Fine specificity of anti-MSP119 antibodies and multiplicity of Plasmodium falciparum merozoite surface protein 1 types in individuals in Nigeria with sub-microscopic infection

Plasmodium falciparum transmission based on merozoite surface protein 1 (msp1) and 2 (msp2) gene diversity and antibody responses in Ibadan, Nigeria

Background

Nigeria is a major contributor to the global malaria burden. The genetic diversity of malaria parasite populations as well as antibody responses of individuals in affected areas against antigens of the parasite can reveal the transmission intensity, a key information required to control the disease. This work was carried out to determine the allelic frequency of highly polymorphic Plasmodium falciparum genes and antibody responses against schizont crude antigens in an area of Ibadan, Nigeria.

Materials and methods

Blood was collected from 147 individuals with symptoms suspected to be malaria. Malaria infection was determined using a rapid diagnostic test (RDT), and msp1 and msp2 were genotyped by a nested PCR method. In addition, levels of IgG directed against P. falciparum FCR3S1.2 schizont extract was measured in ELISA.

Results

Approximately 25% (36/147) were positive for a P. falciparum infection in RDT, but only 32 of the positive samples were successfully genotyped. MAD20 was the most prevalent and K1 the least prevalent of the msp1 alleles. For msp2, FC27 was more prevalent than 3D7. The mean multiplicities of infection (MOI) were 1.9 and 1.7 for msp1 and msp2, respectively. IgG levels correlated positively with age, however there was no difference in median antibody levels between RDT-positive and RDT-negative individuals.

Conclusion

Low MOI has before been correlated with low/intermediate transmission intensity, however, in this study, similar levels of P. falciparum-specific antibodies between infected and non-infected individuals point more towards a high level of exposure and a need for further measures to control the spread of malaria in this area.

Plasmodium relictum MSP-1 capture antigen-based ELISA for detection of avian malaria antibodies in African penguins (Spheniscus demersus)

Avian malaria, caused by Plasmodium spp. and transmitted by mosquitos, is a leading cause of mortality of captive penguins. Antimalarial drugs are currently used to control infections in penguins. However, the effectiveness of treatment reduces significantly by the time the clinical signs appear, while early and unnecessary treatment interferes with development of protective immunity. Therefore, for suppressing parasitemia without affecting the development of immunity in captive penguins, antimalaria drugs need to be administered at the right time, which requires reliable diagnostic tools that can determine the levels of circulating antimalaria antibodies. In the present study, we have developed an enzyme-linked immunosorbent assay (ELISA) diagnostic assay based on the merozoite surface protein 1 (MSP-1) of P. relictum isolate SGS1 to specifically detect and relatively quantify antimalaria antibodies in penguins. We expressed and purified a truncated P. relictum isolate SGS1 MSP-1 and optimized its biotinylation and subsequent conjugation to streptavidin alkaline phosphatase for signal generation in ELISA. We tested the assay by analyzing sera obtained from penguins at the Baltimore Zoo, from Spring through Fall, and found that levels of detectable antibodies against MSP-1 varied seasonally for individual penguins, consistent with the expected seasonal variations in avian malaria prevalence. Corroboratively, we analyzed the sensitivity of the assay by titrating positive sera and found that the signal intensity generated was serum concentration-dependent, thus validating the ability of the assay to detect and relatively quantify the levels of antimalaria antibodies in penguin sera.

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ELISA based on MSP1 for detection and quantification of antibodies against Plasmodium relictum in birds was developed.

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Assay was validated to detect and quantify levels of antimalaria antibodies in infected penguins' sera.

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Assay detected varied antibody levels against MSP-1 in penguin sera consistent with seasonal variations in malaria prevalence.

Genetic diversity of Plasmodium falciparum isolates in Nigeria. A review

Background

The complexity of infection in malaria-endemic areas is exacerbated by the presence of genetically diverse Plasmodium falciparum strains. There is a risk that more virulent or drug-resistant versions of the disease may arise. Therefore, we reviewed most reported molecular markers that have been detailed to date in Nigeria.

