Five cases of vector-borne Francisella tularensis holarctica infections in south-western Germany and genetic diversity

Systematic Review: Clinical Features, Antimicrobial Treatment, and Outcomes of Human Tularemia, 1993-2023

BACKGROUND

Francisella tularensis, the causative agent of tularemia, is endemic throughout the Northern Hemisphere and requires as few as 10 organisms to cause disease, making this potential bioterrorism agent one of the most infectious bacterial pathogens known. Aminoglycosides, tetracyclines, and, more recently, fluoroquinolones are used for treatment of tularemia; however, data on the relative effectiveness of these and other antimicrobial classes are limited.

METHODS

Nine databases, including Medline, Global Health, and Embase, were systematically searched for articles containing terms related to tularemia. Articles with case-level data on tularemia diagnosis, antimicrobial treatment, and patient outcome were included. Patient demographics, clinical findings, antimicrobial administration, and outcome (eg, intubation, fatality) were abstracted using a standardized form.

RESULTS

Of the 8878 publications identified and screened, 410 articles describing 870 cases from 1993 to 2023 met inclusion criteria. Cases were reported from 35 countries; more than half were from the United States, Turkey, or Spain. The most common clinical forms were ulceroglandular, oropharyngeal, glandular, and pneumonic disease. Among patients treated with aminoglycosides (n = 452 [52%]), fluoroquinolones (n = 339 [39%]), or tetracyclines (n = 419 [48%]), the fatality rate was 0.7%, 0.9%, and 1.2%, respectively. Patients with pneumonic disease who received ciprofloxacin had no fatalities and the lowest rates of thoracentesis/pleural effusion drainage and intubation compared to those who received aminoglycosides and tetracyclines.

CONCLUSIONS

Aminoglycosides, fluoroquinolones, and tetracyclines are effective antimicrobials for treatment of tularemia, regardless of clinical manifestation. For pneumonic disease specifically, ciprofloxacin may have slight advantages compared to other antimicrobials.

Ulceroglandular form of tularemia after squirrel bite: a case report

Background

The diagnosis of tularemia is not often considered in Germany as the disease is still rare in this country. Nonetheless, Francisella tularensis, the causative agent of tularemia, can infect numerous animal species and should, therefore, not be neglected as a dangerous pathogen. Tularemia can lead to massively swollen lymph nodes and might even be fatal without antibiotic treatment. To our knowledge, the case described here is the first report of the disease caused by a squirrel bite in Germany.

Case presentation

A 59-year-old German woman with a past medical history of hypothyroidism and cutaneous lupus erythematosus presented at the emergency room at St. Katharinen Hospital with ongoing symptoms and a swollen right elbow persisting despite antibiotic therapy with cefuroxime for 7 days after she had been bitten (right hand) by a wild squirrel (Eurasian red squirrel). After another 7 days of therapy with piperacillin/tazobactam, laboratory analysis using real-time polymerase chain reaction (PCR) confirmed the suspected diagnosis of tularemia on day 14. After starting the recommended antibiotic treatment with ciprofloxacin, the patient recovered rapidly.

Conclusion

This is the first report of a case of tularemia caused by a squirrel bite in Germany. A naturally infected squirrel has recently been reported in Switzerland for the first time. The number of human cases of tularemia has been increasing over the last years and, therefore, tularemia should be taken into consideration as a diagnosis, especially in a patient bitten by an animal who also presents with headache, increasing pain, lymphadenitis, and fever, as well as impaired wound healing. The pathogen can easily be identified by a specific real-time PCR assay of wound swabs and/or by antibody detection, for example by enzyme-linked immunosorbent assay (ELISA), if the incident dates back longer than 2 weeks.

Vector-Borne Tularemia: A Re-Emerging Cause of Cervical Lymphadenopathy

Tularemia is a zoonosis caused by the highly invasive bacterium Francisella tularensis. It is transmitted to humans by direct contact with infected animals or by vectors, such as ticks, mosquitos, and flies. Even though it is well-known as a tick-borne disease, it is usually not immediately recognised after a tick bite. In Slovenia, tularemia is rare, with 1-3 cases reported annually; however, the incidence seems to be increasing. Ulceroglandular tularemia is one of its most common forms, with cervical colliquative lymphadenopathy as a frequent manifestation. The diagnosis of tularemia largely relies on epidemiological information, clinical examination, imaging, and molecular studies. Physicians should consider this disease a differential diagnosis for a neck mass, especially after a tick bite, as its management significantly differs from that of other causes. Tularemia-associated lymphadenitis is treated with antibiotics and surgical drainage of the colliquated lymph nodes. Additionally, tularemia should be noted for its potential use in bioterrorism on behalf of the causative agents' low infectious dose, possible aerosol formation, no effective vaccine at disposal, and the ability to produce severe disease. This article reviews the recent literature on tularemia and presents a case of an adult male with tick-borne cervical ulceroglandular tularemia.

