Mosquito-borne diseases

Mosquito-borne Diseases in Ohio

Mosquito-borne diseases

Diseases spread by mosquitoes are a concern in Ohio each year.  Mosquito-borne diseases that may occur locally in Ohio include:

There are also several mosquito-borne diseases that Ohioans can acquire when traveling that could be brought back into Ohio:

Prevent mosquito bites

The most effective way to prevent mosquito-borne diseases is to prevent being bitten by mosquitoes.  In Ohio, mosquito-borne illnesses are most often transmitted during the warmest months, May through October.

Being aware of mosquito and mosquito-borne disease activity in your area allows you to take action to protect yourself and others: avoid mosquitoes and mosquito bites, plan ahead for mosquitoes while traveling and stop mosquitoes from breeding in and around your home.

AVOID mosquitoes and mosquito bites

Use insect repellents when you go outdoors:

  • Apply repellents on exposed skin that are registered with the U.S. Environmental Protection Agency (EPA).  EPA-registered insect repellents are proven safe and effective, even for pregnant and breastfeeding women.
  • Wear clothing treated with permethrin or another EPA-registered repellent for extra protection.
  • Use products according to label instructions to optimize safety and effectiveness.
  • Don't spray repellents on the skin under your clothing.

Take care during peak mosquito biting hours:

  • Take extra care to use repellents from dusk to dawn.
  • Wear light-colored clothing, long-sleeved shirts or jackets and long pants to protect against mosquito bites.
  • Consider avoiding outdoor activities during peak mosquito biting hours.
  • Use mosquito netting when sleeping outdoors or in an unscreened structure.

PLAN ahead for mosquitoes while traveling

Check travel notices for mosquito-borne and other disease transmission updates:

  • Visit the Centers for Disease Control and Prevention (CDC)'s Travelers' Health website to search for the latest health notices for the country you're traveling to.

Speak to your healthcare provider regarding risks:

  • Talk to your healthcare provider about your travel plans and measures you can take to reduce your risk of mosquito-borne diseases.
  • Depending on which country(ies) you are visiting, malaria chemoprophylaxis or yellow fever vaccination may be recommended or required.  An International Certificate of Vaccination (ICV) may be required for travelers to gain entry into certain countries.

Pack appropriately to protect yourself from mosquitoes:

  • Bring EPA-registered insect repellent to use when outdoors.
  • Consider bringing clothing treated with permethrin or another EPA-registered repellent for extra protection.
  • Pack light-colored clothing, long-sleeved shirts or jackets and long pants to protect against mosquito bites.
  • Purchase mosquito netting to use when sleeping outdoors or in an unscreened structure.

STOP mosquitoes from breeding in and around your home

Don't let mosquitoes breed around your home:

  • Empty standing water from flowerpots, buckets, barrels, tarps/covers and wheel barrows on a regular basis.
  • Discard trash such as tin cans, plastic containers and other water-holding containers that have accumulated on your property.
  • Dispose of discarded tires properly.  Drill holes in tire swings so water drains out.
  • Change the water in pet dishes frequently.
  • Replace the water in bird baths weekly.
  • Check and clean clogged roof gutters at least twice annually so they will drain properly.
  • Aerate ornamental pools or stock them with mosquito-eating fish.
  • Clean and chlorinate swimming pools, even those that are not being used.
  • Keep children's wading pools empty and on their sides when they aren't being used.
  • Consider using products containing Bacillus thuringiensis israelensis (Bti), available at many garden and home improvement stores, to control mosquito larvae in containers that are too large to empty.  Follow label instructions.

Stop mosquitoes from coming indoors:

  • Install or repair screens on windows and doors.
  • Use air conditioning, if you have it.

