Abstract:
Background: Placental malaria (PM) causes adverse pregnancy outcomes in the mother and her foetus. It is difficult
to study PM directly in humans due to ethical challenges. This study set out to bridge this gap by determining the
outcome of PM in non-immune baboons in order to develop a non-human primate model for the disease.
Methods: Ten pregnant baboons were acquired late in their third trimester (day 150) and randomly grouped as
seven infected and three non-infected. Another group of four nulligravidae (non-pregnant) infected was also included
in the analysis of clinical outcome. Malaria infection was intravenously initiated by Plasmodium knowlesi blood-stage
parasites through the femoral vein on 160th day of gestation (for pregnant baboons). Peripheral smear, placental
smear, haematological samples, and histological samples were collected during the study period. Median values of
clinical and haematological changes were analysed using Kruskal-Wallis and Dunn’s Multiple Comparison Test.
Parasitaemia profiles were analysed using Mann Whitney U test. A Spearman’s rank correlation was run to determine
the relationship between the different variables of severity scores. Probability values of P <0.05 were considered
significant.
Results: Levels of white blood cells increased significantly in pregnant infected (34%) than in nulligravidae infected
baboons (8%). Placental parasitaemia levels was on average 19-fold higher than peripheral parasitaemia in the same
animal. Infiltration of parasitized erythrocytes and inflammatory cells were also observed in baboon placenta. Malaria
parasite score increased with increase in total placental damage score (rs = 0.7650, P <0.05) and inflammatory score
(rs = 0.8590, P <0.05). Although the sample size was small, absence of parasitized erythrocytes in cord blood and
foetal placental region suggested lack of congenital malaria in non-immune baboons.
Conclusion: This study has demonstrated accumulation of parasitized red blood cells and infiltration of inflammatory
cells in the placental intravillous space (IVS) of baboons that are non-immune to malaria. This is a key feature of
placental falciparum malaria in humans. This presents the baboon as a new model for the characterization of malaria
