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Are mosquitoes the key to curbing disease?

The Wolbachia parasite prevents dengue fever from multiplying and leaves males infertile (Photo: CDC - public domain)
The Wolbachia parasite prevents dengue fever from multiplying and leaves males infertile (Photo: CDC - public domain)

Like many residents of Maputo, Mozambique, Isabelle is very familiar with mosquitoes and ten years ago, she was treated for malaria. Yet she has misgivings about plans to release specially reared mosquitoes to curb the spread of disease. In this guest blog, she considers if her worries are justified, and what the alternatives might be.

I grew up near a marshy area in the suburbs of Maputo, Mozambique – a country I would call the malaria capital of the world. It’s an environment where swarms and swarms of mosquitoes hover and feed outdoors from dusk until dawn. If you kill one horde, another takes its place in less than 10 minutes.

So, having spent half my life in this pest-ridden region, the thought of people releasing thousands of these insects into the wild is a little disconcerting. In fact, this is exactly what happened: as a response to the pandemic of the potentially deadly dengue fever (transmitted by mosquitoes), Brazilian researchers have recently introduced mosquitoes infected with a parasitic micro-organism called Wolbachia, which acts as a vaccine against dengue and prevents its spread to humans.

A scientific breakthrough or potential mistake?

Wolbachia is a common bacteria that affects many insects, and it has a major impact on mosquitoes. First, it prevents the dengue virus from multiplying in the host. Second, it disrupts reproduction: if a male mosquito, infected with Wolbachia, fertilises the eggs of a female without the bacteria, those eggs won’t turn into larvae. If both the male and female are infected, their offspring will also carry Wolbachia, and will die before becoming functioning adults. Male mosquitoes don’t feed on blood, and the insects will not be able to transmit Wolbachia to people. The ultimate aim is that these mosquitoes will breed, multiply, and become dominant.

If this works, it will truly be one of the greatest scientific achievements. However, if something goes wrong, it could potentially be disastrous. Mosquitoes are highly mobile, adaptive, and cunning creatures. Their ability to hide, bite, and escape is almost unparalleled. A release of this type and scale raises a few concerns; in the event that it turns out to be a mistake, recalling them is close to impossible. There is also the fact that another species of mosquito carries dengue and will continue to spread the disease.

Plagued by malaria & dengue

Over here, we receive a mosquito bite every couple of minutes, so intuitively, it’s worrying that these insects are being freed instead killed. The Ebola virus has been creating more and more panic, but we shouldn’t forget about malaria and dengue fever, two killers carried and spread by the same host. I suffered from malaria over a decade ago, but I still remember the pain and delirium to this day. I was fortunate enough to have had access to effective treatment and recovered quickly. So many others are not half as lucky.

Mosquito nets for internally displaced persons.
Alternatives to Wolbachia-infected mosquitoes include the careful use of mosquito nets.
Here, SOS Children and Red Cross workers hand out nets to refugees in the Central
African Republic.

The World Health Organization (WHO) reports that Africa accounts for 85% of malaria cases and 90% of malaria deaths worldwide. Most of these deaths occur in children under five years of age, and every 30 seconds, a child dies from malaria. The latter statistic is particularly relevant to the Millennium Development Goals, one of which is to reduce child mortality. The death rates are mostly caused by barriers to healthcare.

The other vector-borne disease, dengue fever, is potentially deadly and has no vaccine or specific medication. It primarily affects Asian and Latin American nations, and has become one of the leading causes of hospitalisation and deaths among children in those areas. The global incidence rate has sharply increased in the past few decades, and now around half of the world’s population is at risk from dengue.

Both diseases are each transferred by specific types of mosquitos: certain species of the Anopheles genus (carrying the malaria parasite) and Aedes genus (carrying the dengue virus). Mosquitoes don’t only transmit these two infections; they are also responsible for others such as yellow fever and the West Nile virus. Apart from death, the illnesses have knock-on effects such as absenteeism in schools, lower work productivity, and reduced tourism in affected areas. An effective means of eliminating or drastically limiting the prevalence of these diseases would not only reduce human suffering and death, but have far-reaching social and economic benefits as well.

Weighing the alternatives

There are other measures – already in place – that we can improve and intensify. We know that mosquitoes flourish in warm and wet conditions, and while we cannot control the climate, we can use this knowledge to our advantage. First, it cannot be stressed enough how important mosquito nets are (especially insecticide-treated nets). At an average price of £3 or less, this is the most cost-effective approach. Similarly, window and door screens are essential.

Regular and widespread fumigation/spraying helps too, but it is not the best solution because of the environmental hazard. Storage containers for collecting rainwater need to be covered and cleaned properly, as they are hotspots for breeding mosquitoes. Environmental management is also crucial for cleaning up solid waste areas and egg-laying habitats. Of course, healthcare systems in the mosquito-infested regions need to be strengthened, seeing as many deaths occur due to limited or no access to treatment. Efficient surveillance of mosquito populations, as well as accurate diagnosis of diseases, will fortify these preventative measures.

Malaria and dengue fever require long-term control; they cannot be eradicated after a one-time suppression. Understandably, the focus is on Ebola at the moment. But even before the outbreak occurred, there was not enough attention on diseases carried by mosquitoes, and now they will take even more of a backseat.

The release of the Wolbachia-infected mosquitoes is an interesting and potentially positive step. Nonetheless, it is an unpredictable strategy. If we really want to achieve significant success in overcoming malaria and dengue fever, such radical steps have to be reinforced by more research and reliable preventative methods.

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