- Mosquitoes cause at least 2.7 million deaths every year.
- About 500 million cases of mosquito-borne diseases occur annually.
- 90% of mosquito-borne illnesses occur in Africa.
- There are over 3,500 species of mosquitoes. The estimated number of total mosquitoes in the world is in the quadrillions.
Mosquitoes are a part of our everyday lives. They’re the cause of that natural buzzing background noise on nature walks and the annoying itchy bumps that come after. We’ve learned to live with the reality of mosquitoes, treating them as a simple nuisance. However, most people don’t realize that this reality is much more serious.
In fact, mosquitoes are considered the deadliest animals in the world. It may seem impossible that these tiny, pesky critters can do so much damage, but they can. In fact, mosquito bites result in over 1 million deaths every year. The majority of these deaths are due to mosquito-borne diseases, most prominently malaria. Mosquitoes have caused epidemics across the entire world and the statistics are startling.
Basic Mosquito Facts
Mosquitoes have been around since the Jurassic period, making them about 210 million years old. They’ve been mentioned all throughout history and records of mosquito-borne illnesses date back to 300 B.C. Mosquitoes are a part of our lives, and while they may just seem like an everyday nuisance, they’re actually the top killers in the world.
Globally, there are approximately 3,000 different species of mosquitoes. In North America alone, you could be bitten by up to 150 different species. There are trillions, realistically even quadrillions, of mosquitoes in the world, and they really are the deadliest creatures on the planet. Of course, these tiny bugs don’t do it all on their own. What makes mosquitoes so dangerous is their capacity to transmit viruses or other parasites that cause devastating diseases.
It’s worth noting that only female mosquitoes bite. Both males and females feed mainly on fruit and plant nectar, but females also need the protein in blood to help their eggs develop. They don’t have teeth, though — the females “bite” with a long, pointed mouthpart called a proboscis. They use the serrated proboscis to pierce the skin and locate a capillary, then draw blood through one of two tubes. The bumps or “bites” that we see form on our skin are actually an allergic reaction to mosquitoes’ saliva. When the mosquito feeds on human blood, it injects saliva into our skin, and the itchy bump is the result of a mild immune system reaction to it.
Mosquitoes have six legs and their coloring varies from grey to black, with some having white, green or blue markings. Individually, mosquitoes are pretty hard to spot as they fly because of their small size (they’re very small — 1⁄8” – 3⁄8” long). They’re usually active from dusk to dawn and tend to like dark, damp areas near stagnant water.
A mosquito can drink up to three times its weight in blood, although it’s very difficult for someone to die from blood loss caused by a mosquito. For an average person, losing two liters of blood becomes life-threatening. The average mosquito bite drains 0.01 to 0.001 milliliters of blood. This means it would take somewhere between 200,000 and 2 million mosquito bites to kill you from blood loss. What you really need to worry about is all of the diseases that these insects can carry.
Mosquito-borne diseases and illnesses are caused by bacteria, viruses, or parasites transmitted by mosquitoes. They can transmit diseases without being affected themselves and are responsible for over 1 million deaths each year. Nearly 700 million people get a mosquito-borne illness each year. The most prominent mosquito-borne diseases include malaria, West Nile virus, yellow fever, dengue, chikungunya, and Zika virus. In the United States, the instances of mosquito-borne diseases have skyrocketed in the past years:
West Nile Virus
West Nile Virus (WNV) was first identified in a woman in the West Nile district of Uganda in the year 1937. It was identified in birds (crows and Columbiformes) in the Nile delta region in 1953. Birds are the natural hosts of the virus, but this was not discovered until 1997. Over the past 50 years, human infections attributable to WNV have been reported in several countries.
The most common mosquito-borne disease in the United States is WNV. The virus came to the U.S. in 1999. Scientists first identified it in a feverish woman in Uganda – the West Nile district – in 1937. There were large outbreaks of the virus reported in Israel, South Africa, and Romania up through the late ’90s. The virus first appeared in the United States in 1999 with an epidemic in New York.
