Marine Infectious Disease Dynamics and Outbreak Thresholds: Contact Transmission, Pandemic Infection, and the Potential Role of Filter Feeders

Disease-causing organisms can have significant impacts on marine species and communities. However, the dynamics that underlie the emergence of disease outbreaks in marine ecosystems still lack the equivalent level of description, conceptual understanding, and modeling context routinely present in the terrestrial systems. Here, we propose a theoretical basis for modeling the transmission of marine infectious diseases (MIDs) developed from simple models of the spread of infectious disease. The models represent the dynamics of a variety of host-pathogen systems including those unique to marine systems where transmission of disease is by contact with waterborne pathogens both directly and through filter-feeding processes. Overall, the analysis of the epizootiological models focused on the most relevant processes that interact to drive the initiation and termination of epizootics. A priori, systems with multi-step disease infections (e.g., infection-death-particle release-filtration-transmission) reduced dependence on individual parameters resulting in inherently slower transmissions rates. This is demonstrably not the case; thus, these alternative transmission pathways must also considerably increase the rates of processes involved in transmission. Scavengers removing dead infected animals may inhibit disease spread in both contact-based and waterborne pathogen-based diseases. The capacity of highly infected animals, both alive and dead, to release a substantial number of infective elements into the water column, making them available to suspension feeders results in such diseases being highly infective with a very small low-abundance refuge . In these systems, the body burden of pathogens and the relative importance between the release and the removal rate of pathogens in the host tissue or water column becomes paramount. Two processes are of potential consequence inhibiting epizootics. First, large water volumes above the benthic susceptible populations can function as a sink for pathogens. Second, unlike contact-based disease models in which an increase in the number of susceptible individuals in the population increases the likelihood of transmission and epizootic development, large populations of filter feeders can reduce this likelihood through the overfiltration of infective particles

Understanding uncertainty in temperature effects on vector-borne disease: A Bayesian approach

Extrinsic environmental factors influence the distribution and population dynamics of many organisms, including insects that are of concern for human health and agriculture. This is particularly true for vector-borne infectious diseases, like malaria, which is a major source of morbidity and mortality in humans. Understanding the mechanistic links between environment and population processes for these diseases is key to predicting the consequences of climate change on transmission and for developing effective interventions. An important measure of the intensity of disease transmission is the reproductive number $R_0$. However, understanding the mechanisms linking $R_0$ and temperature, an environmental factor driving disease risk, can be challenging because the data available for parameterization are often poor. To address this we show how a Bayesian approach can help identify critical uncertainties in components of $R_0$ and how this uncertainty is propagated into the estimate of $R_0$. Most notably, we find that different parameters dominate the uncertainty at different temperature regimes: bite rate from 15-25$^\circ$ C; fecundity across all temperatures, but especially $\sim$25-32$^\circ$ C; mortality from 20-30$^\circ$ C; parasite development rate at $\sim$15-16$^\circ$C and again at $\sim$33-35$^\circ$C. Focusing empirical studies on these parameters and corresponding temperature ranges would be the most efficient way to improve estimates of $R_0$. While we focus on malaria, our methods apply to improving process-based models more generally, including epidemiological, physiological niche, and species distribution models.Comment: 27 pages, including 1 table and 3 figure

Inflammatory bowel disease [IBD] and physical activity : a study on the impact of diagnosis on the level of exercise amongst patients with IBD

