Biology Reference
In-Depth Information
finding for malaria elimination as opposed to control necessitates diagnostic
methods that are more sensitive as well as easier to perform than microscopy
if we are to successfully eliminate relapsing malaria in the tropics ( Tanner
and de Savigny, 2008 ). Field deployable PCR systems as well as loop medi-
ated isothermal PCR (LAMP), which does not require a thermocycler, gives
hope that technology will eventually evolve to enable the sensitive detection
of vivax malaria parasites in the blood of asymptomatic persons.
1.3. Hypnozoites and Implications for Elimination
The residual hepatic forms of the vivax parasite known as hypnozoites have
been explained in chapter 2, volume 80. This important evolutionary adap-
tation allows vivax malaria to remain in the liver waiting for favourable
transmission conditions that usually coincide with rains producing mos-
quito habitat ( Shortt and Garnham, 1948 ). Hypnozoites have profound
implications for malaria control and elimination. The clinically silent reser-
voir of parasites which can, at unpredictable and lengthy intervals, reinfect
the bloodstream gives vivax malaria a great advantage against any malaria
elimination program. In endemic areas, it is not possible to distinguish new
infections from old relapses as they are clinically equivalent, however, the
public health implications are quite different. Ongoing transmission can
be defeated using current methods such as ITN, but the chain of trans-
mission will not be ended until the residual liver parasites are eliminated
along with the risk of internal re-establishment of malaria transmission. The
only method of eliminating hypnozoites is the use of 8-aminoquinoline
drugs such as primaquine. Hypnozoite elimination has been possible at the
community-level in large military populations where mass drug admin-
istration can be enforced but has been accomplished only very rarely in
endemic civilian populations ( Hill and Amatuzio, 1949 ; Kaneko, 2010 ).
Vivax malaria elimination in large populations will require some form of
mass drug administration. This will involve either determining how to safely
use the potentially toxic drug primaquine or discovery of another drug
capable of killing hypnozoites without the risk of haemolysis in those with
a genetic polymorphism leading to glucose-6-phosphate dehydrogenase
(G6PD) deficiency (see chapter 4, volume 81).
The public health challenge presented by P. vivax hypnozoites to malaria
elimination can be summarized as one of program length and completeness.
The tools exist today to control malaria even in areas of high endemicity
if sufficient resources and political will can be applied to rapid diagnosis
and treatment with effective drugs coupled with distribution of ITN to
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