Journal of Vector Borne Diseases

RESEARCH ARTICLE
Year
: 2021  |  Volume : 58  |  Issue : 4  |  Page : 311--316

Malaria parasite density and plasma apolipoprotein A1 in symptomatic and asymptomatic infections in Nigerian children


Bose E Orimadegun1, Georgina O Odaibo2, Adebola E Orimadegun3, Emmanuel O Agbedana1, Catherine O Falade4,  
1 Department of Chemical Pathology, College of Medicine, University of Ibadan, Ibadan, Nigeria
2 Department of Virology, College of Medicine, University of Ibada, Ibadan, Nigeria
3 Institute of Child Health, College of Medicine, University of Ibadan, Ibadan, Nigeria
4 Department of Pharmacology & Therapeutics, College of Medicine, University of Ibadan, Ibadan, Nigeria

Correspondence Address:
Dr. Bose E Orimadegun
Department of Chemical Pathology, College of Medicine, University of Ibadan, Ibadan
Nigeria

Abstract

Background & objectives: Alterations in plasma apolipoproteins in individuals with malaria infection and their potential roles in the pathogenesis are known but the link between the malaria parasite density and apolipoprotein A1 (apo-A1) level is insufficiently understood. This study was conducted to determine whether the plasma apo-A1 level is influenced by the degree of parasitaemia in malaria infections. Methods: In a case-control study, a convenient sample of children aged 2–10 years with uncomplicated malaria cases (UMC), asymptomatic parasitaemia cases (APC) and healthy children without parasitaemia (HCP) was recruited. The cases consisted of 61 UMC and 21 APC, while the controls consisted of 24 HCP. Levels of apo-A1 was determined using immunoturbidimetric assay and compared among the different degrees of parasite density. Results: Of the 82 participants with parasitaemia, density was ≤1000/μL in 12, 1001-10000/μL in 21 and >10000/μL in 49 children. There was significant difference among the mean values of apolipoprotein A1 of the three groups, viz: UMC [91.4 (95% CI: 81.3, 101.5) mg/dL], APC [67.0 (95% CI: 48.9, 84.9) mg/dL] and HCP [99.0 (95% CI: 76.6, 121.3) mg/dL], p=0.029. Post-hoc analysis revealed that the mean plasma level of apo-A1 in HCP was significantly higher than APC by 32.0±12.4 mg/dL and UMC by 7.5±4.2 mg/dL. However, there were no differences in the mean apolipoprotein A1 levels among the three groups of parasite density. Interpretation & conclusion: The presence of parasitaemia causes a remarkable reduction in apolipoprotein A1 level that was not influenced by the degree of parasitaemia.



How to cite this article:
Orimadegun BE, Odaibo GO, Orimadegun AE, Agbedana EO, Falade CO. Malaria parasite density and plasma apolipoprotein A1 in symptomatic and asymptomatic infections in Nigerian children.J Vector Borne Dis 2021;58:311-316


How to cite this URL:
Orimadegun BE, Odaibo GO, Orimadegun AE, Agbedana EO, Falade CO. Malaria parasite density and plasma apolipoprotein A1 in symptomatic and asymptomatic infections in Nigerian children. J Vector Borne Dis [serial online] 2021 [cited 2022 Jul 1 ];58:311-316
Available from: https://www.jvbd.org/text.asp?2021/58/4/311/318309


Full Text



 Introduction



Malaria affects several millions of children in sub- Saharan Africa, sharing nearly 80% of global malaria burden with India despite years of concerted efforts to control the disease. According to the World Health Organization’s 2019 report on malaria for the period 2015-2017, “no significant progress has been made in reducing global malaria burden”[1]. Of the five countries reported to have contributed nearly half of all malaria cases worldwide, Nigeria leads the Democratic Republic of Congo, Mozambique, India and Uganda by contributing 25% of the cases[1]. The net result of this menace is that approximately 55 million out of an estimated 219 million cases of global malaria occurred in Nigeria in 2015 to 2017; the majority of which were children and pregnant women. Children under 5 years of age remain the most vulnerable group to malaria, accounting for 61% of the 266,000 global malaria deaths in 2017, of which 19% occurred in Nigeria[1].

