August 20, 2018, by Emma Thorne
World Mosquito Day 2018 – why malaria continues to bite
On World Mosquito Day, Edward Rea, a research fellow working on malaria parasite cell biology and development with Professor Rita Tewari in the School of Life Sciences, discusses why the fight against this mosquito-borne disease is far from over.
Are you itching for a holiday? Got the travel bug? Just hope that itch isn’t a bite, and the bug isn’t something more sinister. We all know the pain and annoyance that mosquitoes can cause when we go on holiday – but we don’t all know about the 700,000 people killed by diseases spread by mosquitoes every year.
World Mosquito Day is an annual event that recognises the discovery by Sir Ronald Ross in 1897 that malaria is transmitted by female Anopheline mosquitoes. We have since discovered that many other tropical diseases are spread by various biting insects, including dengue fever, yellow fever, Zika virus, filariasis, leishmaniasis, and African sleeping sickness. These diseases have a huge impact on global health and represent a significant financial burden on developing countries.
Most of these diseases have very few treatments, and some have no cure. Even malaria, which has seen the greatest reduction in mortality in the past century, relies on just a handful of different drugs. For all of these diseases, resistance is a constant and growing problem which threatens to reverse the progress we have made in our attempt to eradicate these diseases. Most of these vector-borne diseases are limited to Sub-Saharan Africa and South East Asia but climate change is threatening to expand the territory of these insects outside the tropics, putting most of the world’s population in danger.
Mosquitos are the vector for malaria, and represent a significant opportunity for controlling this disease. One of the greatest successes in recent global efforts towards the eradication of malaria has been the campaign for insecticide treated bed nets. By placing a large net over people’s beds, they are protected from mosquitos for a large portion of the mosquito’s active hours. If the mosquitos can’t bite people then they cannot spread the disease. Previous attempts in the 60’s and 70’s at eradication involved widespread DDT spraying to reduce mosquito populations. This was devastating to malaria, but also to the surrounding ecosystems, as DDT kills all insects, not just mosquitos, and is toxic to many birds and fish. Unfortunately, both of these methods are becoming less effective due to the spread of insecticide resistance in insect populations. An alternative option is to target the parasites within the mosquitos – the transmission stages.
When a mosquito bites and infected patient, they ingest a number of specialised sex cells, known as gametocytes, which are the source of transmission. These sex cells develop within the mosquito, and make thousands more cells which can continue the infection by spreading in the mosquito saliva. This side of the parasite life cycle is much less well understood, and work at the University of Nottingham aims to determine how these parasites develop and proliferate within the mosquito. If we can understand the critical mechanisms involved and then develop effective drugs, these can become exciting opportunities to permanently wipe out the threat of malaria.
World Mosquito Day serves as a reminder that while we have achieved a lot, we still have a long way to go. Mosquitos don’t discriminate, as you may know from high profile cases like Cheryl Cole, who contracted malaria in 2010. There are many charities that provide excellent support to workers trying to eliminate malaria, like Sport Relief, and Malaria No More, and we encourage you to donate whatever you can spare.