Influence of male gonadal hormones on the parasitemia and humoral response of male Calomys callosus infected with the Y strain of Trypanosoma cruzi

Prevalence and factors associated with Babesia bigemina infection in Crioula Lageana cattle breed

The objective of this study was to determine the prevalence of Babesia bigemina infection and associated risk factors in Crioula Lageana cattle, a Brazilian native breed known for its tick resistance. Blood samples were collected from 311 registered cattle (62 males, 249 females) from conservation nucleus properties in Santa Catarina State, Brazil. Samples underwent DNA extraction and nested PCR targeting the rap-1a gene for B. bigemina detection. Animals were categorized by sex, age class, and tick presence during sampling. An epidemiological questionnaire assessed potential risk factors. The overall B. bigemina prevalence was 60% (186/311; 95% CI: 56,95%-62,67%). Males showed significantly higher infection rates (79%; 49/62) compared to females (55%; 137/249; OR=3.36, p<0.001). Bulls (81%; 26/32) and calves (78%; 56/72) exhibited higher infection rates than cows (50%; 70/141) and heifers (52%; 34/66; p<0.001). Tick presence during sampling increased infection probability (OR=2.00, p=0.006). Contact with other animal species (OR=1.57, p=0.037) and regular veterinary care (OR=6.77, p=0.009) were identified as significant risk factors. Results indicate enzootic instability in the studied population, with distinct sex-based susceptibility patterns. These findings provide baseline data for developing targeted control strategies for B. bigemina in Crioula Lageana breeding programs.

Prevalence of Trypanosoma cruzi, the Etiologic Agent of Chagas Disease, Infection in Texas Skunks (Mammalia: Mephitidae)

Background: Chagas disease is one of the world's most neglected tropical diseases, infecting over six million people across the Americas. The hemoparasite Trypanosoma cruzi is the etiological agent for the disease, circulating in domestic, peridomestic, and sylvatic transmission cycles that are maintained by triatomine vectors and a diversity of wild and synanthropic hosts. Public health and wildlife management interventions targeting the interruption of T. cruzi transmission rely on an understanding of the dynamics driving the ecology of this zoonotic pathogen. One wildlife host that purportedly plays a role in the transmission of Chagas disease within the southern United States is the striped skunk (Mephitis mephitis), although infection prevalence in this species is poorly understood. Materials and Methods: To this end, we conducted a PCR-based surveillance of T. cruzi in 235 wild skunks, representing 4 species, across 76 counties and 10 ecoregions in Texas, United States, along with an evaluation of risk factors associated with the infection. Results: We recovered an overall T. cruzi prevalence of 17.9% for all mephitid taxa aggregated, ranging between 6.7% for plains spotted skunks (Spilogale putorius interrupta) and 42.9% for western spotted skunks (Spilogale gracilis). We report the first cases of T. cruzi infection in plains spotted and American hog-nosed skunks (Conepatus leuconotus), of important note for conservation medicine since populations of both species are declining within Texas. Although not statistically significant, we also detected trends for juveniles to exhibit greater infection risk than adults and for differential sex biases in T. cruzi prevalence between taxa, which align with variations in species-specific seasonal activity patterns. No geographic or taxonomic risk factors were identified. Conclusion: Our study contributed key data for population viability analyses and epidemiologic models in addition to providing a baseline for future T. cruzi surveillance among skunks and other wildlife species.

Calomys callosus: An Experimental Animal Model Applied to Parasitic Diseases Investigations of Public Health Concern

The appearance and spread of parasitic diseases around the world aroused the interest of the scientific community to discover new animal models for improving the quality and specificity of surveys. Calomys callosus is a rodent native to South America, an easy handling model, with satisfactory longevity and reproducibility. C. callosus is susceptible to toxoplasmosis and can be used as experimental model for the study the pathogenesis, treatment, vertical transmission, and ocular toxoplasmosis. C. callosus can also be used to study cutaneous and visceral leishmaniasis, as the animals present cutaneous lesions, as well as parasites in the organs. C. callosus has epidemiological importance in Chagas disease, and since it is a Trypanosoma cruzi natural host in which rodents show high parasitemia and lethality, they are also effective as a model of congenital transmission. In the study of schistosomiasis, Schistosoma mansoni was proven to be a C. callosus natural host; thus, this rodent is a great model for fibrosis, hepatic granulomatous reaction, and celloma associated with lymphomyeloid tissue (CALT) during S. mansoni infection. In this review, we summarize the leading studies of parasitic diseases that used C. callosus as a rodent experimental model, describing the main uses and characteristics that led them to be considered an effective model.

