Outbreaks of tularemia in a boreal forest region depends on mosquito prevalence

Thoracic manifestations of tularaemia: a case series

BACKGROUND

Tularaemia is a zoonotic disease caused by Francisella tularensis, a highly virulent bacterium that affects humans and small wild animals. It is transmitted through direct contact with infected animals or indirectly through contaminated soil, water or arthropod bites (e.g. ticks). Primary thoracic manifestations of tularaemia are infrequent and, therefore, a diagnostic challenge for clinicians.

METHODS

We report six tularaemia cases with exclusively thoracic involvement diagnosed in a clinic for pulmonary diseases in Bavaria between 10/2020 and 02/2022.

RESULTS

All patients lived or were active in rural areas, four reported a recent tick bite. All patients presented with thoracic lymphadenopathy and pulmonary tumours or consolidations; all underwent bronchoscopy with EBUS-TBNA of lymph nodes, three lung biopsies as well. Five patients showed inflammatory changes in the endobronchial mucosa. The main histological findings were necrotic epithelioid granulomas with remarkable granulocyte infiltration. All cases were identified by positive serology, five by PCR (here identification of F.t. ssp. Holarctica) from biopsy as well. As first-line therapy, oral ciprofloxacin was given (5/6); in 2/6 cases, a combination of quinolone-rifampicin was given.

CONCLUSIONS

Pulmonary tularaemia may occur after tick bites and without extrathoracic manifestations. In patients who present with thoracic lymphadenopathy and pulmonary consolidations and who are exposed to increased outdoor activities, tularaemia should be included in the diagnostic pathway. Histologically, the presence of neutrophil-granulocyte infiltrations might help to distinguish tularaemia from other granulomatous infections, e.g. tuberculosis. The combination of quinolone-rifampicin rather than i.v. gentamicin reduced length of hospital stay in two patients.

Functional characterization of Francisella tularensis subspecies holarctica genotypes during tick cell and macrophage infections using a proteogenomic approach

Tularemia is a vector-borne disease caused by the Gram-negative bacterium Francisella tularensis. Known hosts and vectors in Europe are hare and ticks. F. tularensis is transmitted from ticks and animals, but also from the hydrotelluric environment and the consumption of contaminated water or food. A changing climate expands the range in which ticks can live and consequently might contribute to increasing case numbers of tularemia. Two subspecies of F. tularensis are human pathogenic. Francisella tularensis tularensis (Ftt) is endemic in North America, while Francisella tularensis holarctica (Fth) is the only subspecies causing tularemia in Europe. Ft is classified as a category A bioterrorism agent due to its low infectious dose, multiple modes of transmission, high infectivity and potential for airborne transmission and has become a global public health concern. In line with the European survey and previous phylogenetic studies, Switzerland shows the co-distribution of B.6 and B.12 strains with different geographical distribution and prevalence within the country. To establish itself in different host environments of ticks and mammals, F. tularensis presumably undergoes substantial changes on the transcriptomics and proteomic level. Here we investigate the transcriptomic and proteomic differences of five strains of Fth upon infection of rabbit macrophages and tick cells.

Water and mosquitoes as key components of the infective cycle of Francisella tularensis in Europe: a review

Francisella tularensis is the pathogen of tularemia, a zoonotic disease that have a broad range of hosts. Its epidemiology is related to aquatic environments, particularly in the subspecies holarctica. In this review, we explore the role of water and mosquitoes in the epidemiology of Francisella in Europe. F. tularensis epidemiology has been linked to natural waters, where its persistence has been associated with biofilm and amebas. In Sweden and Finland, the European countries where most human cases have been reported, mosquito bites are a main route of transmission. F. tularensis is present in other European countries, but to date positive mosquitoes have not been found. Biofilm and amebas are potential sources of Francisella for mosquito larvae, however, mosquito vector capacity has not been demonstrated experimentally, with the need to be studied using local species to uncover a potential transmission adaptation. Transstadial, for persistence through life stages, and mechanical transmission, suggesting contaminated media as a source for infection, have been studied experimentally for mosquitoes, but their natural occurrence needs to be evaluated. It is important to clear up the role of different local mosquito species in the epidemiology of F. tularensis and their importance in all areas where tularemia is present.

Mosquitoes provide a transmission route between possums and humans for Buruli ulcer in southeastern Australia

Buruli ulcer, a chronic subcutaneous infection caused by Mycobacterium ulcerans, is increasing in prevalence in southeastern Australia. Possums are a local wildlife reservoir for M. ulcerans and, although mosquitoes have been implicated in transmission, it remains unclear how humans acquire infection. We conducted extensive field survey analyses of M. ulcerans prevalence among mosquitoes in the Mornington Peninsula region of southeastern Australia. PCR screening of trapped mosquitoes revealed a significant association between M. ulcerans and Aedes notoscriptus. Spatial scanning statistics revealed overlap between clusters of M. ulcerans-positive Ae. notoscriptus, M. ulcerans-positive possum excreta and Buruli ulcer cases, and metabarcoding analyses showed individual mosquitoes had fed on humans and possums. Bacterial genomic analysis confirmed shared single-nucleotide-polymorphism profiles for M. ulcerans detected in mosquitoes, possum excreta and humans. These findings indicate Ae. notoscriptus probably transmit M. ulcerans in southeastern Australia and highlight mosquito control as a Buruli ulcer prevention measure.

