Antibiotic treatment of rickettsiosis, recent advances and current concepts

Neurotransmitter System-Targeting Drugs Antagonize Growth of the Q Fever Agent, Coxiella burnetii, in Human Cells

Coxiella burnetii is a highly infectious, intracellular, Gram-negative bacterial pathogen that causes human Q fever, an acute flu-like illness that can progress to chronic endocarditis. C. burnetii is transmitted to humans via aerosols and has long been considered a potential biological warfare agent. Although antibiotics, such as doxycycline, effectively treat acute Q fever, a recently identified antibiotic-resistant strain demonstrates the ability of C. burnetii to resist traditional antimicrobials, and chronic disease is extremely difficult to treat with current options. These findings highlight the need for new Q fever therapeutics, and repurposed drugs that target eukaryotic functions to prevent bacterial replication are of increasing interest in infectious disease. To identify this class of anti-C. burnetii therapeutics, we screened a library of 727 FDA-approved or late-stage clinical trial compounds using a human macrophage-like cell model of infection. Eighty-eight compounds inhibited bacterial replication, including known antibiotics, antipsychotic or antidepressant treatments, antihistamines, and several additional compounds used to treat a variety of conditions. The majority of identified anti-C. burnetii compounds target host neurotransmitter system components. Serotoninergic, dopaminergic, and adrenergic components are among the most highly represented targets and potentially regulate macrophage activation, cytokine production, and autophagy. Overall, our screen identified multiple host-directed compounds that can be pursued for potential use as anti-C. burnetii drugs.

IMPORTANCECoxiella burnetii causes the debilitating disease Q fever in humans. This infection is difficult to treat with current antibiotics and can progress to long-term, potentially fatal infection in immunocompromised individuals or when treatment is delayed. Here, we identified many new potential treatment options in the form of drugs that are either FDA approved or have been used in late-stage clinical trials and target human neurotransmitter systems. These compounds are poised for future characterization as nontraditional anti-C. burnetii therapies.

Clinically-diagnosed Mediterranean Spotted Fever in Malta

BACKGROUND

Mediterranean Spotted Fever (MSF) is a tick-borne zoonosis caused by Rickettsia conorii which is endemic in Malta, an island in the South Mediterranean that is a popular tourist destination. Diagnosis is frequently based on clinical manifestations as laboratory results are often limited to a retrospective diagnosis. We describe the clinical presentation, diagnosis and treatment of children <16 years who presented with MSF from 2011 to 2016.

METHOD

The demographics, clinical findings, laboratory results, management and outcome of all children hospitalised with suspected MSF based on the presence of fever and an eschar, were retrieved from their case notes.

RESULTS

Over the five-year study period six children, aged between 17 months and 15 years, were diagnosed with MSF. All children had contact with ticks and the majority presented in summer. Laboratory results were non-specific and included elevated inflammatory markers, lymphocytosis/lymphopenia and hyponatraemia. Serological and molecular techniques were used for diagnosis. Response to clarithromycin or doxycycline was immediate.

CONCLUSION

MSF should be included in the differential diagnosis of fever, rash and an eschar in children who travel to Malta. Despite advances in molecular diagnostics, clinical diagnosis remains important in the management of children with suspected MSF.

Development of a Novel Loop-Mediated Isothermal Amplification (LAMP) Assay for the Detection of Rickettsia spp

We developed a novel loop-mediated isothermal amplification (LAMP) method to detect Rickettsia spp., including Rickettsia prowazekii and R. typhi. Species-specific LAMP primers were developed for orthologous genes conserved among Rickettsia spp. The selected modified primers could detect all the Rickettsia spp. tested. The LAMP method was successfully used to detect 100 DNA copies of Rickettsia spp. within approximately 60 min at 63℃. Therefore, this method may be an excellent tool for the early diagnosis of rickettsiosis in a laboratory or in the field.

