Why Do We Feel Sick When Infected--Can Altruism Play a Role?

Ambient temperature leads to differential immune strategies in the subterranean rodent Ctenomys talarum

Animal thermoregulation may have significant costs and compete directly or indirectly with other energetically demanding processes, such as immune function. Although the subterranean environment is characterized by thermally stable conditions, small changes in ambient temperature could be critical in shaping immunity. However, little is known about the effects of ambient temperature, in naturally varying ranges, on immunity of wild species. Therefore, to evaluate the effect of short-term exposure to ambient temperatures on energy metabolism and body temperature during the acute phase immune response (APR) in the subterranean rodent Ctenomys talarum, 70 adult animals were divided into three experimental groups and exposed twice for 1 h to 15, 25 or 32°C (below, at or near the upper limit of the thermoneutral zone, respectively) before and after injection with saline (control) or lipopolysaccharide (LPS, which induces the APR). Animals exposed to 25 and 32°C showed a similar APR pattern, characterized by fever (average: 37.1 and 37.7°C, respectively), a 16% increase in O2 consumption and an increase in the neutrophil/lymphocyte ratio (N/L). Body mass loss and symptoms of sickness behavior were detected from 3 and 1 h post-injection, respectively. Individuals exposed to 15°C increased their metabolic rate by 60%, showed frequent hypothermia (34.3°C on average) and the characteristic N/L increase was attenuated. Body mass loss and sickness behavior were mostly detected 24 h post-injection. Our results suggest that the thermoregulation costs in C. talarum may limit the energy available for immunity, leading to different strategies to cope with infection.

Vitamin C co-administration with artemether-lumefantrine abrogates chronic stress exacerbated Plasmodium berghei-induced sickness behaviour, inflammatory and oxidative stress responses in mice

This study evaluated the effects of vitamin C and artemether-lumefantrine (AL) on sickness behaviour and oxido-inflammatory response in chronically stressed mice infected with Plasmodium berghei. Sickness behaviour severity was examined with weight and assessment of mice behaviours. Results showed that stress increased parasitaemia in infected mice. Vitamin C co-administration with AL increased parasite clearance over AL alone, and modulated inflammatory cytokines (TNF-α, IL-1β, IL-10, IL-12) and antioxidant parameters in plasma and brain tissue. Conclusively, stress worsens malaria-induced sickness behaviour and up-regulates the inflammatory and oxidative stress response. Co-administration of vitamin C with AL appears to counteract these detrimental effects.

Beyond digestion: Exploring how the gut microbiota modulates human social behaviors

For a long time, traditional medicine has acknowledged the gut's impact on general health. Contemporary science substantiates this association through investigations of the gut microbiota, the extensive community of microorganisms inhabiting our gastrointestinal system. These microscopic residents considerably improve digestive processes, nutritional absorption, immunological function, and pathogen defense. Nevertheless, a variety of gastrointestinal and extra-intestinal disorders can result from dysbiosis, an imbalance of the microbial composition of the gut microbiota. A groundbreaking discovery is the gut-brain axis, a complex communication network that links the enteric and central nervous system (CNS). This bidirectional communication allows the brain to influence gut activities and vice versa, impacting mental health and mood disorders like anxiety and depression. The gut microbiota can influence this communication by creating neurotransmitters and short-chain fatty acids, among other biochemical processes. These factors may affect our mental state, our ability to regulate our emotions, and the hypothalamic-pituitary-adrenal (HPA) axis. This study aimed to explore the complex interrelationships between the brain and the gut microbiota. We also conducted a thorough examination of the existing understanding in the area of how microbiota affects social behaviors, including emotions, stress responses, and cognitive functions. We also explored the potential of interventions that focus on the connection between the gut and the brain, such as using probiotics to treat diseases of the CNS. This research opens up new possibilities for addressing mental health and neurological conditions in an innovative manner.

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.

An immune challenge induces a decline in parental effort and compensation by the mate

Immune defense is fundamental to diminish the negative effects of the attack of infectious agents, yet the activation of the immune system entails costs and may compromise other life-history traits such as reproduction. In reproductive brown booby pairs (Sula leucogaster), we experimentally imposed an immune challenge during incubation, by intraperitoneally injecting Escherichia coli lipopolysaccharide (LPS), in either the male or the female. We aimed to test whether activation of the immune response results in (1) an increase in oxidative stress parameters, (2) a decline in post-hatching parental care in the treated individual, and (3) a compensation of the post-hatching parental effort by the nontreated mate. We found that activation of the immune response during incubation did not increase oxidative damage to lipids or total antioxidant capacity. However, mounting an immune response compromised parental effort during the chick-rearing period: compared to controls, LPS-treated parents showed roughly a 50% decline in the rate of preening and offspring feeding in response to begging. Interestingly, mates of LPS-treated parents increased their feeding rate suggesting parental care compensation. According to a scenario of full compensation, the decline in parental effort of LPS-treated parents did not result in poorer offspring growth or immune response, or increased levels of oxidative stress parameters. These findings suggest that in a long-lived species with long-lasting biparental care, an immune challenge compromises parental care, favoring parental compensation as a strategy to mitigate costs in terms of offspring success.

Immune challenge affects risk sensitivity and locomotion in mosquitofish (Gambusia holbrooki)

The immune system is crucial in responding to disease-causing pathogens. However, immune responses may also cause stereotypical changes in behaviour known as sickness behaviours, which often include reduced activity. Sickness behaviours are thought to have an important role in conserving energy required to support the immune response; however, little is known about how they manifest over time or in relation to risk, particularly in fishes. Here, we induced an immune response in mosquitofish (Gambusia holbrooki) by inoculating them with Escherichia coli lipopolysaccharide (LPS). We subsequently tested batches of fish at 24 h intervals and examined: locomotory behaviour, tendency to use a refuge and fast-start response immediately following a threat stimulus (measured as peak acceleration). Control and LPS-treated fish behaved similarly on days 1, 3 and 4. However, 2 days post-inoculation, LPS fish swam more slowly and spent more time in the refuge than control fish, although no difference in post-threat peak acceleration was found. Our findings suggest that sickness behaviours peak roughly 2 days following exposure to LPS and are relatively short-lived. Specifically, immune-challenged individuals exhibit reduced locomotion and exploratory behaviour, becoming more risk averse overall while still retaining the ability to respond acutely to a threat stimulus.

