MALARIA ELIMINATION IN ZANZIBAR - Soper Strategies

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FIGURE 7: DAILY FERRY TRAFFIC ROUTES AND CAPACITIES FIGURE 8: FERRY PASSENGER NUMBERS FOR ALL ENTRY POINTS INTO ZANZIBAR (2006 AND 2007) Types of Travelers Although data on ferry and airport traffic permits estimation of the number of people migrating from the mainland to Zanzibar, importation risk is only affected by the subset of those migrants who are infected with malaria parasites. Different subgroups of migrants will likely be at very different risks for importing malaria Tourism represents the principal income source for Zanzibar and brings in visitors from all over the world. Typically, three categories of tourist exist on Zanzibar (Heita-Mwampamba, 2003): 20 Tanga Tanga to Wete: Infrequent service Daily capacity: Data not availabe Tanzania Zanzibar 45,000 40,000 35,000 30,000 25,000 20,000 15,000 10,000 5,000 Zanzibar Town to Mkoani, Daily capacity: 625 Zanzibar Town Der es Salaam to Zanzibar Town Daily capacity: 1,810 Unguja Dar Es Salaam MONTHS Pemba Mkoani Mkoani to Zanzibar Town Daily capacity: 625 a. Those arriving as part of a journey that includes mainland Tanzania or Kenya–typically, but not exclusively (see below) backpackers staying at low budget accommodation (making up around 70% of Unguja tourist accommodation) b. Those exclusively visiting the islands through package deals c. Expatriate families and upper-class citizens from the mainland Wete J F M A M J J A S O N D J F M A M J J A S O N D Data from the Zanzibar Commission for Tourism indicate that tourists in groups (a) and (b) have almost doubled in the last five years, from 87,511 in 2002 to 143,265 in 2007. The vast majority of tourists visiting Zanzibar are from non-malaria endemic countries (Guerra et al., 2008). Just 15.5% of tourists in 2007 came from potentially malaria endemic regions in 2007, with the majority of countries and regions of origin of low or zero transmission (Hay et al., 2009). Our analysis suggests that tourists represent a low risk group for malaria importation to Zanzibar. Many tourists will be taking prophylactic medication, and most will spend little time in highrisk areas. However, it should be noted that holiday packages involving mainland safaris in malaria-endemic regions, followed by a visit to Zanzibar, are popular. Numbers do not exist on those taking this type of vacation. Recent survey data have shown that 69% of tourists to Zanzibar come as part of a package deal (Tanzania Ministry of Natural Resources and Tourism, 2007) involving flights direct to Zanzibar (or changing briefly at Dar Es Salaam), and remaining on the islands (often within resorts) for the entire stay. These package holiday tourists (~100,000 visitors a year) represent an extremely low risk group for imported infections. At this time, little information is available on the number of non-tourist travelers to Zanzibar arriving by air, ferry, or informal boat, though mobile phone data analyses (see below) have provided valuable data. Some of these travelers may be businesspeople who will stay in Zanzibar only briefly, migrant workers who will remain for weeks or months, or Zanzibar residents returning home from abroad. Much more information is needed on identifying the types of people traveling to Zanzibar especially by ferry or informal boat, since these individuals are much less likely to be taking malaria prophylaxis than those arriving by air. Migrants Given that different subgroups of migrants may have different average risks of being infected, the probability a specific traveler is carrying malaria is greatly dependent upon where he or she originated. Detailed maps of malaria prevalence are now available (Hay et al., 2009); unfortunately, data on the origin of migrants to Zanzibar are sparse, incomplete and outdated, making confident recommendations difficult for this key group in quantifying importation risk. Nevertheless, limited survey data on the origin of migrants regularly coming to Zanzibar to work in the tourist industry do exist (Gossling and Schulz, 2005), and are shown in Figure 9(a). Comparison of these locations with a map of P. falciparum malaria transmission intensity for 2007, measured in terms of parasite prevalence (Figure 9(b)), suggests that the majority of migrants to Zanzibar come from the relatively lower transmission areas of the mainland. A measure of P. falciparum parasite prevalence per person can be calculated by weighting the parasite prevalence maps in Figure 9(b) by the population distribution in Figure 9(c). When this per person prevalence is combined with the percentage of all Zanzibar migrants originating in each region, a simple index of relative Imported Case Risk (ICR) can be calculated. The ICR identifies
