Search

The host’s hormonal environment determines the susceptibility, the course, and severity of several parasite infections. In most cases the infection disturbs the host environment, and activates immune responses that end up affecting the endocrine system. In the other hand, a number of reports indicate that parasites have reproductive systems, and some others have shown that these organisms synthetize sex steroid hormones. We have shown that cysticerci, the larval stage of Taenia solium and Taenia crassiceps ORF and WFU, synthesize steroid hormones. This capacity was modified by drugs that act inhibiting the steroid synthesizing enzymes, or blocking the parasite’s hormone receptors. We have also shown that the cysticerci of T. crassiceps WFU and T. solium have the capacity to synthesize corticosteroids as deoxicorticosterone and corticosterone. We also reviewed the effects of insulin on these parasites, and the receptors found for this hormone. A deep knowledge of the parasite’s endocrine properties will contribute to understand their reproduction and the reciprocal interactions with the host. Likewise, may also help designing tools to combat the infection in clinical situations.

One of the most common tools in conservation physiology is the assessment of environmental stress via glucocorticoid measurement. However, little is known of its relationship with other stress related biomarkers, and how the incidence of an immune challenge during a long-term stress could affect individuals overall stress response. We investigated here the relationship between basal and post-acute stress fecal cortisol metabolite (FC) with different antioxidant enzymes, oxidative damage, and immune parameters in the fish-eating Myotis (Myotis vivesi). We found that in both basal and post-stress conditions, FC was highly related to a number of antioxidant enzymes and immune parameters, but no to oxidative damage. We also assessed changes of FC through the seasons. Basal FC samples and stress reactivity after a short-duration stress, displayed similar levels during summer, autumn and early winter, albeit lower concentrations in late winter. Stress reactivity after long-duration stress was greater in summer and early winter. Finally, we tested the effect of a simultaneous exposition to a long-strong-stress stimulus with an immune response stimulation by administrating adrenocorticotropic hormone (ACTH) and phytohemaglutanin (PHA) after 42 h. Results showed that when both stimulus were administrated, FC concentrations, inflammation and some antioxidant activity were lowered in comparison to the control and individual administration of the challenges. Our findings support the idea that animals maintain constant basal GC levels when living in challenging environments, but response to acute stress differs seasonally and immune defense mechanisms and stress response might be compromised when confronted with multiple challenges.

Risk taking decisions related to the unpredictability of resource availability (risk-sensitive foraging theory) have typically been explained by behavioral ecology and psychology approaches. However, little attention has been given to the physiological condition of animals as a factor that can infl uence the direction of foraging preferences. We evaluated the role of steroid hormones testosterone (T) and corticosterone (CORT) on the foraging preferences expressed by white-eared hummingbirds Hylocharis leucotis in a risk-sensitivity experiment. We recorded choices made by male individuals to fl oral arrays with constant and variable rewards (sugar concentration), and associated these with steroid hormone levels quantifi ed at the start of the experiments. We found that males with higher T levels behave as risk-prone foragers as they perform more visits to fl ower arrays with variable rewards. Interestingly, CORT levels were similar regardless whether individuals visited both types of array. According to our results, T seems to infl uence the foraging preferences of male hummingbirds. Individuals with higher levels of this hormone, made more rapid, frequent visits to fl owers with variable rewards, and behave consistently as risk-prone foragers, compared to males with low T levels. Th ese are exciting avenues for future work, particularly considering recent evidence that individuals may exhibit behavioral diff erences, denoting an apparent personality, which may be associated with phisiological condition infl uencing how they respond behaviorally to environmental variation.

