Seasonality in malaria transmission: implications for case-management with long-acting artemisinin combination therapy in sub-Saharan Africa.
BACKGROUND
Long-acting artemisinin-based combination therapy (LACT) offers the potential to prevent recurrent malaria attacks in highly exposed children. However, it is not clear where this advantage will be most important, and deployment of these drugs is not rationalized on this basis.


METHODS
To understand where post-treatment prophylaxis would be most beneficial, the relationship between seasonality, transmission intensity and the interval between malaria episodes was explored using data from six cohort studies in West Africa and an individual-based malaria transmission model. The total number of recurrent malaria cases per 1000 child-years at risk, and the fraction of the total annual burden that this represents were estimated for sub-Saharan Africa.


RESULTS
In settings where prevalence is less than 10 %, repeat malaria episodes constitute a small fraction of the total burden, and few repeat episodes occur within the window of protection provided by currently available drugs. However, in higher transmission settings, and particularly in high transmission settings with highly seasonal transmission, repeat malaria becomes increasingly important, with up to 20 % of the total clinical burden in children estimated to be due to repeat episodes within 4 weeks of a prior attack.


CONCLUSIONS
At a given level of transmission intensity and annual incidence, the concentration of repeat malaria episodes in time, and consequently the protection from LACT is highest in the most seasonal areas. As a result, the degree of seasonality, in addition to the overall intensity of transmission, should be considered by policy makers when deciding between ACT that differ in their duration of post-treatment prophylaxis.
MRC Tropical Epidemiology Group, LSHTM, London, UK. matthew.cairns@lshtm.ac.uk.
Matthew E
ME
Cairns
MRC Centre for Outbreak Analysis and Modelling, Imperial College London, London, UK. patrick.walker@imperial.ac.uk.
Patrick G T
PG
Walker
MRC Centre for Outbreak Analysis and Modelling, Imperial College London, London, UK. lucy.okell@imperial.ac.uk.
Lucy C
LC
Okell
MRC Centre for Outbreak Analysis and Modelling, Imperial College London, London, UK. jamie.griffin@imperial.ac.uk.
Jamie T
JT
Griffin
MRC Centre for Outbreak Analysis and Modelling, Imperial College London, London, UK. tini.garske@imperial.ac.uk.
Tini
T
Garske
Kintampo Health Research Centre, Kintampo, Ghana. kwakupoku.asante@kintampo-hrc.org.
Kwaku Poku
KP
Asante
Kintampo Health Research Centre, Kintampo, Ghana. seth.owusu-agyei@kintampo-hrc.org.
Seth
S
Owusu-Agyei
Faculty of Infectious and Tropical Diseases, LSHTM, London, UK. ddiallo@path.org.|PATH-Malaria Vaccine Initiative, Dakar, Senegal. ddiallo@path.org.
Diadier
D
Diallo
Malaria Research and Training Centre, Bamako, Mali. adicko@icermali.org.
Alassane
A
Dicko
Faculty of Infectious and Tropical Diseases, LSHTM, London, UK. badara.cisse@lshtm.ac.uk.|Université Cheikh Anta Diop, Dakar, Sénégal. badara.cisse@lshtm.ac.uk.
Badara
B
Cisse
Faculty of Infectious and Tropical Diseases, LSHTM, London, UK. brian.greenwood@lshtm.ac.uk.
Brian M
BM
Greenwood
Faculty of Infectious and Tropical Diseases, LSHTM, London, UK. daniel.chandramohan@lshtm.ac.uk.
Daniel
D
Chandramohan
MRC Centre for Outbreak Analysis and Modelling, Imperial College London, London, UK. azra.ghani@imperial.ac.uk.
Azra C
AC
Ghani
MRC Tropical Epidemiology Group, LSHTM, London, UK. paul.milligan@lshtm.ac.uk.
Paul J
PJ
Milligan
D000962:Antimalarials / Q000627:therapeutic use*; D037621:Artemisinins / Q000627:therapeutic use*; D002648:Child; D002675:Child, Preschool; D003430:Cross-Sectional Studies; D004359:Drug Therapy, Combination; D006801:Humans; D015994:Incidence; D008288:Malaria / Q000188:drug therapy* / Q000453:epidemiology* / Q000635:transmission; D012621:Seasons
D000962:Antimalarials; D037621:Artemisinins; C031327:artemisinin