While everyone has the right to live healthily throughout their lifetime, providing adequate health care is a serious challenge [1]. Malaria is a global health concern, with 214 million cases reported in 2015. Approximately 438,000 of the cases resulted in death, 88% of which occurred in African [2]. The other report showed 212 million cases of malaria with 429,000 deaths [3], where 92% of the deaths were reported to have occurred in African, followed by South-East Asia (6%) and Eastern Mediterranean Region (2%). Further, an estimated 216 million global malaria cases were reported, of which 90% were in Africa [4]. Every year, many international travellers fall ill with malaria while visiting endemic regions, and more than 10,000 visitors have confirmed to have fallen sick with the disease after returning home; however, the cases are underreported, which means that the real number of illness cases is much higher [5]. A recent estimate shows a significant burden of malaria on health systems and the broader economy, particularly in Africa, which places a significant economic burden on households in paying for prevention and treatment [6]. Insecticide-treated mosquito nets (ITNs) were identified as the most effective malaria prevention approach [7] and have decreased malaria incidences by 50% in various settings and malaria mortality rates by 55% in children under five years old in Sub-Saharan Africa [4]. African heads of government set a target of 60% coverage of bed nets for use by pregnant women and children under five years by 2005 following the Abuja summit in 2000 [8]. Since the introduction of the intervention strategy, there has been significant success in the malaria programme. Between 2000 and 2015, malaria cases decreased by 48% worldwide [2]. However, the disease remains the leading cause of maternal and child morbidity and mortality in low-resource countries; for example, Ethiopia accounts for 6% of malaria cases worldwide and about 12% of global concerns and deaths from Plasmodium vivax [9]. The general coverage of mosquito nets for households in malaria-prone areas is one of Ethiopia’s primary vector control and prevention initiatives to ensure unlimited access to ITNs and the spraying of households with indoor residual spray (IRS) in targeted areas [5,10]. Thus, the cumulative number of ITNs exceeded 65 million, and about six million households in malaria-prone areas sprayed yearly with IRS [11]. However, malaria continues to be a serious public health challenge in Ethiopia [12]. Further, Ethiopia set an objective to have a community with appropriate knowledge and health-seeking behaviours regarding malaria prevention and control by 2020 [13]. In addition, ownership and utilisation, net care and repair through demand creation, and familiarity are the critical points to be implemented. More than 50 million Ethiopian people are at risk of contracting malaria, representing nearly two-thirds of the total population, and 75% of the land is malaria-prone [14,15]. In 2010, the Ethiopian health minister, in line with the Millennium Development Goals and the Roll-Back Malaria Initiative, planned to cut malaria morbidity and mortality by 50% by 2015; however, although good progress was made in the fight against malaria during the period, the goal was not achieved [16]. Peter [17] indicated general improvements in malaria prevention and control, but a low level of knowledge and use of malaria intervention tools was reported. Further, the study reported weak public awareness and practice towards malaria prevention and control alternatives, persistent misunderstandings about malaria, and unsatisfactory malaria control practices [18]. Previous studies investigated knowledge, attitudes, and practices related to malaria prevention options such as ITNs [7,18–21] — these studies provide information on the prevention of malaria, but they did not explore the in-context socio-economic aspects and knowledge of households to explain the relationship. Additionally, most of these studies relied on the assessment of knowledge about malaria with specific study populations. Studies indicate that Ethiopian communities are not well aware of the multi-dimensional challenges of the disease despite the acrimonious facts, misuse of ITN, and unsatisfactory malaria control methods reported [22–26]. Therefore, it is pertinent to consider the impact of knowledge on strategic interventions to prevent the spread of the disease. To the best of our knowledge, none of the previous studies considers the role of malaria knowledge in the relationship between ITNs and malaria. In addition, no previous study tested the moderating role of household_income in strengthening the relationship between strategic interventions and malaria based on malaria_knowledge. Our study, therefore, measured the influence of malaria knowledge and household_income in the relationship intending to investigate the effect of ITNs on malaria prevalence, with knowledge and household_income playing a mediating and moderating role, respectively.
Apart from this fundamental contribution, this study contributes to the existing literature in numerous ways. First, we observed the changes in the outcome of the direct relationship between ITN and malaria, besides the moderation-mediation effect. Second, we considered national-level aggregate panel data with a significant number of observations for study. Third, this is the first study in Ethiopia to evaluate the ITN_malaria relationship in the context of malaria knowledge and household income as a mediating-moderating effect. Finally, we conducted our analyses using structural equation modelling and the random effect model of the panel data estimation technique. The rest of the paper is organised as follows. Section 2 explains the theoretical background. Section 3 discusses the hypothesis development. Section 4 presents the analysis and results. Finally Section 5 focuses on the discussion and implications of the findings.
