The effects of Trichinella infection on intersexual interactions between mice

Parasitic infection may influence mating behaviour in at least two ways: (1) by creating a selection pressure for mate choice based on apparent resistance to infection and (2) by reducing the likelihood of an infected individual mating through induced changes in its physiology or behaviour. These two possibilities were tested using a nematode infection in laboratory mice. Female CFLP mice were infected with larvae of the aphasmid nematode Trichinella spiralis and allowed to interact with uninfected males which were either experienced or inexperienced in term of having previously copulated. Both the responses of males towards infected and uninfected females and the responses of females towards males were recorded. Overall, males were significantly less likely to mount, copulate and show other behaviours related to copulation with infected females. When experienced and inexperienced males were considered separately, experienced males showed significantly more investigatory activity towards infected females, but infection did not appear to affect responses by inexperienced males. Infected females were more likely to avoid or respond aggressively to attempts to mount by males and the latency to the first attempt to mount correlated positively with the frequency of avoidance/aggression towards approaching males. The results suggest that infection in females influences intersexual interactions by inducing a disinclination to accept mounts and copulate. The functional implications for parasite transmission are considered.     

Parasite-induced suppression of aggregation under predation risk in a freshwater amphipod: Sociality of infected amphipods

Recent findings suggest that grouping with conspecifics is part of the behavioural defences developed by amphipod crustaceans to face predation risk by fish. Amphipods commonly serve as intermediate hosts for trophically transmitted parasites. These parasites are known for their ability to alter intermediate host phenotype in a way that promotes predation by definitive hosts, where they reproduce. If aggregation in amphipods dilutes the risk to be preyed on by fish, then it may dilute the probability of transmission for the parasite using fish as definitive hosts. Using experimental infections, we tested whether infection with the fish acanthocephalan Pomphorhynchus laevis alters attraction to conspecifics in the amphipod intermediate host Gammarus pulex. We also measured G. pulex's activity and reaction to light to detect potential links between changes in aggregation and changes in other behaviours. The attraction to conspecifics in the presence of predator cue, a behaviour found in uninfected gammarids, was cancelled by the infection, while phototaxis was reversed and activity unchanged. We found no correlation between the three behaviours in infected amphipods, while activity and aggregation were negatively correlated in uninfected individuals after the detection of predation cue. The physiological causes and the adaptive value of aggregation suppression are discussed in the context of a multidimensional manipulation.     

Sex-specific behavioural symptoms of viral gut infection and Wolbachia in Drosophila melanogaster

All organisms are infected with a range of symbionts spanning the spectrum of beneficial mutualists to detrimental parasites. The fruit fly Drosophila melanogaster is a good example, as both endosymbiotic Wolbachia, and pathogenic Drosophila C Virus (DCV) commonly infect it. While the pathophysiology and immune responses against both symbionts are the focus of intense study, the behavioural effects of these infections have received less attention. Here we report sex-specific behavioural responses to these infections in D. melanogaster. DCV infection caused increased sleep in female flies, but had no detectable effect in male flies. The presence of Wolbachia did not reduce this behavioural response to viral infection. We also found evidence for a sex-specific cost of Wolbachia, as male flies infected with the endosymbiont became more lethargic when awake. We discuss these behavioural symptoms as potentially adaptive sickness behaviours.     

Metabolomic Profiling of Faecal Extracts from Cryptosporidium parvum Infection in Experimental Mouse Models

