Not sharks or snakes or lions. In the case of deadly animals, mosquitoes are the most dangerous in the world. They can be small and fragile, but their ability to carry and transmit diseases cause millions of deaths each year around the world. Only malaria caused 438,000 deaths in 2015, according to data from the World Health Organization (WHO). Their competitors may be big, strong and scary, but don’t cause even a third of mosquitoes’ casualties: snakes make about 125,000 fatal victims worldwide each year, lions make 200 victims and sharks just 55, according to WHO data.
Several viruses are transmitted by mosquitoes and other arthropods – the “arboviruses”. The best-known are the Aedes and Culex mosquitoes. The list of diseases that can be transmitted is huge and ranges from the most known as dengue, chikungunya and zika, to the more exotic ones, such as filariasis and West Nile fever, and also malaria, yellow fever and leishmaniasis. Some cause no more than a discomfort that resembles the common cold, but many can be fatal.
Small, but dangerous
The Aedes mosquito is one of the smallest – it has only seven millimeters – and also one of the most dangerous. It is responsible for transmitting various diseases, including dengue, zika, chikungunya and yellow fever.
Dengue is the one that with the highest number of cases: a recent estimate published by Bhatt and colleagues in Nature magazine indicates 390 million infections by the disease each year, of which 96 million were manifested clinically. According to WHO, dengue is endemic in more than 128 countries, with about 3.8 million people at risk.
Chikungunya had more than 37,000 confirmed cases in the Americas recorded in 2015 by the Pan American Health Organization (PAHO). Zika had more than 91,000 probable cases recorded up to April this year in epidemiological bulletin of the Ministry of Health of Brazil. Both diseases have been documented in more than 60 countries in Africa, Asia, the Americas and Europe.
Despite the huge numbers, most of the time these diseases are mild or moderate. However, some cases may be serious. Classic dengue rarely has serious consequences, but hemorrhagic dengue can lead to death. “Severe cases of the disease are very rare, and mortality rate is relatively low – about 40 deaths per 100,000 cases recorded (0.04%)”, says Otávio Clark, CEO and team leader of Evidências – Kantar Health.
The main risk of zika is the infection of pregnant women, which may cause microcephaly and other complications n babies. Furthermore, zika virus is also associated with Guillain-Barré syndrome (a rare disease in which the immune system attacks peripheral nerves cells, causing muscle weakness and loss of sensation).