Mutation of wbtJ, a N-formyltransferase involved in O-antigen synthesis, results in biofilm formation, phase variation and attenuation in Francisella tularensis

Two clinically important subspecies, Francisella tularensis subsp. tularensis (type A) and F. tularensis subsp. holarctica (type B) are responsible for most tularaemia cases, but these isolates typically form a weak biofilm under in vitro conditions. Phase variation of the F. tularensis lipopolysaccharide (LPS) has been reported in these subspecies, but the role of variation is unclear as LPS is crucial for virulence. We previously demonstrated that a subpopulation of LPS variants can constitutively form a robust biofilm in vitro, but it is unclear whether virulence was affected. In this study, we show that biofilm-forming variants of both fully virulent F. tularensis subspecies were highly attenuated in the murine tularaemia model by multiple challenge routes. Genomic sequencing was performed on these strains, which revealed that all biofilm-forming variants contained a lesion within the wbtJ gene, a formyltransferase involved in O-antigen synthesis. A ΔwbtJ deletion mutant recapitulated the biofilm, O-antigen and virulence phenotypes observed in natural variants and could be rescued through complementation with a functional wbtJ gene. Since the spontaneously derived biofilm-forming isolates in this study were a subpopulation of natural variants, reversion events to the wbtJ gene were detected that eliminated the phenotypes associated with biofilm variants and restored virulence. These results demonstrate a role for WbtJ in biofilm formation, LPS variation and virulence of F. tularensis.

Pathogenicity and virulence of Francisella tularensis

Tularaemia is a zoonotic disease caused by the Gram-negative bacterium, Francisella tularensis. Depending on its entry route into the organism, F. tularensis causes different diseases, ranging from life-threatening pneumonia to less severe ulceroglandular tularaemia. Various strains with different geographical distributions exhibit different levels of virulence. F. tularensis is an intracellular bacterium that replicates primarily in the cytosol of the phagocytes. The main virulence attribute of F. tularensis is the type 6 secretion system (T6SS) and its effectors that promote escape from the phagosome. In addition, F. tularensis has evolved a peculiar envelope that allows it to escape detection by the immune system. In this review, we cover tularaemia, different Francisella strains, and their pathogenicity. We particularly emphasize the intracellular life cycle, associated virulence factors, and metabolic adaptations. Finally, we present how F. tularensis largely escapes immune detection to be one of the most infectious and lethal bacterial pathogens.

Case report: tularaemia in a white-handed gibbon (Hylobates lar), Germany

In 2021, a white-handed gibbon (Hylobates lar) succumbed to illness shortly after transfer from one zoo to another in Germany, due to Francisella tularensis subsp. holarctica infection. To determine the source of infection, whole genome sequencing of the gibbon-derived isolate was performed and wild pest rodents (and captive squirrels) from both zoos were screened for F. tularensis. The F. tularensis whole genome sequence obtained from the gibbon was closely related to previous subclade B.281 sequences obtained from hares from Baden-Wuerttemberg, the same region where the gibbon was first housed. However, F. tularensis DNA was detected in one Norway rat from the receiving zoo. Therefore, neither zoo can be excluded as the source of infection.

Characterization of three Francisella tularensis genomes from Oklahoma, USA

Francisella tularensis , the causative agent for tularaemia, is a Tier 1 select agent, and a pan-species pathogen of global significance due to its zoonotic potential. Consistent genome characterization of the pathogen is essential to identify novel genes, virulence factors, antimicrobial resistance genes, for studying phylogenetics and other features of interest. This study was conducted to understand the genetic variations among genomes of F. tularensis isolated from two felines and one human source. Pan-genome analysis revealed that 97.7 % of genes were part of the core genome. All three F. tularensis isolates were assigned to sequence type A based on single nucleotide polymorphisms (SNPs) in sdhA. Most of the virulence genes were part of the core genome. An antibiotic resistance gene coding for class A beta-lactamase was detected in all three isolates. Phylogenetic analysis showed that these isolates clustered with other isolates reported from Central and South-Central USA. Assessment of large sets of the F. tularensis genome sequences is essential in understanding pathogen dynamics, geographical distribution and potential zoonotic implications.

Is clinical primary care surveillance for tularaemia a useful addition to laboratory surveillance? An analysis of notification data for Finland, 2013 to 2019

BackgroundIn Finland, surveillance of tularaemia relies on laboratory-confirmed case notifications to the National infectious Diseases Register (NIDR).AimThe aim of the study was to assess the suitability and usefulness of clinical surveillance as an addition to laboratory notification to improve tularaemia surveillance in Finland.MethodsWe retrieved NIDR tularaemia surveillance and primary healthcare data on clinically diagnosed tularaemia cases in Finland between 2013 and 2019. We compared incidences, demographic distributions and seasonal trends between the two data sources.ResultsThe median annual incidence was 0.6 (range: 0.1-12.7) and 0.8 (range: 0.6-7.2) per 100,000 for NIDR notifications and primary healthcare notifications, respectively. Cases reported to NIDR were slightly older than cases reported to primary healthcare (median: 53 years vs 50 years, p = 0.04), but had similar sex distribution. Seasonal peaks differed between systems, both in magnitude and in timing. On average, primary healthcare notifications peaked 3 weeks before NIDR. However, peaks in NIDR were more pronounced, for example in 2017, monthly incidence per 100,000 of NIDR notifications peaked at 12.7 cases in September, while primary healthcare notifications peaked at 7.2 (1.8 ratio) in August.ConclusionsClinically diagnosed cases provide a valuable additional data source for surveillance of tularaemia in Finland. A primary healthcare-based system would allow for earlier detection of increasing incidences and thereby for early warning of outbreaks. This is crucial in order to implement targeted control and prevention measures as early as possible.

