The Most Common Mosquito-Borne Diseases

Mosquitoes are among the most dangerous animals of the world, for the diseases they transmit kill millions every year. In 2015, 438,000 individuals died from malaria alone. The species Aedes aegypti can carry chikungunya, dengue, yellow fever, and Zika—and over half of the individuals in the world live in the same areas as that mosquito. Mosquito-borne diseases can be prevented, as some have vaccines.

Many mosquito species lay their eggs in standing water, so another way to prevent illness is to reduce the number of places where they can lay their eggs. This can mean filling in ruts or removing buckets or tires that collect water. Windows and doors should have screens on them to keep mosquitoes out. Individuals who have to work outside should wear clothes to cover their skin as well as hats with mosquito netting to protect the face and neck. Similarly, they should use insect repellents.

Malaria

Malaria is transmitted by mosquitoes that belong to the Anopheles genus. According to the World Health Organization, there were 216 million cases in over ninety countries. The vast majority occur in Sub-Saharan Africa with eighty-eight percent of total cases reported and ninety percent of the deaths. The disease is actually caused by parasites in the Plasmodium genus. Five species can infect humans, with P. vivax and P. falciparum causing the most cases.

An infected person will typically start to develop symptoms ten to fifteen days after being bitten. The early signs, which include a headache, fever, and chills, can be mild and thus not immediately recognized as anything serious. As the disease progresses, though, it can affect tissues and organs like the blood, respiratory system, and brain. Disease caused by P. falciparum is the most severe and can kill within twenty-four hours.

Zika Virus

The Zika virus is transmitted by the species Aedes albopictus and Aedes aegypti, which are found in over 130 countries. It was first discovered in 1947 in monkeys in Uganda, and five years later, the first cases in humans were reported. Outbreaks of Zika have been reported in Asia, Africa, the Americas, and the Pacific. Individuals who contract Zika virus either experience no symptoms or mild ones and they generally develop them three to fourteen days after being bitten.

Symptoms include fever, conjunctivitis (pink eye), headache, joint and muscle pain, rash, and malaise. The virus can also trigger neuropathy, myelitis, and Guillain-Barré syndrome, especially in adults and older children. The virus, however, is best known as a teratogen, for it can cause congenital disabilities like microcephaly, which is characterized by an abnormally small head and brain. It can also cause complications of pregnancy like premature birth, miscarriage, and stillbirth.

West-Nile Virus

The West-Nile Virus is transmitted by mosquitoes of the Culex genus, which is one of the three most common genera in the world. The disease has been reported in western Asia, North America, Africa, Europe, and the Middle East. The mosquitos pick up the virus from infected birds and transmit it to horses and humans.

While the virus causes no symptoms in about eighty percent of patients, the other twenty percent develop symptoms of a potentially fatal disease of the nervous system. Individuals with weakened immune systems or those over fifty are the most susceptible to the deadly neurological form. Such unfortunates start developing symptoms within three to fourteen days after being bitten, and those symptoms include high fever, stiffened neck, headache, disorientation, tremors, muscle weakness, convulsions, stupor, coma, and paralysis. There is so far no human vaccine.

Dengue Fever

Dengue fever, or simply dengue, is transmitted chiefly by the Aedes aegypti mosquito, which is found in the Americas, Africa, Asia, and Europe. Dengue is thus endemic in at least 128 countries, and over 3.9 billion individuals, over half the world’s population, are at risk. A vaccine for individuals between nine and forty-five living in endemic areas was introduced in late 2015.

Dengue causes symptoms similar to those seen in the flu, such as high fever, swollen glands, nausea, vomiting, and pain behind the eyes. Most develop symptoms four to ten days after being bitten. About three to seven days after being bitten, some individuals develop a condition called severe dengue or dengue hemorrhagic fever. While the patient’s fever drops a little, they produce other symptoms like persistent vomiting, severe stomach pains, bleeding gums, blood in their vomit, rapid breathing, restlessness, and fatigue. Without medical care, the patient can die in one or two days.

Yellow Fever

Yellow fever is yet another disease transmitted by mosquitoes in the Aedes genus, especially A. aegypti. Another mosquito genus, Haemagogus, can infect individuals in South and Central America. It can be transmitted from monkeys to humans and from humans to humans. The “yellow” part of the name refers to the fact it can cause jaundice. There is a vaccine available, and a large initiative began in 2017 to vaccinate and treat individuals.

While many don’t develop symptoms, those who do get them about three to six days after being bitten. Symptoms include fever, backache, headache, nausea, vomiting, and loss of appetite. In most cases, the symptoms fade after three to four days, but some unfortunate patients enter a toxic phase after they seem to be recovering. In this phase, their fever returns and the virus attacks their kidneys, liver, and possibly other organs or systems. The patient develops jaundice, vomiting, stomach pains, and dark urine, and can also start bleeding from the stomach, nose, eyes, or mouth. About fifty percent of patients who develop the toxic phase die within a week to ten days.