For most people in the United States and Europe, mosquitoes leave only itchy red bumps. However, in the rest of the world, mosquitoes can cause serious illness or death.
Only the female mosquito ingests blood, as she needs protein and iron to produce eggs. When a mosquito bites, she injects saliva and anti-coagulants into the wound. It is through these substances that a virus or parasite can be transmitted to a human or animal.
Mosquitoes transmit diseases to over 700 million people per year. In most developed countries, diseases are very limited and deaths are comparatively rare, but in Africa, South and Central America, Mexico and Asia, millions of infections and deaths result from mosquito-borne diseases.
Mosquitoes' role in spreading disease was first understood around the turn of the 20th century. In 1898, British physician Sir Ronald Ross, then working in Calcutta, proved that mosquitoes were transmitting malaria. Prior to this, Carlos Finlay of Cuba had suggested the same about yellow fever, as had Josiah Nott and Patrick Manson about the parasite filariasis. Ross's and Finlay's protocols were implemented with significant success by Walter Reed and the U.S. Army Medical Board during construction of the Panama Canal.
Malaria--this disease is caused by a protozoa parasite. Symptoms include fever, chills, headache, joint pain, vomiting and convulsions. Each year, 515 million people are infected with malaria, and 1 to 3 million people, mostly children, die from the disease annually.
Yellow fever--caused by a virus in mosquito saliva. Symptoms are fever, headache, chills, nausea, vomiting and bleeding into the skin. Severe cases cause internal hemorrhaging, coma and death. Annually, there are 200,000 infections and 30,000 deaths.
Encephalitis/West Nile--at least six types of encephalitis diseases are transmitted by mosquitoes. Symptoms for all of these include headache, fever, sensitivity to light, weakness and seizures. Fatalities are not uncommon.
Dengue fever--caused by one of four viruses present in mosquito saliva. Symptoms include headache, joint and muscle pain, fever, severe dizziness, bleeding from the mucous membranes, and bloody vomit/diarrhea. There are an estimated 50 million cases per year, with a fatality rate of 2.5 percent, or an estimated 125,000 deaths.
Epidemic polyarthritis/Ross River virus--is endemic to Australia and Papua New Guinea. While symptoms can persist for up to 6 months, only 400 people per year are infected, and the virus is rarely fatal. Symptoms include fever, headache, joint pain and rash.
Filariasis-- is a parasite endemic to Asia, Africa, Central and South America. The parasite lodges in the lymphatic system and causes thickening of the surrounding skin and tissues, known as elephantiasis. This generally affects the lower extremities, including the genitals. Worldwide, 120 million people are currently infected.
Most of the mosquito-borne diseases are now endemic to South and Central America, parts of Asia and Africa. Some of the encephalitis viruses, like West Nile, Japanese encephalitis and Western and Eastern equine encephalitis, do cause infections in the United States, Japan and Europe.
There are a number of different ways to minimize the effects of mosquito-borne diseases. Most of them can be treated with antibiotics and antivirals; there is even a vaccine for yellow fever. Developed countries spray for mosquitoes and regularly check levels of animal mortality, as most of these diseases can also be transmitted to animals through mosquito bites. In developing countries, mosquito nets are a common and economical solution. Preventing bites prevents disease. There are also organizations that work to get vaccinations to the impoverished and medicine to those who are already sick.