Spatiotemporal Changes in Plasmodium vivax msp142 Haplotypes in Southern Mexico: From the Control to the Pre-Elimination Phase.

For 20 years, Plasmodium vivax has been the only prevalent malaria species in Mexico, and cases have declined significantly and continuously. Spatiotemporal genetic studies can be helpful for understanding parasite dynamics and developing strategies to weaken malaria transmission, thus facilitating the elimination of the parasite. The aim of the current contribution was to analyze P. vivax-infected blood samples from patients in southern Mexico during the control (1993-2007) and pre-elimination phases (2008-2011). Nucleotide and haplotype changes in the pvmsp142 fragment were evaluated over time. The majority of multiple genotype infections occurred in the 1990s, when the 198 single nucleotide sequences exhibited 57 segregating sites, 64 mutations, and 17 haplotypes. Nucleotide and genetic diversity parameters showed subtle fluctuations from across time, in contrast to the reduced haplotype diversity and the increase in the R2 index and Tajima's D value from 2008 to 2011. The haplotype network consisted of four haplogroups, the geographical distribution of which varied slightly over time. Haplogroup-specific B-cell epitopes were predicted. Since only high-frequency and divergent haplotypes persisted, there was a contraction of the parasite population. Given that 84% of haplotypes were exclusive to Mesoamerica, P. vivax flow is likely circumscribed to this region, representing important information for parasite surveillance.

Vaccination against babesiosis using recombinant GPI-anchored proteins.

The increase in human babesiosis is of major concern to health authorities. In the USA, most of these cases are due to infections with Babesia microti, whereas in Europe B. divergens is the major cause of clinical disease in humans. Here we review the immunological and biological literature of glycosylphosphatidylinositol (GPI)-anchored merozoite proteins of human Babesia parasites with emphasis on their role in immunity, and provide some new bioinformatical information on B. microti GPI-Anchored Proteins (GPI-AP). Cattle can be vaccinated with soluble parasite antigens (SPA) of Babesia divergens that are released by the parasite during proliferation. The major component in SPA preparations appeared to be a 37 kDa merozoite surface protein that is anchored in the merozoite membrane by a GPI anchor. Animals could be protected by vaccination with the recombinant 37 kDa protein expressed in Escherichia coli, provided the protein had a hydrophobic terminal sequence. Based on this knowledge, a recombinant vaccine was developed against Babesia canis infection in dogs, successfully. In order to identify similar GPI-AP in B. microti, the genome was analysed. Here it is shown that B. microti encodes all proteins necessary for GPI assembly and its subsequent protein transfer. In addition, in total 21 genes encoding for GPI-AP were detected, some of which reacted particularly strongly with sera from B. microti-infected human patients. Reactivity of antibodies with GPI-anchored merozoite proteins appears to be dependent on the structural conformation of the molecule. It is suggested that the three-dimensional structure of the protein that is anchored in the membrane is different from that of the protein that has been shed from the merozoite surface. The significance of this protein's dynamics in parasite biology and immune evasion is discussed. Finally, we discuss developments in tick and Babesia vaccine research, and the role such vaccines could play in the control of human babesiosis.

The malaria parasite Plasmodium relictum in the endemic avifauna of eastern Cuba.

Island populations are vulnerable to introduced pathogens, as evidenced by extinction or population decline of several endemic Hawaiian birds caused by the malaria parasite, Plasmodium relictum (order Haemosporida). We analyzed blood samples from 363 birds caught near Guantánamo Bay, Cuba, for the presence of haemosporidian infections. We characterized parasite lineages by determining nucleotide variation of the parasite's mitochondrial cyt b gene. Fifty-nine individuals were infected, and we identified 7 lineages of haemosporidian parasites. Fifty individuals were infected by 6 Haemoproteus sp. lineages, including a newly characterized lineage of Haem. (Parahaemoproteus) sp. CUH01. Nine individuals carried the P. relictum lineage GRW4, including 5 endemic Cuban Grassquits (Tiaris canorus) and 1 migratory Cape May Warbler (Setophaga tigrina). A sequence of the merozoite surface protein gene from one Cuban Grassquit infected with GRW4 matched that of the Hawaiian haplotype Pr9. Our results indicate that resident and migratory Cuban birds are infected with a malaria lineage that has severely affected populations of several endemic Hawaiian birds. We suggest GRW4 may be associated with the lack of several bird species on Cuba that are ubiquitous elsewhere in the West Indies. From the standpoint of avian conservation in the Caribbean Basin, it will be important to determine the distribution of haemosporidian parasites, especially P. relictum GRW4, in Cuba as well as the pathogenicity of this lineage in species that occur and are absent from Cuba.

Merozoite-Protein Loaded Liposomes Protect against Challenge in Two Murine Models of Plasmodium Infection.

Liposomes loaded with GPI-anchored proteins induce a strong and effective response against protozoan pathogens when immunized in mice. On the basis of results using Plasmodium falciparum merozoite proteins loaded on liposomes, we tested whether a similar approach would be protective in the P. yoelii XL and P. berghei NK65 models of lethal murine malaria infections. We also analyzed the enhancing capacity of additional adjuvants. As expected, merozoite protein loaded liposomes provided strong humoral responses (IgG titers of 105 against MSP119) in BALB/c and C57BL/6 host backgrounds and showed total protection in lethal challenges (100% survival) with P. yoelii, while protection against lethal challenge with P. berghei NK was at least partial (11%-20% in C57BL/6 mice and no protection in BALB/c). Thus, immunization with proteoliposomes is not only highly immunogenic but also provides a protective response in widely used murine models of malaria.