Main body of the abstract

In this review, we have summarized the genetic diversity of P. falciparum in Nigeria using the two well-reported genes (msp1 and msp2) as genetic diversity biomarkers. The review includes the findings obtained from research conducted in all major geopolitical regions of the country. We found that MSP-2 infection complexity is generally moderate to high in the North-central region. However, in the South-West, there were several regions where the multiplicity of infection (MOI) was either low or extremely high.

Conclusion

Understanding how Nigeria's malaria situation fits into various reports on P. falciparum genetic variation can improve treatment and immunization options. This review will be helpful for future treatment strategies that would be tailored to the specific needs of Nigeria's malaria-endemic populations.

Impact of age of first exposure to Plasmodium falciparum on antibody responses to malaria in children: a randomized, controlled trial in Mozambique

Background

The impact of the age of first Plasmodium falciparum infection on the rate of acquisition of immunity to malaria and on the immune correlates of protection has proven difficult to elucidate. A randomized, double-blind, placebo-controlled trial using monthly chemoprophylaxis with sulphadoxine-pyrimethamine plus artesunate was conducted to modify the age of first P. falciparum erythrocytic exposure in infancy and assess antibodies and malaria risk over two years.

Methods

Participants (n = 349) were enrolled at birth to one of three groups: late exposure, early exposure and control group, and were followed up for malaria morbidity and immunological analyses at birth, 2.5, 5.5, 10.5, 15 and 24 months of age. Total IgG, IgG subclasses and IgM responses to MSP-1₁₉, AMA-1, and EBA-175 were measured by ELISA, and IgG against variant antigens on the surface of infected erythrocytes by flow cytometry. Factors affecting antibody responses in relation to chemoprophylaxis and malaria incidence were evaluated.

Results

Generally, antibody responses did not vary significantly between exposure groups except for levels of IgM to EBA-175, and seropositivity of IgG1 and IgG3 to MSP-1₁₉. Previous and current malaria infections were strongly associated with increased IgG against MSP-1₁₉, EBA-175 and AMA-1 (p < 0.0001). After adjusting for exposure, only higher levels of anti-EBA-175 IgG were significantly associated with reduced clinical malaria incidence (IRR 0.67, p = 0.0178).

Conclusions

Overall, the age of first P. falciparum infection did not influence the magnitude and breadth of IgG responses, but previous exposure was critical for antibody acquisition. IgG responses to EBA-175 were the strongest correlate of protection against clinical malaria.

Trial registration

ClinicalTrials.gov: NCT00231452.

Genetic diversity of Plasmodium falciparum isolates from naturally infected children in north-central Nigeria using the merozoite surface protein-2 as molecular marker

OBJECTIVE

To characterize the genetic diversity of Plasmodium falciparum (P. falciparum) field isolates in children from Lafia, North-central Nigeria, using the highly polymorphic P. falciparum merozoite surface protein 2 (MSP-2) gene as molecular marker.

METHODS

Three hundred and twenty children were enrolled into the study between 2005 and 2006. These included 140 children who presented with uncomplicated malaria at the Dalhatu Araf Specialist Hospital, Lafia and another 180 children from the study area with asymptomatic infection. DNA was extracted from blood spot on filter paper and MSP-2 genes were genotyped using allele-specific nested PCR in order to analyze the genetic diversity of parasite isolates.

RESULTS

A total of 31 and 34 distinct MSP-2 alleles were identified in the asymptomatic and uncomplicated malaria groups respectively. No difference was found between the multiplicity of infection in the asymptomatic group and that of the uncomplicated malaria group (P>0.05). However, isolates of the FC27 allele type were dominant in the asymptomatic group whereas isolates of the 3D7 allele type were dominant in the uncomplicated malaria group.

CONCLUSIONS

This study showed a high genetic diversity of P. falciparum isolates in North-central Nigeria and is comparable to reports from similar areas with high malaria transmission intensity.

