Brook Yockey

Laboratory analysis of tularemia in wild-trapped, commercially traded prairie dogs, Texas, 2002.

Oropharyngeal tularemia was identified as the cause of a die-off in captured wild prairie dogs at a commercial exotic animal facility in Texas. From this point source, Francisella tularensis–infected prairie dogs were traced to animals distributed to the Czech Republic and to a Texas pet shop. F. tularensis culture isolates were recovered tissue specimens from 63 prairie dogs, including one each from the secondary distribution sites. Molecular and biochemical subtyping indicated that all isolates were F. tularensis subsp. holarctica (Type B). Microagglutination assays detected antibodies against F. tularensis, with titers as great as 1:4,096 in some live animals. All seropositive animals remained culture positive, suggesting that prairie dogs may act as chronic carriers of F. tularensis. These findings demonstrate the need for additional studies of tularemia in prairie dogs, given the seriousness of the resulting disease, the fact that prairie dogs are sold commercially as pets, and the risk for pet-to-human transmission.

Pneumonic Plague Cluster, Uganda, 2004

In a case cluster, pneumonic plague transmission was compatible with respiratory droplet rather than aerosol transmission.

Virulence differences among Francisella tularensis subsp. tularensis clades in mice.

Francisella tularensis subspecies tularensis (type A) and holarctica (type B) are of clinical importance in causing tularemia. Molecular typing methods have further separated type A strains into three genetically distinct clades, A1a, A1b and A2. Epidemiological analyses of human infections in the United States suggest that A1b infections are associated with a significantly higher mortality rate as compared to infections caused by A1a, A2 and type B. To determine if genetic differences as defined by molecular typing directly correlate with differences in virulence, A1a, A1b, A2 and type B strains were compared in C57BL/6 mice. Here we demonstrate significant differences between survival curves for infections caused by A1b versus A1a, A2 and type B, with A1b infected mice dying earlier than mice infected with A1a, A2 or type B; these results were conserved among multiple strains. Differences were also detected among type A clades as well as between type A clades and type B with respect to bacterial burdens, and gross anatomy in infected mice. Our results indicate that clades defined within F. tularensis subsp. tularensis by molecular typing methods correlate with virulence differences, with A1b strains more virulent than A1a, A2 and type B strains. These findings indicate type A strains are not equivalent with respect to virulence and have important implications for public health as well as basic research programs.

Lack of Antimicrobial Resistance in Yersinia pestis Isolates from 17 Countries in the Americas, Africa, and Asia

ABSTRACT Yersinia pestis is the causative agent of plague, a fulminant disease that is often fatal without antimicrobial treatment. Plasmid (IncA/C)-mediated multidrug resistance in Y. pestis was reported in 1995 in Madagascar and has generated considerable public health concern, most recently because of the identification of IncA/C multidrug-resistant plasmids in other zoonotic pathogens. Here, we demonstrate no resistance in 392 Y. pestis isolates from 17 countries to eight antimicrobials used for treatment or prophylaxis of plague.

Outbreak of Francisella novicida Bacteremia Among Inmates at a Louisiana Correctional Facility

BACKGROUND Francisella novicida is a rare cause of human illness despite its close genetic relationship to Francisella tularensis, the agent of tularemia. During April-July 2011, 3 inmates at a Louisiana correctional facility developed F. novicida bacteremia; 1 inmate died acutely. METHODS We interviewed surviving inmates; reviewed laboratory, medical, and housing records; and conducted an environmental investigation. Clinical and environmental samples were tested by culture, real-time polymerase chain reaction (PCR), and multigene sequencing. Isolates were typed by pulsed-field gel electrophoresis (PFGE). RESULTS Clinical isolates were identified as F. novicida based on sequence analyses of the 16S ribosomal RNA, pgm, and pdpD genes. PmeI PFGE patterns for the clinical isolates were indistinguishable. Source patients were aged 40-56 years, male, and African American, and all were immunocompromised. Two patients presented with signs of bacterial peritonitis; the third had pyomyositis of the thigh. The 3 inmates had no contact with one another; their only shared exposures were consumption of municipal water and of ice that was mass-produced at the prison in an unenclosed building. Swabs from one set of ice machines and associated ice scoops yielded evidence of F. novicida by PCR and sequencing. All other environmental specimens tested negative. CONCLUSIONS To our knowledge, this is the first reported common-source outbreak of F. novicida infections in humans. Epidemiological and laboratory evidence implicate contaminated ice as the likely vehicle of transmission; liver disease may be a predisposing factor. Clinicians, laboratorians, and public health officials should be aware of the potential for misidentification of F. novicida as F. tularensis.

Virulence difference between the prototypic Schu S4 strain (A1a) and Francisella tularensis A1a, A1b, A2 and type B strains in a murine model of infection.

