Infectious diseases and social distancing in nature

Avoidance of infection

Since our first understanding of the nature of pathogen and parasite transmission, avoidance of infectious diseases has been an essential component of public health and epidemic suppression. Avoidance reduces an individual's risk of contacting pathogens. Humans are not the only host organisms that avoid their pathogens and parasites, though. In nature, infection avoidance is widespread in vertebrates, invertebrates, and even plants. Examining avoidance from this unified taxonomic perspective gives insights into its function, form, evolution, and application. In this Primer, we functionally define avoidance, outline its taxonomic breadth, provide an overview of what is known about its mechanisms and evolution, and identify applications of basic avoidance knowledge across fields as diverse as public health, conservation, and agriculture. We also highlight key open questions directing research into the future.

Fire ants exhibit self-medication but lack preventive behavioral immunity against a viral pathogen

Behavioral immunity in ants encompasses collective behaviors that help defend against pathogens and parasites by reducing infection risks and limiting disease spread. However, much of the research has focused on fungal pathogens, leaving the behavioral immunity responses to viral pathogens largely unexplored. This study represents the first attempt to characterize behavioral immunity in ants against viral pathogens using the red imported fire ant, Solenopsis invicta and one of its common viruses, Solenopsis invicta virus 3 (SINV-3), as the model system. Given that SINV-3 infection has been shown to cause adverse effects on fire ants, we hypothesized that fire ants may mount behavioral immunity defenses against SINV-3 infection, specifically through avoidance behavior, organizational segregation worker discrimination, and self-medication. Surprisingly, none of the preventive behavioral immunity behaviors we tested were observed, suggesting fire ants' inability to detect or mount collective defenses against SINV-3 infection. However, SINV-3-infected fire ants exhibited increased consumption of reactive oxygen species (ROS)-containing food, providing evidence of therapeutic self-medication. These findings suggest that while no evidence suggest fire ants employing preventive behavioral immunity against SINV-3, they may mitigate the effects of infection through self-medication, highlighting a different adaptive strategy in response to viral pathogens. This study opens new avenues for understanding the adaptive strategies of ants to cope with viral pathogens.

Assessing the Sociodemographic Factors Associated With Mycobacterium tuberculosis Complex Infection Among Free-Ranging Long-Tailed Macaques (Macaca fascicularis) in Thailand

The threat of disease transmission at the intersection of human-wildlife interfaces underscores the urgent need for detailed studies on the transmission of human-borne pathogens across species, especially among nonhuman primates in urban areas. This research focuses on the social and demographic determinants of Mycobacterium tuberculosis complex (MTBC) infection in free-ranging long-tailed macaques (Macaca fascicularis) in Thailand. Behavioral observations and noninvasive biological specimens (freshly defecated feces and rope-baited oral samples) were collected from 98 long-tailed macaques living in Wat Khao Thamon, southern Thailand, between August 2021 and February 2022. We detected the MTBC antigen using IS6110 nested-PCR method in 11 out of 98 monkeys (11.22%). Logistic GLMs revealed that the risk of MTBC acquisition was higher among macaques with frequent human-macaque interactions, whereas increased social grooming of conspecifics showed a nonsignificant trend toward reducing the risk. Our findings suggest that anthropogenic exposure increases the risk of MTBC infection among macaques, but this risk may be mitigated (socially buffered) by increased within-group affiliative interactions. More generally, the potential for increased disease prevalence in wildlife with frequent human interactions or reduced social buffering highlights the need to consider animal socio-demography when developing strategies to understand and prevent the transmission of diseases between humans and wildlife.

Social ageing can protect against infectious disease in a group-living primate

The benefits of social living are well established, but sociality also comes with costs, including infectious disease risk. This cost-benefit ratio of sociality is expected to change across individuals' lifespans, which may drive changes in social behaviour with age. To explore this idea, we combine data from a group-living primate for which social ageing has been described with epidemiological models to show that having lower social connectedness when older can protect against the costs of a hypothetical, directly transmitted endemic pathogen. Assuming no age differences in epidemiological characteristics (susceptibility to, severity and duration of infection), older individuals suffered lower infection costs, which was explained largely because they were less connected in their social networks than younger individuals. This benefit of 'social ageing' depended on epidemiological characteristics and was greatest when infection severity increased with age. When infection duration increased with age, social ageing was beneficial only when pathogen transmissibility was low. Older individuals benefited most from having a lower frequency of interactions (strength) and network embeddedness (closeness) and benefited less from having fewer social partners (degree). Our study provides a first examination of the epidemiology of social ageing, demonstrating the potential for pathogens to influence the evolutionary dynamics of social ageing in natural populations.This article is part of the discussion meeting issue 'Understanding age and society using natural populations'.

Using Latent Class Analysis to Characterize Sickness Signaling in Relation to Familism and Public and Private Religiosity in a Stratified US Sample

BACKGROUND

In response to contracting an infection, individuals usually display a suite of external signs (including sickness behavior) as an outward indication of illness. This context-dependent phenomenon seems to weigh the benefits and costs of eliciting sympathy by indicating sickness versus hiding signs of illness to avoid exposing others to potential infection. In a dynamically social species like humans, non-kin may be as likely to respond to these signs with care as family members, particularly fellow church members. We explore the relative contributions of religiosity and familism in shaping self-reported sickness signaling styles as two dimensions central to human altruism using latent class analysis (LCA).

METHODS

LCA was used to characterize the signaling styles of the study participants. Data come from a large 2018 survey (n = 1259) of sickness and health behaviors among US adults. We used denomination public (church attendance) and private religiosity (time spent in prayer, meditation, etc.) and the God Locus of Health Control scale to assess the impact of God on health. Sickness signaling style was assessed with the SicknessQ and three additional items. Covariates included age, gender, education, and income.

RESULTS

We identified four classes (Familiar, Moderate, Gregarious, and Stoic) tied to signaling styles. The Familiar Signaling class displayed sickness verbally to familiar others, were the oldest, and were least guided by an internal sense of religion. The Moderate Signaling class was younger and had lower public and private religiosity (except regarding health issues) than the Stoic and Gregarious Signaling classes. The Gregarious class signaled to both close others and strangers and scored highest in familism and religiosity. The Stoic class did not verbally signal but indicated sickness worsening when around both close others and strangers, were less likely to be married or endorse private religiosity, and were least likely to recall recent illness as severe.

CONCLUSION

The signaling classes strongly resembled aspects of the introvert-ambivert-extrovert spectrum. We conclude that variation is important at multiple levels, including personality types, and potentially prevents the loss of immunological diversity.