Role of Hormonal Circuitry Upon T Cell Development in Chagas Disease: Possible Implications on T Cell Dysfunctions

T cell response plays an essential role in the host resistance to infection by the protozoan parasite Trypanosoma cruzi, the causative agent of Chagas disease. This infection is often associated with multiple manifestations of T cell dysfunction, both during the acute and the chronic phases of disease. Additionally, the normal development of T cells is affected. As seen in animal models of Chagas disease, there is a strong thymic atrophy due to massive death of CD4⁺CD8⁺ double-positive cells by apoptosis and an abnormal escape of immature and potentially autoreactive thymocytes from the organ. Furthermore, an increase in the release of corticosterone triggered by T. cruzi-driven systemic inflammation is strongly associated with the alterations seen in the thymus of infected animals. Moreover, changes in the levels of other hormones, including growth hormone, prolactin, and testosterone are also able to contribute to the disruption of thymic homeostasis secondary to T. cruzi infection. In this review, we discuss the role of hormonal circuits involved in the normal T cell development and trafficking, as well as their role on the thymic alterations likely related to the peripheral T cell disturbances largely reported in both chagasic patients and animal models of Chagas disease.

Trypanosoma cruzi infection in genetically selected mouse lines: genetic linkage with quantitative trait locus controlling antibody response

Trypanosoma cruzi infection was studied in mouse lines selected for maximal (AIRmax) or minimal (AIRmin) acute inflammatory reaction and for high (H_III) or low (L_III) antibody (Ab) responses to complex antigens. Resistance was associated with gender (females) and strain—the high responder lines AIRmax and H_III were resistant. The higher resistance of H_III as compared to L_III mice extended to higher infective doses and was correlated with enhanced production of IFN-γ and nitric oxide production by peritoneal and lymph node cells, in H_III males and females. We also analyzed the involvement of previously mapped Ab and T. cruzi response QTL with the survival of Selection III mice to T. cruzi infections in a segregating backcross [F1(H_III×L_III) ×L_III] population. An Ab production QTL marker mapping to mouse chromosome 1 (34.8 cM) significantly cosegregated with survival after acute T. cruzi infections, indicating that this region also harbors genes whose alleles modulate resistance to acute T. cruzi infection.

Experimental infection of Calomys callosus with atypical strains of Toxoplasma gondii shows gender differences in severity of infection

There is a significant genetic diversity of Toxoplasma gondii in Brazil. Two parasite isolates were recently obtained from chickens in Uberlândia, Minas Gerais state, Brazil, namely, TgChBrUD1 and TgChBrUD2. In this study, we investigated Calomys callosus susceptibility to these atypical T. gondii strains. Male and female animals were intraperitoneally infected with tachyzoites and monitored to evaluate body weight change, morbidity, and mortality. Immunohistochemical assay and qPCR were performed to determine the parasitism in liver, spleen, and brain. Our data showed that TgChBrUD2-infected males died earlier than TgChBrUD1-infected males and 100% of mortality was observed after 10 and 12 days of infection, respectively. Also, TgChBrUD1-infected females died earlier than TgChBrUD1-infected males and 100% of mortality was observed after 9 and 12 days of infection, respectively. Both strains were able to induce a decrease in body weight of males, but only the TgChBrUD1 strain induced an increase in body weight of females. TgChBrUD2-infected females had significantly higher parasite load in both liver and spleen in comparison to TgChBrUD1-infected females, but no significant difference was found between genders or strains when males were infected. There was higher parasitism in the liver than the brain from both males and females infected with either strain. In conclusion, C. callosus specimens are susceptible to both T. gondii atypical strains with differences between males and females in severity of infection. These findings open new prospects for understanding different aspects of T. gondii infection, including reinfection and vertical transmission with these atypical strains when utilizing this experimental model.

Effect of sex steroids on Babesia microti infection in mice

Sex-based-differences are known to affect susceptibility to protozoan infections, but their effects on parasitemia and clinical symptoms in Babesia infections remain unclear. We examined the sex-based susceptibility of various mouse strains to Babesia microti Munich strain infection. In all strains, male mice exhibited significantly higher peak parasitemia and more severe anemia than female mice. Testosterone and estradiol-17β treatment caused an increase in parasitemia and aggravation of anemia. Orchidectomized male mice receiving testosterone exhibited smaller splenic macrophage populations three days after infection, smaller B cell populations 10 days after infection, and reduced splenic tumor necrosis factor-α and interferon-γ mRNA expression than mice that did not receive testosterone. Mice receiving estradiol-17β did not exhibit immunosuppressive effects. Thus, a weakened and delayed innate immunity response may lead to acquired immunity failure. The results suggested that testosterone directly affects T or B cells, leading to delayed acquired immunity, dramatically increased parasitemia, and severe anemia.

