Tag: Mosquito-Borne Disease

2024 Mosquito-Borne Disease Year In Review

West-Nile-Virus-UK-spread-Europe-outbreak-1001738

Exploring the Impact of Mosquito-Borne Diseases In 2024

In 2024, the U.S. was impacted by 27 individual weather and climate disasters—the second most on record, behind 28 disasters in 2023¹. Climate change appears to be increasing the frequency, intensity, and regional impact of hurricanes, storms, and heat waves. These events, in addition to other human-caused activities like deforestation, not only foster environments that enable mosquitoes to transmit diseases but also drive mosquito populations into regions that were once less hospitable or affected by certain vector-borne diseases.

This year-in-review examines six of the most widespread mosquito-borne diseases in the U.S., comparing five years of historical data compiled by the U.S. Centers for Disease Control and Prevention (CDC)². While some diseases such as St. Louis Encephalitis saw a decrease in cases, others like Eastern Equine Encephalitis (EEE) rose sharply. EEE made several headlines this past year when an increase in cases was reported in New England, specifically New Hampshire and Massachusetts. Not to mention an increase in dengue outbreaks in North, Central, and South America and the Caribbean which lead to a spike in travel-associated and locally acquired cases in the U.S. These insights can help shape your mosquito management plans and public education initiatives for the year ahead.

*At the time of publishing this information, mosquito-borne disease-related deaths have not been reported by the CDC. Please note, the CDC counts the District of Columbia as a state

Quick Links

West Nile virus

Dengue

Eastern Equine Encephalitis

La Crosse Encephalitis

St. Louis Encephalitis

Jamestown Canyon Virus

West Nile Virus

West Nile virus (WNv) remains the most deadly mosquito-borne illness in the continental U.S. Since its initial detection in 1999, it has become endemic (regularly occurring) in most regions. Although WNv cases significantly declined in 2024 compared to the previous year, the virus remains widespread—reported in every state except Alaska and Oregon. Of the 1,466 cases, more than 72% were classified as neuroinvasive.

Symptoms

While healthy individuals may not notice symptoms, they can range from mild flu-like symptoms such as fevers, headaches, or neck stiffness to severe neurological conditions such as meningitis and encephalitis (brain inflammation), particularly among older populations or those with compromised immune systems. Approximately 5-10% of cases are fatal.

Primary vectors

WNv is most commonly transmitted by mosquitoes from the genera Culex, including Culex pipiens, Culex tarsalis, and Culex quinquefasciatus. Birds also play a notable role in the spread of the virus. When a mosquito bites an infected bird, it can contract the virus and become a carrier. The mosquito can then transmit the virus to humans through later bites.

Year-Over-Year Change in West Nile Virus Cases

2024

1,466 cases (1,063 neuroinvasive)

2023

2,406 cases (1,599 neuroinvasive)

2022

1,132 cases (827 neuroinvasive)

2021

2,911 cases (2,008 neuroinvasive)

2020

731 cases (559 neuroinvasive)

Top 5 states for West Nile Virus Human Case Count

2024 West Nile Virus Human Cases In the U.S.

Cases

Neuroinvasive Cases

States Reporting Human Cases

Dengue

Dengue consists of four distinct viruses, referred to as dengue 1, 2, 3, and 4. It is most prevalent in tropical and subtropical regions. In 2024, over 12 million cases of dengue were reported in North, Central, and South America and the Caribbean. These outbreaks led to a major spike in travel-associated infections in the United States. Last year, the CDC reported 9,255 total cases, including both locally acquired and travel-associated infections. Combined, these cases spanned 53 U.S. jurisdictions, though local transmission occurred in only three states, California, Florida, and Texas.

Symptoms

Dengue symptoms can vary from mild joint pain, headaches, and fever to severe hemorrhagic fever, which can cause blood vessel damage. Contracting the virus a second time greatly increases the risk of severe illness, particularly in young children and older adults. Approximately 1% of cases are fatal.

Primary vectors

Dengue is most often spread to humans by Aedes genus mosquitoes, particularly Aedes aegypti and Aedes albopictus. Additionally, the virus can be transmitted to fetuses during pregnancy.

Year-Over-Year Change in Dengue Cases

2024

6,076 locally acquired cases (3,179 travel-related)

2023

1,104 locally acquired cases (1,452 travel-related)

2022

1,044 locally acquired cases (1,494 travel-related)

2021

609 locally acquired cases (205 travel-related)

2020

983 locally acquired cases (354 travel-related)

Top 5 states for Dengue Human Case Count

2024 Dengue Human Cases In the U.S.

Locally Acquired Cases

Travel-associated Cases

States Reporting Locally Acquired Human Cases

Eastern Equine Encephalitis

Eastern Equine Encephalitis (EEE) is a rare but potentially deadly mosquito-borne disease primarily found in Northeast, Mid-Atlantic, and Gulf Coast states. In 2024, EEE made several headlines with reports reaching a five-year high with 19 confirmed cases—the third-highest count since 2005.

