Human mobility and factors associated with malaria importation in Lusaka district, Zambia: a descriptive cross sectional study.

BACKGROUND: Malaria is a major public health problem in Zambia with an estimated 4 million confirmed cases and 2389 deaths reported in 2015. Efforts to reduce the incidence of malaria are often undermined by a number of factors such as human mobility which may lead to introduction of imported infections. The aim of this study was to establish the burden of malaria attributed to human mobility in Lusaka district and identify factors associated with malaria importation among residents of Lusaka district. METHODS: A cross sectional study was conducted in five randomly selected health facilities in Lusaka district from November 2015 to February 2016. Data was collected from 260 patients who presented with malaria and whose status was confirmed by rapid diagnostic test or microscopy. Each confirmed malaria case was interviewed using a structured questionnaire to establish their demographic characteristics, travel history and preventive measures. Travel history was used as a proxy to classify cases as either imported or local. Residency was also used as a secondary proxy for importation to compare characteristics of residents vs non-residents in relation to malaria importation. Logistic regression was used to determine factors associated with malaria importation among residents of Lusaka district. RESULTS: Out of 260 cases, 94.2% were classified as imported cases based on participants' travel history. There were 131 (50.4%) males and 129 (49.6%) females. Age distribution ranged from 0 to 68 years with a median age of 15 years (IQR 8-27). Imported cases came from all the ten provinces of Zambia with the Copperbelt Province being the highest contributor (41%). Of all imported cases, use of prophylaxis was found to be highly protective [AOR = 0.22 (95% CI 0.06-0.82); p-value = 0.024]. Other factors that significantly influence malaria transmission and importation by residents include duration of stay in a highly endemic region [AOR = 1.25 (95% CI 1.09-1.44); p-value = 0.001] and frequency of travel [AOR = 3.71 (95% CI 1.26-10.84); p-value = 0.017]. CONCLUSION: Human mobility has influenced malaria transmission in Lusaka district through a number of factors by importing infections. This leads to onward transmission and poses a challenge to malaria elimination and control. However, taking of prophylaxis is highly protective and must be highly recommended.

Distinct parasite populations infect individuals identified through passive and active case detection in a region of declining malaria transmission in southern Zambia.

BACKGROUND: Substantial reductions in the burden of malaria have been documented in parts of sub-Saharan Africa, with elimination strategies and goals being formulated in some regions. Within this context, understanding the epidemiology of low-level malaria transmission is crucial to achieving and sustaining elimination. A 24 single-nucleotide-polymorphism Plasmodium falciparum molecular barcode was used to characterize parasite populations from infected individuals identified through passive and active case detection in an area approaching malaria elimination in southern Zambia. METHODS: The study was conducted in the catchment area of Macha Hospital in Choma District, Southern Province, Zambia, where the parasite prevalence declined over the past decade, from 9.2% in 2008 to less than 1% in 2013. Parasite haplotypes from actively detected, P. falciparum-infected participants enrolled in a serial cross-sectional, community-based cohort study from 2008 to 2013 and from passively detected, P. falciparum-infected individuals enrolled at five rural health centres from 2012 to 2015 were compared. Changes in P. falciparum genetic relatedness, diversity and complexity were analysed as malaria transmission declined. RESULTS: Actively detected cases identified in the community were most commonly rapid diagnostic test negative, asymptomatic and had submicroscopic parasitaemia. Phylogenetic reconstruction using concatenated 24 SNP barcode revealed a separation of parasite haplotypes from passively and actively detected infections, consistent with two genetically distinct parasite populations. For passively detected infections identified at health centres, the proportion of detectable polyclonal infections was consistently low in all seasons, in contrast with actively detected infections in which the proportion of polyclonal infections was high. The mean genetic divergence for passively detected infections was 34.5% for the 2012-2013 transmission season, 37.8% for the 2013-2014 season, and 30.8% for the 2014-2015 season. The mean genetic divergence for actively detected infections was 22.3% in the 2008 season and 29.0% in the 2008-2009 season and 9.9% across the 2012-2014 seasons. CONCLUSIONS: Distinct parasite populations were identified among infected individuals identified through active and passive surveillance, suggesting that infected individuals detected through active surveillance may not have contributed substantially to ongoing transmission. As parasite prevalence and diversity within these individuals declined, resource-intensive efforts to identify the chronically infected reservoir may not be necessary to eliminate malaria in this setting.