Cryptosporidiosis is a gastrointestinal disease in humans and animals caused by infection with the protozoan parasite Cryptosporidium. In healthy individuals, the disease manifests mainly as acute self-limiting diarrhoea, but may be chronic and life threatening for those with compromised immune systems. Control and treatment of the disease is challenged by the lack of sensitive diagnostic tools and broad-spectrum chemotherapy. Metabolomics, or metabolite profiling, is an emerging field of study, which enables characterisation of the end products of regulatory processes in a biological system. Analysis of changes in metabolite patterns reflects changes in biochemical regulation, production and control, and may contribute to understanding the effects of Cryptosporidium infection in the host environment. In the present study, metabolomic analysis of faecal samples from experimentally infected mice was carried out to assess metabolite profiles pertaining to the infection. Gas-chromatography mass spectrometry (GC-MS) carried out on faecal samples from a group of C. parvum infected mice and a group of uninfected control mice detected a mean total of 220 compounds. Multivariate analyses showed distinct differences between the profiles of C. parvum infected mice and uninfected control mice,identifying a total of 40 compounds, or metabolites that contributed most to the variance between the two groups. These metabolites consisted of amino acids (n = 17), carbohydrates (n = 8), lipids (n = 7), organic acids (n = 3) and other various metabolites (n = 5), which showed significant differences in levels of metabolite abundance between the infected and uninfected mice groups (p < 0.05). The metabolites detected in this study as well as the differences in abundance between the C. parvum infected and the uninfected control mice, highlights the effects of the infection on intestinal permeability and the fate of the metabolites as a result of nutrient scavenging by the parasite to supplement its streamlined metabolism.     

Host behaviour alteration by its parasite: from brain gene expression to functional test

Many parasites with complex life cycles modify their intermediate hosts'' behaviour, presumably to increase transmission to their final host. The threespine stickleback (Gasterosteus aculeatus) is an intermediate host in the cestode Schistocephalus solidus life cycle, which ends in an avian host, and shows increased risky behaviours when infected. We studied brain gene expression profiles of sticklebacks infected with S. solidus to determine the proximal causes of these behavioural alterations. We show that infected fish have altered expression levels in genes involved in the inositol pathway. We thus tested the functional implication of this pathway and successfully rescued normal behaviours in infected sticklebacks using lithium exposure. We also show that exposed but uninfected fish have a distinct gene expression profile from both infected fish and control individuals, allowing us to separate gene activity related to parasite exposure from consequences of a successful infection. Finally, we find that selective serotonin reuptake inhibitor-treated sticklebacks and infected fish do not have similarly altered gene expression, despite their comparable behaviours, suggesting that the serotonin pathway is probably not the main driver of phenotypic changes in infected sticklebacks. Taken together, our results allow us to predict that if S. solidus directly manipulates its host, it could target the inositol pathway.     

Parasite manipulation of brain monoamines in California killifish (Fundulus parvipinnis) by the trematode Euhaplorchis californiensis

California killifish (Fundulus parvipinnis) infected with the brain-encysting trematode Euhaplorchis californiensis display conspicuous swimming behaviours rendering them more susceptible to predation by avian final hosts. Heavily infected killifish grow and reproduce normally, despite having thousands of cysts inside their braincases. This suggests that E. californiensis affects only specific locomotory behaviours. We hypothesised that changes in the serotonin and dopamine metabolism, essential for controlling locomotion and arousal may underlie this behaviour modification. We employed micropunch dissection and HPLC to analyse monoamine and monoamine metabolite concentrations in the brain regions of uninfected and experimentally infected fish. The parasites exerted density-dependent changes in monoaminergic activity distinct from those exhibited by fish subjected to stress. Specifically, E. californiensis inhibited a normally occurring, stress-induced elevation of serotonergic metabolism in the raphae nuclei. This effect was particularly evident in the experimentally infected fish, whose low-density infections were concentrated on the brainstem. Furthermore, high E. californiensis density was associated with increased dopaminergic activity in the hypothalamus and decreased serotonergic activity in the hippocampus. In conclusion, the altered monoaminergic metabolism may explain behavioural differences leading to increased predation of the infected killifish by their final host predators.     

Sexual selection in an isopod with Wolbachia‐induced sex reversal: males prefer real females

A variety of genetic elements encode traits beneficial to their own transmission. Despite their ‘selfish’ behaviour, most of these elements are often found at relatively low frequencies in host populations. This is the case of intracytoplasmic Wolbachia bacteria hosted by the isopod Armadillidium vulgare that distort the host sex ratio towards females by feminizing the genetic males they infect. Here we tested the hypothesis that sexual selection against Wolbachia‐infected females could maintain a polymorphism of the infection in populations. The infected neo‐females (feminized males) have lower mating rates and received less sperm relative to uninfected females. Males exhibited an active choice: they interacted more with uninfected females and made more mating attempts. A female behavioural difference was also observed in response to male mating attempts: infected neo‐females more often exhibited behaviours that stop the mating sequence. The difference in mating rate was significant only when males could choose between the two female types. This process could maintain a polymorphism of the infection in populations. Genetic females experimentally infected with Wolbachia are not exposed to the same sexual selection pressure, so the infection alone cannot explain these differences.     

