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