Abstract
BackgroundViet Nam has made tremendous progress towards reducing mortality and morbidity associated with malaria in recent years. Despite the success in malaria control, there has been a recent increase in cases in some provinces. In order to understand the changing malaria dynamics in Viet Nam and measure progress towards elimination, the aim of this study was to describe and quantify spatial and temporal trends of malaria by species at district level across the country.MethodsMalaria case reports at the Viet Nam National Institute of Malariology, Parasitology, and Entomology were reviewed for the period of January 2009 to December 2015. The population of each district was obtained from the Population and Housing Census-2009. A multivariate (insecticide-treated mosquito nets [ITN], indoor residual spraying [IRS], maximum temperature), zero-inflated, Poisson regression model was developed with spatial and spatiotemporal random effects modelled using a conditional autoregressive prior structure, and with posterior parameters estimated using Bayesian Markov chain Monte Carlo simulation with Gibbs sampling. Covariates included in the models were coverage of intervention (ITN and IRS) and maximum temperature.ResultsThere was a total of 57,713 Plasmodium falciparum and 32,386 Plasmodium vivax cases during the study period. The ratio of P. falciparum to P. vivax decreased from 4.3 (81.0% P. falciparum; 11,121 cases) in 2009 to 0.8 (45.0% P. falciparum; 3325 cases) in 2015. Coverage of ITN was associated with decreased P. falciparum incidence, with a 1.1% (95% credible interval [CrI] 0.009%, 1.2%) decrease in incidence for 1% increase in the ITN coverage, but this was not the case for P. vivax, nor was it the case for IRS coverage. Maximum temperature was associated with increased incidence of both species, with a 4% (95% CrI 3.5%, 4.3%) and 1.6% (95% CrI 0.9%, 2.0%) increase in P. falciparum and P. vivax incidence for a temperature increase of 1 °C, respectively. Temporal trends of P. falciparum and P. vivax incidence were significantly higher than the national average in Central and Central-Southern districts.ConclusionInterventions (ITN distribution) and environmental factors (increased temperature) were associated with incidence of P. falciparum and P. vivax during the study period. The factors reviewed were not exhaustive, however the data suggest distribution of resources can be targeted to areas and times of increased malaria transmission. Additionally, changing distribution of the two predominant malaria species in Viet Nam will require different programmatic approaches for control and elimination.
Highlights
Viet Nam has made tremendous progress towards reducing mortality and morbidity associated with malaria in recent years
Descriptive analysis There was a total of 57,713 P. falciparum and 32,386 P. vivax cases during the study period
The proportion of the population covered by insecticide-treated mosquito nets (ITN) and Indoor residual spraying (IRS) declined slightly from a high in 2010 (14% ITNs and 3% IRS coverage at the national level) through the study period (Figs. 2, 3 and 4)
Summary
Viet Nam has made tremendous progress towards reducing mortality and morbidity associated with malaria in recent years. Despite the success in malaria control, there has been a recent increase in cases in some provinces. Over the last 15 years, malaria cases and deaths across the region have declined and all countries in the region are pursuing the goal of malaria elimination, with the last countries (including Viet Nam) aiming for elimination by 2030 [18]. Since the 1990s, Viet Nam has made tremendous progress in reducing mortality and morbidity associated with malaria [19,20,21,22]. Following a successful reduction of malaria case numbers by 97% and deaths by 99.8% between 1991 and 2014, the Viet Nam National Institute of Malariology, Parasitology, and Entomology (NIMPE) are pursuing an agenda of progressive elimination [27,28,29,30]. Indoor residual spraying (IRS) is carried out both as a routine preventive measure in some areas, in areas of low coverage of ITN, and in response to outbreaks [21, 26]
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