Agranulocytosis leads to intestinal Echinococcus multilocularis oncosphere invasion and hepatic metacestode development in naturally resistant Wistar rats.

Susceptibility to Echinococcus multilocularis infection considerably varies among intermediate (mostly rodents) and dead-end host species (e.g. humans and pig), in particular regarding intestinal oncosphere invasion and subsequent hepatic metacestode development. Wistar rats are highly resistant to infection and subsequent diseases upon oral inoculation with E. multilocularis eggs, however, after immunosuppressive treatment with dexamethasone, rats become susceptible. To address the role of the cellular innate immunity, Wistar rats were individually or combined depleted of natural killer (NK) cells, macrophages (MΦ) and granulocytes (polymorphonuclear cells, PMN) prior to E. multilocularis egg inoculation. Although NK cell and MΦ depletion did not alter the resistance status of rats, the majority of PMN-depleted animals developed liver metacestodes within 10 weeks, indicating that PMN are key players in preventing oncosphere migration and/or development in Wistar rats. In vitro studies indicated that resistance is not caused by neutrophil reactive oxygen species or NETosis. Also, light microscopical examinations of the small intestine showed that oral inoculation of E. multilocularis eggs does not elicit a mucosal neutrophil response, suggesting that the interaction of oncospheres and neutrophils may occur after the former have entered the peripheral blood. We suggest to consider granulocytes as mediators of resistance in more resistant species, such as humans.

Cellular and molecular changes and immune response in the intestinal mucosa during Trichinella spiralis early infection in rats.

BACKGROUND: The main targets of the host's immune system in Trichinella spiralis infection are the adult worms (AW), at the gut level, and the migrant or newborn larvae (NBL), at systemic and pulmonary levels. Most of the studies carried out in the gut mucosa have been performed on the Payer's patches and/or the mesenteric lymph nodes but not on the lamina propria, therefore, knowledge on the gut immune response against T. spiralis remains incomplete. METHODS: This study aimed at characterizing the early mucosal immune response against T. spiralis, particularly, the events taking place between 1 and 13 dpi. For this purpose, Wistar rats were orally infected with muscle larvae of T. spiralis and the humoral and cellular parameters of the gut immunity were analysed, including the evaluation of the ADCC mechanism exerted by lamina propria cells. RESULTS: A marked inflammation and structural alteration of the mucosa was found. The changes involved an increase in goblet cells, eosinophils and mast cells, and B and T lymphocytes, initially displaying a Th1 profile, characterised by the secretion of IFN-γ and IL-12, followed by a polarization towards a Th2 profile, with a marked increase in IgE, IgG1, IL-4, IL-5 and IL-13 levels, which occurred once the infection was established. In addition, the helminthotoxic activity of lamina propria cells demonstrated the role of the intestine as a place of migrant larvae destruction, indicating that not all the NBLs released in the gut will be able to reach the muscles. CONCLUSIONS: The characterization of the immune response triggered in the gut mucosa during T. spiralis infection showed that not only an effector mechanism is directed toward the AW but also towards the NBL as a cytotoxic activity was observed against NBL exerted by lamina propria cells.

Gastrointestinal effects of ivermectin treatment in rats infected with Strongyloides venezuelensis.