Francisella and tularemia in western Asia, Iran: a systematic review

Tularemia or rabbit fever is a transmissible disease from animals, rodents, and insects to human populations that is caused by Francisella tularensis. Epidemiological studies showed that tularemia is endemic throughout most different regions of the world. Recent evidence documented the transmission of the F. tularensis in a different part of Asia. Because there is no updated review information for tularemia in Iran, we performed this systematic review. In this study, we systematically explored biomedical databases (Google Scholar, Scopus, PubMed, and Web of sciences) to identify epidemiology, reservoirs, and carriers of Francisella in animal and human clinical specimens from 2010 to 2020, either in English or in Persian. Different studies have shown the different frequencies of F. tularensis among human and animal resources in eighteen provinces of Iran. In total, 1242 human clinical specimens, 1565 animal samples, and 355 environmental water samples were investigated to find F. tularensis in different provinces of Iran. According to the collected documents, 94 human clinical samples, 69 water samples, and 26 animal specimens were introduced as positive samples for the F. tularensis. According to studies, thirteen species of rodent and hare presented as an inter-epizootic reservoir. Only one species of tick (D. marginatus) was introduced as a vector for Francisella in Iran. According to these results, it is essential for exclusive attention to the prevalence of F. tularensis in different provinces of Iran. Furthermore, special planning should be done for prevention, control of the outbreak, and proper treatment of the tularemia.

PEDIATRIC TULAREMIA– A CASE SERIES FROM A SINGLE CENTER IN SWITZERLAND

Background

The incidence of tularemia has recently increased throughout Europe. Pediatric tularemia typically presents with ulceroglandular or glandular disease and requires antimicrobial therapy not used in the empirical management of childhood acute lymphadenitis. We describe the clinical presentation and course in a case series comprising 20 patients.

Methods

This is a retrospective analysis of a single-center case series of microbiologically confirmed tularemia in patients <16 years of age diagnosed between 2010 and 2021.

Results

Nineteen patients (95%) presented with ulceroglandular (n = 14) or glandular disease (n = 5), respectively. A characteristic entry site lesion (eschar) was present in 14 (74%). Fever was present at illness onset in 15 patients (75%) and disappeared in all patients before targeted therapy was initiated. The diagnosis was confirmed by serology in 18 patients (90%). While immunochromatography was positive as early as on day 7, a microagglutination test titer 1:≥160 was found no earlier than on day 13. Sixteen patients (80%) were initially treated with an antimicrobial agent ineffective against F. tularensis. The median delay (range) from illness onset to initiation of targeted therapy was 12 (6–40) days. Surgical incision and drainage were ultimately performed in 12 patients (60%).

Conclusions

Pediatric tularemia in Switzerland usually presents with early, self-limiting fever and a characteristic entry site lesion with regional lymphadenopathy draining the scalp or legs. Particularly in association with a tick exposure history, this presentation may allow early first-line therapy with an agent specifically targeting F. tularensis, potentially obviating the need for surgical therapy.

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.

Biting insects in a rapidly changing Arctic

Biting insects have a long-standing reputation for being an extreme presence in the Arctic, but it is unclear how they are responding to the rapid environmental changes currently taking place in the region. We review recent advances in our understanding of climate change responses by several key groups of biting insects, including mosquitoes, blackflies, and warble/botflies, and we highlight the significant knowledge gaps on this topic. We also discuss how changes in biting insect populations could impact humans and wildlife, including disease transmission and the disruption of culturally and economically important activities. Future work should integrate scientific with local and traditional ecological knowledge to better understand global change responses by biting insects in the Arctic and the associated consequences for the environmental security of Arctic communities.

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.

Tularemia as a Mosquito-Borne Disease

Francisella tularensis (Ft) is the etiological agent of tularemia, a disease known for over 100 years in the northern hemisphere. Ft includes four subspecies, of which two are the etiologic agents of tularemia: Ft subsp. tularensis (Ftt) and Ft subsp. holarctica (Fth), mainly distributed in North America and the whole northern hemisphere, respectively. Several routes of human infection with these bacteria exist, notably through bites of Ixodidae ticks. However, mosquitoes represent the main vectors of Fth in Scandinavia, where large tularemia outbreaks have occurred, usually during the warm season. The mechanisms making mosquitoes vectors of Fth are still unclear. This review covers the inventory of research work and epidemiological data linking tularemia to mosquitoes in Scandinavia and highlights the gaps in understanding mosquitoes and Ft interactions.

Mechanisms Affecting the Acquisition, Persistence and Transmission of Francisella tularensis in Ticks

Over 600,000 vector-borne disease cases were reported in the United States (U.S.) in the past 13 years, of which more than three-quarters were tick-borne diseases. Although Lyme disease accounts for the majority of tick-borne disease cases in the U.S., tularemia cases have been increasing over the past decade, with >220 cases reported yearly. However, when comparing Borrelia burgdorferi (causative agent of Lyme disease) and Francisella tularensis (causative agent of tularemia), the low infectious dose (<10 bacteria), high morbidity and mortality rates, and potential transmission of tularemia by multiple tick vectors have raised national concerns about future tularemia outbreaks. Despite these concerns, little is known about how F. tularensis is acquired by, persists in, or is transmitted by ticks. Moreover, the role of one or more tick vectors in transmitting F. tularensis to humans remains a major question. Finally, virtually no studies have examined how F. tularensis adapts to life in the tick (vs. the mammalian host), how tick endosymbionts affect F. tularensis infections, or whether other factors (e.g., tick immunity) impact the ability of F. tularensis to infect ticks. This review will assess our current understanding of each of these issues and will offer a framework for future studies, which could help us better understand tularemia and other tick-borne diseases.

