Rickettsial infections--a threat to travellers?

Diagnosis of Spotted Fever Group Rickettsioses in U.S. Travelers Returning from Africa, 2007-2016

Spotted fever group rickettsioses (SFGRs), such as African tick bite fever (ATBF), are among the most commonly diagnosed diseases for ill travelers returning from southern Africa. We summarized demographic, clinical, and diagnostic features of imported SFGR cases in U.S. travelers returning from Africa who had laboratory specimens submitted to the Centers for Disease Control and Prevention. Diagnosis of SFGR was performed by indirect immunofluorescence antibody assay, immunohistochemical staining, polymerase chain reaction (PCR), or culture. Cases were defined as probable SFGR, confirmed SFGR, or confirmed ATBF. Clinical and epidemiological categorical variables were described as counts and proportions; continuous variables were described using geometric mean titers, median, and range. One hundred and twenty-seven patients satisfied laboratory criteria for confirmed or probable SFGR. Fever was the most common symptom (N = 88; 69%), followed by ≥ 1 eschars (N = 70; 55%). Paired serums were submitted for 36 patients (28%); 12 patients (33%) had nonreactive initial serum sample but converted to a titer ≥ 64 with the convalescent sample. Twenty-seven patients (21%) had infection with Rickettsia africae based on PCR analysis of eschar swab (N = 8) or biopsy (N = 23). Fifteen patients had eschar biopsy or swab samples and serum sample(s) submitted together; 9 (60%) had PCR-positive eschar results and nonreactive acute serology. Health-care providers should consider SFGR when evaluating patients for a febrile illness with eschar and compatible foreign travel history. Polymerase chain reaction testing of eschar biopsies or swabs provides a confirmed diagnosis in early stages of disease; eschar swabs or biopsies are an underutilized diagnostic technique.

Severe interstitial pneumonia due to murine typhus in a patient returning from Bali

Murine typhus has been increasingly reported as a cause of fever in returning travelers from Southeast Asia. We report a case of a previously healthy traveler returning from Bali with an non-specific febrile illness which quickly progressed to a severe form of interstitial pneumonia. After a careful epidemiological evaluation and laboratory analysis, murine typhus was diagnosed.

Development of Recombinase Polymerase Amplification Assays for Detection of Orientia tsutsugamushi or Rickettsia typhi

Sensitive, specific and rapid diagnostic tests for the detection of Orientia tsutsugamushi (O. tsutsugamushi) and Rickettsia typhi (R. typhi), the causative agents of scrub typhus and murine typhus, respectively, are necessary to accurately and promptly diagnose patients and ensure that they receive proper treatment. Recombinase polymerase amplification (RPA) assays using a lateral flow test (RPA-nfo) and real-time fluorescent detection (RPA-exo) were developed targeting the 47-kDa gene of O. tsutsugamushi or 17 kDa gene of R. typhi. The RPA assay was capable of detecting O. tsutsugamushi or R. typhi at levels comparable to that of the quantitative PCR method. Both the RPA-nfo and RPA-exo methods performed similarly with regards to sensitivity when detecting the 17 kDa gene of R. typhi. On the contrary, RPA-exo performed better than RPA-nfo in detecting the 47 kDa gene of O. tsutsugamushi. The clinical performance of the O. tsutsugamushi RPA assay was evaluated using either human patient samples or infected mouse samples. Eight out of ten PCR confirmed positives were determined positive by RPA, and all PCR confirmed negative samples were negative by RPA. Similar results were obtained for R. typhi spiked patient sera. The assays were able to differentiate O. tsutsugamushi and R. typhi from other phylogenetically related bacteria as well as mouse and human DNA. Furthermore, the RPA-nfo reaction was completed in 20 minutes at 37^oC followed by a 10 minute incubation at room temperature for development of an immunochromatographic strip. The RPA-exo reaction was completed in 20 minutes at 39^oC. The implementation of a cross contamination proof cassette to detect the RPA-nfo fluorescent amplicons provided an alternative to regular lateral flow detection strips, which are more prone to cross contamination. The RPA assays provide a highly time-efficient, sensitive and specific alternative to other methods for diagnosing scrub typhus or murine typhus.