We aimed to evaluate the effects of ivermectin treatment on gastrointestinal morphology and function after Strongyloides venezuelensis infection. Male rats composed Control (C), Parasitized (Sv), Ivermectin (IVM) and Parasitized and treated with Ivermectin (Sv/IVM) groups. IVM and Sv/IVM groups were subdivided according to IVM: single dose of 200 µg/kg (IVM1 and Sv/IVM1) or three repeated doses of 200 µg/kg at 24 h intervals (IVM3 and Sv/IVM3). First dose of IVM was administered after peak of infection. Eggs per gram (EPG), mean gastric emptying time (MGET), mean cecum arrival time (MCAT) and mean small intestinal transit time (MSITT) were evaluated. Measurements were performed before drug and at peak of infection, first day post peak of infection and 30 days post infection. Same time intervals were simulated for uninfected animals. Number of recovered worms and intestinal morphometry were also rated. Data were analyzed by ANOVA and correlated by Dunnett and Pearson (p < 0.05). Sv/IVM1 and Sv/IVM3 showed reduction of EPG and worms, although only group SV/IVM3 eradicate them. Hastened gastric emptying and slowed intestinal transit provoked by S. venezuelensis infection can be reverted by a single administration of IVM after peak of infection, even without total parasite elimination. Although three consecutive doses of IVM were more efficient to eradicate the parasite, drug administration impaired gastrointestinal function and morphology. IVM alone affected gastrointestinal parameters in uninfected animals for prolonged periods, especially in high doses. In control, there were strong negative correlations between MSITT and muscle layers. Strongyloides venezuelensis infection abolishes such correlations. Longitudinal muscle was thinner in IVM3 and Sv/IVM3 groups and circular thicker in Sv group. Revisiting the action of traditional drugs broadens knowledge in the parasite-host interface and may result in the development of more accurate therapeutic strategies.

Parasitological and transcriptomic comparison of Strongyloides ratti infections in natural and in suboptimal permissive hosts.

The nematode genus Strongyloides consists of fairly species-specific small intestinal parasites of various vertebrates, among them the human pathogen S. stercoralis. Between the parthenogenetic parasitic generations these worms can also form single facultative sexual free-living generations. In addition to their primary hosts, several species can also live more or less well in other permissive hosts, which are sometimes not very closely related with the normal host. For example, S. stercoralis can also infect dogs and non-human primates. Here we compare the infection and reproductive success over time and the gene expression profiles as determined by quantitative sequencing of S. ratti parasitizing in its natural host rat and in the permissive host gerbil. We show that in gerbils fewer infective larvae successfully establish in the host, but those that do accomplish this survive and reproduce for longer and produced a higher proportion of males during the first two month of infection. Globally, the gene expression profiles in the two hosts are very similar. Among the relatively few differentially expressed genes, astacin-like and acetylcholinesterase genes are prominently represented. In the future it will be interesting to see if these changes in the suboptimal host are indeed ecologically sensible responses to the different host.

Is the Oriental House Rat (Rattus tanezumi) a Potential Reservoir for Trypanosoma evansi in Thailand?

Trypanosoma evansi is a protozoan blood parasite and etiologic agent of "surra," a disease affecting a wide range of domestic and wild mammals, some identified as potential reservoirs. Although T. evansi has been detected in several small wild rodent species, their role in the epidemiology of surra is unclear. There is molecular evidence of T. evansi in wild rodents in Asia, but it is not known whether they can carry the parasite for sufficient time to significantly contribute to the epidemiology of surra. We assessed the susceptibility of the Oriental house rat (OHR; Rattus tanezumi) to T. evansi infection. Five adult male OHRs trapped in Bangkhen district, Bangkok, Thailand, and five laboratory Wistar rats (Rattus norvegicus) as positive controls, were experimentally infected with a local strain of T. evansi. The five controls and three of the five OHRs were highly susceptible and rapidly exhibited the high levels of parasitemia usually observed in Wistar rats. They died or were euthanized just prior to expected death. Two OHRs presented fluctuating levels of parasitemia, without obvious clinical signs, throughout 40 d of monitoring. These results highlight the moderate susceptibility of some OHRs and their ability to carry the infection over time. Along with the molecular evidence of T. evansi in captured OHRs (demonstrated elsewhere), our results bring new information on the potential role of OHRs in the complex epidemiology of surra.

Experimental comparison of pathogenic potential of two sibling species Anisakis simplex s.s. and Anisakis pegreffii in Wistar rat.

