Isolation of recurrent mycobacteium isolates from sputum smear negative relapse at the central reference tuberculosis laboratory in Nairobi, Kenya

Abstract

Pregnant women have increased susceptibility to malaria infection. In these women, malaria parasites are frequently found sequestered in the placental intervillous spaces, a condition referred to as placental malaria (PM). Placental malaria threatens the health of the mother and the child's life by causing intrauterine growth retardation, abortions, still births and reduction in gestational age. An estimated 24 million pregnant women in SubSaharan Africa are at risk. Mechanisms responsible for increased susceptibility in pregnant women are not fully understood. Baboons are susceptible to Plasmodium knowlesi and have similar host pathogen interactions and reproductive physiology similar to humans, making them attractive for the development as a model for studying mechanisms underlying development of placental malaria. This study exploited the susceptibility of baboons to Plasmodium knowlesi infection to develop a non-human primate (baboon) model for studying PM. The main objective of the study was to demonstrate PM and characterize immunological mechanisms underlying the pathogenesis of PM in baboons infected with Plasmodium knowlesi. The pregnancies of three time mated adult female baboons and their gestational levels (one in its second trimester and two in their third trimester) were confirmed by ultrasonography. On the 150th day of gestation, the pregnant baboons were infected with Plasmodium knowlesi H strain parasites together with four non pregnant controls. Peripheral parasitaemia development was monitored on a daily basis from two days post inoculation. Collection of sera, plasma, mononuclear cells and haematological samples was done on a weekly basis. Peripheral blood mononuclear cells (PBMC) were stimulated in culture with concanavalin A and P. knowlesi antigens and their proliferation quantified. Sera cytokine and immunoglobulin concentrations were measured by ELISA using respective enzyme conjugated antibodies. Two pregnant baboons aborted (one on day 6 and the other on day 7 post infection) and cesarean section was only done on one baboon. Smears prepared from placental blood demonstrated the presence Plasmodium knowlesi parasites in all the sampled placentas. On average, the pregnant baboons had more than 29 fold higher placental parasitaemia than simultaneous peripheral parasitaemia. This shows that Plasmodium knowlesi preferentially sequesters in the baboon placenta just like Plasmodium falciparum does in humans. Two baboons that had high placental parasitaemia experienced abortion, which is a sequele of human placental malaria. Results indicate that PM in this model is associated with significant (P < 0.05) suppression of immunoglobulin G, Interferon gamma, and interleukin 6 responses. Tumour necrosis factor alpha responses were significantly upregulated (P < 0.05) while immunoglobulin M, interleukin 10, interleukin 12, interleukin 4 and PBMC proliferation responses did not differ from controls (P > 0.05). These data are consistent with some findings from human studies, showing the feasibility of this model for studying mechanisms underlying placental malaria. The study has contributed valuable data to be used in further studies and the development of preventative, control and therapeutic measures against PM in women