Perception of unfamiliar caregivers during sickness - Using the new Caregiver Perception Task (CgPT) during experimental endotoxemia

Social withdrawal is a well-established part of sickness behavior, but in some contexts sick animals might gain from keeping close instead of keeping away. For instance, sick individuals are more willing to be near known individuals who can provide care and safety (close others) compared to when healthy. Yet, interactions with some strangers might also be beneficial (i.e., healthcare professionals), but it is not known how sickness interplay with social behavior towards such individuals. Here, we assessed if sickness affects perception of caregivers, and developed a new task, the Caregiver Perception Task (CgPT). Twenty-six participants performed the CgPT, once after an injection of lipopolysaccharide (LPS, 0.8 ng/kg body weight, n = 24), and once after an injection of saline (n = 25), one hour and forty-five minutes post-injection. During the task, participants watched short video clips of three types of caregivers: a healthcare professional taking care of a sick individual, a healthcare professional not taking care of a sick individual, and a non-healthcare professional taking care of their sick adult child or partner. After each video clip, the likability, trustworthiness, professionalism, and willingness to interact with and receive care from the caregiver were rated on visual analogue scales. Results showed that participants injected with saline rated healthcare professionals who did not take care of a sick individual less positively on all aspects compared to healthcare professionals who took care of a sick individual. Moreover, compared to saline, LPS increased the participants' willingness to receive care from healthcare professionals and non-healthcare professionals providing care, but not from healthcare professionals not providing care. Thus, our results indicate that sick individuals may approach unknown individuals with potential to provide care and support.

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.

How behavioural ageing affects infectious disease

Ageing is associated with profound changes in behaviour that could influence exposure and susceptibility to infectious disease. As well as determining emergent patterns of infection across individuals of different ages, behavioural ageing could interact with, confound, or counteract age-related changes in other traits. Here, we examine how behavioural ageing can manifest and influence patterns of infection in wild animals. We discuss a range of age-related changes that involve interactions between behaviour and components of exposure and susceptibility to infection, including social ageing and immunosenescence, acquisition of novel parasites and pathogens with age, changes in spatial behaviours, and age-related hygiene and sickness behaviours. Overall, most behavioural changes are expected to result in a reduced exposure rate, but there is relatively little evidence for this phenomenon, emerging largely from a rarity of explicit tests of exposure changes over the lifespan. This review offers a framework for understanding how ageing, behaviour, immunity, and infection interact, providing a series of hypotheses and testable predictions to improve our understanding of health in ageing societies.

Discriminating between sick and healthy faces based on early sickness cues: an exploratory analysis of sex differences

Background and objectives

It has been argued that sex and disease-related traits should influence how observers respond to sensory sickness cues. In fact, there is evidence that humans can detect sensory cues related to infection in others, but lack of power from earlier studies prevents any firm conclusion regarding whether perception of sickness cues is associated with sex and disease-related personality traits. Here, we tested whether women (relative to men), individuals with poorer self-reported health, and who are more sensitive to disgust, vulnerable to disease, and concerned about their health, overestimate the presence of, and/or are better at detecting sickness cues.

Methodology

In a large online study, 343 women and 340 men were instructed to identify the sick faces from a series of sick and healthy photographs of volunteers with an induced acute experimental inflammation. Participants also completed several disease-related questionnaires.

Results

While both men and women could discriminate between sick and healthy individuals above chance level, exploratory analyses revealed that women outperformed men in accuracy and speed of discrimination. Furthermore, we demonstrated that higher disgust sensitivity to body odors is associated with a more liberal decision criterion for categorizing faces as sick.

Conclusion

Our findings give strong support for the human ability to discriminate between sick and healthy individuals based on early facial cues of sickness and suggest that women are significantly, although only slightly, better at this task. If this finding is replicated, future studies should determine whether women's better performance is related to increased avoidance of sick individuals.

Effects of physical activity in child and adolescent depression and anxiety: role of inflammatory cytokines and stress-related peptide hormones

Depression and anxiety are the most common mental illnesses affecting children and adolescents, significantly harming their well-being. Research has shown that regular physical activity can promote cognitive, emotional, fundamental movement skills, and motor coordination, as a preventative measure for depression while reducing the suicide rate. However, little is known about the potential role of physical activity in adolescent depression and anxiety. The studies reviewed in this paper suggest that exercise can be an effective adjunctive treatment to improve depressive and anxiety symptoms in adolescents, although research on its neurobiological effects remains limited.

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.

Trade-offs between immunity and competitive ability in fighting ant males

BACKGROUND

Fighting disease while fighting rivals exposes males to constraints and trade-offs during male-male competition. We here tested how both the stage and intensity of infection with the fungal pathogen Metarhizium robertsii interfere with fighting success in Cardiocondyla obscurior ant males. Males of this species have evolved long lifespans during which they can gain many matings with the young queens of the colony, if successful in male-male competition. Since male fights occur inside the colony, the outcome of male-male competition can further be biased by interference of the colony's worker force.

RESULTS

We found that severe, but not yet mild, infection strongly impaired male fighting success. In late-stage infection, this could be attributed to worker aggression directed towards the infected rather than the healthy male and an already very high male morbidity even in the absence of fighting. Shortly after pathogen exposure, however, male mortality was particularly increased during combat. Since these males mounted a strong immune response, their reduced fighting success suggests a trade-off between immune investment and competitive ability already early in the infection. Even if the males themselves showed no difference in the number of attacks they raised against their healthy rivals across infection stages and levels, severely infected males were thus losing in male-male competition from an early stage of infection on.

CONCLUSIONS

Males of the ant C. obscurior have a well-developed immune system that raises a strong immune response very fast after fungal exposure. This allows them to cope with mild pathogen exposures without compromising their success in male-male competition, and hence to gain multiple mating opportunities with the emerging virgin queens of the colony. Under severe infection, however, they are weak fighters and rarely survive a combat already at early infection when raising an immune response, as well as at progressed infection, when they are morbid and preferentially targeted by worker aggression. Workers thereby remove males that pose a future disease threat by biasing male-male competition. Our study thus reveals a novel social immunity mechanism how social insect workers protect the colony against disease risk.

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.

Microbiome and immuno-metabolic dysregulation in patients with major depressive disorder with atypical clinical presentation

Depression is highly prevalent (6% 1-year prevalence) and is the second leading cause of disability worldwide. Available treatment options for depression are far from optimal, with response rates only around 50%. This is most likely related to a heterogeneous clinical presentation of major depression disorder (MDD), suggesting different manifestations of underlying pathophysiological mechanisms. Poorer treatment outcomes to first-line antidepressants were reported in MDD patients endorsing an "atypical" symptom profile that is characterized by preserved reactivity in mood, increased appetite, hypersomnia, a heavy sensation in the limbs, and interpersonal rejection sensitivity. In recent years, evidence has emerged that immunometabolic biological dysregulation is an important underlying pathophysiological mechanism in depression, which maps more consistently to atypical features. In the last few years human microbial residents have emerged as a key influencing variable associated with immunometabolic dysregulations in depression. The microbiome plays a critical role in the training and development of key components of the host's innate and adaptive immune systems, while the immune system orchestrates the maintenance of key features of the host-microbe symbiosis. Moreover, by being a metabolically active ecosystem commensal microbes may have a huge impact on signaling pathways, involved in underlying mechanisms leading to atypical depressive symptoms. In this review, we discuss the interplay between the microbiome and immunometabolic imbalance in the context of atypical depressive symptoms. Although research in this field is in its infancy, targeting biological determinants in more homogeneous clinical presentations of MDD may offer new avenues for the development of novel therapeutic strategies for treatment-resistant depression.