Epidemiological investigation of a tularaemia outbreak after a hare hunt in Bavaria, Germany, 2018

In November 2018, a tularaemia outbreak occurred in Bavaria, Germany, among participants of a hare hunt and butchery employees handling the hares. We conducted an epidemiological outbreak investigation, including a retrospective cohort study among hunting participants, to identify likely transmission routes and activities associated with infection. Twelve of 41 participants were antibody-positive for Francisella (F.) tularensis (attack rate: 29%). Cases reported influenza-like symptoms (n = 11), lymphadenopathy (n = 1) and conjunctivitis (n = 1). Infection only occurred in those hunting participants present while hares were processed, while risk of infection was highest when directly involved (RR = 10.0; 95%CI: 2.6-392). F. tularensis was isolated from 1/4 hares. Only two individuals reported using some of the recommended personal protective equipment (PPE). Occurrence of mainly non-specific symptoms, likely due to early treatment, was not indicative of a specific transmission route. Transmissions via direct (skin/mucosa) contact and by inhalation of contaminated aerosols seem plausible. Promoting and increasing appropriate use of PPE among people processing hares is crucial to prevent future outbreaks.

Vaccine-related major cutaneous reaction size correlates with cellular-mediated immune responses after tularaemia immunisation

Objectives

Francisella tularensis, the causative agent of tularaemia, is an exceptionally infectious bacterium, potentially fatal for humans if left untreated and with the potential to be developed as a bioweapon. Both natural infection and live-attenuated vaccine strain (LVS) confer good protection against tularaemia. LVS vaccination is traditionally administered by scarification, and the formation of a cutaneous reaction or take at the vaccination site is recognised as a clinical correlate of protection. Although previous studies have suggested that high antibody titres following vaccination might serve as a useful surrogate marker, the immunological correlates of protection remain unknown.

Methods

We investigated the host T-cell-mediated immune (T-CMI) responses elicited following immunisation with LVS vaccine formulated by the DynPort Vaccine Company (DVC-LVS) or the United States Army Medical Research Institute of Infectious Diseases (USAMRIID-LVS). We compared T-CMI responses prompted by these vaccines and correlated them with take size.

Results

We found that both LVS vaccines elicited similar T-CMI responses. Interestingly, take size associated with the T cells' ability to proliferate, secrete IFN-γ and mobilise degranulation, suggesting that these responses play an essential role in tularaemia protection.

Conclusions

These results renew the appreciation for vaccination through the scarification as a prime route of inoculation to target pathogens driving specific T-CMI responses and provide further evidence that T-CMI plays a role in protection from tularaemia.

Tularaemia: a case report and review

Tularaemia is a rare infectious disease caused by Francisella tularensis. In Poland, F. tularensis infections are caused by F. tularensis subspecies holarctica (type B). The disease is widespread among multiple animal species. Humans are usually infected via insect bites and less commonly by other routes (contact with animals, inhalation of contaminated aerosol or dust, or oral route). In recent years, the prevalence of tularaemia in Poland was slightly more than dozen cases per year. Depending on the route of infection, the disease has various clinical presentations, of which the most common is the ulceroglandular form. We present a typical case of this clinical form, along with information on epidemiology, clinical presentation, diagnosis, and treatment of this rare disease. Because of a low prevalence and miscellaneous clinical features, the diagnosis is often delayed. Tularaemia should be included in the differential diagnosis of fever with local lymph node enlargement as well as atypical cases of upper airway infections and pneumonia.

Large outbreak of tularaemia, central Sweden, July to September 2019

On 31 of July 2019, the Public Health Agency of Sweden was alerted about an increasing number of tularaemia cases in Gävleborg, a county in central Sweden. The number of cases increased thereafter peaking at about 150 reports of illnesses every week. As at 6 October, a total of 979 cases (734 laboratory-confirmed) have been reported, mainly from counties in central Sweden. The outbreak is now considered over (as at 14 October).

Molecular identification of the source of an uncommon tularaemia outbreak, Germany, autumn 2016

Background

In 2016, an uncommon outbreak of oropharyngeal tularaemia involving six human cases occurred in Germany, caused by drinking contaminated fresh must after a grape harvest.

Aim

We describe the details of laboratory investigations leading to identification of the outbreak strain, its characterisation by next generation sequencing (NGS) and the finding of the possible source of contamination.

Methods

We incubated wine samples in different media and on agar plates. NGS was performed on DNA isolated from young wine, sweet reserve and an outbreak case’s lymph node. A draft genome of the outbreak strain was generated. Vertebrate-specific PCRs using primers targeting the mitochondrial cytochrome b gene and product analyses by blast search were used to identify the putative source of must contamination.

Results

No bacterial isolate could be obtained. Analysis of the draft genome sequence obtained from the sweet reserve attributed this sequence to Francisella tularensis subsp. holarctica, belonging to the B.12/B.34 phylogenetic clade (erythromycin-resistant biovar II). In addition, the DNA sequence obtained from the case’s isolate supported our hypothesis that infection was caused by drinking contaminated must. The vertebrate-specific cytochrome b sequence derived from the young wine and the sweet reserve could be assigned to Apodemus sylvaticus (wood mouse), suggesting that a wood mouse infected with F. tularensis may have contaminated the must.

Conclusion

The discovered source of infection and the transmission scenario of F. tularensis in this outbreak have not been observed previously and suggest the need for additional hygienic precautionary measures when processing and consuming freshly pressed must.

