The persistence of time: the lifespan of Bacillus anthracis spores in environmental reservoirs

Anthrax is a lethal bacterial zoonosis primarily affecting herbivorous wildlife and livestock. Upon host death Bacillus anthracis vegetative cells form spores capable of surviving for years in soil. Anthrax transmission requires host exposure to large spore doses. Thus, conditions that facilitate higher spore concentrations or promote spore survival will increase the probability that a pathogen reservoir infects future hosts. We investigated abiotic and pathogen genomic variation in relation to spore concentrations in surface soils (0-1 cm depth) at 40 plains zebra (Equus quagga) anthrax carcass sites in Namibia. Specifically, how initial spore concentrations and spore survival were affected by seasonality associated with the timing of host mortality, local soil characteristics, and pathogen genomic variation. Zebras dying of anthrax in wet seasons-the peak season for anthrax in Etosha National Park-had soil spore concentrations 1.36 orders of magnitude higher than those that died in dry seasons. No other variables considered affected spore concentrations, and spore survival rates did not differ among sites. Surface soils at these pathogen reservoirs remained culture positive for a range of 3.8-10.4 years after host death. Future research could evaluate if seasonal patterns in spore concentrations are driven by differences in sporulation success or levels of terminal bacteremia.

Disease or drought: environmental fluctuations release zebra from a potential pathogen-triggered ecological trap

When a transmission hotspot for an environmentally persistent pathogen establishes in otherwise high-quality habitat, the disease may exert a strong impact on a host population. However, fluctuating environmental conditions lead to heterogeneity in habitat quality and animal habitat preference, which may interrupt the overlap between selected and risky habitats. We evaluated spatio-temporal patterns in anthrax mortalities in a plains zebra (Equus quagga) population in Etosha National Park, Namibia, incorporating remote-sensing and host telemetry data. A higher proportion of anthrax mortalities of herbivores was detected in open habitats than in other habitat types. Resource selection functions showed that the zebra population shifted habitat selection in response to changes in rainfall and vegetation productivity. Average to high rainfall years supported larger anthrax outbreaks, with animals congregating in preferred open habitats, while a severe drought forced animals into otherwise less preferred habitats, leading to few anthrax mortalities. Thus, the timing of anthrax outbreaks was congruent with preference for open plains habitats and a corresponding increase in pathogen exposure. Given shifts in habitat preference, the overlap in high-quality habitat and high-risk habitat is intermittent, reducing the adverse consequences for the population.

Treatment patterns of docetaxel and paclitaxel in patients with early-stage breast cancer in a community oncology center

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Background: Docetaxel and paclitaxel have been widely used in treating breast cancer (BC). This study aimed to describe real-world treatment patterns of two taxanes in early-stage BC. Methods: Georgia Oncology Specialist Database (GOSD) was used and contained chemotherapy, medical and pharmacy claims, and lab results for nearly 170,000 patients with various types of cancer (2003–2008). Patients with stage I-III BC receiving doxirubicin-cyclophosphamide-taxane (ACT) were identified, and their pre-taxane and on-taxane periods (from first to last dose of docetaxel/paclitaxel) were examined. Number of cycles was compared using Student's t-test. Taxane dose schedule and the use of other chemotherapy in pre- and on-taxane periods were compared using Chi-Square test. A similar analysis was replicated using Pharmetrics database (2003–2008) in BC patients on ACT regimen with prior mastectomy. Results: In GOSD, 79 docetaxel (7.9%, 58.2%, 34.2% in stage I, II, III, respectively) and 139 paclitaxel (10.8%, 64.7%, 25.5% in stage I, II, III, respectively) patients were identified. Compared with paclitaxel, docetaxel patients completed more cycles (4.9 vs. 3.9, p < 0.001), were less frequently on weekly schedule, and more frequently on every-two-week (Q2w) or every-three-week (Q3W) schedules (2.5% vs. 15.2%, 27.9% vs. 62.6%, and 41.8% vs. 0%; p < 0.001). 22.8% of docetaxel patients received AC followed by docetaxel (AC>T) and 77.22% received ACT concurrently, while 100% of paclitaxel patients were on AC>T regimen. In Pharmetrics data, compared with paclitaxel (n = 211), docetaxel patients (n = 96) completed more cycles (11.3 vs. 4.6, p < 0.001), were less frequently on weekly, while more frequently on Q2W and Q3W schedules (3.1 vs. 9.5%, 9.4% vs. 62.6%, and 59.4% vs. 4.7%; p < 0.001). While 97.6% of paclitaxel patients were on AC>T regimen, AC>T and ACT regimens were evenly split among docetaxel patients (49% vs. 51%). Conclusions: Docetaxel and paclitaxel have different treatment patterns in real-world clinical practice. The patterns in a community oncology center appear to be consistent with national data. A potential limitation of this study is that the potential selection bias may not be fully adjusted.

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