Alteration of the chronic wasting disease species barrier by in vitro prion amplification

Chronic wasting disease (CWD) is a transmissible spongiform encephalopathy (TSE) of cervids now detected in 19 states of the United States, three Canadian provinces, and South Korea. Whether noncervid species can be infected by CWD and thereby serve as reservoirs for the infection is not known. To investigate this issue, we previously used serial protein misfolding cyclic amplification (sPMCA) to demonstrate that CWD prions can amplify in brain homogenates from several species sympatric with cervids, including prairie voles (Microtus ochrogaster) and field mice (Peromyscus spp.). Here, we show that prairie voles are susceptible to mule deer CWD prions in vivo and that sPMCA amplification of CWD prions in vole brain enhances the infectivity of CWD for this species. Prairie voles inoculated with sPMCA products developed clinical signs of TSE disease approximately 300 days prior to, and more consistently than, those inoculated with CWD prions from deer brain. Moreover, the deposition patterns and biochemical properties of protease-resistant form of PrP (PrP(RES)) in the brains of affected voles differed from those in cervidized transgenic (CerPrP) mice infected with CWD. In addition, voles inoculated orally with sPMCA products developed clinical signs of TSE and were positive for PrP(RES) deposition, whereas those inoculated orally with deer-origin CWD prions did not. These results demonstrate that transspecies sPMCA of CWD prions can enhance the infectivity and adapt the host range of CWD prions and thereby may be useful to assess determinants of prion species barriers.     

Modeling routes of chronic wasting disease transmission: environmental prion persistence promotes deer population decline and extinction

Chronic wasting disease (CWD) is a fatal disease of deer, elk, and moose transmitted through direct, animal-to-animal contact, and indirectly, via environmental contamination. Considerable attention has been paid to modeling direct transmission, but despite the fact that CWD prions can remain infectious in the environment for years, relatively little information exists about the potential effects of indirect transmission on CWD dynamics. In the present study, we use simulation models to demonstrate how indirect transmission and the duration of environmental prion persistence may affect epidemics of CWD and populations of North American deer. Existing data from Colorado, Wyoming, and Wisconsin's CWD epidemics were used to define plausible short-term outcomes and associated parameter spaces. Resulting long-term outcomes range from relatively low disease prevalence and limited host-population decline to host-population collapse and extinction. Our models suggest that disease prevalence and the severity of population decline is driven by the duration that prions remain infectious in the environment. Despite relatively low epidemic growth rates, the basic reproductive number, R(0), may be much larger than expected under the direct-transmission paradigm because the infectious period can vastly exceed the host's life span. High prion persistence is expected to lead to an increasing environmental pool of prions during the early phases (i.e. approximately during the first 50 years) of the epidemic. As a consequence, over this period of time, disease dynamics will become more heavily influenced by indirect transmission, which may explain some of the observed regional differences in age and sex-specific disease patterns. This suggests management interventions, such as culling or vaccination, will become increasingly less effective as CWD epidemics progress.     

Passage survival of European and American eels at Francis and propeller turbines

We present the magnitude of losses of European eel Anguilla anguilla and American eel A. rostrata in passage through propeller and Francis turbines at hydroelectric projects. Survival and injury rates and types were turbine type related. Overall, eel survival was higher (mean ± 90% CI = 95.1 ± 5.3%,) and injury rate lower (12.5 ± 10.5) at Francis than propeller turbines (survival = 80.7 ± 6.4%; injury rate = 25.7 ± 7.9%). The common injury type at Francis turbines was bruises and at propeller turbines was severance. Blade shape and thickness of the leading edge of the blades (rounded, thick buckets of Francis turbines v. flatter, sharper edged blades in propeller turbines); eel entry routes into the turbines; their flexible, cylindrical body shape and orientation probably contributed to these differences. Relationship between survival and injury and turbine characteristics was turbine specific. For Francis turbines, one negative correlation (r = −0.986, P < 0.01) between survival and runner speed was found and two positive correlations between injury rates and fish length (r = 0.740, P < 0.10) and number of blades (r = 0.835, P < 0.05) were noted for propeller turbines. Several severely injured eels remained active 48 h after turbine passage suggesting caution is warranted when using telemetric movement for estimating eel survival. We conclude there is a need to (a) better understand travel paths and approach orientation of eels through turbines; (b) determine where only eel passage is of concern at hydropower plants that have both turbine types and therefore preferential operation of Francis turbines may be considered; (c) inform hydropower plant operators where turbine replacement is being considered and downstream eel passage is of concern that replacement by Francis or bulb turbines may prove beneficial for eel passage.     

