Reply to: The decline of malaria in Vietnam, 1991–2014
COMMENT on: Goldlust et al. 2018, The decline of malaria in Vietnam, 1991–2014 Malaria Journal 2018 17:226 This is a study into an important question. However, we strongly disagree with its conclusion that “The decline of malaria in Vietnam can largely be attributed to the adoption of artemisinin-based case management”. No doubt artemisinin-based treatment has had a large contribution but the conclusion that neither vector control nor health system improvement hardly had a significant impact in Vietnam’s decrease in malaria over 23 years is erroneous. There are two aspects to discuss: * The predictor variables used for vector control and health system improvement are not representative for those factors. * The study looks at a period of 23 years as one block without taking into regard the vast epidemiological and socio-economic changes, and variations in their speed of change over this time, that took place in Vietnam. Predictor variables We look first at: Predictor 1: Proportion of treatments with Artemisinin of P.f. over all treatments Predictor 2: The proportion of the population covered by ITN + IRS These covariates differ from each other in an important aspect. Where proportion (1) is invariant to (because divided by) the over time changing (in general: decreasing) total number of treatments, (2) is only invariant to the total population size (which is growing). As such, variable (2) does not take into account the likely reduction in the population at risk over these 23 years. Indeed, Fig. 4 shows that this variable has not shown much change over the years at all (as compared with (1)) and instead of representing a likely increasing coverage over the decreasing total number of people at risk in the later years, it shows a decrease. To perhaps better illustrate the difference between these covariates, a vector control covariate congruent to the one used for treatment would have been: “The proportion of funds used for chemicals to treat ITN among the total for ITN+IRS”. The data may be aggregated in the annual NIMPE reports but could certainly be available somewhere in NIMPE. It would be interesting to see how much this covariate would have contributed to malaria incidence reduction, compared to Art treatment, especially in the first half of the study period. Population sizes in different epidemiological strata (zones) are available at NIMPE but as these were not updated every year in every province and because the stratification methods have changed at least a few times over the study period, we understand that they could not be used to base the vector control predictor on population at risk. The vector control variable, merely by its weak definition, reduces the relative contribution that vector control may have had to the general decline of malaria over the total period. The crucial difference between these two predictors is not discussed under ‘Data limitations’. Even a superficial look at the three graphs showing: (A) – A strong, almost exponential decrease in malaria incidence; (1) – A strong and continuous increase in the proportion of treatments with ART; (2) – a small increase over the first 5-6 years followed by a long period of a slowly decreasing effort in “vector control” makes it obvious that correlations, in whatever model, between (A) and (1) will always be much stronger than between (A) and (2). Figure 4 shows a lack of data about vector control before 1997 in the most malaria endemic Central region and thereafter only a decline. Based on our personal experiences in that region in Vietnam during this period, it is not possibly for this to be a true representation. It is therefore unsurprising vector control comes out as hardly significant overall. The same type of argument applies for the predictors used to represent improvements in the general health care system. Besides having no data before 1997, also for the period after that, the data as analysed do not give credit to the enormous progress in providing health services, especially in the most peripheral (and thus most malaria endemic) areas, in the whole first half of the study period. In the nineties and early 2000’s vast areas in the Central Highlands hardly had any regular primary health care yet, let alone prompt and adequate malaria treatment. In the early period, the Central region Malaria Institute in Quy Nhon was not even able to visit the remote areas due to a lack of navigable roads and of vehicles. If the data found in the NIMPE annual reports cannot represent this improvement then they ought not have been used for this purpose. We are almost sure other data sources must be available in Vietnam for estimating a predictor like: “The proportion of health staff per x population deployed in malaria endemic areas”. Again, we do not doubt the important - and probably in the later stages over-riding - contribution of Artemisinin-based treatments to malaria control in Vietnam. However, the method used is not finely enough tuned for a convincing and fair comparative assessment of this intervention versus vector control and health system improvement over the whole period of 23 years. Other important socio-economic covariates like improved education and general awareness, living and housing standards of the population in malaria areas, were also not studied. Our second point of concern: when looking closely at the ART treatment predictor (1) in Figure 4 it is clear that its use was everywhere still quite limited, and only slowly growing, over the early years from 1991 – 2002/3. However, Figure 1 shows that the decrease in malaria incidence over this period was at least as strong as in the period after that (and in the Northern region even steeper). Notably (see Figure 4) this period covers most of the time that there was at least some increase in predictor (2): the population covered by