Laboratory Methods for Detection of Infectious Agents and Serological Response in Humans With Tick-Borne Infections: A Systematic Review of Evaluations Based on Clinical Patient Samples

Background: For the most important and well-known infections spread by Ixodes ticks, Lyme borreliosis (LB) and tick-borne encephalitis (TBE), there are recommendations for diagnosis and management available from several health authorities and professional medical networks. However, other tick-borne microorganisms with potential to cause human disease are less known and clear recommendations on diagnosis and management are scarce. Therefore, we performed a systematic review of published studies and reviews focusing on evaluation of laboratory methods for clinical diagnosis of human tick-borne diseases (TBDs), other than acute LB and TBE. The specific aim was to evaluate the scientific support for laboratory diagnosis of human granulocytic anaplasmosis, rickettsiosis, neoehrlichiosis, babesiosis, hard tick relapsing fever, tularemia and bartonellosis, as well as tick-borne co-infections and persistent LB in spite of recommended standard antibiotic treatment. Methods: We performed a systematic literature search in 11 databases for research published from 2007 through 2017, and categorized potentially relevant references according to the predefined infections and study design. An expert group assessed the relevance and eligibility and reviewed the articles according to the QUADAS (diagnostic studies) or AMSTAR (systematic reviews) protocols, respectively. Clinical evaluations of one or several diagnostic tests and systematic reviews were included. Case reports, non-human studies and articles published in other languages than English were excluded. Results: A total of 48 studies fulfilled the inclusion criteria for evaluation. The majority of these studies were based on small sample sizes. There were no eligible studies for evaluation of tick-borne co-infections or for persistent LB after antibiotic treatment. Conclusions: Our findings highlight the need for larger evaluations of laboratory tests using clinical samples from well-defined cases taken at different time-points during the course of the diseases. Since the diseases occur at a relatively low frequency, single-center cross-sectional studies are practically not feasible, but multi-center case control studies could be a way forward.

Genotyping of Francisella tularensis subsp. holarctica from Hares in Germany

Francisella tularensis is the causative agent of the zoonotic disease tularemia. In Germany, most human infections are caused by contact with infected hares. The aim of this study was to characterize Francisella tularensis subsp. holarctica strains isolated from hares in Germany and to develop bioinformatics tools to analyze their genetic relatedness. In total, 257 German isolates-obtained mainly from hares (n = 233), other vertebrate animals, and ticks, but also from humans (n = 3)-were analyzed within this study. Publically available sequence data from 49 isolates were used to put our isolates into an epidemiological context and to compare isolates from natural foci and humans. Whole-genome sequences were analyzed using core-genome Multi-Locus-Sequence-Typing, canonical Single Nucleotide Polymorphism (SNP) typing and whole-genome SNP typing. An overall conformity of genotype clustering between the typing methods was found, albeit with a lower resolution for canonical single SNP typing. The subclade distribution, both on local and national levels, among strains from humans and hares was similar, suggesting circulation of the same genotypes both in animals and humans. Whilst close to identical isolates of the same subclade were found distributed over large areas, small geographical foci often harbored members of different subclades. In conclusion, although genomic high-resolution typing was shown to be robust, reproducible and allowed the identification of highly closely related strains, genetic profiling alone is not always conclusive for epidemiological linkage of F. tularensis strains.

Tularemia Goes West: Epidemiology of an Emerging Infection in Austria

The zoonotic disease tularemia is caused by the Gram-negative bacterium Francisella tularensis, with the two major subspecies tularensis and holarctica being responsible for infections in humans and animals. The F. tularensis subspecies holarctica is less virulent and prevalent in Europe and Asia. Over the last few centuries, few epidemic outbreaks and low numbers of infections have been registered in the eastern part of Austria, specifically in the provinces of Lower Austria, Burgenland, and Styria. The reported infections were mostly associated with hunting hares and the skinning of carcasses. Within the last decade, ticks have been identified as important vectors in Tyrol and served as first evidence for the spread of F. tularensis to Western Austria. In 2018, the pathogen was detected in hares in the provinces of Tyrol, Vorarlberg, and Salzburg. We presume that F. tularensis is now established in most regions of Austria, and that the investigation of potential host and vector animals should be spotlighted by public institutions. Tularemia in humans presents with various clinical manifestations. As glandular, ulceroglandular, and typhoidal forms occur in Austria, this infectious disease should be considered as a differential diagnosis of unknown fever.

