Biology Reference
In-Depth Information
visits resulting in a total dose of 315 mg (approximately 5.25 mg/kg). Com-
pliance with drug treatment was 88% and the prevalence of bednet own-
ership was 94%. Although the MDA was only one of several components
of the malaria elimination campaign in Aneityum, the treatment schedule
will have maximised its benefit. Firstly, a sufficiently long-acting and potent
combination of blood schizontocides was used to ensure parasitocidal con-
centrations of drug persisted for long enough to cover the average lifetime
of 5 weeks of
Anopheles farauti
- the major mosquito vector in the region
(
Belkin et al., 1945
). As a result, even mosquitoes that were infected prior
to the beginning of the campaign could not have initiated a new human
infection. Since sulfadoxine + pyrimethamine has sporontocidal activity,
formation of
P. vivax
hypnozoites from inoculations by previously infected
mosquitoes should also have been prevented. Secondly, a (presumably) large
enough total dose of primaquine was provided to eradicate
P. vivax
hypno-
zoites. A weekly 45 mg dose of primaquine is thought to be safe in individ-
uals with mild or moderate enzyme deficiency (
Leslie et al., 2008
). Thirdly,
administration of all drug doses was supervised and, therefore, poor adher-
ence was unlikely. Lastly, population coverage was high. Although weekly
(or regular) dosing of all individuals in a population may be the ideal means
of rapidly reducing
P. vivax
transmission, such a schedule would be very
resource intensive and difficult in larger, more dispersed populations. More
practical schedules need to be explored.
Considering the logistic and financial difficulties of conducting mass
anti-malarial drug administration trials, mathematical models are an attrac-
tive, but complicated, means of gaining insight into the likely effectiveness
of MDA strategies. Ishikawa et al. used a model of
P. vivax
transmission
based on epidemiological data from the Solomon Islands to show that a
hypnozoitocidal course of primaquine administered as a weekly dose over
7 weeks along with chloroquine would result in rapid, and almost total,
reduction in the
P. vivax
parasite index with maintenance of very low trans-
mission for at least 4 years (
Ishikawa et al., 2003
). According to the model, a
single dose of primaquine and chloroquine would result in a similarly rapid
reduction in the parasite index but with a rebound to pre-intervention
levels within 4 years (
Ishikawa et al., 2003
). The longevity of the effect of
the latter regimen is likely to have been overestimated since the authors
appeared to assume that there is a proportionate reduction in the risk of
relapse with each additional dose of primaquine. Data from clinical studies
suggest that the effectiveness of primaquine is more likely to be all or noth-
ing depending on whether a certain threshold total dose is reached (
Gogtay
