The incidence of placental malaria at parturition and its effects on the conceptus have been investigated in The Gambia, West Africa. Malarious placentae occurred in 1300 (20.2%) of 6427 singleton births, in 32 (18.6%) of 172 sets of twins and in none of six sets of triplets. Plasmodium falciparum infections predominated; P. malariae or P. ovale infections were found in only nine instances. In the large group of single births placental malaria occurred less frequently (12.0%) in residents of urban than of other, more rural, communities (27.1%). In the former group incidence showed no clear change with season; in the latter group it was highest in the trimester following the end of the rains and lowest in the second half of the dry season. In both residential groups it was more frequent in primiparae (urban 16.1%; other 46.9%) than in multiparae (urban 8.9%; other 20.3%). The sex of the child did not influence malaria incidence. Dense placental infections were more frequent in primiparae. Stillbirth rates of singleton infants were significantly higher for males than for females, but no clear and consistent relationship between stillbirth and placental malaria was detected. Mean singleton birthweights were depressed by about 170 g in the presence of malaria; the deficits were statistically significant only among first born infants and tended to diminish progressively with increasing maternal parity. No distinct gradient linking birthweight with ascending density of placental parasitaemia was observed. Singleton birthweights of 2.5 kg or less occurred more frequently in association with malarious than non-malarious placentae and the association was more marked among first born than later birth rank infants. Differences between the weights of malarious and non-malarious placentae were small and not significant. The findings of the study are discussed in relation to the widely prevalent view that pregnancy exacerbates maternal malaria by attenuating acquired immunity.

Malaria infection of the placenta in The Gambia, West Africa; its incidence and relationship to stillbirth, birthweight and placental weight

Antibodies raised against a Plasmodium falciparum protein expressed in Escherichia coli reacted with a 220,000-molecular weight antigen of mature blood-stage parasites The protein resembles the sporozoite surface antigen being composed of tandem repeats of 11 amino acids However, it is isolate-specific and the encoding gene is not detectable in strains that do not express the protein

Isolate-specific S-antigen of Plasmodium falciparum contains a repeated sequence of eleven amino acids.

Primary structure and localization of a conserved immunogenic Plasmodium falciparum glutamate rich protein (GLURP) expressed in both the preerythrocytic and erythrocytic stages of the vertebrate life cycle

Publisher Summary This chapter focuses on those forms of genetic diversity that are clearly understood at the deoxyribonucleic acid (DNA) level. The application of recombinant DNA technology to the study of Plasmodium falciparum and other species of Plasmodium has resulted in rapid advances in the understanding of genetic diversity in malaria. Variation in repeat sequences from one isolate to another forms a major component of genetic diversity in Plasmodium. The introduction of pulsed field gradient (PFG) electrophoresis has allowed one to study Plasmodium chromosomes, and there is considerable variation in chromosome size from one parasite clone to another. A major component of this variation appears to be recombinational expansion and contraction of repetitive subtelomeric sequences. As many of the repetitive antigens are also encoded by subtelomeric genes, there is a possible connection between antigenic diversity and chromosome size variation. The results of the first genetic cross between two defined clones of P. falciparum together with the determination of the chromosomal location of many of the genes demonstrate that during the transmission of mixed infections, novel genotypes are generated. The underlying molecular basis for another important form of genetic diversity––namely, resistance to an important antimalarial drug, pyrimethamine––has now been determined. A candidate gene that may underlie resistance to the other major antimalarial drug, chloroquine, can now been cloned. However, before studies at the DNA sequence level, studies using a wide variety of approaches had clearly identified a number of different types of genetic diversity in Plasmodium.

Genetic diversity in Plasmodium falciparum.

https://www.cell.com/cell/pdf/0092-8674(85)90337-X.pdf

Conserved sequences flank variable tandem repeats in two α-antigen genes of Plasmodium falciparum

Gambians with severe Plasmodium falciparum infections frequently have malarial S-antigens in their serum or plasma. Detection of these with the available antisera which are from immune adults is complicated because there are many different S-antigens and none of the antisera contains antibodies to them all. Despite this we found S-antigens in about 60% of a large series of malarious children and demonstrated that this was a considerable underestimate of the true incidence. We also showed that the prevalence of S-antigens was related to the malaria season and to the intensity of infection.

Occurrence of S-antigens in serum in Plasmodium falciparum infections in man

The persistence of heat stable malarial antigens (S-antigens) in the sera of Gambian children following treatment for severe Plasmodium falciparum infections was investigated. In most cases S-antigens ceased to be demonstrable within 7 days but in some they were detected for several weeks and their persistence correlated with both the density of parasitaemia and the antigen titre observed before treatment. An exponential loss of circulating antigen was, in the majority of individuals, accelerated by some other factor which might have been homologous antibody. Renewal of asexual parasitaemia usually resulted in reduction in the rate of antigen loss or in an increase in antigen level. When the aparasitaemic interval was a month or less the antigens associated with different parasitaemic episodes usually showed identical specificities; when the interval was longer they were usually antigenically distinct. These findings may indicate that relapse parasites usually show the same S-antigen specificities as their progenitors while parasites arising from distinct infections tend to show different specificities and could therefore support a view that considerable antigenic heterogeneity exists among the parasites that comprise P. falciparum populations in endemic areas.

Persistence and recurrence of S-antigens in plasmodium falciparum infections in man

Precipitating antibodies and immunoglobulins in P. falciparum infections in the Gambia, West Africa

Sera from Nigeria, West Africa were used in detailed examinations of the S-, L- and R-classes of malarial antigens which are associated with the precipitating antibody response to P. falciparum in Gambia. The Nigerian sera contained antibodies to nearly all of the Gambian malarial antigens which were presented. This indicates a considerable degree of common antigenicity throughout the West African region despite the overall antigenic complexity.

R.J.M. Wilson

Papers

Occurrence of S-antigens in serum in Plasmodium falciparum infections in man

Persistence and recurrence of S-antigens in plasmodium falciparum infections in man

Precipitating antibodies and immunoglobulins in P. falciparum infections in the Gambia, West Africa

Antigens and antibodies associated with Plasmodium falciparum infections in West Africa