Francisella tularensis Subspecies holarctica and Tularemia in Germany

Tularemia is a zoonotic disease caused by Francisella tularensis a small, pleomorphic, facultative intracellular bacterium. In Europe, infections in animals and humans are caused mainly by Francisella tularensis subspecies holarctica. Humans can be exposed to the pathogen directly and indirectly through contact with sick animals, carcasses, mosquitoes and ticks, environmental sources such as contaminated water or soil, and food. So far, F. tularensis subsp. holarctica is the only Francisella species known to cause tularemia in Germany. On the basis of surveillance data, outbreak investigations, and literature, we review herein the epidemiological situation-noteworthy clinical cases next to genetic diversity of F. tularensis subsp. holarctica strains isolated from patients. In the last 15 years, the yearly number of notified cases of tularemia has increased steadily in Germany, suggesting that the disease is re-emerging. By sequencing F. tularensis subsp. holarctica genomes, knowledge has been added to recent findings, completing the picture of genotypic diversity and geographical segregation of Francisella clades in Germany. Here, we also shortly summarize the current knowledge about a new Francisella species (Francisella sp. strain W12-1067) that has been recently identified in Germany. This species is the second Francisella species discovered in Germany.

Genetic Diversity and Spatial Segregation of Francisella tularensis Subspecies holarctica in Germany

Francisella tularensis is an intracellular pleomorphic bacterium and the causative agent of tularemia, a zoonotic disease with a wide host range. Among the F. tularensis subspecies, especially F. tularensis subsp. holarctica is of clinical relevance for European countries. The study presented herein focuses namely on genetic diversity and spatial segregation of F. tularensis subsp. holarctica in Germany, as still limited information is available. The investigation is based on the analysis of 34 F. tularensis subsp. holarctica isolates and one draft genome from an outbreak strain. The isolates were cultured from sample material being that of primarily human patients (n = 25) and free-living animals (n = 9). For six of 25 human isolates, epidemiological links between disease onset and tick bites could be established, confirming the importance of arthropod linked transmission of tularemia in Germany. The strains were assigned to three of four major F. tularensis subsp. holarctica clades: B.4, B.6, and B.12. Thereby, B.6 and B.12 clade members were predominantly found; only one human isolate was assigned to clade B.4. Also, it turned out that eight isolates which caused pneumonia in patients clustered into the B.6 clade. Altogether, eight different final subclades were assigned to clade B.6 (biovar I, erythromycin sensitive) and six to B.12 (biovar II, erythromycin resistant) in addition to one new final B.12 subclade. Moreover, for 13 human and 3 animal isolates, final subclade subdivisions were not assigned (B.12 subdivisions B.33 and B.34, and B.6 subdivision B.45) because official nomenclatures are not available yet. This gives credit to the genetic variability of F. tularensis subsp. holarctica strains in Germany. The results clearly point out that the given genetic diversity in Germany seems to be comparably high to that found in other European countries including Scandinavian regions. A spatial segregation of B.6 and B.12 strains was found and statistically confirmed, and B.12 clade members were predominantly found in eastern parts and B.6 members more in western to southern parts of Germany. The portion of B.12 clade members in northeastern parts of Germany was 78.5% and in southwestern parts 1.9%.

Genetic diversity of Francisella tularensis in Poland with comments on MLVA genotyping and a proposition of a novel rapid v4-genotyping

We investigated the genotypes of Francisella tularensis (F. tularensis) strains isolated in Poland during the period 1953-2013 and studied their genetic relationship to F. tularensis strains isolated in other countries using MLVA. We examined the mosquito and tick samples collected in Poland for the presence of F. tularensis DNA using PCR. Our results revealed a high genetic diversity among the strains of F. tularensis collected from Poland, suggesting that the bacterium is commonly found in the environment. However, we did not detect F. tularensis DNA in ticks and mosquitoes, showing that the arthropod bites might not be the main source of infection. We also propose the application of a practical assay called v4-genotyping that can be directly performed on the clinical and environmental samples. In addition, we discovered genetic variations among Schu S4 reference strains used in various laboratories and showed that MLVA analysis should not be based on amplicon sizes only because point mutations occurring within the MLVA loci might not always be manifested by a change in the amplicon size.

[Painful lymphadenopathy after an insect bite-a case report]

Tularemia is a bacterial zoonosis which is commonly transmitted through tick or insect bites or contact with meat of infected animals. We report the case of a 36-year-old man who developed fever, chills, headaches, and a painful, unilateral, inguinal lymphadenopathy with a red-livid skin discoloration after an insect bite on his abdomen. Ulceroglandular tularemia was diagnosed through polymerase chain reaction (PCR) and serology. Treatment with doxycycline for 21 days resulted in an excellent outcome.

Tularemia: an experience of 13 cases including a rare myocarditis in a referral center in Eastern Switzerland (Central Europe) and a review of the literature

BACKGROUND

Tularemia, a zoonotic disease caused by Francisella tularensis, can cause a broad spectrum of disease in humans including six major clinical presentations: the ulceroglandular, glandular, oculoglandular, oropharyngeal, typhoidal and pneumonic form. The epidemiology and ecology and thus transmission of tularemia are complex, depending on conditions unique to specific locations.

