Malaria
kills 1.2 million people each year, according to new research and published in
the British medical journal the Lancet in February 2012. This is more than
twice as many deaths as reported by the World Malaria Report published in 2011.
Africa is hit the hardest, accounting for nearly 81% of malaria deaths
globally. These deaths primarily occur among children under five years of age
and pregnant women. How do we turn the tide against an ancient scourge, and
ultimately to eradicate the canny malaria parasite?
The economic cost of malaria
Leading
economists have estimated that malaria is responsible for an “economic growth
penalty” of up to 1.3 percent per year in malaria-endemic African countries. Malaria
costs African countries an estimated US$12 billion per year (circa 36% of
Kenya’s annual GDP) in lost productivity. Treatment of severe episodes takes up
to 25% of household income and accounts for up to 40% of public sector health
expenditures in sub Saharan Africa. Professor Jeffery Sachs of the Earth
Institute at Columbia University has shown that the global distribution of
per-capita gross domestic product has a striking correlation with malaria and
poverty. In a paper published in the journal Nature in 2002, Sachs
concluded that where malaria prospers, human societies have prospered the
least.
The
debilitating effect of malaria undermines household productivity. The real
effect of malaria is through the productive time lost by the sick and the
family members who provide care for the sick. Repeated bouts of malaria in smallholder
farm households have been shown to cause a decline in both food security and
income, hence exacerbating poverty. For instance, in Ivory Coast, farmers
suffering from malaria for more than two days out of a growing season had 47%
lower yields and 53% lower revenues than their neighbors who missed no more
than two days.
It
is estimated that malaria accounts for about 15% of health-related absenteeism
form school and may impair as much as 60% of school children’s learning
ability. Cross-country studies of percentages of school-age children in school
have been inversely linked to the prevalence of malaria. Such associations have
persuaded some scholars to speculate that malaria in childhood is likely to
have effects on general cognitive and behavioral development where malaria is
endemic. Our understanding of the precise causal mechanisms remains unclear.
However, of greater significance is the link between malaria during pregnancy and
low birth weight and the correlation between low birth weight and subsequent
cognitive problems.
Malaria and HIV
Scientists
have shown that malaria may be accelerating the spread of HIV in areas of
sub-Saharan Africa where there is a substantial overlap between the two
diseases. HIV infection disrupts the acquired immune response to malaria,
increasing the incidence and severity of malaria. Acute malaria has been shown
to elevate HIV viral load and may increase the risk of HIV transmission. Hence
malaria co-infection in HIV positive individuals could play a key role in
promoting the spread of HIV in sub Saharan Africa. HIV infection may be
associated with reduced efficacy of antimalarial treatment.
A
study published in the Lancet Journal in 2004 revealed that HIV magnifies the
effect of malaria among pregnant women and their infants. HIV-infected pregnant
women have significant alterations in immunity to malaria. Hence HIV positive
women are at greater risk of pregnancy associated malaria and experience
greater rates of anemia and adverse birth outcomes than HIV negative women. More
importantly some therapies for malaria and HIV interact, leading to
unanticipated effects on drug efficacy or toxicity. These interactions remain a
major public health concern in most areas affected by the two diseases. For
instance, caution is advised in the co-administration of quinine with
nevirapine.
Agriculture and climate change
and malaria
Human activity through land use and land use change has been
recognized as critical to mosquito ecology and vector efficiency. Studies in
western Kenya have shown that deforestation is associated with a marked
increase of malaria risk, with vector efficiency increasing by 78%. Similar
studies in the Peruvian Amazon have shown that mosquito-biting rate was 278
times higher in non-forest sites compared to forested areas. Similarly a global
review of the effect of irrigation and large dams on the burden of malaria revealed
that irrigated villages in Rusizi Valley in Burundi had higher malaria
prevalence and 150-fold higher vector efficiency compared neighboring villages
without large dams.
Maize
pollen is known to provide nutrition for mosquito larva. A study published in
2005 in the American Journal of Tropical Medicine and Hygiene showed that the
cumulative incidence of malaria in high maize cultivation areas was 9.5 times
higher than in areas with less maize in Ethiopia. Entomologists have shown that
maize pollen is correlated with duration of larval development and the size of
resulting mosquito adults. Thus, the intensity of maize cultivation is associated
with exacerbated malaria risk.