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.

Implications of Projected Hydroclimatic Change for Tularemia Outbreaks in High-Risk Areas across Sweden

Hydroclimatic change may affect the range of some infectious diseases, including tularemia. Previous studies have investigated associations between tularemia incidence and climate variables, with some also establishing quantitative statistical disease models based on historical data, but studies considering future climate projections are scarce. This study has used and combined hydro-climatic projection outputs from multiple global climate models (GCMs) in phase six of the Coupled Model Intercomparison Project (CMIP6), and site-specific, parameterized statistical tularemia models, which all imply some type of power-law scaling with preceding-year tularemia cases, to assess possible future trends in disease outbreaks for six counties across Sweden, known to include tularemia high-risk areas. Three radiative forcing (emissions) scenarios are considered for climate change projection until year 2100, incuding low (2.6 Wm⁻²), medium (4.5 Wm⁻²), and high (8.5 Wm⁻²) forcing. The results show highly divergent changes in future disease outbreaks among Swedish counties, depending primarily on site-specific type of the best-fit disease power-law scaling characteristics of (mostly positive, in one case negative) sub- or super-linearity. Results also show that scenarios of steeper future climate warming do not necessarily lead to steeper increase of future disease outbreaks. Along a latitudinal gradient, the likely most realistic medium climate forcing scenario indicates future disease decreases (intermittent or overall) for the relatively southern Swedish counties Örebro and Gävleborg (Ockelbo), respectively, and disease increases of considerable or high degree for the intermediate (Dalarna, Gävleborg (Ljusdal)) and more northern (Jämtland, Norrbotten; along with the more southern Värmland exception) counties, respectively.

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).

A Mini-Review of Ixodes Ticks Climate Sensitive Infection Dispersion Risk in the Nordic Region

Climate change in the Nordic countries is projected to lead to both wetter and warmer seasons. This, in combination with associated vegetation changes and increased animal migration, increases the potential incidence of tick-borne diseases (TBD) where already occurring, and emergence in new places. At the same time, vegetation and animal management influence tick habitat and transmission risks. In this paper, we review the literature on Ixodes ricinus, the primary vector for TBD. Current and projected distribution changes and associated disease transmission risks are related to climate constraints and climate change, and this risk is discussed in the specific context of reindeer management. Our results indicate that climatic limitations for vectors and hosts, and environmental and societal/institutional conditions will have a significant role in determining the spreading of climate-sensitive infections (CSIs) under a changing climate. Management emerges as an important regulatory "tool" for tick and/or risk for disease transfer. In particular, shrub encroachment, and pasture and animal management, are important. The results underscore the need to take a seasonal view of TBD risks, such as (1) grazing and migratory (host) animal presence, (2) tick (vector) activity, (3) climate and vegetation, and (4) land and animal management, which all have seasonal cycles that may or may not coincide with different consequences of climate change on CSI migration. We conclude that risk management must be coordinated across the regions, and with other land-use management plans related to climate mitigation or food production to understand and address the changes in CSI risks.

Ecology of Francisella tularensis

Tularemia is a Holarctic zoonosis caused by the gamma proteobacterium Francisella tularensis and is considered to be a vector-borne disease. In many regions, human risk is associated with the bites of flies, mosquitoes, or ticks. But the biology of the agent is such that risk may be fomite related, and large outbreaks can occur due to inhalation or ingestion of contaminated materials. Such well-documented human risk factors suggest a role for these risk factors in the enzootic cycle as well. Many arthropods support the growth or survival of the agent, but whether arthropods (ticks in particular) are obligately required for the perpetuation of F. tularensis remains to be demonstrated. As with most zoonoses, our knowledge of the ecology of F. tularensis has been driven with the objective of understanding human risk. In this review, we focus on the role of the arthropod in maintaining F. tularensis, particularly with respect to long-term enzootic persistence.

The Tick-Borne Diseases STING study: Real-time PCR analysis of three emerging tick-borne pathogens in ticks that have bitten humans in different regions of Sweden and the Aland islands, Finland

A milder climate has during the last decade contributed to an increased density and spreading of ixodid ticks, thus enhancing their role as emerging vectors for pathogenic microorganisms in northern Europe. It remains unclear if they contribute to the occurrence of infections caused by the bacteria Bartonella spp., Francisella tularensis subspecies holarctica and the parasite Toxoplasma gondii in Sweden and on the Åland islands, Finland. In this study, we want to improve understanding of the tick-borne transmission of these pathogens. Volunteers were recruited at primary healthcare centers. Ticks and blood samples were acquired from participants recruited in 2008 and 2009. Health questionnaires were completed, and medical records were acquired where applicable. Feeding time was estimated and screening of pathogens in the ticks was performed through real-time PCR. Ticks (n = 1849) were of mixed developmental stages: 76 larvae, 1295 nymphs, 426 adults and 52 undetermined. All analyzed ticks were considered negative for these pathogens since the CT-values were all below the detection limit for Bartonella spp. (1663 ticks), Francisella spp. (1849 ticks) and Toxoplasma gondii (1813 ticks). We assume that infections with these pathogens are caused by other transmission pathways within these regions of Sweden and the Åland islands, Finland.