Historically, rickettsial pathogens are among the leading causes of morbidity and mortality during military operations. Rickettsial diseases, lately, are reemerging in areas of known abundance or emerging in areas of unknown existence, posing a significant medical concern for local residents and travelers. The diseases are difficult to diagnose as they often share similar symptoms with many other diseases in the same geographical areas. Therefore, it is particularly challenging for clinicians to provide a timely and accurate diagnosis. A recombinase polymerase amplification (RPA)-based nucleic acid detection platform has been used to develop accurate, sensitive, specific, and easy-to-perform assays to detect O. tsutsugamushi or R. typhi, indicative of scrub typhus or murine typhus, respectively. These RPA assays provide similar limits of detection and specificity to that of qPCR. Unlike qPCR, they require no thermocycler and provide multiple end-point monitoring options amendable to different laboratory capabilities. This work presents an alternative assay platform for early detection of O. tsutsugamushi or R. typhi infection so that timely treatment can be prescribed in well-equipped laboratories as well as resource limited areas.

Development of new, broadly reactive, rapid IgG and IgM lateral flow assays for diagnosis of scrub typhus

We evaluated the diagnostic accuracy of two broadly reactive rapid immunochromatographic tests (ICTs) for detection of IgM and IgG against Orientia tsutsugamushi by using archived acute-phase serum samples from 102 patients with laboratory-confirmed scrub typhus, and from 62 archived serum samples from patients with other causes of fever as a negative control. These ICTs were constructed by using a mixture of recombinant proteins: 1) C1, a chimeric protein containing epitopes of the 56-kD antigen from Karp and TA763 strains; 2) Ktr56; and 3) Gmr56. Sensitivities of the ICTs for detection of IgM and IgG were 90.2% (95% confidence interval [CI] = 84.4-96.0%) and 86.3% (95% CI = 80.9-93.8%), respectively. Specificities were 85.5% (95% CI = 73.9-92.2%) and 96.8% (95% CI = 90.3-100%), respectively. Both assays were more sensitive and specific than the standard immune immunofluorescence assay for the early diagnosis of scrub typhus.

Murine typhus as a cause of Fever in travelers from Tunisia and mediterranean areas

BACKGROUND

Travelers are exposed to a variety of health risks in unfamiliar environments and fever is a common problem in patients returning from travel abroad. Rickettsial diseases are increasingly frequently being reported among international travelers. Here we present cases of Rickettsia typhi infection, the agent of murine typhus, that were identified in our laboratory the last year, in travelers from Tunisia.

METHODS

For each patient we tested an acute-phase serum sample and for one patient we tested a convalescent-phase serum sample. IgG and IgM antibody titers were estimated with use of the microimmunofluorescence (MIF) assay. Western blot (WB) assay was performed for all the patients.

RESULTS

We identified three cases of murine typhus after a travel in Tunisia. All cases were observed during late summer and early autumn and patients were suffering by persistent fever. None of them presented rash or inoculation eschar. MIF was positive for Rickettsia sp. in the acute-phase serum samples of two patients. In one patient, two acute-phase serum samples were Rickettsia sp. negative whereas a third convalescent-phase serum sample that was obtained 2 weeks after was Rickettsia sp. positive. By WB assay we identified infection by R typhi. A treatment was immediately started and patients became apyretic.

CONCLUSIONS

In the countries of North Europe, although autochthones cases of murine typhus have not been described, sporadic cases of R typhi infection are identified in travelers who visited murine typhus endemic areas. Murine typhus should be considered in the diagnosis of febrile illness without rash in travelers returning from disease endemic areas, like the south Mediterranean area.