A NEW NITROGEN-FIXING NON-LEGUME: CHAMAEBATIA FOLIOLOSA (ROSACEAE)

Specimens of Chamaebatia foliolosa Benth. with nodule structures on their roots fix atmospheric nitrogen. The nodules are similar to those of other non-legumes in gross morphology and structure, containing hyphal strands, some with club-shaped vesicles at their ends. A fixation rate of 130 nmoles N₂ per g fresh weight per hr is reported by using ¹⁵N₂ as a tracer. Equivalent rates of acetylene reduction were observed.     

Using expert knowledge to incorporate uncertainty in cause‐of‐death assignments for modeling of cause‐specific mortality

Implicit and explicit use of expert knowledge to inform ecological analyses is becoming increasingly common because it often represents the sole source of information in many circumstances. Thus, there is a need to develop statistical methods that explicitly incorporate expert knowledge, and can successfully leverage this information while properly accounting for associated uncertainty during analysis. Studies of cause‐specific mortality provide an example of implicit use of expert knowledge when causes‐of‐death are uncertain and assigned based on the observer's knowledge of the most likely cause. To explicitly incorporate this use of expert knowledge and the associated uncertainty, we developed a statistical model for estimating cause‐specific mortality using a data augmentation approach within a Bayesian hierarchical framework. Specifically, for each mortality event, we elicited the observer's belief of cause‐of‐death by having them specify the probability that the death was due to each potential cause. These probabilities were then used as prior predictive values within our framework. This hierarchical framework permitted a simple and rigorous estimation method that was easily modified to include covariate effects and regularizing terms. Although applied to survival analysis, this method can be extended to any event‐time analysis with multiple event types, for which there is uncertainty regarding the true outcome. We conducted simulations to determine how our framework compared to traditional approaches that use expert knowledge implicitly and assume that cause‐of‐death is specified accurately. Simulation results supported the inclusion of observer uncertainty in cause‐of‐death assignment in modeling of cause‐specific mortality to improve model performance and inference. Finally, we applied the statistical model we developed and a traditional method to cause‐specific survival data for white‐tailed deer, and compared results. We demonstrate that model selection results changed between the two approaches, and incorporating observer knowledge in cause‐of‐death increased the variability associated with parameter estimates when compared to the traditional approach. These differences between the two approaches can impact reported results, and therefore, it is critical to explicitly incorporate expert knowledge in statistical methods to ensure rigorous inference.     

Insecticidal and nematicidal properties of microbial metabolites

Summary Metabolites from 942 microbial isolates were screened for insecticidal and nematicidal properties. The isolates included 302 streptomycetes, 502 novel actinomycetes including representatives of 18 genera, 28 unidentified aerobic actinomycetes, 70 fungi and 40 bacteria other than actinomycetes. When diluted 10-fold, the metabolites from 55 isolates caused nearly 100% mortality in mosquito larvae (Aedes aegypti) within 24 h. These isolates included 27 isolates ofStreptomyces, four ofActinoplanes, three isolates each ofActinomadura andStreptoverticillium, two isolates each ofMicromonospora, Bacillus andPaecilomyces, and one isolate each ofMicropolyspora, Nocardiopsis, Streptosporangium, Oerskovia, Thermomonospora, Chainia, Pseudomonas, Fusarium, Monilia andSyncephalestrum. Two fungal isolates could not be identified to the generie level. Extracts from the culture broth of 18 isolates caused 100% mortality in mosquito larvae within 15 min to 24 h at a concentration of 1000 ppm. The LC₅₀ of partially purified products from two isolates was 1–2.5 ppm and that of the semipurified preparations from four other isolates was 50 ppm. Valinomycin was identified as an active component in the culture broth from one isolate. The culture broth from 15 isolates of aerobic actinomycetes and 4 of fungi were toxic toPanagrellus redivivus (Nematoda); these included 12 isolates with selective nematicidal properties.Michigan Agriculture Experiment Station, Journal Article No. 12321.     

Herbicidal activity of the antibiotics geldanamycin and nigericin

Geldanamycin and nigericin, phytotoxic metabolites from a strain ofStreptomyces hygroscopicus, were tested for herbicidal activity and selectivity on a range of crop and weed species. In petri dish bioassays, geldanamycin reduced radicle growth of all species tested, whereas nigericin inhibited 7 of 10. The two compounds in mixture appeared to be additive rather than synergistic in effect. In assays with seeds and seedlings in field soil, geldanamycin showed significant preemergence activity on proso millet, barnyardgrass, garden cress, and giant foxtail. It had no postemergence herbicidal effect on any of the species tested. Nigericin had preemergence activity on garden cress and large crabgrass and postemergence activity on garden cress and velvetleaf. The postemergence effect of nigericin on velvetleaf was especially striking, with leaves showing symptoms of injury within 24–48 h of treatment. Doses as low as 0.3 kg/ha caused damage. The primary herbicidal effect of both compounds was slowing of seed germination or seedling growth, although some plants were killed, especially at higher rates of application. Herbicidal effects were most pronounced for 1 to 2 weeks after treatment and diminished thereafter.