OBJECTIVES: There are little data available on the pathology caused by the sibling species Anisakis simplex s.s. and Anisakis pegreffii. The differences shown in their ability to penetrate the muscle of fish may also be manifested in humans. The purpose of this study is to confirm possible differences in pathogenicity between A. simplex s.s. and A. pegreffii using an experimental model which simulates infection in humans. METHODS: Female Wistar rats were infected with 190 Anisakis type I L3 larvae from the Iberian coastline. After the animal was sacrificed, these L3 larvae were then recovered and identified via PCR-RFLP of the ITS1-5.8S-ITS2. A logistic regression analysis was performed searching for association between experimental pathogenic potential and species. RESULTS: The distribution of A. simplex s.s. and A. pegreffii between Atlantic and Mediterranean waters of the Iberian Peninsula showed statistically significant differences (P < 0.001) which were not observed in the hybrid genotypes (P > 0.3). 21.6% showed pathogenic potential, interpreted as the capacity of the larvae to cause lesions, stick to the gastrointestinal wall or penetrate it. The species variable showed association with the pathogenic role of the larva (P = 0.008). Taking A. simplex s.s. as our reference, the OR for A. pegreffii is 0.351 (P = 0.028). CONCLUSIONS: Despite this difference, A. pegreffii is also capable of causing anisakiasis, being responsible for 14.3% of the penetrations of the gastric mucosa found in rats, which justifies both species being considered aetiologic agents of this parasitic disorder.

Phylogenetic, morphological and behavioural analyses support host switching of Trypanosoma (Herpetosoma) lewisi from domestic rats to primates.

We characterized four Brazilian trypanosomes isolated from domestic rats and three from captive non-human primates that were morphologically similar to T. lewisi, a considered non-pathogenic species restricted to rodents and transmitted by fleas, despite its potential pathogenicity for infants. These isolates were identified as T. lewisi by barcoding using V7V8 SSU rDNA sequences. In inferred phylogenetic trees, all isolates clustered tightly with reference T. lewisi and T. lewisi-like trypanosomes from Europe, Asia and Africa and despite their high sequence conservation formed a homogeneous clade separate from other species of the subgenus T. (Herpetosoma). With the aim of clearly resolving the relationships between the Brazilian isolates from domestic rats and primates, we compared sequences from more polymorphic ITS rDNA. Results corroborated that isolates from Brazilian rats and monkeys were indeed of the same species and quite close to T. lewisi isolates of humans and rats from different geographical regions. Morphology of the monkey isolates and their behaviour in culture and in experimentally infected rats were also compatible with T. lewisi. However, infection with T. lewisi is rare among monkeys. We have examined more than 200 free-ranging and 160 captive monkeys and found only three infected individuals among the monkeys held in captivity. The findings of this work suggest that proximity of monkeys and infected rats and their exposure to infected fleas may be responsible for the host switching of T. lewisi from their natural rodent species to primates. This and previous studies reporting T. lewisi in humans suggest that this trypanosome can cause sporadic and opportunistic flea-borne infection in primates.

Inducción de placas ateromatosas en ratas Wistar crónicamente infectadas con Trypanosoma cruzi: alimentadas con dieta rica en grasas / Induction of atheromatous plaques in Wistar rats chronically infected with Trypanosoma cruzi: fed high fat diet

En el presente trabajo se investiga la inducción de placas ateromatosas en ratas albinas machos, cepa Wistar (Rattus norvegicus) crónicamente infectadas con Trypanosoma cruzi y alimentadas ad libitum con una dieta rica en grasas de origen vegetal, durante tres meses. La infección crónica evidenciada por pruebas sero-parasitológicas, reveló presenciade anticuerpos IgG anti- T. cruzi y ausencia de parasitemiaspatentes. La dieta rica en grasas produjo en las ratas infectadas (A) y sanas (C) un aumento significativo en el peso (P<0,05), en comparación con las ratas controles (B) y sanas (D) sometidas a la dieta normal. El estudio histopatológicode secciones de la arteria aorta de las ratas del grupo A (infectadas/dieta grasa), mostró abundantes depósitoslipídicos, procesos inflamatorios (vasculitis) y placas ateromatosas en formación. En las secciones de corazón y músculo esquelético se evidenció miocarditis y miositis con características de cronicidad sin parasitismo tisular. Las pruebas inmunohistoquímicas aplicadas a los cortes de arteria,corazón y músculo esquelético de las ratas infectadas A (infectadas/dieta-grasa) y B (infectadas/dieta-normal), mostraron abundantes depósitos antigénicos, lo que indica persistencia de antígenos parasitarios. En conclusión, las ratasinfectadas con T. cruzi alimentadas con la dieta rica en grasas, tienen una mayor propección a desarrollar placas ateromatosas.Los resultados demostraron que una dieta hiperlipídicaes un factor de riesgo para el desarrollo de enfermedadateromatosa en individuos con enfermedad de Chagas

