MALARIA ELIMINATION IN ZANZIBAR - Soper Strategies

test, about 80% of infections could be treated before they have the
opportunity to lead to onwards transmission. In such a situation,
importation would be reduced from 2-8/1000 to 0.4-1.6/1000.
Using these estimates of technically feasible increases in passive
detection and decreases in importation, the simulator was run
multiple times to identify the amount of active case detection
required to maintain elimination.
FIGURE 21: RELATIONSHIP BETWEEN SIMULATED ONWARD TRANSMISSION
AND ACD GIVEN 0% EFFECTIVE ITN COVERAGE AND REDUCED IMPORTATION
2ND GENERATION CASES PER 1000 PERSON-YRS
12
10
8
6
4
2
0
0 50 100 150 200
HOUSES INVESTIGATED AROUND EACH IDENTIFIED INFECTION
The green line indicates predictions for importation = 0.4/1000
while the blue line is for 1.6/1000; the dotted line indicates the
approximate threshold below which WHO criteria for prevention of
reintroduction are met.
Figure 21 demonstrates that at the low range of importation,
0.4/1000, active case detection of about 100 neighboring houses
surrounding each case will be necessary to maintain elimination.
However, at 1.6/1000, active case detection does not appear to
be a viable means of preventing second generation transmission.
While ACD appears to have very large effects on decreasing
transmission in such a scenario, sporadic transmission remains.
As in previous scenarios, even small changes in importation
appear to have large ramifications for Zanzibar’s ability to
maintain elimination.
These results indicate that it is very likely that local transmission
of malaria will occasionally occur on Zanzibar following
elimination. Even countries such as the United States (Filler
et al., 2006) and Belgium (Peleman et al., 2000) continue to
face occasional local transmission due to importation of cases
or infected mosquitoes. Zanzibar therefore must be prepared to
rapidly respond to and contain any malaria outbreaks before they
spread into generalized epidemics. Response teams will need to
be created and trained to be deployable whenever a new malaria
case and/or renewed local transmission is identified.
Focusing on improving surveillance and response capacity has at
least two potential advantages over infinitely maintaining high
levels of personal protection. First, it has the potential to be less
expensive compared to sustained control (see Chapter 3) since it
obviates the need to continually distribute/replace nets or spray
houses. Second, these efforts will contribute towards the strength
1 | Technical Feasibility
of the overall public health system, not just malaria control; for
example the surveillance infrastructure that will be required for
malaria reporting will also allow the monitoring of other diseases
as well, while the trained response teams will be able to focus on
other types of outbreaks during periods in which no malaria is
present. For the foreseeable future, however, Zanzibar should be
prepared to emphasize both surveillance/response and coverage
by interventions including ACTs and ITNs/IRS.
RECOMMENDATIONS
Mathematical models predict that Zanzibar can achieve
elimination if it maintains high levels of its current control
activities. Given current scale-up plans, it may be possible to
eliminate malaria within the decade, but it is essential that scaleup
occurs in all districts and that other preventative measures–
notably IRS–protect the population until high effective levels of
net use are ensured. Once surveys confirm that net usage is greater
than 80% in the general population, it is likely that measures like
IRS can safely be scaled back without jeopardizing the chance for
continued progress against malaria.
We estimate that, given the lead times for grant signing and
procurement, universal coverage with ITNs will not be achieved
in all districts before the end of 2010. We therefore recommend
continuing blanket IRS at least for the next 2 years. Given the
heterogeneity in net coverage today and initial indications that
certain areas have a higher transmission potential, it is highly
likely that IRS will need to continue in targeted areas after this
for an additional 2 years. Survey data on ITN use and the Malaria
Early Epidemic Detection System (MEEDS) data can direct the
decision to scale back spraying in these high risk areas.
Surveillance activities must be strengthened. It is not necessary
for Zanzibar to wait until its surveillance system is “perfect”
before engaging in elimination activities, but strengthening of
surveillance should be emphasized at the same time that nets
are being scaled up if Zanzibar is to achieve elimination in a
sustainable way. Mathematical models indicate the importance of
both passive and active surveillance in identifying cases promptly.
Given Zanzibar’s high innate risk of malaria, withdrawing
control measures like IRS and ITNs after elimination will only
be possible if capacity to rapidly identify cases, swiftly treat them,
and prevent local transmission has been developed.
Zanzibar should plan to maintain universal ITN coverage
until it can confirm reductions in malaria importation and
improvements in surveillance. Once malaria elimination is
achieved, the high innate level of malaria means that control
activities such as nets and IRS can only be relaxed if passive
detection rates are greatly increased and importation risk
greatly reduced. Extensive active case detection will also have
a substantial effect, but preventing reintroduction will prove
extremely challenging without some ongoing prevention
activities. Creation of a very strong response capacity in the
form of deployable teams will act as a final safety net necessary
before reductions in control activities can safely occur. The
strengthening of surveillance activities and enhancement of
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