Zinc and pregnancy: Marked changes on the immune response following zinc therapy for pregnant females challenged with Trypanosoma cruzi

BACKGROUND & AIMS

The occurrence of infectious disease processes during pregnancy has significant effects on maternal health and can lead to adverse pregnancy outcomes. The aim of the present study was to examine the potential role of zinc treatment during Trypanosoma cruzi infection in pregnant animals.

METHODS

Female Wistar rats weighing 180-200 g were used in all experiments. Production of nitric oxide, peritoneal macrophages counts, and concentrations of IFN-γ and TNF-α were measured, and the potential protective effects of zinc on fetal development were assessed at 14-day post-infection.

RESULTS

Nitric oxide concentrations were higher in pregnant zinc-treated animals than in their untreated counterparts, despite similar levels of the macrophages, IFN-γ and TNF-α. Zinc therapy was associated with a significant reduction in parasitemia and cardiac parasite burden. Higher placental and birth weights were observed in animals given prenatal zinc supplementation compared to untreated animals.

CONCLUSIONS

These data confirm the critical importance of adequate zinc intake during the peri-conceptional period and indicate that zinc has an effective role in preventing adverse outcomes of pregnancy and reducing the risk of common infections such as Chagas' disease.

Chagas cardiomyopathy in the context of the chronic disease transition

BACKGROUND

Patients with Chagas disease have migrated to cities, where obesity, hypertension and other cardiac risk factors are common.

METHODOLOGY/PRINCIPAL FINDINGS

The study included adult patients evaluated by the cardiology service in a public hospital in Santa Cruz, Bolivia. Data included risk factors for T. cruzi infection, medical history, physical examination, electrocardiogram, echocardiogram, and contact 9 months after initial data collection to ascertain mortality. Serology and PCR for Trypanosoma cruzi were performed. Of 394 participants, 251 (64%) had confirmed T. cruzi infection by serology. Among seropositive participants, 109 (43%) had positive results by conventional PCR; of these, 89 (82%) also had positive results by real time PCR. There was a high prevalence of hypertension (64%) and overweight (body mass index [BMI] >25; 67%), with no difference by T. cruzi infection status. Nearly 60% of symptomatic congestive heart failure was attributed to Chagas cardiomyopathy; mortality was also higher for seropositive than seronegative patients (p = 0.05). In multivariable models, longer residence in an endemic province, residence in a rural area and poor housing conditions were associated with T. cruzi infection. Male sex, increasing age and poor housing were independent predictors of Chagas cardiomyopathy severity. Males and participants with BMI

CONCLUSIONS

Chagas cardiomyopathy remains an important cause of congestive heart failure in this hospital population, and should be evaluated in the context of the epidemiological transition that has increased risk of obesity, hypertension and chronic cardiovascular disease.

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Key Words Collapse

MESH Headings

• Adolescent
• Adult
• Aged
• Aged, 80 and over
• Antibodies, Protozoan/blood
• Bolivia/epidemiology
• Chagas Cardiomyopathy/complications
• Chagas Cardiomyopathy/epidemiology
• Chagas Cardiomyopathy/mortality
• Chagas Cardiomyopathy/pathology
• Chronic Disease
• DNA, Protozoan/blood
• Enzyme-Linked Immunosorbent Assay
• Female
• Heart Failure/epidemiology
• Heart Failure/etiology
• Humans
• Male
• Middle Aged
• Polymerase Chain Reaction
• Prevalence
• Risk Factors
• Trypanosoma cruzi/genetics
• Trypanosoma cruzi/immunology
• Trypanosoma cruzi/isolation & purification
• Young Adult

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Grants

• 5 P50 AI074285 NIAID NIH HHS
• P50 AI074285 NIAID NIH HHS
• R24 TW007988 FIC NIH HHS
• T35 AI065385 NIAID NIH HHS
• 5 T35 AI065385 NIAID NIH HHS
• D43 TW006581 FIC NIH HHS
• R24TW007988 FIC NIH HHS

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Affiliation(s)