The suffering ape hypothesis

The "fearful ape hypothesis" could be regarded as one aspect of a more general "suffering ape hypothesis": Humans are more likely to experience negative emotions (e.g., fear, sadness), aversive symptoms (e.g., pain, fever), and to engage in self-harming behavior (e.g., cutting, suicide attempts) because these might motivate affiliative, consolatory, and supportive behavior from their prosocial environment thereby enhancing evolutionary fitness.

Varying intensity of simulated infection partially affects the magnitude of the acute-phase immune response in the subterranean rodent Ctenomys talarum

The acute phase response (APR), coordinated by a complex network of components of the immune and neuroendocrine systems, plays a key role in early immune defense. This response can be elicited by a wide variety of pathogens at different intensities (frequencies and doses), hence experimental immune challenges with antigen gradients makes it possible to evaluate sickness progression with a better representation of what occurs in natural systems. However, how infection intensity could shape the APR magnitude in wild species is still poorly understood. Here, the immune response was activated in the subterranean rodent Ctenomys talarum with a gradient of lipopolysaccharide (LPS) doses (0.5, 1, 1.5, and 2 mg/kg of body mass). Changes in body temperature, body mass, and energetic costs were evaluated over time. We also assessed cortisol levels, white blood cells counts and neutrophil: lymphocyte ratios, before and after injection. Results indicated that during the APR, C. talarum shows a hyperthermic response, which is maintained for 6 h, with slight differences among antigen doses in the pattern of thermal response and body mass change. A maximum increase in body temperature of 0.83°C to 1.63°C was observed during the first hour, associated with a metabolic cost that ranged from 1.25 to 1.41 ml O₂ /gh. Although no clear effects of treatment were detected on leukocyte abundance, we found increments in neutrophil: lymphocyte ratios and gradual increases in cortisol levels corresponding to the intensity of simulated infection, which may indicate redistribution of immune cells and enhancement of immune function. An evident sickness syndrome was observed even at the lowest LPS dose that was characterized by an increase in body temperature, energy expenditure, and N: L ratio, as well as a dose-dependent increase in cortisol levels. Although in nature, other constraints and challenges could affect the magnitude and costs of immune responses, C. talarum mounts an effective APR with a low increase in their daily energy expenditure, regardless of LPS dose.

The effect of weaning age on animal performance in lambs exposed to naturally acquired nematode infections

The effects of mixed gastrointestinal nematode (GIN) infections on animal growth and post-weaning activity patterns were investigated in grazing intact ram lambs when naturally exposed to two different infection levels and weaned at different ages. Ewes and their twin-born lambs were turned-out to graze in two permanent pasture enclosures naturally contaminated with GIN the previous year. Ewes and lambs in the low parasite exposure group (LP) were drenched before turn-out and at weaning, respectively, with 0.2 mg ivermectin per kg body weight, whereas those in the high parasite exposure group (HP) were left untreated. Two weaning ages were applied, early weaning (EW) (10 weeks) and late weaning (LW) (14 weeks), respectively. The lambs were then allocated to one out of four groups based on parasite exposure level and weaning age (EW-HP, n = 12; LW-HP, n = 11; EW-LP, n = 13; LW-LP, n = 13). Body weight gain (BWG) and faecal egg counts (FEC) were monitored, in all groups, from the day of early weaning and every four weeks, for 10 weeks. In addition, nematode composition was determined using droplet digital PCR. Activity patterns measured as Motion Index (MI; the absolute value of the 3D acceleration) and lying time were monitored continuously from the day of weaning until four weeks post-weaning using IceQube® sensors. Statistical analyses were performed in RStudio, using mixed models with repeated measures. BWG was 11% lower in EW-HP compared with EW-LP (P = 0.0079) and 12% lower compared with LW-HP (P = 0.018), respectively. In contrast, no difference in BWG was observed between LW-HP and LW-LP (P = 0.97). The average EPG was higher in EW-HP compared with EW-LP (P < 0.001), as well as in EW-HP compared with LW-HP (P = 0.021), and LW-HP compared with LW-LP (P = 0.0022). The molecular investigation showed that animals in LW-HP had a higher proportion of Haemonchus contortus compared with EW-HP. MI was 19% lower in EW-HP compared with EW-LP (P = 0.0004). Daily lying time was 15% shorter in EW-HP compared with EW-LP (P = 0.0070). In contrast, no difference in MI (P = 0.13) and lying time (P = 0.99) between LW-HP and LW-LP was observed. The results suggest that a delayed weaning age may reduce the adverse effects of GIN infection on BWG. Contrarily, an earlier weaning age may reduce the risk of H. contortus infection in lambs. Moreover, the results demonstrates a potential use of automated behaviour recordings as a diagnostic tool for the detection of nematode infections in sheep.

What SARS-CoV-2 does to our brains

Neurological symptoms in SARS-CoV-2-infected patients have been reported, but their cause remains unclear. In theory, the neurological symptoms observed after SARS-CoV-2 infection could be (1) directly caused by the virus infecting brain cells, (2) indirectly by our body’s local or systemic immune response toward the virus, (3) by coincidental phenomena, or (4) a combination of these factors. As indisputable evidence of intact and replicating SARS-CoV-2 particles in the central nervous system (CNS) is currently lacking, we suggest focusing on the host’s immune reaction when trying to understand the neurocognitive symptoms associated with SARS-CoV-2 infection. In this perspective, we discuss the possible immune-mediated mechanisms causing functional or structural CNS alterations during acute infection as well as in the post-infectious context. We also review the available literature on CNS affection in the context of COVID-19 infection, as well as observations from animal studies on the molecular pathways involved in sickness behavior.

Psychological symptoms of illness and emotional distress in advanced cancer cachexia

PURPOSE OF REVIEW

Cachexia induces both physical and psychological symptoms of illness in patients with advanced cancer and may generate emotional distress in patients and families. However, physical symptoms of cachexia received the most emphasis. The aims of this review are to elucidate a link between systemic inflammation underlying cachexia and psychological symptoms and emotional distress, and to advance care strategy for management of psychological symptoms and emotional distress in patients and families.

RECENT FINDINGS

The main themes in the literature covered by this review are psychological symptoms in patients and emotional distress in patients and families. Studies of the underlying biology of cachexia identify the role of the central nervous system to amplify tumor-induced systemic inflammation. The brain mediates a cluster of symptoms, such as sleep disruption, anxiety, cognitive impairment, and reduction in motivated behavior (notably anorexia). These are distressing to patients as well as to families.

SUMMARY

There is growing recognition that holistic multimodal interventions are needed to alleviate psychological symptoms and emotional distress and to improve quality of life in patients with cancer cachexia and families. This is an approach that addresses not only physical health but also psychological, emotional, and social well being issues.

