Detection of Francisella tularensis in voles in Finland

Positive Francisella tularensis meningitis outcome despite delayed identification: a case report

Francisella tularensis is a Gram-negative bacteria, that may cause a zoonotic disease, tularemia. Here, we describe a patient case, where a previously healthy young woman in Northern Finland contacted health care because of fever and headache. Due to the symptoms and lack of further diagnostic tools in primary health care, she was transferred to University Hospital (UH) where ampicillin and ceftriaxone was given empirically. A cerebrospinal fluid sample (CSF) was drawn showing small Gram-negative rods that grew on chocolate agar after 2 days of incubation. Matrix-assisted laser-desorption-ionization time of-flight (Maldi-tof) did not provide identification, but the bacteria was interpreted as sensitive to ciprofloxacin and the treatment was changed to ciprofloxacin. During the time the patient was infected, there were several positive tularemia samples found in the area. Therefore, an in house tularemia nucleic acid method (PCR) was used on the bacterial culture. Additionally, 16S rDNA sequencing was performed and these methods identified the bacteria as F. tularensis. Fortunately, the patient recovered completely with ciprofloxacin and was discharged without any complications. Our case underlines the need to understand the limits of specific diagnostic methods, such as Maldi-tof, used in clinical laboratory settings. It also highlights the need of both clinicians and laboratory staff to be aware of the many clinical presentations of tularemia when working in an endemic area.

Terrestrial and Subterranean Mammals as Reservoirs of Zoonotic Diseases in the Central Part of European Russia

Russia has a number of historical foci of zoonotic anthropogenic diseases. In Central Russia, the Republic of Mordovia is one of such areas, a region being known to have foci of haemorrhagic fever with renal syndrome (HFRS) and tularemia. It therefore requires continuous monitoring. The role of small terrestrial mammals as reservoirs of zoonoses has been previously proven for the region. The aim of this work is to take an integrated approach to assess the role of terrestrial and subterranean small mammals. Subterranean mammals are often not considered important reservoirs of zoonotic pathogens that cause human morbidity. Among small mammals in the wild environment, the bank vole, the yellow-necked mouse and the house mouse play important roles as vectors of zoonoses. Among wild subterranean mammals, the greater mole rat is important as a vector of tularemia and HFRS. We analyzed homogenized internal organs of these animals (lungs, spleen, kidneys). Of all samples from the greater mole rat, 83% were positive for tularemia antigens and 17% were positive forHFRS. None of the analyzed European moles had antigens of tularemia and HFRS. No double infection with both tularemia and hantavirus was detected in the subterranean mammals. Double infection was found among terrestrial mammals in the bank vole and the forest dormouse.

Natural Infection of a European Red Squirrel (Sciurus vulgaris) with Francisella tularensis subsp. Holarctica

Postmortem examination and immunohistochemical and bacteriologic analyses on a free-ranging European red squirrel (Sciurus vulgaris) revealed a systemic infection with Francisella tularensis. Genome sequencing and single-nucleotide polymorphism analysis were consistent with F. tularensis subs. holarctica clade B.45. Tularemia has not previously been reported in this species.

Absence of Francisella tularensis in Finnish Ixodes ricinus and Ixodes persulcatus ticks

Francisella tularensis subsp. holarctica is the causative agent of tularaemia in Europe. Finland is a high-incidence region for tularaemia, with mosquito bites as the most common sources of infection. However, in Central and Western Europe, ticks (Acari: Ixodidae) have been suggested as the main vectors. Indeed, several studies have reported the pathogen from the locally most common human-biting tick species, Ixodes ricinus. In Finland, the occurrence of the pathogen in ticks has started receiving attention only recently. Here, we collate previous tick screening data from Finland regarding F. tularensis as well as present the results from a novel screening of roughly 15 000 I. ricinus and I. persulcatus collected from across the country. In total, 14 878 ticks collected between 2015 and 2020 were screened for F. tularensis using a TaqMan-based qPCR assay targeting the 23 KDa gene. The combined screening efforts of the current and previous studies, encompassing roughly 20 000 ticks, did not find any positive ticks. Given the negative results despite the considerable sample size, it appears that the pathogen is not circulating in local tick populations in Finland. We discuss some possible reasons for the lack of the bacterium in ticks in this high-incidence region of tularaemia.