This work is focused on the induction of atheromatous plaques in male albino rats (Rattus norvegicus), Wistar, chronically infected with Trypanosoma cruzi and fed ad libitum with diet rich in fats of vegetal origin, during three months. The chronic infection detected by serological and parasitological assays, revealed the presence of antibodies IgG anti- T. cruzi and the absence of patents parasitemias. The diet rich in fats produced in the group of infected rats (A) and the group of healthy rats (C) a significant increase in the weight (P<0,05), in comparison with the control group of infected rats (B) and the group of healthy rats (D), fed with a normal diet. The histopathological study of sections of the aorta arteryof the rats of the group (A) (infected/diet fat), showed abundants lipid deposits, inflammatory processes (vasculitis) and atheromatous plaques in development. The sections of the heart and skeletal muscle showed pictures of a myocarditis and myositis with features of chronic tissue without parasitism. The immunohistochemestry assays applied to the cuts of artery, heart and skeletal muscle of the infected rats A (diet/fat) and B (normal/diet), showed abundants antigen deposits. In conclusion, the rats chronically infected with T. cruzi and fed with a diet rich in fats, have a main propensity to develop atheromatous plaques. The results showed that a hyperlipidic diet is a risk factor for the development of atheromatous disease in individuals with Chagas`disease

In vitro effects of resveratrol on Trichinella spiralis.

Resveratrol, a natural phytoalexin found mainly in grapes, possesses antibacterial, antifungal, and antiviral properties. However, there is no information about its effects on helminths such as Trichinella sp. In the present study, we investigated the effects of resveratrol on the viability of Trichinella spiralis life stages in vitro. Adult forms, newborn larvae (NBL), and muscle larvae (ML) were incubated with resveratrol at concentrations varying from 12.5 to 200 microg/ml. Resveratrol showed significant anthelmintic activity against NBL and adult forms of Trichinella, but not against ML. Our results suggest that resveratrol may be useful as a therapeutic agent to treat trichinellosis in early stages and warrant its further assessment in animal models of disease.

Host cell traversal is important for progression of the malaria parasite through the dermis to the liver.

The malaria sporozoite, the parasite stage transmitted by the mosquito, is delivered into the dermis and differentiates in the liver. Motile sporozoites can invade host cells by disrupting their plasma membrane and migrating through them (termed cell traversal), or by forming a parasite-cell junction and settling inside an intracellular vacuole (termed cell infection). Traversal of liver cells, observed for sporozoites in vivo, is thought to activate the sporozoite for infection of a final hepatocyte. Here, using Plasmodium berghei, we show that cell traversal is important in the host dermis for preventing sporozoite destruction by phagocytes and arrest by nonphagocytic cells. We also show that cell infection is a pathway that is masked, rather than activated, by cell traversal. We propose that the cell traversal activity of the sporozoite must be turned on for progression to the liver parenchyma, where it must be switched off for infection of a final hepatocyte.

Infectivity of different genotypes of human Blastocystis hominis isolates in chickens and rats.