Spatial distancing by fungus-exposed Myrmica ants is prompted by sickness rather than contagiousness

The ecological success of ants relies on their high level of sociality and cooperation between genetically related nestmates. However, these group-living insects suffer from elevated risks of disease outbreak in the whole nest. To face this sanitary challenge, social and spatial distancing of pathogen-exposed individuals from susceptible nestmates appear to be simple, although efficient, ways to limit the propagation of contact-transmitted pathogens. Here we question whether spatial distancing in Myrmica rubra ants is an active response of diseased individuals that correlates with their level of infectiousness. We contaminated foragers with spores of Metarhizium brunneum entomopathogenic fungus. We daily tracked the location of these pathogen-exposed individuals and we analyzed their movement patterns until their death on the 5th day post-contamination. Quite unexpectedly, we found that contagious individuals, whose body was covered with infectious spores, did not reduce their mobility nor stayed far away from larvae in order to limit pathogen transmission to healthy nestmates. Spatial distancing occurred later when diseased individuals were no longer contagious because spores had penetrated their body. These sick ants mainly stayed outside the nest, were less mobile and showed a shift from a superdiffusive to subdiffusive walking pattern. Furthermore, these diseased ants did not actively head towards directions that were opposite to the nest entrance. This study found no evidence for early spatial distancing by contaminated M.rubra workers that would fit to the actual risk of colony-wide contagion. Coupled to a lower mobility and area-reduced walking patterns, the late distancing of moribund individuals appears to be a symptom of sickness resulting from fungus-induced physical and physiological dysfunctions. Besides questioning the truly altruistic nature of death in isolation in this system (and potentially others), we discuss about the ecological and physiological constraints that explain the absence of early distancing when some ant species are exposed to pathogens.

The evolution of the human healthcare system and implications for understanding our responses to COVID-19

The COVID-19 pandemic has revealed an urgent need for a comprehensive, multidisciplinary understanding of how healthcare systems respond successfully to infectious pathogens-and how they fail. This study contributes a novel perspective that focuses on the selective pressures that shape healthcare systems over evolutionary time. We use a comparative approach to trace the evolution of care-giving and disease control behaviours across species and then map their integration into the contemporary human healthcare system. Self-care and pro-health environmental modification are ubiquitous across animals, while derived behaviours like care for kin, for strangers, and group-level organizational responses have evolved via different selection pressures. We then apply this framework to our behavioural responses to COVID-19 and demonstrate that three types of conflicts are occurring: (1) conflicting selection pressures on individuals, (2) evolutionary mismatches between the context in which our healthcare behaviours evolved and our globalized world of today and (3) evolutionary displacements in which older forms of care are currently dispensed through more derived forms. We discuss the significance of understanding how healthcare systems evolve and change for thinking about the role of healthcare systems in society during and after the time of COVID-19-and for us as a species as we continue to face selection from infectious diseases.

Peripheral viral challenge increases c-fos level in cerebral neurons

Peripheral viral infection can substantially alter brain function. We have previously shown that intraperitoneal (i.p.) injection of a viral mimetic, polyinosinic-polycytidylic acid (PIC), engenders hyperexcitability of cerebral neurons. Because neuronal activity is invariably associated with their expression of the Cfos gene, the present study was undertaken to determine whether PIC challenge also increases neuronal c-fos protein level. Female C57BL/6 mice were i.p. injected with PIC, and neuronal c-fos was analyzed in the motor cortex by immunohistochemistry. PIC challenge instigated a robust increase in the number of c-fos-positive neurons. This increase reached approximately tenfold over control at 24 h. Also, the c-fos staining intensity of individual neurons increased. AMG-487, a specific inhibitor of the chemokine receptor CXCR3, profoundly attenuated the accumulation of neuronal c-fos, indicating the activation of CXCL10/CXCR3 axis as the trigger of the process. Together, these results show that the accumulation of c-fos is a viable readout to assess the response of cerebral neurons to peripheral PIC challenge, and to elucidate the underlying molecular mechanisms.

Emerging roles for microglia and microbiota in the development of social circuits

Social withdrawal is a core component of the behavioral response to infection. This fact points to a deep evolutionary and biologic relationship between the immune system and the social brain. Indeed, a large body of literature supports such an intimate connection. In particular, immune activation during the perinatal period has been shown to have long-lasting consequences for social behavior, but the neuroimmune mechanisms by which this occurs are only partially understood. Microglia, the resident immune cells of the brain, influence the formation of neural circuits by phagocytosing synaptic and cellular elements, as well as by releasing chemokines and cytokines. Intriguingly, microbiota, especially those that reside within the gut, may also influence brain development via the release of metabolites that travel to the brain, by influencing vagal nerve signaling, or by modulating the host immune system. Here, I will review the work suggesting important roles for microglia and microbiota in social circuit formation during development. I will then highlight avenues for future work in this area, as well as technological advances that extend our capacity to ask mechanistic questions about the relationships between microglia, microbiota, and the social brain.

Signaling sickness: the role of recalled sickness behavior and psychosocial factors in shaping communication style

Background and objectives

Active infection results in several outward signs in humans, including visible symptoms, changes in behavior and possible alterations in skin color and gait. A potential adaptive function of these indicators is to signal distress and elicit care from close others. We hypothesized that sickness behavior, a suite of stereotypical changes in mood and behavior, also serves to communicate health status to others. We further hypothesized that such outward signals/cues of health status would vary based on context and sociocultural norms.

Methodology

We explored self-reported, recalled sickness behavior, communication style, demographics and theoretically relevant cultural factors in a large national US sample (n = 1259) using multinomial probit regressions.

Results

In accordance with predictions, relatively few participants were willing to talk or complain about sickness to strangers. Self-reported, recalled sickness behavior was associated with some communication styles but attention received from others was more consistently associated with potential signaling. Several cultural factors, including stoicism and traditional machismo, were also associated with different sickness signaling styles.

Conclusions and implications

These preliminary, self-reported data lend some tentative support to the sickness behavior signaling hypothesis, though experimental or observational support is needed. The role of cultural norms in shaping how such signals are transmitted and received also deserves further attention as they may have important implications for disease transmission.

Lay Summary

Evolutionary medicine hypothesizes that signs and symptoms of infectious disease—including sickness behavior—have adaptive functions, one of which might be to reliably signal one’s health status to others. Our results suggest that evolved signals like these are likely shaped by cultural factors.

Low-grade systemic inflammation and the workplace

BACKGROUND

Psychosocial and physical stressors can elicit the stress response, co-ordinated by interactions between neuroendocrine and inflammatory processes. The central role of the immune system, specifically low-grade systemic inflammation, is sometimes overlooked in work-related stress research.

OBJECTIVE

To review evidence that work-related psychosocial and physical stressors can stimulate a low-grade systemic inflammation which, through interactions with the neurohormonal systems, may impact on the well-being and productivity of workers.

METHODS

Literature searches were performed by databases and by hand. Databases used included Interface - EBSCOhost Research Databases; PsycINFO; Academic Search Complete; Africa-Wide Information; CINAHL; E-Journals; MEDLINE and PsycARTICLES.