Development of Immunoassays for Detection of Francisella tularensis Lipopolysaccharide in Tularemia Patient Samples

Francisella tularensis is the causative agent of tularemia, a zoonotic bacterial infection that is often fatal if not diagnosed and treated promptly. Natural infection in humans is relatively rare, yet persistence in animal reservoirs, arthropod vectors, and water sources combined with a low level of clinical recognition make tularemia a serious potential threat to public health in endemic areas. F. tularensis has also garnered attention as a potential bioterror threat, as widespread dissemination could have devastating consequences on a population. A low infectious dose combined with a wide range of symptoms and a short incubation period makes timely diagnosis of tularemia difficult. Current diagnostic techniques include bacterial culture of patient samples, PCR and serological assays; however, these techniques are time consuming and require technical expertise that may not be available at the point of care. In the event of an outbreak or exposure a more efficient diagnostic platform is needed. The lipopolysaccharide (LPS) component of the bacterial outer leaflet has been identified previously by our group as a potential diagnostic target. For this study, a library of ten monoclonal antibodies specific to F. tularensis LPS were produced and confirmed to be reactive with LPS from type A and type B strains. Antibody pairs were tested in an antigen-capture enzyme-linked immunosorbent assay (ELISA) and lateral flow immunoassay format to select the most sensitive pairings. The antigen-capture ELISA was then used to detect and quantify LPS in serum samples from tularemia patients for the first time to determine the viability of this molecule as a diagnostic target. In parallel, prototype lateral flow immunoassays were developed, and reactivity was assessed, demonstrating the potential utility of this assay as a rapid point-of-care test for diagnosis of tularemia.

Wild Small Mammals and Ticks in Zoos-Reservoir of Agents with Zoonotic Potential?

Wild small mammals and ticks play an important role in maintaining and spreading zoonoses in nature, as well as in captive animals. The aim of this study was to monitor selected agents with zoonotic potential in their reservoirs and vectors in a zoo, and to draw attention to the risk of possible contact with these pathogens. In total, 117 wild small mammals (rodents) and 166 ticks were collected in the area of Brno Zoo. Antibodies to the bacteria Coxiella burnetii, Francisella tularensis, and Borrelia burgdorferi s.l. were detected by a modified enzyme-linked immunosorbent assay in 19% (19/99), 4% (4/99), and 15% (15/99) of rodents, respectively. Antibodies to Leptospira spp. bacteria were detected by the microscopic agglutination test in 6% (4/63) of rodents. Coinfection (antibodies to more than two agents) were proved in 14.5% (15/97) of animals. The prevalence of C. burnetii statistically differed according to the years of trapping (p = 0.0241). The DNAs of B. burgdorferi s.l., Rickettsia sp., and Anaplasma phagocytophilum were detected by PCR in 16%, 6%, and 1% of ticks, respectively, without coinfection and without effect of life stage and sex of ticks on positivity. Sequencing showed homology with R. helvetica and A. phagocytophilum in four and one positive samples, respectively. The results of our study show that wild small mammals and ticks in a zoo could serve as reservoirs and vectors of infectious agents with zoonotic potential and thus present a risk of infection to zoo animals and also to keepers and visitors to a zoo.