PCR Based Prevalence Study of Francisella Tularensis in Kharkiv, Dnipropetrovsk, and Mykolaiv Oblasts during 2015-2018

INTRODUCTION

Tularaemia is a zoonotic disease caused by the gram-negative bacterium Francisella tularensis, which is endemic to Ukraine. The aim of this work was to provide screening of different field samples (rodent tails, ticks, pellets, water, and hay) to obtain an actual picture of the tularaemia epizootic situation in the Kharkiv, Dnipropetrovsk, and Mykolaiv oblasts.

MATERIAL AND METHODS

Samples were collected using the flag method (for ticks) and break-back traps (for rodents). Also, hay, water and owl pellets were collected for study. The F. tularensis genetic material in samples was detected using a 16S qPCR.

RESULTS

It was found that in Kharkiv oblast, 23% of collected samples were positive for F. tularensis, in Dnipropetrovsk oblast 1.9%, and in Mykolaiv oblast 0.4%.

CONCLUSION

Among the sample types, 34.7% of ticks, 1.8% of rodents, and 36.4% of pellets were positive for F. tularensis. The most frequent carriers of F. tularensis were the D. reticulatus and I. ricinus ticks (74.2% and 29.3%, respectively, of positive results).

Zoonoses and potential zoonoses of bears

Captive and free-ranging wild bears can carry and transmit several zoonotic pathogens. A review of nearly 90 years of scientific publications concerning confirmed and potential zoonotic diseases that can be present in any of the eight species of bears in the world was conducted. The findings were organized amongst the following disease sections: bacterial, viral, protozoal, mycotic, helminth and arthropod-borne. The most commonly reported pathogens of concern were of parasitic (Trichinella, Toxoplasma) and bacterial (Francisella, Brucella) origin.

Francisella tularensis in Swedish predators and scavengers

Tularaemia is a zoonotic disease, in Europe caused by Francisella tularensis subsp. holarctica. Many lagomorphs and a variety of small rodents are wildlife species prone to develop clinical disease, while predators and scavengers are relatively resistant and may serve as sentinels. Blood samples from 656 Swedish wild predators and scavengers were serologically investigated using slide agglutination and microagglutination. In the slide agglutination test, 34 seropositive animals were detected, and they were found among all species investigated: brown bear (Ursus arctos), Eurasian lynx (Lynx lynx), raccoon dog (Nyctereutes procyonoides), red fox (Vulpes vulpes), wild boar (Sus scrofa), wolf (Canis lupus) and wolverine (Gulo gulo). Due to haemolysis the microagglutination test was more difficult to read at low titres, and only 12 animals were classified as seropositive. F. tularensis subsp. holarctica was detected by a polymerase chain reaction in lymphatic tissues of the head in one brown bear, one red fox and one wolf. The significance of this finding regarding possible latency of infection is not clear. In conclusion, the results of this study indicate that all predator and scavenger species included in this study may serve as sentinels for tularaemia in Sweden. Their role as reservoirs is unclear.

Human tularaemia associated with exposure to domestic dogs-United States, 2006-2016

Dogs have been implicated in the zoonotic transmission of numerous pathogens. Whereas cats are known to transmit Francisella tularensis to humans via bite and other routes, the role of dogs in facilitating infection is much less understood. We reviewed tularaemia case investigation records collected through national surveillance during 2006-2016 to summarize those with dog involvement, characterize the nature of dog-related exposure and describe associated clinical characteristics. Among 1,814 human tularaemia cases, 735 (41%) supplemental case investigation records were available for review; and of those, 24 (3.3%) were classified as dog-related. Median age of patients was 51 years (range: 1-82); 54% were female. Two thirds (67%) of cases presented with ulceroglandular/glandular tularaemia; pneumonic (13%) and oropharyngeal (13%) illness occurred less frequently. Dog-related exposures were classified as follows: direct contact via bite, scratch or face snuggling/licking (n = 12; 50%); direct contact with dead animals retrieved by domestic dogs (n = 8; 33%); and contact with infected ticks acquired from domestic dogs (n = 4; 17%). Prevention of dog-related tularaemia necessitates enhanced tularaemia awareness and tick avoidance among pet owners, veterinarians, health care providers and the general public.

Environmental surveillance during an outbreak of tularaemia in hares, the Netherlands, 2015

Tularaemia, a disease caused by the bacterium Francisella tularensis, is a re-emerging zoonosis in the Netherlands. After sporadic human and hare cases occurred in the period 2011 to 2014, a cluster of F. tularensis-infected hares was recognised in a region in the north of the Netherlands from February to May 2015. No human cases were identified, including after active case finding. Presence of F. tularensis was investigated in potential reservoirs and transmission routes, including common voles, arthropod vectors and surface waters. F. tularensis was not detected in common voles, mosquito larvae or adults, tabanids or ticks. However, the bacterium was detected in water and sediment samples collected in a limited geographical area where infected hares had also been found. These results demonstrate that water monitoring could provide valuable information regarding F. tularensis spread and persistence, and should be used in addition to disease surveillance in wildlife.

Bacterial lipoproteins and other factors released by Francisella tularensis modulate human neutrophil lifespan: Effects of a TLR1 SNP on apoptosis inhibition

Francisella tularensis infects several cell types including neutrophils, and aberrant neutrophil accumulation contributes to tissue destruction during tularaemia. We demonstrated previously that F. tularensis strains Schu S4 and live vaccine strain markedly delay human neutrophil apoptosis and thereby prolong cell lifespan, but the bacterial factors that mediate this aspect of virulence are undefined. Herein, we demonstrate that bacterial conditioned medium (CM) can delay apoptosis in the absence of direct infection. Biochemical analyses show that CM contained F. tularensis surface factors as well as outer membrane components. Our previous studies excluded roles for lipopolysaccharide and capsule in apoptosis inhibition, and current studies of [¹⁴C] acetate‐labelled bacteria argue against a role for other bacterial lipids in this process. At the same time, studies of isogenic mutants indicate that TolC and virulence factors whose expression requires FevR or MglA were also dispensable, demonstrating that apoptosis inhibition does not require Type I or Type VI secretion. Instead, we identified bacterial lipoproteins (BLPs) as active factors in CM. Additional studies of isolated BLPs demonstrated dose‐dependent neutrophil apoptosis inhibition via a TLR2‐dependent mechanism that is significantly influenced by a common polymorphism, rs5743618, in human TLR1. These data provide fundamental new insight into pathogen manipulation of neutrophil lifespan and BLP function.

