A method of active case detection to target reservoirs of asymptomatic malaria and gametocyte carriers in a rural area in Southern Province, Zambia

Abstract

Background Asymptomatic reservoirs of malaria parasites are common yet are difficult to detect, posing a problem for malaria control. If control programmes focus on mosquito control and treatment of symptomatic individuals only, malaria can quickly resurge if interventions are scaled back. Foci of parasite populations must be identified and treated. Therefore, an active case detection system that facilitates detection of asymptomatic parasitaemia and gametocyte carriers was developed and tested in the Macha region in southern Zambia. Methods Each week, nurses at participating rural health centres (RHC) communicated the number of rapid diagnostic test (RDT) positive malaria cases to a central research team. During the dry season when malaria transmission was lowest, the research team followed up each positive case reported by the RHC by a visit to the homestead. The coordinates of the location were obtained by GPS and all consenting residents completed a questionnaire and were screened for malaria using thick blood film, RDT, nested-PCR, and RT-PCR for asexual and sexual stage parasites. Persons who tested positive by RDT were treated with artemether/lumefantrine (Coartem ® ). Data were compared with a community-based study of randomly selected households to assess the prevalence of asymptomatic parasitaemia in the same localities in September 2009. Results In total, 186 and 141 participants residing in 23 case and 24 control homesteads, respectively, were screened. In the case homesteads for which a control population was available (10 of the 23), household members of clinically diagnosed cases had a 8.0% prevalence of malaria using PCR compared to 0.7% PCR positive individuals in the control group (p = 0.006). The case and control groups had a gametocyte prevalence of 2.3% and 0%, respectively but the difference was not significant (p = 0.145). Conclusions This pilot project showed that active case detection is feasible and can identify reservoirs of asymptomatic infection. A larger sample size, data over multiple low transmission seasons, and in areas with different transmission dynamics are needed to further validate this approach.

High-resolution micro-epidemiology of parasite spatial and temporal dynamics in a high malaria transmission setting in Kenya

“…To our knowledge, this investigation presents the first genetic data directly linking parasites causing asymptomatic infections among household members with those causing symptomatic disease. Similar to prior studies 19–23 , we previously noted that CC in this cohort were 2.5 times more likely to have RDT+ household members than were control children 2 indicating household-level hotspots of high-risk individuals. Herein, we extended this association using our parasite genotyping approach to quantify the degree of genetic similarity between infected individuals.…”

Efficiency of a Malaria Reactive Test-and-Treat Program in Southern Zambia: A Prospective, Observational Study

“…26 Studies conducted in Zambia, Senegal, and Swaziland found that the number of tested individuals to identify one infected individual ranged from 37 to 250. 11,12,27 In our study area, a mean of 90 RDTnegative residents were tested for each RDT-positive individual identified and a mean of 66 qPCR-negative residents were tested for each qPCR-positive, RDT-negative individual identified. A mean of 24 qPCR-negative residents of index case households were tested for each qPCR-positive, RDTnegative individual identified within an index case household.…”

Malaria rapid diagnostic tests in elimination settings—can they find the last parasite?

“…However, because microscopy requires extensive training, quality materials, and several years of experience to attain and maintain proficiency, routine diagnosis by microscopy is of variable quality, and lower‐density infections are frequently not identified. Nucleic acid‐based tests (NATs) have consistently demonstrated superiority to RDTs and microscopy in detecting infections at levels below the detection limits of a competent microscopist [29–34]. As countries progress towards malaria elimination, the need to detect submicroscopic infections is becoming increasingly important, as reservoirs of infected persons may sustain transmission even without this manifesting in clinical illness.…”