Symptoms

Symptoms include high fever, headache, brain inflammation, seizures, and paralysis. Severe cases are most likely to occur among children and older populations. Approximately 30% of cases are fatal, but evidence suggests survivors develop lifelong immunity to the virus. Horses, pigs, rodents, and some deer species are also susceptible to the disease.

Primary vectors

EEE primarily circulates between birds and the primary mosquito vector species, Culiseta melanura. However, transmission to humans and animals occurs through mosquitoes from the Aedes, Coquillettidia, and Culex genera, which feed on infected birds before biting mammals.

Year-Over-Year Change in Eastern Equine Encephalitis Cases

2024

19 cases (19 neuroinvasive)

2023

7 cases (7 neuroinvasive)

2022

1 case (1 neuroinvasive)

2021

5 cases (5 neuroinvasive)

2020

13 cases (13 neuroinvasive)

Top 5 states for Eastern Equine Encephalitis Human Case Count

2024 Eastern Equine Encephalitis Human Cases Reported In the U.S.

Cases

Neuroinvasive Cases

States Reporting Human Cases

La Crosse Encephalitis

In 2024, La Crosse Encephalitis cases continued their upward trend, with most reports coming from North Carolina and Tennessee. Nearly all reported infections progressed to neuroinvasive disease.

Symptoms

This mosquito-borne disease primarily impacts children, causing symptoms like fever, headache, and nausea. In neuroinvasive cases, it can lead to severe complications such as seizures, disorientation, vision loss, and other serious issues. Approximately 1% of cases are fatal.

Primary vectors

The La Crosse virus is transmitted through the bite of an infected Aedes triseriatus, commonly known as the Eastern treehole mosquito.

Year-Over-Year Change in La Crosse Encephalitis Cases

2024

35 cases (34 neuroinvasive)

2023

31 cases (30 neuroinvasive)

2022

22 cases (19 neuroinvasive)

2021

40 cases (39 neuroinvasive)

2020

88 cases (84 neuroinvasive)

Top 3 states for La Crosse Encephalitis Human Case Count

2024 La Crosse Encephalitis Human Cases In the U.S.

Cases

Neuroinvasive Cases

States Reporting Human Cases

St. Louis Encephalitis

The St. Louis encephalitis virus was first identified in 1933 during an epidemic in St. Louis, Missouri, which led to over 1,000 cases of encephalitis. In 2024, St. Louis Encephalitis cases saw a dramatic decline, with only one reported case in South Carolina—the lowest case count since 2013 when just a single case was also recorded.

Symptoms

Common symptoms include fever, headache, and confusion, with severity often increasing with age. On average, 90% of infected older adults develop brain inflammation. The fatality rate ranges from 3% to 30%.

Primary vectors

The main mosquito vectors for the virus are Culex pipiens, Culex quinquefasciatus, Culex tarsalis, and Culex nigripalpus. Wild birds, such as blue jays, sparrows, robins, and pigeons serve as amplifying hosts.

Year-Over-Year Change in St. Louis Encephalitis Cases

2024

1 case (0 neuroinvasive)

2023

19 cases (13 neuroinvasive)

2022

33 cases (27 neuroinvasive)

2021

17 cases (11 neuroinvasive)

2020

16 cases (14 neuroinvasive)

Top states for St. Louis Encephalitis Human Case Count

2024 St. Louis Encephalitis Human Cases In the U.S.

Case

Neuroinvasive Cases

States Reporting Human Cases

Jamestown Canyon virus

In 2024, the number of Jamestown Canyon virus cases remained consistent with the previous year, with 22 reported cases—15 of which became neuroinvasive. The majority of cases were concentrated in the Great Lakes region. Historically, more than half of all cases have been reported in Wisconsin and Minnesota.

Symptoms

Many people infected with Jamestown Canyon virus do not have symptoms. Those who do may experience fever, headache, muscle soreness, and respiratory issues. Severe infections can lead to disorientation, seizures, and other neurological complications.

Primary vectors

The virus can be spread by different mosquito species, with deer often serving as the amplifying host. Humans are deemed “dead-end” hosts for the virus, as their blood lacks the virus levels necessary to infect mosquitoes and propagate the disease further.