The rapid loss, fragmentation and degradation of tropical forests threaten the survival of many animal species. However, the way in which these phenomena affect animal health has been poorly explored, thus limiting the design of appropriate conservation strategies. To address this, here we identified using linear mixed models the effect of proximal (diet, activity pattern, hunting and logging) and distal (sum of the basal areas of fruiting-tree species [SBAFS], landscape forest cover and degree of forest fragmentation) variables over fecal glucocorticoid metabolite (fGCM) levels–hormones associated with animal health and fitness–of six groups of spider monkeys (Ateles geoffroyi) inhabiting six landscapes with different spatial structures in Mexico. Proximal variables showed a stronger predictive power over fGCMs than distal. In this sense, increases in travel time, the occurrence of hunting, and reductions in rest time and fruit consumption resulted in higher fGCM levels. Regarding distal variables, increases in SBAFS were negatively related to fGCM levels, thus suggesting that food scarcity increases stress hormone levels. Nevertheless, contrary to theoretical expectations, spider monkeys living in smaller tracts of forest spent less time travelling, but the same time feeding on fruit as those in more forested areas. The lower net energy return associated with this combination of factors would explain why, contrary to theoretical expectations, increased forest cover was associated with increased levels of fGCMs in these groups. Our study shows that, at least in the short term, spider monkeys in fragmented landscapes do not always present higher levels of stress hormones compared to those inhabiting continuous forest, and the importance of preserving fruit sources and controlling hunting for reducing the levels of stress hormones in free ranging spider monkeys.

In many cases parasites display highly complex life cycles that include the penetration and permanence of the larva or adults within host organs, but even in those that only have one host, reciprocal, intricate interactions occur. Evidence indicates that steroid hormones have an influence on the development and course of parasitic infections. The host gender's susceptibility to infection, and the related differences in the immune response are good examples of the host-parasite interplay. However, the capacity of these organisms to synthesize their own steroidogenic hormones still has more questions than answers. It is now well-known that many parasites synthesize ecdysteroids, but limited information is available on sex steroid and corticosteroid synthesis. This review intends to summarize some of the existing information in the field. In most, but not all parasitosis the host's hormonal environment determines the susceptibility, the course, and severity of parasite infections. In most cases the infection disturbs the host environment, and activates immune responses that end up affecting the endocrine system. Furthermore, sex steroids and corticosteroids may also directly modify the parasite reproduction and molting. Available information indicates that parasites synthesize some steroid hormones, such as ecdysteroids and sex steroids, and the presence and activity of related enzymes have been demonstrated. More recently, the synthesis of corticosteroid-like compounds has been shown in Taenia solium cysticerci and tapeworms, and in Taenia crassiceps WFU cysticerci. In-depth knowledge of the parasite's endocrine properties will contribute to understand their reproduction and reciprocal interactions with the host, and may also help designing tools to combat the infection in some clinical situations.

Fast-growing mycobacteria such as Mycobacterium sp. and Mycobacterium smegmatis degrade natural sterols. They are a model to study tuberculosis. Interestingly, M. smegmatis has been found in river effluents derived from paper production, and therefore, it would be important to gain further insight into its capacity to synthesize steroids that are potential endocrine disruptors affecting the development and reproduction of fishes. To our knowledge, the capacity of M. smegmatis to synthesize estrogens and even testosterone has not been previously reported. Therefore, the objective of this study was to investigate the capacity of M. smegmatis to synthesize in vitro testosterone and estrogens from tritiated precursors and to investigate the metabolic pathways involved. Results obtained by thin-layer chromatography showed that3H-progesterone was transformed to 17OH-progesterone, androstenedione, testosterone, estrone, and estradiol after 6, 12, or 24 h of incubation.3H-androstenedione was transformed into testosterone and estrogens, mainly estrone, and3H-testosterone was transformed to estrone and androstenedione. Incubation with3H-dehydroepiandrosterone rendered androstenediol, testosterone, and estrogens. This ability to transform less potent sex steroids like androstenedione and estrone into other more active steroids like testosterone and estradiol or vice versa suggests that M. smegmatis can influence the amount of self-synthesized strong androgens and estrogens and can transform those found in the environment.