Most Blastocystis hominis isolates from humans are believed to be potentially zoonotic. This is because B. hominis isolates found in a variety of other host species have been found to have identical or relatively similar genotypes to those found in human isolates. However, the transmission of human B. hominis isolates to other animals has not been confirmed experimentally. In this study, the infectivity associated with several unique human Blastocystis genotypes (subtypes 2, 3, 4 and 7) was therefore investigated by infecting chickens and rats with two isolates of each subtype experimentally. The results showed that one isolate of subtype 4 and one isolate of subtype 7 was capable of infecting both chickens and rats, while two isolates of subtype 2, another isolate of subtype 4, and another isolate of subtype 7 could only infect chickens. Conversely, two isolates of subtype 3 failed to infect either of the animals. These results confirmed that several genotypes from human isolates could infect chickens and/or rats, indicating that chickens and rats are suitable experimental animal models for studying the zoonotic potential of human Blastocystis isolates.

Effect of trypanosoma lewisi infection on the toxoplasma gondii multiplication in white rat peritoneal macrophages

Peritoneal macrophages (PM) from normal Wistar rats were treated in vitro with peritoneal supernatant or sera, obtained from rats infected with 106 Trypanosoma lewisi trypomastigotes before the infection with Toxoplasma gondii tachyzoites. In this experimental model, Toxoplasma multiplication in PM was increased, as compared to macrophages treated with supernatant or sera from control rats not infected with T. lewisi. This effect was observed only if the active supernatant or sera came from rats infected with the T. lewisi 3 to 6 d before Toxoplasma inoculation. Furthermore, immunosuppressive activity was only detectable after at least 24 h incubation with the supernatant or sera. These results are in accordance with our in vivo previous studies which demonstrated a clear immunosuppressive effect of T. lewisi during T.gondii infection of the remarkably resistant Wistar rats.

Some factors influencing transmission of toxoplasma in pregnant rats fed cysts.

An overall 44% transplacental transmission rate was observed in 221 rats fed cysts of 12 Toxoplasma strains at 15 days of pregnancy, with a range of 0-90% transmission. Considerable variability in the transmission rate was seen among different groups of rats that received similar Toxoplasma inocula; this is attributed to genetically based susceptibility to Toxoplasma among individuals of the outbred Wistar strain of rats. Transplacental transmission was more frequent in Long Evans than in Wistar rats. Significant differences in the rate of transmission were not found between rats that were fed similar Toxoplasma inocula 6-8 days or 15 days after conception. The frequency of transmission was not affected by the strain or dose of Toxoplasma used.

[The biological and anatomical-morphological properties of Hymenolepis diminuta tapeworms of WMS il1 and the WMS "strain"]. / Biologiczne i anatomo-morfologiczne wlasciwosci tasiemców Hymenolepis diminuta WMS il1 i WMS "strain".

Crowded infrapopulations of H. diminuta obtained from the WMS il1 inbred line resembled those of the potentially non-inbred WMS strain in not showing either the abrupt reductions in the numbers of worms or the destrobilation described by other autors. Denser populations of both types of tapeworm have a greather abundance of 4 - testis proglottids of the 1p3a type (having 1 testis on the poral side and three on the aporal), and fewer of type 0p3a. Changes in the positioning of genital ducts and pores show a marked positive correlation with the abundance of type 2pla proglottids. Strobilae of H. diminuta WMS il1 contain a relatively greather number of type 0p3a proglottids and fewer of type 1p3a, than those of the WMS "strain"; something which is probably linked with the respective selection of the maternal tapeworms.

Life cycle of Ixodes (Ixodes) loricatus (Acari: Ixodidae) under laboratory conditions.

The life cycle of Ixodes (Ixodes) loricatus Neumann, reared in the laboratory, is described. Engorged females collected from opossums trapped in the states of Minas Gerais and São Paulo, Brazil, which were used to start the laboratory colonies, were designated as BMG and CSP, respectively. Larval and nymphal ticks from both colonies fed separately on Rattus norvergicus Berkenhout or Calomys callosus Rengger, whereas Didelphis marsupialis L and Didelphis albiventris Lund were used as hosts for BMG and CSP adults, respectively. Biological and developmental data obtained from ticks of both the BMG and CSP colonies that were reared separately for two consecutive generations were compared. The percentage of fed or molted ticks reared on C. callosus was higher than that recorded for ticks fed on R. norvergicus in the majority of the observations. Despite significant differences among several of the biological parameters, the pattern of the life cycles of the two tick colonies was similar. Results indicated that the mean life cycle duration of I. (I.) loricatus was approximately 7 mo from parental oviposition to the occurrence of F1 eggs, regardless of geographic origin or host species.

