Low Levels Of Parasitemia Research Articles

Molecular and Microscopic-Based Characterization of Plasmodium spp. in Fars and Hormozgan Provinces, South of Iran.

Despite malaria control programs in recent years, malaria transmission has not been eliminated in Iran. Molecular techniques including PCR, which has proved more sensitive and specific than microscopic examination methods, help to detect infection in low levels of parasitemia and mixed infections. Main our objectives were setting up nested PCR for detection of malaria and evaluating PCR based on plasmodia DNA from blood smears in Fars province, the comparison of this method with traditional microscopy and also evaluate the data in comparison with its neighboring province, Hormozgan. A total of 149 malaria positive samples including 116, 19, and 14 samples from Shiraz, Jask, and Lengeh ports were utilized in this study, respectively. Blood slides were prepared for microscopic observation. DNA from thin smears was extracted and nested PCR was analyzed using rPLU5 and rPLU6 for genus specification, rFAL1, rFAL2, and rVIV1, rVIV2 for P. falciparum and P. vivax detection, respectively. The results showed that 126 (84.6%), 16 (10.7%), and 7 (4.7%) out of 149 cases were positive for P. vivax, P. falciparum, and mixed infections, respectively, by microscopy. The PCR indicated that 95 (63.7%), 15 (10.1%), and 22 (14.8%) cases were infected with P. vivax, P. falciparum, and mixed mentioned species, respectively, and 17 (11.4%) cases were uninfected. Our results confirmed the considerable sensitivity of nested PCR for detection of the mixed infections. Simultaneous application of PCR even based on microscopy slides can facilitate access to the highest level of confidence in malaria researches.

Alpha-tocopherol transfer protein gene inhibition enhances the acquired immune response during malaria infection in mice

Immune response to malaria infection is complex and seems to be regulated by innate and adaptive immune response as well as environmental factors such as host genetics and nutritional status. Previously, we have reported that α-tocopherol transfer protein knockout (α-ttp(Δ)) mice, showing low concentrations of α-tocopherol in circulation, infected with Plasmodium berghei NK65 survived significantly longer as compared with the wild-type mice. In addition, Plasmodium yoelii XL-17, a lethal strain, showed non-lethal virulence in α-ttp(Δ) mice. Thus, we hypothesized that the ability of the α-ttp(Δ) mice to control P. yoelli XL-17 proliferation may allow them to build an efficient immune response against murine malaria infection. On 15 days after infection with P. yoelli XL-17, α-ttp(Δ) mice were challenged to infection with P. berghei NK65. Results indicated that α-ttp(Δ) mice infected with P. yoelli XL-17 built a protective immunity against P. berghei NK65 associated to extremely low levels of parasitemia, a controlled inflammatory response, and a robust antibody response. Moreover, the importance of α-tocopherol for parasite proliferation was remarkable. The results suggest that inhibition of α-tocopherol transfer protein activity is effective for the enhancement of acquired immunity in murine malaria infection.

Submicroscopic malaria parasite carriage: how reproducible are polymerase chain reaction-based methods?

The polymerase chain reaction (PCR)-based methods for the diagnosis of malaria infection are expected to accurately identify submicroscopic parasite carriers. Although a significant number of PCR protocols have been described, few studies have addressed the performance of PCR amplification in cases of field samples with submicroscopic malaria infection. Here, the reproducibility of two well-established PCR protocols (nested-PCR and real-time PCR for the Plasmodium 18 small subunit rRNA gene) were evaluated in a panel of 34 blood field samples from individuals that are potential reservoirs of malaria infection, but were negative for malaria by optical microscopy. Regardless of the PCR protocol, a large variation between the PCR replicates was observed, leading to alternating positive and negative results in 38% (13 out of 34) of the samples. These findings were quite different from those obtained from the microscopy-positive patients or the unexposed individuals; the diagnosis of these individuals could be confirmed based on the high reproducibility and specificity of the PCR-based protocols. The limitation of PCR amplification was restricted to the field samples with very low levels of parasitaemia because titrations of the DNA templates were able to detect < 3 parasites/µL in the blood. In conclusion, conventional PCR protocols require careful interpretation in cases of submicroscopic malaria infection, as inconsistent and false-negative results can occur.