RESULTS

Psychosocial stressors, infections, poor indoor air quality, musculoskeletal injuries and chemicals can stimulate a low-grade systemic inflammation that may adversely affect workers' mental and physical health, as well as productivity. The psychological and physical effects caused by infection-induced inflammation are generally referred to as sickness behaviour and those caused by poor indoor air quality as sick building syndrome.

CONCLUSIONS

Stressor-induced low-grade systemic inflammation can be a causal factor in the physical and behavioural symptoms of work-related stress. It is therefore important that those involved with the health of workers be cognisant of inappropriate or chronic low-grade inflammation as a potential health hazard.

Carry on caring: infected females maintain their parental care despite high mortality

Parental care is a key component of an organism's reproductive strategy that is thought to trade-off with allocation toward immunity. Yet, it is unclear how caring parents respond to pathogens: do infected parents reduce care as a sickness behavior or simply from being ill or do they prioritize their offspring by maintaining high levels of care? To address this issue, we investigated the consequences of infection by the pathogen Serratia marcescens on mortality, time spent providing care, reproductive output, and expression of immune genes of female parents in the burying beetle Nicrophorus vespilloides. We compared untreated control females with infected females that were inoculated with live bacteria, immune-challenged females that were inoculated with heat-killed bacteria, and injured females that were injected with buffer. We found that infected and immune-challenged females changed their immune gene expression and that infected females suffered increased mortality. Nevertheless, infected and immune-challenged females maintained their normal level of care and reproductive output. There was thus no evidence that infection led to either a decrease or an increase in parental care or reproductive output. Our results show that parental care, which is generally highly flexible, can remain remarkably robust and consistent despite the elevated mortality caused by infection by pathogens. Overall, these findings suggest that infected females maintain a high level of parental care, a strategy that may ensure that offspring receive the necessary amount of care but that might be detrimental to the parents' own survival or that may even facilitate disease transmission to offspring.

The Sickness Behavior Inventory-Revised: Sickness behavior and its associations with depression and inflammation in patients with metastatic lung cancer

BACKGROUND

Inflammation may contribute to the high prevalence of depressive symptoms seen in lung cancer. "Sickness behavior" is a cluster of symptoms induced by inflammation that are similar but distinct from depressive symptoms. The Sickness Behavior Inventory-Revised (SBI-R) was developed to measure sickness behavior. We hypothesized that the SBI-R would demonstrate adequate psychometric properties in association with inflammation.

METHOD

Participants with stage IV lung cancer (n = 92) were evaluated for sickness behavior using the SBI-R. Concomitant assessments were made of depression (Patient Hospital Questionniare-9, Hospital Anxiety and Depression Scale) and inflammation [C-reactive protein (CRP)]. Classical test theory (CTT) was applied and multivariate models were created to explain SBI-R associations with depression and inflammation. Factor Analysis was also used to identify the underlying factor structure of the hypothesized construct of sickness behavior. A longitudinal analysis was conducted for a subset of participants.

RESULTS

The sample mean for the 12-item SBI-R was 8.3 (6.7) with a range from 0 to 33. The SBI-R demonstrated adequate internal consistency with a Cronbach's coefficient of 0.85, which did not increase by more than 0.01 with any single-item removal. This analysis examined factor loadings onto a single factor extracted using the principle components method. Eleven items had factor loadings that exceeded 0.40. SBI-R total scores were significantly correlated with depressive symptoms (r = 0.78, p < 0.001) and CRP (r = 0.47, p < 0.001). Multivariate analyses revealed that inflammation and depressive symptoms explained 67% of SBI-R variance.

SIGNIFICANCE OF RESULTS

The SBI-R demonstrated adequate reliability and construct validity in this patient population with metastatic lung cancer. The observed findings suggest that the SBI-R can meaningfully capture the presence of sickness behavior and may facilitate a greater understanding of inflammatory depression.

Invited review: The influence of immune activation on transition cow health and performance-A critical evaluation of traditional dogmas

The progression from gestation into lactation represents the transition period, and it is accompanied by marked physiological, metabolic, and inflammatory adjustments. The entire lactation and a cow's opportunity to have an additional lactation are heavily dependent on how successfully she adapts during the periparturient period. Additionally, a disproportionate amount of health care and culling occurs early following parturition. Thus, lactation maladaptation has been a heavily researched area of dairy science for more than 50 yr. It was traditionally thought that excessive adipose tissue mobilization in large part dictated transition period success. Further, the magnitude of hypocalcemia has also been assumed to partly control whether a cow effectively navigates the first few months of lactation. The canon became that adipose tissue released nonesterified fatty acids (NEFA) and the resulting hepatic-derived ketones coupled with hypocalcemia lead to immune suppression, which is responsible for transition disorders (e.g., mastitis, metritis, retained placenta, poor fertility). In other words, the dogma evolved that these metabolites and hypocalcemia were causal to transition cow problems and that large efforts should be enlisted to prevent increased NEFA, hyperketonemia, and subclinical hypocalcemia. However, despite intensive academic and industry focus, the periparturient period remains a large hurdle to animal welfare, farm profitability, and dairy sustainability. Thus, it stands to reason that there are alternative explanations to periparturient failures. Recently, it has become firmly established that immune activation and the ipso facto inflammatory response are a normal component of transition cow biology. The origin of immune activation likely stems from the mammary gland, tissue trauma during parturition, and the gastrointestinal tract. If inflammation becomes pathological, it reduces feed intake and causes hypocalcemia. Our tenet is that immune system utilization of glucose and its induction of hypophagia are responsible for the extensive increase in NEFA and ketones, and this explains why they (and the severity of hypocalcemia) are correlated with poor health, production, and reproduction outcomes. In this review, we argue that changes in circulating NEFA, ketones, and calcium are simply reflective of either (1) normal homeorhetic adjustments that healthy, high-producing cows use to prioritize milk synthesis or (2) the consequence of immune activation and its sequelae.

Sickness behaviors across vertebrate taxa: proximate and ultimate mechanisms

There is nothing like a pandemic to get the world thinking about how infectious diseases affect individual behavior. In this respect, sick animals can behave in ways that are dramatically different from healthy animals: altered social interactions and changes to patterns of eating and drinking are all hallmarks of sickness. As a result, behavioral changes associated with inflammatory responses (i.e. sickness behaviors) have important implications for disease spread by affecting contacts with others and with common resources, including water and/or sleeping sites. In this Review, we summarize the behavioral modifications, including changes to thermoregulatory behaviors, known to occur in vertebrates during infection, with an emphasis on non-mammalian taxa, which have historically received less attention. We then outline and discuss our current understanding of the changes in physiology associated with the production of these behaviors and highlight areas where more research is needed, including an exploration of individual and sex differences in the acute phase response and a greater understanding of the ecophysiological implications of sickness behaviors for disease at the population level.

