Abstract
In October 2007, the Bill and Melinda Gates Foundation and the Director General of the WHO joined together to declare that the eradication of malaria was the only acceptable long-term goal for a disease that takes so many lives. The readers of Tropical Doctor who provide clinical care for the millions with malaria will warmly welcome that aim – but may reasonably ask what it means in practice for the work of clinicians on the ground.
Since the collapse of the global eradication campaign in 1969, there has been unwillingness to discuss elimination or eradication at all and this new departure is a very positive step. Eradication is when malaria no longer exists anywhere in the world, elimination is where malaria transmission has ceased in a defined geographical area (essentially ‘local eradication’). Neither the WHO nor the Gates Foundation imply that global eradication is possible now using existing tools. If the determination is there backed by substantial resources there is however no reason to think that significantly improved control of malaria in large areas of world cannot be achieved and new and better tools for eradication developed.
While global eradication of malaria is a long-term aspiration, an intermediate goal is eliminating malaria (meaning preventing malaria transmission) in defined geographical areas. This strategy is particularly attractive in areas which have natural barriers to malaria reinvading, such as islands, and where there is some additional gain to the rest of the world. Eliminating malaria in South East Asia, for example, might benefit other areas because drug resistance has mostly originated from South East Asia.
Eliminating falciparum malaria from large parts of mainland Asia is technically feasible, although this does not mean it is politically feasible or sustainable. Malaria in many parts of Asia is now at a much lower level of transmission than it was during the 1960s. Available tools for malaria control are roughly as powerful as they were in that period, but we would be attacking a much weaker target. Eliminating vivax malaria from areas of Asia would be a bigger challenge because of the relapsing nature of the disease.
In Africa where the great burden of malaria exists, there are many areas where malaria transmission is limited or even does not occur. These include most of South Africa, highland areas (over 1000 m) and urban areas where increasing proportions of the at-risk population live. There are however many rural areas of Africa, particularly in Central and West Africa, where transmission is over 100 times that needed to maintain malaria in the population – that means that even if malaria transmission were reduced 100 times it would still not be near eradication. The vectors in this part of Africa are much more effective at transmitting malaria than those in Asia, Europe and the Americas. Eliminating malaria in these areas is currently not possible because transmission is simply too high.
Malaria in these parts of Africa could however be substantially reduced using currently available tools. Examples of successful control are occurring in Africa where areas previously known for their high endemicity have become areas of relatively low transmission over about 10 years, including The Gambia, Zanzibar and some parts of Kenya. 1 This reduction in malaria is often unrecognized by public health services or clinicians yet is a practical reality.
The readers of Tropical Doctor who are helping to shape the debate on elimination and eradication in their own countries should bear three things in mind. The first is that malaria elimination and eradication are most politically popular in places where malaria is a massive problem; unfortunately these are also the areas where it is technically most difficult to achieve. Secondly, even in low transmission settings, elimination of malaria will be a long and expensive process. The final stage of all eradication campaigns always takes much longer than enthusiasts expect, as those who have been involved in the polio, filariasis and leprosy eradication campaigns are well aware. 2 The third is that areas of the world where elimination is least technically realistic are the ones where the greatest number of malaria deaths occur. It is essential that any efforts to eliminate malaria, do not detract from maximizing of control malaria in the areas where the greatest burden exists.
A serious attempt at eliminating malaria in an area will have substantial implications for clinicians. In the long run it should significantly reduce their workload, but will require significant changes to current practice. It will inevitably begin with an ‘attack’ phase aimed at reducing transmission using anti-vector measures such as residual spraying, bed-nets and possibly mass drug administration. It is unlikely this phase would involve those providing clinical care (and if it does it will fail - there is not the capacity for practicing clinicians to take on the huge logistical challenge this would present). If this initial phase is successful, the transmission of malaria will fall sharply. The first implication for clinicians is that they will see a much smaller number of patients with malaria. It will become increasingly important however to identify those cases accurately. In many areas, particularly in Africa, there is good evidence of substantial overdiagnosis of malaria in healthcare settings. 3 In areas of lower transmission, malaria must be laboratory confirmed, either by using a Rapid Diagnostic Test (RDT) or good quality microscopy. Clinical diagnosis should only be considered an acceptable standard of care in areas of very high transmission – by definition not areas where elimination is occurring. Accurately identifying cases of malaria and, as importantly, identifying those cases that do not have malaria will be essential for malaria any elimination campaigns to succeed. Without this it will not be possible to determine whether control interventions are succeeding, and very importantly where they are failing. This will require a substantial change in medical practice to improve diagnosis, and will not be easy.
Malaria transmission will not simply stop even during a very successful elimination campaign, but will go from very high, to high, to low, with a tail of many years before it is finally eliminated. The second major change for health services will be the changing clinical picture of the disease. Due to decreasing exposure to malaria, the population will over time have reduced immunity. Initially, immunity in adults will be high, but as the population of children born in a period of low transmission ages, an increasingly large cohort of adults with little previous exposure to malaria will become exposed and become sick. Experience from South East Asia demonstrates that adults will bear an increasing burden of disease. Currently, in much of Africa, adult severe malaria is exceptionally rare and frequently overdiagnosed; in the transition between hyperendemic malaria (now) and elimination it may become relatively much more common.
The implications for clinical services are broad. As clinicians, we have to adapt to the changing epidemiology of the disease, firstly accepting that not all fevers are due to malaria, secondly that the only way to diagnose the disease is by laboratory confirmation, thirdly that reporting true cases of malaria plays an important role as reported malaria guides control efforts. With or without new resources to eliminate or eradicate malaria, the epidemiology of malaria is changing and clinicians in Africa and elsewhere need to reflect that in their daily practice.