Year-Over-Year Change in Jamestown Canyon Virus Cases

2024

22 cases (15 neuroinvasive)

2023

21 cases (15 neuroinvasive)

2022

12 cases (11 neuroinvasive)

2021

32 cases (21 neuroinvasive)

2020

13 cases (10 neuroinvasive)

Top 3 states for Jamestown Canyon Virus Human Case Count:

2024 Jamestown Canyon virus Human Cases Reported In the U.S.

Locally Acquired Cases

Neuroinvasive Cases

States Reporting Human Cases

Utilizing Data to Drive Effective Integrated Mosquito Management Programs

The 2024 data underscore the growing threat of mosquito-borne diseases and the need for adaptive solutions and strategies, such as Integrated Mosquito Management (IMM) programs. IMM programs incorporate adult and larval mosquito control, surveillance and disease testing, and public education to stay ahead of evolving environmental challenges, reduce the risk of insecticide resistance, and keep our communities safe from vector-borne diseases. Through a proactive approach, we can build a strong foundation for long-term mosquito prevention and control.

SOURCES

1 NOAA National Centers for Environmental Information (NCEI) U.S. Billion-Dollar Weather and Climate Disasters (2025). https://www.ncei.noaa.gov/access/billions/

2 U.S. Centers for Disease Control and Prevention (CDC). https://www.cdc.gov/

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Since 1992, Vector Disease Control International (VDCI) has taken pride in providing municipalities, mosquito abatement districts, industrial sites, planned communities, homeowners associations, and golf courses with the tools they need to run effective mosquito control programs. We are determined to protect the public health of the communities in which we operate. Our mosquito control professionals have over 100 years of combined experience in the field of public health, specifically vector disease control. We strive to provide the most effective and scientifically sound mosquito surveillance and control programs possible based on an Integrated Mosquito Management approach recommended by the American Mosquito Control Association (AMCA) and Centers for Disease Control and Prevention (CDC). VDCI is the only company in the country that can manage all aspects of an integrated mosquito management program, from surveillance to disease testing to aerial application in emergency situations.

Mosquito-Borne Disease

Reduce Mosquito-Borne Diseases with Disease Testing

Colleague-counting-mosquitos-close-up-oversholder

How Data Collection and Testing Help Reduce Mosquito-Borne Diseases

Mosquitoes are known to transmit several dangerous diseases that can pose a threat to human health. In the United States, mosquito-borne diseases such as West Nile virus, Eastern equine encephalitis virus, and dengue have all caused significant harm to communities nationwide – making the prevention of mosquito-borne diseases crucial for helping keep citizens safe.

Proactively reducing the spread of these diseases starts with effective mosquito surveillance as part of an Integrated Mosquito Management (IMM) plan. Once adult mosquitoes are collected from various traps, they are sorted, identified, and analyzed in a lab where they undergo several tests, including disease testing. By testing adult mosquitoes for diseases, we can identify areas where disease-carrying mosquitoes are present and take appropriate action to reduce their population – ultimately reducing the spread of mosquito-borne diseases.

How Mosquito-Borne Disease Testing Works

Integrated Mosquito Management plans require extensive knowledge of mosquito species, breeding activities, and population dynamics to be successful. By conducting regular adult mosquito surveillance, experts can steadily monitor local populations, allowing us to detect mosquito-borne diseases weeks before they can be transmitted to humans or animals. Here’s how the disease testing process works:

Our expert entomologists strategically set adult mosquito traps throughout a given area. Various mosquito traps are used depending on what information is desired. Each trap has its own unique advantages, many attract specific mosquito species, thereby focusing efforts to collect certain mosquito species that are more likely to carry disease. Traps are typically set weekly for regular population monitoring.
Once a mosquito sample is collected, our entomologists will take them back to the lab for mosquito-borne disease testing.
To identify which diseases are present in mosquito populations, our laboratory technicians will run PCR and RAMP® WNv tests. PCR tests allow us to detect different pathogens that are present inside the mosquito, while RAMP® tests are designed to detect West Nile virus, a commonly found mosquito-borne disease in the U.S.
If a mosquito sample tests positive for any mosquito-borne diseases, our entomologists will report the results to all appropriate local and state health departments. With this data, experts can determine the severity of a disease outbreak and respond with effective mosquito management solutions. This often involves returning to the area where the sample was collected and employing adult and larval mosquito control efforts.

Testing Best Practices

Mosquito-borne disease testing is crucial for helping support effective and environmentally responsible mosquito control. It’s important to follow industry best practices when testing mosquitoes for diseases such as West Nile and malaria.

Test mosquitoes regularly to ensure we detect the presence of mosquito-borne diseases in a timely manner.
Test mosquitoes trapped in various parts of the community to ensure we are casting a wide net for mosquito surveillance in the whole community.
Use mosquito-borne disease testing results to drive IMM programs and reduce the spread of disease.

