Malaria Treatment & Prevention
New Global Malaria Map Reveals Hot Spots in Asia and Latin America
Fyi From the ASTMH conference
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From: American Society of Tropical Medicine and Hygiene
Date: Mon, Dec 5, 2011 at 12:47 PM
Subject: New Global Malaria Map Reveals Hot Spots in Asia and Latin America
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As One Type of Malaria Declines, New Map Reveals another Strain –
Impervious to Interventions – Holding Steady in Parts of Asia and Latin
America
**
New data on prevalence of “the last parasite left standing” unveiled in
first-of-its kind map by malaria experts at
ASTMH meeting, along with new data on deadliness, lack of treatment
*(Philadelphia, Pa., USA – December 5, 2011) With signs of declining
malaria deaths in Africa raising hopes of eradicating the disease
worldwide, researchers unveiled today at the annual meeting of the American
Society of Tropical Medicine and Hygiene (ASTMH) a new malaria map that is
the first to identify on a global scale where the long-lasting and
potentially deadly form of malaria—a parasite known as *Plasmodium vivax*—has
a firm foothold in large swaths of South Asia and parts of Latin America.
“This map helps us understand just how difficult it is going to be to
eradicate malaria,” said Peter Gething, PhD, who led the University of
Oxford’s Malaria Atlas Project (MAP) team that produced the study of
*vivax*burden. “It shows that in substantial parts of the world,
*vivax* malaria is endemic and transmission is significant. Unfortunately,
the tools for fighting this type of malaria range from ineffective to
non-existent.”
Other studies being discussed at ASTMH—the world’s largest gathering of
public and private sector malaria scientists, clinicians and program
professionals—and published in the December issue of the *American Journal
of Tropical Medicine and Hygiene*, add to mounting evidence that
*vivax*malaria may be killing people far more often than previously
thought;
confirm that existing treatments are inadequate and potentially toxic to
millions; and shed light on the level of precaution that travelers should
take when visiting these regions (see *Backgrounder* for further
information).
While not as deadly as the *Plasmodium falciparum* malaria parasite that is
predominant in Africa, *vivax* is more common throughout the world, with an
estimated 2.85 billion people at risk of infection. And with its unique
ability to relapse by hiding in the liver for months or even years,
*vivax*is harder to detect and cure.
The MAP team produced an analysis last year depicting only where *vivax* is
known to exist. Malaria experts immediately called for a map pinpointing
where the disease is most prevalent, noting that such a tool is essential
to mounting an effective fight against this form of malaria.
Hotspots for *vivax* malaria highlighted by MAP include substantial parts
of India. Rates are high even in urban areas like Mumbai, where
malaria—once thought of largely as a disease of rural areas—was previously
uncommon. Papua New Guinea also has a high rate of infections and
transmission, as do significant parts of Indonesia and Myanmar (including
Yangon). In the Americas, the area of greatest concern is a large but
sparsely populated portion of the Northern Amazon, most of which is in
Brazil. But the hotspot also includes parts of Peru, Colombia and
Venezuela. In Central America, almost all of Nicaragua is a hotspot for *
vivax* malaria, as are parts of Honduras and Guatemala.
In Africa, Gething said that while *vivax* is known to exist, infection
rates appear to be “very, very low” for most of the continent, though the
map indicates a moderate but stable level of vivax transmission in parts of
the Horn of Africa and throughout Madagascar.
*Stealth Disease Burden: “Large Reservoir” of Vivax Infections Hiding in
the Liver*
Researchers considered an area to be a *vivax* malaria hot spot if the data
analysis yielded infection rates that exceeded 7 percent. Gething noted
that this threshold might be considered relatively low for
*falciparum*infections. But he said it’s high for vivax in part
because the figure
accounts only for parasites that are detectable in the blood, and also
because *vivax* disease rates have proven hard to reduce.
He noted that in areas where *vivax* is endemic, at any given time, there
are many people carrying vivax parasites only in their liver, from which
they periodically emerge to cause new infections in the blood stream. But,
he said, this “large reservoir” of *vivax* is difficult to quantify with
existing surveillance tools, chiefly because there is currently no simple
test for detecting the liver parasites.
“One person with *vivax* actually can represent multiple malaria infections
over many years in a single community and each time the parasite moves from
the liver to the blood, it contributes anew to disease burden and
transmission,” Gething said.
The disease burden caused by *vivax* relapse, he said, is exacerbated by a
lack of treatment options. Medicines such as the artemisinin combination
therapies (ACTs) that are used to cure *falciparum* infections can help
treat acute bloodstream *vivax* infections. But only one
drug—primaquine—can clear *vivax* parasites from the liver and thus provide
a long-term cure to this type of malaria.
However, in a cruel twist of evolution, a hereditary condition that may
have evolved in response to malaria exposures can make the drug toxic,
sometimes fatally so, to some people who live in vivax-endemic areas. At
ASTMH, another team of researchers from the Malaria Atlas Project will
present a map depicting the prevalence of the condition, known as G6PD
deficiency, within malaria-endemic countries. Preliminary data indicate
that this condition is relatively common in *vivax*-endemic Southeast Asia,
though the highest rates are found in sub-Saharan Africa. The condition is
also observed in the Americas, though at lower rates.
“We hope that by mapping the prevalence of G6PD deficiency we can provide
evidence that will help contribute towards determining the risks and
benefits of using primaquine, which is an important, yet potentially
dangerous drug,” said Rosalind Howes, the lead investigator on the project.
Even when primaquine is not toxic, the fact that it requires a 14-day
regimen has made it impractical for areas where people have little or no
access to even modest levels of health care—which is the majority of the
malaria-endemic regions of the world.
Meanwhile, bednets and indoor spraying, which, coupled with ACTs, have
helped reduce malaria deaths in Africa, appear to have had little impact on
*vivax*. One reason is that the mosquitoes that transmit *vivax* typically
bite outdoors, rather than indoors in the home. And RTS,S, the malaria
vaccine candidate in Phase 3 trials that may soon be commercially
available, does not target *vivax*.
This persistence of the *vivax* parasite in the face of a massive global
campaign to eliminate malaria has prompted some malaria fighters to dub it
“the last parasite standing.”
Malaria experts say even though *vivax* still appears to be less deadly
than falciparum, growing evidence of its link to fatalities warrant giving
it a higher profile in the global malaria eradication campaign.
“It’s time to step-up the fight against *vivax* malaria and stop looking at
this form of the disease as relatively mild and tolerable,” said Peter J.
Hotez, MD, PhD, noted infectious disease expert and president of ASTMH. “We
expect to emerge from this year’s conference with a far better view of the
state of *vivax* infections around the world and with new knowledge on
treatment challenges that can guide a global strategy focused on
eradicating all forms of malaria.”
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