Autor/a:
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Hetzel, Manuel W.; Reimer, Lisa J.; Gideon, Gibson; Koimbu, Gussy; Barnadas, Céline; Makita, Leo; Siba, Peter; Mueller, Ivo
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Abstract:
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BACKGROUND: Papua New Guinea exhibits a complex malaria
epidemiology due to diversity in malaria parasites, mosquito
vectors, human hosts, and their natural environment.
Heterogeneities in transmission and burden of malaria at various
scales are likely to affect the success of malaria control
interventions, and vice-versa. This manuscript assesses changes
in malaria prevalence, incidence and transmission in sentinel
sites following the first national distribution of long-lasting
insecticidal nets (LLINs). METHODS: Before and after the
distribution of LLINs, data collection in six purposively
selected sentinel sites included clinical surveillance in the
local health facility, household surveys and entomological
surveys. Not all activities were carried out in all sites.
Mosquitoes were collected by human landing catches. Diagnosis of
malaria infection in humans was done by rapid diagnostic test,
light microscopy and PCR for species confirmation. RESULTS:
Following the roll-out of LLINs, the average monthly malaria
incidence rate dropped from 13/1,000 population to 2/1,000
(incidence rate ratio = 0.12; 95 % CI: 0.09-0.17; P < 0.001).
The average population prevalence of malaria decreased from 15.7
% pre-LLIN to 4.8 % post-LLIN (adjusted odds ratio = 0.26; 95 %
CI: 0.20-0.33; P < 0.001). In general, reductions in
incidence and prevalence were more pronounced in infections with
P. falciparum than with P. vivax. Additional morbidity
indicators (anaemia, splenomegaly, self-reported fever) showed a
decreasing trend in most sites. Mean Anopheles man biting rates
decreased from 83 bites/person/night pre-LLIN to 31 post-LLIN (P
= 0.008). Anopheles species composition differed between sites
but everywhere diversity was lower post-LLIN. In two sites,
post-LLIN P. vivax infections in anophelines had decreased but
P. falciparum infections had increased despite the opposite
observation in humans. CONCLUSIONS: LLIN distribution had
distinct effects on P. falciparum and P. vivax. Higher
resilience of P. vivax may be attributed to relapses from
hypnozoites and other biological characteristics favouring the
transmission of P. vivax. The effect on vector species
composition varied by location which is likely to impact on the
effectiveness of LLINs. In-depth and longer-term epidemiological
and entomological investigations are required to understand when
and where residual transmission occurs and whether observed
changes are sustained. |