Sick bats stay home alone: fruit bats practice social distancing when faced with an immunological challenge

Along with its many advantages, social roosting imposes a major risk of pathogen transmission. How social animals reduce this risk is poorly documented. We used lipopolysaccharide challenge to imitate bacterial infection in both a captive and a free‐living colony of an extremely social, long‐lived mammal—the Egyptian fruit bat. We monitored behavioral and physiological responses using an arsenal of methods, including onboard GPS to track foraging, acceleration sensors to monitor movement, infrared video to record social behavior, and blood samples to measure immune markers. Sick‐like (immune‐challenged) bats exhibited an increased immune response, as well as classic illness symptoms, including fever, weight loss, anorexia, and lethargy. Notably, the bats also exhibited behaviors that would reduce pathogen transfer. They perched alone and appeared to voluntarily isolate themselves from the group by leaving the social cluster, which is extremely atypical for this species. The sick‐like individuals in the open colony ceased foraging outdoors for at least two nights, thus reducing transmission to neighboring colonies. Together, these sickness behaviors demonstrate a strong, integrative immune response that promotes recovery of infected individuals while reducing pathogen transmission inside and outside the roost, including spillover events to other species, such as humans.

Infectious diseases and social distancing in nature

Spread of contagious pathogens critically depends on the number and types of contacts between infectious and susceptible hosts. Changes in social behavior by susceptible, exposed, or sick individuals thus have far-reaching downstream consequences for infectious disease spread. Although "social distancing" is now an all too familiar strategy for managing COVID-19, nonhuman animals also exhibit pathogen-induced changes in social interactions. Here, we synthesize the effects of infectious pathogens on social interactions in animals (including humans), review what is known about underlying mechanisms, and consider implications for evolution and epidemiology.

Bidirectional interactions between host social behaviour and parasites arise through ecological and evolutionary processes

An animal's social behaviour both influences and changes in response to its parasites. Here we consider these bidirectional links between host social behaviours and parasite infection, both those that occur from ecological vs evolutionary processes. First, we review how social behaviours of individuals and groups influence ecological patterns of parasite transmission. We then discuss how parasite infection, in turn, can alter host social interactions by changing the behaviour of both infected and uninfected individuals. Together, these ecological feedbacks between social behaviour and parasite infection can result in important epidemiological consequences. Next, we consider the ways in which host social behaviours evolve in response to parasites, highlighting constraints that arise from the need for hosts to maintain benefits of sociality while minimizing fitness costs of parasites. Finally, we consider how host social behaviours shape the population genetic structure of parasites and the evolution of key parasite traits, such as virulence. Overall, these bidirectional relationships between host social behaviours and parasites are an important yet often underappreciated component of population-level disease dynamics and host-parasite coevolution.

Mobility and infectiousness in the spatial spread of an emerging fungal pathogen

Emerging infectious diseases can have devastating effects on host communities, causing population collapse and species extinctions. The timing of novel pathogen arrival into naïve species communities can have consequential effects that shape the trajectory of epidemics through populations. Pathogen introductions are often presumed to occur when hosts are highly mobile. However, spread patterns can be influenced by a multitude of other factors including host body condition and infectiousness. White-nose syndrome (WNS) is a seasonal emerging infectious disease of bats, which is caused by the fungal pathogen Pseudogymnoascus destructans. Within-site transmission of P. destructans primarily occurs over winter; however, the influence of bat mobility and infectiousness on the seasonal timing of pathogen spread to new populations is unknown. We combined data on host population dynamics and pathogen transmission from 22 bat communities to investigate the timing of pathogen arrival and the consequences of varying pathogen arrival times on disease impacts. We found that midwinter arrival of the fungus predominated spread patterns, suggesting that bats were most likely to spread P. destructans when they are highly infectious, but have reduced mobility. In communities where P. destructans was detected in early winter, one species suffered higher fungal burdens and experienced more severe declines than at sites where the pathogen was detected later in the winter, suggesting that the timing of pathogen introduction had consequential effects for some bat communities. We also found evidence of source-sink population dynamics over winter, suggesting some movement among sites occurs during hibernation, even though bats at northern latitudes were thought to be fairly immobile during this period. Winter emergence behaviour symptomatic of white-nose syndrome may further exacerbate these winter bat movements to uninfected areas. Our results suggest that low infectiousness during host migration may have reduced the rate of expansion of this deadly pathogen, and that elevated infectiousness during winter plays a key role in seasonal transmission. Furthermore, our results highlight the importance of both accurate estimation of the timing of pathogen spread and the consequences of varying arrival times to prevent and mitigate the effects of infectious diseases.

Sickness and the Social Brain: Love in the Time of COVID

As a highly social species, inclusion in social networks and the presence of strong social bonds are critical to our health and well-being. Indeed, impaired social functioning is a component of numerous neuropsychiatric disorders including depression, anxiety, and substance use disorder. During the current COVID-19 pandemic, our social networks are at risk of fracture and many are vulnerable to the negative consequences of social isolation. Importantly, infection itself leads to changes in social behavior as a component of "sickness behavior." Furthermore, as in the case of COVID-19, males and females often differ in their immunological response to infection, and, therefore, in their susceptibility to negative outcomes. In this review, we discuss the many ways in which infection changes social behavior-sometimes to the benefit of the host, and in some instances for the sake of the pathogen-in species ranging from eusocial insects to humans. We also explore the neuroimmune mechanisms by which these changes in social behavior occur. Finally, we touch upon the ways in which the social environment (group living, social isolation, etc.) shapes the immune system and its ability to respond to challenge. Throughout we emphasize how males and females differ in their response to immune activation, both behaviorally and physiologically.

Let fever do its job: The meaning of fever in the pandemic era

Although fever is one of the main presenting symptoms of COVID-19 infection, little public attention has been given to fever as an evolved defense. Fever, the regulated increase in the body temperature, is part of the evolved systemic reaction to infection known as the acute phase response. The heat of fever augments the performance of immune cells, induces stress on pathogens and infected cells directly, and combines with other stressors to provide a nonspecific immune defense. Observational trials in humans suggest a survival benefit from fever, and randomized trials published before COVID-19 do not support fever reduction in patients with infection. Like public health measures that seem burdensome and excessive, fevers involve costly trade-offs but they can prevent infection from getting out of control. For infections with novel SARS-CoV-2, the precautionary principle applies: unless evidence suggests otherwise, we advise that fever should be allowed to run its course. Lay summary: For COVID-19, many public health organizations have advised treating fever with medicines such as acetaminophen or ibuprofen. Even though this is a common practice, lowering body temperature has not improved survival in laboratory animals or in patients with infections. Blocking fever can be harmful because fever, along with other sickness symptoms, evolved as a defense against infection. Fever works by causing more damage to pathogens and infected cells than it does to healthy cells in the body. During pandemic COVID-19, the benefits of allowing fever to occur probably outweigh its harms, for individuals and for the public at large.