A Novel qPCR Assay for the Detection of African Animal Trypanosomosis in Trypanotolerant and Trypanosusceptible Cattle Breeds

This study was conducted to (i) determine the prevalence of African Animal Trypanosomosis (AAT) in tsetse challenged areas, (ii) compare conventional with qPCR detection systems and (iii) evaluate the host genetic background and biology as risk factors. AAT prevalence studies are often confronted with low levels of parasitaemia. Hence, we designed a novel qPCR assay using primers and species specific probes amplifying the Internal Transcribed Spacer 1 (ITS1) gene. Thereby all three AAT species could be detected simultaneously. 368 individuals from three cattle types (Baoulé, Zebu and hybrids) originating from 72 farms in Burkina Faso were analysed. Farmers were interviewed and morphometric measurements of the cattle taken. A chi-squared test and a logistic regression model were calculated to detect associations with infection. In our study, the overall rate of prevalence detected with the novel qPCR assay was 11.14%. Compared to conventional PCR we identified a concordance of 91.30%. We tested 41 animals positive for trypanosome DNA, five animals showed multiple infections. Zebus were twice as often infected (21.74%) compared to Baoulé (9.70%) and hybrids (9.57%). Trypanosoma vivax is the dominant species (9.24%), as compared to T. congolense (2.44%) and T. brucei (0.82%). The chi-squared tests linking the infection events to the breeds (Zebu vs. Baoulé and Zebu vs. hybrids) were on the border of significance. No significant association with other tested parameters could be detected. We introduce a novel qPCR technique for the fast, sensitive and simultaneous detection of the three AAT species. Our results suggest that associations with breed and infection exist since Zebu cattle are more likely to be infected compared to Baoulé and hybrids. Indigenous taurine cattle breeds, like the Baoulé, therefore provide a unique and valuable genetic resource.

Changes in B Cell Populations and Merozoite Surface Protein-1-Specific Memory B Cell Responses after Prolonged Absence of Detectable P. falciparum Infection

Clinical immunity to malaria declines in the absence of repeated parasite exposure. However, little is known about how B cell populations and antigen-specific memory B cells change in the absence of P. falciparum infection. A successful indoor residual insecticide spraying campaign in a highland area of western Kenya, led to an absence of blood-stage P. falciparum infection between March 2007 and April 2008. We assessed memory B cell responses in 45 adults at the beginning (April 2008) and end (April 2009) of a subsequent 12-month period during which none of the adults had evidence of asymptomatic parasitemia or clinical disease. Antibodies and memory B cells to the 42-kDa portion of the merozoite surface protein-1 (MSP-142) were measured using ELISA and ELISPOT assays, respectively. B cell populations were characterized by flow cytometry. From 2008 to 2009, the prevalence of MSP-142-specific memory B cells (45% vs. 55%, respectively, P = 0.32) or antibodies (91% vs. 82%, respectively, P = 0.32) did not differ significantly, although specific individuals did change from positive to negative and vice versa, particularly for memory B cells, suggesting possible low-level undetected parasitemia may have occurred in some individuals. The magnitude of MSP-142-specific memory B cells and levels of antibodies to MSP-142 also did not differ from 2008 to 2009 (P>0.10 for both). However, from 2008 to 2009 the proportions of both class-switched atypical (CD19+IgD-CD27-CD21-IgM-) and class-switched activated (CD19+IgD-CD27+CD21-IgM-) memory B cells decreased (both P<0.001). In contrast, class-switched resting classical memory B cells (CD19+IgD-CD27+CD21+IgM-) increased (P<0.001). In this area of seasonal malaria transmission, a one- year absence of detectable P. falciparum infection was not associated with changes in the prevalence or level of MSP-142 specific memory B cells, but was associated with major changes in overall memory B cell subsets.

Antitrypanosomal Effects of Crude Ethanolic Extract of Artemisia herba alba Follwing Experimental infection of Rabbits

