The evolution of costly acquired immune memory

A key feature of the vertebrate adaptive immune system is acquired immune memory, whereby hosts launch a faster and heightened response when challenged by previously encountered pathogens, preventing full infection. Here, we use a mathematical model to explore the role of ecological and epidemiological processes in shaping selection for costly acquired immune memory. Applying the framework of adaptive dynamics to the classic SIR (Susceptible-Infected-Recovered) epidemiological model, we focus on the conditions that may lead hosts to evolve high levels of immunity. Linking our work to previous theory, we show how investment in immune memory may be greatest at long or intermediate host lifespans depending on whether immunity is long lasting. High initial costs to gain immunity are also found to be essential for a highly effective immune memory. We also find that high disease infectivity and sterility, but intermediate virulence and immune period, increase selection for immunity. Diversity in host populations through evolutionary branching is found to be possible but only for a limited range of parameter space. Our model suggests that specific ecological and epidemiological conditions have to be met for acquired immune memory to evolve

Herd immunity

Herd immunity is an important yet often misunderstood concept in epidemiology. As immunity accumulates in a population — naturally during the course of an epidemic or through vaccination — the spread of an infectious disease is limited by the depletion of susceptible hosts. If a sufficient proportion of the population is immune — above the ‘herd immunity threshold’ — then transmission generally cannot be sustained. Maintaining herd immunity is therefore critical to long-term disease control. In this primer, we discuss the concept of herd immunity from first principles, clarify common misconceptions, and consider the implications for disease control. Much is being said about herd immunity these days. But the concept, though seemingly simple, is often misunderstood. Ben Ashby and Alex Best explain what exactly herd immunity is, how it is achieved in a population, how it is lost, and what it means for disease control.</p

Evolution of host resistance towards pathogen exclusion: the role of predators

Question: Can increased host resistance drive a pathogen to extinction? Do more complex ecosystems lead to significantly different evolutionary behaviour and new potential extinctions? Mathematical method: Merging host-parasite models with predator-prey models. Analytically studying evolution using adaptive dynamics and trade-off and invasion plots, and carrying out numerical simulations. Key assumptions: Mass action (general mixing). All individuals of a given phenotype are identical. Only prey vulnerable to infection. Mutations are small and rare (however, the assumption on the size of mutation is relaxed later). In simulations, very small (negligible) populations are at risk of extinction. Conclusions: The presence of the predator can significantly change evolutionary outcomes for host resistance to a pathogen and can create branching points where none occurred previously. The pathogen (and sometimes the predator) is protected from exclusion if we take mutations to be arbitrarily small; however, relaxing the assumption on mutation size can lead to its exclusion. Increased resistance can drive the predator and/or pathogen to extinction depending on inter-species dynamics, such as the predator's preference for infected prey. Predator co-evolution can move exclusion boundaries and prevent the predator's own extinction if its rate of mutation is high enough (with respect to that of the prey)

Automated prompting technologies in rehabilitation and at home

Purpose - The purpose of this paper is to test the efficacy of an interactive verbal prompting technology (Guide) on supporting the morning routine. Data have already established the efficacy of such prompting during procedural tasks, but the efficacy of such prompting in tasks with procedural and motivational elements remains unexamined. Such tasks, such as getting out of bed in the morning and engaging in personal care, are often the focus of rehabilitation goals. Design/methodology/approach - A single-n study with a male (age 61) who had severe cognitive impairment and was having trouble completing the morning routine. An A-B-A'-B'-A?-B? design was used, with the intervention phase occurring both in an in-patient unit (B, B') and in the participant's own home (B?). Findings - Interactive verbal prompting technology (Guide) significantly reduced support worker prompting and number of errors in the in-patient setting and in the participant's own home. Research limitations/implications - The results suggest that interactive verbal prompting can be used to support motivational tasks such as getting out of bed and the morning routine. This study used a single subject experimental design and the results need to be confirmed in a larger sample. Originality/value - This is the first report of use of interactive verbal prompting technology to support rehabilitation of a motivational task. It is also the first study to evaluate Guide in a domestic context

Tools and techniques for rational points on curves

We give algorithms to compute Coleman integrals on superelliptic curves over unramified extensions of the p-adics, and apply these via Chabauty methods to determine the set of rational points on such curves. We also determine the solution to an explicit instance of the Shafarevich conjecture by finding all elliptic curves with good reduction outside of the first 6 primes, subject to a heuristic. We use a combination of non-abelian Chabauty and the Mordell--Weil sieve to determine the rational points on several quotient modular curves, and therefore classify pairs of elliptic curves over the rationals with 67-, 73-, and 107-isogenies. We give methods to explicitly compute Coleman integrals on modular curves using a canonical lift of Frobenius and canonical local coordinates in each residue disk, and discuss the problem of computing the Weil pairing in finite rings

Understanding the role of eco-evolutionary feedbacks in host-parasite coevolution

It is widely recognised that eco-evolutionary feedbacks can have important implications for evolution. However, many models of host-parasite coevolution omit eco-evolutionary feedbacks for the sake of simplicity, typically by assuming the population sizes of both species are constant. It is often difficult to determine whether the results of these models are qualitatively robust if eco-evolutionary feedbacks are included. Here, by allowing interspecific encounter probabilities to depend on population densities without otherwise varying the structure of the models, we provide a simple method that can test whether eco-evolutionary feedbacks per se affect evolutionary outcomes. Applying this approach to explicit genetic and quantitative trait models from the literature, our framework shows that qualitative changes to the outcome can be directly attributable to eco-evolutionary feedbacks. For example, shifting the dynamics between stable monomorphism or polymorphism and cycling, as well as changing the nature of the cycles. Our approach, which can be readily applied to many different models of host-parasite coevolution, offers a straightforward method for testing whether eco-evolutionary feedbacks qualitatively change coevolutionary outcomes.</p