Biology Reference
In-Depth Information
Evidence for declining chloroquine efficacy against
P. vivax
, albeit less
pronounced as that observed in New Guinea, has also been reported from
other parts of the Indonesia archipelago (
Sutanto et al., 2009
,
2010
), South
Korea (
Lee et al., 2009
), Myanmar (
Guthmann et al., 2008
), Thailand
(
Phyo et al., 2011
;
Rijken et al., 2011
), Ethiopia (
Yohannes et al., 2011
;
Ketema et al., 2011
), Madagascar (
Barnadas et al., 2008
), India (
Srivastava
et al., 2008
) and Brazil (
de Santana Filho et al., 2007
). Indeed there is now
evidence that the efficacy of chloroquine against
P. vivax
is declining in
most locations where vivax malaria is endemic (
Price et al., 2009
;
Douglas
et al., 2010
).
In endemic regions where populations have limited access to health
care, the inability to reliably eradicate the liver stages of the parasite and
emerging chloroquine resistance by the blood stages of parasite, can result
in
P. vivax
becoming a chronic relapsing disease exacerbated by a complex
array of co-morbidities: nutritional, genetic and immunological disorders.
In this context, high-grade chloroquine resistance is likely to make a sig-
nificant contribution to reports of severe and fatal vivax malaria, which was
previously assumed to be a benign infection (
Price et al., 2009
). The effects
of declining drug efficacy are manifestly worse in the most vulnerable pop-
ulations, such as young children and pregnant women (
Poespoprodjo et al.,
2008
,
2009
).
6.1.2. Non-chloroquine treatment regimens of
P. vivax
Almost all antimalarial drugs with activity against
P. falciparum
demonstrate
intrinsic activity against the asexual stages of
P. vivax.
The main excep-
tion to this being the antifolate drugs which exhibit low potency (
Darlow
et al., 1982
) and vulnerability to the rapid development of drug resistance
(
Pukrittayakamee et al., 2000
;
Tjitra et al., 2002
). Clinical trials of mefloquine
(
Maguire et al., 2006a
), atovaquone + proguanil (
Lacy et al., 2002
), halofan-
trine (
Baird et al., 1995a
), piperaquine (
Ratcliff et al., 2007a
;
Karunajeewa
et al., 2008b
), artesunate (
Ratcliff et al., 2007a
;
Karunajeewa et al., 2008b
)
and pyronaridine (
Poravuth et al., 2011
) show these antimalarial agents to
exhibit good efficacy against chloroquine-resistant
P. vivax
. These clinical
studies are supported by
in vitro
studies conducted in an area of high-grade
CQR (
Price et al., 2010
;
Russel et al., 2008
). However, a degree of
in vitro
and
in vivo
cross-resistance has been observed between chloroquine and
amodiaquine (
Hasugian et al., 2009
), and this may account for the high rates
of recurrence in clinical studies conducted in Papua, Indonesia (
Hasugian
et al., 2007
) and Papua New Guinea (
Karunajeewa et al., 2008b
).