Potential for Hydroclimatically Driven Shifts in Infectious Disease Outbreaks: The Case of Tularemia in High-Latitude Regions

Hydroclimatic changes may be particularly pronounced in high-latitude regions and can influence infectious diseases, jeopardizing regional human and animal health. In this study, we consider the example of tularemia, one of the most studied diseases in high-latitude regions, which is likely to be impacted by large regional hydroclimatic changes. For this disease case, we use a validated statistical model and develop a method for quantifying possible hydroclimatically driven shifts in outbreak conditions. The results show high sensitivity of tularemia outbreaks to certain combinations of hydroclimatic variable values. These values are within the range of past regional observations and may represent just mildly shifted conditions from current hydroclimatic averages. The methodology developed also facilitates relatively simple identification of possible critical hydroclimatic thresholds, beyond which unacceptable endemic disease levels may be reached. These results call for further research on how projected hydroclimatic changes may affect future outbreaks of tularemia and other infectious diseases in high-latitude and other world regions, with particular focus on critical thresholds to high-risk conditions. More research is also needed on the generality and spatiotemporal transferability of statistical disease models.

Sindbis virus polyarthritis outbreak signalled by virus prevalence in the mosquito vectors

Polyarthritis and rash caused by Sindbis virus (SINV), was first recognised in northern Europe about 50 years ago and is known as Ockelbo disease in Sweden and Pogosta disease in Finland. This mosquito-borne virus occurs mainly in tropical and sub-tropical countries, and in northern Europe it is suggested to cause regularly reoccurring outbreaks. Here a seven-year cycle of SINV outbreaks has been referred to in scientific papers, although the hypothesis is based solely on reported human cases. In the search for a more objective outbreak signal, we evaluated mosquito abundance and SINV prevalence in vector mosquitoes from an endemic area in central Sweden. Vector mosquitoes collected in the River Dalälven floodplains during the years before, during, and after the hypothesised 2002 outbreak year were assayed for virus on cell culture. Obtained isolates were partially sequenced, and the nucleotide sequences analysed using Bayesian maximum clade credibility and median joining network analysis. Only one SINV strain was recovered in 2001, and 4 strains in 2003, while 15 strains were recovered in 2002 with significantly increased infection rates in both the enzootic and the bridge-vectors. In 2002, the Maximum Likelihood Estimated infection rates were 10.0/1000 in the enzootic vectors Culex torrentium/pipiens, and 0.62/1000 in the bridge-vector Aedes cinereus, compared to 4.9/1000 and 0.0/1000 in 2001 and 0.0/1000 and 0.32/1000 in 2003 Sequence analysis showed that all isolates belonged to the SINV genotype I (SINV-I). The genetic analysis revealed local maintenance of four SINV-I clades in the River Dalälven floodplains over the years. Our findings suggest that increased SINV-I prevalence in vector mosquitoes constitutes the most valuable outbreak marker for further scrutinising the hypothesized seven-year cycle of SINV-I outbreaks and the mechanisms behind.

Epidemiological survey of tularemia in Ilam Province, west of Iran

Background

Francisella tularensis is the causative agent of tularemia in humans and a large number of animal species. Considering recent evidence of the circulation of this bacterium in different parts of Iran, especially in the western provinces, the aim of current study was to determine the tularemia seroprevalence in the human population living in Ilam Province.

Methods

In 2015, 360 serum samples were collected from five groups of people: ranchers (n = 112), farmers (n = 79), butchers and slaughterhouse workers (n = 61), Nature Conservation Officers (n = 34), and referents of medical diagnostic laboratories (n = 74). These samples were tested for the presence of anti- F. tularensis IgG antibodies using the ELISA method.

Results

According to the ELISA manufacturer cutoffs, we found that 10 (2.78%) and 9 (2.5%) sera, respectively, were positive or borderline for F. tularensis IgG antibodies. The highest tularemia seroprevalence was observed among farmers (7.59%).

Conclusions

Our results strongly support the circulation of tularemia in Ilam Province. Because no human tularemia case has been reported so far in this province, we recommend specific education programs to increase knowledge of local health care professionals about this important zoonotic disease.

Zoonoses under our noses

One Health is an effective approach for the management of zoonotic disease in humans, animals and environments. Examples of the management of bacterial zoonoses in Europe and across the globe demonstrate that One Health approaches of international surveillance, information-sharing and appropriate intervention methods are required to successfully prevent and control disease outbreaks in both endemic and non-endemic regions. Additionally, a One Health approach enables effective preparation and response to bioterrorism threats.

Tularemia as a waterborne disease: a review

Francisella tularensis is a Gram-negative, intracellular bacterium causing the zoonosis tularemia. This highly infectious microorganism is considered a potential biological threat agent. Humans are usually infected through direct contact with the animal reservoir and tick bites. However, tularemia cases also occur after contact with a contaminated hydro-telluric environment. Water-borne tularemia outbreaks and sporadic cases have occurred worldwide in the last decades, with specific clinical and epidemiological traits. These infections represent a major public health and military challenge. Human contaminations have occurred through consumption or use of F. tularensis-contaminated water, and various aquatic activities such as swimming, canyoning and fishing. In addition, in Sweden and Finland, mosquitoes are primary vectors of tularemia due to infection of mosquito larvae in contaminated aquatic environments. The mechanisms of F. tularensis survival in water may include the formation of biofilms, interactions with free-living amoebae, and the transition to a 'viable but nonculturable' state, but the relative contribution of these possible mechanisms remains unknown. Many new aquatic species of Francisella have been characterized in recent years. F. tularensis likely shares with these species an ability of long-term survival in the aquatic environment, which has to be considered in terms of tularemia surveillance and control.