Tularaemia in European Brown Hares (Lepus europaeus) and Mountain Hares (Lepus timidus) Characterized by Histopathology and Immunohistochemistry: Organ Lesions and Suggestions of Routes of Infection and Shedding

Tularaemia is an emerging zoonotic infectious disease caused by the bacterium Francisella tularensis. In Sweden, hares are considered to be key species in the epidemiology of tularaemia. The aim of this study was to characterize the pathology of natural tularaemia infection in European brown hares (EBHs) (Lepus europaeus) and mountain hares (MHs) (Lepus timidus) in Sweden, in order to better understand the presentation of disease and the routes of infection, body dissemination and shedding of F. tularensis. During 2000-2013, 49 EBHs and 37 MHs were diagnosed with tularaemia. Enlargement of the spleen was seen in 80% of EBHs and 62% of MHs. Necrosis was often obvious in the bone marrow, liver, lung and spleen, but 30% of the hares had no lesions or minimal gross lesions. On microscopical examination of tissues from 27 EBHs and three MHs, necrosis was seen in the majority of samples of liver, spleen, bone marrow, lymph node and adrenal glands and was common in the lungs and brain meninges. Immunohistochemistry for Francisella spp. detected bacteria in association with necrosis and inflammation. In several cases, Francisella spp. were also found inside blood vessels, in the renal pelvis, in lactating mammary glands, in bronchioles and in the skin, associated with tick bites. Using quantitative polymerase chain reaction, two genotypes of F. tularensis subsp. holarctica were found; canSNP group B.6, all belonging to subgroup B.7, and canSNP group B.12. There were no differences in pathology between the genotypes. Our results indicate that the urinary tract and mammary glands are important routes for the shedding of F. tularensis. Hunters may not be aware of the risks of contracting tularaemia while handling hares, since infected hares do not always show noticeable gross lesions.

Pneumonic tularaemia: experience of 58 cases from 2000 to 2012 in Northern Finland

BACKGROUND

Pneumonic tularaemia is less common clinical form of tularaemia compared with the ulceroglandular form, with only a limited number of case reports and case series in Europe. In Finland, Northern Ostrobothnia is an endemic area of tularaemia with occasional seasonal outbreaks.

METHODS

In our study, a consecutive series of 58 pneumonic tularaemia cases diagnosed and treated in Oulu University Hospital in 2000-2012 were retrospectively analysed in terms of epidemiology, clinical course, and prognosis.

RESULTS

The incidence of pneumonic tularaemia showed peaks in cycles of a few years and most cases were diagnosed in late summer or early autumn. Respiratory symptoms were absent in 47% of patients, and 7% had normal chest X-ray. The chest computed tomography (CT) was performed in 81% of patients, demonstrating variable findings associated with pneumonic tularaemia. Bronchoscopy was performed for 22 (38%) patients and four (18%) of these also proceeded into mediastinoscopy. Moreover, thoracoscopy was performed for one (2%) patient. Two (3%) patients were treated shortly in the intensive care unit (ICU) during their stay in hospital. No mortality was observed.

CONCLUSIONS

Most cases of pneumonic tularaemia are diagnosed during the seasonal outbreaks. The lack of specific symptoms often complicates the diagnosis and leads to unnecessarily invasive examinations.

Francisella tularensis prevalence and load in Dermacentor reticulatus ticks in an endemic area in Central Europe

A total of 7778 host-seeking adult Dermacentor reticulatus (Ixodida: Ixodidae) ticks were examined for the prevalence of Francisella tularensis holarctica (Thiotrichales: Francisellaceae) in a natural focus of tularaemia in the floodplain forest-meadow ecosystem along the lower reaches of the Dyje (Thaya) river in South Moravia (Czech Republic) between 1995 and 2013. Ticks were pooled (10 specimens per pool) and their homogenates inoculated subcutaneously in 4-week-old specific pathogen-free mice. Dead mice were sectioned, their spleens cultivated on thioglycollate-glucose-blood agar and impression smears from the spleen, liver and heart blood were Giemsa-stained. Sixty-four pools were positive for F. tularensis: the overall minimum infection rate (MIR) was 0.82%. Overall MIRs for the 4714 female and 3064 male D. reticulatus examined were 0.89 and 0.72%, respectively; MIRs fluctuated across years between 0.0 and 2.43%. The estimated bacterial load in infected ticks varied from 0.84 to 5.34 log₁₀ infectious F. tularensis cells per tick (i.e. from about seven to 220 000 cells). Ticks with low loads were more prevalent; more than 1000 infectious cells were detected in 24 ticks (0.3% of all ticks and 37.5% of infected ticks). Monitoring of D. reticulatus for the presence and cell numbers of F. tularensis may be a valuable tool in the surveillance of tularaemia.