The potential of remote sensing for improved infectious disease ecology research and practice

Outbreaks of COVID-19 in humans, Dutch elm disease in forests, and highly pathogenic avian influenza in wild birds and poultry highlight the disruptive impacts of infectious diseases on public health, ecosystems and economies. Infectious disease dynamics often depend on environmental conditions that drive occurrence, transmission and outbreaks. Remote sensing can contribute to infectious disease research and management by providing standardized environmental data across broad spatial and temporal extents, often at no cost to the user. Here, we (i) conduct a review of primary literature to quantify current uses of remote sensing in disease ecology; and (ii) synthesize qualitative information to identify opportunities for further integration of remote sensing into disease ecology. We identify that modern advances in airborne remote sensing are enabling early detection of forest pathogens and that satellite data are most commonly used to study geographically widespread human diseases. Opportunities remain for increased use of data products that characterize vegetation, surface water and soil; provide data at high spatio-temporal and spectral resolutions; and quantify uncertainty in measurements. Additionally, combining remote sensing with animal telemetry can support decision-making for disease management by providing insights into wildlife disease dynamics. Integrating these opportunities will advance both research and management of infectious diseases.

Genetic Variation in Trophic Avoidance Behaviour Shows Fruit Flies are Generally Attracted to Bacterial Substrates

Pathogen avoidance behaviours are often assumed to be an adaptive host defence. However, there is limited experimental data on heritable, intrapopulation phenotypic variation for avoidance, a strong prerequisite for adaptive responses to selection. We investigated trophic pathogen avoidance in 122 inbred Drosophila melanogaster lines, and in a derived outbred population. Using the FlyPAD system, we tracked the feeding choice that flies made between substrates that were either clean or contained a bacterial pathogen. We uncovered significant, but weakly heritable variation in the preference index amongst fly lines. However, instead of avoidance, most lines demonstrated a preference for substrates containing several bacterial pathogens, showing avoidance only for extremely high bacterial concentrations. Bacterial preference was not associated with susceptibility to infection and was retained in flies with disrupted immune signalling. Phenotype-genotype association analysis indicated several novel genes (CG2321, CG2006, and ptp99A) associated with increased preference for the bacterial substrate, while the amino-acid transporter sobremesa was associated with greater aversion. Given the known fitness benefits of consuming high-protein diets, our results suggest that bacterial attraction may instead reflect a dietary preference for protein over carbohydrate. More work quantifying intrapopulation variation in avoidance behaviours is needed to fully assess its importance in host-pathogen evolutionary ecology.

Pathogen-specific social immunity is associated with erosion of individual immune function in an ant

Contagious diseases are a major threat to societies in which individuals live in close contact. Social insects have evolved collective defense behaviors, such as social care or isolation of infected workers, that prevent outbreaks of pathogens. It has thus been suggested that individual immunity is reduced in species with such 'social immunity'. However, this hypothesis has not been tested functionally. Here, we characterize the immune response of the ant Lasius niger using a combination of genomic analysis, experimental infections, gene expression quantification, behavioural observations and pathogen quantifications. We uncover a striking specialization of immune responses towards different pathogens. Systemic individual immunity is effective against opportunistic bacterial infections, which are not covered by social immunity, but is not elicited upon fungal infections, which are effectively controlled by social immunity. This specialization suggests that immune layers have evolved complementary functions predicted to ensure the most cost-effective response against a wide range of pathogens.

Anthropogenic impacts at the interface of animal spatial and social behaviour

Human disturbance is contributing to widespread, global changes in the distributions and densities of wild animals. These anthropogenic impacts on wildlife arise from multiple bottom-up and top-down pathways, including habitat loss, resource provisioning, climate change, pollution, infrastructure development, hunting and our direct presence. Animal behaviour is an important mechanism linking these disturbances to population outcomes, although these behavioural pathways are often complex and can remain obscured when different aspects of behaviour are studied in isolation from one another. The spatial-social interface provides a lens for understanding how an animal's spatial and social environments interact to determine its spatial and social phenotype (i.e. measurable characteristics of an individual), and how these phenotypes interact and feed back to reshape environments. Here, we review studies of animal behaviour at the spatial-social interface to understand and predict how human disturbance affects animal movement, distribution and intraspecific interactions, with consequences for the conservation of populations and ecosystems. By understanding the spatial-social mechanisms linking human disturbance to conservation outcomes, we can better design management interventions to mitigate undesired consequences of disturbance.This article is part of the theme issue 'The spatial-social interface: a theoretical and empirical integration'.

Juvenile agile frogs spatially avoid ranavirus-infected conspecifics

Exposure to contagious pathogens can result in behavioural changes, which can alter the spread of infectious diseases. Healthy individuals can express generalized social distancing or avoid the sources of infection, while infected individuals can show passive or active self-isolation. Amphibians are globally threatened by contagious diseases, yet their behavioural responses to infections are scarcely known. We studied behavioural changes in agile frog (Rana dalmatina) juveniles upon exposure to a Ranavirus (Rv) using classic choice tests. We found that both non-infected and Rv-infected focal individuals spatially avoided infected conspecifics, while there were no signs of generalized social distancing, nor self-isolation. Avoidance of infected conspecifics may effectively hinder disease transmission, protecting non-infected individuals as well as preventing secondary infections in already infected individuals. On the other hand, the absence of self-isolation by infected individuals may facilitate it. Since infection status did not affect the time spent near conspecifics, it is unlikely that the pathogen manipulated host behaviour. More research is urgently needed to understand under what circumstances behavioural responses can help amphibians cope with infections, and how that affects disease dynamics in natural populations.

Droplet Micro-Sensor and Detection of Respiratory Droplet Transmission

Droplet transmission is the primary infection route for respiratory diseases like COVID-19 and influenza, but small and low-cost wearable droplet detection devices are a significant challenge. Herein, a respiratory droplet micro-sensor based on graphene oxide quantum dots (GOQDs) assembled onto SiO2 microspheres by the nebulized natural deposition is presented. Benefiting from the energy dissipation of the microsphere to droplets, the sensor can detect droplets as far as 2 m from coughing. With this sensor, droplet signal variations caused by some factors like distance, speech, angles, and wind directions are explored, and the effectiveness of different protective measures in preventing droplet transmission is evaluated. This droplet detection technology is expected to be utilized for the development of personal detection and protection devices against infectious respiratory diseases.

Fully integrated and automated centrifugal microfluidic chip for point-of-care multiplexed molecular diagnostics

Public health events caused by pathogens have imposed significant economic and societal burdens. However, conventional methods still face challenges including complex operations, the need for trained operators, and sophisticated instruments. Here, we proposed a fully integrated and automated centrifugal microfluidic chip, also termed IACMC, for point-of-care multiplexed molecular diagnostics by harnessing the advantages of active and passive valves. The IACMC incorporates multiple essential components including a pneumatic balance module for sequential release of multiple reagents, a pneumatic centrifugation-assisted module for on-demand solution release, an on-chip silicon membrane module for nucleic acid extraction, a Coriolis force-mediated fluid switching module, and an amplification module. Numerical simulation and visual validation were employed to iterate and optimize the chip's structure. Upon sample loading, the chip automatically executes the entire process of bacterial sample lysis, nucleic acid capture, elution quantification, and isothermal LAMP amplification. By optimizing crucial parameters including centrifugation speed, direction of rotation, and silicone membrane thickness, the chip achieves exceptional sensitivity (twenty-five Salmonella or forty Escherichia coli) and specificity in detecting Escherichia coli and Salmonella within 40 min. The development of IACMC will drive advancements in centrifugal microfluidics for point-of-care testing and holds potential for broader applications in precision medicine including high-throughput biochemical analysis immune diagnostics, and drug susceptibility testing.

