The Natural History of Pneumonic Tularemia in Female Fischer 344 Rats after Inhalational Exposure to Aerosolized Francisella tularensis Subspecies tularensis Strain SCHU S4

Abstract

The inbred Fischer 344 rat is being evaluated for testing novel vaccines and therapeutics against pneumonic tularemia. Although primary pneumonic tularemia in humans typically occurs by inhalation of aerosolized bacteria, the rat model has relied on intratracheal inoculation of organisms because of safety and equipment issues. We now report the natural history of pneumonic tularemia in female Fischer 344 rats after nose-only inhalational exposure to lethal doses of aerosolized Francisella tularensis subspecies tularensis, strain SCHU S4. Our results are consistent with initial uptake of aerosolized SCHU S4 from the nasal cavity, lungs, and possibly the gastrointestinal tract. Bacteremia with hematogenous dissemination was first detected 2 days after exposure. Shortly thereafter, the infected rats exhibited fever, tachypnea, and hypertension that persisted for 24 to 36 hours and then rapidly decreased as animals succumbed to infection between days 5 and 8 after exposure. Tachycardia was observed briefly, but only after the core body temperature and blood pressure began to decrease as the animals were near death. Initial neutrophilic and histiocytic inflammation in affected tissues became progressively more fibrinous and necrotizing over time. At death, as many as 10 10 colony-forming units were found in the lungs, spleen, and liver. Death was attributed to sepsis and disseminated intravascular coagulation. Overall, the pathogenesis of pneumonic tularemia in the female F344 rat model appears to replicate the disease in humans. (Am J Pathol 2017, 187: 252e267; http://dx

Aerosol prime-boost vaccination provides strong protection in outbred rabbits against virulent type A Francisella tularensis

“…Lung, liver, spleen, and bone marrow are primary targets for bacterial replication and pathogenesis although all organs can be affected, including heart and brain [ 3 – 8 ]. The widespread infection is thought to induce septic shock, disseminated intravascular coagulation and/or acute respiratory distress syndrome resulting in multi-organ failure and death [ 1 , 6 ].…”

The Cynomolgus Macaque Natural History Model of Pneumonic Tularemia for Predicting Clinical Efficacy Under the Animal Rule

“…We have performed full genome sequencing and compared DNA sequences of NIAID cell bank NR-10492 and the Schu S4 isolate used in the above referenced study (Molins et al, 2014 ). We also compared virulence of these two F. tularensis Schu S4 isolates side by side with the F. tularensis MA00-2987 in Fischer 344 rat model of pneumonic tularemia (Hutt et al, 2017 ). No rats ( n = 10/group) that were exposed to target dose of 100 cfu aerosolized NIAID cell bank NR-10492 Schu S4 or MA00-2987 survived after 7 days post-exposure, while all rats exposed to aerosolized Schu S4 isolate that was used in Molins et al ( 2014 ) survived through Day 21 post-exposure (manuscript in preparation).…”

“…Genome sequence annotation and analysis of NIAID cell banks NR-28534 and NR-10492 showed a single nucleotide polymorphism (SNP) in genomic DNA at location 1,767,864 of the published reference Schu S4 genome (GenBank number AJ749949.2 ) which is located in intergenic region between open reading frames FTT_1698c (predicted formate dehydrogenase) and FTT_r08 (predicted 5S ribosomal RNA). NIAID cell banks NR-28534 and NR-10492 contain two copies of Francisella pathogenicity island (FPI) and are highly virulent in Fischer rats when administered by aerosol (LD 50 <1 cfu, Hutt et al, 2017 ).…”

Multiplex Detection of Three Select Agents Directly from Blood by Use of the GeneXpert System

“…The assay sensitivity was 100% for each bacterial species spiked at the LOD. These results suggest that the assay may have the capacity to detect bloodstream infections at the early stages of bacteremia, when the bacterial load is shown to be 1 to 10 CFU/ml (12)(13)(14)(15)(16), and often, traditional culturing methods fail to detect these low numbers (6,11). Indeed, a uniplex version of the F. tularensis assay was able to detect this species directly from the blood of infected macaques on the first day of fever in a subset of animals; and overall, the assay was positive for blood samples drawn sooner after infection than those samples that ultimately became positive by standard blood culture or conventional real-time PCR (6).…”