Alicia I. Hidron Division of Infectious Diseases, Department of Medicine, Emory University School of Medicine, Atlanta, Georgia, United States of America
Robert H. Gilman Asociacion Benefica PRISMA, Lima, Peru Facultad de Ciencias y Filosofía, Universidad Peruana Cayetano Heredia, Lima, Peru
Juan Justiniano Hospital Universitario Japones, Santa Cruz de la Sierra, Bolivia
Anna J. Blackstock Division of Parasitic Diseases, Centers for Disease Control and Prevention, Atlanta, Georgia, United States of America Atlanta Research and Education Foundation, Decatur, Georgia, United States of America
Carlos LaFuente Hospital Universitario Japones, Santa Cruz de la Sierra, Bolivia
Walter Selum Hospital Universitario Japones, Santa Cruz de la Sierra, Bolivia
Martiza Calderon Facultad de Ciencias y Filosofía, Universidad Peruana Cayetano Heredia, Lima, Peru
Manuela Verastegui Facultad de Ciencias y Filosofía, Universidad Peruana Cayetano Heredia, Lima, Peru
Lisbeth Ferrufino Hospital Universitario Japones, Santa Cruz de la Sierra, Bolivia
Eduardo Valencia Facultad de Ciencias y Filosofía, Universidad Peruana Cayetano Heredia, Lima, Peru
Jeffrey A. Tornheim Mount Sinai School of Medicine, New York, New York, United States of America
Seth O'Neal Oregon Health Sciences University, Portland, Oregon, United States of America
Robert Comer Wake Forest University Health Sciences, Winston-Salem, North Carolina, United States of America
Gerson Galdos-Cardenas Asociacion Benefica PRISMA, Lima, Peru
Caryn Bern Division of Parasitic Diseases, Centers for Disease Control and Prevention, Atlanta, Georgia, United States of America
for the Chagas Disease Working Group in Peru and Bolivia

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Gonadectomy inhibits development of experimental amoebic liver abscess in hamsters through downregulation of the inflammatory immune response

Incidence of amoebic liver abscess (ALA) in human males is considerably higher than in females, suggesting a role for sex hormones in this parasite infection. We describe here the effect of hamster gonadectomization on the development of ALA. After monitoring the decrease of oestradiol in females and testosterone in males to undetectable levels by ELISA and Radio Immuno Assay (RIA) in serum, hamsters were intraportally infected with Entamoeba histolytica trophozoites and killed 7 days later. ALA was absent in 50% of male and 15% of female gonadectomized (Gdx) hamsters, in comparison with 100% infection in non-Gdx controls. This protection against ALA in Gdx hamsters was concomitant to a comparatively scarce inflammatory infiltrate and necrosis surrounding clusters of trophozoites in the liver tissue, as well as to a lack of response of spleen cells to Con A, evaluated in proliferation assays. As tissue damage in ALA has been associated with a local inflammatory Th1 response, we determined the profile of response in hamsters by immunohistochemistry on liver sections. In contrast to strong Th1 responses in non-Gdx animals, Gdx females and males exhibited Th2 and Th3 profiles of cytokines, respectively, suggesting that protection against ALA following gonadectomization, could be related to downregulation of liver Th1 response during amoebic infection.

Blood parasitaemia in a high latitude flexible breeder, the white-winged crossbill,Loxia leucoptera: contribution of seasonal relapse versus new inoculations

We measured seasonal changes in the prevalence of haematozoa (Leucocytozoon fringillinarum, Haemoproteus fringillae, andTrypanosoma avium) in free-ranging White-winged Crossbills,Loxia leucoptera, over 1·5 year in Fairbanks, Alaska, USA. This prevalence was low during early winter.L. fringillinarumprevalence increased in late winter/early spring, in the absence of vectors, suggesting relapse of latent infection. By contrast, the prevalence ofT. aviumandH. fringillaedid not increase until mid-spring, coincident with the emergence of putative vectors and suggestive of new inoculations. The winter breeding period was not associated with lower body condition or elevated blood heterophil/lymphocyte ratios than the summer post-breeding period. Thus, birds unlikely perceived their breeding effort as particularly stressful. Adult males in May and June had low plasma testosterone and their blood prevalence ofL. fringillinarum, but not other haemoparasites, was higher than in adult females. This difference may have resulted from sex differences in behaviour and/or plumage colouration – bright red in males, dull green/yellow in females. Species in which reproduction and vector abundance are seasonally dissociated may constitute important models for investigating the respective contribution of reproductive hormones, breeding effort, and vector abundance to patent and latent hemoparasitic infections and to new inoculations.

Trypanosoma cruzi: do different sylvatic strains trigger distinct immune responses?