Targeted knockout of the Rickettsia rickettsii OmpA surface antigen does not diminish virulence in a mammalian model system

Strains of Rickettsia rickettsii, the causative agent of Rocky Mountain spotted fever (RMSF), differ dramatically in virulence despite >99% genetic homology. Spotted fever group (SFG) rickettsiae produce two immunodominant outer membrane proteins, rickettsial OmpA (rOmpA) and rOmpB, which are conserved throughout the SFG and thought to be fundamental to pathogenesis. rOmpA is present in all virulent strains of R. rickettsii but is not produced in the only documented avirulent strain, Iowa, due to a premature stop codon. Here we report the creation of an isogenic ompA mutant in the highly virulent strain Sheila Smith by insertion of intronic RNA to create a premature stop codon 312 bp downstream of the 6,747-bp open reading frame initiation site (int312). Targeted insertion was accomplished using an LtrA group II intron retrohoming system. Growth and entry rates of Sheila Smith ompA::int312 in Vero cells remained comparable to those of the wild type. Virulence was assessed in a guinea pig model by challenge with 100 PFU of either ompA::int312 Sheila Smith or the wild type, but no significant difference in either fever peak (40.5°C) or duration (8 days) were shown between the wild type and the knockout. The ability to disrupt genes in a site-specific manner using an LtrA group II intron system provides an important new tool for evaluation of potential virulence determinants in rickettsial disease research.

R. rickettsii rOmpA is an immunodominant outer membrane autotransporter conserved in the spotted fever group. Previous studies and genomic comparisons suggest that rOmpA is involved in adhesion and may be critical for virulence. Little information is available for rickettsial virulence factors in an isogenic background, as limited systems for targeted gene disruption are currently available. Here we describe the creation of an rOmpA knockout by insertion of a premature stop codon into the 5′ end of the open reading frame using a group II intron system. An isogenic rOmpA knockout mutation in the highly virulent Sheila Smith strain did not cause attenuation in a guinea pig model of infection, and no altered phenotype was observed in cell culture. We conclude that rOmpA is not critical for virulence in a guinea pig model but may play a role in survival or transmission from the tick vector.

Diagnosis and treatment of tick infestation and tick-borne diseases with cutaneous manifestations

Hard and soft ticks may be associated directly or indirectly with a number of dermatoses, both infectious and inflammatory in origin. Morbidity may occur as a result of tick bites, tick toxicosis, and even infestation. These arthropod vectors may transmit life-threatening protozoan, bacterial, rickettsial, and viral diseases with systemic and cutaneous findings. Additionally, ticks may transmit more than one pathogen with subsequent human coinfection. This article reviews the presentation of tick-borne illnesses and the medical management of these diseases. Among others, diseases such as ehrlichiosis, anaplasmosis, babesiosis, tularemia, borrelioses, tick-borne encephalitides, rickettsial spotted fevers, and tick typhus are discussed in this article. The recognition of skin manifestations associated with these diseases is paramount to early diagnosis and treatment initiation.

Fever in returned travellers presenting in the United Kingdom: recommendations for investigation and initial management

International travel is increasing. Most physicians and general practitioners will encounter returned travellers with fever and the majority of travel-related infection is associated with travel to the tropics. In those returning from the tropics malaria must always be excluded, and HIV considered, from all settings. Common causes of non-malarial fever include from Africa rickettsial diseases, amoebic liver abscess and Katayama syndrome; from South and South East Asia, enteric fever and arboviral infection; from the Middle East, brucellosis and from the Horn of Africa visceral leishmaniasis. Other rare but important diseases from particular geographical areas include leptospirosis, trypanosomiasis and viral haemorrhagic fever. North and South America, Europe and Australia also have infections which are geographically concentrated. Empirical treatment may have to be started based on epidemiological probability of infection whilst waiting for results to return. The evidence base for much of the management of tropical infections is limited. These recommendations provide a pragmatic approach to the initial diagnosis and management of fever in returned travellers, based on evidence where it is available and on consensus of expert opinion where it is not. With early diagnosis and treatment the majority of patients with a potentially fatal infection related to travel will make a rapid and full recovery.