Epidemiological and health economic implications of symptom propagation in respiratory pathogens: A mathematical modelling investigation

BACKGROUND

Respiratory pathogens inflict a substantial burden on public health and the economy. Although the severity of symptoms caused by these pathogens can vary from asymptomatic to fatal, the factors that determine symptom severity are not fully understood. Correlations in symptoms between infector-infectee pairs, for which evidence is accumulating, can generate large-scale clusters of severe infections that could be devastating to those most at risk, whilst also conceivably leading to chains of mild or asymptomatic infections that generate widespread immunity with minimal cost to public health. Although this effect could be harnessed to amplify the impact of interventions that reduce symptom severity, the mechanistic representation of symptom propagation within mathematical and health economic modelling of respiratory diseases is understudied.

METHODS AND FINDINGS

We propose a novel framework for incorporating different levels of symptom propagation into models of infectious disease transmission via a single parameter, α. Varying α tunes the model from having no symptom propagation (α = 0, as typically assumed) to one where symptoms always propagate (α = 1). For parameters corresponding to three respiratory pathogens-seasonal influenza, pandemic influenza and SARS-CoV-2-we explored how symptom propagation impacted the relative epidemiological and health-economic performance of three interventions, conceptualised as vaccines with different actions: symptom-attenuating (labelled SA), infection-blocking (IB) and infection-blocking admitting only mild breakthrough infections (IB_MB). In the absence of interventions, with fixed underlying epidemiological parameters, stronger symptom propagation increased the proportion of cases that were severe. For SA and IB_MB, interventions were more effective at reducing prevalence (all infections and severe cases) for higher strengths of symptom propagation. For IB, symptom propagation had no impact on effectiveness, and for seasonal influenza this intervention type was more effective than SA at reducing severe infections for all strengths of symptom propagation. For pandemic influenza and SARS-CoV-2, at low intervention uptake, SA was more effective than IB for all levels of symptom propagation; for high uptake, SA only became more effective under strong symptom propagation. Health economic assessments found that, for SA-type interventions, the amount one could spend on control whilst maintaining a cost-effective intervention (termed threshold unit intervention cost) was very sensitive to the strength of symptom propagation.

CONCLUSIONS

Overall, the preferred intervention type depended on the combination of the strength of symptom propagation and uptake. Given the importance of determining robust public health responses, we highlight the need to gather further data on symptom propagation, with our modelling framework acting as a template for future analysis.

Associating with kin selects for disease resistance and against tolerance

Behavioural and physiological resistance are key to slowing epidemic spread. We explore the evolutionary and epidemic consequences of their different costs for the evolution of tolerance that trades off with resistance. Behavioural resistance affects social cohesion, with associated group-level costs, while the cost of physiological resistance accrues only to the individual. Further, resistance, and the associated reduction in transmission, benefit susceptible hosts directly, whereas infected hosts only benefit indirectly, by reducing transmission to kin. We therefore model the coevolution of transmission-reducing resistance expressed in susceptible hosts with resistance expressed in infected hosts, as a function of kin association, and analyse the effect on population-level outcomes. Using parameter values for guppies, Poecilia reticulata, and their gyrodactylid parasites, we find that: (1) either susceptible or infected hosts should invest heavily in resistance, but not both; (2) kin association drives investment in physiological resistance more strongly than in behavioural resistance; and (3) even weak levels of kin association can favour altruistic infected hosts that invest heavily in resistance (versus selfish tolerance), eliminating parasites. Overall, our finding that weak kin association affects the coevolution of infected and susceptible investment in both behavioural and physiological resistance suggests that kin selection may affect disease dynamics across systems.

Olfactory self-recognition in two species of snake

Mark tests, in which an animal uses a mirror to locate and examine an otherwise unnoticeable mark on its own body, are commonly used to assess self-recognition, which may have implications for self-awareness. Recently, several olfactory-reliant species have appeared to pass odour-based versions of the mark test, though it has never been attempted in reptiles. We conducted an odour-based mark test on two species of snakes, Eastern gartersnakes and ball pythons, with widely divergent ecologies (i.e. terrestrial foragers that communally brumate versus semi-arboreal ambush predators that do not). We find that gartersnakes, but not ball pythons, pass the test, and a range of control tests suggest this is based on self-recognition. Gartersnakes are more social than ball pythons, supporting recent suggestions that social species are more likely to self-recognize. These results open the door to examination of the ecology of self-recognition, and suggest that this ability may evolve in response to species-specific ecological challenges, some of which may align with complexity of social structures.

Social networks reveal sex- and age-patterned social structure in Butler's gartersnakes (Thamnophis butleri)

Sex- and age-based social structures have been well documented in animals with visible aggregations. However, very little is known about the social structures of snakes. This is most likely because snakes are often considered non-social animals and are particularly difficult to observe in the wild. Here, we show that wild Butler's Gartersnakes have an age and sex assorted social structure similar to more commonly studied social animals. To demonstrate this, we use data from a 12-year capture-mark-recapture study to identify social interactions using social network analyses. We find that the social structures of Butler's Gartersnakes comprise sex- and age-assorted intra-species communities with older females often central and age segregation partially due to patterns of study site use. In addition, we find that females tended to increase in sociability as they aged while the opposite occurred in males. We also present evidence that social interaction may provide fitness benefits, where snakes that were part of a social network were more likely to have improved body condition. We demonstrate that conventional capture data can reveal valuable information on social structures in cryptic species. This is particularly valuable as research has consistently demonstrated that understanding social structure is important for conservation efforts. Additionally, research on the social patterns of animals without obvious social groups provides valuable insight into the evolution of group living.

Targeted treatment of injured nestmates with antimicrobial compounds in an ant society

Infected wounds pose a major mortality risk in animals. Injuries are common in the ant Megaponera analis, which raids pugnacious prey. Here we show that M. analis can determine when wounds are infected and treat them accordingly. By applying a variety of antimicrobial compounds and proteins secreted from the metapleural gland to infected wounds, workers reduce the mortality of infected individuals by 90%. Chemical analyses showed that wound infection is associated with specific changes in the cuticular hydrocarbon profile, thereby likely allowing nestmates to diagnose the infection state of injured individuals and apply the appropriate antimicrobial treatment. This study demonstrates that M. analis ant societies use antimicrobial compounds produced in the metapleural glands to treat infected wounds and reduce nestmate mortality.