Strains of Trypanosoma cruzi are multiclonal populations that can be classified in groups or genotypes, differing in pathogenicity, virulence, and histotropism. In this experiment the distinct behavior of two strains of T. cruzi, MORC-1 and MORC-2, was documented. Blood parasitemia, spleen proliferation, nitric oxide, histopathology of the spleen and heart were used as tools to evaluate parasite persistence. Groups of male mice were separated and divided in three groups: Control (C), Infected (IM-1) and Infected (IM-2). The peak of parasitemia occurred on 10days post infection for both strains. LPS stimulated animals, infected MORC-2 group displayed significant higher concentrations of NO when compared to infected MORC-1 group (P<0.05). For ConA stimulated lymphoproliferation, infected MORC-1 group displayed higher proliferation index as compared to infected MORC-2 group. An opposite behavior for IL-4 and TNF-alpha was observed according to the strain. For MORC-1 enhanced concentrations of IL-4 were present with concomitant reduced levels of TNF-alpha, while for MORC-2 enhanced concentrations of TNF-alpha and reduced levels of IL-4 were found. The histopathology of heart and spleen showed important differences in which MORC-1 displayed statistically enhanced number of amastigote in the heart and spleen as compared to MORC-2. Concluding, each strain triggered a distinct immune response with enhanced cytokine TH-1 profile for MORC-2 and TH-2 for MORC-1.

Experimental Chagas' disease in orchiectomized Calomys callosus infected with the CM strain of Trypanosoma cruzi

The incidence and progression of disorders associated with an unbalanced immune response has among many factors the gender as a contributory factor. The aims of this work were to evaluate the effects of orchiectomy and the immune response during the experimental Trypanosoma cruzi infection. Young adult, male Calomys callous were i.p. inoculated with 1 x 10(5) blood trypomastigotes of the CM strain of T. cruzi and divided in groups: Control, Sham and Castrated. Castrated group displayed significantly lower values for prostate and seminal vesicle weights indicating a drastic drop of testosterone plasmatic levels. Orchiectomized animals also displayed lesser number of blood parasites, enhanced lytic antibody percentage, splenocyte proliferation and NO concentration when compared to its sham and control counterparts, indicating that steroid gonadal ablation actually influences immune response triggering a more efficient cellular and humoral response which led animals to become more resistant against T. cruzi infection.

Steroidogenic capacity of Trypanosoma cruzi trypomastigotes

American Trypanosomiasis is caused by the hemoflagellate Trypanosoma cruzi (T. cruzi) and affects millions of persons causing variable degrees of digestive and heart disturbances. As far as we concerned, T. cruzi capacity to synthesize steroid hormones has not been investigated. Therefore, the aim of this work was to investigate the capacity of T. cruzi trypomastigotes to transform tritiated steroid precursors into androgens and estrogens. The T. cruzi Tulahuén strain was obtained from mice blood. The trypomastigotes were cultured for 6 and 24h in Dulbbeco's modified Eagle's medium plus FCS and antibiotics. Tritiated dehydroepiandrosterone or androstendione were added to the culture media and parasites were incubated for 6 or 24h. The cultures were centrifuged and ether extracted. The steroids were analyzed by thin layer chromatography (TLC) in two solvent systems. After incubation with 3H-androstenedione, T. cruzi trypomastigotes synthesized 3H-testosterone (T), 3H-17beta-estradiol (E2) and 3H-estrone (E1). Metabolism of 3H-DHEA by the parasites yielded 3H-androstendione and 3H-androstendiol at 6h of incubation. The recrystallization procedure further demonstrated the 3H-androstendiol and 3H-17beta-estradiol syntheses. Results indicate for the first time that T. cruzi trypomastigotes produce androgens and estrogens when incubated in the presence of steroid precursors and suggest the presence of active parasite steroidogenic enzymes.

Could cyclophosphamide exert a protective role avoiding esophagic neuron loss in Calomys callosus infected with Trypanosoma cruzi?

The protective role of cyclophosphamide was studied in this work. Young male Calomys callosus were infected with Trypanosoma cruzi and allowed to age. Cyclophosphamide therapy was administered to animals during acute and late chronic phases of infection. Esophageal neurons were counted, displaying enhanced neuronal loss for the young and treated infected groups. For aged and cyclophosphamide treated animals, a protection was observed through a reduced loss of neurons as compared to the young and infected groups. Enhanced nitric oxide concentrations were observed for young animals as compared to aged counterparts. Splenocyte proliferation was reduced during the acute phase in comparison with those found in the chronic phase. Morphometry of neuronal body displayed a significant reduction concerning the area, perimeter, diameter and volume for aged animals as compared to young groups. These results indicate that the protective effects of cyclophosphamide together with process of neuroplasty of peripheral nervous system could lead to a protection against neuronal loss.

