Infrequent exposure to malarial parasites associated with increased infections

1. Reduction in maternal antimalarial IgG levels was associated with decreased prevalence of malaria over a 10-year period in pregnant women. 

2. Decrease in the prevalence of malaria over 10-year period in pregnant women was associated with increasing maternal parasite densities and larger adverse effect of infection on both mother and newborn.

Evidence Rating: 2 (Good)    

Study Rundown: Maintaining immunity to malaria requires boosting over time. Consequently, a reduction in population-level immunity to malaria may result from a decrease in exposure to P. falciparium. This phenomenon is particularly important for pregnant women, who are at increased risk of infection during pregnancy. VAR2CSA are antibodies found in pregnant women directed against P. falciparium CS2 strain which can reduce the clinical burden of malaria during pregnancy. In Mahica District in Souther Mozambique, the degree of malaria transmission has decreased over time. The researchers in this study aimed to better understand how the declining prevalence of malaria in pregnant women impacts antimalarial immunity and the effect of infection via parasitologic and immunologic markers. The researchers found that a decline in the prevalence of malaria was associated with lower levels of antimalarial IgG, greater maternal parasite densities, and worse maternal/newborn clinical effects.

Click to read the study, published today in NEJM

Relevant Reading: Malaria resurgence: A systematic review

In-Depth [prospective cohort]: The study included 1819 Mozambican women who delivered infants between 2003-2012 and were part of two clinical trials of antimalarial drugs between 2003-2005 (sulfadoxine-pyrimethamine x2) and 2010-2012 (meflouine x2 or sulfadoxine-pyremethamine x2 if HIV negative vs. TMP-SMX if HIV positive). The primary outcome variables included maternal microscopic infection and level of anti-CS2 IgG antibodies. Secondary variables included qPCR positivity for maternal infection, peripheral and placental blood infections, submicroscopic infections and levels of IgG antibodies against R29.

The prevalence of maternal infection decreased from 11% in the 2003-2005 trial to 2% in the 2010-2012 trial (adjusted OR=0.19; 95%[CI] = 0.12-0.3, p<0.001). Similar decreases were observed in secondary outcomes. Anti-CS2 IgG was lower in 2010-2012 than in 2003-2005 (adjusted OR=0.44; 95%[CI]=0.35-0.54, p<0.001). Parasite densities on peripheral blood analysis with qPCR were higher in 2010-2012 (409±1569 genomes/mL) than in 2003-2005 (44±169 genomes/mL) with p=0.02.

Image: PD

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