Bacteriostatic and bactericidal activities of tigecycline against Coxiella burnetii and comparison with those of six other antibiotics

The present article is a study of the in vitro susceptibility of eight Greek Coxiella burnetii isolates, derived from patients with acute Q fever, and two reference strains of Coxiella burnetii to tigecycline. The bacteriostatic activity of tigecycline was compared with those of six other antibiotics using a shell vial assay. The MICs of the examined antibiotics were as follows: tigecycline ranged from 0.25 to 0.5 microg/ml; doxycycline, trovafloxacin, and ofloxacin ranged from 1 to 2 microg/ml; linezolid and clarithromycin ranged from 2 to 4 microg/ml; and ciprofloxacin ranged from 4 to 8 microg/ml. Tigecycline was effective in inhibiting the infection of Vero cells by C. burnetii. No bactericidal activity was observed against C. burnetii at 4 microg/ml.

Rickettsioses and the international traveler

The rickettsioses--zoonotic bacterial infections transmitted to humans by arthropods--were for many years considered to be oddities in travel medicine. During the previous 2 decades, however, reports of >450 travel-associated cases have been published worldwide, the vast majority being murine typhus caused by Rickettsia typhi, Mediterranean spotted fever caused by Rickettsia conorii, African tick bite fever caused by Rickettsia africae, and scrub typhus caused by Orientia tsutsugamushi. Most patients present with a benign febrile illness accompanied by headache, myalgia, and cutaneous eruptions, but severe complications and fatalities are occasionally seen. Current microbiological tests include culture, polymerase chain reaction, and serological analysis, of which only the latter method is widely available. Tetracyclines are the drugs of first choice and should be prescribed whenever a case of rickettsiosis is suspected. Preventive measures rely on minimizing the risk of arthropod bites when traveling in areas of endemicity.

Q fever endocarditis in the United States

Infections due to Coxiella burnetii, the causative organism of Q fever, are extremely rare in North America. Endocarditis due to the organism has an unusual presentation and poses echocardiographic and laboratory challenges in establishing a diagnosis. We describe the presentation and clinical course of a 40-year-old American man with Q fever endocarditis and briefly discuss the salient issues regarding this entity.

Endemic infectious diseases of Afghanistan

The current crisis in Afghanistan has resulted in an influx of Western military personnel, peacekeepers, humanitarian workers, and journalists. At the same time, unprecedented numbers of internally displaced persons and refugees have overwhelmed much of the already fragile infrastructure, setting the stage for outbreaks of infectious diseases among both foreigners and local populations. This review surveys the literature concerning the infectious diseases of Afghanistan and south-central Asia, with particular emphasis on diseases not typically seen in the Western world.

In vitro susceptibility of Coxiella burnetii to linezolid in comparison with its susceptibilities to quinolones, doxycycline, and clarithromycin

The in vitro susceptibility to linezolid shown by nine Greek isolates of Coxiella burnetii derived from patients with acute Q fever was investigated. MICs of linezolid were compared with those of pefloxacin, ciprofloxacin, ofloxacin, trovafloxacin, doxycycline, and clarithromycin using the shell vial assay. MICs of linezolid and clarithromycin ranged from 2 to 4 microg/ml; those of doxycycline, trovafloxacin, and ofloxacin ranged from 1 to 2 microg/ml; those of pefloxacin ranged from 1 to 4 microg/ml; and those of ciprofloxacin ranged from 4 to 8 microg/ml. Linezolid was effective in controlling intracellular parasites in cultures of Vero cells infected by C. burnetii. No bactericidal activity by linezolid was obtained against C. burnetii at 8 microg/ml.

Steroids treatment of granulomatous hepatitis complicating Coxiella burnetii acute infection

Granulomatous hepatitis associated with Coxiella burnetii acute infection has an adverse clinical course in some patients. Surprisingly, it does not respond to antibiotic but to steroids treatment. A hypersensitivity mechanism has been implicated. A case of granulomatous hepatitis complicating C. burnetii acute infection is reported, which was refractory to antibiotics but, as in four other cases previously reported, showed a complete response to steroids. This case was found to support findings that moderate doses of steroids can be useful in patients with granulomatous hepatitis complicating C. burnetii infection and showing no response to antibiotic treatment.