West Nile virus can cause a lethal neurological disease in humans. However, approximately 80% of people who are infected will not show any symptoms. The virus can also cause severe disease and death in horses. There are currently vaccines that are available for use in horses, but none yet for people.
As of January 8, 2019, a total of 49 states and the District of Columbia have reported West Nile virus infections in people, birds, and mosquitoes in 2018. WNV is becoming increasingly prominent across the entire United States. Overall, 2,544 cases of West Nile virus disease in people have been reported to CDC. The virus is slowly becoming less prominent in the U.S. The following graph shows the cases and deaths in the U.S. from 1999-2017:
About 20% of people who become infected with WNV will develop West Nile fever. Symptoms include fever, headache, tiredness, body aches, nausea, vomiting, swollen lymph glands, and occasionally a skin rash. It’s estimated that 1 in 150 people that become infected with the West Nile virus will develop a more severe form of the disease.
WHO states that “since WNV outbreaks in animals precede human cases, the establishment of an active animal health surveillance system to detect new cases in birds and horses is essential in providing early warning for veterinary and human public health authorities.”
In 2015, malaria alone caused 438,000 deaths. That same year, 3.4 million people were at risk of catching malaria worldwide. The World Health Organization estimates that between 300 and 500 million cases of malaria occur each year and a child dies from malaria every 30 seconds. Malaria is endemic in 91 countries, with about 40% of the world’s population at risk. The following graph shows the change rate of the malaria case from 2010-2016, by region:
Remember, it’s not the mosquito itself that kills, but rather a parasite the mosquito carries. Only female mosquitoes of the Anopheles genus carry the disease. You’ll find the Anopheles all over the world, with the exception of Antarctica. The mosquito is able to transmit the disease by biting someone infected with malaria and then passing it along to the next person it feeds on.
Malaria is a blood-transmitted disease, which means you can’t contract it from casual contact with another person. Because it is transmitted through the blood, you can contract it from a contaminated transfusion or needle. However, mosquitoes are primarily to blame for the spread of this deadly infection which can kill just 24 hours after symptom onset.
In 2017, an estimated 219 million cases of malaria occurred worldwide and 90% of these cases occurred in Africa.
That same year, there were an estimated 435,000 malaria deaths worldwide. Children aged under 5 years are the most vulnerable group affected by the disease. In fact, in 2017, they accounted for 61% of all malaria deaths worldwide.
According to the latest World Malaria Report, released in November of 2018, there were 219 million cases of malaria in 2017, up from 217 million cases in 2016. In 2017, five countries accounted for nearly half of all malaria cases worldwide: Nigeria (25%), the Democratic Republic of the Congo (11%), Mozambique (5%), India (4%) and Uganda (4%). In 2018, it was reported that 11 countries accounted for 70% of all malaria cases. Those countries included: Burkina Faso, Cameroon, the Democratic Republic of the Congo, Ghana, Mali, Mozambique, Niger, Nigeria, Uganda, Tanzania, and India.
One of the main issues surrounding the epidemic of malaria is the lack of international funding. The latest WHO report also indicated that the global community fell short of the $4.4 billion required for malaria elimination and control in 2017. The global fight against malaria is still reliant on external funding. Only $3.1 billion was made available for malaria programs and activities worldwide, and only $2.2 billion of these funds came from international financing.
The worldwide incidence of dengue has increased 30-fold in the past 30 years, and recently, more countries have been reporting their first outbreaks of the disease. Zika, dengue, chikungunya, and yellow fever are all transmitted to humans by the Aedes aegypti mosquito. More than half of the world’s population live in areas where this mosquito species is present. Dengue is one of the most important mosquito-borne virus diseases, with 2500 million people worldwide at risk of infection and 20 million cases a year in more than 100 countries.