Support your community surveillance and control programs:

  • Mosquito control activities are most often handled at the local level, through county or city government.  The type of mosquito control methods used by a program depends on the time of year, the type of mosquitoes to be controlled and the habitat structure.  Methods can include elimination of mosquito larval habitats, application of insecticides to kill mosquito larvae or spraying insecticides from trucks or aircraft to kill adult mosquitoes.  Your local mosquito control program can provide information about the type of products being used in your area.  Check with your local health department for more information.
  • Report dead birds to local authorities.  Dead birds may be a sign that West Nile virus and other arboviruses are circulating between birds and the mosquitoes in an area.  By reporting dead birds to local health departments, you can play an important role in monitoring mosquito-borne diseases.  Local agencies have different policies for collecting and testing birds, so check with your local health department for more information.

Mosquitoes in Ohio

Each summer, mosquitoes are a familiar biting pest in backyards, parks and campgrounds.  Most are merely a nuisance and not major vectors of disease.  In fact, only a few of the 59 species of mosquitoes in Ohio can transmit disease.

  However, the diseases these mosquitoes can carry are very serious ones, such as encephalitis and malaria in humans and heartworm in dogs.

  Therefore, it is always advisable to take preventive measures to protect yourself and your family against mosquito bites.

Asian tiger mosquito

Name:  Asian tiger mosquito (Aedes albopictus).

Distribution:  Throughout the eastern United States.  In Ohio, it has been found in nearly all of the southern counties, but ly occurs in others.

Habitat:  Outdoors in vegetation.  Lays eggs in both natural and artificial containers including used tires, plastic containers, treeholes and clogged gutters.

Hosts:  Opportunistic blood feeder on a variety of animals and humans.

Transmits:  Potential to transmit chikungunya, dengue and Zika viruses.

Active:  Most active during the day in shady conditions.

Comments:  Aggressive biter.  Asian tiger mosquitoes were imported into the United States in the 1980s.  They have spread through the United States and become established because of their ability to survive temperate climates.

Eastern treehole mosquito

Name:  Eastern treehole mosquito (Aedes triseriatus).

Distribution:  Throughout Ohio.

Habitat:  Wooded areas, parks.  Lays eggs in artificial containers in trash dumps or backyards and the natural treeholes of silver maple, oak and beech trees.

Hosts:  Mammals, particularly small mammals such as chipmunks and squirrels.

Transmits:  La Crosse virus.

Active:  Most active during the day in shady conditions.  Keeps near wooded areas to lay eggs in deciduous forests.

Comments:  Ohio has reported more cases of La Crosse virus disease than any other states in the United States, averaging about 20 cases per year.

Malaria mosquitoes

Name:  Common malaria mosquito (Anopheles quadrimaculatus), woodland malaria mosquito (Anopheles punctipennis).

Distribution:  Throughout Ohio.

Habitat:  Lays eggs in permanent and semi-permanent bodies of water with vegetation such as ponds, marshes and ditches.  The woodland malaria mosquito may also lay eggs in slow-moving streams with vegetation.

Hosts:  Humans.

Transmits:  Potential to transmit Plasmodium species parasites that cause malaria.

Active:  Most active at dusk and dawn and during the night.

Comments:  Malaria was eliminated from the United States in the early 1950s.  However, the potential for malaria to be transmitted in the United States still exists.

Northern house mosquito

Name:  Northern house mosquito (Culex pipiens).

Distribution:  Widespread throughout Ohio.

Habitat:  Weeds, shrubs, tall grass.  Lays eggs in catch basins, stagnant water in ditches and containers of water with high organic matter (e.g., flowerpot saucers, clogged rain gutters).

Hosts:  Prefers to feed on birds.

Transmits:  St. Louis encephalitis and West Nile viruses.

Active:  Most active at dusk and dawn.

Comments:  West Nile virus was first identified in Ohio in 2001, and it is now established where cases occur each year and seasonal epidemics flare up under certain conditions in the summer and continue into the fall.

Yellow fever mosquito

Name:  Yellow fever mosquito (Aedes aegypti).

Distribution:  Tropical and sub-tropical climates.  Found in the United States primarily in the southern tier states.

Habitat:  Urban areas near and inside homes.  Lays eggs in man-made containers, pools of fresh rainwater.