Rising to the Challenge: Mounting an Acute Phase Immune Response Has No Long-Term Negative Effects on Captive Sparrow Migratory Body Composition or Migratory Restlessness

Migratory animals may trade-off between investing energy in immune defense versus investing in energy reserves needed for seasonal migration. However, these trade-offs are often masked by other sources of variation and may not be detected through observational field studies of free-living animals. Moreover, observational studies can rarely distinguish the costs of pathogenic infection from those of mounting an immune response. To disentangle such effects, we conducted an immune challenge experiment. We captured song sparrows (Melospiza melodia) and white-throated sparrows (Zonotrichia albicollis) in autumn migratory condition, challenged the sparrows with non-infectious antigens that induce an acute-phase immune response, then monitored body composition and migratory restlessness behavior. For both species, body mass was higher the day after exposure to keyhole limpet hemocyanin (KLH) compared to controls. White-throated sparrows, but not song sparrows, increased lean mass 1 week after exposure to lipopolysaccharide (LPS), suggesting that effects of immune upregulation on body composition may be long-lasting and specific to certain combinations of hosts and antigens. White-throated sparrows exposed to KLH increased nocturnal migratory restlessness (Zugunruhe) for the week following exposure. These findings suggest that short-term activation of the acute immune response does not constrain migratory physiology in these songbirds.

Impact of nanotechnology on conventional and artificial intelligence-based biosensing strategies for the detection of viruses

Recent years have witnessed the emergence of several viruses and other pathogens. Some of these infectious diseases have spread globally, resulting in pandemics. Although biosensors of various types have been utilized for virus detection, their limited sensitivity remains an issue. Therefore, the development of better diagnostic tools that facilitate the more efficient detection of viruses and other pathogens has become important. Nanotechnology has been recognized as a powerful tool for the detection of viruses, and it is expected to change the landscape of virus detection and analysis. Recently, nanomaterials have gained enormous attention for their value in improving biosensor performance owing to their high surface-to-volume ratio and quantum size effects. This article reviews the impact of nanotechnology on the design, development, and performance of sensors for the detection of viruses. Special attention has been paid to nanoscale materials, various types of nanobiosensors, the internet of medical things, and artificial intelligence-based viral diagnostic techniques.

Let's stick together: Infection enhances preferences for social grouping in a songbird species

Acute infections can alter foraging and movement behaviors relevant to sociality and pathogen spread. However, few studies have directly examined how acute infections caused by directly transmitted pathogens influence host social preferences. While infected hosts often express sickness behaviors (e.g., lethargy) that can reduce social associations with conspecifics, enhanced sociality during infection might be favored in some systems if social grouping improves host survival of infection. Directly assaying social preferences of infected hosts is needed to elucidate potential changes in social preferences that may act as a form of behavioral tolerance (defined as using behavior to minimize fitness costs of infection). We tested how infection alters sociality in juvenile house finches (Haemorhous mexicanus), which are both highly gregarious and particularly susceptible to infection by the bacterial pathogen Mycoplasma gallisepticum (MG). We inoculated 33 wild-caught but captive-held juvenile house finches with MG or media (sham control). At peak infection, birds were given a choice assay to assess preference for associating near a flock versus an empty cage. We then repeated this assay after all birds had recovered from infection. Infected birds were significantly more likely than controls to spend time associating with, and specifically foraging near, the flock. However, after infected birds had recovered from MG infection, there were no significant differences in the amount of time birds in each treatment spent with the flock. These results indicate augmented social preferences during active infection, potentially as a form of behavioral tolerance. Notably, infected birds showed strong social preferences regardless of variation in disease severity or pathogen loads, with 14/19 harboring high loads (5-6 log10 copies of MG) at the time of the assay. Overall, our results show that infection with a directly transmitted pathogen can augment social preferences, with important implications for MG spread in natural populations.

Sequential epidemic-like spread between agglomerates of self-propelled agents in one dimension

Motile organisms can form stable agglomerates such as cities or colonies. In the outbreak of a highly contagious disease, the control of large-scale epidemic spread depends on factors like the number and size of agglomerates, travel rate between them, and disease recovery rate. While the emergence of agglomerates permits early interventions, it also explains longer real epidemics. In this work, we study the spread of susceptible-infected-recovered (SIR) epidemics (or any sort of information exchange by contact) in one-dimensional spatially structured systems. By working in one dimension, we establish a necessary foundation for future investigation in higher dimensions and mimic micro-organisms in narrow channels. We employ a model of self-propelled particles which spontaneously form multiple clusters. For a lower rate of stochastic reorientation, particles have a higher tendency to agglomerate and therefore the clusters become larger and less numerous. We examine the time evolution averaged over many epidemics and how it is affected by the existence of clusters through the eventual recovery of infected particles before reaching new clusters. New terms appear in the SIR differential equations in the last epidemic stages. We show how the final number of ever-infected individuals depends nontrivially on single-individual parameters. In particular, the number of ever-infected individuals first increases with the reorientation rate since particles escape sooner from clusters and spread the disease. For higher reorientation rate, travel between clusters becomes too diffusive and the clusters too small, decreasing the number of ever-infected individuals.

The walking sick: Perception of experimental sickness from biological motion

Identification of sick conspecifics allows for avoidance of infectious threats, and is therefore an important behavioral defense against diseases. Here, we investigated if humans can identify sick individuals solely from biological motion and posture (using point-light displays). Additionally, we sought to determine which movements and sickness parameters would predict such detection. We collected video clips and derived point-light displays (one stride presented in a loop) of sick walkers (injected with lipopolysaccharide at 2.0 ng/kg body weight) and the same walkers when healthy (injected with saline). We then presented these displays to two groups, one group classified each walker as sick or healthy (study 1, n = 106), and the other group scored the walkers' health on a visual analogue scale (study 2, n = 106). The raters were able to identify sick individuals above chance, and rated sick walkers as having worse health, both from observing video clips and point-light displays. Furthermore, both sickness detection and worse apparent health were predicted by inflammation-induced increase in rigidity and slower walking, but not other cues. Altogether, these findings indicate that biological motion can serve as a sickness cue, possibly allowing humans to identify sick conspecifics from a distance, and thereby allowing for disease avoidance.

Evolution of pathogens with cross-immunity in response to healthcare interventions

Cross-immunity, as an evolutionary driver, can contribute to pathogen evolution, particularly pathogen diversity. Healthcare interventions aimed at reducing disease severity or transmission are commonly used to control diseases and can also induce pathogen evolution. Understanding pathogen evolution in the context of cross-immunity and healthcare interventions is crucial for infection control. This study starts by modelling cross-immunity, the extent of which is determined by strain traits and host characteristics. Given that all hosts have the same characteristics, full cross-immunity between residents and mutants occurs when mutation step sizes are small enough. Cross-immunity can be partial when the step size is large. The presence of partial cross-immunity reduces pathogen load and shortens the infectious period inside hosts, reducing transmission between hosts and improving host population survival and recovery. This study focuses on how pathogens evolve through small and large mutational steps and how healthcare interventions affect pathogen evolution. Using the theory of adaptive dynamics, we found that when mutational steps are small (only full cross-immunity is present), pathogen diversity cannot occur because it maximises the basic reproduction number. This results in intermediate values for both pathogen growth and clearance rates. However, when large mutational steps are allowed (with full and partial cross-immunity present), pathogens can evolve into multiple strains and induce pathogen diversity. The study also shows that different healthcare interventions can have varying effects on pathogen evolution. Generally, low levels of intervention are more likely to induce strain diversity, while high levels are more likely to result in strain reduction.