In vitro susceptibility of Coxiella burnetii to trovafloxacin in comparison with susceptibilities to pefloxacin, ciprofloxacin, ofloxacin, doxycycline, and clarithromycin

The antibiotic susceptibilities of eight Greek isolates of Coxiella burnetii to trovafloxacin were determined by the shell vial assay. MICs of trovafloxacin and ofloxacin ranged from 1 to 2 microg/ml, those of pefloxacin ranged from 1 to 4 microg/ml, those of ciprofloxacin ranged from 4 to 8 microg/ml, those of doxycycline ranged from 1 to 2 microg/ml, and those of clarithromycin ranged from 2 to 4 microg/ml. Trovafloxacin exhibited no activity against C. burnetii at 4 microg/ml.

Unusual aspects of acute Q fever-associated hepatitis

We describe a 37-year-old farmer with a 3-week history of fevers and hepatitis, in whom Q fever was diagnosed. The diagnosis was based on the findings of characteristic "ring" granulomas on a bone marrow biopsy specimen and confirmed by complement-fixation antibody tests to Coxiella burnetii. Unusual aspects of this case included (1) relatively low complement-fixation antibody titers, (2) prolonged prothrombin time, (3) false-positive results of a serologic test for the human immunodeficiency virus (HIV), and (4) ring granulomas that progressed to atypical granulomas in biopsy specimens.

Epitope mapping of the Sta58 major outer membrane protein of Rickettsia tsutsugamushi

Binding studies of 160 overlapping, synthetic octapeptides from the hydrophilic regions of the Sta58 major outer membrane protein of Rickettsia tsutsugamushi with sera from patients with scrub typhus revealed 15 immunodominant peptides which are recognized by all the sera tested. Further analysis of the specificity of peptide binding with five of these peptides indicated that the peptides showed significantly stronger binding to scrub typhus patients' sera than they did to sera from patients with other febrile illnesses common in the region, i.e., malaria, dengue fever, typhoid fever, and leptospirosis. The main antibody class binding to these peptides appears to be immunoglobulin M, and there appears to be little correlation between reactivity with peptides and antibody titers measured by the indirect immunoperoxidase test.

In vitro activities of ceftriaxone and fusidic acid against 13 isolates of Coxiella burnetii, determined using the shell vial assay

The susceptibilities of 13 isolates of Coxiella burnetii to fusidic acid and ceftriaxone were determined by use of the recently described shell vial assay (D. Raoult, H. Torres, and M. Drancourt, Antimicrob. Agents Chemother, 35:2070-2077, 1991). At a concentration of 4 micrograms/ml, ceftriaxone was bacteriostatic for four isolates and slowed the multiplication of the other nine. Fusidic acid at a concentration of 2 micrograms/ml was bacteriostatic for six isolates and slowed the multiplication of three others. These results show that these compounds could be effective in the phagolysosome of C. burnetii-infected cells.

[Coxiella burnetii endocarditis on a bioprosthetic valve: review of the literature apropos of a case]

A 51-year-old woman, originating from Algeria, developed Q fever endocarditis on porcine bioprosthetic mitral valve. She had chronic course with nonspecific symptoms, such as dyspnea and fever, hepatosplenomegaly, and developed progressive cardiac failure. Worsening of hemodynamic state led to prosthetic valve replacement. Hemocultures were all negative, and the diagnosis of Q fever was unexpectedly performed by systematic screening for specific serum antibody to Coxiella burnetti. High phase I and II specific IgG and IgA antibody titers against C burnetii were found. The patient was treated by doxycycline and ofloxacin, and improved rapidly. Prosthetic valve constitutes likely predisposing factor for the development of chronic Q fever endocarditis. This observation emphasizes the need to search for Q fever in prosthetic valve dysfunction, in particular when hemocultures are negative.