Before 1970, only 9 countries had experienced severe dengue epidemics. The disease is now endemic in more than 100 countries in the WHO regions of Africa, the Americas, the Eastern Mediterranean, South-East Asia, and the Western Pacific. The America, South-East Asia and Western Pacific regions are the most seriously affected.
About half of the world’s population is at risk of dengue infection. Each year, an estimated 390 million dengue infections occur around the world. Of these, 500,000 cases develop into dengue hemorrhagic fever, a more severe form of the disease, which results in up to 25,000 deaths annually worldwide.
The infection causes flu-like symptoms and occasionally develops into a potentially fatal illness called severe dengue.
The global incidence of dengue has grown dramatically in recent decades. From 1990-2015, the number of global dengue cases has fluctuated, but remained high:
Dengue is found in tropical and sub-tropical climates around the world, mostly in urban and semi-urban areas. Severe dengue is a leading cause of serious illness and death among children in multiple Asian and Latin American countries. Unfortunately, there is no specific treatment for dengue/ severe dengue, but early detection and access to proper medical care can lower fatality rates to under 1%.
An estimated 500,000 people with severe dengue require hospitalization each year with an estimated 2.5% case fatality rate. Globally, there has been a decline of 28% in case fatality; studies also show that there has been a significant improvement in case management between 2010 and 2016 on the country level.
Since 2014, there have been significant increases in dengue infection cases in numerous countries across the world. Fortunately, in 2017, a significant reduction was reported in the number of dengue cases in the Americas – from 2,177,171 cases in 2016 to 584,263 cases in 2017. However, numbers are beginning to rise again, with reports in 2018 showing new outbreaks in Bangladesh, Cambodia, India, Myanmar, Malaysia, Pakistan, the Philippines, Thailand, and Yemen.
Many major cities of the world, especially in North and South America, are at risk of potentially devastating epidemics of yellow fever because they are infested with Aedes aegypti mosquitoes which can transmit the disease. It is endemic in 33 countries in Africa and 11 countries in South America. The yellow fever virus can be transmitted by mosquitoes which feed on infected animals in forests and then feed on humans traveling through the forest. The greatest risk of an epidemic occurs when infected humans return to urban areas and are fed on by the domestic vector mosquito Aedus aegypti, which then spreads the infection to more humans in the area.
Globally, in 2017, t here were 876 reported cases of dengue. 47 countries in Africa (34) and Central and South America (13) are either endemic to or have regions that are endemic to yellow fever. A modeling study based on African data sources estimated there were 84,000-170,000 severe cases of yellow fever during 2013. That same year, there were approximately 29,000-60,000 deaths caused by the infection. The following graph shows the reported cases of yellow fever across the world from 1980-2017:
Occasionally, travelers who visit yellow fever endemic countries may bring the disease to other countries that are unaffected by it. In order to prevent this “importation of the disease,” many countries require proof of vaccination against yellow fever before issuing a visa, particularly if travelers come from, or have visited yellow fever endemic areas.
In past centuries (17th to 19th), yellow fever was transported to North America and Europe, causing large outbreaks that disrupted economies, development and in some cases even decimated populations. The magnitude of this disease resonates across borders and oceans. Unfortunately, there is currently no antiviral vaccination to treat yellow fever. Prompt detection of the disease is crucial for controlling outbreaks but underreporting and access to medical care is a major issue worldwide. WHO has stated that the true number of yellow fever cases is estimated to be 10 to 250 times what is now being reported.
Chikungunya was first identified during an outbreak in southern Tanzania in 1952. It is an RNA virus that belongs to the alphavirus genus of the family Togaviridae. The name “chikungunya” comes from a word in the Kimakonde language, meaning “to become contorted. It describes the stooped appearance of sufferers with joint pain, which is caused by the disease. Other symptoms include muscle pain, headache, nausea, fatigue and rash. There is no cure for chikungunya and treatment usually focuses on relieving the symptoms.
Chikungunya virus disease became a nationally notifiable condition in 2015. Cases are reported to CDC by state and local health departments using standard case definitions.