Spatial dynamics of synergistic coinfection in rock-paper-scissors models

We investigate the spatial dynamics of two-disease epidemics reaching a three-species cyclic model. Regardless of their species, all individuals are susceptible to being infected with two different pathogens, which spread through person-to-person contact. We consider that the simultaneous presence of multiple infections leads to a synergistic amplification in the probability of host mortality due to complications arising from any of the co-occurring diseases. Employing stochastic simulations, we explore the ramifications of this synergistic coinfection on spatial configurations that emerge from stochastic initial conditions. Under conditions of pronounced synergistic coinfection, we identify the emergence of zones inhabited solely by hosts affected by a singular pathogen. At the boundaries of spatial domains dominated by a single disease, interfaces of coinfected hosts appear. The dynamics of these interfaces are shaped by curvature-driven processes and display a scaling behavior reflective of the topological attributes of the underlying two-dimensional space. As the lethality linked to coinfection diminishes, the evolution of the interface network's spatial dynamics is influenced by fluctuations stemming from waves of coinfection that infiltrate territories predominantly occupied by a single disease. Our analysis extends to quantifying the implications of synergistic coinfection at both the individual and population levels Our outcomes show that organisms' infection risk is maximized if the coinfection increases the death due to disease by 30% and minimized as the network dynamics reach the scaling regime, with species populations being maximum. Our conclusions may help ecologists understand the dynamics of epidemics and their impact on the stability of ecosystems.

Behavioural individuality determines infection risk in clonal ant colonies

In social groups, infection risk is not distributed evenly across individuals. Individual behaviour is a key source of variation in infection risk, yet its effects are difficult to separate from other factors (e.g., age). Here, we combine epidemiological experiments with chemical, transcriptomic, and automated behavioural analyses in clonal ant colonies, where behavioural individuality emerges among identical workers. We find that: (1) Caenorhabditis-related nematodes parasitise ant heads and affect their survival and physiology, (2) differences in infection emerge from behavioural variation alone, and reflect spatially-organised division of labour, (3) infections affect colony social organisation by causing infected workers to stay in the nest. By disproportionately infecting some workers and shifting their spatial distribution, infections reduce division of labour and increase spatial overlap between hosts, which should facilitate parasite transmission. Thus, division of labour, a defining feature of societies, not only shapes infection risk and distribution but is also modulated by parasites.

Bat behavioral immune responses in social contexts: current knowledge and future directions

Animals often mount complex immune responses to infections. Aside from cellular and molecular defense mechanisms, animals can alter their behavior in response to infection by avoiding, resisting, or tolerating negative effects of pathogens. These behaviors are often connected to cellular and molecular immune responses. For instance, sickness behaviors are a set of behavioral changes triggered by the host inflammatory response (e.g., cytokines) and could aid in resisting or tolerating infection, as well as affect transmission dynamics if sick animals socially withdraw or are being avoided by others. To fully understand the group and population level transmission dynamics and consequences of pathogen infections in bats, it is not only important to consider cellular and molecular defense mechanisms, but also behavioral mechanisms, and how both interact. Although there has been increasing interest in bat immune responses due to their ability to successfully cope with viral infections, few studies have explored behavioral anti-pathogen defense mechanisms. My main objective is to explore the interaction of cellular and molecular defense mechanisms, and behavioral alterations that results from infection in bats, and to outline current knowledge and future research avenues in this field.

Physics-Informed Neural Networks Integrating Compartmental Model for Analyzing COVID-19 Transmission Dynamics

Modelling and predicting the behaviour of infectious diseases is essential for early warning and evaluating the most effective interventions to prevent significant harm. Compartmental models produce a system of ordinary differential equations (ODEs) that are renowned for simulating the transmission dynamics of infectious diseases. However, the parameters in compartmental models are often unknown, and they can even change over time in the real world, making them difficult to determine. This study proposes an advanced artificial intelligence approach based on physics-informed neural networks (PINNs) to estimate time-varying parameters from given data for the compartmental model. Our proposed PINNs method captures the complex dynamics of COVID-19 by integrating a modified Susceptible-Exposed-Infectious-Recovered-Death (SEIRD) compartmental model with deep neural networks. Specifically, we modelled the system of ODEs as one network and the time-varying parameters as another network to address significant unknown parameters and limited data. Such structure of the PINNs method is in line with the prior epidemiological correlations and comprises the mismatch between available data and network output and the residual of ODEs. The experimental findings on real-world reported data data have demonstrated that our method robustly and accurately learns the dynamics and forecasts future states. Moreover, as more data becomes available, our proposed PINNs method can be successfully extended to other regions and infectious diseases.

Novel pathogen introduction triggers rapid evolution in animal social movement strategies

Animal sociality emerges from individual decisions on how to balance the costs and benefits of being sociable. Novel pathogens introduced into wildlife populations should increase the costs of sociality, selecting against gregariousness. Using an individual-based model that captures essential features of pathogen transmission among social hosts, we show how novel pathogen introduction provokes the rapid evolutionary emergence and coexistence of distinct social movement strategies. These strategies differ in how they trade the benefits of social information against the risk of infection. Overall, pathogen-risk-adapted populations move more and have fewer associations with other individuals than their pathogen-risk-naive ancestors, reducing disease spread. Host evolution to be less social can be sufficient to cause a pathogen to be eliminated from a population, which is followed by a rapid recovery in social tendency. Our conceptual model is broadly applicable to a wide range of potential host-pathogen introductions and offers initial predictions for the eco-evolutionary consequences of wildlife pathogen spillover scenarios and a template for the development of theory in the ecology and evolution of animals' movement decisions.

First impressions of a new face are shaped by infection concerns

Along with a classical immune system, we have evolved a behavioral one that directs us away from potentially contagious individuals. Here I show, using publicly available cross-cultural data, that this adaptation is so fundamental that our first impressions of a male stranger are largely driven by the perceived health of his face. Positive (likeable, capable, intelligent, trustworthy) and negative (unfriendly, ignorant, lazy) first impressions are affected by facial health in adaptively different ways, inconsistent with a mere halo effect; they are also modulated by one's current state of health and inclination to feel disgusted by pathogens. These findings, which replicated across two countries as different as the USA and India, suggest that instinctive perceptions of badness and goodness from faces are not two sides of the same coin but reflect the (nonsymmetrical) expected costs and benefits of interaction. Apparently, pathogens run the show-and first impressions come second. Lay Summary: Our first impressions of strangers (whether they seem trustworthy, intelligent, unfriendly, or aggressive) are shaped by how healthy their faces look and by our unconscious motivation to avoid infections. Bad and good impressions turn out to reflect the concrete, potentially vital, expected costs and benefits of interacting with our fellow humans. Apparently, pathogens run the show-and first impressions come second.

