Immune Responses in Malaria and Vaccine Strategies

Prevalence and factors associated with childhood malaria and anaemia in Osun state, Nigeria: a baseline household malariometric study

BACKGROUND

Under-5 children have been known to bear a significant burden of malaria in endemic countries. Though significant progress has been made towards malaria prevention and control in Nigeria, it is expected that the addition of new malaria prevention strategy, such as perennial malaria chemoprevention (PMC) can contribute to a more rapid decline in malaria cases. This study aimed to determine the prevalence and factors associated with malaria and anaemia among children aged 2-18 months in Osun State.

METHODS

A cross-sectional household malariometric study was conducted in 80 communities across eight Local Government areas (LGAs) in Osun State. Ethical approval was obtained from Osun State Health Research Ethical Committee (OSHREC/PRS/569T312/ on the 22nd of May 2023. Malaria test positivity was determined by rapid diagnostic test (RDT) and microscopy. In addition, haemoglobin levels were measured using Haemocue® Hb 201. Caregivers were interviewed on malaria management practices using tools adapted from Nigeria Malaria Indicator Survey.

RESULTS

A total of four hundred children aged 2-18 months were assessed in this study, which was conducted in July 2023. The caregivers were mostly the biological mothers of the children (n = 387, 96.8%). Female children were 51.8% and their male counterparts 48.2% respectively. Malaria positivity rate by RDT was 36.8% and this was higher in children aged 13-18 months (48.0%) and followed by those aged 7-12 months (44.0%). By microscopy, the positivity rate was 12.5% overall, with 15.0% positivity rate among children aged 7-12 months, about 13.5% among those 13-18 months and those aged 2-6 months had the least positivity rate whether by microscopy (8.5%) or RDT (18.5%). Overall, the prevalence of severe anaemia was 4.0%, moderate was 37.3%, mild was 18.3% and the normal was 40.4% respectively. However, higher proportion of moderate anaemia (7.0-9.9 haemoglobin (g/dL)) was reported in older children. Children from medium wealth households (aOR = 0.549; 95% CI 0.306-0.986) and those from rich households (aOR = 0.543; 95% CI 0.283-1.042) had 45.0% reduction in the odds of having malaria, when compared with their counterparts from poor households. In addition, children aged 7-12 months (aOR = 2.856; 95% CI 1.524-5.354) and those aged 13-18 months (aOR = 4.269; 95% CI 2.422-7.526) had higher odds of malaria infection, respectively, when compared with children aged 2-6 months.

CONCLUSION

Malaria infection and anaemia were found to be higher in older children. Household wealth and child's age were significantly associated with malaria infection. These findings would inform the positioning of PMC intervention touch-points to reduce malaria burden in young children.

Pooled prevalence and risk factors of malaria among children aged 6-59 months in 13 sub-Saharan African countries: A multilevel analysis using recent malaria indicator surveys

BACKGROUND

Every 75 seconds, a child under five dies of malaria. Mainly children, aged between six months and five years, are at the highest risk for malaria. These children lost maternal immunity and did not yet developed specific immunity to the infection. Under the age of five, children bear the highest burden of malaria in Sub-Saharan Africa (SSA). Many individual and community level factors could contribute to malaria prevalence remaining high among under-five children in the region. Thus, this study aimed to assess the pooled prevalence of malaria among children aged 6-59 months and identify potential factors associated with malaria by using recent Malaria Indicator Surveys in 13 SSA countries.

METHODS

Data for this study were drawn from recent 13 Sub-Saharan African countries Malaria Indicator Surveys (MIS). A total weighted sample of 60,541 children aged 6-59 months was included. STATA version 14.2 was used to clean, code and analyze the data. Multilevel logistic regression was employed to identify factors associated with malaria. Adjusted odds ratio with 95% CI and a P value <0.05 was reported to indicate statistical association. Model fitness and comparison were done using Inter cluster correlation coefficient, Median odds ratio, proportional change in variance, and deviance.

