typhus infection: analysis of immunity to Rickettsia mooseri infection of guinea pigs

To study the mechanisms of immunity to Rickettsia mooseri (R. typhi) infection, sera and splenic cells collected from nonimmune and immune guinea pigs were inoculated separately into syngeneic nonimmune recipients which were subsequently challenged intradermally. Protection was measured by comparing the course of the challenge infections of recipients with infections initiated with the same rickettsial inocula in nonimmune animals. Recipients of splenic cells collected 21 days after donor infection were protected from lesion development at sites of intradermal challenge and showed fewer rickettsiae in their kidneys. Cells obtained from nonimmune donors did not protect against either skin lesion development at sites of challenge or kidney infection. Antibody-containing sera collected 21 days after donor infection, but not normal sera, reduced levels of kidney infection, but immune sera did not protect against the development of lesions at sites of intradermal challenge. It was concluded that both immune sera and immune splenic cells possess capacities to effect a partial control of the systemic phase of R. mooseri infection in guinea pigs, but that immune splenic cells possess a capacity not shared by immune sera, i.e., the capacity to protect from infection at local sites of intradermal inoculation.

In vitro stimulation of human peripheral blood lymphocytes by soluble and membrane fractions of renografin-purified typhus group rickettsiae

Cell-free extracts of disrupted Renografin-purified Rickettsia typhi and R. prowazekii were evaluated as antigens in lymphocyte transformation assays for cell-mediated immunity to typhus group rickettsiae in 19 individuals with and 9 without histories of exposure to these organisms. Exposure consisted of clinical disease, vaccination with epidemic typhus vaccine, or occupational exposure to these agents. Both the soluble and membrane fractions of disrupted purified rickettsiae were used, and transformation of peripheral blood lymphocytes (PBL) was determined in microcultures by incorporation of [(3)]thymidine. Of the antigen concentrations tested (1 to 400 mug/ml), 10mug/ml appeared to be the most satisfactory. At this concentration, PBL transformation was highly reproducible and correlated well with donor exposure and the presence of enzyme-linked immunosorbent assay anti-typhus group immunoglobulin G. At higher concentrations, PBL from both exposed and control donors often responded to a lipopolysaccharide-like component present in these preparations. Specific transformation responses to rickettsial fractions were detected in several individuals decades after infection or vaccination, indicating that both fractions contained antigens associated with persisting cell-mediated immunity in humans. Generally, stimulation indexes with the soluble fraction were slightly greater than those obtained with corresponding concentrations of the membrane preparation, and in three individuals transformation was observed only with the soluble fraction. PBL transformation to soluble fractions also appeared to have some species specificity, since PBL from individuals with documented R. typhi infections were more responsive to the homologous soluble preparation than to the soluble fraction of R. prowazekii. PBL transformation also correlated well with homologous but only poorly with heterologous enzyme-linked immunosorbent assay immunoglobulin G titers.

[3Autochthonous cases of murine typhus in France?]

Three men native from Northern Africa, aged more than 40 years, but by their profession in France with narrow contacts to rats, present clinical signs of typhus. Serology (FCT and FAT) gives positive results with R. prowazeki and R. typhi which have a strait antigenic community. Following assays of absorption of the sera by the two antigens and light differences of titers we conclude that two cases are Brill-Zinsser illnesses, but one is really an autochtone case of murin typhus. The last affirmation is confirmed by the detection of specific IgM-antibodies.

Mechanisms of immunity in typhus infection: adoptive transfer of immunity to Rickettsia mooseri

When nonimmune guinea pigs are inoculated intradermally (i.d.) with Rickettsia mooseri (R. typhi), the rickettsiae replicate at the site of inoculation, leading to the development of a grossly observable lesion. In contrast, guinea pigs which have recovered from R. mooseri infection are resistant to challenge and prevent both rickettsial growth and the formation of lesions. To study the mechanisms of this immunity, sera or splenic cells collected from nonimmune or immune guinea pigs were inoculated separetely into nonimmune recipients. Splenic cells collected from immune donors protected R. mooseri-naive recipients from i.d. challenge as measured by control of rickettsial growth and by prevention of development of lesions at i.d. sites of inoculation. In contrast, serum from immune and nonimmune doners failed to protect nonimmune recipients by either criterion.