ITN/IRS. This was also the period in which ITN were introduced for the first time and soon became preferred and dominant over IRS. Of course this first happened in the most malaria endemic districts, so the use of ITN by people most at risk grew fastest exactly in this period. Based on a visual evaluation of the graphs alone, we can predict that if the same analysis is repeated separately for each half of the whole period (1991-2002 and 2003 – 2014) one will find very contrasting conclusions as to the relative attributions of ART treatment versus vector control in the two periods. One could say that the situation in Vietnam before 2003 (much more malaria in general and much less access to good treatment for the population most at risk) would more resemble the situation in Africa - where the 68% attribution to ITN for malaria reduction was found. After 2003, with an already roughly 90% reduced malaria burden since 1991, it is likely that continued improving case detection and treatment coverage with ART–based regimens has played a more important role in further reducing malaria than vector control. No attempt has been made to consider, or even mention, the possible influence of changes in the malaria epidemiology over this quarter of a century in Vietnam. NIMPE has many more data in its archives and indeed this may form a ‘Goldmine’ (no pun intended) for further studies in this respect. For instance, the anopheline fauna has definitely changed as a result of changes in land use (deforestation, agricultural chemicals etc.) and surely also due to vector control: With a group of Vietnamese colleagues, we studied the long-term changes in the micro-epidemiology of malaria in a small group of villages, Khanh Phu (Khanh Hoa province) between 1993 and 2016. In the nineties this area manifested holo-endemic malaria (> 80 infective bites per person per year). The most abundant malaria vector in the villages, and responsible for 80% of these bites, was Anopheles minimus. Immediately after the whole village started to sleep under ITN, from August 1998, An. minimus disappeared and malaria incidence also crashed with 80%, without any change in treatment regimens or case detection. In 2016 when the observations ended, An. minimus was still absent from the area. The only other vector, An. dirus, was and is unaffected in its population size by any vector control method thus far tested. The ITN are still useful but only for those who live very near the forest or overnight in the forests. In villages further than about 5 km from the forest, there is hardly any malaria infection risk anymore in this area. So people could just as well stop using ITN there – because they don’t work? Well no, because they have done their work already: no An. minimus anymore. Any researcher coming to study Khanh Phu after 1998, if unaware of the history, would conclude that using ITN makes no sense in these villages. The success story of malaria control in Vietnam since 1991 cannot be summarized by the sweeping, generalized conclusion: “The decline of malaria in Vietnam can largely be attributed to the adoption of artemisinin-based case management.” Readers without more detailed knowledge of the rich history will just take away from this article that vector control and peripheral health system improvement did not play a significant role in Vietnam while the opposite is true. This not just amounts to falsification of history but may influence future decisions of national malaria control program managers. The study has not applied the methods and data that would be needed to fairly assess this issue in Vietnam. Ron P. Marchand Nguyễn Tuyên Quang
Reply to: Bed nets used to protect against malaria do not last long in a semi-arid area of Ethiopia: a cohort study
If nets only function for a year or two, why are they a prinicpal element of the WHO and US PMI strategies? Wouldn't it make more sense to use permanent elements such as swamp drainage and elimination or filling of breeding sites? That seems more sensible, doesn't it?
Reply to: Perspective: End malaria for good: a review of current strategies and future novelties for malaria elimination in Nigeria
While it is encouraging to see the recent progress against malaria in Nigeria, we have to be aware that this is not a short-term battle. Malaria has been around for centuries and is embedded in African ecology. So we must see the fight against malaria as a continuing battle.
Reply to: Plasmodium vivax Recurrences
This is the 2017 publication (see link provided above) in which the suggestion was initially made. Results of new research carried out at (mainly but not only) the University of Glasgow and Harvard University now further support the hypothesis, i.e. what was pointed out previously. Namely and specifically, that parasites in bone marrow or the spleen might be a source(s) of recurring vivax malaria (in addition to hypnozoites). I am drawing attention to this matter, raised in the 2017 paper for the first time ever at length (click on link in the blog), primarily because it is of fundamental practical significance in the field of malariology.
I still think that hypnozoites give rise to recurrent vivax malaria, as I thought when introducing the term “hypnozoite” in the late 1970s and predicting the existence of this stage in the plasmodial life cycle. However, I currently believe (since 2010/2011) that as far as extra-vascular (non-circulating) parasites are concerned, vivax malarial recurrences can also have non-hypnozoite forms as their origin. It would be very surprising to find that this is not the case. Up until recently, the idea seems to have been regarded with outright disbelief or scepticism by absolutely everybody (other than me) in the malarial world. But the situation has changed.
Reply to: 1st Malaria World Congress: 1-5 July 2018, Australia
I will forward your request to the Congress Secretariat.