RESULTS

The pooled prevalence of malaria among children aged 6-59 months was found to be 27.41% (95% CI: 17.94%-36.88%). It ranges from 5.04% in Senegal to 62.57% in Sierra Leone. Aged 36-47 months (AOR = 3.54, 95% CI 3.21-3.91), and 48-59 months (AOR = 4.32, 95% CI 3.91-4.77), mothers attended primary education (AOR = 0.78, 95% CI 0.73-0.84), richer (AOR = 0.35, 95% CI 0.32-0.39), and richest household (AOR = 0.16, 95% CI 0.14-0.19), number of three and more under-five children (AOR = 1.35, 95% CI 1.26-1.45), improved floor material (AOR = 0.65, 95% CI 0.57-0.73), improved wall material (AOR = 0.73, 95% CI 0.64-0.84), improved roof material (AOR = 0.70, 95% CI 0.51-0.93), insecticide-treated bed net (ITN) use (0.56, 95% CI 0.51-0.62), not anemic (AOR = 0.05, 95% CI 0.04-0.06), rural resident (AOR = 2.16, 95% CI 2.06-2.27), high community ITN use (AOR = 0.40, 95% CI 0.24-0.63) and high community poverty (AOR = 2.66, 95% CI 2.53-2.84) were strongly associated with malaria.

CONCLUSIONS AND RECOMMENDATIONS

Almost 3 out of 10 children were infected by malaria in 13 SSA countries. Malaria infection remains one of the main killers of children aged 6-59 months in the SSA. This study revealed that older under-five children living in large families with low incomes in rural areas are most vulnerable to malaria infection. Our results clearly indicate that ITN utilization and improved housing are promising means to effectively prevent malaria infection among children aged 6-59 months. It is therefore important to note that households with low wealth quintiles and rural residents should be prioritized in any mass distribution of ITNs. This has to be accompanied by education using mass media to enhance community awareness.

Host-pathogen interaction in arthropod vectors: Lessons from viral infections

Haematophagous arthropods can harbor various pathogens including viruses, bacteria, protozoa, and nematodes. Insects possess an innate immune system comprising of both cellular and humoral components to fight against various infections. Haemocytes, the cellular components of haemolymph, are central to the insect immune system as their primary functions include phagocytosis, encapsulation, coagulation, detoxification, and storage and distribution of nutritive materials. Plasmatocytes and granulocytes are also involved in cellular defense responses. Blood-feeding arthropods, such as mosquitoes and ticks, can harbour a variety of viral pathogens that can cause infectious diseases in both human and animal hosts. Therefore, it is imperative to study the virus-vector-host relationships since arthropod vectors are important constituents of the ecosystem. Regardless of the complex immune response of these arthropod vectors, the viruses usually manage to survive and are transmitted to the eventual host. A multidisciplinary approach utilizing novel and strategic interventions is required to control ectoparasite infestations and block vector-borne transmission of viral pathogens to humans and animals. In this review, we discuss the arthropod immune response to viral infections with a primary focus on the innate immune responses of ticks and mosquitoes. We aim to summarize critically the vector immune system and their infection transmission strategies to mammalian hosts to foster debate that could help in developing new therapeutic strategies to protect human and animal hosts against arthropod-borne viral infections.

Systems biology of malaria explored with nonhuman primates

"The Primate Malarias" book has been a uniquely important resource for multiple generations of scientists, since its debut in 1971, and remains pertinent to the present day. Indeed, nonhuman primates (NHPs) have been instrumental for major breakthroughs in basic and pre-clinical research on malaria for over 50 years. Research involving NHPs have provided critical insights and data that have been essential for malaria research on many parasite species, drugs, vaccines, pathogenesis, and transmission, leading to improved clinical care and advancing research goals for malaria control, elimination, and eradication. Whilst most malaria scientists over the decades have been studying Plasmodium falciparum, with NHP infections, in clinical studies with humans, or using in vitro culture or rodent model systems, others have been dedicated to advancing research on Plasmodium vivax, as well as on phylogenetically related simian species, including Plasmodium cynomolgi, Plasmodium coatneyi, and Plasmodium knowlesi. In-depth study of these four phylogenetically related species over the years has spawned the design of NHP longitudinal infection strategies for gathering information about ongoing infections, which can be related to human infections. These Plasmodium-NHP infection model systems are reviewed here, with emphasis on modern systems biological approaches to studying longitudinal infections, pathogenesis, immunity, and vaccines. Recent discoveries capitalizing on NHP longitudinal infections include an advanced understanding of chronic infections, relapses, anaemia, and immune memory. With quickly emerging new technological advances, more in-depth research and mechanistic discoveries can be anticipated on these and additional critical topics, including hypnozoite biology, antigenic variation, gametocyte transmission, bone marrow dysfunction, and loss of uninfected RBCs. New strategies and insights published by the Malaria Host-Pathogen Interaction Center (MaHPIC) are recapped here along with a vision that stresses the importance of educating future experts well trained in utilizing NHP infection model systems for the pursuit of innovative, effective interventions against malaria.