Trypanosoma cruzi: orchiectomy and dehydroepiandrosterone therapy in infected rats

The ability of gonadal hormones to influence and induce diverse immunological functions during the course of a number of parasitic infections has been extensively studied in the latest decades. Dehydroepiandrosterone and its sulfate are the most abundant steroid hormones secreted by the human adrenal cortex and are considered potent immune-activators. The effects of orchiectomy on the course of Trypanosoma cruzi infection in rats, treated and untreated with DHEA were examined, by comparing blood and cardiac parasitism, macrophage numbers, nitric oxide and IFN-gamma levels. Orchiectomy enhanced resistance against infection with elevated numbers of macrophages, enhanced concentrations of NO and IFN-gamma and reduced amastigote burdens in heart when compared to control animals. DHEA replacement exerted a synergistic effect, up-modulating the immune response. Male sex steroids appear to play fundamental role in determining the outcome of disease, through the regulation and modulation of the activity of the immune response.

Alterations triggered by steroid gonadal hormones in triglycerides and the cellular immune response of Calomys callosus infected with the Y strain of Trypanosoma cruzi

Calomys callosus is a wild rodent found naturally infected with different Trypanosoma cruzi strains. In the work described here, groups of male and female C. callosus were subjected to orchiectomy, ovariectomy and sham operation. One month after surgery, animals were inoculated intraperitoneally (i.p.) with 4x10(4) blood trypomastigotes of the "Y" strain of T. cruzi. Parasitemia, triglycerides, nitric oxide (NO) and concanavalin A (ConA)-induced proliferation were evaluated. Parasitemia during the course of infection was significantly higher in infected and sham operated animals as compared to infected orchiectomized animals. The opposite was observed in the ovariectomized and infected group. Orchiectomized and infected animals displayed elevated triglyceride levels, as well as a more vigorous immune response, with higher splenocyte proliferation and elevated concentrations of NO. Ovariectomy resulted in an impaired immune response, as observed by a reduction of splenocyte proliferation and NO concentration. The results suggest a pivotal role for gonadal hormones in the modulation of triglyceride levels and the magnitude of the immune response during the acute phase of T. cruzi infection.

Influence sexual dimorphism on the persistence of blood parasites in infected Calomys callosus

Gender has long been known to be a contributory factor in the incidence and progression of disorders associated with immune system disregulation. The aims of this experiment were to verify the influences of sexual dimorphism on the persistence of blood parasites out of the acute phase of infection. Male and female Calomys callosus were separated and infected with two strains of Trypanosoma cruzi, and let age until 120 days. Xenogiagnostic, culture of organs and blood, histopathology and lytic antibody percentages were evaluated on late chronic phase. Xenodiagnosis, hemoculture and lytic antibody percentages were positive from 45 until 120 days. For both strains in adrenal and heart, amastigote burdens were present until 45 days, scarcely found on 60 days and absent on 120 days. Steroid hormones, although having a protective role, does not enable animals to get completely rid of the infection. Even without showing apparent signs of pathological unbalance, parasites persists, hidden throughout the host's body.

Parasite community interactions: Trypanosoma cruzi and intestinal helminths infecting wild golden lion tamarins Leontopithecus rosalia and golden-headed lion tamarins L. chrysomelas (Callitrichidae, L., 1766)

The parasite prevalence and infection intensity in primate wild populations can be affected by many variables linked to host and/or parasite ecology or either to interparasite competition/mutualism. In this study, we tested how host sex, age, and place of origin, as well parasitic concomitant infections affect the structure of golden lion and golden-headed lion tamarins parasite community, considering Trypanosoma cruzi and intestinal helminths infection in these primates. A total of 206 tamarins from two Atlantic Coastal rain forest areas in Brazil were tested during 4 years for prevalence of T. cruzi infection and helminth prevalence. Three intestinal helminth groups showed high prevalences in both tamarin species: Prosthenorchis sp., Spiruridae, and Trichostrongylidae. An association between presence of T. cruzi infection and higher intestinal helminth prevalence was found in both tamarin species. Two explanations for this association seem to be plausible: (1) lower helminth-linked mortality rates in T. cruzi-infected tamarins and (2) lower elimination rates of helminths in such tamarins. A higher frequency of T. cruzi-positive blood cultures was significantly correlated to female tamarins and to the presence of Trichostrongylidae infection. The possibility of an increase in the transmissibility of T. cruzi and the three analyzed helminths in lion tamarins with concomitant infections is discussed.

