Malaria Risk Factors in North West Tanzania: The Effect of Spraying, Nets and Wealth

Abstract

Malaria prevalence remains high in many African countries despite massive scaling-up of insecticide treated nets (ITN) and indoor residual spraying (IRS). This paper evaluates the protective effect of pyrethroid IRS and ITNs in relation to risk factors for malaria based on a study conducted in North-West Tanzania, where IRS has been conducted since 2007 and universal coverage of ITNs has been carried out recently. In 2011 community-based cross-sectional surveys were conducted in the two main malaria transmission periods that occur after the short and long rainy seasons. These included 5,152 and 4,325 children aged 0.5–14 years, respectively. Data on IRS and ITN coverage, household demographics and socio-economic status were collected using an adapted version of the Malaria Indicator Survey. Children were screened for malaria by rapid diagnostic test. In the second survey, haemoglobin density was measured and filter paper blood spots were collected to determine age-specific sero-prevalence in each community surveyed. Plasmodium falciparum infection prevalence in children 0.5–14 years old was 9.3% (95%CI:5.9–14.5) and 22.8% (95%CI:17.3–29.4) in the two surveys. Risk factors for infection after the short rains included households not being sprayed (OR = 0.39; 95%CI:0.20–0.75); low community net ownership (OR = 0.45; 95%CI:0.21–0.95); and low community SES (least poor vs. poorest tertile: OR = 0.13, 95%CI:0.05–0.34). Risk factors after the long rains included household poverty (per quintile increase: OR = 0.89; 95%CI:0.82–0.97) and community poverty (least poor vs. poorest tertile: OR = 0.26, 95%CI:0.15–0.44); household IRS or high community ITN ownership were not protective. Despite high IRS coverage and equitable LLIN distribution, poverty was an important risk factor for malaria suggesting it could be beneficial to target additional malaria control activities to poor households and communities. High malaria prevalence in some clusters and the limited protection given by pyrethroid IRS and LLINs suggest that it may be necessary to enhance established vector control activities and consider additional interventions.

Carriage of sub-microscopic sexual and asexual Plasmodium falciparum stages in the dry season at Navrongo, Ghana

“…Since parasite density is controlled by acquired immunity in the infected host 7 adults are more likely than children to carry sub-microscopic infections. 29,30 Our study showed a higher prevalence of sub-microscopic infections among older children and adults (>5years) than among children <5years (10.3% versus 3.4%) which is expected. On the other hand, prevalence by microscopy was highest among children <5 years (10.3%), an indication of higher parasite densities among the children who are still in the process of building up their protective immunity.…”

Insecticide-treated net effectiveness at preventing Plasmodium falciparum infection varies by age and season

“…Previous studies examining the effect of ITN use on infection prevalence have relied on microscopy to measure P. falciparum prevalence [10, 13, 30–33], however 47% of all infections detected in these surveys were sub-microscopic and SAC were more likely to have sub-microscopic infections than younger children [14]. Unlike microscopy, rtPCR can detect prevalent low-density asymptomatic infection.…”

Description and lessons learned from the 2014 Dengue outbreak in Dar es Salaam, Tanzania. Knowledge, attitudes and bite prevention practices among those with confirmed Dengue

“…It is generally recognised that people with low SES are usually prone to vector-borne diseases [29][30][31][32] including Dengue, although not in all cases as shown by a recent systematic review of the link between Dengue and Socioeconomic status [33]. Our study described the group that is more at risk than others and the spatial distribution of Dengue virus cases has been produced.…”