The Question
With the prevalence of Plasmodium falciparum malaria in Zanzibar at historic lows, what are the causes of the remaining cases and how can control be improved?
What We Found
The analysis suggests that citizens of Zanzibar who travel to malaria endemic regions are likely to be the single most important source of importation.
Why It Matters
Enhanced prevention and control strategies aimed at mitigating pathogen importation would eventually cause malaria to disappear from most of the island, except possibly in a few residual foci if no imported infections occurred.
Abstract
The prevalence of Plasmodium falciparum malaria in Zanzibar has reached historic lows. Improving control requires quantifying malaria importation rates, identifying high-risk travelers, and assessing onwards transmission.
Estimates of Zanzibar’s importation rate were calculated through two independent methodologies. First,
mobile phone usage data and ferry traffic between Zanzibar and mainland Tanzania were re-analyzed using
a model of heterogeneous travel risk. Second, a dynamic mathematical model of importation and
transmission rates was used.
Zanzibar residents traveling to malaria endemic regions were estimated to contribute 1–15 times more
imported cases than infected visitors. The malaria importation rate was estimated to be 1.6 incoming
infections per 1,000 inhabitants per year. Local transmission was estimated too low to sustain transmission
in most places.
Malaria infections in Zanzibar largely result from imported malaria and subsequent transmission.
Plasmodium falciparum malaria elimination appears feasible by implementing control measures based
on detecting imported malaria cases and controlling onward transmission.
Keywords
ACTs,
elimination,
malaria mapping
