This year, the theme of World Health Day on 7 April is “vector-borne diseases.” To many people living in Europe or North America, this might seem like an odd choice. Thanks to the success of malaria elimination efforts conducted more than 50 years ago, the wealthier nations of the world are relatively free of the burden of infectious diseases transmitted to humans by animal intermediaries – anything from mosquitoes, to flies, to snails, to rodents, to birds.
But the fact is that vector-borne diseases continue to exact a huge toll on humanity. Every year, they cause at least one million deaths worldwide and drain billions of dollars from the global economy through lost productivity (i.e., sick days away from work) and higher healthcare costs.
It’s important to note that the wealthier countries of the world aren’t immune to vector-borne diseases. One case in point is West Nile Virus, a mosquito-transmitted arbovirus that was originally identified in the West Nile District of Uganda in 1937. The first recorded case occurred in the United States in 1999, when someone in New York City was bitten by a mosquito that had picked up the virus from a recent traveller from Africa. Since then, West Nile has spread across North America and it causes hundreds of hospitalizations and dozens of deaths each year.
Even more challenging is dengue fever, a virus that was largely confined to the western Pacific until the Second World War. Since then, human migration and global commerce have helped dengue – and the mosquito species that transmits it, Aedes aegypti, – to spread worldwide.
Today, the United States stands at risk because A. aegypti has established habitats in the US states that border on the Gulf of Mexico. While most people who are infected with dengue never develop active disease, it can cause severe symptoms in a small percentage of people. More than half a million people worldwide suffer these symptoms every year, and dengue causes an estimated 25,000 deaths annually.
Altogether, one billion people worldwide are infected by vector-borne diseases each year, and one-sixth of the illnesses and disabilities that humanity suffers are caused by them. So the question is, how can we humans bite back?
The good news is that recent human history has shown that we can turn the tide. At the start of the 20th century, malaria was endemic to nearly every nation on earth. Today, malaria has been eliminated in more than 100 countries worldwide. We have also made huge progress since 2000 in reducing the burden of malaria in the regions of the world where it remains highly prevalent. By increasing access to timely diagnosis, effective treatment and low-cost interventions such as bed nets, deaths from malaria have fallen more than 40 percent in Africa, and malaria incidence has dropped an amazing 25 percent. Altogether, an estimated 3.3 million lives have been saved.
But we won’t be in a position to defeat malaria, dengue, and other vector-borne diseases without dedicated investment in research and development for new drugs, vaccines, diagnostics and novel vector-control methods. While the current tools we have are helping the world make huge strides in reducing deaths and disabilities caused by these diseases, we don’t yet have the tools required to stop them altogether.
For dengue, we need to stay focused on developing a safe and effective vaccine that can prevent people from becoming actively infected with the disease. If we can short-circuit the cycle of human infection, we can reduce or potentially interrupt transmission by removing the human reservoir that harbours the virus.
We also need better approaches to vector control (i.e., keeping A. aegypti away from humans). This means exploring new technologies such as effective spatial repellents, that can protect people from frequent contact with mosquitoes, as well as identifying strategies that can affect the life cycle of A. aegypti, reducing the volume of mosquitoes that are capable of transmitting the virus to humans.
For malaria, we need to pursue the development of more effective drugs and better diagnostics with the goal of developing tools that can get the malaria parasite out of people once and for all. Until recently, the goal of malaria drug development has been to develop medicines that can quickly alleviate human suffering and save lives. But most treatments for malaria don’t actually eliminate the parasite from the human body. This means that human beings can harbor the parasite that causes malaria for more than a decade, making malaria resurgence likely in high-burden environments such as tropical Africa.
To address this challenge, we need to pursue the development of a one-pill complete cure for malaria as well as a highly accurate point-of-care diagnostic that can detect the presence of the malaria parasite with a simple blood or urine test, identifying those who need treatment. And like dengue, we need to stay invested in the development of a malaria vaccine that can prevent infection in children and help accelerate elimination.
We should be more confident than ever that we can develop these next-generation tools. In just the past two years, we have identified potential diagnostics, drugs and vector-control methods for human African trypanosomiasis that could make it possible to eliminate a disease that once killed millions. We have also brought to market a new preventive vaccine for Japanese encephalitis that is 1/1,000th the cost of its predecessor and has the potential to save 15,000 lives per year.
When people come together with resources, commitment and public will, there is no challenge that’s equal to the power of human innovation.
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Dr. Lance Gordon is Director of the Neglected Infectious Diseases Program and Dr. Alan Magill is the Director of Malaria Program in the Global Health Division of the Bill & Melinda Gates Foundation.
Image: A mosquito caught in a plastic box by researchers. REUTERS/Tobias Schwarz