Infection and nutrition are intimatelyrelated from the coincidental shared pathways of poverty to effects onmetabolism and immunity1. Distinguishing the contributions ofinfectious diseases and nutrition as causes of death is complex. In mostreporting systems and global disease burden estimations, infectious diseasesrepresent an immediate, direct cause of death, while mortality attributed tomalnutrition may only be recognized as a cause of death when it is severeenough to cause clinical manifestations2. However, Pelletier et al. suggestedthat malnutrition, by virtue of its synergistic relationship with infectiousdisease, caused 56% of child mortality, a much larger fraction than classificationof “nutritional deficiencies”2.
Similarly, community-based studiesof malaria reveal that this infection contributes to under-five mortality morethan would be attributed to malaria-specific deaths alone2. Importantly, both malaria andundernutrition are highly prevalent in sub-Saharan Africa and often sharecommon spatial distributions3–5. The precise clinical relationshipsbetween undernutrition and malaria have been the subject of competinghypotheses. Nutritional interventions appeared to exacerbate the clinicaloutcomes of malaria infection in Nigeria6–9 and Senegal7, leading some to suggest thatnutrient deficiency, notably iron10, may protect against malaria. Whileother studies found no significant association11,12 and more recent cross-sectionalstudies offer no support to the hypothesis that under-nutrition protectionagainst malaria infection and disease progression13,14. In fact, increased risks of pooroutcomes of malaria are described in several studies13 indicate that malnutrition andmalaria form a vicious circle that has a large impact on morbidity andmortality among the most vulnerable in the population, likely operating throughbroad effects on the functional capacity of the immune system4,15. In Somalia, there are high levels ofacute malnutrition in the South Central zone, estimated to be at least 35%;followed by Puntland zone and lowest levels are in Somaliland zone16.
A similar pattern is observed in thedistribution of malaria in Somalia17. Plasmodium falciparum parasite rate(PfPR) is estimated to range from 0–9% in the north of Somalia and from 0–52%in south of Somalia, with high PfPR locations occurring in the denselypopulated regions between the Juba and Shabelle rivers. Majority of the area inthe northern part of Somalia have been reported to have a PfPR of <5% with asmall number of locations in Puntland and on the south-western border betweenSomaliland and Ethiopia having PfPR of >5–9%. In the south, PfPR is loweralong the two rivers, compared to the area in between18,19. Thereare several pathways that may explain the comorbidity. On one hand, children indeveloping countries are at a higher risk of both malnutrition and infectionsdue to environmental conditions, and thus more prone to concurrent conditionsoccurring by chance20.
Both are subject to seasonal variation drivenby weather and food supply. On the other hand, malnutrition compromises theimmunity, leaving the child susceptible to infection21;and malaria may result in anorexia, weight-loss or, when pregnant women areinfected, low birth weight. The overlapping epidemiology may beexplored by joint mapping of the two health conditions to quantify thecorrelation structures between their relative risks by modelling common anddisease-specific observed effects and spatial patterns simultaneously22. In this study, we aimed to undertakethe first nationwide investigation of ecological co-morbidity of wasting andlow mid upper arm circumference (MUAC) with falciparummalaria in Somalia to determine the spatial patterns of these health conditions.A shared component model was used to fit common and indicator-specificunobserved and unmeasured spatial risks 23,24.