Abstract:
Human movement impacts the spread and transmission of infectious diseases. Recently, a
large reservoir of Plasmodium falciparum malaria was identified in a semi-arid region of
northwestern Kenya historically considered unsuitable for malaria transmission. Under-
standing the sources and patterns of transmission attributable to human movement would
aid in designing and targeting interventions to decrease the unexpectedly high malaria bur-
den in the region. Toward this goal, polymorphic parasite genes (ama1, csp) in residents
and passengers traveling to Central Turkana were genotyped by amplicon deep sequenc-
ing. Genotyping and epidemiological data were combined to assess parasite importation.
The contribution of travel to malaria transmission was estimated by modelling case repro-
ductive numbers inclusive and exclusive of travelers. P. falciparum was detected in 6.7%
(127/1891) of inbound passengers, including new haplotypes which were later detected in
locally-transmitted infections. Case reproductive numbers approximated 1 and did not
change when travelers were removed from transmission networks, suggesting that trans-
mission is not fueled by travel to the region but locally endemic. Thus, malaria is not only
prevalent in Central Turkana but also sustained by local transmission. As such, interrupting
importation is unlikely to be an effective malaria control strategy on its own, but targeting
interventions locally has the potential to drive down transmission.