Estimating the size of European rabbits consumed by predators: Relationship between body mass and tooth dimensions

A method for estimating body mass of European rabbitsOryctolagus cuniculus (Linnaeus, 1758) based on tooth dimensions is proposed. Regression models identified significant relationships between the body mass of 87 rabbits and individual tooth length, breadth, product of tooth length and breadth, and whether or not the individual was infected with myxomatosis. Dimensions of 10 of 14 different teeth explained over 80% of variation in body mass, and those teeth were selected as adequate predictors of rabbit body mass. Models were tested using teeth from 16 additional rabbits of known body mass. Body mass, predicted on the basis of 9 of the 10 selected teeth, was statistically indistinguishable from the observed values for all 16 individuals. When myxomatosis infection status of the rabbit was included in the model, all 10 selected teeth yielded predictions statistically indistinguishable from those observed. Prediction errors can be computed permitting statistical comparison of the average predicted value of body mass from different samples of rabbits. The model is useful in estimating rabbit body masses from teeth recovered from feces of predators and it will facilitate testing of hypotheses on size-selective predation. The method was applied to rabbit teeth found in fecal samples from the Iberian lynxLynx pardinus collected over a one-year period. Lynx preyed preferentially upon younger rabbits during the peak breeding period of this lagomorph.     

Antibacterial alkoxybenzamide inhibitors of the essential bacterial cell division protein FtsZ

3-Methoxybenzamide is a weak inhibitor of the essential bacterial cell division protein FtsZ. Exploration of the structure–activity relationships of 3-methoxybenzamide analogues led to the identification of potent anti-staphylococcal compounds.     

Transmission Dynamics and Prospects for the Elimination of Canine Rabies

Rabies has been eliminated from domestic dog populations in Western Europe and North America, but continues to kill many thousands of people throughout Africa and Asia every year. A quantitative understanding of transmission dynamics in domestic dog populations provides critical information to assess whether global elimination of canine rabies is possible. We report extensive observations of individual rabid animals in Tanzania and generate a uniquely detailed analysis of transmission biology, which explains important epidemiological features, including the level of variation in epidemic trajectories. We found that the basic reproductive number for rabies, R₀, is very low in our study area in rural Africa (~1.2) and throughout its historic global range (<2). This finding provides strong support for the feasibility of controlling endemic canine rabies by vaccination, even near wildlife areas with large wild carnivore populations. However, we show that rapid turnover of domestic dog populations has been a major obstacle to successful control in developing countries, thus regular pulse vaccinations will be required to maintain population-level immunity between campaigns. Nonetheless our analyses suggest that with sustained, international commitment, global elimination of rabies from domestic dog populations, the most dangerous vector to humans, is a realistic goal.     

Latent class evaluation of the performance of serological tests for exposure to Brucella spp. in cattle,sheep, and goats in Tanzania

BackgroundBrucellosis is a neglected zoonosis endemic in many countries, including regions of sub-Saharan Africa. Evaluated diagnostic tools for the detection of exposure to Brucella spp. are important for disease surveillance and guiding prevention and control activities.Methods and findingsBayesian latent class analysis was used to evaluate performance of the Rose Bengal plate test (RBT) and a competitive ELISA (cELISA) in detecting Brucella spp. exposure at the individual animal-level for cattle, sheep, and goats in Tanzania. Median posterior estimates of RBT sensitivity were: 0.779 (95% Bayesian credibility interval (BCI): 0.570–0.894), 0.893 (0.636–0.989), and 0.807 (0.575–0.966), and for cELISA were: 0.623 (0.443–0.790), 0.409 (0.241–0.644), and 0.561 (0.376–0.713), for cattle, sheep, and goats, respectively. Sensitivity BCIs were wide, with the widest for cELISA in sheep. RBT and cELISA median posterior estimates of specificity were high across species models: RBT ranged between 0.989 (0.980–0.998) and 0.995 (0.985–0.999), and cELISA between 0.984 (0.974–0.995) and 0.996 (0.988–1). Each species model generated seroprevalence estimates for two livestock subpopulations, pastoralist and non-pastoralist. Pastoralist seroprevalence estimates were: 0.063 (0.045–0.090), 0.033 (0.018–0.049), and 0.051 (0.034–0.076), for cattle, sheep, and goats, respectively. Non-pastoralist seroprevalence estimates were below 0.01 for all species models. Series and parallel diagnostic approaches were evaluated. Parallel outperformed a series approach. Median posterior estimates for parallel testing were ≥0.920 (0.760–0.986) for sensitivity and ≥0.973 (0.955–0.992) for specificity, for all species models.ConclusionsOur findings indicate that Brucella spp. surveillance in Tanzania using RBT and cELISA in parallel at the animal-level would give high test performance. There is a need to evaluate strategies for implementing parallel testing at the herd- and flock-level. Our findings can assist in generating robust Brucella spp. exposure estimates for livestock in Tanzania and wider sub-Saharan Africa. The adoption of locally evaluated robust diagnostic tests in setting-specific surveillance is an important step towards brucellosis prevention and control.     