Shock response induced in rat brain and spleen during primary infection with Trichinella spiralis larvae.

An infection approach was adopted for examining consequential heat shock (HS) or stress response in brain and spleen tissues from Wistar rats. Stress in this system was due to interactions with the infecting helminth, Trichinella spiralis, or its body-dwelling larval stages, or products thereof. It was argued that in the infection model used, elements effecting stress in the brain would differ from those in the spleen. HS responses were measured by quantitation of 4 levels of HS proteins (HSP25, HSP60, HSP70 and HSP90) with time, in infected and uninfected rat tissues using an assay depending on immunoblotting specifically to detect the separate HSPs and image analysis to measure HSP content. In brain and spleen tissue from uninfected rats, a continuous expression of the above HSPs was observed at levels which hardly varied throughout the experiment. In contrast, HSP25, HSP60 and HSP70 levels in infected rat tissues varied and apparently depended on 'infection cycle'-related events. Thus, an enhanced expression of HSP25 and HSP60 and of these plus HSP70 was observed at certain, yet different, time-points during infection in rat spleen and rat brain, respectively. Interestingly, HSP90 expression in spleen tissue from infected rats versus controls, was significantly reduced throughout the experiment suggesting some important (as yet undefined) role for HSP90 in the infection cycle. These studies seem to have provided evidence for the occurrence of soluble factors causing altered HSP expression at both sides of the blood-brain barrier in rats with a primary T. spiralis infection.

Obtención de metacercarias de Fasciola hepatica en Lymnaea cubensis y relación parásito-hospedero en ratas Wistar y ratones Balb/c / Fasciola hepatica metacercarie collection in Lymnaea cubensis, and parasite-host-relation in Winstar rats an Balb/c mice

Fueron realizados dos experimentos, en experimento I con dos métodos (necropsia y bolsa de polietileno) para colectar y comparar las metacercarias obtenidas, el experimento II que fue desarrollado para determinar la potencia invasiva de las metacercarias obtenidas en un biotipo artificial, usando ratas Wistard y ratones Balb/c inoculados con 20 y 5-10 metacercarias, respectivamente. Se encontró que el número de metacercarias obtenidas con el uso de las bolsas de polietileno es considerablemente superior (P< 0.01) a las obtenidas por disección con un total de 1 442 metacercarias y una media de 12.87 por hospederos, mientras que en el método de las bolsas de polietileno la media fue de 29.31 y el total de 3 313. La potencia invasiva (PI) y la extensión de la invasión (EI) en las ratas fue más alta en la tercera semana (PI, 23 por ciento; EI, 80 por ciento), similar a los ratones inoculados con 10 metacercarias (PI, 23 por ciento; EI, 80 por ciento). Hubo 100 por ciento de hígados afectados por ambas dosis en la tercera semana. Se concluye que el método de las bolsas de polietileno es más efectivo que la disección facilitando la obtención de gran número de formas invasivas con alta calidad, limpieza y fácil desprendimiento de las metacercarias desde la superficie de enquistamiento: así como el hecho de que la potencia invasiva y la extensión de la invasión obtenida valida su uso en las investigaciones con modelos de Fasciola hepatica en ratas y ratones con dosis apropiadas de 20 y 10 metacercarias por ratas y ratones, respectivamente

A novel Na+/HCO3--codependent choline transporter in the syncytial epithelium of the cestode Hymenolepis diminuta.