When a mosquito pool tests positive for a disease, the results of these tests are immediately communicated to government and health officials. This allows decision-makers to act quickly to reduce the spread of mosquito-borne diseases within their communities. By following these best practices, we can arm public officials with the knowledge they need to make control decisions to reduce the spread of mosquito-borne diseases.

Why Mosquito-Borne Disease Testing and Surveillance Matters

Mosquito-borne diseases can have severe consequences on the health and well-being of our communities nationwide. These diseases are transmitted through mosquito bites and can cause symptoms ranging from fever, rash, and neurological problems. Mosquito-borne disease testing and mosquito surveillance provide data and insights to drive a more effective IMM plan that works to reduce mosquito breeding sites and control both nuisance and disease-carrying mosquitoes.

A successful IMM program involves more than mosquito-borne disease testing. Several key pillars, including adult mosquito and larval surveillance, employing a variety of control strategies, and implementing public education within the community, are all part of a comprehensive program’s success. Citizens can help reduce the spread of mosquito-borne diseases by following the 4Ds: Defend, Dress, Drain, and Dusk & Dawn. Applying an EPA-approved mosquito repellent and wearing close-toe shoes, light-colored clothing, and long sleeves and pants while outdoors can significantly protect you from mosquito bites. Draining any standing water that could be a potential mosquito breeding site significantly reduces the mosquito population and the application of insecticides. In addition, limiting your outdoor exposure time, especially from dusk to dawn when mosquitos are most active, will lessen your chances of being bitten. When a comprehensive IMM program is established, it will protect public health and keep our communities safe.

Importance of Integrated Mosquito Management

Our scientific experts at VDCI have the experience, knowledge, and equipment required to implement a comprehensive IMM plan. A proactive approach to mosquito surveillance reduces mosquito-borne diseases and provides adequate time to respond to disease threats before becoming a serious issue to the public. With our industry-leading experts guiding mosquito management strategies in the communities we serve, you can rest assured that your citizens are protected.

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Mosquito-Borne Disease

2023 Mosquito-Borne Disease Year In Review

Exploring the Impact of Mosquito-Borne Diseases In 2023

In recent years, the United States has experienced an increase in the abundance and distribution of mosquito-borne diseases. The expansion of mosquito habitats, fueled by climate change, urban development, and other human-related factors poses considerable risks to public health. The need for increased vigilance and proactive strategies is clear in the 2023 data reported by the Centers for Disease Control (CDC) and Prevention, which indicates a resurgence of locally acquired malaria, a dramatic increase in West Nile virus cases, and shifts in the distribution of diseases like La Crosse encephalitis, Eastern equine encephalitis, dengue, Jamestown Canyon virus, and St. Louis encephalitis. In our 2023 review, we analyze the details of each disease, including case counts, notable trends, and the potential impact on public health.

*Please note, at the time of publishing this information, mosquito-borne disease-related deaths have not been reported by the CDC.

Quick Links

Malaria

While uncommon in the United States, 9 locally acquired malaria cases were reported across Florida (7 cases), Texas (1 case), and Maryland (1 case) during the summer of 2023. Though believed to be isolated events, the majority of these cases were caused by Plasmodium vivax, a protozoal parasite that infects the blood of its host and causes disease in humans.

Malaria can present with symptoms such as fever, chills, and flu-like illness. Severe cases may result in complications affecting the kidneys, lungs, and blood vessels. It is crucial to note that malaria can affect individuals of all ages, and prompt diagnosis is essential for effective treatment.

Typically, the United States records over 1,000 imported cases of malaria each year and zero locally acquired cases. According to the CDC, locally acquired mosquito-borne malaria has not been reported in the United States since 2003, when 8 cases were identified in Palm Beach County, FL. The main vector for malaria in the Eastern United States is Anopheles quadrimaculatus. The occurrence of 9 locally acquired malaria cases in 2023 serves as a reminder that mosquito dynamics are subject to change, and proactive measures are essential to address potential shifts in disease transmission patterns.

West Nile virus

The frequency of West Nile virus infections reported in 2023 were more than double what we saw in 2022. With torrential rains and flooding across many of the western states a total of 2,406 human disease cases were reported and many of those (n=1,599) experienced the most severe form of infection, including neuroinvasive symptoms. The top 5 states affected by this surge include Colorado (626 cases), California (367 cases), Nebraska (150 cases), Illinois (113 cases), and South Dakota (93 cases). With 47 states reporting cases in 2023, compared to 43 in 2022, the virus continues to pose a widespread threat.

