[Catalyst 2018]

methods of
MOSQUITO VECTOR
SURVEILLANCE
rR
and population control
o w a i s f a z a l
BACKGROUND
A variety of mosquito vector surveillance
and control programs have been instituted
over the past few decades with the intention
of limiting the spread of infectious diseases
such as dengue, malaria, and the Zika virus.
With the major public health threat of
mosquito populations spanning across the
globe, it is imperative that we continue to
develop effective methods of controlling the
mosquito population as well as designing
and implementing novel solutions on an
international scale. While these programs
have displayed varying degrees of success, this
review analyzes various methods that seem
to be effective in combating vector incidence
and prevalence within endemic populations
worldwide. Specifically, we will analyze vector
control initiatives involving Aedes albopictus
populations in Yorke Island off the coast of
Australia as well as the control of Anopheles
gambiae populations in Brazil in order to
determine trends in effective mosquito vector
control systems.
YORKE ISLAND
A particularly successful mosquito vector
surveillance program was implemented in
the recent Yorke island mosquito control
initiative. Consistently low densities of Aedes
albopictus populations have been recorded
six years following the program’s inception in
2005. Following the success of the program,
project leaders have claimed that the use
of insecticides appeared to be the most
important component of their intervention
program, with inspection cycles and public
outreach also playing key roles in limiting
the prevalence of the endemic mosquito
population. 1
SOURCE REDUCTION
Successful vector surveillance programs
rely heavily on the utilization of a process
known as source reduction. 2 Source reduction
essentially involves the systematic removal of
potential mosquito breeding sites, effectively
diminishing the growth rates of endemic
mosquito populations significantly. This
process was heavily used in Yorke Island, as
any containers that could potentially hold
water and support larval development were
removed, destroyed, placed under cover,
34 | CATALYST
or treated with pellets or briquettes of the
insect growth regulator s-methoprene.
The s-methoprene was applied to smaller
containers in the form of 15g pellets at a rate
of one pellet per liter of estimated container
volume. Larger containers, such as rainwater
tanks and wells, were treated with ProLink
XR Briquets applied at one briquet per
5000 liters of water. 3 Containers that could
not be removed had their interior surfaces
also sprayed with the residual pyrethroid
bifenthrin to kill adult mosquitoes that came
in contact with them. 4 Samples of larvae were
collected from infested containers for species
identification on a weekly basis in order to help
monitor the efficacy of the insecticide usage.
Thus, the larval habitats of the local Aedes
mosquito species were totally decimated in
the region and mosquito vector populations
declined by as much as 98% according to
recent estimates in 2016. 5
5
Our increasingly
interconnected global
climate is highly vulnerable
to infectious disease
pandemics spread through
vectors such as mosquitoes,
and we must continue
to refine our mosquito
population control methods
to combat this threat.
ACTIVE SURVEILLANCE
Furthermore, it is also imperative to have
reliable methods of approximating the number
of vectors within specific regions of a target
area. In order to address this issue, the Yorke
Island initiative enlisted the support of local
public health officials in order to conduct active
surveillance of target areas and to obtain an
accurate count of mosquito prevalence in
select regions of the island. 6 For each round of
surveillance, larval densities were expressed as
number of positive containers per 100 houses
for the Aedes albopictus species. Moreover,
local populations in vector endemic regions
were surveyed at regular intervals in order to
corroborate results of any other independent,
ongoing vector density studies. 7 All in all, the
teams conducted sweep-net sampling on a
total of 230 different sites, providing data
on precise locations as well as population
densities of vector groups throughout the
vector endemic regions. 8
VECTOR MONITORING
AND THE CORDON SANITAIRE STRATEGY
One of the most crucial qualities of a
successful mosquito vector surveillance and
control program is to be able to monitor
changes in mosquito vector populations
in response to the usage of specific vector
control tactics. 9 In conjunction with the above
methods, being able to accurately examine
vector trends over the period of time that a
vector control program is in place is key. A
strategy used by Yorke island public health
officials that combines monitoring with some
of the more direct methods of combating
vector populations is the cordon sanitaire
strategy, which is an integrated approach
composed of harborage spraying, source
reduction, insecticide treatment of containers,
lethal tire piles, mosquito population
monitoring and public awareness campaigns
supported by local authorities and local
media. 10
BRAZIL
The eradication of the accidentally introduced
Anopheles gambiae mosquito species
from 54,000 km 2 of largely ideal habitat in
northeast Brazil is regarded as one of the
most effective mosquito control campaigns
in scientific history. 11 This successful program
was implemented in the 1930s and early
1940s through an integrated program that
relied overwhelmingly upon larval control
mechanisms. In the decades following the
implementation of the program, similar
initiatives utilized comparable strategies
in order to successfully combat vector
populations in Egypt as well as rural Zambia. 12
ROUTINE VECTOR INSPECTION CYCLES
The total coverage of the A. gambiae mosquito
population was achieved primarily through
the combination of large numbers of field
workers with strictly enforced task-allocation
and supervision systems. Each individual field
worker, known as a larval inspector, was given
a fixed area in which to identify and treat
potential breeding sites and for which he or