Brain‐encysting trematodes and altered monoamine activity in naturally infected killifish Fundulus parvipinnis

This paper presents novel evidence to address mechanisms by which trematode parasites effect behavioural changes in naturally infected fish hosts. California killifish Fundulus parvipinnis infected with the brain‐encysting trematode Euhaplorchis californiensis display conspicuous swimming behaviours that render them 30 times more likely to be eaten by birds, the parasite's final host. Prevalence of E. californiensis reaches nearly 100% in most F. parvipinnis populations, with parasite biomass constituting almost 2% of F. parvipinnis biomass in some locations. Despite having thousands of cysts on their brains, infected fish grow and mature at rates comparable to those of uninfected populations. The lack of general pathology combined with the specificity of the altered behaviours suggests that the behavioural changes are due to parasite manipulation. The monoamine neurotransmitters serotonin and dopamine, which control locomotion and social behaviour in fishes and other vertebrates, were examined to explore the underlying mechanisms of this behaviour modification. Whereas previous studies were similarly conducted with experimentally infected fish, in this study, brain dopaminergic and serotonergic activity were analysed in naturally infected fish to assess how E. californiensis may alter F. parvipinnis monoamines in a naturally occurring system. A parasite density‐associated decrease in serotonergic activity occurred in the hippocampus of naturally infected fish, as well as a decrease in dopaminergic activity in the raphe nuclei, suggesting that E. californiensis inhibits serotonin and dopamine signaling in naturally infected F. parvipinnis. The neurochemical profile of infected fish is consistent with the hypothesis that E. californiensis affects brain monoaminergic systems in order to induce impulse‐driven, active, and aggressive behaviour in its hosts.     

The attraction trick: males in early stages of disease become more chemically attractive to Nile tilapia (Oreochromis niloticus) females

In aquatic systems, olfaction plays an important role in acquiring information about the social environment and influences important behaviours in various contexts, including predator avoidance, foraging, aggressive and reproductive behaviour and mate selection. As the presence of diseases might modify individual odour, fish may use the variability in conspecifics’ odours as an indicator of the health status and infectious load of potential mates. Here, female Nile tilapia were tested for their ability to detect infected males and discriminate between bacterial infected and uninfected individuals by means of chemical cues. Females were allowed to choose between the odours of males infected by Aeromonas hydrophila bacteria and uninfected males. The findings show that female Nile tilapia initially showed a preference for infected males in terms of their first choice in a dichotomous choice test, but the total duration of time spent with the stimulus from infected males was not longer than that for the uninfected males. This may indicate that males at early stages of infection, i.e., without advanced clinical signs of infection, emit odours that allow them to enjoy the benefits of socialization when the infection is not yet detected by conspecifics. Thus, in the context of reproduction, males might attract female partners and have some chance of reproducing, before being avoided.     

Toxoplasma infection and response to novelty in mice

Three groups of mice were infected with Toxoplasma and used for behavioral testing using a Y-maze. One group was infected when adult and two groups congenitally, one of these born to dams infected during gestation, the other to dams chronically infected prior to mating. In an initial habituation period each mouse was exposed to a black arm and stem of the maze, entrance to a white arm being blocked by a transparent door. In a subsequent free-choice trial both arms were black and the mouse was free to explore all parts of the maze. During both periods infected mice were more active than controls. Infected mice engaged in less grooming behavior indicative of less approach-avoidance conflict than controls prior to entry into a choice arm at the beginning of the free-choice trial. Infected mice spent more time in the familiar than in the novel (previously blocked) arm during the free-choice trial; conversely, uninfected mice spent more time in the novel than in the familiar arm. It is suggested that the reported behavioural changes would lead to dissemination of the infection in the environment by ultimately making infected mouse intermediate hosts more susceptible to predation by domestic cats, the definitive hosts of Toxoplasma.     

