Eradicating Malaria in Poor Nations: The Potential of Vector Control Measures and Vaccine Development

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Abstract

Although malaria is a growing problem affecting several hundred million people each year, many malarial countries lack successful disease control programs. Worldwide malaria incidence rates are dramatically increasing, generating fear among many people who are witnessing malaria control initiatives fail. In this paper, I explore two options for malaria control in poor countries: (1) the production and distribution of a malaria vaccine and (2) the control of mosquitoes that harbor the malaria parasite. I show that the development of a malaria vaccine is indeed likely, although it will take several years to produce because of both biological obstacles and insufficient research support. The distribution of such a vaccine, as suggested by some economists, will require that wealthy states promise a market to pharmaceutical companies who have traditionally failed to investigate diseases affecting the poorest of nations. Several scientists have recommended that prior to the development of a malaria vaccine, vector control programs, such as those using Bti toxin, should be implemented in regions with low vector capacity. This analysis indicates that both indigenous programs in malarial regions and molecular approaches to parasite control are unlikely to provide sustainable solutions to the malaria problem, although some may assist in controlling malaria burdens. The successful eradication of malaria, however, will require sustained support from wealthy nations to develop a malaria vaccine.

 

Obstacles to the eradication of malaria

In 1999, the World Health Organization (WHO) estimated that over 300 million clinical cases of malaria occur annually from among the 2.3 billion people (almost one-third of the world’s population) who are at risk of infection with the malaria parasite. An estimated 1.1 million people annually die from the disease. While these numbers are shocking, they are probably underestimates of the world’s malaria burden given that only a fraction of malaria cases are reported each year and that deaths among children with chronic malaria are often attributed to other illnesses. These statistics may vary by a factor of three, depending on the method of estimation (WHO, 1999). In Africa alone, the 28 million reported cases of malaria are believed to represent only 5-10% of the total malaria incidence on the continent (Hamoudi & Sachs, 1999).

 

Malaria is clearly a global challenge in need of an immediate and sustained solution. Unlike AIDS, dysentery, or other diseases affecting the tropics, malaria cannot be totally controlled by behavioral changes or education. Rather, the disease is determined by climate and ecology–malaria risk is geographically specific to tropical and subtropical zones, primarily because its pathological vector is the mosquito. And while it is true that most malarial countries are also poor countries, several wealthy nations, such as the United Arab Emirates and Oman, face serious malaria problems.

 

A recent study by economists John Gallup and Jeffrey Sachs reveals that although poverty does not appear to determine malaria risk, the prevalence of malaria has an enormous impact on a country’s economy. Malaria dramatically inhibits economic growth (probably by restricting individual worker productivity, tourism, foreign investment, and transportation), although poverty does not appear to determine the prevalence of malaria (Gallup & Sachs, 1998). Some analysts have estimated the economic burden of malaria at 0.6-1.0% of GDP in Africa, although recent reports indicate that the economic impact of the disease on national income is likely to be much higher (Shepard, 1991; Bloom & Sachs, 1998).

 

The high incidence rates of malaria are, in fact, affected by the unusual nature of the parasite itself and its vector, the mosquito. Not only is the malaria parasite itself highly complex, but its vector is a sexually reproducing organism capable of mixing genes during reproduction. As a result, mosquitoes quickly evolve to acquire drug resistance. It is also believed that the malaria parasite co-evolved with the human species, so the two organisms are probably well-adapted to one another (Hamoudi, 2000).

 

The species-specific behavior of mosquitoes in some regions, however, has allowed for the success of malaria control programs in those areas, while mosquitoes in other regions have posed significant obstacles to those attempting to prevent malaria infection. In some temperate regions where malaria has been eradicated, mosquitoes spend their winter in hibernation or a non-reproductive state. Control programs have used this fact to their advantage by using insecticide and drug treatments during the mosquito “off-season”.

 

In tropical zones where mosquitoes do not hibernate, individuals often receive multiple malaria infections. But populations of people in malaria endemic regions such as sub-Saharan Africa do not appear to develop protective, sterilizing immunity to the disease. Rather, they develop a non-sterilizing immunity that suppresses clinical symptoms of the conditions, allowing those infected persons to appear healthy while malaria parasites develop and circulate in their blood. These dangerously inconspicuous parasite reservoirs develop in endemic populations, inhibiting the treatment of infected individuals while providing sources for the propagation of this disease. Mosquitoes in temperate regions, on the other hand, re-infect individuals rarely. People in these regions exhibit decipherable symptoms of malaria upon infection, and can be treated promptly (Hamoudi & Sachs, 1999).

 

Educational prevention programs. Given our current understanding of obstacles to effective malaria control (particularly in tropical regions), we can discuss several options for both short- and long-term control programs. Malaria reduction efforts paralleling those of AIDS control initiatives–namely, programs using education and distribution of protective devices (condoms to prevent HIV infection, bednets to prevent malaria)–have supported malaria control initiatives in several regions. The use of treated bednets and curtains has substantially curtailed malaria incidence rates in China and Vietnam and has reduced child mortality rates by as much as 63% in African trials (WHO, 1999). But programs distributing bednets and other protective devices offer no panacea to the malaria problem.

 

In fact, the effectiveness of protective devices is often curtailed by the activities of governments privatizing their industrial sectors or agricultural markets, often under pressure from international lending institutions aiming to

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