Most animal species are infected with multiple parasite species; however, the role of interspecific parasite interactions in influencing parasite dynamics and shaping parasite communities has been unclear. Although laboratory studies have found evidence of cross-immunity, immunosuppression and competition, analyses of hosts in the field have generally concluded that parasite communities are little more than random assemblages. Here we present evidence of consistent interspecific interactions in a natural mammalian system, revealed through the analysis of parasite intensity data collected from a free-ranging rabbit (Oryctolagus cuniculus) population, sampled monthly for a period of 23 yr. The wild rabbit plays host to a diverse gut helminth community that reflects the communities seen in other economically important domestic herbivores. These findings suggest that parasite interactions could have profound implications for the dynamics of parasite communities. The efficacy of parasite control programmes could be jeopardized if such interactions are not taken into account. In contrast, a clear understanding of such interactions may provide the basis for the development of more environmentally acceptable methods of parasite control.

Transmission is a fundamental step in the life cycle of every parasite but it is also one of the most challenging processes to model and quantify. In most host–parasite models, the transmission process is encapsulated by a single parameter β. Many different biological processes and interactions, acting on both hosts and infectious organisms, are subsumed in this single term. There are, however, at least two undesirable consequences of this high level of abstraction. First, nonlinearities and heterogeneities that can be critical to the dynamic behaviour of infections are poorly represented; second, estimating the transmission coefficient β from field data is often very difficult. In this paper, we present a conceptual model, which breaks the transmission process into its component parts. This deconstruction enables us to identify circumstances that generate nonlinearities in transmission, with potential implications for emergent transmission behaviour at individual and population scales. Such behaviour cannot be explained by the traditional linear transmission frameworks. The deconstruction also provides a clearer link to the empirical estimation of key components of transmission and enables the construction of flexible models that produce a unified understanding of the spread of both micro- and macro-parasite infectious disease agents.This article is part of the themed issue ‘Opening the black box: re-examining the ecology and evolution of parasite transmission’.

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There is great interest in the occurrence and consequences of interspecific interactions among co-infecting parasites. However, the extent to which interactions occur is unknown, because there are no validated methods for their detection. We developed a model that generated abundance data for two interacting macroparasite (e.g., helminth) species, and challenged the data with various approaches to determine whether they could detect the underlying interactions. Current approaches performed poorly - either suggesting there was no interaction when, in reality, there was a strong interaction occurring, or inferring the presence of an interaction when there was none. We suggest the novel application of a generalized linear mixed modelling (GLMM)-based approach, which we show to be more reliable than current approaches, even when infection rates of both parasites are correlated (e.g., via a shared transmission route). We suggest that the lack of clarity regarding the presence or absence of interactions in natural systems may be largely attributed to the unreliable nature of existing methods for detecting them. However, application of the GLMM approach may provide a more robust method of detection for these potentially important interspecific interactions from ecological data.

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Water, sanitation, and hygiene (WaSH) are foundational public health interventions for infectious disease control. Renewed efforts to end open defecation and provide universal access to safe drinking water, sanitation, and hygiene by 2030 are being enacted through the Sustainable Development Goals. However, results from clinical trials 1-3 question the efficacy of conventional rural WaSH approaches in low-income and middle-income countries (LMICs). Randomised trials in Bangladesh, 1 Kenya, 2 and Zimbabwe, 3 which introduced household pit latrines, hand-washing with soap, and point-of-use water chlorination, found no effect on child growth, and two of the three trials found no reductions in diarrhoea in children. We have, therefore, called for transformative WaSH approaches, 4 to more effectively reduce pathogen burden and promote child health and growth in LMICs. However, currently, it remains uncertain what transformative WaSH entails. We hypothesise that exposure to animal faeces is currently an under-recognised threat to human health. Estimates published in 2018 have highlighted the scale of animal faecal hazards, 5 which are not explicitly addressed by conventional WaSH strategies. Globally, 80% of the faecal load is estimated to come from livestock animals, including two-thirds of faeces at the household level. 5 Research addressing the effect of domestic and wild animal faeces on WaSH effectiveness is scarce 6,7 and collaboration between the WaSH, public health, and animal health sectors in LMICs insufficient. 6 As an interdisciplinary group of researchers, policy makers, and practitioners in One Health, epidemiology, veterinary medicine, child health, nutrition, microbiology, geography, social science, WaSH, and animal ecology, we met (on May 22-23, 2019) to focus attention on the neglected burden of domestic and wild animal faecal exposure among rural households in LMICs. We contend that without adding safe management of animal faeces to current programmes focused solely on human waste, rural WaSH programmes will insufficiently reduce faecal exposure from all sources to the extent needed to improve child health. To emphasise this, we propose a paradigm shift in WaSH terminology, by upgrading the

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Current analytical models of the mammalian immune system typically assume a specialist predator-prey relationship between invading pathogens and the active components of the immune response. However, in reality, the specific immune system is not immediately effective following invasion by a novel pathogen. First, there may be an explicit time delay between infection and immune initiation and, second, there may be a gradual build-up in immune efficacy (for instance, during the period of B-cell affinity maturation) during which the immune response develops, before reaching maximal specificity to the pathogen. Here, we use a novel theoretical approach to show that these processes, together with the presence of long-lived immune memory, decouple the immune response from current pathogen levels, greatly changing the dynamics of the pathogen-immune system interaction and the ability of the immune response to eliminate the pathogen. Furthermore, we use this model to show how distributed primary immune responses combine with immune memory to greatly affect the optimal virulence of the pathogen, potentially resulting in the evolution of highly virulent pathogens.