Human infectious diseases and the changing climate in the Arctic

Climatic factors, especially temperature, precipitation, and humidity play an important role in disease transmission. As the Arctic changes at an unprecedented rate due to climate change, understanding how climatic factors and climate change affect infectious disease rates is important for minimizing human and economic costs. The purpose of this systematic review was to compile recent studies in the field and compare the results to a previously published review. English language searches were conducted in PubMed, ScienceDirect, Scopus, and PLOS One. Russian language searches were conducted in the Scientific Electronic Library "eLibrary.ru". This systematic review yielded 22 articles (51%) published in English and 21 articles (49%) published in Russian since 2012. Articles about zoonotic and vector-borne diseases accounted for 67% (n = 29) of the review. Tick-borne diseases, tularemia, anthrax, and vibriosis were the most researched diseases likely to be impacted by climatic factors in the Arctic. Increased temperature and precipitation are predicted to have the greatest impact on infectious diseases in the Arctic.

Tick-borne pathogens in Finland: comparison of Ixodes ricinus and I. persulcatus in sympatric and parapatric areas

BACKGROUND

Almost 3500 tick samples, originally collected via a nationwide citizen science campaign in 2015, were screened to reveal the prevalence and distribution of a wide spectrum of established and putative tick-borne pathogens vectored by Ixodes ricinus and I. persulcatus in Finland. The unique geographical distribution of these two tick species in Finland allowed us to compare pathogen occurrence between an I. ricinus-dominated area (southern Finland), an I. persulcatus-dominated area (northern Finland), and a sympatric area (central Finland).

RESULTS

Of the analysed ticks, almost 30% carried at least one pathogen and 2% carried more than one pathogen. A higher overall prevalence of tick-borne pathogens was observed in I. ricinus than in I. persulcatus: 30.0% (604/2014) versus 24.0% (348/1451), respectively. In addition, I. ricinus were more frequently co-infected than I. persulcatus: 2.4% (49/2014) versus 0.8% (12/1451), respectively. Causative agents of Lyme borreliosis, i.e. bacterial genospecies in Borrelia burgdorferi (sensu lato) group, were the most prevalent pathogens (overall 17%). "Candidatus Rickettsia tarasevichiae" was found for the first time in I. ricinus ticks and in Finnish ticks in general. Moreover, Babesia divergens, B. venatorum and "Candidatus Neoehrlichia mikurensis" were reported for the first time from the Finnish mainland.

CONCLUSIONS

The present study provides valuable information on the prevalence and geographical distribution of various tick-borne pathogens in I. ricinus and I. persulcatus ticks in Finland. Moreover, this comprehensive subset of ticks revealed the presence of rare and potentially dangerous pathogens. The highest prevalence of infected ticks was in the I. ricinus-dominated area in southern Finland, while the prevalence was essentially equal in sympatric and I. persulcatus-dominated areas. However, the highest infection rates for both species were in areas of their dominance, either in south or north Finland.

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

Tularemia is a rare zoonotic disease in Germany. Francisella tularensis has been isolated previously from ticks in southern Germany underscoring the importance of ticks (Ixodes ricinus) in tularemia transmission, but there have been only few reports from this region with single cases or small case series of tick-borne transmissions of tularemia. We report five cases of non-game animal associated tularemia diagnosed from 2010 to 2016 in southwestern Germany - Baden-Wuerttemberg. Our case series and molecular typing (MLVA) results add published clinical experience to this underdiagnosed disease and consolidate previous findings regarding tick-borne transmission of tularemia and phylogenetic diversity in Germany.

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.

The potential for flower nectar to allow mosquito to mosquito transmission of Francisella tularensis

Francisella tularensis is disseminated in nature by biting arthropods such as mosquitoes. The relationship between mosquitoes and F. tularensis in nature is highly ambiguous, due in part to the fact that mosquitoes have caused significant tularemia outbreaks despite being classified as a mechanical vector of F. tularensis. One possible explanation for mosquitoes being a prominent, yet mechanical vector is that these insects feed on flower nectar between blood meals, allowing for transmission of F. tularensis between mosquitoes. Here, we aimed to assess whether F. tularensis could survive in flower nectar. Moreover, we examined if mosquitoes could interact with or ingest and transmit F. tularensis from one source of nectar to another. F. tularensis exhibited robust survivability in flower nectar with concentrations of viable bacteria remaining consistent with the rich growth medium. Furthermore, F. tularensis was able to survive (albeit to a lesser extent) in 30% sucrose (a nectar surrogate) over a period of time consistent with that of a typical flower bloom. Although we observed diminished bacterial survival in the nectar surrogate, mosquitoes that fed on this material became colonized with F. tularensis. Finally, colonized mosquitoes were capable of transferring F. tularensis to a sterile nectar surrogate. These data suggest that flower nectar may be capable of serving as a temporary source of F. tularensis that could contribute to the amplification of outbreaks. Mosquitoes that feed on an infected mammalian host and subsequently feed on flower nectar could deposit some F. tularensis bacteria into the nectar in the process. Mosquitoes subsequently feeding on this nectar source could potentially become colonized by F. tularensis. Thus, the possibility exists that flower nectar may allow for vector-vector transmission of F. tularensis.

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.

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.