High prevalence of dhfr and dhps molecular markers in Plasmodium falciparum in pregnant women of Nchelenge district, Northern Zambia.

BACKGROUND: Sulphadoxine-pyrimethamine (SP) is the recommended drug for intermittent preventive treatment in pregnancy (IPTp) in most African countries, including Zambia. However, malaria is still one of the leading causes of morbidity and mortality in pregnant women despite reports of greater than 50% of women taking at least two doses of SP in IPTp. Studies have shown that resistance to SP is associated with mutations in the dhfr and dhps gene of Plasmodium falciparum. This study examined the prevalence of dhfr and dhps polymorphisms in P. falciparum found in pregnant women of Nchelenge district. METHOD: This cross-sectional study was conducted in 2013 in Nchelenge, a holoendemic area with malaria prevalence estimated at 50% throughout the year. Three rural health centres were randomly selected and a census survey carried out at each health centre. A questionnaire was administered and malaria testing done using RDT and microscopy, with collection of a dried blood spot. A chelex extraction was done to extract parasite DNA from dried blood spots followed by nested PCR and enzyme restriction digestion. RESULTS: Of the enrolled participants (n = 375), the median age of the women was 23. The prevalence of malaria by PCR was 22%. The PCR positive samples examined (n = 72) showed a high prevalence of dhfr triple (Asn-108 + Arg-59 + Ile-59) mutant (68%) and dhps double (Gly -437 + Glu-540) mutant (21%). The quintuple haplotype was found in 17% with 2 samples with an additional Gly-581mutation. In addition 6% mutations at Val-16 were found and none found at Thr-108 respectively, these both confer resistance to cycloguanil. Multivariate analysis showed that there was an association between malaria and women aged 30-34 years old p < 0.05(AOR: 0.36) at 95% CI. CONCLUSION: This study showed a high number of mutations in the dhfr and dhps genes. The high malaria endemicity in the general population of this area may have contributed to the high prevalence of resistant parasites in pregnant women, suggesting a need to examine the efficacy of SP given that it is the only approved drug for IPTp in Zambia.

Comparison of HIV prevalence, incidence, and viral load suppression in Zambia population-based HIV impact assessments from 2016 and 2021.

BACKGROUND: The Zambian government has implemented a public health response to control the HIV epidemic in the country. Zambia conducted a population-based HIV impact assessment (ZAMPHIA) survey in 2021 to assess the status of the HIV epidemic to guide its public health programs. METHODS: ZAMPHIA 2021 was a cross-sectional two-stage cluster sample household survey among persons aged ≥15 years conducted in Zambia across all 10 provinces. Consenting participants were administered a standardized questionnaire and whole blood was tested for HIV according to national guidelines. HIV-1 viral load (VL), recent HIV infection, and antiretroviral medications were tested for in HIV-seropositive samples. Viral load suppression (VLS) was defined as <1000 copies/ml. ZAMPHIA 2021 results were compared to ZAMPHIA 2016 for persons aged 15-59 years (i.e., the overlapping age ranges). All estimates were weighted to account for nonresponse and survey design. RESULTS: During ZAMPHIA 2021, of 25 483 eligible persons aged ≥15 years, 18 804 (73.8%) were interviewed and tested for HIV. HIV prevalence was 11.0% and VLS prevalence was 86.2% overall, but was <80% among people living with HIV aged 15-24 years and in certain provinces. Among persons aged 15-59 years, from 2016 to 2021, HIV incidence declined from 0.6% to 0.3% ( P -value: 0.07) and VLS prevalence increased from 59.2% to 85.7% ( P -value: <0.01). DISCUSSION: Zambia has made substantial progress toward controlling the HIV epidemic from 2016 to 2021. Continued implementation of a test-and-treat strategy, with attention to groups with lower VLS in the ZAMPHIA 2021, could support reductions in HIV incidence and improve overall VLS in Zambia.