The Role of Peridomestic Rodents as Reservoirs for Zoonotic Foodborne Pathogens

Although rodents are well-known reservoirs and vectors for a number of zoonoses, the functional role that peridomestic rodents serve in the amplification and transmission of foodborne pathogens is likely underappreciated. Clear links have been identified between commensal rodents and outbreaks of foodborne pathogens throughout Europe and Asia; however, comparatively little research has been devoted to studying this relationship in the United States. In particular, regional studies focused on specific rodent species and their foodborne pathogen reservoir status across the diverse agricultural landscapes of the United States are lacking. We posit that both native and invasive species of rodents associated with food-production pipelines are likely sources of seasonal outbreaks of foodborne pathogens throughout the United States. In this study, we review the evidence that identifies peridomestic rodents as reservoirs for foodborne pathogens, and we call for novel research focused on the metagenomic communities residing at the rodent-agriculture interface. Such data will likely result in the identification of new reservoirs for foodborne pathogens and species-specific demographic traits that might underlie seasonal enteric disease outbreaks. Moreover, we anticipate that a One Health metagenomic research approach will result in the discovery of new strains of zoonotic pathogens circulating in peridomestic rodents. Data resulting from such research efforts would directly inform and improve upon biosecurity efforts, ultimately serving to protect our food supply.

Tularemia: a re-emerging tick-borne infectious disease

Tularemia is a bacterial disease of humans, wild, and domestic animals. Francisella tularensis, which is a Gram-negative coccobacillus-shaped bacterium, is the causative agent of tularemia. Recently, an increase in the number of human tularemia cases has been noticed in several countries around the world. It has been reported mostly from North America, several Scandinavian countries, and certain Asian countries. The disease spreads through vectors such as mosquitoes, horseflies, deer flies, and ticks. Humans can acquire the disease through direct contact of sick animals, consumption of infected animals, drinking or direct contact of contaminated water, and inhalation of bacteria-loaded aerosols. Low infectious dose, aerosol route of infection, and its ability to induce fatal disease make it a potential agent of biological warfare. Tularemia leads to several clinical forms, such as glandular, ulceroglandular, oculoglandular, oropharyngeal, respiratory, and typhoidal forms. The disease is diagnosed through the use of culture, serology, or molecular methods. Quinolones, tetracyclines, or aminoglycosides are frequently used in the treatment of tularemia. No licensed vaccine is available in the prophylaxis of tularemia and this is need of the time and high-priority research area. This review mostly focuses on general features, importance, current status, and preventive measures of this disease.

Coxiella burnetii and Francisella tularensis in wild small mammals from the Czech Republic

Wild rodents are an important source of the tick-borne pathogens Coxiella burnetii and Francisella tularensis. The aim of our study was to assess the prevalence of antibodies and possible coexistence of these pathogens in wild small mammals from three localities in the Czech Republic. A total of 614 wild small mammals (324 Apodemus flavicollis, 145 Myodes glareolus, 50 Sorex araneus, 48 A. sylvaticus, 40 A. agrarius, six Microtus arvalis and one Talpa europaea) were trapped between 2012 and 2015. Their sera or heart extracts were examined by modified indirect enzyme-linked immunosorbent assay, with the detection of antibodies against C. burnetii and F. tularensis in 12 % and 7 % of animals, respectively; coinfection was identified in 4.4 % of animals. The prevalence of C. burnetii and F. tularensis antibodies statistically differed according to animal species and sex (p < 0.05); the seroprevalence of C. burnetii (p < 0.05) also differed in the sampling period. The highest prevalence of antibodies against C. burnetii and F. tularensis was detected in the case of M. glareolus (24 % and 14 %, respectively).

Detection of Francisella tularensis in three vole species in Central Europe

Francisella tularensis is a zoonotic, gram-negative bacterium that causes tularemia in humans. Depending on its subspecies and the route of transmission, mild to lethal courses have been reported. F. tularensis subsp. holarctica is the only subspecies found in Europe and affects a plenitude of vertebrates including lagomorphs and rodents. Population outbreaks of certain rodent species are likely to be involved in the transmission of this pathogen. This molecular survey aims to evaluate the presence of F. tularensis in small mammals from three Central European countries. Using a real-time polymerase chain reaction, F. tularensis DNA was detected in common voles (Microtus arvalis) from Switzerland and in field voles (Microtus agrestis) and a bank vole (Myodes glareolus) from Germany, but not in any other small mammal species. All common voles from the Czech Republic were negative for F. tularensis DNA. The prevalence in the three vole species varied between 1.3% and 3.0%. In conclusion, Francisella tularensis DNA was detected in three vole species in two of three countries investigated. The observed low prevalence raises questions on the role of voles for the transmission of Francisella tularensis in Central Europe.

Phylogenetic Lineages of Francisella tularensis in Animals

Tularemia is a zoonotic disease caused by the facultative intracellular bacterium Francisella tularensis. This microorganism can infect a plethora of animal species and its ecology is particularly complex. Much research was performed to understand its biology but many questions are still open, especially concerning the life cycle of this bacterium in the environment related to physical and biological parameters. Numerous animals are major hosts of F. tularensis but precise reservoir species are not yet well defined. Moreover, the exact range of species susceptible to tularemia is not clear and is complicated by the differences in virulence and ecology observed among the subspecies of F. tularensis. Indeed, different life cycles in nature, including the animal species concerned, were previously described for F. tularensis subsp. tularensis and F. tularensis subsp. holarctica. Recently, molecular techniques showing adequate discrimination between strains were developed, leading to the possibility to investigate links between phylogenetic lineages and infection in animals. New perspectives in research are now possible thanks to the information available and the simplicity of the molecular procedures. Current studies are unfolding the evolution of F. tularensis and these developments will lead to the elucidation of geographical and ecological differences observed by veterinarians, microbiologists and conservation biologists. However, systematic, coordinated collection of data and extensive sampling are important to efficiently assemble the findings of future research.

Rodentia

This chapter includes diseases of animals in the order Rodentia, in which there are over 2000 species representing 40% of all mammals. This incredibly diverse order includes members inhabiting every continent, either naturally or in human-made environments. While rodents have been the cause or implicated in disease transmission that has lead to human pandemics, such as the Black Death, and the decimation of certain animal species, like island-dwelling birds; genetically modified rodents have contributed significantly to the advancement of biomedical research and human health. There are more than 50 species of endangered rats, mice, voles, squirrels, and marmots. The recent extinction of the Bramble Cay melomys represents the first human-induced rodent extinction linked to climate change. Rodents are the reservoir host of several human and domestic pathogens of concern listed by OIE. Herein, we highlight those diseases of rodents that lead to clinically important gross and microscopic lesions.

Outbreak of tularaemia connected to a contaminated well in the Västra Götaland region in Sweden

Tularaemia, is a zoonotic disease caused by the bacterium Francisella tularensis. This disease has been reported in Sweden since 1931 and its wide distribution in the country poses a challenge for understanding the transmission, ecology and epidemiology of the disease. In Sweden, the disease is usually transmitted by mosquitoes, but in this study we could show that consumption of well water was epidemiologically linked to the outbreak, by isolating F. tularensis from the water. In this article, we describe an outbreak of tularaemia in the region of Västra Götaland in the southwest of Sweden in spring of 2013.

Consequences of organ choice in describing bacterial pathogen assemblages in a rodent population

High-throughput sequencing technologies now allow for rapid cost-effective surveys of multiple pathogens in many host species including rodents, but it is currently unclear if the organ chosen for screening influences the number and identity of bacteria detected. We used 16S rRNA amplicon sequencing to identify bacterial pathogens in the heart, liver, lungs, kidneys and spleen of 13 water voles (Arvicola terrestris) collected in Franche-Comté, France. We asked if bacterial pathogen assemblages within organs are similar and if all five organs are necessary to detect all of the bacteria present in an individual animal. We identified 24 bacteria representing 17 genera; average bacterial richness for each organ ranged from 1·5 ± 0·4 (mean ± standard error) to 2·5 ± 0·4 bacteria/organ and did not differ significantly between organs. The average bacterial richness when organ assemblages were pooled within animals was 4·7 ± 0·6 bacteria/animal; Operational Taxonomic Unit accumulation analysis indicates that all five organs are required to obtain this. Organ type influences bacterial assemblage composition in a systematic way (PERMANOVA, 999 permutations, pseudo-F 4,51 = 1·37, P = 0·001). Our results demonstrate that the number of organs sampled influences the ability to detect bacterial pathogens, which can inform sampling decisions in public health and wildlife ecology.

High-risk regions and outbreak modelling of tularemia in humans

Sweden reports large and variable numbers of human tularemia cases, but the high-risk regions are anecdotally defined and factors explaining annual variations are poorly understood. Here, high-risk regions were identified by spatial cluster analysis on disease surveillance data for 1984-2012. Negative binomial regression with five previously validated predictors (including predicted mosquito abundance and predictors based on local weather data) was used to model the annual number of tularemia cases within the high-risk regions. Seven high-risk regions were identified with annual incidences of 3·8-44 cases/100 000 inhabitants, accounting for 56·4% of the tularemia cases but only 9·3% of Sweden's population. For all high-risk regions, most cases occurred between July and September. The regression models explained the annual variation of tularemia cases within most high-risk regions and discriminated between years with and without outbreaks. In conclusion, tularemia in Sweden is concentrated in a few high-risk regions and shows high annual and seasonal variations. We present reproducible methods for identifying tularemia high-risk regions and modelling tularemia cases within these regions. The results may help health authorities to target populations at risk and lay the foundation for developing an early warning system for outbreaks.

High and novel genetic diversity of Francisella tularensis in Germany and indication of environmental persistence

In Germany tularemia is a re-emerging zoonotic disease. Therefore, we investigated wild animals and environmental water samples for the presence and phylogenetic diversity of Francisella tularensis in the poorly studied Berlin/Brandenburg region. The phylogenomic analysis of three isolates from wild animals revealed three new subclades within the phylogenetic tree of F. tularensis [B.71 from a raccoon dog (Nyctereutes procyonoides); B.74 from a red fox (Vulpes vulpes), and B.75 from a Eurasian beaver (Castor fiber albicus)]. The results from histological, PCR, and genomic investigations on the dead beaver showed that the animal suffered from a systemic infection. Indications were found that the bacteria were released from the beaver carcass into the surrounding environment. We demonstrated unexpectedly high and novel phylogenetic diversity of F. tularensis in Germany and the fact that the bacteria persist in the environment for at least one climatic season. These findings support a broader host species diversity than previously known regarding Germany. Our data further support the assumption derived from previous serological studies of an underestimated frequency of occurrence of the pathogen in the environment and in wild animals. F. tularensis was isolated from animal species not previously reported as natural hosts in Germany.

Tularaemia: clinical aspects in Europe

Tularaemia is a zoonotic disease caused by Francisella tularensis, a Gram-negative, facultative intracellular bacterium. Typically, human and animal infections are caused by F tularensis subspecies tularensis (type A) strains mainly in Canada and USA, and F tularensis subspecies holarctica (type B) strains throughout the northern hemisphere, including Europe. In the past, the epidemiological, clinical, therapeutic, and prognostic aspects of tularaemia reported in the English medical literature were mainly those that had been reported in the USA, where the disease was first described. Tularaemia has markedly changed in the past decade, and a large number of studies have provided novel data for the disease characteristics in Europe. In this Review we aim to emphasise the specific and variable aspects of tularaemia in different European countries. In particular, two natural lifecycles of F tularensis have been described in this continent, although not fully characterised, which are associated with different modes of transmission, clinical features, and public health burdens of tularaemia.

Environmental Monitoring and Surveillance of Rodents and Vectors for Francisella tularensis Following Outbreaks of Human Tularemia in Georgia

Tularemia is a re-emerging bacterial zoonosis, broadly distributed across the northern hemisphere. In Georgia, there is a history of human tularemia outbreaks dating back to the 1940s. In response to outbreaks, health officials initiated long-term field surveillance and environmental monitoring. The objective of our study was to obtain information from 57 years of field surveys to identify species that play a role in the occurrence Francisella tularensis subsp. holarctica in the environment in Georgia. We collected historical data on human outbreaks, field collections, population dynamics of the common vole (Microtus arvalis), and conducted surveys on small mammals and vectors from five regions in Georgia during 1956-2012. Bacterial isolation was conducted using standard culturing techniques, and isolation rates for species were obtained for a subset of years. We used a Spearman rank correlation to test for associations between the density of the common vole and isolation rates. From 1956 through 2012, there were four recorded outbreaks of human tularemia (362 cases). A total of 465 bacterial isolates of F. tularensis subsp. holarctica were obtained from 27 species and environmental samples. The number of isolations was highest in the common vole (M. arvalis; 149 isolates; 32%) and Dermacentor marginatus ticks (132 isolates; 28%); isolation rates ranged between 0-0.91% and 0-0.47%, respectively. Population dynamics of the common vole were not correlated with the isolation rate. Given the history of tularemia re-emergence in Georgia, continued field surveys and environmental monitoring may provide an early indication of outbreak risk in humans. In conclusion, our findings provide evidence of long-standing foci of F. tularensis subsp. holarctica that are likely maintained by the common vole-tick cycle.

Incidence and seroprevalence of tularaemia in Finland, 1995 to 2013: regional epidemics with cyclic pattern

We studied the incidence of reported tularaemia by year and region and the prevalence of antibodies against Francisella tularensis in the adult general population in Finland. Moreover, we assessed the correlation between vole population cycles and human tularaemia outbreaks. The seroprevalence study made use of serum samples from a nationwide population-based health survey (Health 2000). The samples of 1,045 randomly selected persons, representative for the Finnish population in each region, were screened with an enzyme-linked immunosorbent assay (ELISA) for the presence of IgG antibodies against F. tularensis, and positive results were further confirmed by immunoblotting. A serological response to F. tularensis was found in 2% (95% confidence interval: 1.1–3.5) of the population. Incidence and seroprevalence were highest in the same areas, and vole population peaks clearly preceded tularaemia outbreaks one year later.

Monitoring biothreat agents (Francisella tularensis, Bacillus anthracis and Yersinia pestis) with a portable real-time PCR instrument

In the event of suspected releases or natural outbreaks of contagious pathogens, rapid identification of the infectious agent is essential for appropriate medical intervention and disease containment. The purpose of this study was to compare the performance of a novel portable real-time PCR thermocycler, PikoReal™, to the standard real-time PCR thermocycler, Applied Biosystems® 7300 (ABI 7300), for the detection of three high-risk biothreat bacterial pathogens: Francisella tularensis, Bacillus anthracis and Yersinia pestis. In addition, a novel confirmatory real-time PCR assay for the detection of F. tularensis is presented and validated. The results show that sensitivity of the assays, based on a dilution series, for the three infectious agents ranged from 1 to 100 fg of target DNA with both instruments. No cross-reactivity was revealed in specificity testing. Duration of the assays with the PikoReal and ABI 7300 systems were 50 and 100 min, respectively. In field testing for F. tularensis, results were obtained with the PikoReal system in 95 min, as the pre-PCR preparation, including DNA extraction, required an additional 45 min. We conclude that the PikoReal system enables highly sensitive and rapid on-site detection of biothreat agents under field conditions, and may be a more efficient alternative to conventional diagnostic methods.

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.

Experimental Infection of voles with Francisella tularensis indicates their amplification role in tularemia outbreaks

Tularemia outbreaks in humans have been linked to fluctuations in rodent population density, but the mode of bacterial maintenance in nature is unclear. Here we report on an experiment to investigate the pathogenesis of Francisella tularensis infection in wild rodents, and thereby assess their potential to spread the bacterium. We infected 20 field voles (Microtus agrestis) and 12 bank voles (Myodes glareolus) with a strain of F. tularensis ssp. holarctica isolated from a human patient. Upon euthanasia or death, voles were necropsied and specimens collected for histological assessment and identification of bacteria by immunohistology and PCR. Bacterial excretion and a rapid lethal clinical course with pathological changes consistent with bacteremia and tissue necrosis were observed in infected animals. The results support a role for voles as an amplification host of F. tularensis, as excreta and, in particular, carcasses with high bacterial burden could serve as a source for environmental contamination.