When you think of an animal with a deadly bite, what comes to mind? A lion, a great white shark or possibly a crocodile. True, these animals can certainly take a large chunk out of you but, in the whole scheme of things, they have nothing on the deadliest biters: small arthropods such as mosquitoes, sandflies and ticks.

And what makes their bite so deadly?

When these arthropods hone in on humans for a blood meal, they transmit disease-causing parasites into our blood during the feeding process. These arthropods are known as disease vectors because they transmit disease causing parasites from person to person – or indeed between humans and other animals.

It is thought that more than half the world’s population are at risk from vector-borne diseases, so you can understand why World Health Day 2014 is focusing on them.

Malaria and dengue fever are probably the two best known, and they are transmitted by different types of mosquitoes  – Anopheles and Aedes respectively. Mosquitoes are also responsible for transmitting Japanese encephalitis, Chikungunya, yellow fever and Lymphatic filariasis. The latter are not currently household names in much of the world, but with increased travel to tropical regions, and global warming encouraging mosquitoes to migrate beyond the tropics, these are likely to become all too familiar threats worldwide.

Lymphatic filariasis  or elephantiasis is a Neglected Tropical disease and currently 120 million people – twice the population of the UK – are infected with the roundworms that cause the disease. The parasites infect the lymphatic system and the kidneys, and can lead to swelling and thickening of skin tissues. The immune system is commonly weakened and this leads to co-infection with other pathogens, increasing significantly the morbidity, disability and mortality of infected people. An article published today in Infectious Diseases of Poverty shows that approximately 88% of patients with lymphatic filariasis are also infected with a pathogenic fungus.

Flies are a merely a nuisance in the UK, but in many parts of the world they move into the realms of health hazard because of the diseases that they carry. In mid-continental Africa, between the Sahara and the Kalahari deserts, the tik-tik fly –  AKA the tsetse fly – transmits the protozoan parasite that causes sleeping sickness – an infection of the nervous system that disrupts the sleep pattern and can lead to death.

Finally, not all vector-borne diseases are transmitted by ‘biters’. Water snails harbour the parasite that causes schistosomiasis, releasing the parasite larvae into water sources from where people become infected.

The fight to both protect people from and treat people with these diseases is ongoing. Progress is incremental, and there are always new issues developing. Resistance to insecticides is just one of many examples. What is certainly clear is that research into these diseases is needed as much as ever, and that initiatives like World Health Day are imperative for raising awareness of the work that still needs to be done.

Find out more

You can learn more about the World Health Day 2014 campaign on the WHO website.

The latest open access research on vector-borne diseases can be found in: