While larvicides essentially accomplish their goal and reduce larval prevalence by as much as 90%, this may not be enough to substantially reduce malaria infections. Anopheles mosquitoes have the ability to breed in various habitats such as water collected in tire tracks or even areas with fresh or salt water. [CDC] As evidenced in the picture above, human factors and everyday actions inadvertently contribute to the creation of more potential habitats. While the creation of these breeding sites are inevitable in countries in sub-Saharan Africa, it is evidence of the lack of political mobility and public awareness concerning the importance of vector control and preventative steps. The importance of managing and surveying static water sites, should be stressed and highly publicized.
Through the implementation of malaria vector control education, communities can learn how to manage their own environments to help maintain low malarial transmission rates. Individuals within the community can learn to fill these sites and potentially avoid their creation. Of the larvicides discussed, the bacterial larvacides seem to be the most effective. However, it should not be utilized as a sole form of vector control, since it is almost impossible to treat every potential habitat. In areas, like sub-Saharan Africa with high levels of endemicity, a few habitats are enough to breed a few larvae capable of maintaining the malaria burden. [Gilles, H. et al., 1993] In order to reduce malaria transmission “mosquito larval habitats [should be] well defined, accessible and therefore manageable.” [Fillinger et. al, 2006] While this is ideal, situations comprising all three factors are uncommon. The value of larvicides should not be disregarded but, rather, incorporated with additional forms of control, like insecticide treated bed nets, and drugs, in order to maximize the reductions in malaria transmission.
INSECTICIDE TREATED BED NETS
Insecticide treated bed nets are a necessary preventative measure in regions with endemic malaria since the 20% reduction in mortality has significant benefits for pregnant women and young children, whom are the most susceptible to the disease. However, the use of insectide treated bed nets raise two issues; one of economics, the other of a lack of public health infrastructures geared towards educating at risk communities. In the Sichuan study, 87% of community members used ITNs which explains why the bed nets were so effective, resulting in a 70% reduction in malaria infection. With such compelling evidence, why don’t endemic regions adopt this same strategy? Well that is the ultimate goal, but ITNs are simply not cheap, in order to achieve community coverage, WHO estimates that the continent of Africa, alone needs 320 million. Since most people in the Sichuan providence already owned bed nets, the Sichuan study did not have to incorporate funding for acquiring these bed nets, transporting them, nor their distribution. While ITNs can be viewed as a costly expenditure to those in poorer regions, this mode of vector control is very cost effective in terms of life years gained and averted clinical treatment. [Wiseman, et al., 2003]
Placing finances aside, a resurfacing problem with ITN’s is making sure individuals and communities use them properly. The CDC estimates that less than 5% of ITNs will get re-treated. Endemic regions that do not normally use bed nets will need to be persuaded to use them regularly and follow the re-treatment regimen. The Roll Back Malaria Program helps achieve this by supporting communal re-treatments. Further, persuasion can consist of the development of public health infrastructures designed to implement programs about vector awareness and proper ITN use. This pathway is critical in enabling community members to understand why certain precautions are necessary and it allows them to exercise some autonomy. However, we must keep in mind that re-treatment of ITN’s is not free, and for those that cannot afford it, alternative measures, resulting in free re-treatments may need to be explored.
While financing mass distributions is a substantial problem, a resurfacing problem with ITNs is making sure individuals and communities use them properly. Endemic regions that do not normally use bed nets will need to be persuaded to use them regularly and follow the re-treatment regimen. The Roll Back Malaria Programme (RBM) helps achieve this by supporting communal re-treatments. Further, persuasion can consist of the development of public health infrastructures designed to implement programs about vector awareness and proper ITN use. This pathway is critical in enabling community members to understand why certain precautions are necessary and it allows them to exercise some autonomy. This autonomy can be extended even further as the RBM Program support the production of ITNs by local factories. While these measures are vital to reducing the transmissibility of malaria, it is still beneficial to combine this type of control with additional modes, such as drug treatment, bacterial larvicides, and, of course, indoor residual spraying.