Stay close, but not too close: aerial image analysis reveals patterns of social distancing in seal colonies

Many species aggregate in dense colonies. Species-specific spatial patterns provide clues about how colonies are shaped by various (a)biotic factors, including predation, temperature regulation or disease transmission. Using aerial imagery, we examined these patterns in colonies on land of two sympatric seal species: the harbour seal and grey seal. Results show that the density of grey seals on land is twice as high as that of harbour seals. Furthermore, the nearest neighbour distance (NND) of harbour seals (median = 1.06 m) is significantly larger than that of grey seals (median = 0.53 m). Avoidance at small distances (i.e. social distancing) was supported by spatial simulation: when the observed seal locations were shuffled slightly, the frequency of the smallest NNDs (0-25 cm) increased, while the most frequently observed NNDs decreased. As harbour seals are more prone to infectious diseases, we hypothesize that the larger NNDs might be a behavioural response to reduce pathogen transmission. The approach presented here can potentially be used as a practical tool to differentiate between harbour and grey seals in remote sensing applications, particularly in low to medium resolution imagery (e.g. satellite imagery), where morphological characteristics alone are insufficient to differentiate between species.

Immune challenge affects reproductive behaviour in the guppy (Poecilia reticulata)

Immunocompetence and reproduction are among the most important determinants of fitness. However, energetic and metabolic constraints create conflict between these two life-history traits. While many studies have explored the relationship between immune activity and reproductive fitness in birds and mammals inoculated with bacterial endotoxin, very few have focused on fish. Fish have been neglected in this area due, in part, to the claim that they are largely resistant to the immune effects of endotoxins. However, the present study suggests that they are susceptible to significant effects with respect to reproductive behaviour. Here, we examined the reproductive behaviour of male guppies following exposure to bacterial lipopolysaccharides (LPS) in comparison to that of male guppies in a control treatment. Additionally, we investigated the responses of females to these males. We show that although immune challenge does not suppress general activity in male guppies, it significantly reduces mating effort. While females showed no difference in general activity as a function of male treatments, they did exhibit reduced group cohesion in the presence of LPS-exposed males. We discuss this in the context of sickness behaviours, social avoidance of immune-challenged individuals and the effects of mounting an immune response on reproductive behaviour.

Death comes for us all: relating movement-integrated habitat selection and social behavior to human-associated and disease-related mortality among gray wolves

Avoiding death affects biological processes, including behavior. Habitat selection, movement, and sociality are highly flexible behaviors that influence the mortality risks and subsequent fitness of individuals. In the Anthropocene, animals are experiencing increased risks from direct human causes and increased spread of infectious diseases. Using integrated step selection analysis, we tested how the habitat selection, movement, and social behaviors of gray wolves vary in the two months prior to death due to humans (being shot or trapped) or canine distemper virus (CDV). We further tested how those behaviors vary as a prelude to death. We studied populations of wolves that occurred under two different management schemes: a national park managed for conservation and a provincially managed multi-use area. Behaviors that changed prior to death were strongly related to how an animal eventually died. Wolves killed by humans moved slower than wolves that survived and selected to be nearer roads closer in time to their death. Wolves that died due to CDV moved progressively slower as they neared death and reduced their avoidance of wet habitats. All animals, regardless of dying or living, maintained selection to be near packmates across time, which seemingly contributed to disease dynamics in the packs infected with CDV. There were no noticeable differences in behavior between the two management areas. Overall, habitat selection, movement, and sociality interact to put individuals and groups at greater risks, influencing their cause-specific mortality.

The Influence of COVID-19 in Endocrine Research: Critical Overview, Methodological Implications and a Guideline for Future Designs

The COVID-19 pandemic has changed many aspects of people's lives, including not only individual social behavior, healthcare procedures, and altered physiological and pathophysiological responses. As a result, some medical studies may be influenced by one or more hidden factors brought about by the COVID-19 pandemic. Using the literature review method, we are briefly discussing the studies that are confounded by COVID-19 and facemask-induced partiality and how these factors can be further complicated with other confounding variables. Facemask wearing has been reported to produce partiality in studies of ophthalmology (particularly dry eye and related ocular diseases), sleep studies, cognitive studies (such as emotion-recognition accuracy research, etc.), and gender-influenced studies, to mention a few. There is a possibility that some other COVID-19 related influences remain unrecognized in medical research. To account for heterogeneity, current and future studies need to consider the severity of the initial illness (such as diabetes, other endocrine disorders), and COVID-19 infection, the timing of analysis, or the presence of a control group. Face mask-induced influences may confound the results of diabetes studies in many ways.

Group size rather than social status influences personal immune efficacy in a socially polymorphic bee

The evolution of group living is associated with increased pressure from parasites and pathogens. This can be offset by greater investment in personal immune defences and/or the development of cooperative immune defences (social immunity). An enduring question in evolutionary biology is whether social-immune benefits arose in response to an increased need in more complex societies, or arose early in group living and helped facilitate the evolution of more complex societies. In this study, we shed light on this question through investigating how immunity varies intraspecifically in a socially polymorphic bee. Using a novel immune assay, we show that personal antibacterial efficacy in individuals from social nests is higher than that of solitary individuals, but that this can be explained by higher densities in social nests. We conclude that personal immune effects are likely to play a role in the social/solitary transition in this species. These patterns are consistent with the idea that social immunity evolved secondarily, following the evolution of group living. The flexibility of the individual immune system may have favoured a reliance on its use during the facultative phase early in social evolution.

Prospects of Microfluidic Technology in Nucleic Acid Detection Approaches

Conventional diagnostic techniques are based on the utilization of analyte sampling, sensing and signaling on separate platforms for detection purposes, which must be integrated to a single step procedure in point of care (POC) testing devices. Due to the expeditious nature of microfluidic platforms, the trend has been shifted toward the implementation of these systems for the detection of analytes in biochemical, clinical and food technology. Microfluidic systems molded with substances such as polymers or glass offer the specific and sensitive detection of infectious and noninfectious diseases by providing innumerable benefits, including less cost, good biological affinity, strong capillary action and simple process of fabrication. In the case of nanosensors for nucleic acid detection, some challenges need to be addressed, such as cellular lysis, isolation and amplification of nucleic acid before its detection. To avoid the utilization of laborious steps for executing these processes, advances have been deployed in this perspective for on-chip sample preparation, amplification and detection by the introduction of an emerging field of modular microfluidics that has multiple advantages over integrated microfluidics. This review emphasizes the significance of microfluidic technology for the nucleic acid detection of infectious and non-infectious diseases. The implementation of isothermal amplification in conjunction with the lateral flow assay greatly increases the binding efficiency of nanoparticles and biomolecules and improves the limit of detection and sensitivity. Most importantly, the deployment of paper-based material made of cellulose reduces the overall cost. Microfluidic technology in nucleic acid testing has been discussed by explicating its applications in different fields. Next-generation diagnostic methods can be improved by using CRISPR/Cas technology in microfluidic systems. This review concludes with the comparison and future prospects of various microfluidic systems, detection methods and plasma separation techniques used in microfluidic devices.