There is potential growing interest in the context of exploring the medicinal effect of Artemisia spp in relation to parasitic diseases in many parties of the world. In this study, however, use of Artemisia herba alba as anti-parasitic source is exclusively new contribution to the currently available data base. The present work of the experimental nature was conducted to evaluate the antitrypanosomal efficacy of crude ethanolic extracts (CEE) of the aerial parts of Artemisia herba alba against Trypanosoma evansi infection in animal model. A total of thirty rabbits (n=30) of approximately 5 - 6 months old, weighing 1.5 - 2.5 kg were divided into six main groups of five animals each. Animals in Group1 (pre-infection) were treated intraperitoneally (I.P) with 100 mg kg -1 of CEE from two days before T. evansi infection until 4 days after infection. Group 2 (concurrent) was infected and concurrently treated with 100 mg kg -1 of CEE for 6 days. Group 3 (post-infection) was treated with 100 mg kg -1 of CEE 6 days after detection of parasitaemia. Group 4 (positive control) was treated intramuscular (I.M) with 3.5 mg kg -1 Berenil® (Diminazene aceturate) after establishment of parasitaemia following T. evansi infection. Group 5 (negative control) was infected with T. evansi only once with 1 ml of 5×10 5 of T. evansi while group 6 serves as reference group and treated intraperitoneally with Alsever's solution. The results indicated significant difference (p<0.05) in the context of reduction in the extent of clinical signs, low levels of parasitaemia and mortality pattern in animals received crude ethanolic extracts (CEE) of Artemisia herba alba compared to those served as negative group. Similarly, there was also haematologically significant difference (p<0.05) where low mean levels of PCV was observed in the groups 1-4 respectively. In contrast, there was no statistically significant difference in almost all investigated parameters between standard group (positive control) and treatment group. In conclusion, both CEE of A. herba-alba and Berenil® showed relatively aparasitaemia and normal heamatologic values in the infected rabbits, thereby confirming their antiparasitic properties.

Comparative diagnostic methods for canine ehrlichiosis

The efficacy of blood and buffy coat smear examination, commercially available dot-enzyme-linked immunosorbent assay (ELISA) kit, and nested polymerase chain reaction (PCR) was evaluated in the diagnosis of canine ehrlichiosis in 40 dogs exhibiting symptoms suggestive of the disease. The intracytoplasmic rickettsial organisms were seen in the smears of only 1 dog (2.5%) with an extremely low level of parasitemia. Nested PCR with 16S rRNA revealed characteristic 378 bp bands indicating positive reaction in 8 (20.0%) dogs and sera samples of 21 (52.5%) dogs revealed anti-Ehrlichia antibodies. The dog that revealed organisms in the blood also showed positive results with the other 2 methods. Similarly all the sera samples of dogs with nPCR positive results were also positive for anti-Ehrlichia antibodies. The 8 dogs that exhibited positive results by nPCR and dot-ELISA were studied for clinical, hematological, and biochemical characterization of the disease. Fever, depression, anorexia, anemia, splenomegaly, and bleeding tendency were the common symptoms associated with the disease. Thrombocytopenia was the most consistent hematological finding, followed by anemia. Biochemical analysis revealed hyperglobulinemia with a reverse albumin:globulin ratio in 3 cases.

Prime-boost vaccination with plasmid DNA followed by recombinant vaccinia virus expressing BgGARP induced a partial protective immunity to inhibit Babesia gibsoni proliferation in dogs

A heterologous prime-boost vaccination regime with DNA and recombinant vaccinia virus (rvv) vectors expressing relevant antigens has been shown to induce effective immune responses against several infectious pathogens. In this study, we describe the effectiveness of the prime-boost strategy by immunizing dogs with a recombinant plasmid followed by vaccinia virus, both of which expressed the glutamic acid-rich protein (BgGARP) of Babesia gibsoni. The dogs immunized with the prime-boost regime developed a significantly high level of specific antibodies against BgGARP when compared with the control groups. The antibody level was strongly increased after a booster immunization with a recombinant vaccinia virus. Two weeks after the booster immunization with a recombinant vaccinia virus expressing BgGARP, the dogs were challenged with B. gibsoni parasite. The dogs immunized with the prime-boost regime showed partial protection, manifested as a significantly low level of parasitemia. These results indicated that this type of DNA/rvv prime-boost immunization approach may have use against B. gibsoni infection in dogs.

Hemoparasite and hematological parameters in Nile tilapia

The accelerated growth of finfish aquaculture has resulted in a series of health problems, including blood disorders by hemoparasites; there are scarce studies about these agents and their impact in actual intensive farming. The aim of this study was to identify and quantify the hemoparasites present in monocytes and erythrocytes in the blood of tilapia and their correlation with the hematological profile. Blood samples were collected from caudal vessels of 15 cage-reared Nile tilapia (Oreochromis niloticus), with 70 ± 10 g weight on average, from Itambaraca Municipality, Parana State, Brazil. The total red blood cells, mean corpuscular volume, hematocrit, total and differential white blood cells counts, and the number of thrombocytes were determined in blood smears stained with May-Grunwald–Giemsa–Wright and Quick Panoptic. The results showed the presence of pleomorphic cytoplasmic inclusions with corrugated appearance and basophilic staining, mainly in monocytes, suggesting Anaplasmataceae parasitemia and inclusions with the same morphological characteristics in erythrocytes of one Nile tilapia. The hematological analysis showed no significant difference (P < 0.05) between infected and not infected fish, and therefore, there was no correlation between parasitemia and hematological profile. These observations allow us to infer that the intracytoplasmic inclusions in monocytes and erythrocytes are compatible with the family Anaplasmataceae. There was no correlation between the blood profile and low level of parasitemia.