Francisella tularensis Susceptibility to Antibiotics: A Comprehensive Review of the Data Obtained In vitro and in Animal Models

The antibiotic classes that are recommended for tularaemia treatment are the aminoglycosides, the fluoroquinolones and the tetracyclines. However, cure rates vary between 60 and 100% depending on the antibiotic used, the time to appropriate antibiotic therapy setup and its duration, and the presence of complications, such as lymph node suppuration. Thus, antibiotic susceptibility testing (AST) of F. tularensis strains remains of primary importance for detection of the emergence of antibiotic resistances to first-line drugs, and to test new therapeutic alternatives. However, the AST methods reported in the literature were poorly standardized between studies and AST data have not been previously evaluated in a comprehensive and comparative way. The aim of the present review was to summarize experimental data on antibiotic susceptibilities of F. tularensis obtained in acellular media, cell models and animal models since the introduction of fluoroquinolones in the treatment of tularaemia in 1989. We compiled MIC data of 33 antibiotics (including aminoglycosides, fluoroquinolones, tetracyclines, macrolides, β-lactams, chloramphenicol, rifampicin, and linezolid) against 900 F. tularensis strains (504 human strains), including 107 subsp. tularensis (type A), 789 subsp. holarctica (type B) and four subsp. mediasiatica strains, using various AST methods. Specific culture media were identified or confirmed as unsuitable for AST of F. tularensis. Overall, MICs were the lowest for ciprofloxacin (≤ 0.002–0.125 mg/L) and levofloxacin, and ranged from ≤ 0.016 to 2 mg/L for gentamicin, and 0.064 to 4 mg/L for doxycycline. No resistant strain to any of these antibiotics was reported. Fluoroquinolones also exhibited a bactericidal activity against intracellular F. tularensis and lower relapse rates in animal models when compared with the bacteriostatic compound doxycycline. As expected, lower MIC values were found for macrolides against type A and biovar I type B strains, compared to biovar II type B strains. The macrolides were more effective against F. tularensis grown in phagocytic cells than in acellular media.

Cat-bite-induced Francisella tularensis infection with a false-positive serological reaction for Bartonella quintana

Introduction. Tularaemia is caused by infection with Francisella tularensistransmitted via direct contact with an infected hare carcass or indirectly through the bites of vectors, but may be cat-bite-associated as well. Medical history and reliable diagnostic analysis are important in order to differentiate it from other cat-associated infections, e.g. Bartonella spp.

Casepresentation. A healthy 56-year-old man was examined because of a cat-bite-associated ulceroglandular wound on his right thumb. Nineteen days after the cat bite occurred, a serology test was positive for anti-Bartonella quintana, but negative for anti-F. tularensis. Since Bartonella infections are rare in Sweden, another serology test was analysed 2 weeks later with a positive result for anti-F. tularensis. The patient was treated with doxycycline for 14 days and recovered. The patient was re-sampled after 18 months to obtain a convalescent sample. The acute and the convalescent samples were both analysed at a reference centre, with negative results for anti-Bartonella spp. this time.

Conclusion. This case is enlightening about the importance of extending the medical history and re-sampling the patient for antibody detection when the clinical suspicion of cat-bite-associated tularaemia is high. The false-positive result for anti-B. quintana antibodies may have been due to technical issues with the assay, cross-reactivity or both.

Pilot Cross-Sectional Study of Three Zoonoses (Lyme Disease, Tularaemia, Leptospirosis) among Healthy Blood Donors in Eastern Slovakia

OBJECTIVE

The aim of the study was to determine the seroprevalence of three zoonotic infections among healthy blood donors/volunteers in Eastern Slovakia.

METHODS

Sera from 124 blood donors were investigated for the presence of antibodies against Borrelia burgdorferi, Francisella tularensis and Leptospira pomona. The participants also completed the questionnaire about demographic, exposure and epidemiological characteristics. Two serological methods were used for the diagnosis: the enzyme linked protein A/G assay (ELPAGA) and the Western blot (WB). First, sera were screened by ELPAGA (except for leptospirosis).

RESULTS

The observed seroprevalence was 15% for Lyme borreliosis (LB) and 4% for tularaemia (TUL). The results were confirmed by WB. Positive IgG antibodies (WB method) were detected only in 1.6% of examined for LB and 0.8% for TUL. Our results did not identify any antibodies against Leptospira pomona agent in the examined healthy blood donors group.

CONCLUSIONS

ELPAGA seroprevalence for TUL was significantly higher in blood donors working in the agricultural area in the direct contact with hay, straw, manure, and agricultural land. Our outputs determine tick bite as a significant risk factor for LB. The study confirms the explosion of tick-borne diseases in the healthy population of people. The exposure risk for leptospirosis seems to be minimal.

Complement sensitivity and factor H binding of European Francisella tularensis ssp. holarctica strains in selected animal species

Francisella tularensis is a Gram-negative bacterium, the causative agent of the zoonotic disease tularaemia. The bacterium has developed several extracellular and intracellular strategies to evade the hosts' innate and adaptive immune responses. The aims of the study were to examine complement sensitivity of wild and attenuated F. tularensis ssp. holarctica strains in animal hosts of distinct sensitivity to the bacterium, to compare the complement-evading ability of wild strains of different phylogeographic background, and to examine the role of factor H in the host-pathogen interactions. Complement sensitivity assays were carried out on various F. tularensis ssp. holarctica wild strains and on the attenuated live vaccine strain (LVS) with sera of the highly sensitive house mouse (Mus musculus), the moderately sensitive European brown hare (Lepus europaeus) and the relatively resistant cattle (Bos taurus). Specific binding of complement regulator factor H to bacterial membrane proteins was examined by Western blot assays. All wild strains interacted with the hosts' complement system and showed no significant differences in their survivability. The attenuated LVS was resistant to serum killing in mouse, but was lysed in the sera of hare and cattle. Direct binding of factor H to F. tularensis membrane proteins was not detected.