Mosquitoes from the genera Culex are recognized as the primary vectors of the disease worldwide and in the U.S. Among these, Culex pipiens, Culex tarsalis, and Culex quinquefasciatus are the main species responsible for transmitting West Nile virus in the U.S. West Nile virus symptoms range from mild flu-like symptoms to severe neurological conditions. Older adults are particularly vulnerable to severe cases, experiencing complications such as meningitis and brain inflammation.

Year Over Year Change

2023

2,406 cases (1,599 neuroinvasive)

2022

1,132 cases (827 neuroinvasive)

2021

2,911 cases (2,008 neuroinvasive)

2020

731 cases (559 neuroinvasive)

Top 5 states for Human Case Count:

2023 West Nile virus Cases In the U.S.

2023 Human Case Count

2022 Human Case Count

States* reporting cases 2023

States* reporting cases 2022

*note: CDC counts District of Columbia as a state

La Crosse Encephalitis

La Crosse encephalitis witnessed an increase in human cases, with 31 reported in 2023, including 30 neuroinvasive cases. Ohio (12 cases), Tennessee (5 cases), and West Virginia (5 cases) led the 10 states that reported cases.

This mosquito-borne disease primarily affects children and can lead to symptoms such as fever, headache, nausea, and, in severe cases, neuroinvasive complications. The transmission of the La Crosse virus occurs through the bite of an infected Aedes triseriatus, commonly known as the Eastern tree-hole mosquito.

Year Over Year Change

2023

31 cases (30 neuroinvasive)

2022

22 cases (19 neuroinvasive)

2021

40 cases (39 neuroinvasive)

2020

88 cases (84 neuroinvasive)

Top 3 states for Human Case Count:

2023 La Crosse Encephalitis Cases In the U.S.

2023 Human Case Count

2022 Human Case Count

States reporting cases 2023

States reporting cases 2022

Eastern Equine Encephalitis

Though there was only 1 case of Eastern Equine Encephalitis in 2022, 7 cases were reported by 4 states in 2023. All cases were neuroinvasive and occurred in the southeast – Alabama (3 cases), Florida (2 cases), Georgia (1 case), and Louisiana (1 case).

While it primarily circulates between birds and the mosquito species Culiseta melanura, transmission to humans and animals can occur through mosquitoes of the Aedes, Coquillettidia, and Culex genera. These mosquitoes feed on infected birds and subsequently bite mammals, spreading the virus.

This disease poses a significant risk, especially among older adults and young children. Symptoms include high fever, headache, and, in severe cases, brain inflammation. The impact on vulnerable populations emphasizes targeted public health campaigns and mosquito control efforts.

Year Over Year Change

2023

7 cases (7 neuroinvasive)

2022

1 case (1 neuroinvasive)

2021

5 cases (5 neuroinvasive)

2020

13 cases (13 neuroinvasive)

Top 4 states for Human Case Count:

2023 Eastern Equine Encephalitis Cases In the U.S.

2023 Human Case Count

2022 Human Case Count

States reporting cases 2023

States reporting cases 2022

Jamestown Canyon Virus

Jamestown Canyon virus experienced a notable increase, with 21 human cases reported in 2023, 15 of which were neuroinvasive. Of the 7 states that reported cases, Wisconsin led with 9 human case counts, followed by Michigan (5 cases), Minnesota (2 cases), New Hampshire (2 cases), Illinois (1 case), New Jersey (1 case), and New York (1 case).

The virus can be spread by different types of mosquitoes, with deer often serving as the amplifying host. Symptoms may include fever, headache, and neurological issues in severe cases. While not often fatal, the virus can cause long-term neurological complications. However, humans are deemed “dead-end” hosts for the virus, as their blood lacks the virus levels necessary to infect mosquitoes and propagate the disease further.

Year Over Year Change

2023

21 cases (15 neuroinvasive)

2022

12 cases (11 neuroinvasive)

2021

32 cases (21 neuroinvasive)

2020

13 cases (10 neuroinvasive)

Top 4 states for Human Case Count:

2023 Jamestown Canyon Virus Cases In the U.S.

2023 Human Case Count

2022 Human Case Count

States reporting cases 2023

States reporting cases 2022

St. Louis Encephalitis

St. Louis encephalitis reported 19 cases in 2023 (13 neuroinvasive), a notable decrease from 2022. Of the 3 reporting states, California recorded the highest number (17 cases), followed by South Carolina (1 case) and Washington (1 case).

Culex pipiens, Culex quinquefasciatus, Culex tarsalis, and Culex nigripalpus are the predominant mosquito vectors. Wild birds are amplifying hosts, yet typically remain asymptomatic.

