10
UWI TODAY
– SUNDAY 1ST FEBRUARY, 2015
The
Chikungunya
Effect
UWI
TODAY
SPECIAL REPORT
If someone tells you that mosquitoes
cannot cross
highways and that that might be useful information in
preventing their spread, youmight blink twice. But if that
someone is
Dave Chadee
, entomologist, parasitologist,
andaProfessorof EnvironmentalHealthat theDepartment
of Life Sciences at The UWI, you might think twice. He is
internationally recognized as an expert on mosquitoes
and has done a substantial amount of research on the
accursed Aedes aegypti mosquito, the carrier of Yellow
Fever, Dengue and the Chikungunya virus.
On June 12, 2014, he presented a paper on“Vector Control
Management in the Caribbean region: Lessons ignored”
at an event held by CARPHA, the Caribbean Public
Health Agency, and CKLN, the Caribbean Knowledge and
Learning Network in Port of Spain. He lamented that the
same vector control strategies have been used for the
past 25 to 30 years without success and it was way past
the time to invest in new strategies based on scientific
research.
He looked at four of the major programmes used
regionally, questioning their efficacy under today’s
conditions.
•
Focal-perifocal applications
(putting insecticide into potable water containers).
•
Space spraying – ULV trucks and dyna-fogging.
•
Residual sprayings.
•
Health education with source reduction as the main
pillar.
Failures in these programmes could be attributed to a
series of common factors.
•
Treatments are universally applied whether suitable
or not, such as applying the same programme to
the BlueMountains in Jamaica and the flat Barbados
landscape.
•
Ignoring an outbreak and hoping it will go away (for
good).
•
Using the same approach (like pesticides) and not
taking into account that resistance develops over
time.
•
The decline of community support, particularlywhen
measures seem ineffective.
•
Accepting non-technical advice.
Time to Swat Away
those Old Techniques
Sprays are useless in this mosquito war
By Vaneisa Baksh
The aerial sprayings, he said, are ineffective because they
do not sufficiently penetrate houses to kill the resting
mosquitoes. (His research showed that they love to loll off
in our bedrooms after a bloodmeal.) They also negatively
affect almost all living things: asthmatics and people
with respiratory illnesses; pollinators like butterflies, bees
and birds; aquaria fish and chickens on a farm, pigs in
piggeries. Generally, the sprays disrupt the functioning
of the entire ecosystem; while the mosquitoes keep
humming along their merry way.
Professor Chadee, who spent many years at the Insect
Vector Control Division, has in the past complained that
his recommendations for vector control programmes to
the Government of the Republic of Trinidad and Tobago
have been largely ignored. He offered several suggestion
for a different approach to the growing problem of
mosquito-driven epidemics.
His expertise has been sought in several countries seeking
to fight such outbreaks. In the period between 2007 and
2014, he has been to Italy, Brazil, Mauritius, Sri Lanka,
the Seychelles, and Reunion Island – there were major
outbreaks in the last four. There, “a suite of interventions
programmes was developed, including conventional
vector control, and with the addition of the Sterile Insect
Technology (SIT)” he tells me. SIT is like birth control, he
says, sterilizing immature male mosquitoes via radiation
and releasing them back into the wild to mate. Since the
eggs produced are not viable, the population eventually
collapses. It worked in Mauritius and Reunion Island.
Although it is expensive, a pilot project is to be
implemented in St.Vincent, says Dr James Hospedales, the
Executive Director of CARPHA, who has also complained
that the “same-old, same-old” strategies of the past few
decades are simply not working.
“We have to change the vector control paradigms,”he said.
“We have to stop the knee-jerk responses. Governments
could spray every day and it would not help; the
mosquitoes have become resistant.”
And it isnot vector control thatneedsdifferent approaches,
he says, this Chikungunya virus is a wake-up call to the
region. “We have to look at epidemic control too.”
“If this were a lethal virus,” he says grimly, “we would be
inmonkey pants.”He warns that the migratory pattern of
the virus shows that it is heading southward and it is here
in the region to stay.
From 1954 to 2004, Dr Hospedales notes, there were
about a million cases of ChikV with outbreaks first in
Africa, then South Asia, and Southeast Asia. That is over
a fifty-year period. Since the first case of ChikV in the
Americas was reported inDecember 2013 in Saint Martin/
Sint Maarten, there are now about a million cases in the
region, with 23 of the 24 CARPHAmember states affected
as at October 27, 2014. Less than one year.
As in Dengue and Chikungunya there are similar
trajectories, and Dr Hospedales points to a recent one,
the Zika virus, which is following the same path and may
reasonably be expected to hit the region. It is likeDengue,
he says, and may be lethal. Coupled with Professor
Chadee’s observation that the Dengue outbreaks had
become more frequent over the years, turning up every
five years or so, and his prediction that even that will
soon become as frequent as every two years; it is of
enough gravity to warrant a major shift in public health
strategies, because clearly, the mosquitoes are winning
these battles.
Among the strategies proposed by Professor Chadee,
based on research that has been so prolonged and
detailed that he has had Dengue twice (along with
Dengue Hemorrhagic Fever), are some particularly
innovative ones.
Based on investigations of several households, his team
was able to ascertain that mosquitoes overwhelmingly
prefer to rest in bedrooms (81.9%) (see Table 1) and they
liked walls best. It explains why DDT was effective when
it was applied to walls, and the sprays were not – as they
were not as concentrated.
His research on the travelling habits of the mosquitoes
revealed two features that he is certain can be applied to
stopping them in their tracks. The first is that mosquitoes
do not cross highways.
“Aedes aegyptimosquitoes, andby extension, theDengue
virus do not cross over highways, so you are ‘genetically’
“Whenamosquito
takesabloodmeal, it first inoculates
an anticlotting agent so that the blood will flow up
through the mosquito’s mouth parts (the proboscis)
and fill its digestive system. The anticlotting agent is
usually infectedwith the virus so transmission occurs at
that time – when a stinging sensation is felt. The blood
in the digestive system is used by themosquito for the
production of eggs by removing the proteins. If the
bloodmeal is infected, the viruswill growand replicate,
pass through the peritrophicmembrane and infect the
haemocoel or blood of the mosquito. The virus in the
haemocoel migrates to the mosquito’s salivary glands
and is released simultaneously with the anticoagulant
during blood feeding.”
– Professor Dave Chadee
Madame
Mosquito
at work