Ecological Sensing Through Taste and Chemosensation Mediates Inflammation: A Biological Anthropological Approach

Ecological sensing and inflammation have evolved to ensure optima between organism survival and reproductive success in different and changing environments. At the molecular level, ecological sensing consists of many types of receptors located in different tissues that orchestrate integrated responses (immune, neuroendocrine systems) to external and internal stimuli. This review describes emerging data on taste and chemosensory receptors, proposing them as broad ecological sensors and providing evidence that taste perception is shaped not only according to sense epitopes from nutrients but also in response to highly diverse external and internal stimuli. We apply a biological anthropological approach to examine how ecological sensing has been shaped by these stimuli through human evolution for complex interkingdom communication between a host and pathological and symbiotic bacteria, focusing on population-specific genetic diversity. We then focus on how these sensory receptors play a major role in inflammatory processes that form the basis of many modern common metabolic diseases such as obesity, type 2 diabetes, and aging. The impacts of human niche construction and cultural evolution in shaping environments are described with emphasis on consequent biological responsiveness.

Olfactory Communication of Sickness Cues in Respiratory Infection

Animals detect sick conspecifics by way of body odor that enables the receiver to avoid potential infectious transmission. Human observational studies also indicate that different types of disease are associated with more or less aversive smells. In addition, body odors from otherwise healthy human individuals smell more aversive as a function of experimentally induced systemic inflammation. To investigate if naturally occurring immune activation also gives rise to perceivable olfactory changes, we collected body odor samples during two nights from individuals with a respiratory infection as well as when they were healthy. We hypothesized that independent raters would rate the body odor originating from sick individuals as smelling more aversive than when the same individuals were healthy. Even though body odor samples from sick individuals nominally smelled more intense, more disgusting, and less pleasant and healthy than the body odor from the same individuals when healthy, these effects were not statistically significant. Moreover, raters filled out three questionnaires, Perceived Vulnerability to Disease, Disgust Scale, and Health Anxiety, to assess potential associations between sickness-related personality traits and body odor perception. No such association was found. Since experimentally induced inflammation have made body odors more aversive in previous studies, we discuss whether this difference between studies is due to the level of sickness or to the type of trigger of the sickness response.

Behavioral changes associated with fever in transition dairy cows

Dairy cows are often diagnosed with fever without showing clinical symptoms of disease. The aim of this study was to investigate changes in feeding, social, and lying behaviors of cows with fever but without clinical disease, as compared with healthy cows. After parturition, dairy cows of mixed parities were housed in a dynamic group of 20. In the freestall pen, cows had access to 12 electronic feed bins, 2 electronic water bins, and 24 lying stalls. Feeding and social behaviors were recorded using the electronic feed bins, and lying behaviors were measured using electronic data loggers attached to the cow. Rectal body temperature was assessed on a daily basis, and fever defined as a body temperature >39.5°C. All cows were examined for metritis every third day after calving, and all other diseases (e.g., mastitis, ketosis) were diagnosed as per farm protocol. Cows with multiple days of fever (n = 8) and cows with 1 d of fever (n = 18) that were not diagnosed with a clinical disease were compared with a matched sample of healthy cows (i.e., cows that were not clinically ill and never had a fever recorded) of the same parity (categorized as primiparous vs. multiparous). Feeding, social, and lying behaviors were compared for the first 2 d of fever in cows with multiple days of fever, and the day of fever in cows with 1 d of fever. Cows of both fever groups spent less time feeding compared with controls (135 vs. 181 ± 7.6 min/d for multiple fever days, and 158 vs. 185 ± 9.7 min/d for 1 d of fever). Cows with 1 d of fever ate at a faster rate (109 vs. 91 ± 5 g/min) and had a lower number of replacements at the feed bunk (actor replacements: 9.7 vs. 14.6 ± 1.7 no./d; reactor replacements: 11.1 vs. 15.9 ± 1.6 no./d) compared with healthy controls. Overall, cows with fever showed behavioral changes such as decreased feeding time that are consistent with sickness responses described in other species.

Biology of heat stress; the nexus between intestinal hyperpermeability and swine reproduction

Unfavorable weather conditions are one of the largest constraints to maximizing farm animal productivity. Heat stress (HS), in particular, compromises almost every metric of profitability and this is especially apparent in the grow-finish and reproductive aspects of the swine industry. Suboptimal production during HS was traditionally thought to result from hypophagia. However, independent of inadequate nutrient consumption, HS affects a plethora of endocrine, physiological, metabolic, circulatory, and immunological variables. Whether these changes are homeorhetic strategies to survive the heat load or are pathological remains unclear, nor is it understood if they temporally occur by coincidence or if they are chronologically causal. However, mounting evidence suggest that the origin of the aforementioned changes lie at the gastrointestinal tract. Heat stress compromises intestinal barrier integrity, and increased appearance of luminal contents in circulation causes local and systemic inflammatory responses. The resulting immune activation is seemingly the epicenter to many, if not most of the negative consequences HS has on reproduction, growth, and lactation. Interestingly, thermoregulatory and production responses to HS are only marginally related. In other words, increased body temperature indices poorly predict decreases in productivity. Further, HS induced malnutrition is also a surprisingly inaccurate predictor of productivity. Thus, selecting animals with a "heat tolerant" phenotype based solely or separately on thermoregulatory capacity or production may not ultimately increase resilience. Describing the physiology and mechanisms that underpin how HS jeopardizes animal performance is critical for developing approaches to ameliorate current production issues and requisite for generating future strategies (genetic, managerial, nutritional, and pharmaceutical) aimed at optimizing animal well-being, and improving the sustainable production of high-quality protein for human consumption.

People expressing olfactory and visual cues of disease are less liked

For humans, like other social animals, behaviour acts as a first line of defence against pathogens. A key component is the ability to detect subtle perceptual cues of sick conspecifics. The present study assessed the effects of endotoxin-induced olfactory and visual sickness cues on liking, as well as potential involved mechanisms. Seventy-seven participants were exposed to sick and healthy facial pictures and body odours from the same individual in a 2 × 2 factorial design while disgust-related facial electromyography (EMG) was recorded. Following exposure, participants rated their liking of the person presented. In another session, participants also answered questionnaires on perceived vulnerability to disease, disgust sensitivity and health anxiety. Lower ratings of liking were linked to both facial and body odour disease cues as main effects. Disgust, as measured by EMG, did not seem to be the mediating mechanism, but participants who perceived themselves as more prone to disgust, and as more vulnerable to disease, liked presented persons less irrespectively of their health status. Concluding, olfactory and visual sickness cues that appear already a few hours after the experimental induction of systemic inflammation have implications for human sociality and may as such be a part of a behavioural defence against disease. This article is part of the Theo Murphy meeting issue 'Olfactory communication in humans'.