The proximity of mosquito breeding sites to human habitation is a significant risk factor for chikungunya. The disease mostly occurs in Africa, Asia, and the Indian subcontinent. However, a major outbreak in 2015 affected several countries of the Region of the Americas. Chikungunya has been identified in over 60 countries in Asia, Africa, Europe, and the Americas.
Human chikungunya infection rates in Africa have been low for a number of years, but in 1999–2000 there was a large outbreak in the Democratic Republic of the Congo, and in 2007 there was an outbreak in Gabon. From those years on, the number of outbreaks began to rise significantly in other regions of the world, spreading to Asia, the Indian Subcontinent, parts of Europe, and eventually the Americas, including the U.S. In late 2013, the first local transmission of chikungunya virus in the Americas was identified in Caribbean countries and territories. Local transmission means that mosquitoes in the area have been infected with the virus and are spreading it to people. The virus then spread throughout most of the Americas.
As of January 8, 2019, a total of 90 chikungunya virus disease cases with illness onset in 2018 have been reported to ArboNET from 23 U.S. states (Table & Map). All reported cases occurred in travelers returning from affected areas. No locally-transmitted cases have been reported from U.S. states. However, 2 locally-acquired transmissions were reported in Puerto Rico. The following world graph shows regions of the world where chikungunya has been reported (as of May 2018):
Zika is primarily transmitted through the bite of an infected female Aedes aegypti mosquito. The mosquito becomes infected from biting an infected human and then transmits the virus to another person. The virus can be transmitted from a pregnant woman to her fetus, through sexual contact, blood transfusion, or by a needle. In 1947, the Zika virus was first discovered in a monkey by scientists studying yellow fever in Uganda’s Zika forest.
The first active case of Zika virus found in humans was reported in 1968. Though researchers had found antibodies in the blood of people in both Uganda and in Tanzania as far back as 1952, this was the first known case of the active virus in humans. Through the 60s, 70s, and 80s, a small number of countries in West Africa and Asia found Zika in mosquitoes, and isolated, rare cases were reported in humans.
In 2007, the first major outbreak of the virus occurred in Yap Island, Federated States of Micronesia. Of the suspected 185 cases reported, 49 were confirmed, and 59 were deemed probable. There are an additional 77 suspected cases, but no deaths were reported. In 2008, two American researchers contracted the disease, and one sexually transmitted the virus to his wife. This was the first report of Zika being transmitted sexually.
From 2013-2014 there was a large outbreak of Zika in French Polynesia, with about 32,000 suspected cases. There were also significant outbreaks in the Pacific Islands, including Easter Island, the Cook Islands, and New Caledonia.
In 2015, the Zika virus broke out in the Americas. Brazil sent a report to WHO detailing an illness with skin rash prevalent in the northeastern region. The illness is identified as the Zika virus, and from then on, multiple reports of birth defects and infant mortality began to arise. Many babies developed congenital Zika syndrome, which includes malformations such as limb contractures, high muscle tone, eye abnormalities, and hearing loss. The risk of congenital malformations following infection in pregnancy remains unknown, however, an estimated 5–15% of infants born to women infected with Zika virus during pregnancy have evidence of Zika-related complications. The virus began to be detected in the United States shortly after, turning up in Miami, Florida and making its way into other states like Texas. Pregnant women were advised not to travel to countries where the Zika virus was active.
In 2015, a total of 6 2 symptomatic Zika virus disease cases in the U.S. were reported to the CDC. 10 cases were also reported in U.S. territories. In 2016, that number rose to 5,168 cases in the U.S. and 36,512 symptomatic cases in U.S. territories. Here are the numbers for Zika cases in 2016 by gender and age group:
By 2017, the numbers began to decrease significantly, making their way into the mid-100s and the CDC no longer deemed the virus endemic. However, Zika is still active in the U.S. In 2018, 72 Zika virus disease cases reported in the U.S. and 148 were reported in U.S. territories.