By Bara Vaida
Outbreaks of mosquito-borne illnesses like dengue, chikungunya, West Nile and Zika are rising around the world. While the combination of the U.S.’s cooler climate and mosquito control programs have kept many of the worst mosquito diseases at bay, global travel, changing climate and the expansion of populations into new habitats are increasing Americans’ risks of contracting mosquito-borne diseases.
The Centers for Disease Control and Prevention says the number of diseases from vectors like mosquitos and ticks have tripled since 2004 in the U.S., and West Nile disease is the most common mosquito-borne illness in the continental U.S.
Scientists for the public health agency estimate that hundreds of thousands of Americans are bitten by mosquitoes carrying West Nile virus annually, but for most people, the virus causes no illness. For some however, the virus causes flu-like symptoms and at its worst, it can invade the nervous system, causing brain inflammation and death. There were 2,544 West Nile cases reported in 2018 to the CDC. The agency says it is more likely there were from 42,750 to 99,750 people infected with West Nile, but the cases weren’t reported.
In the U.S. territories, Puerto Rico, the U.S. Virgin Islands and American Samoa, dengue is a common mosquito-borne disease. There were a few local transmission cases of dengue in 2013 in Florida, Hawaii and Texas, but most dengue cases reported were from travelers who developed it elsewhere. In 2019, there have been three dengue cases reported in Puerto Rico, and 62 cases in the continental U.S., all of which were infections developed outside the U.S., according to the CDC.
Other mosquito-borne diseases in the U.S. include eastern equine encephalitis and La Crosse encephalitis. These diseases are rare. In 2017, there were five cases of eastern equine encephalitis reported and 63 cases of La Crosse encephalitis. In 2016, there were 248 cases of chikungunya reported, but all were acquired by people traveling overseas. Zika, (a virus carried by mosquitoes that can cause fetal anomalies and death) has faded as a risk. As of May 2019, no one in the continental U.S. has been infected with Zika.
To understand mosquito-borne diseases and their prevention, public health officials recommend understanding the mosquito life cycle. All mosquitos need two elements to reproduce – blood from an animal or a human and water. Without water, mosquitoes won’t develop, so removing standing water sources near homes is among the most important preventative measures. The second is to have screens on windows and doors.
Public health officials also recommend understanding the differences among mosquitoes. While there are more than 3,000 different species of mosquito, about 150 of them live in North America. A few of those are known to be carriers of disease.
Three of the most important that carry disease include the Culex, the Aedes aegypti, the Aedes albopictus (also known as the Asian tiger mosquito) and the Aedes triseratus. The Culex has been found in every state except Hawaii and New Hampshire and carries West Nile virus, which it gets from biting infected birds. The aegypti are found mostly in the southern U.S., but as the climate has been warming, the mosquito has been spreading northward. The albopictus are found along the East Coast and thrive in city environments. Both the aegypti and albopictus can carry chikungunya, dengue, Zika and eastern equine encephalitis. The triseratus is found in the upper midwest, mid-Atlantic, and Southeastern U.S. and can carry the La Crosse encephalitis virus.
Local public health departments are charged with mosquito testing, monitoring and spraying programs, but not all programs are well resourced. Because of concerns about the impact of spraying on the environment and animals, many states are experimenting with biological alternatives to reduce mosquito populations.
Story ideas
- What is the local forecast for mosquito season? Connect with your local AccuWeather forecasters. The weather service has been producing local “mosquito forecasts.” Find out what they are saying about mosquito populations in your area.
- What is the new research on alternatives to spraying to reduce mosquito populations?
- Is anyone at your local academic institutions researching mosquito control measures?
- Does your local mosquito vector control program have adequate resources? How are they approaching this year’s mosquito season? What are they finding so far in terms of mosquito testing and disease? Are they using any biological alternatives to control mosquitos?
- What kinds of mosquitoes are living in your community?
- How is your state’s mosquito control program handling environmental concerns? What about concerns about bee populations? Are local officials working with beekeepers?
- The CDC strongly recommends that people use mosquito repellant. Walk through the repellants that work and don’t work. Many people are trying things such as essential oils and dryer sheets to repel mosquitos and they don’t work, according to scientists. However, there are alternatives to DEET, the traditional mosquito repellant, that are effective.
Recent Stories
- Summer of mosquito swarms a possibility this year, (WebMD, May 2019)
- First West Nile virus positive mosquitoes found in Illinois (WQAD.com, May 2019)
- Could this mosquito bring zika to Philadelphia? (Philly.com, April 2019)
- Heavy rains, end of drought could help keep West Nile virus subdued for now (Kaiser Health News, April 2019)
- Forecasting mosquitoes global spread: (Science Daily, March 2019)
- Why dengue, malaria and yellow fever will get worse with climate change (Vox, March 2019)
- What you need to know about dengue fever (Consumer Reports, January 2019)
- Researchers look for new ways to tackle old foes (WebMD, August 2018)
- Why the menace of mosquitos will only get worse (New York Times, April 2017)
- It’s mosquito season, the 411 on insect repellants (WebMD, May 2016)
Backgrounding resources
- SciLine: Read this AHCJ post about a June 19 webcast on vector-borne diseases hosted by this service of the American Association for the Advancement of Science.
- EcoLab: Check out this primer on mosquito types.
- Center for Infectious Disease Research and Policy: Check out its mosquito disease page.
- National Pesticide Information Center: Check out its tool for finding community vector-borne control programs.
- Entomological Society of America
- American Mosquito Control Association
Government resources
- Vector Biology home page (National Institutes of Allergy and Infectious Disease).
- Estimated range of disease causing mosquitos in the U.S. (CDC map).
- Preventing mosquito bites (CDC tip sheet).
- CDC offers a map of Zika cases and this travel information map.
- West Nile data map – (CDC, data as of January 2019).
- CDC Morbidity and Mortality Weekly Report, includes additional West Nile and vector-borne disease data.
- Data map on diseases caused by other mosquitos and ticks (CDC).
- National vector-control efforts (National Association of County and City Health Officials).
- “Mosquito Control Capabilities in the U.S.”(PDF report by the National Association of County and City Health Officials, October 2017.
Experts
- Dina M. Fonseca, molecular ecologist and professor at Rutgers School of Environmental and Biological Sciences: 848-932-6853, dina.fonseca@rutgers.edu.
- Shannon LaDeau, disease ecologist, Cary Institute of Ecosystems: 845-677-7600, ext. 204, LADEAUS@caryinstitute.org.
- Janet McAllister, Centers for Disease Control and Prevention entomologist at the arboviral diseases branch of the division of vector-borne diseases, Fort Collins, Colorado. Reach via Kate Fowlie, CDC’s media officer: 404-639-4538, hvz3@cdc.gov.
- Joe Conlon, technical adviser, American Mosquito Control Association: 856-439-9222, conlonamcata@gmail.com.
- Robert Haley, M.D., director of epidemiology, University of Texas Southwestern Medical Center: 214-648-3075.
- Peter Hotez, MD, founding dean of the National School of Tropical Medicine, Baylor College of Medicine, 713-798-1199, hotez@bcm.edu
- Robert Tesh, M.D., George Dock distinguished professor at the department of pathology, microbiology and immunology, University of Texas Medical Branch: 409-747-2431, rtesh@utmb.edu.