The
Intergovernmental Panel on Climate Change (IPCC) concluded that climate change
would be associated both with geographical expansion and contraction of malaria
distribution. According to the projections of the integrated weather–disease
model, malaria will disappear in the northern Sahel but will expand in the
highlands. An increase in temperature, rainfall, and humidity may cause a
proliferation of the malaria-carrying mosquitoes at higher altitudes, resulting
in an increase in malaria transmission in areas in which malaria has not been
previously reported. Under current climate change projections the East African
highlands will turn into malaria epidemic-prone areas by 2050.
Evolution to the rescue
In
order to survive within the red blood cell, the malaria parasite has to remodel
specific proteins and evolutionary pressure has resulted in mutations in the
human red blood cells that prevent this remodeling. Nearly 70 years ago,
British geneticist Anthony Allison established that carriers of one gene that
caused sickle-cell anemia are protected from malaria. Sickle cell anemia is a
genetic disease that slightly alters the structure of hemoglobin, the oxygen
carrying protein in red blood cells. The disease is prevalent in Africa where
incidence of malaria is high. In a study
conducted by Centres for Disease Control and Prevention (CDC) and the Kenya
Medical Research Institute in western Kenya showed that the sickle cell trait
provides 60% protection against overall mortality. Most of this protection
occurs between 2-16 months of life, before the onset of clinical immunity in
areas with intense transmission of malaria.
Malaria Control Initiatives
International
funding for malaria control increased sharply over the last decade, reaching
US$1.5 billion in 2009. Increased global funding resulted in robust expansion
of antimalarial programs: rapid scale-up of distribution of long lasting insecticide-treated
mosquito nets – reaching 76% of the population at risk; expansion of indoor
residual spaying, reaching 13 million in 2005 to 75 million in 2009; increase
in the use of rapid diagnostic test, prior to treatment, for all patients with
suspected malaria from less than 5% at the start of the decade to 35% in 2009.
Because of these interventions, it is estimated that more than 274 million
cases and 1.1 million deaths have been avoided in the past decade.
New
commitments for malaria control programs have stalled, falling short of the
estimated US$6 billion needed beyond. This is especially worrying because
progress and gains against malaria remain fragile in a majority of high-risk
malaria countries in Africa. The stalling of funding for antimalarial programs
is especially troubling. Moreover, a vaccine against malaria, like a HIV
vaccine, remains elusive goal. But there is some hope. A vaccine candidate
known as RTS,S/AS01 is in the midst of a large phase three clinical trial. Results
published so far show that it provides additional protection against clinical
and severe malaria for infants and children in settings where bed nets are also
widely used.
In
his book Mosquitoes, malaria and man: a
history of hostilities since 1880, historian Gordon Harrison wrote in an
eerily prescient manner of the persistence of malaria “Failure so universal, so
apparently ineluctable, must be trying to tell us something. The lesson could
be of course that we have proved incompetent warriors. It could also be that we
have misconstrued the problem”. Researchers from Australia’s Queensland
Institute of Medical Research argue that three factors account for the failure
to maintain control malaria, namely: parasite resistance to safe and affordable
antimalarials and insecticides; the shambolic state of vector control programs
in developing tropical countries, and; the failure to develop a vaccine that
prevents malaria.
Beyond vaccines, pyrethroids, and
antimalarials
To
deal robustly with malaria, Africa must look beyond drug therapy, insecticides
and vaccines. New strategies for malaria control and prevention must deploy
integrated malaria management.
Integrated
malaria management solutions include flexible and adaptive management of
ecological, environmental, hydrological conditions and knowledge of patterns of
malaria transmission, and human settlement planning, which: improve management
of reservoirs and irrigation systems; eradicate vector larvae through
biological control; reduce vector breeding sites; locate human settlement away
from corrals and potential mosquito breeding sites; and, better housing design
and construction.
Integrated
solutions work. Studies have shown that the cost of environmental management
for malaria in copper mining communities in Zambia is lower than the cost of
control programs that utilize insecticides and chemoprophylaxis implemented in
countries like South Africa and Kenya. For Africa integrated management is the
sensible policy approach.
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