Dehydroepiandrosterone affects Trypanosoma cruzi tissue parasite burdens in rats

Dehydroepiandrosterone (DHEA), the predominant steroid hormone produced by adrenal glands has significant effects on the immune system. DHEA enhances immune responses against a wide range of viral, bacterial, and parasitic pathogens. In the present study, we investigated the effects of DHEA treatment during the acute phase of experimental Trypanosoma cruzi infection. Male and female Wistar rats were infected with the Y strain of T. cruzi and treated subcutaneously with 40 mg/kg body weight/day of DHEA. Myocardial parasitism and inflammation were always present in the heart during the acute phase, in male and female infected animals, regardless of DHEA treatment, but the numbers of amastigote nests in cardiomyocytes were significantly lower in DHEA-treated rats. At the end of the acute phase, the nests became rare or virtually absent in all experimental infections. Histological analysis of the adrenal glands showed that treated males displayed an absence of parasites. DHEA treatment also resulted in reduced parasitisim of heart and adrenal glands, as indicated by fewer and smaller amastigote burdens, and less inflammatory infiltrate and tissue disorganization. DHEA treatment also resulted in thymic atrophy as measured both by reduced weight and by a reduction in the number of cultured activated thymocytes. In vitro analysis showed the number of activated macrophages was higher in treated animals. Antibody levels were monitored by complement-mediated lysis. Higher titers were observed in females when compared to males; but DHEA treatment enhanced the percentage of lysis for both sexes. These findings suggest that DHEA can play a role in the control of parasite multiplication.

Melatonin treatment reduces the severity of experimental Trypanosoma cruzi infection

Prior studies show that melatonin enhances the immune response. This study investigated the possible therapeutic effects of melatonin during the course of Trypanosoma cruzi infection. T. cruzi-infected male Wistar rats were orally treated with 5 mg/kg body weight/day of melatonin. Animals treated with melatonin showed a significant reduction in the number of blood trypomastigotes during the acute phase of infection compared with untreated animals (P<0.05). A significant increase in leucocytes numbers during the peak of parasitaemia was also observed (P<0.05). Moreover, both prior and concomitant treatment with melatonin increased interleukin-2 levels, especially 9 days postinfection (P<0.05). Histopathological observations of heart tissue revealed that melatonin administration also resulted in fewer and smaller amastigote burdens, and less inflammatory infiltrate and tissue disorganization, indicating a reduced parasitism of this tissue. These results show that melatonin is effective in controlling parasite replication and suggest that melatonin might serve as an effective therapeutic agent in the treatment of American trypanosomiasis.

The testis in immune privilege

The production, differentiation, and presence of male gametes represent inimitable challenges to the immune system, as they are unique to the body and appear long after the maturation of the immune system and formation of systemic self-tolerance. Known to protect germ cells and foreign tissue grafts from autoimmune attack, the 'immune privilege' of the testis was originally, and somewhat simplistically, attributed to the existence of the blood-testis barrier. Recent research has shown a previously unknown level of complexity with a multitude of factors, both physical and immunological, necessary for the establishment and maintenance of the immunotolerance in the testis. Besides the blood-testis barrier and a diminished capability of the large testicular resident macrophage population to mount an inflammatory response, it is the constitutive expression of anti-inflammatory cytokines in the testis by immune and particularly somatic cells, that represents an essential element for local immunosuppression. The role of androgens in testicular immune regulation has long been underestimated; yet, accumulating evidence now shows that they orchestrate the inhibition of proinflammatory cytokine expression and shift cytokine balance toward a tolerogenic environment. Furthermore, the role of the testicular dendritic cells in suppressing antigen-specific immunity and T-lymphocyte activation is discussed. Finally, the active role mast cells play in the induction and amplification of immune responses, both in infertile humans and in experimental models, highlights the importance of preventing mast cell activation to maintain the immune-privileged status of the testis.

Influence of Trypanosoma cruzi chronic infection in the depletion of esophageal neurons in Calomys callosus

The extent of neuronal loss was studied in this work, in aged female Calomys callosus infected with the MORC-1 strain of Trypanosoma cruzi. Fifteen months after infection, one group of animals was immunosuppressed with cyclophosphamide (CY). Sections of the distal esophagus were collected and stained with cresyl violet. The neuron count was significantly different among groups, with enhanced neuronal loss in the infected group in comparison with the control aged noninfected group. Partial protection against neuronal destruction was observed in animals immunosuppressed with CY. The morphometry of the neuronal body displayed significant alterations concerning area, shape coefficient, and contour index that were statistically increased for the CY-infected group. These results indicate a protective role for CY against neuronal destruction.

Parasite regulation by host hormones: an old mechanism of host exploitation?

Recent experimental evidence suggests that parasites can not only evade immune responses actively but also exploit the hormonal microenvironment within the host to favor their establishment, growth and reproduction. The benefit for parasites of hormonal exploitation is so great that they have evolved structures similar to the steroid and protein hormone receptors expressed in upper vertebrates that can bind to the hormonal metabolites synthesized by the host. This strategy is exemplified by two parasites that respond to adrenal steroids and sexual steroids, respectively: Schistosoma mansoni and Taenia crassiceps. Understanding how the host endocrine system can, under certain circumstances, favor the establishment of a parasite, and characterizing the parasite hormone receptors that are involved might aid the design of hormonal analogs and drugs that affect the parasite exclusively.

