Experimental infection of canine peritoneal macrophages with visceral and dermotropic Leishmania strains

A study was carried out using macrophages cultured from the peritoneal exudate of dogs infected in vitro with three species of Leishmania: L. (L.) chagasi, L. (Viannia) braziliensis and L. (L.) amazonensis with the aim of investigating the growth kinetics and infectivity of these species in the host cell. Results were expressed as the percentage of macrophages infected measured at 24 hr intervals over six days in RPMI - 1640 culture medium at a temperature of 34-35oC. The findings open the possibility of using canine peritoneal cells as a model for the screenning of leishmanicide drugs and to study the pathogenesis of these species.

Experimental toxoplasmosis in Balb/c mice. Prevention of vertical disease transmission by treatment and reproductive failure in chronic infection

In a study of congenital transmission during acute infection of Toxoplasma gondii, 23 pregnant Balb/c mice were inoculated orally with two cysts each of the P strain. Eight mice were inoculated 6-11 days after becoming pregnant (Group 1). Eight mice inoculated on the 10th-15th day of pregnancy (Group 2) were treated with 100 mg/kg/day of minocycline 48 h after inoculation. Seven mice inoculated on the 10th-15th day of pregnancy were not treated and served as a control (Group 3). Congenital transmission was evaluated through direct examination of the brains of the pups or by bioassay and serologic tests. Congenital transmission was observed in 20 (60.6%) of the 33 pups of Group 1, in one (3.6%) of the 28 pups of Group 2, and in 13 (54.2%) of the 24 pups of Group 3. Forty-nine Balb/c mice were examined in the study of congenital transmission of T. gondii during chronic infection. The females showed reproductive problems during this phase of infection. It was observed accentuated hypertrophy of the endometrium and myometrium. Only two of the females gave birth. Our results demonstrate that Balb/c mice with acute toxoplasmosis can be used as a model for studies of congenital T. gondii infection. Our observations indicate the potential of this model for testing new chemotherapeutic agents against congenital toxoplasmosis.

Canine experimental infection: intradermal inoculation of Leishmania infantum promastigotes

Five mixed breed dogs were inoculated intradermally (ID) with cultured virulent stationary phase promastigotes of Leishmania infantum Nicole, 1908 stocks recently isolated. Parasite transformations in the skin of ID infected dogs were monitored from the moment of inoculation and for 48 h, by skin biopsies. Anti-Leishmania antibody levels were measured by indirect immunofluorescence assay, counterimmunoelectrophoresis and direct agglutination test, and clinical conditions were examined. Thirty minutes after ID inoculation the first amastigotes were visualised and 3 to 4 h after inoculation the promastigotes were phagocyted by neutrophils and by a few macrophages. These cells parasitised by amastigotes progressively disappeared from the skin and 24 h after inoculation parasites were no longer observed. Local granulomes were not observed, however, serological conversion for antibodies anti-Leishmania was achieved in all dogs. Direct agglutination test was the only technique positive in all inoculated dogs. Amastigotes were found in the popliteal lymph node in one dog three months after inoculation. This work demonstrates that, with this inoculum, the promastigotes were transformed into amastigotes and were up taken by neutrophils and macrophages. The surviving parasites may have been disseminated in the canine organism, eliciting a humoral response in all cases.

Aotus infulatus monkey is susceptible to Plasmodium falciparum infection and may constitute an alternative experimental model for malaria

Aotus is one of the WHO-recommended primate models for studies in malaria, and several species can be infected with Plasmodium falciparum or P. vivax. Here we describe the successful infection of the species A. infulatus from eastern Amazon with blood stages of P. falciparum. Both intact and splenectomized animals were susceptible to infection; the intact ones were able to keep parasitemias at lower levels for several days, but developed complications such as severe anemia; splenectomized monkeys developed higher parasitemias but no major complications. We conclude that A. infulatus is susceptible to P. falciparum infection and may represent an alternative model for studies in malaria.

Experimental Infection of Aedes albopictus (Diptera: Culicidae) Larvae with the Xiphidiocercariae of a Hematolechid

Aedes albopictus larvae were exposed, either individually or in groups, to different concentrations of xiphidiocercariae of Haematoloechus sp. for parasitological studies. It was observed the acute lethal effect and some aspects of the host-parasite relationship, such as delay or progress in the host life cycle, the number and location of the metacercariae in the host, adult host malformations and the amount of metacercariae required to cause death. A delay in the cycle and a high mortality rate was in general observed. Inside the larvae, the metacercariae were found predominantly in the thorax, abdominal segments and in the head, along with a reduced number in the anal lobe and cervix. It was shown that in addition to the quantity of metacercariae present, their location in the larvae was also relevant in the determination of mortality and anomalies. Malformed adults developed from larvae containing from one to three metacercariae.