Dynamics of a Tularemia Outbreak in a Closely Monitored Free-Roaming Population of Wild House Mice

Infectious disease outbreaks can be devastating because of their sudden occurrence, as well as the complexity of monitoring and controlling them. Outbreaks in wildlife are even more challenging to observe and describe, especially when small animals or secretive species are involved. Modeling such infectious disease events is relevant to investigating their dynamics and is critical for decision makers to accomplish outbreak management. Tularemia, caused by the bacterium Francisella tularensis, is a potentially lethal zoonosis. Of the few animal outbreaks that have been reported in the literature, only those affecting zoo animals have been closely monitored. Here, we report the first estimation of the basic reproduction number R₀ of an outbreak in wildlife caused by F. tularensis using quantitative modeling based on a susceptible-infected-recovered framework. We applied that model to data collected during an extensive investigation of an outbreak of tularemia caused by F. tularensis subsp. holarctica (also designated as type B) in a closely monitored, free-roaming house mouse (Mus musculus domesticus) population in Switzerland. Based on our model and assumptions, the best estimated basic reproduction number R₀ of the current outbreak is 1.33. Our results suggest that tularemia can cause severe outbreaks in small rodents. We also concluded that the outbreak self-exhausted in approximately three months without administrating antibiotics.

About three cases of ulceroglandular tularemia, is this the re-emergence of Francisella tularensis in Belgium?

Tularemia is a zoonosis caused by Francisella tularensis that can be transmitted by several ways to human being and cause different clinical manifestations. We report three clinical cases of tularemia with ulceroglandular presentation in young males acquired during outdoor activities in Southern Belgium. Confirmation of the diagnosis was established by serology. Only three cases of tularemia have been reported in Belgium between 1950 and 2012 by the National Reference Laboratory CODA-CERVA (Ref Lab CODA-CERVA) but re-emergence of tularemia is established in several European countries and F. tularensis is also well known to be present in animal reservoirs and vectors in Belgium. The diagnosis of tularemia has to be considered in case of suggestive clinical presentation associated with epidemiological risk factors.

Epidemiology and ecology of tularemia in Sweden, 1984-2012

Geographic distribution of cases was correlated with the locations of lakes and rivers.

The zoonotic disease tularemia is endemic in large areas of the Northern Hemisphere, but research is lacking on patterns of spatial distribution and connections with ecologic factors. To describe the spatial epidemiology of and identify ecologic risk factors for tularemia incidence in Sweden, we analyzed surveillance data collected over 29 years (1984–2012). A total of 4,830 cases were notified, of which 3,524 met all study inclusion criteria. From the first to the second half of the study period, mean incidence increased 10-fold, from 0.26/100,000 persons during 1984–1998 to 2.47/100,000 persons during 1999–2012 (p<0.001). The incidence of tularemia was higher than expected in the boreal and alpine ecologic regions (p<0.001), and incidence was positively correlated with the presence of lakes and rivers (p<0.001). These results provide a comprehensive epidemiologic description of tularemia in Sweden and illustrate that incidence is higher in locations near lakes and rivers.

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.

Transmission of tularemia from a water source by transstadial maintenance in a mosquito vector

Mosquitoes are thought to function as mechanical vectors of Francisella tularensis subspecies holarctica (F. t. holarctica) causing tularemia in humans. We investigated the clinical relevance of transstadially maintained F. t. holarctica in mosquitoes. Aedes egypti larvae exposed to a fully virulent F. t. holarctica strain for 24 hours, were allowed to develop into adults when they were individually homogenized. Approximately 24% of the homogenates tested positive for F. t. DNA in PCR. Mice injected with the mosquito homogenates acquired tularemia within 5 days. This novel finding demonstrates the possibility of transmission of bacteria by adult mosquitoes having acquired the pathogen from their aquatic larval habitats.

An overview: tularemia and travel medicine

Tularemia is a bacterial zoonotic infection. The disease is endemic in most parts of the world, has been reported through the northern hemisphere between 30 and 71° N latitude. Francisella tularensis causes infection in a wide range of vertebrates (rodents, lagomorphs) and invertebrates (ticks, mosquitoes and other arthropods). Humans can acquire this infection through several routes including; a bite from an infected tick, deerfly or mosquito, contact with an infected animal or its dead body. It can also be spread to human by drinking contaminated water or breathing contaminated dirt or aerosol. Clinical manifestation of this disease varies depending on the biotype, inoculum and port of entry. Infection is potentially life threatening, but can effectively be treated with antibiotics. Travelers visiting rural and agricultural areas in endemic countries may be at greater risk. Appropriate clothing and use of insect repellants is essential to prevent tick borne illness. Travelers also should be aware of food and waterborne disease; avoid consuming potentially contaminated water and uncooked meat. Physicians should be aware of any clinical presentation of tularemia in the patients returning from endemic areas.

The status of tularemia in Europe in a one-health context: a review

The bacterium Francisella tularensis causes the vector-borne zoonotic disease tularemia, and may infect a wide range of hosts including invertebrates, mammals and birds. Transmission to humans occurs through contact with infected animals or contaminated environments, or through arthropod vectors. Tularemia has a broad geographical distribution, and there is evidence which suggests local emergence or re-emergence of this disease in Europe. This review was developed to provide an update on the geographical distribution of F. tularensis in humans, wildlife, domestic animals and vector species, to identify potential public health hazards, and to characterize the epidemiology of tularemia in Europe. Information was collated on cases in humans, domestic animals and wildlife, and on reports of detection of the bacterium in arthropod vectors, from 38 European countries for the period 1992-2012. Multiple international databases on human and animal health were consulted, as well as published reports in the literature. Tularemia is a disease of complex epidemiology that is challenging to understand and therefore to control. Many aspects of this disease remain poorly understood. Better understanding is needed of the epidemiological role of animal hosts, potential vectors, mechanisms of maintenance in the different ecosystems, and routes of transmission of the disease.