Hosts:  Humans.

Transmits:  Chikungunya, dengue, yellow fever and Zika viruses.

Active:  Most active during the day.

Comments:  This species is not established in Ohio.  It cannot survive below freezing temperatures.  However, it has rarely been collected in Ohio during the summer where it was ly transported by people in containers, such as used tires, plant pots, etc.

What time of year are you more ly to encounter mosquitoes?

Mosquitoes are active in Ohio during the warmest months, usually May through October.  Mosquito activity will cease after the first hard frost in the fall.


Mosquito-borne diseases could be prevented by skin cream

Mosquito-borne diseases

A skin cream used to treat warts and skin cancer could help protect people against viral diseases such as Zika and dengue, according to new research from the University of Leeds.

Their findings have identified a new way we might prevent infection from a wide variety of dangerous viruses.

The climate emergency, coupled with an increasingly inter-connected world, has led to an upsurge in potentially deadly mosquito-borne illnesses for which no effective treatments currently exist.

Scientists studied four types of virus transmitted by mosquitos and found that applying a cream within an hour of a mosquito bite dramatically reduced infection rates in their models.

They used two different models to understand the effect of the skin cream — human skin samples and mice. In both cases, applying the skin cream acted a warning signal which caused a rapid activation of the skin's immune response that fights any potential viral threats. This prevented the virus from spreading around the body and causing disease.

The cream, called imiquimod or Aldara, is commonly used to treat genital warts and some forms of skin cancer. The researchers caution that further testing is needed before recommendations can be made for people to start using this cream on mosquito bites.

Their research is published today in Science Translational Medicine.

Lead author Dr Clive McKimmie, from the University of Leeds' School of Medicine, said: “This study shows that a clinically approved, widely used skin cream has the potential to be repurposed as a valuable protector against insect-borne diseases.

“What is especially encouraging about our results is that the cream was effective against a number of distinct viruses, without needing to be targeted to one particular virus.

“If this strategy can be developed into a treatment option then we might be able to use it to tackle a wide range of new emerging diseases that we have not yet encountered.

“Mosquitos are expanding their range across the world as the planet gets hotter due to the climate emergency, so the health impact of mosquito-borne diseases is ly to increase in future.”

There are hundreds of viruses spread by biting mosquitoes which can infect humans.

These include the dengue virus, West Nile virus, Zika virus and chikungunya virus, which have all had large outbreaks in recent years.

This includes the unprecedented West Nile virus outbreak in Europe during the summer of 2018 which saw over 1,300 cases, resulting in 90 deaths. While in 2019, we had the worst year on record for Dengue in the Americas.

At present, there are no anti-viral medicines and few vaccines to help combat these infections.

How does it work?

When a mosquito bites the skin, the body reacts in a very specific way to try and mitigate the physical trauma of the skin being punctured.

The bite causes a wound healing repair mechanism to begin, however, the skin does not prepare itself to respond to viral attack.

This means mosquito-borne viruses that enter the skin through a bite are able to replicate quickly with little anti-viral response in the skin and then spread throughout the body.

By applying skin cream after a bite, researchers found that they could pre-emptively activate the immune system's inflammatory response before the virus becomes a problem. The cream encouraged a type of immune cell in the skin, called a macrophage, to suddenly spring into action to fight off the virus before it could spread around the body.

Co-author Dr Steven Bryden, who carried out the research as part of his PhD at Leeds, said: “By boosting the immune system and not targeting a specific virus, this strategy has the potential to be a 'silver bullet' for a wide range of distinct mosquito-borne viral diseases.”

What did the researchers do?

Researchers from the University of Leeds and the University of Glasgow looked at four different viruses transmitted by mosquitos.

Two of the viruses — Zika and chikungunya — were tested on samples of human skin.

Small skin samples were taken from 16 volunteers and kept in healthy condition in the laboratory. They cut each sample in half and allowed both halves to be infected by virus.

After an hour they applied skin cream to one half of each sample, leaving the other half without treatment. Two days later they measured how well the virus had infected and replicated within the skin.