Plasmodium falciparum—Malaria in Pregnant African Immigrants Often Goes Unrecognized

We report four cases of asymptomatic Plasmodium falciparum malaria in pregnant African women. They had immigrated to Finland 3 to 13 months earlier. The disease was revealed only by anemia. The diagnosis relied on blood smear which showed a parasitemia <0.2% in three cases. Medical personnel should be informed about the possibility of afebrile forms of malaria in pregnant women even months after immigration. Very low levels of parasitemia may call for a more sensitive diagnostic approach such as polymerase chain reaction.

Challenges in surveillance and response

Surveillance in the context of malaria elimination will needs to shift from measuring reductions in morbidity and mortality to detecting infections (with or without symptoms). The malaria elimination surveillance research and development agenda needs to develop tools and strategies for active and prompt detection of infection. The capacity to assess trends and respond without delay will need to be developed, so that surveillance itself becomes an intervention. Research is needed to develop sensitive field tests that can detect low levels of parasitaemia and/or evidence of recent infection. Examples of recent work on surveillance and response issues in several African countries will be discussed to illustrate approaches in active case detection and case investigations, cell phone reporting and response, and strategies to access mobile populations.

A direct comparison of real time PCR on plasma and blood to detect Plasmodium falciparum infection in children

BackgroundEstimation of Plasmodium falciparum parasitaemia can vary with the method used and time of sampling. Quantitative real time PCR (qPCR) on whole blood or plasma samples has previously been shown to be more sensitive than thick film microscopy. However the efficiencies of each method have not been compared using samples obtained from infants less than one year old.MethodsA multiple of statistical approaches were used to compare the performance of qPCR on whole blood or plasma to detect the 18 S ribosomal gene of P. falciparum in 548 samples from children aged 2.5 or 24 months. Parasite prevalence in matched samples was compared using Mcnemar’s test and agreement of positive results quantified as Kappa scores. Parasite prevalences between different age groups were compared by Fisher’s test. Results from analyses by thick film microscopy were also available from children at 24 months and their correlation to each qPCR method examined by the Spearman’s test. Finally the association of P. falciparum infection with the incidence of multiple malaria episodes from contact to 24 months of age was evaluated using negative binomial regression.ResultsThese analyses showed that qPCR from whole blood detected approximately 3-fold more cases of infection than plasma qPCR. Both qPCR methods agreed well with each other although qPCR from plasma had a greater agreement with microscopy (96.85%) than did qPCR from blood (69.7%). At 24 months the prevalence of infection detected by all methods was associated with anaemia (p < 0.05).ConclusionsThe data presented here demonstrates that low levels of parasitaemia are better detected by qPCR using parasite DNA from whole blood than from plasma. However plasma samples provide a viable substitute when parasite smears are unavailable.

Plasmodium falciparumin Asymptomatic Immigrants from Sub-Saharan Africa, Spain

<i>Plasmodium falciparum</i>in Asymptomatic Immigrants from Sub-Saharan Africa, Spain

Anti-IL-2 Treatment Impairs the Expansion of Treg Cell Population during Acute Malaria and Enhances the Th1 Cell Response at the Chronic Disease

Plasmodium chabaudi infection induces a rapid and intense splenic CD4+ T cell response that contributes to both disease pathogenesis and the control of acute parasitemia. The subsequent development of clinical immunity to disease occurs concomitantly with the persistence of low levels of chronic parasitemia. The suppressive activity of regulatory T (Treg) cells has been implicated in both development of clinical immunity and parasite persistence. To evaluate whether IL-2 is required to induce and to sustain the suppressive activity of Treg cells in malaria, we examined in detail the effects of anti-IL-2 treatment with JES6-1 monoclonal antibody (mAb) on the splenic CD4+ T cell response during acute and chronic P. chabaudi AS infection in C57BL/6 mice. JES6-1 treatment on days 0, 2 and 4 of infection partially inhibits the expansion of the CD4+CD25+Foxp3+ cell population during acute malaria. Despite the concomitant secretion of IL-2 and expression of high affinity IL-2 receptor by large CD4+ T cells, JES6-1 treatment does not impair effector CD4+ T cell activation and IFN-γ production. However, at the chronic phase of the disease, an enhancement of cellular and humoral responses occurs in JES6-1-treated mice, with increased production of TNF-α and parasite-specific IgG2a antibodies. Furthermore, JES6-1 mAb completely blocked the in vitro proliferation of CD4+ T cells from non-treated chronic mice, while it further increased the response of CD4+ T cells from JES6-1-treated chronic mice. We conclude that JES6-1 treatment impairs the expansion of Treg cell population during early P. chabaudi malaria and enhances the Th1 cell response in the late phase of the disease.