Genetic structure of Plasmodium vivax in Nicaragua, a country in the control phase, based on the carboxyl terminal region of the merozoite surface protein-1.

Malaria is still a grave public health problem in tropical areas of the world. The greater genetic diversity of Plasmodium vivax at geographic sites with less control over infection evidences the importance of genetic studies of these parasites. The present genetic study compares P. vivax in Nicaragua, which is still in the control phase, with this species in several other countries. In Nicaragua, P. vivax causes over 80% of malaria cases, most occurring in two remote northern regions. Plasmodium asexual blood-stage antigens, implicated in reticulocyte invasion, are possible molecular markers for analyzing parasite population genetics and for developing vaccines. The aim of this work was to investigate the genetic structure of P. vivax based on the 42kDa merozoite surface protein-1 (PvMSP-142), which may represent a sensitive marker for evaluating malaria transmission control. From blood samples of patients with P. vivax, we amplified PvMSP-142, obtained the nucleotide sequences, and compared them to homologous sequences of parasites from other geographic sites, retrieved from the GenBank. The 92 nucleotide sequences of P. vivax resulted in the resolution of eight haplotypes, six exclusive to Nicaragua. The great nucleotide diversity (π=0.020), the minimal recombination events (Rm=11), and the dN-dS values were similar to other control phase countries. FST values between parasites were low (0.069) for Nicaragua versus Brazil but higher for Nicaragua versus other regions (0.134-0.482). The haplotype network revealed five lineages: two were very frequent in Nicaragua and closely related to American parasites; three have been detected in multiple geographic sites around the world. These results suggest that P. vivax in Nicaragua is a differentiated and genetically diverse population (mainly due to mutation, positive balancing selection and recombination) and that PvMSP-142 may be a sensitive marker for evaluating sustained reduction in malaria transmission and for developing vaccines.

Merozoite surface protein-1 genetic diversityin Plasmodium malariae and Plasmodium brasilianum from Brazil

The merozoite surface protein 1 (MSP1) gene encodes the major surface antigen of invasive forms of the Plasmodium erythrocytic stages and is considered a candidate vaccine antigen against malaria. Due to its polymorphisms, MSP1 is also useful for strain discrimination and consists of a good genetic marker. Sequence diversity in MSP1 has been analyzed in field isolates of three human parasites: P. falciparum, P. vivax, and P. ovale. However, the extent of variation in another human parasite, P. malariae, remains unknown. This parasite shows widespread, uneven distribution in tropical and subtropical regions throughout South America, Asia, and Africa. Interestingly, it is genetically indistinguishable from P. brasilianum, a parasite known to infect New World monkeys in Central and South America. Methods: Specific fragments (1 to 5) covering 60 % of the MSP1 gene (mainly the putatively polymorphic regions), were amplified by PCR in isolates of P. malariae and P. brasilianum from different geographic origin and hosts. Sequencing of the PCR-amplified products or cloned PCR fragments was performed and the sequences were used to construct a phylogenetic tree by the maximum likelihood method. Data were computed to give insights into the evolutionary and phylogenetic relationships of these parasites...

Naturally acquired antibodies to merozoite surface protein (MSP)-1(19) and cumulative exposure to Plasmodium falciparum and Plasmodium vivax in remote populations of the Amazon Basin of Brazil

To infer recent patterns of malaria transmission, we measured naturally acquired IgG antibodies to the conserved 19-kDa C-terminal region of the merozoite surface protein (MSP)-1 of both Plasmodium vivax (PvMSP-1(19)) and Plasmodium falciparum (PfMSP-1(19)) in remote malaria-exposed populations of the Amazon Basin. Community-based cross-sectional surveys were carried out between 2002 and 2003 in subjects of all age groups living along the margins of the Unini and Jaú rivers, Northwestern Brazil. We found high prevalence rates of IgG antibodies to PvMSP-1(19) (64.0 - 69.6 percent) and PfMSP-1(19) (51.6 - 52.0 percent), with significant differences in the proportion of subjects with antibodies to PvMSP-1(19) according to age, place of residence and habitual involvement in high-risk activities, defining some groups of highly exposed people who might be preferential targets of malaria control measures. In contrast, no risk factor other than age was significantly associated with seropositivity to PfMSP-1(19). Only 14.1 percent and 19.3 percent of the subjects tested for antibodies to PvMSP-1(19) and PfMSP-1(19) in consecutive surveys (142 - 203 days apart) seroconverted or had a three fold or higher increase in the levels of antibodies to these antigens. We discuss the extent to which serological data correlated with the classical malariometric indices and morbidity indicators measured in the studied population at the time of the seroprevalence surveys and highlight some limitations of serological data for epidemiological inference.

Merozoite surface protein 2 allelic variation influences the specific antibody response during acute malaria in individuals from a Brazilian endemic area

The antibody response to Plasmodium falciparum parasites of naturally infected population is critical to elucidate the role of polymorphic alleles in malaria. Thus, we evaluated the impact of antigenic diversity of repetitive and family dimorphic domains of the merozoite surface protein 2 (MSP-2) on immune response of 96 individuals living in Peixoto de Azevedo (MT-Brazil), by ELISA using recombinant MSP-2 proteins. The majority of these individuals were carrying FC27-type infections. IgG antibody responses were predominantly directed to FC27 parasites and were correlated to the extension of polymorphism presented by each MSP-2 region. This finding demonstrated the impact of the genetic polymorphism on antibody response and therefore, its importance on malaria vaccine efficacy.