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Science

The mosquito: the world's smallest biggest killer

The world's biggest killers are in fact something so tiny - the mosquito. Worldwide there are 3,500 known species of mosquito. Which are the deadliest and which should be avoided at all costs?

More than 1 million people die every year from mosquito-borne infection and disease - making the mosquito the most deadly animal in the world. We identify the most noxious mosquitoes, their habitats, feeding patterns, as well as mapping their global prevalence.

Anopheles mosquitoes

Carriers of malaria

Known as the "Malaria mosquitoes," there are more than 460 sub-species of Anopheles mosquito (pictured above). With close to 20 percent of the genus capable of spreading the virus to humans, the female Anopheles mosquito transmits malaria after biting an infected human and then passing on the deadly parasite to the next unsuspecting person it gnaws.

This genus of mosquito can be easily identified by the black and white scales on its wings and can be found across the world, with the exception of Antarctica.

While malaria is nowadays limited to tropical areas, with sub-Saharan Africa remaining the hardest hit, many Anopheles genus mosquitoes like and breed in colder climes. Stagnant, clean, unpolluted water is a breeding paradise for this insect.

A blood-borne disease, malaria cannot be contracted from common contact with an infected person, it can, however, be transmitted through contaminated needles or blood transfusion. Anyone can contract malaria, but those likely to fall seriously or fatally ill are the elderly, those with weakened immune systems, children, pregnant women or travelers who have come from an area where malaria is non-existent.

The World Health Organization (WHO) estimates that despite the number of malaria cases dropping by 47 percent over the past 15 years, one child still dies from the disease every minute. While anti-malarial drugs have been developed, there is currently no vaccine available.

Aedes mosquito

Carriers of dengue fever, Japanese encephalitis, Zika virus and yellow fever

Of the three most significant genea of mosquito, the Aedes is the most invasive. These mosquitoes are often carriers of a number of viral infections, such as dengue fever, yellow fever and the Zika virus. Contagion is often accompanied by a fever, headache, nausea and vomiting, muscle and joint pains, rash and in rare cases, encephalitis, which can lead to death.

Originally found in tropical and sub-tropical regions of the world, like the Anopheles mosquito, the Aedes can now be located on all continents other than Antarctica.

This genea of mosquito are visually distinct from other mosquito species, as they have noticeable black and white markings on their legs and back. In contrast to other mosquitoes, Aedes mosquitoes are only active during daylight hours.

Once only found in water-filled habitats, this particular species has adapted to rural, suburban and urban human environments. Notably, the WHO reports, the Aedes has spread from Asia to Africa, the Americas and Europe in recent decades, predominantly through the international trade in used tyres in which eggs are laid when they contain rainwater.

Japanese encephalitis: Transmitted by mosquitoes to humans, domestic pigs and wild birds, Japanese encephalitis is a viral infection which causes inflammation of the membranes surrounding the brain. In most cases, those infected experience mild fever or headaches, but in severe cases infection can be deadly.

Yellow fever: This sub-species of mosquito is responsible, the WHO reports, for infecting almost 200,000 people per year with yellow fever. The acute viral hemorrhagic disease is prevalent in tropical and sub-tropical areas of South America and Africa. More than 30,000 unvaccinated people die each year as a result of becoming infected.

Dengue fever: Once infected, carriers become transmitters and multipliers of dengue fever, acting as a source for uninfected mosquitoes. The virus then circulates through an infected person's bloodstream for two to seven days, during which time they will most likely develop a fever. Once recovered, previously infected humans are provided lifelong immunity against that particular strain of dengue virus.

Zika virus: Only one in five people who contract the mosquito-borne Zika virus display symptoms of infection, which can include nausea, irritability, rash, conjunctivitis and excessive joint or muscle pain. In rare cases, hospitalization is required. Less than 0.01 percent of all reported cases to date have been fatal.

However, that does not mean the virus comes without any associated health risks. The US Centers for Disease Control and Prevention (CDC) reports that the Zika virus is linked to a spike in microcephaly, a birth defect that causes infants to be born with smaller skulls and can lead to permanent brain damage.

The CDC says there were 30 times more cases of Zika reported in Brazil last year than in any year since 2010. As a result, it has advised pregnant women against traveling to Brazil, as well as the following countries: Colombia, El Salvador, French Guiana, Guatemala, Haiti, Honduras, Martinique, Mexico, Panama, Paraguay, Puerto Rico, Suriname, and Venezuela. There is currently no treatment available for Zika, although a

German biotechnology company has developed a test

that reveals whether there are Zika pathogens in a blood sample.

Culex mosquitoes

Carriers of West Nile fever, Japanese encephalitis, lymphatic filariasis and possibly the Zika virus

Frequently referred to as the common house mosquito, the Culex mosquito typically feeds on birds instead of humans, seeking their blood meals at dawn and dusk. This genera includes close to 1,000 sub-species of mosquito and is not considered as much of a threat to human health as the Anopheles and Aedes mosquitoes.

Although not a primary transmitter for mosquito-borne diseases such as malaria, yellow or dengue fever, the drab colored Culex mosquito can spread an array of other diseases that can be harmful to people, such as the West Nile virus, lymphatic filariasis and Japanese encephalitis.

West Nile Virus: Over the past decade, there has been a global increase in the occurrence of West Nile outbreaks, particularly across countries unfamiliar with the virus - including the US, Greece and Russia. This mosquito-borne virus is predominantly found in temperate and tropical regions of the world. Often those who have contracted the virus remain unaware of their infection as the disease is habitually symptom free. No vaccine against the virus currently exists.

Lymphatic filariasis: While the prevalence of West Nile outbreaks has increased, there has been a reduction in the number of cases of lymphatic filariasis. This mosquito-borne disease, which has infected tens of millions of people globally, leaving them either incapacitated or disfigured, is mostly seen in Africa, Asia and the Pacific. Infection occurs when a mosquito infects a human with a parasitic worm, which goes on to severely damage the immune and lymphatic systems. This painful and disfiguring virus often goes unnoticed until later in life.

Zika virus: While the Aedes mosquito was originally thought to be solely responsible for the spread of the Zika virus, scientists are now looking into whether the Culex mosquito could also be to blame for the increased number of infections. The Culex mosquito is up to 20 times more prevalent in Brazil than the Aedes sub-species, which could help explain the intensity of the outbreak there. Although researchers, like Constanica Ayres from the Fiocruz Institute in Recife, say if the Culex is found to be a carrier of Zika, containing the virus' spread could be "more difficult than previously thought."

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