Background and Aims: Inflammatory bowel disease [IBD] can impair patients’ functional capacity with significant negative effects on their quality of life. Our aim was to determine the impact of IBD diagnosis on fitness levels and to assess the levels of engagement in physical activity and fatigue in IBD patient before and after diagnosis. Methods: A prospective multi-centre cross-sectional study was performed. Patients diagnosed with IBD in the previous 18 months were recruited. Inclusion criteria included clinical remission and/or no treatment changes within the previous 6 months. Physical exercise levels were assessed by the Godin score and fatigue levels was assessed by the functional assessment of chronic illness therapy [FACIT] score. Results: In total, 158 patients (100 Crohn’s disease [CD]) were recruited. Mean age was 35.1 years (95% confidence interval [CI] ± 2.0). Gender distribution was approximately equal [51.3% male]. The Mean Harvey Bradshaw and Simple Clinical Colitis Activity indices were 2.25 [95% CI ± 0.40] and 1.64 [95% CI ± 0.49], respectively. The mean Godin score difference before and after IBD diagnosis was 6.94 [p = 0.002]. Patients with ulcerative colitis [UC] [41.8%] were more likely than patients with CD [23.0%] to reduce their exercise levels [p = 0.04]. FACIT scores were lower in patients who had experienced relapses [p = 0.012] and had severe disease [p = 0.011]. Approximately one-third of patients reduced their activity level following IBD diagnosis. Conclusions: Patients were significantly less physically active after a diagnosis of IBD and this was more apparent in UC. Identification of the risk factors associated with loss of fitness levels would help to address the reduced patient quality of life.peer-reviewe

Clostridium difficile infection in Polish pediatric outpatients with inflammatory bowel disease

The prevalence of Clostridium difficile infection (CDI) in pediatric patients with inflammatory bowel disease (IBD) is still not sufficiently recognized. We assessed the prevalence of CDI and recurrences in outpatients with IBD. In addition, the influence of IBD therapy on CDI and antimicrobial susceptibility of the potentially causative C. difficile strains was assessed. This was a prospective, single-center, observational study. All specimens were obtained between January 2005 and January 2007 from the IBD outpatient service and screened for C. difficile and its toxins. C. difficile isolates were genotyped by PCR ribotyping. Diagnosis of Crohn’s disease (CD) and ulcerative colitis (UC) was based on Porto criteria. Severity of disease was assessed using the Hyams scale (for Crohn’s disease) and the Truelove–Witts scale (for ulcerative colitis). One hundred and forty-three fecal samples from 58 pediatric IBD patients (21 with Crohn’s disease and 37 with ulcerative colitis) were screened. The risk of C. difficile infection was 60% and was independent of disease type (CD or UC) (χ2 = 2.5821, df = 3, p = 0.4606). About 17% of pediatric IBD patients experienced a recurrence of CDI. All C. difficile strains were susceptible to metronidazole, vancomycin and rifampin. A high prevalence of C. difficile infection and recurrences in pediatric outpatients with IBD was observed, independent of disease type. There was no significant correlation between C. difficile infection and IBD therapy. PCR ribotyping revealed C. difficile re-infection and relapses during episodes of IBD in pediatric outpatients

Utilizing Spatial Demographic and Life History Variation to Optimize Sustainable Yield of a Temperate Sex-Changing Fish

Fish populations vary geographically in demography and life history due to environmental and ecological processes and in response to exploitation. However, population dynamic models and stock assessments, used to manage fisheries, rarely explicitly incorporate spatial variation to inform management decisions. Here, we describe extensive geographic variation in several demographic and life history characteristics (e.g., size structure, growth, survivorship, maturation, and sex change) of California sheephead (Semicossyphus pulcher), a temperate rocky reef fish targeted by recreational and commercial fisheries. Fish were sampled from nine locations throughout southern California in 2007–2008. We developed a dynamic size and age-structured model, parameterized separately for each location, to assess the potential cost or benefit in terms of fisheries yield and conservation objectives of changing minimum size limits and/or fishing mortality rates (compared to the status quo). Results indicate that managing populations individually, with location-specific regulations, could increase yield by over 26% while maintaining conservative levels of spawning biomass. While this local management approach would be challenging to implement in practice, we found statistically similar increases in yield could be achieved by dividing southern California into two separate management regions, reflecting geographic similarities in demography. To maximize yield, size limits should be increased by 90 mm in the northern region and held at current levels in the south. We also found that managing the fishery as one single stock (the status quo), but with a size limit 50 mm greater than the current regulations, could increase overall fishery yield by 15%. Increases in size limits are predicted to enhance fishery yield and may also have important ecological consequences for the predatory role of sheephead in kelp forests. This framework for incorporating demographic variation into fisheries models can be exported generally to other species and may aid in identifying the appropriate spatial scales for fisheries management