Biology Reference
In-Depth Information
P. vivax
relapses as a 14-day course of primaquine at a dose of 22.5 mg/day
in combination with doxycycline (
Elmes et al., 2008
). The shortened treat-
ment duration may improve patient adherence, however tafenoquine has
the same propensity to cause haemolysis in those with G6PD deficiency
as primaquine and is also contraindicated in pregnant women (
Crockett
and Kain, 2007
). Given its long elimination half-life, reversal of haemolysis,
should it occur, is likely to be more difficult with tafenoquine than with
primaquine. Bulaquine is a prodrug of primaquine which is marketed in
India as a 5-day regimen of 25 mg/day for prevention of
P. vivax
relapses
(
Krudsood et al., 2006
). The small number of clinical trials of this drug to
date have had methodological weaknesses and there appears to be little
interest in developing this agent further (
Krudsood et al., 2006
;
Valecha
et al., 2001
). NPC1161B, another 8-aminoquinoline, is in Phase I develop-
ment. It has shown good tissue schizontocidal activity against
P. cynomolgi
(a
close relative of
P. vivax
) in rhesus monkeys but no published data exist on
its use in humans (
LaMontagne et al., 1982
).
4. REDUCING
P.VIVAX
TRANSMISSION USING MASS
DRUG ADMINISTRATION
Evidence from co-endemic regions shows that on average, individ-
uals gain immunity to
P. vivax
malaria more rapidly than to
P. falciparum
malaria and consequently, a higher proportion of
P. vivax
infections is
asymptomatic (
Tjitra et al., 2008
;
Genton et al., 2008
;
Luxemburger et al.,
1996
;
Michon et al., 2007
;
Karyana et al., 2008
). Studies from Southern
Papua, The Solomon Islands and Vanuatu suggest that between 71% and
97% of all microscopically patent
P. vivax
infections in these regions are
asymptomatic (
Karyana et al., 2008
;
Harris et al., 2010
;
Kinzer et al., 2010
).
The proportion of sub-patent
P. vivax
infections that are asymptomatic is
likely to be even higher. Passive detection and treatment of individuals with
symptomatic vivax malaria will clearly have limited impact on
P. vivax
trans-
mission. Alternative chemotherapeutic strategies for reducing transmission
of asymptomatic infections include mass screening and treatment (MSAT)
and MDA.
Certain biological features of
P. vivax
infections present unique chal-
lenges for the MSAT strategy in particular. Sub-patent
P. vivax
blood-stage
infections can be transmitted relatively efficiently (
Bousema and Drakeley,
2011
;
Jeffery, 1952
;
Bharti et al., 2006
). Cross-sectional studies employing
PCR-based diagnostic methodology show that microscopy underestimates