For Zika virus they found that the skin that did not receive the treatment contained over 70 times more virus than the skin which received the treatment.

Similarly, for chikungunya virus the skin that did not receive the treatment contained over 600 times more virus than the skin which received the treatment. In both cases, treated skin did not release any infectious virus, meaning virus would not have spread and caused disease in the body had this occurred in a person.

Three distinct viruses — Semliki Forest, chikungunya and Bunyamwera — were tested on mice. This allowed the researchers to understand whether the skin cream could stop viruses from infecting and causing damage to the rest of the body.

Mice were infected with virus at mosquito bites. One hour later, half of the mice had the skin cream applied to their bites and the other half did not. Two weeks after infection with the deadly Semliki Forest virus, the survival rate for the mice that did not receive the cream was 0%, compared to 65% survival for those that did receive the treatment.

Chikungunya virus causes arthritis in the joints in both humans and mice. To measure the extent of viral infection, researchers looked at the number of ankle joints in each mouse's body that had become infected with virus.

Two weeks after being infected with chikungunya virus, 70% of mice that did not receive the cream had virus in their ankle joints, compared to 30% for those that did receive the treatment. In addition, in mice that were treated, those joints that were infected had 90-times less virus, suggesting joints had been protected from more severe infection.

The researchers also looked at Bunyamwera virus, which is genetically distant from the other viruses, to understand if the cream could be effective against a wide range of diseases.

After infection with Bunyamwera virus, they found that mice that did not receive the cream had up to 10,000 infectious virus particles per millilitre in their bloodstream, compared to less than 100 infectious virus particles for those that received the treatment.

Co-author Dr Kave Shams, an NHS dermatology consultant from the University of Leeds' School of Medicine, said: “It is too soon for us to recommend that people use this cream on their mosquito bites, as further testing and development is needed to ensure it can be used safely and effectively for this purpose. But we are hopeful that one day this discovery could help a vast number of people to avoid disease, particularly in parts of the world hardest hit by these devastating diseases.

“If we can repurpose this cream into an anti-viral treatment option, it could be a useful addition to mosquito repellent as a way of avoiding infection from harmful diseases.

“This approach could be particularly valuable for people at high risk of infection, such as those with a suppressed immune system, and in times of disease outbreak.”

The researchers are now hoping to find collaborators so they can start testing whether the cream can reduce viral infections in human populations.

Funding for the research was provided by the Biotechnology and Biological Sciences Research Council and the Wellcome Trust.

Story Source:

Materials provided by University of Leeds. Note: Content may be edited for style and length.


Mosquito-borne Diseases

Mosquito-borne diseases

Mosquito-borne diseases are those spread by the bite of an infected mosquito. These diseases can be caused by viruses or a parasite. Viruses cause the majority of mosquito-borne diseases, and there are no medications to treat the symptoms caused by these viruses. Some mosquito species found in Connecticut are capable of spreading viruses that can cause disease in humans.

Illness associated with these diseases ranges from mild to significant, and some can cause death. In Connecticut, surveillance is conducted to identify travel-related diseases (diseases acquired the state or the country) and diseases that can be spread by mosquitoes in the state.

The Connecticut Department of Public Health conducts surveillance for the following mosquito-borne diseases:

California Serogroup viruses (e.g. Jamestown Canyon, LaCrosse)

Chikungunya virus


Eastern Equine Encephalitis


Saint (St.) Louis Encephalitis

West Nile virus

Yellow fever

Zika virus

The most effective way to avoid getting sick from mosquito-borne diseases is to prevent mosquito bites.

National Mosquito-borne viral disease Surveillance Summary

Connecticut Mosquito Management Program

The Connecticut Mosquito Management Program is a collaborative effort involving the Department of Energy and Environmental Protection, Connecticut Agricultural Experiment Station, Department of Public Health, Department of Agriculture, and the University of Connecticut Department of Pathobiology and Veterinary Science. The program provides information about the species of mosquitoes found in Connecticut and guidance about how to protect yourself and your community from mosquitoes and mosquito-borne diseases.