There are indications that clinical manifestations of malaria vary between susceptible individuals, ranging from asymptomatic, uncomplicated to life-threatening, and that the pathogenesis and pathophysiology of these morbidity varieties is incompletely understood. Studies have shown that malaria manifestations involve a complex range of parasite-host interactions and diverse immune responses affecting both parties[2],[3]. Essentially, the parasite relies on the metabolic exchange with the human host to ensure continued existence[2],[3]. Some of the explanations put forward in literature for the variability of malaria manifestations in children are immune responses and excessive inflammation that are significantly influenced by the interaction between malaria parasites’ and hosts’ nutrient-derived metabolites during the acute phase of infection[4],[5]. There are many known nutrient-derived metabolites that contribute to innate and adaptive immune responses, including lipids and trace elements[6].

More attention has been drawn in recent years to the role of lipids and lipoprotein metabolism in the pathogenesis and pathophysiology of infectious diseases[7],[8]. A variety of changes in plasma concentrations of lipids and lipoprotein metabolism have been attributed to infection and inflammation occurring in several diseases[9]. Significant changes during infection and inflammation include increased triglyceride levels due to increased low-density lipoprotein levels and decreased high-density lipoprotein (HDL) levels[10],[11]. Another recently emphasized dynamic is the role of lipoproteins in the immune system and the acute phase response in infectious diseases. Generally, infections induce oxidation of LDL cholesterol, which in turn plays important anti-infective roles, and there is evidence that lipoproteins may detoxify lipopolysaccharide and lipoteichoic acid[5]. In the case of malaria infection, the nature and magnitude of the parasite-induced immune response determine the clinical outcome of the acute malaria episode as well as the susceptibility to subsequent attacks[12],[13]. This complex interaction between the metabolism of lipids and the modulation of host immune responses during malaria is a relatively new and emerging area of interest.

Studies have investigated plasma lipid alterations during malaria illness in both children and adults but data on apolipoproteins are limited. A systematic review and meta-analysis published by Visser et al. 2013, revealed that cholesterol, high-density lipoproteins (HDL) and low-density lipoproteins (LDL) concentrations are lower in malaria than healthy controls. However, only five studies reported apolipoproteins (Apo) and the data were insufficient for meta-analysis[14]. Another publication in 2017, after the systematic review, reported no significant difference in Apo A1 of malaria patients compared with health controls[15]. Besides, we had earlier investigated the effects of malaria infection on plasma lipids among Nigeria children[16]. Although, our previous study demonstrated alterations in plasma apolipoproteins (apo-A1) levels during malaria infections[16] the link between the degree of malaria parasite density and the apo-A1 level was not explored. This study was conducted to determine whether the level of apo-A1 is affected by the degree of parasitaemia in individuals with uncomplicated and asymptomatic malaria infections.

 Material & Methods



Study design and setting

We conducted a case-control study at the Kola Daisi Foundation (KDF) Health Centre, a primary health facility in suburban area of Ibadan, Nigeria and two rural nursery and primary schools in Akinyele Local Government Area of Ibadan, Nigeria. Study participants comprised uncomplicated malaria cases (UMC), asymptomatic parasitaemia cases (APC) and healthy children without parasitaemia (HCP).

Study population, sample size and sampling

Children aged 2 to 10 years were enrolled into the study. This category of individuals was accessed through nursery and primary schools and outpatient clinics. Children in the target age group are also relatively more susceptible to malaria infection than others in endemic areas such as Ibadan, south-west, Nigeria. However, infants were excluded in the study because of the inconvenience of blood sample collection in primary health facility and school environment where cases and controls were recruited, respectively. Using the mean ±standard deviation plasma apo-A1 level of 129.7±48.3 mg/dL obtained in apparently healthy children in our previous study[17] at 95% level of confidence and power of 80%, a minimum of 20 participants were required in each group as hypothesized difference of 40 mg/dL was envisage. Sixty-one children who presented with history of fever and microscopically confirmed malaria parasitaemia [uncomplicated malaria cases (UMC)] were consecutively enrolled into the study at KDF health centre. The controls were randomly selected from apparently healthy children aged 2-10 years in two schools. Forty-five school children with a history of fever for two weeks prior to study visits, whose parents gave their consent, were enrolled, screened for malaria parasitaemia, and subsequently classified as 21 asymptomatic parasitaemia children (APC) and 24 healthy controls without parasitaemia (HCP).