CASE SERIES AND METHODS

Thirteen cases with different forms of the disease and one very rare case of a myocarditis are reported, discussed, and reviewed within the scope of current literature.

CONCLUSION

Tularemia is a rare, but emerging disease in Central Europe with glandular and ulceroglandular disease as its predominant forms. Transmission is mainly caused by contact with lagomorphs, rodents and tick bites. However, domestic cats may play an important role in transmission too. Myocarditis is probably a worldwide, but very rare manifestation of tularemia.

Control of Lyme borreliosis and other Ixodes ricinus-borne diseases

Lyme borreliosis (LB) and other Ixodes ricinus-borne diseases (TBDs) are diseases that emerge from interactions of humans and domestic animals with infected ticks in nature. Nature, environmental and health policies at (inter)national and local levels affect the risk, disease burden and costs of TBDs. Knowledge on ticks, their pathogens and the diseases they cause have been increasing, and resulted in the discovery of a diversity of control options, which often are not highly effective on their own. Control strategies involving concerted actions from human and animal health sectors as well as from nature managers have not been formulated, let alone implemented. Control of TBDs asks for a “health in all policies” approach, both at the (inter)national level, but also at local levels. For example, wildlife protection and creating urban green spaces are important for animal and human well-being, but may increase the risk of TBDs. In contrast, culling or fencing out deer decreases the risk for TBDs under specific conditions, but may have adverse effects on biodiversity or may be societally unacceptable. Therefore, in the end, nature and health workers together must carry out tailor-made control options for the control of TBDs for humans and animals, with minimal effects on the environment. In that regard, multidisciplinary approaches in environmental, but also medical settings are needed. To facilitate this, communication and collaboration between experts from different fields, which may include patient representatives, should be promoted.

Tularemia in Germany-A Re-emerging Zoonosis

Tularemia, also known as “rabbit fever,” is a zoonosis caused by the facultative intracellular, gram-negative bacterium Francisella tularensis. Infection occurs through contact with infected animals (often hares), arthropod vectors (such as ticks or deer flies), inhalation of contaminated dust or through contaminated food and water. In this review, we would like to provide an overview of the current epidemiological situation in Germany using published studies and case reports, an analysis of recent surveillance data and our own experience from the laboratory diagnostics, and investigation of cases. While in Germany tularemia is a rarely reported disease, there is evidence of recent re-emergence. We also describe some peculiarities that were observed in Germany, such as a broad genetic diversity, and a recently discovered new genus of Francisella and protracted or severe clinical courses of infections with the subspecies holarctica. Because tularemia is a zoonosis, we also touch upon the situation in the animal reservoir and one-health aspects of this disease. Apparently, many pieces of the puzzle need to be found and put into place before the complex interaction between wildlife, the environment and humans are fully understood. Funding for investigations into rare diseases is scarce. Therefore, combining efforts in several countries in the framework of international projects may be necessary to advance further our understanding of this serious but also scientifically interesting disease.

Francisella tularensis and other bacteria in hares and ticks in North Rhine-Westphalia (Germany)

Tularemia is a zoonotic disease caused by the bacterium Francisella tularensis. The disease can be transmitted to humans through contact with infected animals such as the European brown hare (Lepus europaeus) and ticks as vectors. The aim of this study was to isolate F. tularensis from ticks and hares in North Rhine-Westphalia using cysteine heart agar to determine their genetic relatedness and to identify other bacteria that grow on this medium. 848 European brown hares and 1556 questing ticks (all Ixodes ricinus) from forests were tested using cultivation and MALDI-TOF mass spectrometry or partial 16S rRNA gene sequencing. The majority of F. tularensis isolates from hares (n=24; 96%) and genomic F. tularensis DNA recovered from ticks belonged to the basal genetic clade IV and subclade B.18. These isolates were sensitive to erythromycin and were assigned to biovar I. Only a single strain isolated from a hare was assigned to basal clade I (B.12/B.35). All isolates were sensitive to tetracycline, doxycycline, streptomycin, gentamicin, chloramphenicol, and ciprofloxacin. Only 4 tick pools were positive for F. tularensis and cultivation was not successful in any of the pools. Most of the other isolated bacteria belonged to the order Bacillales with 36 Staphylococcus isolates, 9 Bacillus isolates and 8 Paenibacillus isolates. Prominent members of Enterobacterales were represented by different genera like Pantoea, Erwinia, Raoultella etc. Several of the bacterial species were soil or plant-associated, but some of the bacterial species were found in I. ricinus for the first time. Our results showed that F. tularensis was detected only in few ticks of an endemic area, but ticks were also infected by several other bacteria with zoonotic potential. Therefore, a wider spectrum of pathogens should be considered if a patient was bitten by a tick.