Identification and characterization of the merozoite surface protein 1 (msp1) gene in a host-generalist avian malaria parasite, Plasmodium relictum (lineages SGS1 and GRW4) with the use of blood transcriptome

Background

The merozoite surface protein 1 (msp1) is one of the most studied vaccine candidate genes in mammalian Plasmodium spp. to have been used for investigations of epidemiology, population structures, and immunity to infections. However methodological difficulties have impeded the use of nuclear markers such as msp1 in Plasmodium parasites causing avian malaria. Data from an infection transcriptome of the host generalist avian malaria parasite Plasmodium relictum was used to identify and characterize the msp1 gene from two different isolates (mtDNA lineages SGS1 and GRW4). The aim was to investigate whether the msp1 gene in avian malaria species shares the properties of the msp1 gene in Plasmodium falciparum in terms of block variability, conserved anchor points and repeat motifs, and further to investigate the degree to which the gene might be informative in avian malaria parasites for population and epidemiological studies.

Methods

Reads from 454 sequencing of birds infected with avian malaria was used to develop Sanger sequencing protocols for the msp1 gene of P. relictum. Genetic variability between variable and conserved blocks of the gene was compared within and between avian malaria parasite species, including P. falciparum. Genetic variability of the msp1 gene in P. relictum was compared with six other nuclear genes and the mtDNA gene cytochrome b.

Results

The msp1 gene of P. relictum shares the same general pattern of variable and conserved blocks as found in P. falciparum, although the variable blocks exhibited less variability than P. falciparum. The variation across the gene blocks in P. falciparum spanned from being as conserved as within species variation in P. relictum to being as variable as between the two avian malaria species (P. relictum and Plasmodium gallinaceum) in the variable blocks. In P. relictum the highly conserved p19 region of the peptide was identified, which included two epidermal growth factor-like domains and a fully conserved GPI anchor point.

Conclusion

This study provides protocols for evaluation of the msp1 gene in the avian malaria generalist parasite P. relictum. The msp1 gene in avian Plasmodium shares the genetic properties seen in P. falciparum, indicating evolutionary conserved functions for the gene. The data on the variable blocks of the gene show that the msp1 gene in P. relictum might serve as a good candidate gene for future population and epidemiological studies of the parasite.

Diversity covering AMA1-MSP119 fusion proteins as malaria vaccines

To overcome polymorphism in the malaria vaccine candidate Plasmodium falciparum apical membrane antigen 1 (PfAMA1), fusion protein chimeras comprised of three diversity-covering (DiCo) PfAMA1 molecules (D1, D2, and D3) and two allelic variants of the C-terminal 19-kDa region of merozoite surface protein 1 (MSP119) (variants M1 and M2) were generated. A mixture of fusion proteins (D1M1/D2M2D3) and the D1M1D2M2D3 fusion were compared to a single-unit mixture (D1/D2/D3/M1) in an immunological study in groups of rabbits. Following immunization, titers of antibodies (Abs) against four naturally occurring PfAMA1 alleles were high for all groups, as were growth inhibition assay (GIA) levels against two antigenically distinct laboratory parasite strains. Fusion of AMA1 to MSP119 did not suppress levels of antibodies against the AMA1 component. In addition, the breadth of antibody responses was unaffected. Anti-AMA1 antibodies were largely responsible for parasite growth inhibition, as shown in reversal-of-inhibition experiments by adding competing AMA1 antigen. For all groups, titration of the MSP119 antigen into the GIA led to only a small decrease in parasite inhibition, although titers of antibodies against MSP119 were increased 15-fold for the groups immunized with fusion proteins. GIA with affinity-purified anti-MSP119 antibodies showed that the 50% inhibitory concentrations of the anti-MSP119 antibody preparations were in the same order of magnitude for all animals tested, leading to the conclusion that fusing MSP119 to PfAMA1 leads to a small but significant increase in functional antibody levels. This study shows that combination of multiple vaccine candidates in fusion proteins may lead to improved characteristics of the vaccine.