Can Inflammation Predict Social Media Use? Linking a Biological Marker of Systemic Inflammation with Social Media Use Among College Students and Middle-Aged Adults

Drawing on recent evidence that inflammation may promote social affiliative motivation, the present research proposes a novel perspective that inflammation may be associated with more social media use. In a cross-sectional analysis of a nationally representative sample, Study 1 (N = 863) found a positive association between C-reactive protein (CRP), a biomarker of systemic inflammation, and the amount of social media use by middle-aged adults. Study 2 (N = 228) showed that among college students CRP was prospectively associated with more social media use 6 weeks later. Providing stronger evidence of the directionality of this effect, Study 3 (N = 171) showed that in college students CRP predicted increased social media use in the subsequent week even after controlling for current week's use. Additionally, in exploratory analyses of CRP and different types of social media use in the same week, CRP was only associated with using social media for social interaction and not for other purposes (e.g., entertainment). The present research sheds light on the social effects of inflammation and highlights potential benefits of using social media as a context for studying the impact of inflammation on social motivation and behavior.

The coevolution of the spread of a disease and competing opinions in multiplex networks

The COVID-19 pandemic has resulted in a proliferation of conflicting opinions on physical distancing across various media platforms, which has had a significant impact on human behavior and the transmission dynamics of the disease. Inspired by this social phenomenon, we present a novel UAP-SIS model to study the interaction between conflicting opinions and epidemic spreading in multiplex networks, in which individual behavior is based on diverse opinions. We distinguish susceptibility and infectivity among individuals who are unaware, pro-physical distancing and anti-physical distancing, and we incorporate three kinds of mechanisms for generating individual awareness. The coupled dynamics are analyzed in terms of a microscopic Markov chain approach that encompasses the aforementioned elements. With this model, we derive the epidemic threshold which is related to the diffusion of competing opinions and their coupling configuration. Our findings demonstrate that the transmission of the disease is shaped in a significant manner by conflicting opinions, due to the complex interaction between such opinions and the disease itself. Furthermore, the implementation of awareness-generating mechanisms can help to mitigate the overall prevalence of the epidemic, and global awareness and self-awareness can be interchangeable in certain instances. To effectively curb the spread of epidemics, policymakers should take steps to regulate social media and promote physical distancing as the mainstream opinion.

Death is overrated: the potential role of detection in driving virulence evolution

A common assumption in the evolution of virulence theory literature is that pathogens transmit better when they exploit their host more heavily, but by doing so, they impose a greater risk of killing their host, thus truncating infectious periods and reducing their own opportunities for transmission. Here, I derive an equation for the magnitude of this cost in terms of the infection fatality rate, and in doing so, I show that there are many cases where mortality costs are too small to plausibly constrain increases in host exploitation by pathogens. I propose that pathogen evolution may often be constrained by detection costs, whereby hosts alter their behaviour when infection is detectable, and thus reduce pathogen opportunities for onward transmission. I then derive an inequality to illustrate when mortality costs or detection costs impose stronger constraints on pathogen evolution, and I use empirical data from the literature to demonstrate that detection costs are frequently large in both human and animal populations. Finally, I give examples of how evolutionary predictions can change depending on whether costs of host exploitation are borne out through mortality or detection.

Variation in leisure sport conflicts and coping strategies depending on participation type and proximity during the COVID-19 pandemic

Introduction

New conflict types have arisen in leisure sports activities due to social regulations designed to address COVID-19. We analyze the differences in conflict-inducing factors and coping strategies across various types of leisure sports and levels of spatial proximity.

Methods

Korean adults aged between 20 and 60 years, who had participated in leisure sports activities since the COVID-19 outbreak in January 2020, were surveyed, and 508 responses were collected for analysis. The differences in leisure sports conflicts and coping strategies across the types of leisure sports participation and spatial proximity were tested.

Results

The results show that conflict due to prejudice was higher in typical indoor sports activities, such as Pilates, yoga, and gym workouts, whereas conflict due to competition or not observing etiquette was higher in indoor golf. Second, conflict due to prior expectations and prejudice was high in outdoor sports activities, such as jogging and hiking. Finally, all participants showed avoidance behavior, but it was observed more frequently in outdoor sports than indoor sports.

Discussion

The study reveals how much leisure conflict is induced by various types of leisure sports participation, particularly during outdoor activities, which usually feature a relatively low density of participants. It underscores the necessity of developing structural approaches to resolving leisure conflicts in dangerous spaces or requiring intensive management and creating new leisure sports activities.

Mother-to-daughter transmission of hygienic anti-parasite behaviour in mandrills

Social animals are particularly exposed to infectious diseases. Pathogen-driven selection pressures have thus favoured the evolution of behavioural adaptations to decrease transmission risk such as the avoidance of contagious individuals. Yet, such strategies deprive individuals of valuable social interactions, generating a cost-benefit trade-off between pathogen avoidance and social opportunities. Recent studies revealed that hosts differ in these behavioural defences, but the determinants driving such inter-individual variation remain understudied. Using 6 years of behavioural and parasite data on a large natural population of mandrills (Mandrillus sphinx), we showed that, when parasite prevalence was high in the population, females avoided grooming their conspecifics' peri-anal region (PAR), where contagious gastro-intestinal parasites accumulate. Females varied, however, in their propensity to avoid this risky body region: across years, some females consistently avoided grooming it, while others did not. Interestingly, hygienic females (i.e. those avoiding the PAR) were less parasitized than non-hygienic females. Finally, age, dominance rank and grooming frequency did not influence a female's hygiene, but both mother-daughter and maternal half-sisters exhibited similar hygienic levels, whereas paternal half-sisters and non-kin dyads did not, suggesting a social transmission of this behaviour. Our study emphasizes that the social inheritance of hygiene may structure behavioural resistance to pathogens in host populations with potential consequences on the dynamics of infectious diseases.

Evolutionary Aspects of Infections: Inflammation and Sickness Behaviors

Sickness behavior was conceptualized initially as the behavioral counterpart of the fever response to infectious pathogens. It helps to raise body temperature to its higher setpoint and to maintain it at this new level and it has the additional benefit of enabling a weakened organism to protect itself from other dangers. The discovery of the behavioral effects of proinflammatory cytokines produced by activated immune cells provided a cellular and molecular basis to this phenomenon. The administration of cytokines or cytokine inducers like lipopolysaccharide to healthy rodents allowed to reveal the similarities and differences between inflammation-induced sickness behavior and the fever response. It also led to the understanding of how the inflammatory response that is triggered at the periphery can propagate into the brain and induce the behavioral manifestations of sickness. At the behavioral level, the demonstration that sickness behavior is the expression of a motivational state that reorganizes perception and action in face of a microbial pathogen just like fear in face of a predator appeared at first glance to strengthen the adaptive value of this behavior. However, all aspects of sickness behavior are not always favorable for the organism. This is the case for anorexia that is beneficial in the context of bacterial infection but detrimental in the context of viral infection. In addition, studies of sickness behavior in natural conditions revealed that like any other defensive behavior, sickness behavior requires trade-offs between its survival benefits for the sick individual and the costs incurred especially in the context of gregarious groups. Thanks to these studies, evidence is emerging that sickness behavior is much more variable in its expression than initially thought, and that part of this variability depends not only on the pathogen and the social context in which the infection develops but also on individual factors including species, sex, age, nutrition, and physiological status.