Data collection and laboratory analysis

General physical examination was done; weight and height were documented. A validated questionnaire was used to obtain information on socio-demographic characteristics and clinical findings by the physician. Venepuncture and finger pricks were carried out by trained professionals using aseptic technique. Peripheral blood films were prepared according to recommended standard procedure as described in a previous publication[17]. The level of apo-A1 was determined by immunoturbidimetric assay using the Fortress Diagnostics™ kit (Fortress Diagnostics, United Kingdom).

Data analysis

Data were entered into a computer and analysed using Statistical Package for Social Scientists (SPSS) 20.0 for Windows (IBM Corp, Armont, NY, USA). Data were summarised as mean, standard deviation, median and range. Analysis of variance (ANOVA) was used to compare apo-A1 levels among the three groups of parasite categories. Post-hoc analyses were also done. Values and differences were graphically displayed using the box and whisker plot. p value less than 0.05 was considered statistically significant.

Ethical statement

Ethical approval was obtained from UI-UCH Ethics Review Committee (UI/UCH ERC assigned number UI/ EC/17/0268). Individual informed consent was obtained from the parents/guardians of prospective enrolees in KDF Health Centre. Permission was sought from school head teachers and written informed consent were obtained from parents for the children accessed in schools. The study was carried out in line with the ethical principles as stipulated in the Declaration of Helsinki. Symptomatic children needing medical attention received appropriate care according to the standard treatment protocol of the health centre.

 Results



Characteristics of participants

The study participants included 61 uncomplicated malaria cases and 21 asymptomatic parasitaemia cases of malaria, as well as 24 apparently healthy controls without malaria parasitaemia. There were 55 (55.6%) males and 51 (45.4%) females. [Table 1] shows the distributions of participants by sex and nutritional status. There was no significant difference between the three groups. The median parasite count for uncomplicated malaria cases was significantly higher than that for the asymptomatic malaria group, p <0.001 [Table 1].{Table 1}

Apolipoprotein A1 levels in participants

[Figure 1] displays box and whisker plots showing the distribution of apolipoprotein A1 as median, interquartile range and minimum and maximum values. The mean levels of apolipoprotein A1 for children with uncomplicated malaria (UMC) [91.4 mg/dL (95% CI= 81.3, 101.5], asymptomatic malaria parasitaemia (APC) [67.0 mg/dL [95% CI= 48.9, 84.9)], and healthy control without patent parasitaemia (HCP) [99.0 mg/dL [95% CI = 76.6, 121.3)] were significantly different (p= 0.029). The results of the post-hoc analysis in [Table 2] showed that there was no significant difference between the mean apolipoprotein A1 levels in UMC and APC (p= 0.081). However, the mean apolipoprotein A1 level in the UMC group was 7.5±4.2 mg/dL higher than that in the HPC group (p = 0.043). The mean apolipoprotein A1 levels in the HPC group were 32.0±12.4 mg / dL higher than APC (p = 0.032).{Figure 1}{Table 2}

Apolipoprotein A1 levels and degree of parasitaemia The malaria parasite density ranged from 40 to

204,840 μL/mL (median = 17,390 μL/mL). The median parasite density of the UMC group (median = 26,320 μL/ mL) was significantly higher than that of APC (median = 932 μL/mL), p <0.001. The mean plasma apolipoprotein A1 levels were compared among the three categories of parasite density as shown in [Table 3]. There were no statistically significant differences in mean apolipoprotein A1 levels within and between UMC and APC groups.{Table 3}

 Discussion



This study showed that the magnitude of the observed lowering effect of malaria infection on apo-A1 is the same in children with uncomplicated and asymptomatic malaria cases and it is not related to the degree of parasitaemia. Although low plasma apo-A1, hypocholesterolaemia and hypertriglyceridemia have been reported in uncomplicated and complicated malaria patients from the same target population of our study[17],[18], none of the reports provided information on the effect of parasite density. To our knowledge, no data are available in the literature to indicate whether changes in plasma apolipoprotein are related to the level of parasitaemia and our data would appear to be the first to investigate this relationship. The search for newer molecules to target for malaria treatment and controls continues to be the focus of discussion as malaria remains a major contributor to child morbidity and deaths in endemic areas. Several published articles have implicated and discussed the roles of lipids in the pathogenesis of malaria and its potential for therapeutic targets, but little is known about apolipoprotein which plays important role in maintenance of erythrocyte membrane[19]. Mechanisms for changes in the level of lipids in malaria infections and their impact also constitute controversies in literature, although several hypotheses have already been put forward[20].