Association of climatic factors with infectious diseases in the Arctic and subarctic region--a systematic review

Background

The Arctic and subarctic area are likely to be highly affected by climate change, with possible impacts on human health due to effects on food security and infectious diseases.

Objectives

To investigate the evidence for an association between climatic factors and infectious diseases, and to identify the most climate-sensitive diseases and vulnerable populations in the Arctic and subarctic region.

Methods

A systematic review was conducted. A search was made in PubMed, with the last update in May 2013. Inclusion criteria included human cases of infectious disease as outcome, climate or weather factor as exposure, and Arctic or subarctic areas as study origin. Narrative reviews, case reports, and projection studies were excluded. Abstracts and selected full texts were read and evaluated by two independent readers. A data collection sheet and an adjusted version of the SIGN methodology checklist were used to assess the quality grade of each article.

Results

In total, 1953 abstracts were initially found, of which finally 29 articles were included. Almost half of the studies were carried out in Canada (n=14), the rest from Sweden (n=6), Finland (n=4), Norway (n=2), Russia (n=2), and Alaska, US (n=1). Articles were analyzed by disease group: food- and waterborne diseases, vector-borne diseases, airborne viral- and airborne bacterial diseases. Strong evidence was found in our review for an association between climatic factors and food- and waterborne diseases. The scientific evidence for a link between climate and specific vector- and rodent-borne diseases was weak due to that only a few diseases being addressed in more than one publication, although several articles were of very high quality. Air temperature and humidity seem to be important climatic factors to investigate further for viral- and bacterial airborne diseases, but from our results no conclusion about a causal relationship could be drawn.

Conclusions

More studies of high quality are needed to investigate the adverse health impacts of weather and climatic factors in the Arctic and subarctic region. No studies from Greenland or Iceland were found, and only a few from Siberia and Alaska. Disease and syndromic surveillance should be part of climate change adaptation measures in the Arctic and subarctic regions, with monitoring of extreme weather events known to pose a risk for certain infectious diseases implemented at the community level.

All-time high tularaemia incidence in Norway in 2011: report from the national surveillance

Tularaemia has mainly been a sporadic disease in Norway. In 2011, 180 persons (3.7 per 100,000 population) were diagnosed with tularaemia. This article describes the epidemiological and clinical features of tularaemia cases during a year with exceptionally high tularaemia incidence. Data from the national reference laboratory for tularaemia combined with epidemiological data from the Norwegian Surveillance System for Communicable Diseases (MSIS) were used. The incidence of tularaemia varied greatly between counties, but almost every county was involved. The majority (77.8 %) of the cases were diagnosed during the autumn and winter months. The geographic distribution also showed seasonal patterns. Overall, oropharyngeal tularaemia (41.1 %) was the most common clinical presentation, followed by glandular (14.4 %), typhoidal (14.4 %), respiratory (13.3 %) and ulceroglandular (12.8 %) tularaemia. From January to April, oropharyngeal tularaemia dominated, from May to September, ulceroglandular tularaemia was most common, whereas from October to December, there was an almost even distribution between several clinical forms of tularaemia. Eighty-five (47.2 %) of all tularaemia cases were admitted to, or seen as outpatients in, hospitals. An unexpectedly high number (3.9 %) of the patients had positive blood culture with Francisella tularensis. The clinical manifestations of tularaemia in Norway in 2011 were diverse, and changing throughout the year. Classification was sometimes difficult due to uncharacteristic symptoms and unknown mode of transmission. In rodent years, tularaemia is an important differential diagnosis to keep in mind at all times of the year for a variety of clinical symptoms.

Tularaemia: a challenging zoonosis

In recent years, several emerging zoonotic vector-borne infections with potential impact on human health have been identified in Europe, including tularaemia, caused by Francisella tularensis. This remarkable pathogen, one of the most virulent microorganisms currently known, has been detected in increasingly new settings and in a wide range of wild species, including lagomorphs, rodents, carnivores, fish and invertebrate arthropods. Also, a renewed concern has arisen with regard to F. tularensis: its potential use by bioterrorists. Based on the information published concerning the latest outbreaks, the aim of this paper is to review the main features of the agent, its biology, immunology and epidemiology. Moreover, special focus will be given to zoonotic aspects of the disease, as tularaemia outbreaks in human populations have been frequently associated with disease in animals.

Detection of Francisella tularensis in voles in Finland

Francisella tularensis is a highly virulent intracellular bacterium causing the zoonotic disease tularemia. It recurrently causes human and animal outbreaks in northern Europe, including Finland. Although F. tularensis infects several mammal species, only rodents and lagomorphs seem to have importance in its ecology. Peak densities of rodent populations may trigger tularemia outbreaks in humans; however, it is still unclear to which extent rodents or other small mammals maintain F. tularensis in nature. The main objective of this study was to obtain information about the occurrence of F. tularensis in small mammals in Finland. We snap-trapped 547 wild small mammals representing 11 species at 14 locations around Finland during 6 years and screened them for the presence of F. tularensis DNA using PCR analysis. High copy number of F. tularensis-specific DNA was detected in tissue samples of five field voles (Microtus agrestis) originating from one location and 2 years. According to DNA sequences of the bacterial 23S ribosomal RNA gene amplified from F. tularensis-infected voles, the infecting agent belongs to the subspecies holarctica. To find out the optimal tissue for tularemia screening in voles, we compared the amounts of F. tularensis DNA in lungs, liver, spleen, and kidney of the infected animals. F. tularensis DNA was detectable in high levels in all four organs except for one animal, whose kidney was F. tularensis DNA-negative. Thus, at least liver, lung, and spleen seem suitable for F. tularensis screening in voles. Thus, liver, lung, and spleen all seem suitable for F. tularensis screening in voles. In conclusion, field voles can be heavily infected with F. tularensis subsp. holarctica and thus potentially serve as the source of infection in humans and other mammals.

