Antibodies are central to acquired immunity against malaria. Plasmodium falciparum elicits antibody responses against many of its protein components, but there is also formation of antibodies against different parts of the red blood cells, in which the parasites spend most of their time. In the absence of a decisive intervention such as a vaccine, people living in malaria endemic regions largely depend on naturally acquired antibodies for protection. However, these antibodies do not confer sterile immunity and the mechanisms of action are still unclear. Most studies have focused on the inhibitory effect of antibodies, but here, we review both the beneficial as well as the potentially harmful roles of naturally acquired antibodies, as well as autoantibodies formed in malaria. We discuss different studies that have sought to understand acquired antibody responses against P. falciparum antigens, and potential problems when different antibodies are combined, such as in naturally acquired immunity.

Babesia is spread to humans via ticks or blood transfusions. Severity of Plasmodium falciparum malaria is strongly correlated to the ABO blood group of the patient. Babesia divergens is an intraerythrocytic parasite with many similarities to malaria, but the impact of ABO on the susceptibility to and progression of the infection in humans is unknown. We have now cultured B. divergens in human group A, B and O erythrocytes in vitro and measured rates of multiplication. The predilection for the different erythrocyte types was also determined using an in vitro erythrocyte preference assay when the parasites were grown in group A, B or O erythrocytes over time and then offered to invade differently stained erythrocytes of all the blood types at the same time. The results showed no difference in multiplication rates for the different blood types, and the parasite exhibited no obvious morphological differences in the different blood types. When cultured first in one blood type and then offered to grow in the others, the preference assay showed that there was no difference between the A, B or O blood groups. In conclusion, this indicates that individuals of the different ABO blood types are likely to be equally susceptible to B. divergens infections.

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.

Genetic diversity in Plasmodium falciparum poses a significant challenge to malaria control and elimination. This is particularly important for developing fully efficacious vaccines, which should include valuable blood stage antigens. Several antigen candidates are highly diverse and require further understanding. We surveyed the genetic diversity of the highly polymorphic merozoite surface protein 2 (MSP2) in 2761 P. falciparum isolates collected across Sub-Saharan Africa. Using PCR-based genotyping and long-read sequencing, we identified extensive diversity among msp2 size variants and sequences. Some size variants were more prevalent than others across different geographical regions, transmission intensities, and time points. These variants comprised multiple unique sequences, of which several were geographically and temporally widespread. Our study reveals greater msp2 sequence diversity than previously known, while also identifying interesting similarities in sequence and gene length across Sub-Saharan Africa. These findings support the further exploration of common msp2 variants in relation to parasite virulence and vaccine development.

Human babesiosis is an emerging disease as more cases are being reported worldwide. Most cases in Europe are caused by Babesia divergens, whereas most cases in North America are due to Babesia microti. While B. microti is also found throughout Europe, it appears to be less pathogenic. We generated high-quality nuclear and organellar genome assemblies of two B. divergens and two B. microti isolates from Germany by long-read sequencing and compared them with each other and with the reference RI B. microti from the US. Variants of VESA1 (variant erythrocyte surface antigen 1) and secreted antigen 1/3 dominated the genes of the B. divergens isolates. The B. microti isolates and RI B. microti lacked VESA1. However, the B. microti isolates were different by their lack of 37 other proteins found in RI B. microti. These RI-specific proteins were intracellular, secreted, and membrane-bound. The lack of one or more of these genes by the new B. microti isolates may be the reason for why US strains are more pathogenic than B. microti from Europe. The ability of B. divergens to evade the immune system using VESA1, perhaps in combination with some secreted antigens, may be responsible for its higher pathogenicity compared with the European B. microti strains. This study has improved our understanding of the pathogenesis of babesiosis, and the new genomic data provided here has increased the repertoire of available genomic information about Babesia, especially since our new B. microti genomes are the first from Europe.

Babesia is an intraerythrocytic parasite transmitted by ticks or through blood transfusion, and it can cause babesiosis with symptoms such as fever, anemia, and organ failure. The parasite is closely related to the mosquito-borne Plasmodium falciparum, which causes malaria. Several studies have shown that individuals with blood group O have a reduced risk of severe malaria compared to individuals with other ABO blood groups. Whether or not this is also the case for babesiosis has not yet been clearly investigated. In this study, serum samples from over 650 individuals were analyzed using an ELISA assay to detect antibodies against Babesia divergens. The ABO blood groups of the same samples were determined using a conventional method. There was no difference in B. divergens IgG antibody levels between the different ABO blood groups, nor was there any difference in the percentage of positive reactions in the ELISA against B. divergens between the different blood groups. This could indicate that the development and maintenance of B. divergens antibodies are not influenced by ABO blood groups.