Why Care: Complex Evolutionary History of Human Healthcare Networks

One of the striking features of human social complexity is that we provide care to sick and contagious individuals, rather than avoiding them. Care-giving is a powerful strategy of disease control in human populations today; however, we are not the only species which provides care for the sick. Widespread reports occurring in distantly related species like cetaceans and insects suggest that the building blocks of care for the sick are older than the human lineage itself. This raises the question of what evolutionary processes drive the evolution of such care in animals, including humans. I synthesize data from the literature to evaluate the diversity of care-giving behaviors and conclude that across the animal kingdom there appear to be two distinct types of care-behaviors, both with separate evolutionary histories: (1) social care behaviors benefitting a sick individual by promoting healing and recovery and (2) community health behaviors that control pathogens in the environment and reduce transmission within the population. By synthesizing literature from psychology, anthropology, and biology, I develop a novel hypothesis (Hominin Pathogen Control Hypothesis) to explain how these two distinct sets of behaviors evolved independently then merged in the human lineage. The hypothesis suggests that social care evolved in association with offspring care systems whereas community health behaviors evolved as a type of niche construction. These two types of behaviors merged in humans to produce complex, multi-level healthcare networks in humans. Moreover, each type of care increases selection for the other, generating feedback loops that selected for increasing healthcare behaviors over time. Interestingly, domestication processes may have contributed to both social care and community health aspects of this process.

Metabolic Adaptations to Infections at the Organismal Level

Metabolic processes occurring during host-microbiota-pathogen interactions can favorably or negatively influence host survival during infection. Defining the metabolic needs of the three players, the mechanisms through which they acquire nutrients, and whether each participant cooperates or competes with each other to meet their own metabolic demands during infection has the potential to reveal new approaches to treat disease. Here, we review topical findings in organismal metabolism and infection and highlight four emerging lines of investigation: how host-microbiota metabolic partnerships protect against infection; competition for glucose between host and pathogen; significance of infection-induced anorexia; and redefinition of the role of iron during infection. We also discuss how these discoveries shape our understanding of infection biology and their likely therapeutic value.

Persistence of pain in humans and other mammals

Evolutionary models of chronic pain are relatively undeveloped, but mainly concern dysregulation of an efficient acute defence, or false alarm. Here, a third possibility, mismatch with the modern environment, is examined. In ancestral human and free-living animal environments, survival needs urge a return to activity during recovery, despite pain, but modern environments allow humans and domesticated animals prolonged inactivity after injury. This review uses the research literature to compare humans and other mammals, who share pain neurophysiology, on risk factors for pain persistence, behaviours associated with pain, and responses of conspecifics to behaviours. The mammal populations studied are mainly laboratory rodents in pain research, and farm and companion animals in veterinary research, with observations of captive and free-living primates. Beyond farm animals and rodent models, there is virtually no evidence of chronic pain in other mammals. Since evidence is sparse, it is hard to conclude that it does not occur, but its apparent absence is compatible with the mismatch hypothesis. This article is part of the Theo Murphy meeting issue 'Evolution of mechanisms and behaviour important for pain'.

Emotional expressions of the sick face

To handle the substantial threat posed by infectious diseases, behaviors that promote avoidance of contagion are crucial. Based on the fact that sickness depresses mood and that emotional expressions reveal inner states of individuals to others, which in turn affect approach/avoidance behaviors, we hypothesized that facial expressions of emotion may play a role in sickness detection. Using an experimental model of sickness, 22 volunteers were intravenously injected with either endotoxin (lipopolysaccharide; 2 ng/kg body weight) and placebo using a randomized cross-over design. The volunteers were two hours later asked to keep a relaxed expression on their face while their facial photograph was taken. To assess the emotional expression of the sick face, 49 participants were recruited and were asked to rate the emotional expression of the facial photographs of the volunteers when sick and when healthy. Our results indicate that the emotional expression of faces changed two hours after being made temporarily sick by an endotoxin injection. Sick faces were perceived as more sick/less healthy, but also as expressing more negative emotions, such as sadness and disgust, and less happiness and surprise. The emotional expressions mediated 59.1% of the treatment-dependent change in rated health. The inclusion of physical features associated with emotional expressions to the mediation analysis supported these results. We conclude that emotional expressions may contribute to detection and avoidance of infectious individuals and thereby be part of a behavioral defense against disease.

The Inclusive Behavioral Immune System

Although living in social groups offers many advantages, it comes at a cost of increased transmissible disease. The behavioral immune system (BIS) is thought to have evolved as a first line of defense against such infections. It acts by minimizing the contact of yet uninfected hosts with potential pathogens. The BIS has been observed in a wide range of animals including insects, amphibians and mammals, but most research has focused on humans where the BIS is guided by complex cognitive and emotional processing. When researchers discuss the evolutionary origin of the BIS, they assess how it raises individual fitness. What would happen though if we shift our attention to the evolutionary unit of selection – the gene? Success would be measured as the change in the gene’s prevalence in the entire population, and additional behaviors would come to our attention – those that benefit relatives, i.e., behaviors that raise inclusive fitness. One widely-recognized example of the inclusive BIS is social immunity, which is prevalent among eusocial organisms such as bees and ants. Their colonies engage in a collaborative protective behavior such as grooming and the removal of infected members from the nest. Another example may be sickness behavior, which includes the behavioral, cognitive and emotional symptoms that accompany infection, such as fatigue, and loss of appetite and social interest. My colleague and I recently suggested that sickness behavior has evolved because it reduces the direct and indirect contact between an infected host and its healthy kin – improving inclusive fitness. These additional behaviors are not carried out by the healthy individuals, but rather by whole communities in the first case, and by already infected individuals in the second. Since they step beyond the classical definition of BIS, it may be useful to broaden the term to the inclusive behavioral immune system.

Disease Tolerance as an Inherent Component of Immunity

Pathogenic organisms exert a negative impact on host health, revealed by the clinical signs of infectious diseases. Immunity limits the severity of infectious diseases through resistance mechanisms that sense and target pathogens for containment, killing, or expulsion. These resistance mechanisms are viewed as the prevailing function of immunity. Under pathophysiologic conditions, however, immunity arises in response to infections that carry health and fitness costs to the host. Therefore, additional defense mechanisms are required to limit these costs, before immunity becomes operational as well as thereafter to avoid immunopathology. These are tissue damage control mechanisms that adjust the metabolic output of host tissues to different forms of stress and damage associated with infection. Disease tolerance is the term used to define this defense strategy, which does not exert a direct impact on pathogens but is essential to limit the health and fitness costs of infection. Under this argument, we propose that disease tolerance is an inherent component of immunity.

No evidence for kin protection in the expression of sickness behaviors in house mice

When infected, animals change their behaviors in several ways, including by decreasing their activity, their food and water intake, and their interest in social interactions. These behavioral alterations are collectively called sickness behaviors and, for several decades, the main hypotheses put forward to explain this phenomenon were that engaging in sickness behaviors facilitated the fever response and improved the likelihood of host survival. However, a new hypothesis was recently proposed suggesting that engaging in sickness behaviors may serve to protect kin. We tested this kin protection hypothesis by combining a field and a laboratory experiment in house mice. In both experiments, we induced sickness behaviors by administration of a pro-inflammatory agent. In the field experiment, we then collected genetic data and assessed whether relatedness affected the intensity of sickness behaviors. In the lab experiment, we manipulated relatedness in small social groups and assessed whether having a closely related individual (a sibling) in the group altered social interactions or visits to common resources (such as food and water containers) once immune-challenged. Our results do not support the kinship protection hypothesis and therefore advance our understanding of why such an apparently costly set of behavioral changes would be evolutionarily maintained.