Spotted fever rickettsiosis infection in a traveler from Sri Lanka

A case is reported of travel-acquired tick-borne spotted fever rickettsiosis from Sri Lanka. Little is known about rickettsial disease in Sri Lanka and this case may be the first documented instance of travel-acquired spotted fever group rickettsiosis from that origin.

Questions on Mediterranean spotted fever a century after its discovery

Mediterranean spotted fever (MSF) was first described in 1910. Twenty years later, it was recognized as a rickettsial disease transmitted by the brown dog tick. In contrast to Rocky Mountain spotted fever (RMSF), MSF was thought to be a benign disease; however, the first severe case that resulted in death was reported in France in the 1980s. We have noted important changes in the epidemiology of MSF in the last 10 years, with emergence and reemergence of MSF in several countries. Advanced molecular tools have allowed Rickettsia conorii conorii to be classified as a subspecies of R. conorii. New clinical features, such as multiple eschars, have been recently reported. Moreover, MSF has become more severe than RMSF; the mortality rate was as high as 32% in Portugal in 1997. Whether Rhipicephalus sanguineus is the only vector and reservoir for R. conorii conorii is a question not yet answered.

Doxycycline versus azithromycin for treatment of leptospirosis and scrub typhus

Leptospirosis and scrub typhus are important causes of acute fever in Southeast Asia. Options for empirical therapy include doxycycline and azithromycin, but it is unclear whether their efficacies are equivalent. We conducted a multicenter, open, randomized controlled trial with adult patients presenting with acute fever (<15 days), without an obvious focus of infection, at four hospitals in Thailand between July 2003 and January 2005. Patients were randomly allocated to receive either a 7-day course of doxycycline or a 3-day course of azithromycin. The cure rate, fever clearance time, and adverse drug events were compared between the two study groups. A total of 296 patients were enrolled in the study. The cause of acute fever was determined for 151 patients (51%): 69 patients (23.3%) had leptospirosis; 57 patients (19.3%) had scrub typhus; 14 patients (4.7%) had murine typhus; and 11 patients (3.7%) had evidence of both leptospirosis and a rickettsial infection. The efficacy of azithromycin was not inferior to that of doxycycline for the treatment of both leptospirosis and scrub typhus, with comparable fever clearance times in the two treatment arms. Adverse events occurred more frequently in the doxycycline group than in the azithromycin group (27.6% and 10.6%, respectively; P = 0.02). In conclusion, doxycycline is an affordable and effective choice for the treatment of both leptospirosis and scrub typhus. Azithromycin was better tolerated than doxycycline but is more expensive and less readily available.

Scrub typhus imported to Scandinavia

We present the first 3 cases of confirmed scrub typhus imported to Scandinavia. The patients were infected in Thailand, Laos and Sri Lanka, respectively. Treatment with ciprofloxacin and doxycycline lead to rapid cure in 2 of the patients, while the third patient, who was not treated, had a prolonged convalescence. Specific antibodies against Orientia tsutsugamushi, the causative agent of scrub typhus, were detected in all 3 cases.

Threats to international travellers posed by tick-borne diseases

To date, 14 tick-borne diseases have been reported in international travellers, the majority of cases being Lyme borreliosis caused by Borrelia burgdorferi sensu lato in North America and Eurasia, African tick bite fever caused by Rickettsia africae in sub-Saharan Africa and eastern Caribbean, and Central European encephalitis caused by tick-borne encephalitis virus in Europe. The clinical presentation is frequently non-specific, and tick-borne diseases should always, in the absence of other likely diagnoses, be suspected in travellers with flu-like symptoms following a recent visit to tick-infested areas. Feasible microbiological diagnostic tests are widely unavailable, at least outside areas of endemicity where many infected travellers present. Empiric treatment with doxycycline should be considered in suspected cases of tick-borne bacterial diseases. Since ecotourism and adventure travel are increasingly popular worldwide, the incidence of travel-associated tick-borne diseases is likely to increase in the future.