Absorption of exogenous choline by the cestode Hymenolepis diminuta was found to be both Na+- and HCO3--dependent and, at pH 6 to 7, accounted for up to 65% of the total choline uptake. Na+/HCO3- dependent choline uptake was activated at approximately 6 mM HCO3- (EC50 approximately 9 mM), and, above 100 mM Na+, the rate of uptake was directly proportional to the Na+ concentration. Atempts to uncouple Na+-dependent uptake from HCO3--dependent uptake were not successful: K+-depolarization was without effect on HCO3--dependent choline uptake, and use of valinoomycin to hyperpolarize the brush-border membrane resulted in inhibition of uptake. Na-/HCO3--dependent choline uptake was not associated with solvent drag. The Na+/HCO3--dependent choline uptake displayed a Q10 of 6.4 (27 degrees to 37 degrees) and a relatively high activation energy of 126 kJ x mol(-1). At pH 6.0 and 7.0, Na-/HCO3--dependent choline uptake rates were similar, but Na+/HCO3--dependent choline uptake was reduced at pH 5.0. The Na+/HCO3--dependent choline uptake, at pH 7.0, displayed a Kt of approximately 500 microM and a Vmax of 4.01 pmol x mg wet weight(-1) x min(-1). The Na+/HCO3--dependent choline uptake was hemicholinium-3 sensitive, but not significantly inhibited by 200 microM bumetanide, 100 microM amiloride, benzamil, or EIPA or by 1 mM 4,4'-diisothiocyano-2,2'-stilbene disulfonate (DIDS) or 4-acetamido-4'-isothiocvanostilbene-2,2'-disulfonic acid (SITS). Although it remains to be shown that HCO3- uptake is coupled directly to both choline and Na+ uptake, the data suggest that choline up take occurs via choline/Na+/HCO3--co-trans porter.

Description of a Blastocystis species from Rattus norvegicus.

Two isolates (WR1 and WR2) of Blastocystis from laboratory-bred Wistar rats were axenized by a method of colony growth in soft agar combined with antibiotic treatment. The colonies were cultured in Iscove's modified Dulbecco's medium (IMDM) and Bacto agar mixture supplemented with 10% horse serum in the presence of thioglycollate. The cells from the colonies had an ameboid outline with a central body. Large inclusions were seen in the central body of some cells. Some granular forms were also found. In the axenic culture of isolate WR2, about one-third of the organisms were granular forms. Cysts were found in the axenic culture of both isolates. This is the first report of such cyst formation in in vitro culture. The karyotypic patterns of both isolates of the rat Blastocystis were analyzed by pulsed-field gel electrophoresis (PFGE). A total of 13 chromosomal bands were separated, ranging from 1.86 Mb to 295 kb. The karyotypic patterns of the rat Blastocystis were different from those of B. hominis and reptilian Blastocystis. On the basis of the above-mentioned differences, the rat Blastocystis is assigned as B. ratti sp. nov.

Cardiac sympathetic-parasympathetic balance in rats with experimentally-induced acute chagasic myocarditis.

To clarify the mechanism responsible for the transient sinus tachycardia in rats with acute chagasic myocarditis, we have examined the cardiac sympathetic-parasympathetic balance of 29 rats inoculated with 200,000 parasites (Trypanosoma cruzi). Sixteen infected animals and 8 controls were studied between days 18 and 21 after inoculation (acute stage). The remaining 13 infected animals and 9 controls were studied between days 60 and 70 after inoculation (sub-acute stage). Under anesthesia (urethane 1.25 g/kg), all animals received intravenous atenolol (5 mg/kg) and atropine (10 mg/kg). Acute stage: The baseline heart rate of the infected animals was significantly higher than that of the controls (P < 0.0001). The magnitude of the negative chronotropic response to atenolol was 4 times that of the controls (P < 0.00001). This response correlated with the baseline heart rate (r = -0.72, P < 0.001). The heart rate responses to the beta-blocker and to atropine, of the infected animals studied during the sub-acute stage, were not different from controls. These findings suggest that cardiac sympathetic activity is transiently enhanced and cardiac parasympathetic activity is not impaired, in rats with acute chagasic myocarditis. The transient predominance of cardiac sympathetic activity could explain, in part, the sinus tachycardia observed in the acute stage of experimentally-induced chagasic myocarditis.