Case report: fatal seronegative rickettsial infection diagnosed by the polymerase chain reaction

Utility of ultra-rapid real-time PCR for detection and prevalence of Rickettsia spp. in ticks

Background

Rickettsia spp. are important tick-borne pathogens that cause various human and animal diseases worldwide. A tool for rapid and accurate detection of the pathogens from its vectors is necessary for prevention of Rickettsioses propagation in humans and animals, which are infested by ticks. Therefore, this study was conducted to evaluate a molecular tool, ultra-rapid real-time PCR (UR-qPCR), for rapid and accurate detection of Rickettsia spp. from 5644 ticks in 408 pools collected from livestock and their surrounding environments in Gangwon and Jeju province in South Korea.

Results

The UR-qPCR of Rickettsia DNA showed a limit of detection of 2.72 × 10¹ copies of Rickettsia DNA and no cross reaction with other tick-borne pathogens, namely Anaplasma phagocytophilum, Ehrlichia chaffeensis, E. canis, Toxoplasma gondii, and Borrelia burgdorferi. In addition, the PCR assay also showed possibility of various Rickettsia species detection including R. monacensis, “Candidatus R. longicornii”, R. japonica, R. roultii, and R. tamurae. The collected ticks were identified with major species belonged to Haemaphysalis longicornis (81.62%), followed by H. flava (15.19%), and Ixodes nipponensis (3.19%). Rickettsia detection from tick samples using the UR-qPCR showed that the minimum infection rate (MIR) of Rickettsia in collected ticks was 1.24‰ and that all positive pools contained H. longicornis, equal to the MIR of 1.39‰ of this species. Additionally, MIR of Rickettsia spp. detected in ticks collected in Gangwon and Jeju was 1.53‰ and 0.84‰, respectively. Furthermore, the sequencing results of the 17 kDa protein antigen gene and ompA gene showed that Rickettsia spp. sequences from all pools were related to “Candidatus R. longicornii” and “Candidatus R. jingxinensis”.

Conclusions

The UR-qPCR system was demonstrated to be useful tool for accurate and rapid detection of Rickettsia from its vector, ixodid ticks, within 20 min. The data on Rickettsia spp. in ticks detected in this study provide useful information on the distribution of Rickettsia in previously unstudied Korean provinces, which are important for the prevention and control of the spread of rickettsioses in both animals and humans in the country.

Current tools for the diagnosis and detection of spotted fever group Rickettsia

Spotted fever group (SFG) rickettsiae causes a number of diseases in humans worldwide, which can range from mild to highly lethal. Since the clinical presentations of rickettsioses caused by SFG rickettsiae are variable and may be similar to the diseases caused by other rickettsiae, such as Orientia tsutsugamushi (agent for scrub typhus), Coxiella burnetii (agent for Q fever) and the typhus group rickettsiae (agents for epidemic and murine typhus), the accurate diagnosis of infections caused by SFG Rickettsia remains challenging especially in resource-poor settings in developing countries. This review summarizes the various diagnostic and detection tools that are currently available for the confirmation of infections by SFG rickettsiae. The advantages and challenges pertaining to the different serological and molecular detections methods, as well as new assays in development, are discussed. The utility of the detection tools contributing to the surveillance of SFG rickettsiae in arthropods and animals are reviewed.

Israeli Spotted Fever in Sicily. Description of two cases and minireview

Mediterranean spotted fever (MSF) is endemic in Italy, where Rickettsia conorii subsp. conorii was thought to be the only pathogenic rickettsia and Rhipicephalus sanguineus the vector and main reservoir. R. conorii subsp. israelensis, which belongs to the R. conorii complex, is the agent of Israeli spotted fever (ISF); apart from Israel, it has also been found in Italy (Sicily and Sardinia) and in different regions of Portugal. We describe here two severe cases of ISF which occurred in otherwise healthy Italian adults. Their characteristics are analyzed and discussed in the light of other 91 cases found through a systematic review of international literature.

Strategies for detecting rickettsiae and diagnosing rickettsial diseases

Rickettsial diseases and scrub typhus constitute a group of the oldest known vector-borne diseases. The cosmopolitan distribution of the vectors that transmit rickettsiae and orientiae leads to a worldwide prevalence of these diseases. Despite their significant historical status, detection and diagnosis of these diseases are still evolving today. Serological methods remain among the most prevalent techniques used for the detection/diagnosis of rickettsial diseases and scrub typhus. Molecular techniques have been instrumental in increasing the sensitivity/specificity of diagnosis, identifying new Rickettsia and Orientia species and have enhanced epidemiological capabilities when used in combination with serological methods. In this review, we discuss these techniques and their associated pros and cons.

Fatal Rickettsia conorii subsp. israelensis infection, Israel

Underdiagnosis of fatal spotted fever may be attributed to nonspecific clinical features and insensitive acute-phase serologic studies. We describe the importance of molecular and immunohistochemical methods in establishing the postmortem diagnosis of locally acquired Israeli spotted fever due to Rickettsia conorii subsp. israelensis in a traveler returning to Israel from India.

Fatal Israeli spotted fever in a UK traveler to South Portugal

A 63-year-old previously healthy woman developed a severe systemic infection 5 days after returning from a holiday to Southern Portugal. She subsequently died, and polymerase chain reaction of a blood sample was positive for Rickettsia conorii ssp israeliensis. The prevalence of severe forms of this illness in the Mediterranean Basin is discussed.