Experimental models of Schistosoma mansoni infection

Experimental models of Schistosoma mansoni infections in mammals have contributed greatly to our understanding of the pathology and pathogenesis of infection. We consider here hepatic and extrahepatic disease in models of acute and chronic infection. Experimental schistosome infections have also contributed more broadly to our understanding of granulomatous inflammation and our understanding of Th1 versus Th2 related inflammation and particularly to Th2-mediated fibrosis of the liver.

Angiostrongylus costaricensis and experimental infection of Sarasinula marginata II: elimination routes

Angiostrongylus costaricensis intermediate hosts are terrestrial mollusks mostly belonging to the Veronicellidae family. In the present investigation we focused on the mechanisms of larval expulsion from Sarasinula marginata infected with A. costaricensis. Twenty-five mollusks were individually infected with 5000 L1 and sacrificed at 30 min and 1, 2, 4, 6, and 8 h post-infection and at days 1, 2, 4, 5, 6, 8, 10, 11, 12, 14, 15, 16, 20, 21, 22, 25, 26, 28, and 30 post-infection; the mollusks were then fixed and stained. Diverse organs involved throughout the course of the migratory routes of larvae from oral penetration on were specified and the mechanisms of larval access to the fibromuscular layer through the kidney, rectum, and vascular system were defined. The elimination of L3, derived from oral and/or cutaneous infections, appears to depend on granulomas located close to the excretory ducts of mucous cells.

Leishmania braziliensis: partial control of experimental infection by interleukin-12 p40 deficient mice

Resistance to infection by Leishmania major has been associated with the development of a Th1 type response that is dependent on the presence of interleukin 12 (IL-12). In this work the involvement of this cytokine in the response to infection by L. braziliensis, a less virulent species in the mouse model, was evaluated. Our results show that while interferon (IFN-g) deficient (-/-) mice inoculated L. braziliensis develop severe uncontrolled lesions, chronic lesions that remained under control up to 12 weeks of infection were observed in IL-12p40 -/- mice. IL 12p40 -/- mice had fewer parasites in their lesions than IFN-g-/- mice. Lymph node cells from IL-12p40 -/- were capable of producing low but consistent levels of IFN-g suggestive of its involvement in parasite control. Furthermore, as opposed to previous reports on L. major-infected animals, no switch to a Th2 response was observed in IL-12p40 -/- infected with L. braziliensis.

Experimental hepatic fibrosis due to Capillaria hepatica infection (differential features presented by rats and mice)

Rats and mice are among the most susceptible hosts for the helminth Capillaria hepatica. More information on the similarities and differences between the hepatic pathology presented by these two parasite hosts are needed, since they may represent good models for the study of hepatic fibrosis. Early changes are similar for both hosts and are represented by necro-inflammatory lesions around dead parasites and their eggs and diffuse and intense reactive hepatitis. Although worms remain alive longer in mice than in rats, hepatic changes are more rapidly and deeply modulated in the former, even leading to almost complete disappearance of fibrosis. As for the rats, the modulation of the focal lesions is followed by the formation of septal fibrosis, a process where fine and long fibrous septa appear connecting portal spaces and central veins in such a way as to form a final morphologic picture of cirrhosis. Hepatic functional changes usually present good correlations with the morphologic findings at the different phases of the infection evolution. Therefore C. hepatica infection in rats and mice represent two different models of hepatic fibrosis and these differences, if properly known and understood, can be explored to answer different questions regarding several aspects of hepatic fibrosis

Experimental kinetics of infection induced by Yersinia pseudotuberculosis isolated from stock animals

The course of in vivo infection of five isolates of Yersinia pseudotuberculosis was followed for three weeks in Swiss mice. The strains were isolated from diarrheic and normal feces and mesenteric lymph nodes of healthy and sick stock animals. Four strains of serogroup O:3 and one of serogroup O:1a, with and without the virulence plasmid, were inoculated intragastrically and intravenously in the mice. Groups of five animals were sacrificed at 6 h and 3, 6, 10, 15, and 21 days after inoculation, and organs and tissues were checked for possible macroscopic alterations. Development of infection was monitored at these times by performing viable bacterial counts in homogenates of selected tissues. The animals were cheked daily for clinical alterations. The results of the study showed that strains with the virulence plasmid infected organs and tissues at various times and at varying intensity by both routes of infection, the strain of type O:1a being the most invasive. Moreover, clinical and pathological alterations occurred only in animals inoculated with bacteria carrying the virulence plasmid, regardless of the route of infection.

Alteration in the endogenous intestinal flora of swiss webster mice by experimental Angiostrongylus costaricensis infection

The association between worm infections and bacterial diseases has only recently been emphasized. This study examined the effect of experimental Angiostrongylus costaricensis infection on endogenous intestinal flora of Swiss Webster mice. Eight mice aging six weeks were selected for this experiment. Four were infected with A. costaricensis and the other four were used as controls. Twenty eight days after the worm infection, all mice in both groups were sacrificed and samples of the contents of the ileum and colon were obtained and cultured for aerobic and anaerobic bacteria. In the mice infected with A. costaricensis there was a significant increase in the number of bacteria of the endogenous intestinal flora, accompanied by a decrease in the number of Peptostreptococcus spp. This alteration in the intestinal flora of mice infected by the nematode may help to understand some bacterial infections described in humans.

