Sustained Malaria Transmission despite Reactive Screen-and-Treat in a Low-Transmission Area of Southern Zambia

Abstract

Malaria elimination strategies are designed to more effectively identify and treat infected individuals to interrupt transmission. One strategy, reactive screen-and-treat, starts with passive detection of symptomatic cases at health facilities. Individuals residing within the index case and neighboring households are screened with a malaria rapid diagnostic test (RDT) and treated if positive. However, it is unclear to what extent this strategy is effective in reducing transmission. Reactive screen-and-treat was implemented in Choma district, Southern Province, Zambia, in 2013, in which residents of the index case and neighboring households within 140 m were screened with an RDT. From March 2016 to July 2018, the screening radius was extended to 250-m, and additional follow-up visits at 30 and 90 days were added to evaluate the strategy. Plasmodium falciparum parasite prevalence was measured using an RDT and by quantitative PCR (qPCR). A 24-single nucleotide polymorphism molecular bar-code assay was used to genotype parasites. Eighty-four index case households with 676 residents were enrolled between March 2016 and March 2018. Within each season, parasite prevalence declined significantly in index households at the 30-day visit and remained low at the 90-day visit. However, parasite prevalence was not reduced to zero. Infections identified by qPCR persisted between study visits and were not identified by RDT. Parasites identified within the same household were most genetically related; however, overall parasite relatedness was low and similar across time and space. Thus, despite implementation of a reactive screen-and-treat program, parasitemia was not eliminated, and persisted in targeted households for at least 3 months.

Understudied Anophelines Contribute to Malaria Transmission in a Low-Transmission Setting in the Choma District, Southern Province, Zambia

“…In the Choma District, Southern Province, Zambia, Plasmodium falciparum parasite prevalence decreased from 9% in 2008 to 1% in 2013 as measured by RDT, but low levels of malaria transmission still occur, with annual parasite prevalence ranging from 1% to 3% under active case surveillance. 8 – 10 Since 2013, the government of Zambia has used a reactive test-and-treat strategy to help identify active zones of transmission and to treat parasitemic residents. 11 According to this protocol, index cases are identified after testing positive for malaria by RDT at a local health facility.…”

Performance of highly sensitive and conventional rapid diagnostic tests for clinical and subclinical Plasmodium falciparum infections, and hrp2/3 deletion status in Burundi

“…A study conducted in western Kenya estimated 95% of transmission stemming from subclinical carriers [10]. RDTs are the key diagnostic tool for strategies to target the subclinical reservoir, for example through active [11,12] or reactive case detection [13,14],…”

Scientific Findings of the Southern and Central Africa International Center of Excellence for Malaria Research: Ten Years of Malaria Control Impact Assessments in Hypo-, Meso-, and Holoendemic Transmission Zones in Zambia and Zimbabwe

“…12 Overall, RTAT reduced malaria in the index and surrounding households over time, but not to a meaningful extent. 22 Cases tended to cluster within a household but not within the screening radii and only 11% of index households had at least one additional case. 10,16 Of the total cases detected by RTAT, 60% were within the case household, 10% were within a 140-m radius of the household, and 30% were between 140 and 250 m of the household.…”