those regions from where the greatest numbers of imported cases in migrants are likely to originate, as depicted in Figure 9(d). Patterns of malaria in origin regions can be highly seasonal, although great geographic variation exists in the intensity of transmission and the amount of the year during which it occurs. By accounting for the main transmission season months (Tanser et al., 2003) of each origin region, temporal changes in relative ICR can be examined to estimate when numbers of imported cases in migrants are likely to be highest. Estimates of the fraction of infected persons in each origin region at a given time were combined with migration rates from each region to estimate the proportion of migrants travelling to Zanzibar with P. falciparum (Pf) infections over time. Moreover, the proportion of these ferry passengers traveling to Unguja and Pemba were assumed to match the ferry capacity proportions shown in Figure 8, summed over a month. FIGURE 9 (A) ORIGINS OF MIGRANTS TO ZANZIBAR 2 (C) POPULATION DENSITY PER 100M GRID SQUARE 4 Estimates These relative ICR estimates are depicted in Figure 10. They demonstrate a great range in imported infections risk from migrants through the year and between islands, reflecting traffic numbers, passenger origins and transmission seasons in the regions where passengers originate. Further data on ferry passenger travel histories is required to confirm ferry passenger composition, but analyses of mobile phone data (below) indicate that an overwhelming majority of ferry passengers simply travel between Zanzibar and Dar es Salaam. 2 Scale shows percentage of total migrants (Gossling and Schulz, 2005) 3 Hay et al., 2009 4 Tatem et al., 2008 (B) P. FALCIPARUM PARASITE PREVALENCE IN 2007 3 (D) RELATIVE IMPORTED CASE RISK (ICR) FROM MIGRANTS HIGH ICR LOW 1 | Technical Feasibility FIGURE 10: RELATIVE IMPORTED CASE RISK (ICR) BY MONTH FROM MAINLAND MIGRANTS UNGUJA PEMBA JANUARY FEBRUARY MARCH APRIL MAY JUNE JULY AUGUST SEPTEMBER OCTOBER NOVEMBER DECEMBER Control efforts on the mainland will have a significant effect on imported infection numbers. In the analysis described here, we have not attempted to adjust for such effects. In reality, however, the current coverage of interventions like bednets, IRS, and prompt treatment with ACTs will likely greatly reduce the true number of imported cases. A careful analysis of the coverage of these interventions in mainland districts where migrants to Zanzibar originate will be necessary to assess the magnitude of the potential reduction; such reductions are likely to be significant and should increase over time as scale-up campaigns continue in Tanzania (Figure 11). FIGURE 11: ITN COVERAGE AMONG CHILDREN UNDER THE AGE OF 5 YEARS PROJECTED TO JULY 2007 (NOOR ET AL., 2009) 21
Page 1: PHOTO: © SASJA VAN VECHGEL MALARIA
Page 5: ACKNOWLEDGEMENTS The feasibility as
Page 9 and 10: EXECUTIVE SUMMARY Over the past sev
Page 11 and 12: Financial Feasibility The optimal m
Page 13 and 14: INTRODUCTION BACKGROUND In October
Page 15 and 16: FIGURE 2.1: AVERAGE MONTHLY RAINFAL
Page 17 and 18: CHAPTER 1: TECHNICAL FEASIBILITY IN
Page 19 and 20: to below 1% with IRS (Bhattarai et
Page 21: DEFINING IMPORTATION RISK As illust
Page 25 and 26: PROBABILITY OF ACQUIRING INFECTION
Page 27 and 28: NUMBER OF INFECTED INDIVIDUALS achi
Page 29 and 30: PERCENTAGE OF INDIVIDUALS INFECTED
Page 31 and 32: the same time, it is expected that
Page 33 and 34: test, about 80% of infections could
Page 35 and 36: CHAPTER 2: OPERATIONAL FEASIBILITY
Page 37 and 38: DATA COLLECTION METHODS A robust su
Page 39 and 40: most secondary cases but would occa
Page 41 and 42: TABLE 5: RAPID RESPONSE ACTION FOR
Page 43 and 44: up. It will also allow for the iden
Page 45 and 46: TABLE 7: PRE-ELIMINATION AND ELIMIN
Page 47 and 48: essential components of an eliminat
Page 49 and 50: THE ZANZIBAR HEALTH CARE SYSTEM THE
Page 51 and 52: community needs to be aware that fe
Page 53 and 54: conditions. Health worker motivatio
Page 55 and 56: A key challenge will be that as an
Page 57 and 58: The ZMCP is relatively well staffed
Page 59 and 60: elaborate entomological surveillanc
Page 61 and 62: COMMUNITY INVOLVEMENT ON ZANZIBAR Z
Page 63 and 64: �� Communities should, as far a
Page 65 and 66: preventive measures, mainly related
Page 67: CONCLUSIONS This chapter considers
Page 70 and 71: elimination will raise two major fi
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INDOOR RESIDUAL SPRAYING As noted a
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analysis be conducted. Moreover, gi
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FIGURE 30: AVERAGE COST PER YEAR FO
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which are being explored by the glo
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portion of those costs). Before thi
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REFERENCES Afridi MK (2009). Use of
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Jacobs, Lesley A (9/2007). Rights a
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Sandberg, Ingstad K, Bjune G (2007)
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World Health Organization, Global M
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