Angiostrongylus costaricensis: complete redescription of the migratory pathways based on experimental Sigmodon hispidus infection

Angiostrongylus costaricensis lives in the cecal and mesenteric arteries of its vertebrate hosts, and causes an inflammatory disease in humans. To investigate unknown aspects of the abdominal angiostrogyliasis pathogenesis, infected Sigmodon hispidus were sequentially studied in different times of infection. The study revealed that L3 goes alternatively through two migratory courses during its development into an adult worm: lymphatic/venous-arterial and venous portal pathways. The former is considered the principal one, because it is used by most of the larvae. Like other metastrongylides, A. costaricensis passes over the pulmonary circulation to migrate from the lymphatic system to the arterial circulation, where they circulate during some days before reaching their definitive habitat. The oviposition by mature females began on 15th day. Eggs and L1 were detected mainly in the intestine and stomach, surrounded by inflammatory reaction constituted by macrophages, monocytes, and eosinophils. They were also spread to the lungs, mesenteric lymph nodes, pancreas, spleen, and kidneys. The larvae (L1) exhibited the centripetal capacity to invade the lymphatic and venous vessels of the intestine and mesentery. Adult worms that developed in the venous intrahepatic pathway migrated downstream to reach the mesenteric veins and laid eggs that embolized in the portal hepatic vessels.

Experimental infection of Leishmania (L.) chagasi in a cell line derived from Lutzomyia longipalpis (Diptera:Psychodidae)

The present work describes the in vitro infection of a cell line Lulo, derived from Lutzomyia longipalpis embryonic tissue, by Leishmania chagasi promastigotes. This infection process is compared with a parallel one developed using the J774 cell line. The L. chagasi MH/CO/84/CI-044B strain was used for experimental infection in two cell lines. The cells were seeded on glass coverslips in 24-well plates to reach a final number of 2 x 10(5) cells/well. Parasites were added to the adhered Lulo and J774 cells in a 10:1 ratio and were incubated at 28 and 37ºC respectively. After 2, 4, 6, 8, and 10 days post-infection, the cells were extensively washed with PBS, fixed with methanol, and stained with Giemsa. The number of internalized parasites was determined by counting at least 400 cultured cells on each coverslip. The results showed continuous interaction between L. chagasi promastigotes with the cell lines. Some ultrastructural characteristics of the amastigote forms were observed using transmission electron microscopy. The highest percentage of infection in Lulo cells was registered on day 6 post-infection (29.6%) and on day 4 in the J774 cells (51%). This work shows similarities and differences in the L. chagasi experimental infection process in the two cell lines. However, Lulo cells emerge as a new model to study the life-cycle of this parasite.

Aluminum hydroxide associated to Schistosoma mansoni 22.6 kDa protein abrogates partial protection against experimental infection but not alter interleukin-10 production

The need to develop a vaccine against schistosomiasis led several researches and our group to investigate proteins from Schistosoma mansoni as vaccine candidates. Sm22.6 is a protein from S. mansoni that shows high identity with Sj22.6 and Sh22.6 (79 and 91%, respectively). These proteins are associated with high levels of IgE and protection to reinfection. Previously, we have shown that Sm22.6 induced a partial protection of 34.5% when used together with Freund's adjuvant and produced a Th0 type of immune response with interferon-g and interleukin-4. In this work, mice were immunized with Sm22.6 alone or with aluminum hydroxide adjuvant and high levels of IgG, IgG1, and IgG2a were measured. Unfortunately, no protection was detected. Since IL-10 is a modulating cytokine in schistosomiasis, we also observed a high level of this molecule in splenocytes of vaccinated mice. In conclusion, we did not observe the adjuvant effect of aluminum hydroxide associated with rSm22.6 in protective immunity.

Experimental infection parameters in Galea spixii (Rodentia: Caviidae) with Leishmania infantum chagasi

In order to better understand the epidemiological transmission network of leishmaniasis, an endemic disease in Northeast Brazil, we investigated the susceptibility of Spix yellow-toothed cavies (Galea spixii) to the Leishmania infantum chagasi parasite. Nine cavies were experimentally infected, separated into three groups and monitored at 30, 90 and 180 days, respectively. Amastigotes were identified in the spleen slides of two cavies killed 180 days after infection. Antibodies against the L. i. chagasi were identified in one of the cavies. This demonstrates that G. spixii is in fact capable of maintaining a stable infection by L. i. chagasi without alterations in biochemical and hematological parameters of the host and without perceivable micro and macroscopic lesions.