Targeting Asymptomatic Malaria Infections: Active Surveillance in Control and Elimination
et al. (2013) Targeting Asymptomatic
Malaria Infections: Active Surveillance in Control and Elimination. PLoS Med 10(6): e1001467. doi:10.1371/
journal.pmed.1001467
Targeting Asymptomatic Malaria Infections: Active Surveillance in Control and Elimination
Hugh J. W. Sturrock 1 2
Michelle S. Hsiang 1 2
Justin M. Cohen 1 2
David L. Smith 1 2
Bryan Greenhouse 1 2
Teun Bousema 1 2
Roly D. Gosling 1 2
0 AI089674]. TB is supported by a Grand Challenge Grant of the Bill & Melinda Gates Foundation (No. OPP1024438). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript
1 Funding: HJWS and RDG are supported by a grant from the Bill & Melinda Gates Foundation [
2 1 Malaria Elimination Initiative, Global Health Group, University of California, San Francisco, United States of America, 2 Department of Pediatrics, University of California, San Francisco, United States of America , 3 Clinton Health Access Initiative, Boston, MA , United States of America, 4 Department of Epidemiology, Johns Hopkins Bloomberg School of Public Health, Baltimore, United States of America, 5 Department of Medicine, University of California, San Francisco, United States of America, 6 Department of Immunology and Infection, London School of Hygiene and Tropical Medicine , London , United Kingdom , 7 Department of Medical Microbiology, Radboud University Nijmegen Medical Centre , Nijmegen , The Netherlands
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The scale-up of interventions has
reduced malaria burden and transmission
across a number of countries [13]. As
transmission declines, it often becomes
increasingly focal [4], and programs need
to adapt and target the remaining parasite
reservoirs, deploying resources with
increasing granularity. At very low
transmission intensity, elimination of malaria
may involve finding and treating
individual infections.
At large spatial scales, infections tend to
cluster into foci related to environmental,
climatic, and ecological suitability for
vectors and transmission [5]. At smaller
scales within these foci, hotspots, which
consist of a household or groups of
households, maintain higher transmission
of malaria and a consistent reservoir of
parasites throughout the year [4,68]
(Figure 1, Box 1). Infections are also
clustered in certain demographic hot
populations, or hotpops, associated with
demographic risk factors for transmission
[911] (Figure 2, Box 1). In low
transmission or elimination settings, strategies for
detecting and targeting these clusters of
infection, whether geographic or
demographic, become important strategies to
reduce the local parasite reservoir and
interrupt transmission [12].
All malaria control programs have
passive surveillance systems that, to
greater or lesser degrees, identify, treat, and
report individuals with malaria who
present to health facilities. While useful for
intelligence gathering, passive surveillance
alone has a limited impact on malaria
transmission as only symptomatic patients
The Policy Forum allows health policy makers
around the world to discuss challenges and
opportunities for improving health care in their
societies.
receive treatment when they seek medical
care. It is well known, however, that
whether transmission is low or high, the
majority of infections, including carriers of
gametocytes (the life parasite stage
responsible for onward transmission to
mosquitoes), are asymptomatic [1318].
To overcome the inherent limitations of
passive surveillance and to target the
asymptomatic parasite pool, as well as
symptomatic infections in individuals who
do not or cannot seek treatment, a number
of programs have adopted active case
detection (ACD) strategies [12]. Despite
its increasing popularity across a number
of countries, and recommendation by the
World Health Organization (WHO) for
use in malaria elimination [12], the
diversity of ACD methods and the relative
strengths and weaknesses of the various
approaches are poorly described. In this
Policy Forum, we discuss the potential role
of ACD in malaria control and
elimination. While we focus on P. falciparum, the
discussion also includes the potential role
of ACD in the control and elimination of
P. vivax.
Active Case Detection Methods
ACD for malaria infection has a variety
of definitions and designs [19]. The WHO
recently revised the definition of ACD [12]
(Box 2) to differentiate methods that test
only febrile individuals (fever screening)
from those that target all individuals (active
infection detection, aggressive active case
detection, or mass screen and treat)
[14,20,21]. While requiring more
resources, approaches that target all people at risk
of infection enable the targeting of the
asymptomatic parasite pool. For the
remainder of this discussion we use the term
ACD to refer to the active detection of
malaria infections in both symptomatically
and asymptomatically infected individuals.
Competing Interests: The authors have declared that no competing interests exist. (...truncated)