Phylogeography of Francisella tularensis subspecies holarctica in Finland, 1993-2011

BACKGROUND

Finland repeatedly reports some of the highest incidences of tularaemia worldwide. To determine genetic diversity of the aetiologic agent of tularaemia, Francisella tularensis, a total of 76 samples from humans (n = 15) and animals (n = 61) were analysed.

METHODS

We used CanSNPs and canINDEL hydrolysis or TaqMan MGB probes for the analyses, either directly from the clinical tissue samples (n = 21) or from bacterial isolates (n = 55).

RESULTS

The genotypes of the strains were assigned to three previously described basal subspecies holarctica clades. The majority of strains (n = 67) were assigned to B.12, a clade reported to dominate in Scandinavia and Eastern Europe. A single strain was assigned to clade B.4, previously reported from North America, Europe and China. The remaining strains (n = 8) were members of clade B.6. Importantly, new diversity was discovered in clade B.6. We describe two newly designed TaqMan MGB probe assays for this new B.6 subclade B.70, and its previously identified sister clade B.11, a clade dominantly found in Western Europe.

CONCLUSIONS

The high genetic diversity of F. tularensis subspecies holarctica present in Finland is consistent with previous findings in Sweden. The results suggest a northern and southern division of the B.6 subclade B.10, where B.11 predominates in Western and Central Europe and B.70 is found in Fennoscandia. Further research is required to define whether the vast diversity of genotypes found is related to different habitats or reservoir species, their different postglacial immigration routes to Fennoscandia, or dynamics of the reservoir species.

Multiple-locus variable-number tandem-repeat analysis of Francisella tularensis from Quebec, Canada

Francisella tularensis is ubiquitous in the Northern Hemisphere. Yet, little is known about the disease and its ecology within Canada as few serological studies have shown exposure to the disease and fewer case studies have been reported. This report is the first to describe the molecular subtyping of F. tularensis isolates within eastern Canada using multiple-locus variable-number tandem-repeat analysis. From 1998 to 2011, a total of 73 specimens were isolated from unique human and animal sources. As expected, F. tularensis subsp. tularensis AI and F. tularensis subsp. holarctica subtypes were observed, corresponding to the known geographical division within this species. The majority of human isolates (78%) and all animal (hare) isolates were of the more virulent, AI type. Half of the B isolates were isolated from patients living in a region of Quebec where muskrat densities are known to be high. A relatively high level of marker diversity was found, suggestive of multiple introductions of the organism to the region, or more likely ongoing endemicity. There was no evidence of ongoing outbreaks or transmission, and the bulk of cases were likely due to interaction between human activity and the environment (e.g. hunting/trapping activities).

SIGNIFICANCE AND IMPACT OF THE STUDY

This study reveals the diversity of Francisella tularensis in eastern Canada using multiple-locus variable-number tandem-repeat analysis. It was initiated to further the understanding of the species within North America as previous studies elucidating the diversity and phylogeography of the species have consisted mostly of specimens from the United States. Type A tularaemia, the most life-threatening subtype of the species and a Category A biothreat agent, is restricted to North America, and this study serves to broaden the knowledge of the epidemiology and diversity of the organism.

Evaluation of tularaemia courses: a multicentre study from Turkey

In this multicentre study, which is the largest case series ever reported, we aimed to describe the features of tularaemia to provide detailed information. We retrospectively included 1034 patients from 41 medical centres. Before the definite diagnosis of tularaemia, tonsillitis (n = 653, 63%) and/or pharyngitis (n = 146, 14%) were the most frequent preliminary diagnoses. The most frequent clinical presentations were oropharyngeal (n = 832, 85.3%), glandular (n = 136, 13.1%) and oculoglandular (n = 105, 10.1%) forms. In 987 patients (95.5%), the lymph nodes were reported to be enlarged, most frequently at the cervical chain jugular (n = 599, 58%), submandibular (n = 401, 39%), and periauricular (n = 55, 5%). Ultrasound imaging showed hyperechoic and hypoechoic patterns (59% and 25%, respectively). Granulomatous inflammation was the most frequent histological finding (56%). The patients were previously given antibiotics for 1176 episodes, mostly with β-lactam/β-lactamase inhibitors (n = 793, 76%). Antituberculosis medications were provided in seven (2%) cases. The patients were given rational antibiotics for tularaemia after the start of symptoms, with a mean of 26.8 ± 37.5 days. Treatment failure was considered to have occurred in 495 patients (48%). The most frequent reasons for failure were the production of suppuration in the lymph nodes after the start of treatment (n = 426, 86.1%), the formation of new lymphadenomegalies under treatment (n = 146, 29.5%), and persisting complaints despite 2 weeks of treatment (n = 77, 15.6%). Fine-needle aspiration was performed in 521 patients (50%) as the most frequent drainage method. In conclusion, tularaemia is a long-lasting but curable disease in this part of the world. However, the treatment strategy still needs optimization.