The parasite's long arm: a tapeworm parasite induces behavioural changes in uninfected group members of its social host

Parasites can induce alterations in host phenotypes in order to enhance their own survival and transmission. Parasites of social insects might not only benefit from altering their individual hosts, but also from inducing changes in uninfected group members. Temnothorax nylanderi ant workers infected with the tapeworm Anomotaenia brevis are known to be chemically distinct from nest-mates and do not contribute to colony fitness, but are tolerated in their colonies and well cared for. Here, we investigated how tapeworm- infected workers affect colony aggression by manipulating their presence in ant colonies and analysing whether their absence or presence resulted in behavioural alterations in their nest-mates. We report a parasite-induced shift in colony aggression, shown by lower aggression of uninfected nest-mates from parasitized colonies towards conspecifics, potentially explaining the tolerance towards infected ants. We also demonstrate that tapeworm-infected workers showed a reduced flight response and higher survival, while their presence caused a decrease in survival of uninfected nest-mates. This anomalous behaviour of infected ants, coupled with their increased survival, could facilitate the parasites'' transmission to its definitive hosts, woodpeckers. We conclude that parasites exploiting individuals that are part of a society not only induce phenotypic changes within their individual hosts, but in uninfected group members as well.     

Infection of male rats with Toxoplasma gondii results in enhanced delay aversion and neural changes in the nucleus accumbens core

Rats infected with the protozoan parasite Toxoplasma gondii exhibit reduced avoidance of predator odours. This behavioural change is likely to increase transmission of the parasite from rats to cats. Here, we show that infection with T. gondii increases the propensity of the infected rats to make more impulsive choices, manifested as delay aversion in an intertemporal choice task. Concomitantly, T. gondii infection causes reduction in dopamine content and neuronal spine density of the nucleus accumbens core, but not of the nucleus accumbens shell. These results are consistent with a role of the nucleus accumbens dopaminergic system in mediation of choice impulsivity and goal-directed behaviours. Our observations suggest that T. gondii infection in rats causes a syndromic shift in related behavioural constructs of innate aversion and making foraging decisions.     

Hartmanella culbertsoni: biochemical changes in the brain of the meningoencephalitic mouse.

Meningoencephalitis was produced in albino mice by intranasal inoculation of Hartmanella culbertsoni. In the infected brain phosphatidyl choline (PC), phosphatidyl ethanolamine + phosphatidyl serine (PE + PS), sphingomyelin and cholesterol registered decrease, lysophospholipids and free fatty acids accumulated, and part of the cholesterol was esterified. Phospholipase A (EC 3.1.1.4) and sphingomyelinase (EC 3.1.4.12) were elaborated in the postmitochondrial supernatant fraction. The levels of lipid peroxides, in brain as well as the capacity of brain homogenates to form lipid peroxides in vitro, was higher in the infected animals as compared to the uninfected. The activities of succinate dehydrogenase (EC 1.3.99.1) and cytochrome c oxidase (EC 1.9.3.1) in the mitochondrial fraction of the infected brain decreased while adenosine triphosphatase (EC 3.6.1.3) was stimulated. Addition of cytosol fraction (105,000g supernatant) of infected brain to the mitochondrial fraction of uninfected brain caused inhibition of succinate dehydrogenase and cytochrome c oxidase and stimulation of adenosine triphosphatase. This shows that some toxic substance(s) which inhibits mitochondrial function in brain is produced in the cytosol during infection. This inhibitor was nondialyzable and heat stable.     

Behavioural differences between two captive populations of red jungle fowl (Gallus gallus) with different genetic background,raised under identical conditions

Ex situ conservation of threatened species may lead to behavioural adaptation, which can affect success of reintroduction attempts. In previous studies, we investigated the effects of captivity on the behaviour of red jungle fowl (Gallus gallus) and found that captive populations differed behaviourally as well as genetically. The aim of the present study was to compare the behaviour of two of the previously studied populations, raised under identical conditions. Eggs were collected from birds at Copenhagen zoo (Cop) and Götala research station (Got) and were incubated and hatched together. Twenty-eight birds (16 Got and 12 Cop) were reared together and tested in eight different behavioural tests, measuring different aspects of fear-related behaviours as well as exploratory and social behaviours. The study revealed several differences in fear-related behaviours between the populations but none in exploratory or social behaviours. In general, one of the populations (Cop) showed more intense fear behaviours than the other (Got), which instead were less fearful in their behaviours. This indicates that breeding animals in captivity may lead to behavioural modifications, which can affect the outcome of reintroductions. The results further suggest that fear-related behaviours are dependent on the genetic background of the animals while social behaviours may be more influenced by the social environment. Since fear-related behaviours, such as predator avoidance and fear of humans, are essential for a life in the wild, these aspects are crucial for the breeding of animals in captivity for conservation purposes.     