Prevalence of Plasmodium falciparum and P. vivax in an area of transmission located in Pará State, Brazil, determined by amplification of mtDNA using a real-time PCR assay

The need for a more sensitive and time-efficient assay for malaria has led to the development of molecular assays involving real-time PCR (qPCR), a procedure that has the potential to detect low levels of parasitemia, identify mixed infections, and allow for precise differentiation of species via melting curve analysis or TaqMan fluorescence-labeled probes. Since the first study published in 2001 at least 17 assays have been developed, most of them using SSUrRNA as the target gene. We used qPCR to detect Plasmodium falciparum and P. vivax by amplification of mtDNA; this technique was evaluated on whole-blood samples from people living in areas of malaria transmission in the Brazilian Amazon region located in the area of inclusion of highway BR-163 (Cuiabá-Santarém) in Pará State: São Luiz do Tapajós, a municipal district of Itaituba (N = 74); Três Boeiras, a municipal district of Trairão (N = 134), and São Raimundo, a municipal district of Aveiro (N = 62). The results from the real-time PCR-based method were compared to conventional microscopy and to an established mtDNA-PCR assay. The qPCR (mtDNA) method was 16-19 times more efficient than the conventional PCR (mtDNA) and microscopy for detecting plasmodial infections.

Experimental evaluation of xenodiagnosis to detect trypanosomes at low parasitaemia levels in infected hosts

In Human African Trypanosomosis (HAT) endemic areas, there are a number of subjects that are positive to serological tests but in whom trypanosomes are difficult to detect with the available parasitological tests. In most cases and particularly in West Africa, these subjects remain untreated, thus posing a fundamental problem both at the individual level (because of a possible lethal evolution of the disease) and at the epidemiological level (since they are potential reservoirs of trypanosomes). Xenodiagnosis may constitute an alternative for this type of cases. The objective of this study was to update the use of xenodiagnosis to detect trypanosomes in infected host characterized by low parasitaemia levels. This was carried out experimentally by infecting cattle and pigs with Trypanosoma congolense and T. brucei gambiense respectively, and by feeding tsetse flies (Glossina morsitans submorsitans and G. palpalis gambiensis, from the CIRDES colonies) on these animals at a time when the observed blood parasitaemia were low or undetectable by the classical microscopic parasitological tests used for the monitoring of infected animals. Our results showed that: i) the G. p. gambiensis colony at CIRDES could not be infected with the T. b. gambiense stocks used; ii) midgut infections of G. m. submorsitans were observed with both T. congolense and T. b. gambiense; iii) xenodiagnosis remains positive even at very low blood parasitaemia for both T. congolense and T. b. gambiense; and iv) to implement T. b. gambiense xenodiagnosis, batches of 20 G. m. submorsitans should be dissected two days after the infective meal. These results constitute a first step toward a possible implementation of xenodiagnosis to better characterize the parasitological status of seropositive individuals and the modalities of parasite transmission in HAT foci.

Characterization of haemosporidian infections in warblers and sparrows at south-western European reed beds

The prevalence and intensity of avian haemosporian infections (genera Haemoproteus and Plasmodium) were investigated using molecular techniques and microscopy in nine passerine species at three Portuguese reed beds along a small latitudinal gradient. The effect of age, sex, season, site and year in the infection prevalence was evaluated for some of these host species. Of the sampled birds, 34.5% were infected, all with low level parasitemias. Haemoproteus spp. was only present in migrant species and was not locally transmitted, while Plasmodium spp. infected more species and reached a higher overall prevalence. Prevalence differed among bird species and was affected by different variables for each species: it was associated with age in the Reed Warbler Acrocephalus scirpaceus, with season in the Cetti’s Warbler Cettia cetti and with year in the House Sparrow Passer domesticus. Site did not influence prevalence for any species at this small geographical scale. Reed Warbler adults had already migrated to Africa and contacted with two different parasite faunas, whereas juveniles had not, thereby explaining the importance of age to explain parasitemia in this species. For the resident Cetti’s Warbler, prevalence varied significantly with season, perhaps due to lower food availability in autumn and winter, making birds weaker and more prone to infection.