New therapeutic approaches for treatment of tularaemia: a review

Antibiotic treatment of tularaemia is based on a few drugs, including the fluoroquinolones (e.g., ciprofloxacin), the tetracyclines (e.g., doxycycline), and the aminoglycosides (streptomycin and gentamicin). Because no effective and safe vaccine is currently available, tularaemia prophylaxis following proven exposure to F. tularensis also relies on administration of antibiotics. A number of reasons make it necessary to search for new therapeutic alternatives: the potential toxicity of first-line drugs, especially in children and pregnant women; a high rate of treatment relapses and failures, especially for severe and/or suppurated forms of the disease; and the possible use of antibiotic-resistant strains in the context of a biological threat. This review presents novel therapeutic approaches that have been explored in recent years to improve tularaemia patients' management and prognosis. These new strategies have been evaluated in vitro, in axenic media and cell culture systems and/or in animal models. First, the activities of newly available antibiotic compounds were evaluated against F. tularensis, including tigecycline (a glycylcycline), ketolides (telithromycin and cethromycin), and fluoroquinolones (moxifloxacin, gatifloxacin, trovafloxacin and grepafloxacin). The liposome delivery of some antibiotics was evaluated. The effect of antimicrobial peptides against F. tularensis was also considered. Other drugs were evaluated for their ability to suppress the intracellular multiplication of F. tularensis. The effects of the modulation of the innate immune response (especially via TLR receptors) on the course of F. tularensis infection was characterized. Another approach was the administration of specific antibodies to induce passive resistance to F. tularensis infection. All of these studies highlight the need to develop new therapeutic strategies to improve the management of patients with tularaemia. Many possibilities exist, some unexplored. Moreover, it is likely that new therapeutic alternatives that are effective against this intracellular pathogen could be, at least partially, extrapolated to other human pathogens.

A new dye uptake assay to test the activity of antibiotics against intracellular Francisella tularensis

Francisella tularensis, a facultative intracellular bacterium, is the aetiological agent of tularaemia. Antibiotic treatment of this zoonosis is based on the administration of a fluoroquinolone or a tetracycline for cases with mild to moderate severity, whereas an aminoglycoside (streptomycin or gentamicin) is advocated for severe cases. However, treatment failures and relapses remain frequent, especially in patients suffering from chronic lymph node suppuration. Therefore, new treatment alternatives are needed. We have developed a dye uptake assay for determination of minimal inhibitory extracellular concentrations (MIECs) of antibiotics against intracellular F. tularensis, and validated the method by comparing the results obtained using a CFU-enumerating method. We also compared MIECs with MICs of the same compounds determined using a CLSI broth microdilution method. We tested the activity of 11 antibiotics against two clinical strains of F. tularensis subsp. holarctica isolated in France. Both strains displayed low MICs (≤1 μg/mL) to fluoroquinolones (ciprofloxacin, levofloxacin and moxifloxacin), gentamicin, doxycycline and rifampicin. Higher MICs (≥8 μg/mL) were found for carbapenems (imipenem and meropenem), daptomycin and linezolid. Erythromycin MICs were 4.0 and 16.0 μg/mL, respectively, for the two clinical strains. MIECs were almost the same with the two methods used. They were concordant with MICs, except for erythromycin and linezolid (respectively, four and eight times more active against intracellular F. tularensis) and gentamicin (four to eight times less active against intracellular F. tularensis). This study validated the dye uptake assay as a new tool for determination of the activity of a large panel of antibiotics against intracellular F. tularensis. This test confirmed the intracellular activity of first-line antibiotics used for tularaemia treatment, but also revealed significant activity of linezolid against intracellular F. tularensis.

Bis-indolic compounds as potential new therapeutic alternatives for tularaemia

Francisella tularensis is the etiological agent of tularaemia and a CDC class A biological threat agent. Few antibiotic classes are currently useful in treating tularaemia, including the aminoglycosides gentamicin and streptomycin, fluoroquinolones, and tetracyclines. However, treatment failures and relapses remain frequent and F. tularensis strains resistant to antibiotics have been easily selected in vitro. In this study, we evaluated the activity of new synthetic bis-indole derivatives against this pathogen. Minimum inhibitory concentrations (MICs) of four compounds (dcm01 to dcm04) were determined for the reference strains F. tularensis subsp. holarctica LVS NCTC10857, F. tularensis subsp. novicida CIP56.12 and F. philomiragia ATCC25015, and for 41 clinical strains of F. tularensis subsp. holarctica isolated in France. Minimal bactericidal concentrations (MBCs) were determined for the dcm02 and dcm04 compounds for the LVS and two clinical strains. Killing curves were also determined for the same three strains exposed to dcm04. All tested bis-indole compounds were bacteriostatic against F. tularensis subsp. holarctica strains, with a MIC90 of 8 μg/mL for dcm01, dcm02, and dcm03, and 2 μg/mL for dcm04. Only one strain was resistant to both dcm01 and dcm03, with MICs > 32 μg/mL. In contrast, F. tularensis subsp. novicida was resistant to all derivatives and F. philomiragia was only susceptible to dcm02 and dcm04, with MICs of 16 and 4 μg/mL, respectively. MBC and killing curve experiments revealed significant bactericidal activity (i.e., 3-log reduction of the bacterial inoculum) of the dcm02 and dcm04 compounds only for the LVS strain. In conclusion, we have identified novel synthetic bis-indole compounds that are active against F. tularensis subsp. holarctica. They may be drug candidates for the development of new therapeutic alternatives for tularaemia treatment. Their further characterization is needed, especially identification of their bacterial targets.

Evolution toward high-level fluoroquinolone resistance in Francisella species

OBJECTIVES

Francisella tularensis, a CDC class A potential bioterrorism agent, is a Gram-negative bacterium responsible for tularaemia. Understanding the mechanisms of resistance to antibiotics used as first-line treatment is of major security relevance.

METHODS

We propagated the three parental reference strains Francisella tularensis subsp. holarctica live vaccine strain, Francisella novicida and Francisella philomiragia with increasing concentrations of ciprofloxacin, a fluoroquinolone used as curative and prophylactic treatment for tularaemia. This evolution procedure provided us with high-level ciprofloxacin-resistant mutants and all evolutionary intermediates towards high-level resistance. We determined the resistance levels to other fluoroquinolones (levofloxacin and moxifloxacin) and other antibiotic families (aminoglycosides, tetracyclines and macrolides) and characterized the genetic changes in the fluoroquinolone target genes encoding DNA gyrase and topoisomerase IV.