Therapeutic Efficacy of Artemether-Lumefantrine for Uncomplicated Falciparum Malaria in Northern Zambia.

Artemether-lumefantrine (AL) is a first-line agent for uncomplicated malaria caused by Plasmodium falciparum. The WHO recommends periodic therapeutic efficacy studies of antimalarial drugs for the detection of malaria parasite drug resistance and to inform national malaria treatment policies. We conducted a therapeutic efficacy study of AL in a high malaria transmission region of northern Zambia from December 2014 to July 2015. One hundred children of ages 6 to 59 months presenting to a rural health clinic with uncomplicated falciparum malaria were admitted for treatment with AL (standard 6-dose regimen) and followed weekly for 5 weeks. Parasite counts were taken every 6 hours during treatment to assess parasite clearance. Recurrent episodes during follow-up (n = 14) were genotyped to distinguish recrudescence from reinfection and to identify drug resistance single nucleotide polymorphisms (SNPs) and multidrug resistance protein 1 (mdr1) copy number variation. Day 7 lumefantrine concentrations were measured for correspondence with posttreatment reinfection. All children who completed the parasite clearance portion of the study (n = 94) were microscopy-negative by 72 hours. The median parasite elimination half-life was 2.7 hours (interquartile range: 2.1-3.3). Genotype-corrected therapeutic efficacy was 98.8% (95% CI: 97.6-100). Purported artemisinin and lumefantrine drug resistance SNPs in atp6, 3D7_1451200, and mdr1 were detected but did not correlate with parasite recurrence, nor did day 7 lumefantrine concentrations. In summary, AL was highly effective for the treatment of uncomplicated falciparum malaria in northern Zambia during the study period. The high incidence of recurrent parasitemia was consistent with reinfection due to high, perennial malaria transmission.

Semi-quantitative measurement of the antimalarial lumefantrine from untreated dried blood spots using LC-MS/MS.

Study of the clinical effects of combination therapy for malaria is aided by the ability to measure concentrations of individual partner drugs. Existing methods for measurement of the antimalarial drug lumefantrine (LF) in dried blood spots (DBS) on filter paper rely on chemical pretreatment of the paper to facilitate drug elution. However, in the absence of pretreatment, DBS may still offer some utility for semi-quantitative measurements and pharmacokinetic-pharmacodynamic (PK-PD) analyses. We present a method for semi-quantitation of LF in DBS on untreated filter paper using liquid chromatography tandem mass spectrometry. Optimal recovery was achieved by extraction with acetone-water-formic acid (90:5:5). The range of quantitation was 100-20,000ng/ml. Mean intra- and inter-day accuracy values were 86.6% (coefficient of variation [CV]: 10.1%) and 91.8% (CV: 16.1%), therefore we propose the assay as semi-quantitative. Clinical application was demonstrated in exploratory PK-PD analyses of a drug efficacy trial of artemether-lumefantrine in children with uncomplicated falciparum malaria using post-treatment day 7 samples, parasite clearance times estimated from serial blood smears, and recurrence of malaria out to 35days. The median day 7 concentration among children (n=71) was 111ng/ml (interquartile range: 100-194ng/ml). We used a truncated calibration curve of 100-5000ng/ml for calculations due to low observed concentrations. Calculations using the full calibration curve yielded similar values (+1% avg. deviation). Controlling for participant age, sex, and parasite burden, each log increase in LF day 7 concentration corresponded to a decrease of 7.1h in mean parasite clearance time (95% confidence interval: 0.1-14.3h, P=0.05). A nested case-control study of participants (n=18) with and without recurrent malaria showed mean post-treatment day 7 concentrations of 181ng/ml and 235ng/ml, respectively, but the difference was not significant (P=0.64). A method for semi-quantitation of LF from post-treatment day 7 collections of DBS on untreated filter paper demonstrated clinical application in exploratory PK-PD analyses of parasite clearance and reinfection. Use of DBS will endure in certain study settings by virtue of their ease of collection and resilience. Their utility should continue to be explored as our instruments gain in sensitivity and as clinical pharmacology inquiries are pursued to the field.