Mosquito-borne diseases are those that are transmitted to people through the bite of an infected mosquito.
The diseases spread by mosquitoes can be caused by a parasite, as in the case of malaria, or by viruses, as is the case for Zika fever and numerous others.
Some of these agents, like the parasite that causes malaria, have produced illness in humans for thousands of years, while others such as the chikungunya and Zika viruses have emerged only very recently.
Factors such as urbanization, global travel, and human population growth have increased the potential for mosquitoes to proliferate and hence cause disease on a wider scale.
Viral Diseases Transmitted by Mosquitoes
Many diseases caused by viruses and other types of microorganisms are spread to humans and animals by mosquitoes. A brief description of some important mosquito-borne viral diseases affecting humans is given here. A more in-depth description for some of them is found on the linked pages.
Dengue virus causes dengue fever, a disease characterized by high fever, headache, joint pain, and rash. A more severe form, dengue hemorrhagic fever, can include bleeding and breathing difficulty and is fatal in some cases.
There are four types of dengue virus, and they belong to a class of viruses known as flaviviruses – the family that also includes the West Nile, yellow fever, and Zika viruses. Dengue, transmitted predominantly by Aedes aegypti mosquitoes, is found in more than 100 countries.
Dengue is the most common vector-borne viral disease in the world, causing an estimated 50 to 100 million infections globally each year and 25,000 deaths. In the tropics and subtropics, it is a leading cause of illness and death.
The incidence of dengue has jumped sharply in recent decades as the disease has spread into new geographic regions. While still rare in the United States, the frequency of dengue infection is on the rise and is largely associated with travel to regions in which dengue is circulating, but some cases have been acquired locally.
Yellow fever virus most commonly causes fever, headache, muscle pain, and nausea in those individuals who develop symptoms (many do not); these symptoms can initially be mistaken for malaria. However, a small percentage of symptomatic patients enter a more severe phase where they experience bleeding from the mouth, nose, and eyes and jaundice, a condition affecting the liver and kidneys that produces the yellowing of the skin and eyes for which the virus is named. For about half of the people who progress to this second phase, the disease will lead to death.
The virus, classified as a flavivirus, is generally transmitted by Aedes aegypti mosquitoes, the reason that these mosquitoes are also known as yellow fever mosquitoes.
While no longer a threat in the United States (although in the past it has caused devastating outbreaks), yellow fever is endemic in many countries in Africa and Central and South America. The greatest risk for a yellow fever outbreak occurs when the virus is introduced into heavily populated areas with high mosquito densities where the human population has little or no immunity, as is occurring currently in Africa.
An outbreak of yellow fever was detected in the capital of Angola in December 2015 that has since spread to other regions within Angola and to the neighboring Democratic Republic of Congo. As of June 2016, there have been nearly 1000 cases confirmed in these two countries (mostly in Angola), with many more suspected, and over 300 people have died. A separate outbreak was reported in Brazil in January of 2017.
Unlike many other mosquito-borne viruses, a safe and effective vaccine exists to safeguard against yellow fever. The challenge is to vaccinate people in the affected regions swiftly enough to contain the spread and to maintain sufficient stockpiles of the vaccine so that enough is available during an outbreak; it takes about 12 months to produce additional doses.
For More Information
- Biology of mosquitoes and other vectors
- Information about mosquito and other vector-borne diseases from the WHO
- Life cycle of the Aedes aegypti mosquito
- Maps of the estimated range of Aedes mosquitoes in the United States
- Information about chikungunya virus from the CDC
- Information about dengue from the CDC
- Information about West Nile virus from the CDC
- Information about yellow fever from the CDC
- Information about Zika virus from the CDC