RESULTS

All high-level resistant mutants shared cross-resistance to the tested fluoroquinolones, while some also revealed striking levels of cross-resistance to other clinically relevant antibiotic classes. High-level resistant mutants carried one to three mutations, including some not previously reported. We mapped all mutations onto known topoisomerase three-dimensional structures. Along the pathways towards high-level resistance, we identified complex evolutionary trajectories including polymorphic states and additional resistance mechanisms likely to be associated with efflux processes.

CONCLUSIONS

Our data demonstrated the efficiency and speed of in vitro production of mutants highly resistant to fluoroquinolones in Francisella species. They emphasize the urgent need to identify all antibiotic resistance mechanisms in these species, develop molecular tools for their detection and design new therapeutic alternatives for tularaemia.

Draft genome sequence of Francisella tularensis subsp. holarctica BD11-00177

Francisella tularensis is a facultative intracellular bacterium in the class Gammaproteobacteria. This strain is of interest because it is the etiologic agent of tularemia and a highly virulent category A biothreat agent. Here we describe the draft genome sequence and annotation of Francisella tularensis subsp. holarctica BD11-00177, isolated from the first case of indigenous tularemia detected in The Netherlands since 1953. Whole genome DNA sequence analysis assigned this isolate to the genomic group B.FTNF002–00, which previously has been exclusively reported from Spain, France, Italy, Switzerland and Germany. Automatic annotation of the 1,813,372 bp draft genome revealed 2,103 protein-coding and 46 RNA genes.

Effects of climate change on tularaemia disease activity in Sweden

Tularaemia is a vector-borne infectious disease. A large majority of cases transmitted to humans by blood-feeding arthropods occur during the summer season and is linked to increased temperatures. Therefore, the effect of climate change is likely to have an effect on tularaemia transmission patterns in highly endemic areas of Sweden. In this report, we use simulated climate change scenario data and empirical data of temperatures critical to tularaemia transmission to forecast tularaemia outbreak activity. The five high-endemic counties: Dalarna, Gävleborg, Norrbotten, Värmland and Örebro represent only 14.6% of the total population of Sweden, but have recorded 40.1–81.1% of the number of annual human tularaemia in Sweden from 1997 until 2008. We project here earlier starts and a later termination of future tularaemia outbreaks for the time period 2010–2100. For five localised outbreak areas; Gagnef (Dalarna), Ljusdal (Gävleborg), Harads (Norrbotten), Karlstad (Värmland) and Örebro municipality (Örebro), the climate scenario suggests an approximately 2°C increase in monthly average summer temperatures leading to increases in outbreak durations ranging from 3.5 weeks (Harads) to 6.6 weeks (Karlstad) between 2010 and 2100. In contrast, an analysis of precipitation scenarios indicates fairly stable projected levels of precipitation during the summer months. Thus, there should not be an increased abundance of late summer mosquitoes that are believed to be main vectors for transmission to humans in these areas. In conclusion, the results indicate that the future climate changes will lead to an increased burden of tularaemia in high-endemic areas of Sweden during the coming decades.

Bichat guidelines for the clinical management of tularaemia and bioterrorism-related tularaemia

Francisella tularensis is one of the most infectious pathogenic bacteria known, requiring inoculation or inhalation of as few as 10 organisms to initiate human infection. Inhalational tularaemia following intentional release of a virulent strain of F. tularensis would have great impact and cause high morbidity and mortality. Another route of contamination in a deliberate release could be contamination of water. Seven clinical forms, according to route of inoculation (skin, mucous membranes, gastrointestinal tract, eyes, respiratory tract), dose of the inoculum and virulence of the organism (types A or B) are identified. The pneumonic form of the disease is the most likely form of the disease should this bacterium be used as a bioterrorism agent. Streptomycin and gentamicin are currently considered the treatment of choice for tularemia. Quinolone is an effective alternative drug. No isolation measures for patients with pneumonia are necessary. Streptomycin, gentamicin, doxycycline or ciprofloxacin are recommended for post-exposure prophylaxis.

The proportion of circulating gammadelta T cells increases after the first week of onset of tularaemia and remains elevated for more than a year

In various human intracellular bacterial diseases, an increase of the proportion of circulating Vgamma9Vdelta2 T cells has been observed. The prevalence of the finding among infected subjects and the time course of the elevation remain to be investigated. In the present study, comprising blood samples from a large number of cases of ulceroglandular tularaemia, the percentage of Vgamma9Vdelta2 T cells within the first week of onset of disease (5.3 +/- 0.7% (mean +/- s.e.m.)) did not differ from that of control subjects (5.3 +/- 0. 8%). Thereafter, percentages increased rapidly and within the interval of 8-40 days mean levels were > 20% (P < 0.001). Of 45 individuals sampled within 3 months of onset, 42 showed a percentage of Vgamma9Vdelta2 T cells of > 10%. Significantly increased levels were still recorded at 18 months (13.8 +/- 2.4%; P < 0.05) but not at 24 months (10.2 +/- 2.1%; P > 0.10). Thus, a consistent increase of circulating Vgamma9Vdelta2 T cells was demonstrated in tularaemia. The initial delay and the prolonged course of elevation may suggest a role in immunoregulation and/or immunological memory. Furthermore, the percentage of gammadelta T cells expressing tumour necrosis factor-alpha in response to phorbol myristate acetate was decreased during the first week and up to 40 days after onset, possibly reflecting the modulation of an inflammatory response.