Background: High maternal HIV viral load is an important risk factor for vertical transmission of HIV. In vitro, Plasmodium falciparum malaria antigens increase HIV-1 viral replication in monocytes. In vivo, malaria infection has been associated with a 7-fold increase in HIV-1 plasma concentration in non-pregnant adults. In pregnant women, P. falciparum infection may result in placental sequestration of malaria parasites, accumulation of monocytes, and a pro-inflammatory cytokine response. This could increase HIV replication and concentration in the placenta, thereby facilitating vertical transmission of HIV.

Method: We conducted a cross-sectional study of pregnant Malawian women to investigate whether peripheral and placental P. falciparum malaria infections are associated with high peripheral and placental HIV-1 RNA concentrations, respectively. We collected peripheral blood from consenting women in the third trimester of pregnancy for P. falciparum malaria and HIV-1/2 screening. Quantitative HIV-1 RNA assays were performed on peripheral plasma of HIV positive women. At the onset of active labor, HIV⁺ women received 200 mg oral nevirapine. Upon delivery, we performed quantitative HIV-1 RNA assays on placental plasma and malaria microscopy on placental blood films.

We used the Student t-test to compare means of normally-distributed continuous variables and the c² -test for comparison of categorical variables. Multiple linear regression analysis was performed to control for confounding factors.

Results: There were no statistically significant differences in peripheral plasma HIV-1 RNA concentrations between peripheral parasitemic and non-parasitemic women (mean log₁₀ HIV-1 RNA 4.64 and 4.47, respectively, p = 0.35). In contrast, placental plasma HIV-1 RNA concentrations were significantly higher in women with placental parasitemia than in those without placental parasitemia (mean log₁₀ HIV-1 RNA 4.17 and 3.73, respectively, p = 0.02). In univariate analysis, there was a negative association between cd4 count and placental plasma HIV-1 RNA concentrations, (adjusted R² = 0.09, p < 0.0001). In a multivariate analysis, both placental malaria status and cd4 count were significant predictors of placental HIV-1 RNA concentration (p = 0.01 and p < 0.0001, respectively, combined adjusted R² = 0.11).

These findings suggest that placental malaria results in elevation of placental viral load which might be associated with a high risk of vertical transmission of HIV.