Francisella tularensis subspecies holarctica occurs in Swedish mosquitoes, persists through the developmental stages of laboratory-infected mosquitoes and is transmissible during blood feeding

In Sweden, mosquitoes are considered the major vectors of the bacterium Francisella tularensis subsp. holarctica, which causes tularaemia. The aim of this study was to investigate whether mosquitoes acquire the bacterium as aquatic larvae and transmit the disease as adults. Mosquitoes sampled in a Swedish area where tularaemia is endemic (Örebro) were positive for the presence of F. tularensis deoxyribonucleic acid throughout the summer. Presence of the clinically relevant F. tularensis subsp. holarctica was confirmed in 11 out of the 14 mosquito species sampled. Experiments performed using laboratory-reared Aedes aegypti confirmed that F. tularensis subsp. holarctica was transstadially maintained from orally infected larvae to adult mosquitoes and that 25% of the adults exposed as larvae were positive for the presence of F. tularensis-specific sequences for at least 2 weeks. In addition, we found that F. tularensis subsp. holarctica was transmitted to 58% of the adult mosquitoes feeding on diseased mice. In a small-scale in vivo transmission experiment with F. tularensis subsp. holarctica-positive adult mosquitoes and susceptible mice, none of the animals developed tularaemia. However, we confirmed that there was transmission of the bacterium to blood vials by mosquitoes that had been exposed to the bacterium in the larval stage. Taken together, these results provide evidence that mosquitoes play a role in disease transmission in part of Sweden where tularaemia recurs.

Risk factors for pneumonic and ulceroglandular tularaemia in Finland: a population-based case-control study

Few population-based data are available on factors associated with pneumonic and ulceroglandular type B tularaemia. We conducted a case-control study during a large epidemic in 2000. Laboratory-confirmed case patients were identified through active surveillance and matched control subjects (age, sex, residency) from the national population information system. Data were collected using a self-administered questionnaire. A conditional logistic regression model addressing missing data with Bayesian full-likelihood modelling included 227 case patients and 415 control subjects; reported mosquito bites [adjusted odds ratio (aOR) 9·2, 95% confidence interval (CI) 4·4-22, population-attributable risk (PAR) 82%] and farming activities (aOR 4·3, 95% CI 2·5-7·2, PAR 32%) were independently associated with ulceroglandular tularaemia, whereas exposure to hay dust (aOR 6·6, 95% CI 1·9-25·4, PAR 48%) was associated with pneumonic tularaemia. Although the bulk of tularaemia type B disease burden is attributable to mosquito bites, risk factors for ulceroglandular and pneumonic forms of tularaemia are different, enabling targeting of prevention efforts accordingly.

Biofilms: an advancement in our understanding of Francisella species

Our understanding of the virulence and pathogenesis of Francisella spp. has significantly advanced in recent years, including a new understanding that this organism can form biofilms. What is known so far about Francisella spp. biofilms is summarized here and future research questions are suggested. The molecular basis of biofilm production has begun to be studied, especially the role of extracellular carbohydrates and capsule, quorum sensing and two-component signaling systems. Further work has explored the contribution of amoebae, pili, outer-membrane vesicles, chitinases, and small molecules such as c-di-GMP to Francisella spp. biofilm formation. A role for Francisella spp. biofilm in feeding mosquito larvae has been suggested. As no strong role in virulence has been found yet, Francisella spp. biofilm formation is most likely a key mechanism for environmental survival and persistence. The significance and importance of Francisella spp.’s biofilm phenotype as a critical aspect of its microbial physiology is being developed. Areas for further studies include the potential role of Francisella spp. biofilms in the infection of mammalian hosts and virulence regulation.

Investigation of tularemia outbreak after natural infection of outdoor-housed rhesus macaques (Macaca mulatta) with Francisella tularensis

In the summer and fall of 2010, a series of outdoor-housed rhesus macaques were diagnosed with tularemia. PCR analysis or positive culture confirmed 11 cases, and 9 additional animals with similar clinical signs responded to empiric antibiotic treatment. A serosurvey conducted in the 9 mo after the outbreak found 53% (43 of 81 macaques) seropositivity in the southern outdoor colony, which had an average population of 700 animals. A prospective survey of small mammal reservoirs and arthropod vectors was conducted during the late summer and fall of 2011. PCR analyses of tissues from all 135 mice, 18 ground squirrels, 1 rat, 3 raccoons, 2 cats, and 3 jackrabbits and their fleas were negative for DNA of Francisella tularensis. Conventional PCR evaluation of stored DNA from affected macaques identified the causative organism as F. tularensis subsp. holartica. DNA evaluated from historic cases of tularemia in nonhuman primates confirmed that the organism that infected the colony during the late 1980s likewise was F. tularensis subsp. holartica. The macaque tularemia epizootic of 2010 appears to have been an extreme example of the periodic resurgence of tularemia. No evidence of rodent disease was found in the immediate vicinity during the 2011 interepizootic period. The concurrent widespread seropositivity (53%) and low incidence of clinical disease (2.7%) in 2010 suggests that this strain of Francisella has low pathogenicity in macaques.