This disease primarily affects older adults and can result in symptoms such as fever, headache, and confusion. The severity of symptoms typically increases with age. Approximately 90% of elderly people who become infected with this virus develop brain inflammation, according to the CDC. The fatality rate for cases ranges between 5% and 20%.

Year Over Year Change

2023

19 cases (13 neuroinvasive)

2022

33 cases (27 neuroinvasive)

2021

17 cases (11 neuroinvasive)

2020

16 cases (14 neuroinvasive)

Top 3 states for Human Case Count:

2023 St. Louis Encephalitis Cases In the U.S.

2023 Human Case Count

2022 Human Case Count

States reporting cases 2023

States reporting cases 2022

Dengue

Dengue comprises a group of viruses transmitted to humans through infected mosquitoes of the Aedes genus, specifically Aedes aegypti and Aedes albopictus. Though showing a slight overall decrease, Dengue still poses a considerable public health concern with 2,556 reported cases in 2023. More than half of the cases were travel-associated, but 1,104 were locally acquired. Puerto Rico and Florida emerged as the top jurisdictions reporting locally acquired cases.

Dengue symptoms range from mild fever to severe hemorrhagic fever. Severe cases are more common in young children and older adults. Transmission of the disease to a fetus can also occur during pregnancy.

Year Over Year Change

2023

1,104 cases

1,452 cases

2022

1,044 cases

1,494 cases

2021

609 cases

205 cases

2020

983 cases

354 cases

*Red= Locally Acquired Cases, Grey= Travel Related Cases

Top 4 states for Human Case Count:

2023 Dengue Cases In the U.S.

2023 Human Case Count

2022 Human Case Count

States reporting cases 2023

States reporting cases 2022

Utilizing Data to Drive Informative Mosquito Management Programs

The 2023 data highlights the evolving regional dynamics of mosquito-borne diseases and underscores the importance of tailored, localized efforts to limit the spread. Adult mosquito management, surveillance, disease testing, and public education are pivotal in safeguarding the health of our nationwide communities. Integrated Mosquito Management programs incorporate these key strategies and provide a science-based approach to mosquito control. As we navigate the evolving landscape of mosquito-borne diseases, proactive measures and a collective commitment to public health remain our most impactful tools to combat these growing threats.

Other Noteable Data

Locally acquired malaria found in U.S. for first time in 20 years (2003, 8 cases in Florida)
- 7 cases in Florida – Plasmodium vivax (P. vivax) – June 26 CDC Health Advisory
- 1 case in Texas – Plasmodium vivax (P. vivax) – June 26 CDC Health Advisory
- 1 case in Maryland – Plasmodium falciparum (P. falciparum) – August 28 CDC Health Advisory
West Nile virus case count more than doubles from 2022 (105.65% increase)
La Crosse (31% 🔼) , Eastern Equine (600% 🔼), and Jamestown Canyon (66.66% 🔼) all see human case count increases.
Dengue human case count decreases slightly (🔽 -7.6%)

VDCI Wants To Make Your Community Safer. How Can We Help?

Speak to an expert about implementing an IMM program.

Fill out the information below, and one of our experts will follow up with you shortly.

Mosquito-Borne Disease

VDCI’s 2022 Mosquito-Borne Disease Year In Review

With COVID-19, an ongoing “tripledemic” of multiple respiratory diseases, the economy, and politics dominating the headlines in 2022, vector-borne diseases didn’t get much attention in the national spotlight. However, diseases spread by mosquitoes and ticks are on the leading edge of increasing concerns about climate change, and the experts at VDCI continue to monitor their activity so we can keep the public and our clients informed.

This year in review looks at major mosquito-borne diseases in the United States, summarizes case counts in 2022, and highlights key areas of activity. As we kick off a new year, these data points can inform and shape your integrated mosquito management plans, as well as give you information to provide to your citizens, employees, customers, and the public at large to help them protect themselves and their families from mosquito-borne disease.

Quick Links:

- West Nile
- Dengue
- La Crosse
- Eastern Equine Encephalitis (EEE)
- Chikungunya
- Zika

West Nile Virus

2022 US Case Count: 1,035 human cases; 79 deaths

West Nile continues to be the deadliest mosquito-borne disease in the continental U.S. First reported in 1999, the virus is now considered endemic by public health authorities in most areas.

There are an estimated 200 species of mosquitoes found in the United States; of those, approximately 150 can be vectors of West Nile virus (WNv). Species of the Culex genus are considered to be the primary carriers of the disease both globally and in the U.S., with Culex pipiens, Culex tarsalis, and Culex quinquefasciatus being the primary species that spread West Nile virus in the U.S.