Hymenolepis microstoma: Effect of the mouse bile duct tapeworm on the metabolic rate of CF-1 mice

The metabolic rate of uninfected Mus musculus (CF-1 strain) at 30 C was 1.668 ± 0.032 ccO₂/g/hr (mean ± SE, n = 35). At 2 days postinfection (PI)the metabolic rate of infected mice was 2.64 ± 0.15 ccO₂/g/hr (n = 6), or 58% higher than that of uninfected control mice. Between 2 and 8 days PI there was a steady decrease in the metabolic rate of infected mice, and by Day 15 PI the metabolic rates of infected and uninfected mice were the same. Since gross histopathological changes (e.g., fibrosis of the bile duct and liver) in infected mice are not evident until Day 4 or 5 PI, the increased metabolic rate during the early stage of infection may be a direct response of the mouse to excretory (secretory) products of the developing parasite.     

Cyst formation, increased anti-inflammatory cytokines and expression of chemokines support for Clonorchis sinensis infection in FVB mice

To verify the hypothesis that different pathology of Clonorchis sinensis infection by mouse strains is determined by different responses of cytokines and chemokines, we compared those responses of FVB with those of BALB/c mice. All of FVB mice infected with 30 metacercariae of C. sinensis showed cystic dilatation in the liver, whereas infected BALB/c mice did not. Mature worms were recovered from 19 of 20 liver sections of FVB mice while only one of 20 sections of BALB/c mice revealed a mature worm. In both strains the proportion of CD4⁺ T cells was lower in C. sinensis-infected than in the uninfected group. However, the proportion of CD8⁺ T cells was elevated in C. sinensis-infected from both strains compared to uninfected mice. The Th2-associated anti-inflammatory cytokines such as IL-4, IL-5 and IL-13, IL-10 and TGF-β, were significantly more produced by the lymphocytes of FVB than by those of BALB/c mice. Especially, the 2 anti-inflammatory cytokines, IL-10 and TGF-β, were presumably related with susceptibility and the development of worms in the liver. C. sinensis infected FVB mice also produced more chemokines such as RANTES and MIP-1α in the liver lymphocytes than BALB/c mice. In conclusion, the FVB mice provide the favorable niche for C. sinensis by cyst formation in the bile duct, increased production of Th2-associated anti-inflammatory cytokines and upregulation of chemokines.     

Developmental and reproductive patterns of Triatoma brasiliensis infected with Trypanosoma cruzi under laboratory conditions

The aim of this work was to study the interaction between Trypanosoma cruzi-1 and Triatoma brasiliensis. A group of 1st instar nymphs was initially fed on T. cruzi-infected mice and a control group was fed on uninfected mice. From the second feeding onwards, both groups were otherwise fed on non-infected mice. The resulting adults were grouped in pairs: infected male/uninfected female, uninfected male/infected female, infected male and female and uninfected male/uninfected female. The infection affected only the 1st instar nymphs, which took significantly more time to reach the 2nd instar than uninfected nymphs. The differences in the molting time between the infected and uninfected nymphs from the 2nd to the 5th instars were not statistically significant. Both groups presented similar rates of nymphal mortality and reproductive performance was not significantly affected by infection in any of the treatments.     