The reason for the lack of relationship between the degree of parasitaemia and levels of apo-A1 is not clear. However, it may have something to do with the fact that peripheral malaria parasitaemia is not necessarily a reflection of the parasite load in an infected person. Another possible explanation is that malaria parasites might not have a direct effect on apo-A1 but influence it through decreasing level of HDL-c. Apo-A1 is a structural protein that accounts for about 70% of HDL-c which has been shown to decrease remarkably during malaria infection[20]. In addition, it has also been postulated that plasma apo- A1 was low because the massive release of endotoxin during infections changes the composition of HDL-c by depleting phospholipids and apo-A1[21]. Thus, the degree of the parasite density could not have directly impacted on the apo-A1 level. Notably, our data corroborated this assertion as we found no significant correlation between parasite counts and the level of plasma apo-A1. Some authors have posited that apolipoproteins play a key role in the intra-erythrocyte development of malaria parasites and that if any of its isoforms have different lipid-bearing or transferable properties, it may interfere with the growth of parasites and the progression of malaria[22],[23]. It is conceivable, therefore, that if apolipoproteins could hinder the growth of the parasite, the degree of parasite density should be a function of apolipoproteins level, but this was not found in our study. Accordingly, this line of thinking supports the unlikely direct effect of malaria parasite on human apo-A1 levels.

The low apo-A1 observed in our data agrees with reports of three other groups of researchers[24],[25],[26]. A cross-sectional study of P. falciparum-infected patients and healthy controls found a decrease in patients’ apo-A1 compared to uninfected individuals[24]. Kittl et al.[25] also observed decreased apo-A1 in malaria patients and demonstrated a very strong correlation with HDL-c. In another report of a pilot study which examined the relationship between nutrition and immunity in Colombian children, a remarkably lower level of apo-A1 was found in malaria patients compared to healthy controls[26]. On the contrary, Cuisinier-Raynal et al.[27] and Visser et al.[15] did not detect any significant differences in apo-A1 levels between malaria patients and controls, however, mean apo-A1 values were not reported in the former. The observed low apo-A1 levels in the present study are expected because acute infections and inflammation such as in malaria illness have generally been shown to cause changes in plasma lipoprotein pattern in human, with a typical increase in plasma triglyceride concentrations and a decrease in HDL-c[11],[28]. A recent study has found that levels of lipoprotein in relation to healthy controls, encephalitis, and sepsis are especially disturbed by malaria infection[29].

Besides the host-related acute-phase changes in lipids, there is evidence that the parasite-related lipid profile also changes[29]. It has been put forward that the host lipids and apolipoproteins serve as materials used to form malaria pigment called hemozoin which is the product of free haeme plasmodial detoxification[30]. Also, the evidence that haemozoin is sequestered and constantly engulfed by phagocytes in the liver, spleen, and brain suggests that it plays significant role in malaria immunopathogenesis[31],[32],[33]. Thus, indicating that host plasma lipid alongside apo-A1 might be constantly consumed in the process thereby leading to decreased plasma level. From this observation, it is conceivable that apo-A1 could be a useful biomarker for malaria infection as indicated in the earlier study[17], but the extent to which it is reduced may not necessarily correspond to the level of malaria parasitaemia.

While this study reinforces previous findings on the link between apo-A1 changes during malaria infection, further studies are needed to clarify the mechanisms of reduction in host plasma apo-A1 level and other lipid alterations as well as their role in malaria illness pathogenesis. New treatment strategies such as those capable of lipid metabolism-regulating molecules could be investigated as P. falciparum selectively consume apo-A1 with HDL-c particles. One main limitation of our study is that it was impossible to ascertain whether apo-A1 levels were low because of the malaria episode, or whether the patients were susceptible to malaria infection because of low plasma lipids caused by another mechanism. The answers to these questions could be the subject of future research using a cohort study design to measure baseline Apo A1 levels prior to exposure to malaria infection.

Conflict of interest: None

 Acknowledgements



This research was supported by University of Ibadan MEPI Junior Faculty Research Training Program (UI-MEPI-J) supported the Fogarty International Center at the U.S. National Institutes of Health (NIH) - Project No.: 5D43TW010140-03. Authors are grateful to all the children and their parents/guardians for participating in this study. The authors are also grateful to Mrs Bolatito Akinyele, Mrs Iyabo Abdulsalam and Ms Grace Egunyomi, Malaria Laboratory of the Institute of Advanced Medical Research and Training, University of Ibadan for technical assistance.

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