According to a study recently published in the scientific journal The Lancet Global Health, more than half of infections by malaria during pregnancy are not detectable by microscopy and yes, only by molecular tests and, according to the researcher CISM and do Global Health Institute of Barcelona (ISGlobal) Alfredo Mayor, one of the authors of the article, the data now published reveal the importance of using molecular surveillance to detect infections with low density malaria parasites.
"Silent" infections pose a challenge...
According to data in the article, malaria infection during pregnancy poses a serious risk to the health of mother and baby. However, many infections in pregnant women go unnoticed because they cause few symptoms and are "submicroscopic" (i.e. not detected by the usual microscopy test due to the low number of parasites in the blood, but by more sensitive molecular tests such as PCR) . These "silent" infections pose a challenge, not only to the management and prevention of malaria in pregnant women, but also to malaria elimination efforts.
The study resulted from an analysis of 68 studies conducted between 1995 and 2017 in 27 countries (54 in Africa, 8 in Asia and 7 in the Americas), including Mozambique, whose purpose was to better understand the frequency of these infections globally , as well as associated risk factors, through a systematic review and meta-analysis of these studies. The results illustrate that, on average, 13% of pregnant women had submicroscopic infection and 8% microscopic infection.
Decreased parasite genetic diversity and persistence of immunity
Also according to the study, of the total number of infections detected by molecular methods, the majority were submicroscopic (59%) during pregnancy and up to 74% during childbirth. The highest percentage of submicroscopic infections was observed in areas with less transmission of the disease and "the reasons are complex, but probably have to do with the type of parasite (P. vivax or P. falciparum), the genetic diversity of the parasite and the persistence of immunity in areas where the burden of the disease has rapidly decreased", comments Alfredo Mayor.
For Mayor, “the use of molecular surveillance to detect infections with low-density malaria parasites allows pregnant women to have access to adequate and timely treatment and, ultimately, contributes to reducing parasite transmission, an opportunity to eliminate the disease.”
van Eijk AM, Stepniewska K, Hill J, et al. Prevalence and risk factors for microscopic and submicroscopic malaria infections in pregnancy: a systematic review and meta-analyses. Lancet Global Health. 2023. doi: 10.1016/S2214-109X(23)00194-8 %00