MALARIA ELIMINATION IN ZANZIBAR - Soper Strategies

up. It will also allow for the identification of high risk areas
for reintroduction of the parasite after control. Vectorial
capacity is defined as the number of new inoculations per
day expected from one single human case and described
thus:
VC = ma2 pn / -loge p
Where: ma = human biting rate
p = daily survival rate of the vector (longevity)
e = duration of sporogonic cycle in the vectors
This is a key indicator and requires a number of entomological
monitoring activities to take place. Human biting rate can be
ascertained from landing catches on volunteers or through
light trap assays depending on the ethical considerations of
the country, and it will give an indication of the intensity of
biting in the immediate area. Longevity can be determined
through routine measurement of parity rates via ovarian
dissections from female mosquitoes gleaned from routine
collections. The length of the sporogonic cycle can be
obtained from standard formulae based on temperature
measurements.
�� Response of vector to withdrawal of insecticide spraying
after the application of intensive control measures
Monitoring of the response to the withdrawal of insecticides
will form part of the overall entomological monitoring
efforts and collections will need to measure vector density,
species composition, biting rates, infection rates and
insecticide resistance assays. The bulk of this work will be
obtained from standard entomological collections outlined
above. Standard WHO cone assays can be used to simply
measure insecticide resistance.
�� Environmental changes as a result of developments,
which may affect the vector population
Recording environmental changes that may have an impact
on malaria transmission in the local area; e.g. an increase in
standing water through man made or natural phenomena
Routine entomological monitoring throughout the islands
should be maintained throughout the elimination efforts. These
activities will characterize the vector population throughout the
islands and provide a baseline vector profile before full-scale
control activities are implemented to push for elimination. The
information gathered will also be used to detect any reservoirs
of infections and transmission foci and help to target control
activities, while also defining the susceptibility of certain areas
to re-infection based on the vectorial capacity and transmission
history of the area.
The majority of the entomological monitoring efforts can
be based around field collections that will be augmented by
laboratory work. Most of these activities are low-tech and can
be carried out by adequately trained field teams. The specific
activities needed are:
�� Adult sampling from household knock-down collections
to give an estimation of local vector density and species
composition;
2 | Operational Feasibility
�� Landing or light trap collections to obtain an estimation
of human biting rate for the different vector species both
indoors and out;
�� Mapping and sampling of breeding sites to identify sites that
are positive or negative for larvae and obtain larval density
figures;
�� Standard dissection of collected adult specimens to ascertain
parity (ovarian dissection) and sporozoite rates (salivary gland
dissection). Additionally, simple ELISA tests can be used to
identify blood meal origin; and
�� Live adults can be collected for WHO cone filter paper assays
or CDC bottle bioassays to ascertain a measure insecticide
resistance. Should the technology and staff exist, PCR of
homogenised adults (following dissection) can also be used
for more specific resistance genotyping.
Collection activities should be employed by mobile teams
across the islands, with laboratory support as needed, to build
up a vector database for all regions. This database will provide
crucial information outlining transmission foci and areas highly
susceptible to reinfection, which can be fed into the programme
planning cycle to better target control measures and ensure
they are effective; especially in terms of insecticide resistance.
Moreover, the database will provide information on any changes
in vector behaviour as a result of intensified control measures. For
example, the vectors may begin to rest and/or feed outside rather
than in houses, and this change would require a reorientation in
strategy to ensure interventions are relevant and effective.
It would be prudent to put extra focus on routine monitoring
areas where transit between the islands and the mainland occurs
in order to ensure that any introduced infections are rapidly
detected.
As described above, entomological monitoring is also a key aspect
of outbreak investigation and will help to determine whether an
infection was locally acquired or not, and how far it is likely to
spread based on the vectorial capacity in the area.
Surveillance of Human and Environmental Factors
In addition to case surveillance, the ZMCP should also collect or
have access to data related to human and environmental factors.
Often this will require intensive collaboration with different
ministerial departments. We recommend that the ZMCP collects
or has access to the following information (to be included in the
central database where relevant):
�� Inbound and outbound population movements:
Quantification and tracking of inbound population
movements from malaria endemic areas can serve as a proxy
indicator for importation risk. These figures will also enable
design and planning of potential active case detection rates
at the border.
�� Meteorological and climate data: Excessive rainfall
and floods should be monitored. Collaboration with the
meteorological agency should be initiated and the forecasting
of possible unusual events should be notified in order to
intensify surveillance and alertness for possible local outbreaks.
41