Ecological and health experts in the
country have predicted that climate change will escalate the incidence of
dengue fever in the country unless mitigation strategies are devised soon.
Speaking in an exclusive interview with
the 'Sunday News', a Ministry of Agriculture and Food Security's Tropical
Pesticides Research Institute (TPRI) Vector Ecology and Control specialist, Dr
Eliningaya Kweka, said planning of sanitation programmes to eradicate breeding
sites and abandoned containers was paramount.
"It is important to mow all bushes
and tall grasses in urban areas because many people tend to rest in such areas
while the zebra-striped mosquitoes spreading the dengue virus are known to bite
in daytime and move to shaded areas including indoors, small water containers outdoors
and some natural water bodies under the shade," he said.
Concurring with Dr Kweka, a source at
Muhimbili National Hospital, who preferred anonymity, said climate change could
make the environment promote breeding of mosquitoes.
The source said the most cost-effective
way to control the disease was to control its vector or the mosquito itself.
"Cold climates and lack of rainfall don't favour breeding of the
mosquitoes, so any shift in that direction would see a boom in their
population.
That's for sure," the source
explained. Several studies have predicted that global climate change could
increase the likelihood of dengue epidemics.
In the September 2002 issue of The
Lancet, a senior research fellow at the University of Otago, in New Zealand, Mr
Simon Hales, and colleagues published an empirical model of worldwide dengue
distribution in which they reported that annual average vapour pressure (a
measure of humidity) was the single climate factor that best predicted dengue
fever distribution.
"If humidity were to remain at
1990 levels into the next century, a projected 3.5 billion people would be at
risk of dengue infection in 2085, but assuming humidity increases as projected
by the Intergovernmental Panel on Climate Change, the authors estimate that in
fact 5.2 billion people could be at risk," the Environmental Health Perspectives
website read in part.
Researchers view dengue from a variety
of angles to try to curb the virus's spread. There are no available vaccines or
antivirals for dengue infection, leaving mosquito control as the only current
method for prevention and control. Dr Kweka stressed that more emphasis should
be put on having clean surroundings instead of focusing on widespread spraying
and looking for a vaccine.
Dengue is a viral disease that includes
both dengue fever and the more severe dengue haemorrhagic fever (DHF).
Dengue fever involves a mild fever with
joint aches while DHF, which is usually a disease in children and young adults,
incorporates dengue fever and haemorrhagic lesions or bleeding to death.
Of the 50 million dengue infections
estimated by the World Health Organization (WHO) each year worldwide, there are
500,000 cases of DHF and 22,000 deaths, mainly among children.
Although it may not be the most
devastating of the mosquito- borne diseases - malaria strikes 10 times more
people and yellow fever kills more of its victims - dengue has become a major
public health concern for two reasons: the speed with which it is spreading and
the escalating seriousness of its complications.
Dar es Salaam Regional Commissioner, Mr
Said Meck Sadiki, told 'Sunday News' that he concurred with the conclusion that
there was a need to have cleaner surroundings, adding that, that was his
primary objective.
"I totally agree with you, but
while this is going on we need to ensure that other regions are not affected.
The reason for the plan to spray up-country buses is to ensure that the disease
is contained," he said.
A podcast called This Week in Virology
(TWiV) in October 2008 dealt on the subject of dengue. It said that the
mosquito carrying dengue was the same species as that carrying yellow fever and
was of the Aedes aegypti family.
One of the presenters, Columbia
University Professor of Public Health in Environmental Health Sciences, a
microbiologist and ecologist, Dr Dickson Despommier, said the dengue mosquito
has a totally different lifestyle to the malaria one in terms of biting,
breeding, house preferences and biology.
Dr Despommier said that all mosquitoes
of the Aedes family are temporary water breeders whereby they tend to breed in
discarded empty tins and old tyres. They also breed indoors, in water
collecting containers and pots.
"Usually in the tropics when it
rains, water fills up these tins when later the water evaporates, the contents of
the tin gives off an odour that attracts the mosquito and it, unlike the Culex,
lays its eggs on the sides of the tin and they are not easily seen," he
explained.
He explained that as the water in the
tin continues to evaporate, the eggs dry up and with Aedes aegypti eggs, they
think about the next coming rains and if the water level exceeds the level of
the eggs, they are submerged in water and they revive and hatch after one and
half weeks.
The microbiologist said the best way to
control the mosquitoes, which are also known as tree-hole breeding mosquitoes,
is to police areas and identify their breeding sites and eliminate their
environment.
The other host of the podcast,
Professor of Microbiology and Immunology in the College of Physicians and
Surgeons of Columbia University, Dr Vincent Racaniello, said dengue was a very
unusual pathogens because, unlike others, with it subsequent bites put you at
greater risk.
"Anyone
listening to this will be asking themselves why there is a vaccine for yellow
fever, a very good one at that, and dengue fever seems to be very closely
related to yellow fever, then why haven't we managed to re-engineer that
vaccine and make a super vaccine covering yellow, dengue and even West Nile
Fever?" he queried.
Source: Tanzania
Daily News
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