In areas of stable Malaria transmission like Nigeria, the dynamics of our everyday ‘ordinary malaria infection’ changes for a pregnant woman. Understanding this basic fact is particularly important for new mums who already have to deal with many other physiologic/normal body changes of Pregnancy.
The countdown continues from 50 Things you do Not know about Malaria in Pregnancy as featured in HALA Magazine (Malaria Edition).
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16. Adults in malaria prevalent countries possess an acquired immunity which prevents them from having malaria frequently and also protects against severe complications
17. During pregnancy, this immunity wanes and may only manage to keep the infection at a state where there are no typical symptoms and this happens in a majority of women
18. However, this acquired immunity is unable to perform any more protective functions
19. Women with their first and second pregnancy are at the greatest risk of the hazardous effects of malaria
20. In malaria-endemic regions, each pregnancy allows a woman to develop an immune response that protects against parasite accumulation within the placenta
21. From the third pregnancy women are at lower risk of malaria complication due to this specially acquired immune response to the parasite in the placenta.
22. Malaria in pregnancy is characterized by a unique accumulation of P. falciparum-infected red blood cells (medically called “sequestration”) within the placental bed.
23. Sequestration is the localization of P. falciparum infected red blood cells in the microvasculature of organs such as the kidney, brain and the placenta.
24. This sequestration is made possible by the presence of certain red blood cell chemical receptors present only in pregnant women that permits attachment to the placenta
25. The complications of malaria in pregnancy are therefore caused by the massive sequestration of these infected red blood cells in the placenta
WHAT is unique about Malaria in Pregnancy?
In the tropics, recurrent malaria infection helps adults to develop a form of resistance to malaria as the body system has grown to recognize the P. falciparium parasite. This “resistance” is what is referred to as an “Acquired Immunity” –acquired because no one is born with it.
While this immunity DOES NOT entirely prevent a malaria attack, it helps to safely limit the infection by preventing severe complications of malaria. The natural stress of pregnancy reduces this functionality and P. falciparium additionally adopts a special attachment to the placenta… which can only be present in a pregnant woman.
Infection by the Plasmodium falciparium specie of malaria parasite can have dire consequences during pregnancy. The reason is that the infected red blood cells express a uniquely different subset of variant surface antigens within the PfEMP1 protein family, which is not found in non-pregnant individuals. It is this peculiarity that enables the infected red blood cells to selectively bind with Chondroitin Sulfate A (CSA), which is responsible for cytoadhesion at the placenta receptors. All the attendant complications of malaria to the unborn child is based on the premise of this hidden attachment and multiplication of the malaria parasite within the placenta.
However also within malaria-endemic regions, a natural protective immunity against malaria in pregnancy is also eventually acquired by women in the course of subsequent pregnancies. This special acquired immunity is as a result of developing anti-PfEMP1 antibodies which now recognize those uniquely marked placental infected red blood cells within the woman.
These antibodies are female-specific (that is, not produced by males) and they are parity-dependent (that is, increases with number of pregnancies). Thus with subsequent pregnancies, especially from the third and above, the immune response against the malaria parasites increases and therefore the risk of developing severe consequences of malaria in pregnancy is minimized.
Depending on the prevalence of malaria in an area, it can be expected that as much as 50% of pregnant women may carry malaria parasites in their blood especially within the placenta, without noticing it.