Increased susceptibility to predation and altered anti-predator behaviour in an acanthocephalan-infected amphipod

According to the 'parasitic manipulation hypothesis', phenotypic changes induced by parasites in their intermediate hosts are effective means of increasing trophic transmission to final hosts. One obvious prediction, although seldom tested, is that increased vulnerability of infected prey to an appropriate predator should be achieved by the parasite altering the anti-predator behaviour of its intermediate host. In this study, we tested this prediction using the fish acanthocephalan Pomphorhynchus tereticollis and the freshwater amphipod Gammarus pulex. Firstly, we estimated the relative vulnerability of infected and uninfected gammarids to predation by the bullhead Cottus gobio in the field. Second, we investigated under experimental conditions how two common anti-predator behaviours of aquatic invertebrates, refuge use and short-distance reaction to predator chemical cues, were affected by infection status. We found that the prevalence of infection in the field was 10 times higher among gammarids collected from the stomach contents of bullheads compared with free-ranging individuals collected in the same river. In a microcosm uninfected gammarids, but not infected ones, increased the use of refuge in the presence of a bullhead. Finally, a behavioural experiment using an Y-maze olfactometer showed opposite reactions to predator odour. Whereas uninfected gammarids were significantly repulsed by the chemical cues originating from bullheads, infected ones were significantly attracted to the odour of the predator. Taken together, our results suggest that the alteration of anti-predator behaviour in infected G. pulex might enhance predation by bullheads in the field. Reversing anti-predator behaviour might thus be an efficient device by which parasites with complex life-cycles increase their trophic transmission to final hosts. Further studies should pay more attention to both the increased vulnerability of infected prey to an appropriate predator in the field and the influence of parasitic infection on the anti-predator behaviour of intermediate hosts.     

Social interactions modulate the virulence of avian malaria infection

There is an increasing understanding of the context-dependent nature of parasite virulence. Variation in parasite virulence can occur when infected individuals compete with conspecifics that vary in infection status; virulence may be higher when competing with uninfected competitors. In vertebrates with social hierarchies, we propose that these competition-mediated costs of infection may also vary with social status. Dominant individuals have greater competitive ability than competing subordinates, and consequently may pay a lower prevalence-mediated cost of infection. In this study we investigated whether costs of malarial infection were affected by the occurrence of the parasite in competitors and social status in domestic canaries (Serinus canaria). We predicted that infected subordinates competing with non-infected dominants would pay higher costs than infected subordinates competing with infected dominants. We also predicted that these occurrence-mediated costs of infection would be ameliorated in infected dominant birds. We found that social status and the occurrence of parasites in competitors significantly interacted to change haematocrit in infected birds. Namely, subordinate and dominant infected birds differed in haematocrit depending on the infection status of their competitors. However, in contrast to our prediction, dominants fared better with infected subordinates, whereas subordinates fared better with uninfected dominants. Moreover, we found additional effects of parasite occurrence on mortality in canaries. Ultimately, we provide evidence for costs of parasitism mediated by social rank and the occurrence of parasites in competitors in a vertebrate species. This has important implications for our understanding of the evolutionary processes that shape parasite virulence and group living.     

Eimeria pragensis infection alters the gut microenvironment to favor extrinsic shiga toxin-producing Escherichia coli O157:H7 colonization in mice

We examined the effects of Eimeria pragensis infection on intestinal peristalsis, goblet cell proliferation and intestinal flora in C57BL/6 mice. Intestinal peristalsis was evaluated by radiography using barium at 7 days post-infection (p.i.). The intestinal peristalsis of E. pragensis-infected mice was significantly suppressed compared with uninfected control mice. Twenty-three mice were divided into 5 groups of 4 or 5 mice each; 2 groups of mice were infected with E. pragensis and the others were kept uninfected. At 7 days p.i., E. pragensis-infected and -uninfected mice were sacrificed to examine goblet cell numbers in the intestines, and significant decreases were observed only in the infected mice. Shiga toxin-producing Escherichia coli (STEC) O157:H7 was inoculated orally in mice both infected and uninfected with E. pragensis at 7 days p.i., with the remaining mice used as uninoculated controls. When mice were sacrificed at 2 days after STEC inoculation, STEC was only detected in the intestines of E. pragensis-infected mice. Colonization of STEC was also confirmed by immunohistochemistry on the surface of epithelial cells in concurrently infected/inoculated mice. Also, an overgrowth of residential E. coli was observed only in E. pragensis-infected mice. These results suggest that E. pragensis induces the suppression of intestinal peristalsis and modifies the intestinal environment to facilitate artificially introduced STEC colonization and multiplication, in addition to residential E. coli overgrowth.