Pathology of Placental Malaria in Baboons (Papio anubis) Experimentally Infected with Plasmodium knowlesi

Abstract

Pregnant women are more susceptible to malaria than non-pregnant women. Thissusceptibility is highest in first and second pregnancies of continuous malaria exposure.Placental malaria leads to poor birth outcomes and poor maternal outcomes whichinclude low birth weight (LBW), intrauterine growth retardation (IUGR), abortions, stillbirths, anaemia and mortality. This study set out to characterize placental pathologicalchanges in baboons infected with Plasmodium knowlesi parasites in order to develop amodel that can be used to study placental malaria. Third trimester placentas werecollected via caesarean section (CS) from four pregnant P. knowlesi infected and threepregnant-non infected baboons (Papio anubis). The placentas from all the animals wereexamined for gross pathology and histopathology. Findings of the study revealed thatparasitaemia was six to eight folds higher in the placenta compared to peripheral blood ofthe same baboon. Gross pathology revealed that placentas were intact and had normalmorphological features except in one baboon which showed slight fibrinoids.Histopathological findings showed that placentas from the control baboons had intactvilli, good tissue perfusion and no aggregation of erythrocytes. The placentas frominfected baboons on the other hand showed massive congestion of various layers,disruption of the villi, aggregation of erythrocytes, inflammatory cell infiltration,presence of infected erythrocytes and malaria pigment (haemozoin). The placental tissuesfrom the infected baboons had significantly more pathological changes as compared tothose obtained from the non infected baboons. This was evident when the median scoreswere compared for each parameter using the Mann-Whitney U test. Plasmodium knowlesiinfected placentas had significantly higher scores for damage (MedI = 22.5) compared tothe controls (MedC=13; p<0.05). Negative correlation was observed between placentaldamage and infant weight (r=-0.14, p>0.05) when tested by Spearman’s Rank correlationtest. This study demonstrates that P. knowlesi sequesters in the placenta of baboons anddamages it just like P. falciparum does in the placenta of humans. Consequently, thebaboon model of malaria is expected to gain prominence in the study of control measuresagainst placental malaria.Key Words: Papio anubis, Plasmodium knowlesi, placental malaria, histopathology.