Humans contract WNv when bitten by an infected mosquito. While even healthy adults can contract the disease, West Nile can be especially dangerous for the very young and the very old, as well as anyone with a compromised immune system. Many infected people have no symptoms; however, those that do may have flu-like symptoms, fever, rash, neck stiffness, and headache. For some infected individuals, the disease can be more severe and lead to encephalitis, or swelling of the brain, and be fatal. The U.S. Centers for Disease Control and Prevention (CDC) estimate that 1 in every 150 cases of West Nile lead to the central nervous system being affected, and the onset of neuroinvasive disease. These cases become more severe and can leave people with long-lasting or permanent neurological symptoms.

In 2022*, there were 1,035 human cases of West Nile reported by the CDC in the U.S., with 298 being qualified as neuroinvasive disease. There were 79 fatalities as a result of the disease. Both human cases and deaths from WNv were significantly down from 2021, but since the disease is cyclical, the drop in case counts does not indicate that there is less reason for concern, and some regions of the country reported significantly higher case counts than they’ve ever seen.

Nearly every U.S. state faced West Nile virus, with only 4 reporting no activity of any type: Alaska, Hawaii, Maine, and Montana. None of the 8 reporting U.S. territories had West Nile activity, non-human, or human infections.

States with the highest incidence of human West Nile virus cases
Colorado (204)
California (168)
New York (79)
South Dakota (66)
Nebraska (64)

States with the highest West Nile virus death toll
Colorado (18)
California (11)
Texas (7)
Louisiana (6)
Nebraska (4)
Arizona (4)
Illinois (4)

Get more information on this mosquito-borne disease on our West Nile virus page. If you are concerned about West Nile virus in your community or around your business, connect with us to speak with one of our experts.

Dengue

2022 US Case Count: 1073 human cases, 0 deaths

Dengue is a group of viruses spread to humans by infected Aedes genus mosquitoes, specifically Aedes aegypti and Aedes albopictus; pregnant people can also pass the disease to a fetus. There are 4 common Dengue viruses, denoted as Dengue 1, 2, 3, and 4. Worldwide, there are over 400 million cases annually, and an estimated 40,000 people die each year.

According to the CDC, public health authorities in the United States reported a total of 1,073 cases of Dengue this year. However, the vast majority of those cases were travel-acquired, meaning that the subjects were infected outside of the U.S. Only 59 cases were considered locally transmitted. There were no reported fatalities in the country as a result of Dengue, although this may reflect underreporting.

U.S. territories Guam and Puerto Rico reported a combined total of 828 cases. Unlike the continental U.S., nearly all of these cases in the territories were locally acquired – 820, to be exact. This is not surprising, given the more tropical conditions, and vector abundance in these locales.

One significant development that is worth noting: in 2022, the Dengvaxia vaccine was approved for use in the United States in children august 9 to 16 with laboratory-confirmed results of a previous Dengue infection.

The U.S. case counts in 2022 illustrate a substantial increase in reported cases over both 2021 and 2020, but a slight decrease versus 2019. This could be a reflection of an increase in the traveling public in 2022, since there was a significant post-pandemic return-to-travel. 2019 marked the highest number of Dengue cases reported in the U.S. since 2010 when it became a reportable disease and case counts began being tracked. That makes 2022 the second-highest case count reported in U.S. states in the last 12 years.

This could be an interesting trend to watch around the globe. According to the Pan American Health Organization, in 2022, a number of countries in North, Central, and South America saw substantial increases in human Dengue cases over 2021.

Americas (North, South, Central), 5 countries with highest increases in Dengue human cases

Country	2021 Dengue Cases	2022 Dengue Cases	Percentage Increase
United States	117	1073	⬆️817.094%
Panama	3095	11172	⬆️260.969%
El Salvador	5572	16542	⬆️196.877%
Guatemala	2861	8407	⬆️193.848%
Nicaragua	36741	97541	⬆️165.483%

The World Health Organization (WHO) tracks Dengue activity around the globe and in early January 2023, issued an update on Dengue in the Western Pacific Region, indicating that activity has substantially increased in many countries including Lao, Malaysia, the Philippines, Singapore, and Viet Nam.

Get more facts and information about Dengue virus from VDCI.

La Crosse Virus Disease

2022 US Case Count: 21 human cases

La Crosse virus is typically spread by Aedes triseriatus, commonly called the Eastern treehole mosquito. This disease most commonly affects children and teenagers.

La Crosse virus disease is endemic in the United States and is considered a reportable illness.

Symptoms of La Crosse virus are similar to those of other mosquito-borne diseases and include fever, headache, nausea and vomiting, and fatigue. However, it can become dangerous if it becomes La Cross encephalitis, which results in infection of the brain that can manifest through seizures, disorientation, loss of vision, and other serious conditions. Fatalities are rare.