Theoretical Background
The Health Belief Model
Theory of the health belief model (HBM) was first introduced by a group of U.S_public health service social psychologists in the 1950s seeking to understand and explain why most people fail to participate in preventive and detective health measures [27]. The model remains the most widely employed theories of health behaviour [28] and the most commonly recognised approach in the health field [29]. The HBM hypothesises that health-related action depends upon the simultaneous occurrence of three classes of factors: (1) The existence of sufficient motivation (or health concern) to make health issues salient or relevant. (2) The belief that one is susceptible (vulnerable) to a severe health problem or to the sequelae of that illness or condition, which is often viewed as a perceived threat. (3) The belief that following a particular health recommendation would be beneficial in reducing the perceived threat at a subjectively-acceptable cost. Furthermore, the theory is based on the understanding that a person will take health-related action if that person believes they are susceptible to the condition (perceived susceptibility); the condition has serious consequences (perceived severity); taking action would reduce their vulnerability to the condition or its severity (perceived benefits); and these benefits outweigh the cost of taking action (perceived barriers) [30]. The response is accepted more easily if the person is exposed to factors that prompt measures (cues to action) and is confident in their ability to act successfully (self- efficacy) [31]. This study employed the theory of the HBM, holding that the independent variable (ITNs) should influence the dependent variable (malaria prevalence) through mediating variables (malaria knowledge) and moderating variables (household income). If a person has a good level of knowledge and a positive attitudes towards malaria prevention strategies, and if intervention tools are accessible to a vulnerable group at risk, they are more likely to practice preventive measures, thus reducing their risk of contracting malaria, and treat malaria patients effectively. Furthermore, a person who has more income and is knowledgeable about the programme, is more likely to access ITN to protect themselves from malaria. Thus, mediation as an indirect effect occurs when the causal effect of an independent variable (X) on a dependent variable (Y) is transmitted by a mediator (M) [32] while the moderating variable is the interaction terms at which the strength of the relationship between two variables is dependent on a third variable. The HBM is a tool to explore the perceptions and beliefs about malaria and the use of strategic interventions such as ITN [33]. The theory guided this study in establishing the relationship between the explanatory variable (ITNs) and the outcome variable (malaria prevalence), and we examined whether household income has a moderating effect on the direct and indirect relationship (through malaria knowledge). Figure 1 illustrates the proposed relationship.
Hypothesis Development
Insecticide-treated mosquito nets (ITNs) and malaria prevalence
Net distribution is an integral part of a selective vector control strategy for malaria protection, and ITNs have been identified as having a significant impact on malaria (3,13,26). Regular use of ITNs has been reported to reduce the overall death risk by 20% and the number of clinical malaria episodes in young children by 50% [35]. Insecticide-treated mosquito nets were reported to be used as a preventive measures against malaria [36]. For malaria control, ITN and IRS are recommended as the cornerstone of the strategy by the World Health Organization (WHO) [2,38]. Ethiopia implemented selective vector control methods, such as ITNs, IRS, and environmental management to fight against malaria [39]. The impressive decline in child mortality has been attributed to the implementation of vector control methods, such as ITN and IRS [37]. Another study also reveals the decline in malaria morbidity and mortality due to the introduction of vector control intervention methods [40]. However, malaria remains a major health problem in Ethiopia [41]. In addition, the government is working towards eradicating malaria by providing technical and material support; however, malaria still prevalent every rainy season, especially in the lowland areas of Ethiopia [42]. Inadequate knowledge about malaria and lack of ITNs were observed in some areas [43], which challenged the programme's success in prevention and control. Regular use of ITNs was reported to prevent malaria [44], and it was also believed that ITN prevents mosquito bites if used regularly.
Therefore, we hypothesised the following:
Hypothesis 1: Insecticide-treated mosquito nets reduces malaria prevalence.