Immune Stimulation via Wounding Alters Chemical Profiles of Adult Tribolium castaneum

Group-living individuals experience immense risk of disease transmission and parasite infection. In social and in some non-social insects, disease control with immunomodulation arises not only via individual immune defenses, but also via infochemicals such as contact cues and (defensive) volatiles to mount a group-level immunity. However, little is known about whether activation of the immune system elicits changes in chemical phenotypes, which may mediate these responses. We here asked whether individual immune experience resulting from wounding or injection of heat-killed Bacillus thuringiensis (priming) leads to changes in the chemical profiles of female and male adult red flour beetles, Tribolium castaneum, which are non-social but gregarious. We analyzed insect extracts using GC-FID to study the chemical composition of (1) cuticular hydrocarbons (CHCs) as candidates for the transfer of immunity-related information between individuals via contact, and (2) stink gland secretions, with analysis of benzoquinones as main active compounds regulating 'external immunity'. Despite a pronounced sexual dimorphism in CHC profiles, wounding stimulation led to similar profile changes in males and females with increases in the proportion of methyl-branched alkanes compared to naïve beetles. While changes in the overall secretion profiles were less pronounced, absolute amounts of benzoquinones were transiently elevated in wounded compared to naïve females. Responses to priming were insignificant in CHCs and secretions. We suggest that changes in different infochemicals after wounding may mediate immune status signaling in the context of both internal and external immune responses in groups of this non-social insect, thus showing parallels to social immunity.

Evolution and Ecology of Parasite Avoidance

Parasite avoidance is a host defense that reduces the contact rate with parasites. We investigate avoidance as a primary driver of variation among individuals in the risk of parasitism and the evolution of host-parasite interactions. To bridge mechanistic and taxonomic divides, we define and categorize avoidance by its function and position in the sequence of host defenses. We also examine the role of avoidance in limiting epidemics and evaluate evidence for the processes that drive its evolution. Throughout, we highlight important directions to advance our conceptual and theoretical understanding of the role of avoidance in host-parasite interactions. We emphasize the need to test assumptions and quantify the effect of avoidance independent of other defenses. Importantly, many open questions may be most tractable in host systems that have not been the focus of traditional behavioral avoidance research, such as plants and invertebrates.

Spatial organisation plasticity reduces disease infection risk in rock-paper-scissors models

We study a three-species cyclic game system where organisms face a contagious disease whose virulence may change by a pathogen mutation. As a responsive defence strategy, organisms' mobility is restricted to reduce disease dissemination in the system. The impact of the collective self-preservation strategy on the disease infection risk is investigated by performing stochastic simulations of the spatial version of the rock-paper-scissors game. Our outcomes show that the mobility control strategy induces plasticity in the spatial patterns with groups of organisms of the same species inhabiting spatial domains whose characteristic length scales depend on the level of dispersal restrictions. The spatial organisation plasticity allows the ecosystems to adapt to minimise the individuals' disease contamination risk if an eventual pathogen alters the disease virulence. We discover that if a pathogen mutation makes the disease more transmissible or less lethal, the organisms benefit more if the mobility is not strongly restricted, thus forming large spatial domains. Conversely, the benefits of protecting against a pathogen causing a less contagious or deadlier disease are maximised if the average size of groups of individuals of the same species is significantly limited, reducing the dimensions of groups of organisms significantly. Our findings may help biologists understand the effects of dispersal control as a conservation strategy in ecosystems affected by epidemic outbreaks.

Ranavirus infection-induced avoidance behaviour in wood frog juveniles: do amphibians socially distance?

Hosts may limit exposure to pathogens through changes in behaviour, such as avoiding infected individuals or contaminated areas. Here, we tested for a behavioural response to ranavirus infection in juvenile wood frogs (Rana sylvatica) because the majority of dispersal between populations occurs during this life stage. We hypothesized that if infections are transmissible and detectable at this life stage, then susceptibles would display avoidance behaviours when introduced to an infected conspecific. Despite no apparent signs of infection, we observed a greater distance between susceptible-infected pairs, compared to pairs of either two infected or two susceptible animals. Further, distances between susceptible-infected pairs were positively related to the infection intensity of the focal exposed frog, suggesting the cue to avoid infected conspecifics may become more detectable with more intense infections. Although we did not quantify whether the transmission was affected by their distancing, our findings suggest that juvenile frogs have the potential to reduce terrestrial transmission of ranaviruses through avoidance behaviours.

Aspergillus-bees: A dynamic symbiotic association

Besides representing one of the most relevant threats of fungal origin to human and animal health, the genus Aspergillus includes opportunistic pathogens which may infect bees (Hymenoptera, Apoidea) in all developmental stages. At least 30 different species of Aspergillus have been isolated from managed and wild bees. Some efficient behavioral responses (e.g., diseased brood removal) exerted by bees negatively affect the chance to diagnose the pathology, and may contribute to the underestimation of aspergillosis importance in beekeeping. On the other hand, bee immune responses may be affected by biotic and abiotic stresses and suffer from the loose co-evolutionary relationships with Aspergillus pathogenic strains. However, if not pathogenic, these hive mycobiota components can prove to be beneficial to bees, by affecting the interaction with other pathogens and parasites and by detoxifying xenobiotics. The pathogenic aptitude of Aspergillus spp. likely derives from the combined action of toxins and hydrolytic enzymes, whose effects on bees have been largely overlooked until recently. Variation in the production of these virulence factors has been observed among strains, even belonging to the same species. Toxigenic and non-toxigenic strains/species may co-exist in a homeostatic equilibrium which is susceptible to be perturbed by several external factors, leading to mutualistic/antagonistic switch in the relationships between Aspergillus and bees.

Social effects of rabies infection in male vampire bats (Desmodus rotundus)

Rabies virus (RABV) transmitted by the common vampire bat (Desmodus rotundus) poses a threat to agricultural development and public health throughout the Neotropics. The ecology and evolution of rabies host-pathogen dynamics are influenced by two infection-induced behavioural changes. RABV-infected hosts often exhibit increased aggression which facilitates transmission, and rabies also leads to reduced activity and paralysis prior to death. Although several studies document rabies-induced behavioural changes in rodents and other dead-end hosts, surprisingly few studies have measured these changes in vampire bats, the key natural reservoir throughout Latin America. Taking advantage of an experiment designed to test an oral rabies vaccine in captive male vampire bats, we quantify for the first time, to our knowledge, how rabies affects allogrooming and aggressive behaviours in this species. Compared to non-rabid vampire bats, rabid individuals reduced their allogrooming prior to death, but we did not detect increases in aggression among bats. To put our results in context, we review what is known and what remains unclear about behavioural changes of rabid vampire bats (resumen en español, electronic supplementary material, S1).