Comparison of fitted survival curves.

<p>A) Survival curves (fitted for all data from round 1 and round 2) are shown for mice infected with <i>F. tularensis</i> groups (A1a, A1b, A2 and type B) using drop point (solid lines) and observed time of death (dashed lines). The time at which each mouse expired (solid circles) or reached drop point (open circles) was reached is shown below the graph. B) Survival curve comparison between two infections performed at different times using the same A1b strain MA00-2987. The first MA00-2987 infection is denoted as (••• — •••). During this infection, mice were allowed to expire and drop point was subsequently identified and used as the endpoint for generating the survival curve. The second MA00-2987 infection is denoted as (——). Mice were euthanized at drop point during this infection for generation of the survival curve. The time at which each mouse reached drop point is shown below the graph as squares (1^st round) or circles (2^nd round).</p

Temperature curves.

<p>Mice (n = 14 mice for each of the four <i>F. tularensis</i> infection groups) infected in round 1 and round 2 with <i>F. tularensis</i> groups (A1a, A1b, A2 and type B) are shown. Mice were infected with <i>F. tularensis</i> and temperature was monitored every 1–2 hours until mice expired.</p

Length of infection phase for mice infected with each <i>F. tularensis</i> group (A1a, A1b, A2 and type B).

a<p>All lengths were measured in hours.</p

A representative mouse subcutaneous temperature curve in response to infection with <i>F. tularensis</i> type B is shown.

<p>P1, P2 and P3 represent phase 1 (normal phase), phase 2 (febrile phase) and phase 3 (hypothermic phase), respectively. Black dots on the temperature curve labeled CP1 and CP2 represent change point 1 and change point 2, respectively.</p

PFGE analysis of <i>F. tularensis</i> strains.

<p>A diagram depicting the eight <i>F. tularensis</i> strains used to infect mice (two strains per each of the four <i>F. tularensis</i> groups, A1a, A1b, A2 and type B). <i>F. tularensis</i> subsp. <i>tularensis</i> strain Schu S4 (A1a) and LVS (type B) were included in the dendogram as reference strains.</p

<i>Francisella tularensis</i> strains used in this study.

<p><i>Francisella tularensis</i> strains used in this study.</p

Weight loss and spleen, liver and lung weights for mice infected with <i>F. tularensis</i> A1a, A1b, A2, and type B.

<p>C57BL/6J mice (n = 14/group) were challenged intradermally with 10-20 CFU of <i>F. tularensis</i> A1a, A1b, A2, and type B. Mice were weighed prior to infection and at time of death. Organs were harvested and weighed at time of death. <b>A</b>) Mouse weight (grams) for each infection group and both control groups. No statistical difference was observed between round 1 and round 2. <b>B</b>) Spleen weight (grams) for each infection group and both control groups. No statistical difference was observed between round 1 and round 2. <b>C</b>) Liver weight (grams) for each infection group and both control groups. No statistical difference was observed between round 1 and round 2. <b>D</b>) Lung weight (grams) for each infection group and both control groups. A statistical difference was observed between round 1 and round 2. For all graphs, significant differences (p<0.05) in Log₁₀ CFU within round 1 infections and within round 2 infections are shown by different letters (A, B, etc.). If two strains have the same letter, no significant differences were identified between them.</p

Bacterial burden of <i>F. tularensis</i> within the blood, spleen, liver and lungs of infected mice.

<p>C57BL/6J mice (n = 14/group) were challenged intradermally with 10-20 CFU of <i>F. tularensis</i> A1a, A1b, A2, and type B. At time of death, organs were harvested and blood was taken from each mouse. <b>A</b>) Bacterial burden (Log₁₀ CFU/ml) within blood samples of all infection groups. No statistical difference was observed between round 1 and round 2. <b>B</b>) Bacterial burden (Log₁₀ CFU/spleen) within spleens of all infection groups. A statistical difference was observed between round 1 and round 2. <b>C</b>) Bacterial burden (Log₁₀ CFU/liver) within livers of all infection groups. No statistical difference was observed between round 1 and round 2. <b>D</b>) Bacterial burden (Log₁₀ CFU/lung) within lungs of all infection groups. A statistical difference was observed between round 1 and round 2. For all graphs, significant differences (p<0.05) in Log₁₀ CFU within round 1 infections and within round 2 infections are shown by different letters (A, B, etc.). If two strains have the same letter, no significant differences were identified between them.</p

Survival curves of naïve mice following challenge with <i>F. tularensis</i> A1a, A1b, A2 and type B.

<p>C57BL/6J mice (n = 14/group; n = 7/strain) were challenged intradermally with 10–20 CFU of <i>F. tularensis</i> A1a (strains OK01-2528 and MO02-4195), A1b (strains MD00-2970 and MA00-2987), A2 (strains WY96-3418 and NM99-1823) and type B (strains KY99-3387 and MI00-1730), and survival was monitored over time. <b>A</b>) Time of death for n = 14 mice per <i>F. tularensis</i> group (A1a, A1b, A2 and type B). Circles represent mice infected in round 1(n = 7) and triangles represent mice infected in round 2 (n = 7). <b>B</b>) Step-down survival curves for proportion of mice surviving over time (hours). Data shown is from round 1 and round 2 for A1a, A1b, A2 and type B data. Median times of death are noted as a bold cross. <b>C</b>) Fitted survival curves for proportion of mice surviving over time (hours) using a Weibull distribution for combined (n = 14 mice/group) round 1 and round 2 A1a, A1b, A2 and type B data.</p

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

<div><p>Background</p><p>Plague is a life-threatening disease caused by the bacterium, <i>Yersinia pestis</i>. 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 <i>Y</i>. <i>pestis</i> genotypes causing human disease.</p><p>Methodology/Principal Findings</p><p>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 <i>Y</i>. <i>pestis</i> 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.</p><p>Conclusions/Significance</p><p>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 <i>Y</i>. <i>pestis</i> 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 <i>Y</i>. <i>pestis</i> subpopulations in the West Nile region will be useful for identifying ecologic and environmental factors associated with elevated plague risk.</p></div