MALARIA ELIMINATION IN ZANZIBAR - Soper Strategies
MALARIA ELIMINATION IN ZANZIBAR - Soper Strategies
MALARIA ELIMINATION IN ZANZIBAR - Soper Strategies
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FIGURE 7: DAILY FERRY TRAFFIC ROUTES AND CAPACITIES<br />
FIGURE 8: FERRY PASSENGER NUMBERS FOR ALL ENTRY PO<strong>IN</strong>TS <strong>IN</strong>TO<br />
<strong>ZANZIBAR</strong> (2006 AND 2007)<br />
Types of Travelers<br />
Although data on ferry and airport traffic permits estimation of<br />
the number of people migrating from the mainland to Zanzibar,<br />
importation risk is only affected by the subset of those migrants<br />
who are infected with malaria parasites. Different subgroups of<br />
migrants will likely be at very different risks for importing malaria<br />
Tourism represents the principal income source for Zanzibar<br />
and brings in visitors from all over the world. Typically, three<br />
categories of tourist exist on Zanzibar (Heita-Mwampamba,<br />
2003):<br />
20<br />
Tanga<br />
Tanga to Wete: Infrequent service<br />
Daily capacity: Data not availabe<br />
Tanzania Zanzibar<br />
45,000<br />
40,000<br />
35,000<br />
30,000<br />
25,000<br />
20,000<br />
15,000<br />
10,000<br />
5,000<br />
Zanzibar Town to Mkoani,<br />
Daily capacity: 625<br />
Zanzibar Town<br />
Der es Salaam to Zanzibar Town<br />
Daily capacity: 1,810<br />
Unguja<br />
Dar Es Salaam<br />
MONTHS<br />
Pemba<br />
Mkoani<br />
Mkoani to Zanzibar Town<br />
Daily capacity: 625<br />
a. Those arriving as part of a journey that includes mainland<br />
Tanzania or Kenya–typically, but not exclusively (see below)<br />
backpackers staying at low budget accommodation (making<br />
up around 70% of Unguja tourist accommodation)<br />
b. Those exclusively visiting the islands through package deals<br />
c. Expatriate families and upper-class citizens from the mainland<br />
Wete<br />
J F M A M J J A S O N D J F M A M J J A S O N D<br />
Data from the Zanzibar Commission for Tourism indicate<br />
that tourists in groups (a) and (b) have almost doubled in the<br />
last five years, from 87,511 in 2002 to 143,265 in 2007. The<br />
vast majority of tourists visiting Zanzibar are from non-malaria<br />
endemic countries (Guerra et al., 2008). Just 15.5% of tourists<br />
in 2007 came from potentially malaria endemic regions in 2007,<br />
with the majority of countries and regions of origin of low or zero<br />
transmission (Hay et al., 2009).<br />
Our analysis suggests that tourists represent a low risk group for<br />
malaria importation to Zanzibar. Many tourists will be taking<br />
prophylactic medication, and most will spend little time in highrisk<br />
areas. However, it should be noted that holiday packages<br />
involving mainland safaris in malaria-endemic regions, followed<br />
by a visit to Zanzibar, are popular. Numbers do not exist on<br />
those taking this type of vacation. Recent survey data have shown<br />
that 69% of tourists to Zanzibar come as part of a package deal<br />
(Tanzania Ministry of Natural Resources and Tourism, 2007)<br />
involving flights direct to Zanzibar (or changing briefly at Dar Es<br />
Salaam), and remaining on the islands (often within resorts) for<br />
the entire stay. These package holiday tourists (~100,000 visitors<br />
a year) represent an extremely low risk group for imported<br />
infections.<br />
At this time, little information is available on the number<br />
of non-tourist travelers to Zanzibar arriving by air, ferry, or<br />
informal boat, though mobile phone data analyses (see below)<br />
have provided valuable data. Some of these travelers may be<br />
businesspeople who will stay in Zanzibar only briefly, migrant<br />
workers who will remain for weeks or months, or Zanzibar<br />
residents returning home from abroad. Much more information<br />
is needed on identifying the types of people traveling to Zanzibar<br />
especially by ferry or informal boat, since these individuals are<br />
much less likely to be taking malaria prophylaxis than those<br />
arriving by air.<br />
Migrants<br />
Given that different subgroups of migrants may have different<br />
average risks of being infected, the probability a specific traveler<br />
is carrying malaria is greatly dependent upon where he or she<br />
originated. Detailed maps of malaria prevalence are now available<br />
(Hay et al., 2009); unfortunately, data on the origin of migrants to<br />
Zanzibar are sparse, incomplete and outdated, making confident<br />
recommendations difficult for this key group in quantifying<br />
importation risk. Nevertheless, limited survey data on the origin<br />
of migrants regularly coming to Zanzibar to work in the tourist<br />
industry do exist (Gossling and Schulz, 2005), and are shown<br />
in Figure 9(a). Comparison of these locations with a map of P.<br />
falciparum malaria transmission intensity for 2007, measured<br />
in terms of parasite prevalence (Figure 9(b)), suggests that the<br />
majority of migrants to Zanzibar come from the relatively lower<br />
transmission areas of the mainland.<br />
A measure of P. falciparum parasite prevalence per person can be<br />
calculated by weighting the parasite prevalence maps in Figure<br />
9(b) by the population distribution in Figure 9(c). When this per<br />
person prevalence is combined with the percentage of all Zanzibar<br />
migrants originating in each region, a simple index of relative<br />
Imported Case Risk (ICR) can be calculated. The ICR identifies