Reduced protective effect of Plasmodium berghei immunization by concurrent Schistosoma mansoni infection

Studies on concomitant schistosomiasis and human and experimental malaria have shown a variation in the immunospecific response, as well as an increase in the severity of both parasitoses. In the present study, a murine co-infection model was used to determine the effects of a co-infection with Schistosoma mansoni and Plasmodium berghei on the protective immunity acquired by repeated malarial infections and subsequent curative treatment with chloroquine. Our results have demonstrated that, compared to an infection with P. berghei only, the co-infection increases the malarial parasitaemia and decreases the survival rate. Indeed, mice that were immunized by infection and treatment with drug displayed no mortality whereas co-infected mice showed a reduced protective efficacy of immunization against P. berghei (mortality > 60 percent). Interestingly, this high mortality rate was not associated with high levels of parasitaemia. Our findings support the idea of a suppressive effect of a Schistosoma co-infection on the anti-malarial protection by immunization. This result reveals a possible drawback of the development of anti-malarial vaccines, especially considering the wide endemic areas for both parasitoses.

Effect of the Aedes fluviatilis saliva on the development of Plasmodium gallinaceum infection in Gallus (gallus) domesticus

Effect of Aedes fluviatilis saliva on the development of Plasmodium gallinaceum experimental infection in Gallus (gallus) domesticus was studied in distinct aspects. Chickens subcutaneously infected with sporozoites in the presence of the mosquito salivary gland homogenates (SGH) showed higher levels of parasitaemia when compared to those ones that received only the sporozoites. However, the parasitaemia levels were lower among chickens previously immunized by SGH or non-infected mosquito bites compared to the controls, which did not receive saliva. High levels of anti-saliva antibodies were observed in those immunized chickens. Moreover, 53 and 102 kDa saliva proteins were recognized by sera from immunized chickens. After the sporozoite challenge, the chickens also showed significant levels of anti-sporozoite antibodies. However, the ability to generate anti-sporozoites antibodies was not correlated to the saliva immunization. Our results suggest that mosquito saliva components enhance P. gallinaceum parasite development in naive chickens. However, the prior exposure of chickens to salivary components controls the parasitemia levels in infected individuals.

Vertical toxoplasmosis in a murine model. Protection after immunization with antigens of Toxoplasma gondii incorporated into liposomes

Distinct Toxoplasma gondii antigens were entrapped within liposomes and evaluated for their ability to protect Balb/c mice against congenital transmission: soluble tachyzoite antigen (L/STAg), soluble tissue cyst antigen (L/SCAg), soluble tachyzoite plus tissue cyst (L/STCAg) or purified 32kDa antigen of tachyzoite (L/pTAg). Soluble tachyzoite antigen alone in PBS (STAg) or emulsified in Freund's Complete Adjuvant (FCA/STAg) was also evaluated. Dams were inoculated subcutaneously with these antigens 6, 4 and 2 weeks prior to a challenge with four tissue cysts of the P strain of T. gondii orally between 10 and 14 days of pregnancy. Significant diminution differences were observed between the frequency of infected pups born of the dams immunized with the antigens incorporated into liposomes and that of pups born of the dams immunized with antigen emulsified in FCA or non immunized group (p<0.05). There was a significant decrease in the number of pups born dead in the groups L/STAg, L/SCAg and L/pTAg when compared with pups from all other groups (p <0.05). All dams immunized with or without adjuvant showed an antibody response and a proliferation of T-cells. However, no correlation was found between immune response and protection against the challenge

Immune response to sporozoite and blood stage antigens among subjects exposed to malaria in Brazil: a review

A proteçäo contra malária adquirida por indivíduos expostos em áreas endêmicas é amplamente modulada pelo padräo de transmissäo. No Brasil, crianças e adultos säo igualmente acometidos e a infecçäo tende a ser seguida de doença clínica com sintomas de intensidade variável podendo ocorrer vários episódios sucessivos de malária por Plasmodium vivax e/ou P. falciparum. Entretanto, as taxas de prevalência variam dentro de uma mesma área endêmica sendo os casos relatados distribuídos de forma näo homogênea. Nesta revisäo säo discutidos os estudos atuais sobre a resposta imune humora e celular dirigida contra esporozoítas e formas sagüíneas de P. falciparum e P. vivax entre brasileiros expostos a diferentes situaçoes de transmissäo, enfatizando nossos estudos prévios conduzidos no Estado de Mato Grosso e em um foco de transmissäo localizado fora da área endêmica. O estudo da resposta imune naturalmente adquirida por populações expostas a baixos níveis de transmissäo poderá fornecer informaçoes importantes para o esclarecimento de aspectos relevantes sobre os mecanismos envolvidos na proteçäo contra a doença. Esses conhecimentos somados aos muitos verificados para as áreas hiperendêmicas poderäo permitir a escolha de possíveis vacinas protetoras e também a avaliaçäo adequada de voluntários vacinados nas áreas endêmicas.

Difference in susceptibility to lysis between clones of the Y strain of Trypanosoma cruzi

Three clones isolated from the Y strain of Trypanosoma cruzi--YP1, YP2 and YP3--were adapted to in vitro cultivation in VERO cells. The recovery of the parasites from the Y strain and clone YP3 was similar after 24 hr of contact with cells (3.2 per cent and 2.7 per cent , respectively) and much lower than the recovery of clones YP1 and YP2 (56.7 per cent and 60.0 per cent of inoculum, respectively). After five days incubation, the ratio Trypomastigotes/Amastigotes released into the supernatants was about 90/10 for clone YP1, YP3 and Y strain, and 50/50 for clone YP2. After nine days, the ratio was 62/38 for clone YP1, 97/3 for clone YP3, 81/19 for Y strain and 50/50 for clone YP2. The susceptibility of tissue culture derived trypomastigotes (TCT) to lysis in the presence of chronic chagasic human sera and human complement was assessed using Complement Mediated Lysis reaction (CML). Trypomastigotes from clone YP2 were consistently less susceptible to CML ( per cent lysis less than 20), than parasites from the other clones and Y strain. Parasites of clone YP3 had susceptibility to CML comparable to that of the Y strain (about 70 per cent ), while TCT of clone YP1 had intermediary susceptibility (40 per cent )