Trypanosoma cruzi: the effects of dehydroepiandrosterone (DHEA) treatment during experimental infection

The aim of this study was to evaluate the efficacy of the immunomodulator dehydroepiandrosterone (DHEA) in the treatment of Trypanosoma cruzi infection and the possible biochemistry alterations in male and female Wistar rats. DHEA also known as the steroid of multiple actions has attracted distinct medical areas. Prior studies show that DHEA enhances immune responses against a wide range of viral, bacterial and parasitic pathogens. Furthermore, administration of DHEA seems to protect animals against obesity and diabetes. Male animals subcutaneous treated with 40 mg/kg body weight/day of DHEA displayed a significant reduction in blood parasites during parasitaemia peak, when compared to untreated animals (P<0.001). For female group parasitaemia was also reduced although values are not statistically significant (P>0.05). Sexual dimorphism was also observed, since females displayed lesser parasitaemia levels compared to males group treated (P>0.05) and untreated (P<0.001). Enhanced leucocytes number was observed in control females when compared to control males (P<0.05). DHEA treatment did not triggered any significant alterations in leucocytes levels (P>0.05). DHEA administration induced an enhanced number of macrophages in infected male (P<0.01). DHEA administration causes a decrease in glucose (P<0.001). Cholesterol and tryglicerides levels did not display results statistically significant (P>0.05) during the treatment. These results suggest that DHEA treatment enhances the immune response as evidenced here by reduced levels of parasites. Up-regulation of the immune system by exogenous DHEA may be useful in the treatment of American tripanosomiasis.

Trypanosoma cruzi: Effects of repetitive stress during the development of experimental infection

Activation of the hypothalamus-pituitary-adrenal axis plays a major role in the suppression of the immune system. We have investigated the effects of repetitive stress on Wistar rats infected with the Y strain of Trypanosoma cruzi and a control group that underwent stressor stimuli by exposure to ether vapor for one minute twice a day. Repetitive stress resulted in an elevated number of circulating parasites accompanies by deep tissue disorganization, and cardiac histopathological alterations. The infected and stressed group displayed a decrease in body weight, and an increased parasite burden in heart tissue, and adrenal glands. Histological analysis of the heart also showed a moderate to severe diffused mononuclear inflammatory process. These results suggest that repetitive stress could be considered an important factor during development of experimental Chagas' disease, enhancing pathogenesis through disturbance of the host's immune system.

Hormonal and immunological mechanisms mediating sex differences in parasite infection

The prevalence and intensity of infections caused by protozoa, nematodes, trematodes, cestodes, and arthropods is higher in males than females. The primary thesis of this review is that immunological differences exist between the sexes that may underlie increased parasitism in males compared to females. Several field and laboratory studies link sex differences in immune function with circulating steroid hormones; thus, the roles of sex steroids, including testosterone, oestradiol, and progesterone, as well as glucocorticoids will be discussed. Not only can host hormones affect responses to infection, but parasites can both produce and alter hormone concentrations in their hosts. The extent to which changes in endocrine-immune interactions following infection are mediated by the host or the parasite will be considered. Although males are more susceptible than females to many parasites, there are parasites for which males are more resistant than females and endocrine-immune interactions may underlie this sex reversal. Finally, although immunological differences exist between the sexes, genetic and behavioural differences may explain some variability in response to infection and will be explored as alternative hypotheses for how differences between the sexes contribute to dimorphic responses to parasites.

Host gender in parasitic infections of mammals: an evaluation of the female host supremacy paradigm

A review of current literature on mammalian hosts' sexual dimorphism (SD) in parasitic infections revealed that (1) it is a scarcely and superficially studied biological phenomenon of considerable significance for individual health, behavior, and lifestyles and for the evolution of species; (2) there are many notable exceptions to the rule of a favorable female bias in susceptibility to infection; (3) a complex network of molecular and cellular reactions connecting the host's immuno-neuroendocrine systems with those of the parasite is responsible for the host-parasite relationship rather than just an adaptive immune response and sex hormones; (4) a lack of gender-specific immune profiles in response to different infections; (5) the direct effects of the host hormones on parasite physiology may significantly contribute to SD in parasitism; and (6) the need to enrich the reductionist approach to complex biological issues, like SD, with more penetrating approaches to the study of cause-effect relationships, i.e., network theory. The review concludes by advising against generalization regarding SD and parasitism and by pointing to some of the most promising lines of research.