Prevention of Experimental Cerebral Malaria by Flt3 Ligand during Infection with Plasmodium berghei ANKA

Dendritic cells are the most potent antigen-presenting cells, but their roles in blood-stage malaria infection are not fully understood. We examined the effects of Flt3 ligand, a cytokine that induces dendritic cell production, in vivo on the course of infection with Plasmodium berghei ANKA. Mice treated with Flt3 ligand showed preferential expansion of CD8(+) dendritic cells and granulocytes, as well as lower levels of parasitemia, and were protected from the development of lethal experimental cerebral malaria (ECM). Rag2 knockout mice treated with Flt3 ligand also showed inhibition of parasitemia, suggesting that this protection was due, at least in part, to the stimulation of innate immunity. However, it was unlikely that the inhibition of ECM was due simply to the reduction in the level of parasitemia. In the peripheral T cell compartment, CD8(+) T cell levels were markedly increased in Flt3 ligand-treated mice after infection. These CD8(+) T cells expressed CD11c and upregulated CXCR3, while the expression of CD137, CD25, and granzyme B was reduced. In the brain, the number of sequestered CD8(+) T cells was not significantly different for treated versus untreated mice, while the proportion of CD8(+) T cells that produce gamma interferon (IFN-γ) and granzyme B was significantly reduced in treated mice. In addition, sequestration of parasitized red blood cells (RBCs) in the brain was reduced, suggesting that altered CD8(+) T cell activation and reduced sequestration of parasitized RBCs culminated in inhibition of ECM development. These results suggest that the quantitative and qualitative changes in the dendritic cell compartment are important for the pathogenesis of ECM.

Disruption of plasmepsin-4 and merozoites surface protein-7 genes in Plasmodium berghei induces combined virulence-attenuated phenotype

Blood stage malaria parasites causing a mild and self limited infection in mice have been obtained with either radiation or chemical mutagenesis showing the possibility of developing an attenuated malaria vaccine. Targeted disruption of plasmepsin-4 (pm4) or the merozoite surface protein-7 (msp7) genes also induces a virulence-attenuated phenotype in terms of absence of experimental cerebral malaria (ECM), delayed increase of parasitemia and reduced mortality rate. The decrease in virulence in parasites lacking either pm4 or msp7 is however incomplete and dependent on the parasite and mouse strain combination. The sequential disruption of both genes induced remarkable virulence-attenuated blood-stage parasites characterized by a self-resolving infection with low levels of parasitemia and no ECM. Furthermore, convalescent mice were protected against the challenge with P. berghei or P. yoelii parasites for several months. These observations provide a proof-of-concept step for the development of human malaria vaccines based on genetically attenuated blood-stage parasites.

Hepatitis B Infection Is Associated with Asymptomatic Malaria in the Brazilian Amazon

BackgroundAreas that are endemic for malaria are also highly endemic for hepatitis B virus (HBV) infection. Nevertheless, it is unknown whether HBV infection modifies the clinical presentation of malaria. This study aimed to address this question.Methodology and FindingsAn observational study of 636 individuals was performed in Rondônia, western Amazon, Brazil between 2006 and 2007. Active and passive case detections identified Plasmodium infection by field microscopy and nested Polymerase Chain Reaction (PCR). HBV infections were identified by serology and confirmed by real-time PCR. Epidemiological information and plasma cytokine profiles were studied. The data were analyzed using adjusted multinomial logistic regression. Plasmodium-infected individuals with active HBV infection were more likely to be asymptomatic (OR: 120.13, P<0.0001), present with lower levels of parasitemia and demonstrate a decreased inflammatory cytokine profile. Nevertheless, co-infected individuals presented higher HBV viremia. Plasmodium parasitemia inversely correlated with plasma HBV DNA levels (r = −0.6; P = 0.0003).ConclusionHBV infection diminishes the intensity of malaria infection in individuals from this endemic area. This effect seems related to cytokine balance and control of inflammatory responses. These findings add important insights to the understanding of the factors affecting the clinical outcomes of malaria in endemic regions.