Top-down or bottom-up regulation of intra-host blood-stage malaria: do malaria parasites most resemble the dynamics of prey or predator?

Knowledge of the factors that limit parasite numbers offers hope of improved intervention strategies as well as exposing the selective forces that have shaped parasite life-history strategies. We develop a theoretical framework with which to consider the intra-host regulation of malaria parasite density. We analyse a general model that relates timing and magnitude of peak parasite density to initial dose under three different regulatory processes. The dynamics can be regulated either by top-down processes (upgradable immune regulation), bottom-up processes (fixed immune response and red blood cell (RBC) limitation) or a mixture of the two. We define and estimate the following key parameters: (i) the rate of RBC replenishment; (ii) the rate of destruction of uninfected RBCs; and (iii) the maximum parasite growth rate. Comparing predictions of this model with experimental results for rodent malaria in laboratory mice allowed us to reject functional forms of immune upregulation and/or effects of RBC limitation that were inconsistent with the data. Bottom-up regulation alone was insufficient to account for observed patterns without invoking either localized depletion of RBC density or merozoite interference. By contrast, an immune function upregulated in proportion to either merozoite or infected RBC density was consistent with observed dynamics. An immune response directed solely at merozoites required twice the level of activation of one directed at infected RBCs.     

The construction and analysis of epidemic trees with reference to the 2001 UK foot-and-mouth outbreak

The case-reproduction ratio for the spread of an infectious disease is a critically important concept for understanding dynamics of epidemics and for evaluating impact of control measures on spread of infection. Reliable estimation of this ratio is a problem central to epidemiology and is most often accomplished by fitting dynamic models to data and estimating combinations of parameters that equate to the case-reproduction ratio. Here, we develop a novel parameter-free method that permits direct estimation of the history of transmission events recoverable from detailed observation of a particular epidemic. From these reconstructed 'epidemic trees', case-reproduction ratios can be estimated directly. We develop a bootstrap algorithm that generates percentile intervals for these estimates that shows the procedure to be both precise and robust to possible uncertainties in the historical reconstruction. Identifying and 'pruning' branches from these trees whose occurrence might have been prevented by implementation of more stringent control measures permits estimation of the possible efficacy of these alternative measures. Examination of the cladistic structure of these trees as a function of the distance of each case from its infection source reveals useful insights about the relationship between long-distance transmission events and epidemic size. We demonstrate the utility of these methods by applying them to data from the 2001 foot-and-mouth disease outbreak in the UK.     

Habitat loss and raptor predation: disentangling long- and short-term causes of red grouse declines

The number of red grouse (Lagopus lagopus scoticus) shot in the UK has declined by 50% during the 20th century This decline has coincided with reductions in the area of suitable habitat and recoveries in the populations of some avian predators. Here we use long-term records of shooting bags and a large-scale manipulation of raptor density to disentangle the effects of habitat loss and raptor predation on grouse populations. The numbers of grouse harvested on the Eskdale half of Langholm Moor in southern Scotland declined significantly during 1913-1990 and grouse bags from the whole moor from 1950 to 1990 exhibited an almost identical but non-significant trend. Hen harriers (Circus cyaneus) and peregrine falcons (Falco peregrinus) were absent or bred at low densities on this moor throughout this period but heather-dominant vegetation declined by 48% between 1948 and 1988. Harrier and peregrine breeding numbers on Langholm Moor increased to high levels following protection in 1990 whilst grouse density and grouse bags declined year after year until shooting was abandoned in 1998. The prediction of a peak in grouse bags on Langholm Moor in 1996 based on the patterns of bags during 1950-1990 was supported by the observed peaks in 1997 on two nearby moors with few raptors which formerly cycled in synchrony with Langholm Moor. This study demonstrates that, whilst long-term declines in grouse bags were most probably due to habitat loss, high levels of raptor predation subsequently limited the grouse population and suppressed a cycle. This study thus offers support to theoretical models which predict that generalist predators may suppress cycles in prey populations.