Mosquito FAQs

West Nile virus FAQs

Eastern Equine encephalitis FAQs

Repellents FAQs

Connecticut Agricultural Experiment Station

The Connecticut Agricultural Experiment Station conducts mosquito trapping across the state during June through October. Mosquitoes are tested for viruses that can cause human disease, including those found in Connecticut such as Eastern Equine Encephalitis virus, Jamestown Canyon virus, and West Nile virus 

Mosquito Trapping and Arbovirus Testing Program

Current Mosquito Testing Results

Past-Years Summaries of Mosquito Testing Results

Identification Guide to the Mosquitoes of Connecticut  

Vector-borne Disease Symposium- Symposium of Mosquito-Borne Disease in Connecticut, held on April 11, 2019.

Additional Resources

Connecticut Provider Reporting Resources

Reporting of Diseases, Emergency Illnesses, Health Conditions, and Laboratory Findings

Connecticut Provider Reporting Information

Reportable Disease Confidential Case Report form, PD-23 

Connecticut Laboratory Reporting Information

Reportable Laboratory Findings form OL-15C

Current List of Reportable Diseases

Connecticut Annual Infectious Diseases Statistics

National Resources

Workplace Safety -Mosquito-Borne Diseases – NIOSH

This page last updated 7/01/2019.


Mosquito-borne Diseases on the Uptick—Thanks to Global Warming

Mosquito-borne diseases


Dear EarthTalk: Is there a link between the recent spread of mosquito-borne diseases around the world and environmental pollution?—Meg Ross, Lantana, Fla.

If by pollution you mean greenhouse gas emissions, then definitely yes. According to Maria Diuk-Wasser at the Yale School of Public Health, the onset of human-induced global warming is ly to increase the infection rates of mosquito-borne diseases malaria, dengue fever and West Nile virus by creating more mosquito-friendly habitats.

“The direct effects of temperature increase are an increase in immature mosquito development, virus development and mosquito biting rates, which increase contact rates (biting) with humans,” she reports.  

To wit, the U.S. Centers for Disease Control and Prevention (CDC) reported a record number of West Nile virus infections in the continental U.S.

in 2012 with some 5,674 documented cases including 286 deaths.

The virus uses insects as hosts where they reproduce and then are transmitted to humans via mosquito bites; it can also be transmitted via blood transfusions, organ transplants and breast feeding.

While it’s still far less common, U.S. cases of mosquito-borne dengue fever—also known as “breakbone fever” for the feeling it gives its victims—rose by 70 percent in 2012 as compared with 2011. The CDC reports 357 cases of dengue fever in the continental U.S. in 2012, up from 251 in 2011.

The majority, 104, was in Florida, but New York had 64 and California 35. Most of the infections were imported on people travelling to the U.S.—Puerto Rico played host to 4,450 dengue fever cases in 2012, up from only 1,507 in 2011.

But some of the cases in Florida ly came from mosquito bites there. The virus behind dengue fever thrives in tropical and sub-tropical environments. The increased warming predicted for the southern U.S.

along with increased flooding means dengue fever will no doubt be spreading north on the backs of mosquitoes into U.S. states that never thought they would have to deal with such exotic outbreaks.

West Nile and dengue fever aren’t the only mosquito-borne diseases on U.S. public health officials’ radar. Chikungunya, which hitches a ride on the ever expanding Asian tiger mosquito and can cause high fever, fatigue, headache, nausea, muscle and joint pain, and a nasty rash in humans, comes from tropical Africa and Asia.

But cases have started appearing in Western Europe in recent years and are expected to make it to the U.S. East Coast at anytime.

wise, Rift Valley fever, which brings with it fever, muscle pain, dizziness, vision loss and even encephalitis, was limited to Kenya only a decade ago but today has spread across the entire African continent and is expected to make an appearance in Europe and the U.S. soon.