Insecticide-treated mosquito nets and malaria knowledge
Effective preventive action is the outcome of public health programmes, which resulted in the implementation of community-based health education. Awareness creation about the programme on prevention and control measures is critical [45], which occurred through iterative actions to strengthen the awareness of the population about malaria prevention. Lack of knowledge about malaria has been reported to be hindering any measures of personal protection [46]. According to the HBM of health and illness, it is not only the participants’ belief that matters but also their knowledge and attitude [47]; hence, the perception of seriousness is based on medical knowledge people own. Better utilisation of ITNs existed among the communities who understand malaria infection and transmission methods [48]. Differences in malaria knowledge have been shown to cause discrepancies in tackling malaria [49] due to differences in strategic utilisation. Similarly, respondents who were knowledgeable about strategic interventions to prevent malaria, such as IRS, were less likely to accept the spray, compared to those who were not knowledgeable, but gaps in knowledge and fears about the effects on health were identified as challenges [50]. Another study reported the influence of knowledge gaps and a wrong perception on the use of insecticide-treated nets to protect oneself from malaria [51], which shows the influence of knowledge on the relationship. Similarly, the study reported better ownership and use of ITN by the communities with good knowledge than by those without the same [52]. Knowledge about malaria transmission and prevention methods was identified as a significant factor in combatting the disease [34]. Furthermore, another study revealed a high level of knowledge among study participants about mosquito vectors and their ability to kill [26]; however, the access and use did not correlate with the practice for protection. The association between age, educational status, and household income were reported to affect the relationship [53]. Moreover, yet another study reported respondents' familiarity with malaria, where 99% had heard of malaria and control methods, with 97% of the participants owning bed nets [7], but only 58.2% of ITNs owned by households were used in the previous night. This may be attributed to the improper delivery of health education in specific communities. The study found that mothers had sufficient awareness and appropriate attitudes towards malaria and ITNs, with a favourable attitude of 74.3% and 51.1% [19], but only 15.6% associated mosquitoes with malaria, and most of them (65.6%) replied that the disease was transmitted due to poor personal hygiene and environmental sanitation. Additionally, another study reported gaps in communities’ understanding of malaria transmission and lack of malaria vector knowledge and malaria transmission patterns [54,55]. Health motivation is the central focus of the health belief model (HBM) to evoke health concerns, forexample, living in a malaria-prone area and the possibility of contracting the disease [31,56]. Thus, we hypothesized the following:
Hypothesis 2: Insecticide-treated mosquito nets are positively associated with knowledge about malaria prevalence.
Knowledge and malaria prevalence
Lack of malaria knowledge is the most critical factor that contributes to several malaria deaths in many communities [57]. Therefore, there is a need for practical health education to improve knowledge about health programmes among the public to control infectious diseases such as malaria. Due to differences in malaria prevention and control practices, the adopted strategy should be tailored according to the environment [25]. The study revealed the achievements of malaria intervention planning based on local knowledge about malaria transmission [58]. In addition, the study found that communities with advanced information about malaria and its burden were interested in prevention and making personnel decisions on how to protect themselves from the disease [59]. Apart from the evidence from various channels, witnessing the death and sufferings of others due to a particular health problem contributes to positive health behaviour [47,60]. To design and implement effective interventions, local knowledge about the prevalence, distribution, and influencing factors were given paramount importance [61]. In addition, similar use of malaria intervention tools was observed in communities with reasonable knowledge about malaria and its consequences [62]. Low willingness to accept IRS was reported because of the lack of communityies awareness of the severity and seriousness of the disease when infected [50]. The individuals belief about the severity of the problem is mostly based on medical information and knowledge, which may motivate one’s decision to act towards self protection [63]. The barriers to the use of the intervention method are not about the cost or access; instead, they are linked to fear of the interventions and limited knowledge about malaria [64]. To achieve optimal health-seeking behaviors in endemic settings, malaria prevention and control programmes should consider local misconceptions and wrong perceptions [65]. Insecticide-treated mosquito nets are an effective method of malaria control; however, school-age children have reported less frequent use of them [66], probably due to the lack of proper knowledge and inadequate education in line with health programmes. Therefore, we formulated our next set of hypotheses:
Hypothesis 3: Knowledge is positively related to malaria prevalence, and
Hypothesis 4: Knowledge links Insecticide-treated nets to malaria prevalence.
The Moderating effect of household-income
Malaria remains the leading cause of morbidity and mortality in low and middle-income countries [67,68]. The burden of chronic diseases is increasing in low and middle-income countries, where it constitutes multiple burdens along with infectious diseases [11]. The study reported a positive association between household income and the use of ITN to protect people from malaria [69]. Further, the study revealed that quality of life and health status are linked to economic, income, and educational status of residents [70]. In addition, the report indicates malaria elimination from high-income countries, while it is a challenge for low and middle-income countries [64]. Similarly, the study revealed the association between income and the practice of malaria preventive actions, where higher income groups are two times more likely to practice the actions than low-income groups [71]. Moreover, the report shows that access to intervention is influenced by household income [8]. Similarly, the study reported that, although ITN was suggested as a means of malaria reduction, the communities with large families and low-incomes are more affected by malaria disease [72]. another study showed that income level, age, educational level, and occupation are significant predictor variable for knowledge on malaria and to use IRS as a control tool [73]. Therefore, we hypothesised the following:
Hypothesis 5: Household income moderates the relationship between insecticide-treated mosquito nets and malaria through knowledge. Thus, the mediated relationship will be stronger for those societies that have a higher income.
Hypothesis 6: Household income moderates the strength of the direct relationship between insecticide-treated nets and malaria. Thus, the relationship will be stronger for an advanced community than for those with lower_incomes.