INDOOR RESIDUAL SPRAYING AND DDT
Studies have shown that IRS is a viable method of controlling malarial vectors, even in conditions when it is not optimal. In a study done of IRS in a Sudanese refugee camp (the insecticide used in this case was less potent than DDT), it was found that overall, childhood mortality due to malaria decreased [Charlwood et al, see Figure 1]
Figure 1: (a) The all-age group, monthly malaria incidence rates for control and intervention refugee camps, eastern Sudan. (b) All-age group monthly malaria mortality for control and intervention camps. (c) Under-5-year age group, monthly malaria incidence rates for control and intervention refugee camps, eastern Sudan. (d) Under-5-year age group monthly malaria mortality for control and intervention camps. The vertical bar in the figures denotes the time of spraying with malathion. Dotted lines and hollow boxes denote rates from intervention camps, solid lines and solid boxes denote control camps. [Figure and caption source Charlwood et al, 2002].
In this case, the results have several interesting implications. First, they demonstrate that IRS usage, even when not using DDT, shows a marked decrease in malaria rates among young children, who are among the most susceptible to the disease. Even more interesting is the fact that the spraying took place in a refugee camp, where shelters are not completely enclosed and thus the spraying does not function optimally. The study demonstrates the tremendous potential of IRS as a vector control method. When implemented according WHO standards (as mentioned, in enclosed spaces and preferably with DDT), IRS is emerging as a viable supplement or even alternative to bednets and other vector control methods.
However, for many global organizations, IRS without DDT is not enough. Despite pressure from organizations such as the World Bank, malaria control initiatives by WHO and even local governments have decided to press on with DDT [BBC]. The environmental and health effects of DDT, they argue, have been greatly exaggerated. Perhaps these environmental and health effects seem inconsequential to national governments faced with staggering malarial epidemics that see DDT as their only choice—it is inexpensive, highly effective, and the least difficult of the insecticides to maintain through a logistical standpoint. “If the wealthiest, most scientifically advanced, and least malarious country of sub-Saharan Africa [South Africa] cannot make do without DDT, how can superendemic countries like Tanzania, Congo, or Mozambique do so? Should they be asked to?” ask Attaran and Maharaj in their plea for DDT. In 2005, the government of Uganda decided to employ DDT to control malaria, despite intense economic and diplomatic pressure by Western countries [IRIN]. In the face of practicality, DDT wins.
But why this intense push for DDT and IRS? What about using bednets exclusively, which are also comparatively cost-effective? Again, the issue is more complicated than it first appears. In a study done in Kenya that compared spraying to bednets, it was found that IRS was not only less than half as expensive as providing bednets, but that it reduced the risk of malaria infection by 75% [Guyatt et al, ]. While roughly half of all people provided with bednets use them, if people sleep in a room sprayed with insecticide they are compelled to be safe from malarial vectors. Also, IRS treated rooms can protect a greater number of people than ITNs. If the aim of a malaria control program is to protect the greatest number of people, then IRS clearly achieves this aim to a greater extent.
Yet there are several drawbacks of using DDT and other IRS methods that extend beyond environmental or health impacts. When compared to bednets, DDT may not be as cost-effective as presumed. As houses that are not at risk for malaria are also sprayed, providing spraying services for all houses may be more expensive that distributing bednets to at-risk houses. Furthermore, funding for programs that involve DDT is extremely limited, as those who control a large part of the funds are in opposition to the use of DDT. Thus, while superendemic countries may be able to implement DDT spraying through their own funds, the sustainability of such programs is precarious.
“Risk-benefit trade-offs are part of public health and medicine,” write Attaran and Maharaj. And it seems that IRS is a method of vector control that can be enforceable, especially when compared to larvicide or ITNs, as it requires effort on the part of individuals only once every couple of months rather than on a weekly or daily basis. In a study of IRS in Mexican villages, Rodriguez et al found that the great majority of villagers reported that spraying with DDT lowered their mosquito problems, and even reduced the presence of other pests such as cockroaches. Conversely, a significant portion of them disliked the smell of the treatment and found it troublesome to move their furniture for the spraying. Perhaps an informational ad campaign that explains the need for and results of IRS can make individuals more willing to participate in such treatment programs.
The future of IRS, especially when it involves DDT, is a complex and interesting frontier that weds new emergent forms of science and sociology. Not since Silent Spring has the scientific element of DDT faced such intense scrutiny, and most of this debate is occurring in Western countries. On the other hand, many African health officials are well aware that the malaria problem was eliminated in the West only through use of DDT [IRIN]. Perhaps the future use of DDT will not only be used as a means of controlling malaria, but as a tool of asserting political autonomy.