While researchers are hard at work to find vaccines against these diseases, concerned Americans can take some basic precautions to minimize their chances of getting mosquito bites. Keep screens on all the windows and doors in the house that can open. Outside, wear long pants and long sleeved shirts when possible and cover up with an insect repellent—the U.S.

Environmental Protection Agency (EPA) says only those formulations containing the chemical DEET have been proven effective but there are plenty of all natural alternatives out there.

In the meantime, our best defense against these diseases may be keeping our carbon footprints down, as the less global warming we cause, the less we’ll have to deal with an onslaught of tropical mosquito-borne diseases.

CONTACTS: Maria Ana Diuk-Wasser PhD,

EarthTalk® is written and edited by Roddy Scheer and Doug Moss and is a registered trademark of E – The Environmental Magazine ( Send questions to: Subscribe: FreeTrial Issue:

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Mosquito-Borne Diseases

Mosquito-borne diseases

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, 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.

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. 

Un 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.


Mosquito Traps

The Alabama Department of Public Health (ADPH) is monitoring mosquitoes and mosquito-borne diseases throughout the state. Two types of adult mosquito traps are placed in various locations overnight. Both operate on portable batteries and use carbon dioxide or special chemical lure in a tube to enhance collections.

The CDC trap is made of a plastic cylinder with a fan and a light that hangs under a plastic pan from a tree limb or other structure. The sentinel trap is a collapsible vinyl barrel with a plastic lid and fan which sits on the ground. For mosquito egg surveillance, six-inch black plastic cups with a drain hole in the side and lined with a special paper are set for about a week.

 See photos of the types of mosquito traps in use below.

What's New?

For an overview on Zika Virus, statistics, and resources, visit Zika Virus.

California serogroup viruses (California encephalitis, Jamestown Canyon, Keystone, La Crosse, Snowshoe hare, Trivittatus viruses) 0 0 0 0 0 0 0
Chikungunya 0 0 0 1 1 1 19
Dengue 0 3 -100% 3 0 5 3 3
Eastern equine encephalitis 0 1 -100% 0 0 0 0 1
Malaria 2 9 -77.8% 9 8 10 11 13
St. Louis encephalitis 0 0 0 1 0 0 1
West Nile 0 5 -100% 28 61 18 9 2
Yellow Fever 0 0 0 0 0 0 0
Zika 0 0 3 4 41 0 0
Total 2 18 -88.9% 43 75 75 24 39

Note: Counts include finalized investigations among Alabama residents as of March 20, 2020.

*As of MMWR Week 12 (week ending on March 21, 2020)

The case definition was updated this year for this condition. 

For questions or concerns regarding insect-borne disease in Alabama, see the Contact Us page, or email us at

Page last updated: March 20, 2020


Mosquito Bite Illnesses

Mosquito-borne diseases

Most people who get West Nile virus don't have any symptoms. About 1 in 5 will have a fever and other flu- symptoms. Feeling worn out could take months to go away completely. A few people get a more serious infection that causes brain swelling, or meningitis. There's a very small chance you could die.

People in 48 of the 50 U.S. states, Africa, Europe, the Middle East, and West and Central Asia have had West Nile.

Mosquitoes can pass on viruses that cause inflammation around your brain and spinal cord. (The brain swelling with a serious West Nile infection is a kind of encephalitis.)

What type you could get depends on where you are:

  • LaCrosse — the 13 states east of the Mississippi River
  • St. Louis — throughout the U.S., especially Florida and Gulf of Mexico states
  • Eastern Equine — Atlantic, Gulf Coast, and Great Lakes states; the Caribbean; Central and South America
  • Japanese — Asia and the Western Pacific

Your doctor can give you medicine to ease your fever and sore throat. You'll need emergency care right away for severe symptoms, such as confusion, seizures, and muscle weakness, to prevent brain damage and other complications.

You can get shots to prevent Japanese encephalitis before you travel to the area.

First found in Africa in the 1940s, this virus has spread to South and Central America, Mexico, the Caribbean, Southeast Asia, and the Pacific Islands.