BackgroundThe use of prototypic strains is common among laboratories studying infectious agents as it promotes consistency for data comparability among and between laboratories. Schu S4 is the prototypic virulent strain of Francisella tularensis and has been used extensively as such over the past six decades. Studies have demonstrated virulence differences among the two clinically relevant subspecies of F. tularensis, tularensis (type A) and holarctica (type B) and more recently between type A subpopulations (A1a, A1b and A2). Schu S4 belongs to the most virulent subspecies of F. tularensis, subspecies tularensis.MethodsIn this study, we investigated the relative virulence of Schu S4 in comparison to A1a, A1b, A2 and type B strains using a temperature-based murine model of infection. Mice were inoculated intradermally and a hypothermic drop point was used as a surrogate for death. Survival curves and the length of temperature phases were compared for all infections. Bacterial burdens were also compared between the most virulent type A subpopulation, A1b, and Schu S4 at drop point.ResultsSurvival curve comparisons demonstrate that the Schu S4 strain used in this study resembles the virulence of type B strains, and is significantly less virulent than all other type A (A1a, A1b and A2) strains tested. Additionally, when bacterial burdens were compared between mice infected with Schu S4 or MA00-2987 (A1b) significantly higher burdens were present in the blood and spleen of mice infected with MA00-2987.ConclusionsThe knowledge gained from using Schu S4 as a prototypic virulent strain has unquestionably advanced the field of tularemia research. The findings of this study, however, indicate that careful consideration of F. tularensis strain selection must occur when the overall virulence of the strain used could impact the outcome and interpretation of results.

Use of Temperature for Standardizing the Progression of Francisella tularensis in Mice

The study of infectious agents, their pathogenesis, the host response and the evaluation of newly developed countermeasures often requires the use of a living system. Murine models are frequently used to undertake such investigations with the caveat that non-biased measurements to assess the progression of infection are underutilized. Instead, murine models predominantly rely on symptomology exhibited by the animal to evaluate the state of the animals health and to determine when euthanasia should be performed. In this study, we used subcutaneous temperature as a non-subjective measurement to follow and compare infection in mice inoculated with Francisella tularensis, a Gram-negative pathogen that produces an acute and fatal illness in mice. A reproducible temperature pattern defined by three temperature phases (normal, febrile and hypothermic) was identified in all mice infected with F. tularensis, regardless of the infecting strain. More importantly and for the first time a non-subjective, ethical, and easily determined surrogate endpoint for death based on a temperature, termed drop point, was identified and validated with statistical models. In comparative survival curve analyses for F. tularensis strains with differing virulence, the drop point temperature yielded the same results as those obtained using observed time to death. Incorporation of temperature measurements to evaluate F. tularensis was standardized based on statistical models to provide a new level of robustness for comparative analyses in mice. These findings should be generally applicable to other pathogens that produce acute febrile disease in animal models and offers an important tool for understanding and following the infection process.

Two Distinct Yersinia pestis Populations Causing Plague among Humans in the West Nile Region of Uganda

Background Plague is a life-threatening disease caused by the bacterium, Yersinia pestis. Since the 1990s, Africa has accounted for the majority of reported human cases. In Uganda, plague cases occur in the West Nile region, near the border with Democratic Republic of Congo. Despite the ongoing risk of contracting plague in this region, little is known about Y. pestis genotypes causing human disease. Methodology/Principal Findings During January 2004–December 2012, 1,092 suspect human plague cases were recorded in the West Nile region of Uganda. Sixty-one cases were culture-confirmed. Recovered Y. pestis isolates were analyzed using three typing methods, single nucleotide polymorphisms (SNPs), pulsed field gel electrophoresis (PFGE), and multiple variable number of tandem repeat analysis (MLVA) and subpopulations analyzed in the context of associated geographic, temporal, and clinical data for source patients. All three methods separated the 61 isolates into two distinct 1.ANT lineages, which persisted throughout the 9 year period and were associated with differences in elevation and geographic distribution. Conclusions/Significance We demonstrate that human cases of plague in the West Nile region of Uganda are caused by two distinct 1.ANT genetic subpopulations. Notably, all three typing methods used, SNPs, PFGE, and MLVA, identified the two genetic subpopulations, despite recognizing different mutation types in the Y. pestis genome. The geographic and elevation differences between the two subpopulations is suggestive of their maintenance in highly localized enzootic cycles, potentially with differing vector-host community composition. This improved understanding of Y. pestis subpopulations in the West Nile region will be useful for identifying ecologic and environmental factors associated with elevated plague risk.

Successful Treatment of Human Plague with Oral Ciprofloxacin

The US Food and Drug Administration recently approved ciprofloxacin for treatment of plague (Yersina pestis infection) based on animal studies. Published evidence of efficacy in humans is sparse. We report 5 cases of culture-confirmed human plague treated successfully with oral ciprofloxacin, including 1 case of pneumonic plague.

Patterns of Human Plague in Uganda, 2008–2016

Plague is a highly virulent fleaborne zoonosis that occurs throughout many parts of the world; most suspected human cases are reported from resource-poor settings in sub-Saharan Africa. During 2008–2016, a combination of active surveillance and laboratory testing in the plague-endemic West Nile region of Uganda yielded 255 suspected human plague cases; approximately one third were laboratory confirmed by bacterial culture or serology. Although the mortality rate was 7% among suspected cases, it was 26% among persons with laboratory-confirmed plague. Reports of an unusual number of dead rats in a patient’s village around the time of illness onset was significantly associated with laboratory confirmation of plague. This descriptive summary of human plague in Uganda highlights the episodic nature of the disease, as well as the potential that, even in endemic areas, illnesses of other etiologies might be being mistaken for plague.