Malaria

Malaria, a serious vector-borne illness, is transmitted to people when a mosquito infected with the protozoan parasite, Plasmodium, bites them. Four different species of Plasmodium cause malaria; p. falciparum, p. malariae, p. ovale, and p. vivax, with p. falciparum and p. vivax posing the greatest public health threat (WHO 2015a). The largest number of malaria deaths can be attributed to the p. falciparum parasite, which is most prevalent on the African continent. P. vivax is also present on the African continent—but its ability to survive higher altitudes and cooler climates means that it has a wider geographic distribution (WHO 2015a). Malaria causes anemia by destroying red blood cells; decreasing the production of new red blood cells, which also leads to iron deficiency (see Iron Deficiency section); and general inflammation (see Inflammation section) (Spottiswoode, Duffy, and Drakesmith 2014). Children under 5 years of age and pregnant women are at a much higher risk for contracting malaria and becoming seriously ill. School-age children are also increasingly recognized as an important population group because, as transmission of malaria among young children is successfully decreased, children fail to build immunity to malaria until later in life. This means that school-age children in previously endemic areas will most likely experience an increase of severe and uncomplicated malaria cases, because they are no longer building an immunity during early childhood (Nankabirwa et al. 2014).

How is malaria categorized?

The gold standard for measuring malaria transmission is entomological inoculation, but it is difficult to measure and lacks precision at low levels of transmission. Thus, communities are categorized as low, moderate, or high transmission areas, using the prevalence of malaria in children 2 to 9 years as a proxy, as defined in Table 1 (WHO 2009). Malaria associated anemia is defined as hemoglobin 80 g/L, which is an indication of malaria morbidity and, thus, useful for tracking the impact of malaria interventions (Korenromp et al. 2004; Roll Back Malaria et al. 2009).

Table 1: Definition of Malaria Transmission Levels

Source: WHO 2015b

How is malaria measured?

The gold standard measure of malaria prevalence is microscopy—blood smears are examined under a microscope to identify malaria parasites. However, rapid diagnostic tests, which can provide results in 15 minutes, can also be used to assess malaria prevalence. They are, generally, becoming the norm to obtain crude estimates of malaria prevalence. The most common rapid diagnostic tests look for antigens that occur with current or recent infection (Florey 2014).

Where can we get these data?

In malaria-endemic countries, surveys that collect malaria prevalence data include—

• Demographic and Health Surveys
• Malaria Indicator Surveys
• Multiple Indicator Cluster Surveys
• National Micronutrient Surveys
• Knowledge, Practice, and Coverage Surveys
• other research or evaluation activities.

These surveys typically collect blood samples from children 6–59 months old and, sometimes, from women of reproductive age. Also, look for other surveys that may include school-aged children.

Information related to malaria diagnosis is sometimes available through the country’s health monitoring information system. Consider the usage of health care services in your context when interpreting findings, because not all people suffering from malaria will seek services at the facility. However, in Africa, care seeking for fever is generally high for children under 5 years of age.

Methodological issues

• Look at the season when the data was collected. Malaria transmission is seasonal in most places, with peaks during and just after the rainy season. Thus, it is important to consider the season when comparing malaria prevalence data collected at different points in time.
• Look at the quality of the techniques used. For microscopy, the type of microscope, the quality of the blood smear, and the technician’s expertise determine the quality of results (Florey 2014). Often, you will not have information on the quality of microscopy data collection unless you were directly involved in the data collection or have obtained this information from those that undertook the survey. If you have this information, include it in your report. For rapid diagnostic tests, the type and brand determine the accuracy of the test and should be reported on—if available (WHO 2015c).
• Look at the type of technique used. Generally, rapid diagnostic tests show higher malaria prevalence than microscopy, because the former test can show false positivity after the infection has been treated (Mappin et al. 2015). Adjustment approaches have been developed to compare malaria prevalence between rapid diagnostics and microscopy data using a regression approach (Mappin et al. 2015). Check to see if this adjustment approach was used when comparing malaria prevalence data collected at different points in time. If it was not used, note this in your limitations. If you have the raw data available, you can apply these adjustments yourself using instruction included in Mappin et al. (2015).
• When using health monitoring information system data, keep in mind that some countries include both clinical and confirmed malaria cases as a data point. Also, countries sometimes make a distinction between “confirmed” and “non-confirmed” malaria. Confirmed implies that some test (either a rapid diagnostic test or microscopy) was conducted for a parasitological-based diagnosis, whereas clinical malaria are cases that are diagnosed with malaria but do not have parasitological confirmation. Be sure to report the definition(s) used in your country’s health monitoring information system.
• If you decide to directly link malaria and anemia in your analysis (e.g., regression), it is important to note that malaria-related anemia can persist after parasitemia has cleared. As a result, cross-sectional data may not capture the full extent of the anemia caused by malaria