Most people don't know they have Zika. The symptoms are mild and usually run their course in less than a week. You may have a fever, joint or muscle pain, pinkeye, or a rash.

The virus has been linked to more serious problems: cases of Guillain-Barre syndrome and a birth defect called microcephaly.

Guillain-Barre is a nervous system disorder that can cause weakness and paralysis. Most people recover over time.

Microcephaly causes a baby's head to be small and not fully develop. Babies with this condition may have developmental and intellectual delays and other problems.

There's no vaccine to prevent the virus. The CDC recommends pregnant women avoid traveling to areas with ongoing Zika infections.

Found mostly in the Caribbean and South America, chikungunya is now spreading in the U.S. It causes severe pain in your joints that may last several weeks. You'll need rest and fluids until symptoms go away. Your doctor may suggest pain relief medicine, too.

You'll ly get a sudden high fever and may bleed a little from your nose or gums. It can be very uncomfortable. Rest and treating the symptoms are the only things you can do for dengue.

Some people get a more severe form, known as dengue hemorrhagic fever. If your small blood vessels become leaky and fluid starts to build up in your belly and lungs, you'll need medical care right away.

Usually people in the U.S. with dengue bring it back with them from warm parts of Africa, Asia, Pacific Islands, Central and South America, and the Caribbean — especially Puerto Rico. In the last 20 years, though, there have been outbreaks in South Texas, Hawaii, and the Florida Keys.

You're not ly to catch yellow fever, because most countries in tropical areas of Africa and the Americas require travelers to get the vaccine for it.

Most people that get yellow fever won't notice anything, but some may feel they have a mild case of the flu.

If you get symptoms, you can relieve them with rest, fluids, and medication, although you could feel weak and tired for several months.

About 15% of people who have mild symptoms will develop severe symptoms after they start feeling better, including a high fever, jaundice (your skin and the whites of your eyes turn yellow), and bleeding. The disease can make your liver and kidneys fail, and it could be fatal.

The oldest mosquito bite illness causes more than 400,000 deaths worldwide each year. No one has gotten sick from malaria parasites in the U.S. since the early 1950s.

But small outbreaks have happened when people who got infected in warm, wet parts of the world came back to the U.S.

Countries around the equator in Africa and tropical islands in the Pacific, such as Papua New Guinea, have the most cases of malaria.

You can take drugs to help prevent malaria when you travel. Researchers are working on a vaccine.

Many mosquitoes live for 2 to 3 months. Most will die or hibernate when the temperature drops below 50 degrees. In the U.S., mosquito season begins in early spring, peaks in the summer, and ends with the first freeze. In parts of the world with warmer weather, they may be active year-round.

The best way to prevent the illnesses they spread is to avoid mosquito bites.

  • Wear light-colored clothing to cover up.
  • Put mosquito repellent “bug spray” on your bare skin.
  • Get rid of places that water can collect around your home.
  • Keep water in pools and landscaping moving.
  • Use screens on your windows or a mosquito net when sleeping outdoors.


State of Connecticut, Mosquito Management Program: “Mosquitos: Frequently Asked Questions.”

American Mosquito Control Association: “Mosquito-Borne Diseases.”

CDC: “West Nile Virus,” “Eastern Equine Encephalitis,” “Japanese Encephalitis,” “Chikungunya virus,” “Dengue Homepage,” “Yellow Fever,” “Malaria,” “Zika Virus,” “Morbidity and Mortality Weekly Report,” “Guillain-Barre syndrome and flu vaccine,” “Facts about Microcephaly.”

Wisconsin Division of Public Health: “West Nile Virus Infection.”

Pal, P. Journal of Virology, published online May 14, 2014.

Pan American Health Organization: “Zika virus infection and Zika fever: Frequently asked questions.”

National Institute of Neurological Disorders and Stroke: “Guillain-Barre Syndrome Fact Sheet.”

The Atlantic: “What to Know About Zika Virus.”

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