Although the CDC’s La Crosse virus website does not reflect case counts after 2020, the agency’s Arbovirus Surveillance System, ArboNet, reports that there were 21 infections in 2022. More than half of these cases were reported in Ohio. The total number of cases is down from 2021, when 34 cases were reported.

U.S. states reporting La Crosse virus cases in 2022

State	Case Count
Minnesota	3
North Carolina	2
Ohio	13
Tennessee	2
West Virginia	1

Eastern Equine Encephalitis (EEE)

2022 US Case Count: No reporting available

While rare, Eastern Equine Encephalitis (EEE) is a mosquito-borne disease that can affect both humans and some animals. While it is propagated between birds and the mosquito species Culiseta melanura, it is spread to humans and animals by species in the Aedes, Coquillettidia, and Culex genera that feed on infected birds and then mammals.

As its name suggests, horses are especially susceptible to the disease. Other animals that can become infected with EEE virus (EEEv) include pigs, rodents, and certain species of deer. Scientists believe that humans who contract and recover from EEEv have lifelong immunity against re-infection.

Approximately 4 – 5% of human EEEv infections lead to contracting Eastern Equine Encephalitis (EEE), which results in swelling of the brain. EEE has a very high mortality rate, with about one-third of those infected succumbing to the disease.

From 2011 – 2020, only 110 human cases of EEEv have been reported in the United States. In 2019, several outbreaks sparked concern and resulted in 38 human cases and 19 deaths, the highest number of deaths reported in a single year from the disease.

As the map below illustrates, these EEEv infections occurred primarily on the East Coast of the U.S., with high concentrations in New England, the Southeastern U.S., and the state of Michigan.

EEEv infections in the U.S. by state, 2011 – 2020

The CDC has not reported on EEEv infections since 2020. However, the U.S. Department of Agriculture’s Animal and Plant Health Inspection Service (APHIS) reported 110 animal cases in 2021. No data is available yet for 2022.

Learn more about EEE and EEEv on VDCI’s Eastern Equine Encephalitis resource page.

Chikungunya virus

2022 U.S. Case Count: 47 human cases (travel acquired)

Chikungunya virus was rarely discussed in the United States prior to 2006, but as global travel increased and climate shifts have occurred, more U.S. citizens have had experiences with Chikungunya in recent years. It is prevalent in the Caribbean, and while most cases remain travel-acquired, documented local transmission first occurred in 2013. Since 2015, Chikungunya has been a reportable illness in the U.S., which means that health officials are required to report any cases.

Spread to humans via the bite of an infected Aedes genus mosquito, particularly Aedes aegptyi or Aedes albopictus, Chikungunya virus infection can leave those infected with symptoms such as fever, joint pain and swelling, muscle aches, headaches, and more; joint pains are one of the most prominent symptoms and can last for months after the virus subsides. Fatalities are rare.

The CDC has not updated its Chikungunya reporting site since 2020, however, through the agency’s National Arbovirus Surveillance System ArboNet website, VDCI notes that 47 cases of the disease were reported by states in 2022. All of these cases were travel acquired. These cases were reported in 21 states, as reflected in the table below.

U.S. states reporting travel-acquired Chikungunya virus cases in 2022

State	Case Count
California	4
Colorado	3
Illinois	8
Iowa	3
Kansas	1
Kentucky	1
Louisiana	1
Massachusetts	2
Minnesota	1
New Hampshire	1
New Jersey	1
New Mexico	1
New York	5
North Carolina	3
Ohio	2
Pennsylvania	2
Tennessee	2
Utah	1
Vermont	1
Virginia	3
Washington	1

In 2021, there were 21 reported travel-acquired cases, so 2022 reflects a 123% increase in overall case counts over the previous year. As with the increase in Dengue, this may reflect a more global trend that is the result of a return to travel post-pandemic.

You can learn more about Chikungunya virus, its history, and its symptoms on VDCI’s resource page.

Zika Virus

2022 U.S. Case Count: 3 human cases (travel acquired)

Like Chikungunya virus, Zika virus has only recently become a significant concern in the United States. But, after significant tropical outbreaks in 2015 and 2016, locally acquired cases were reported in southern states such as Florida and Texas with much media attention, putting the disease on the map in the U.S. with health authorities and the public at large alike.

While Zika virus is spread primarily through the bite of infected Aedes genus mosquitoes, especially Aedes aegypti and Aedes albopictus that are found prevalently in the U.S., it can also be spread through sexual activity, which means that someone does not need to be bitten by a mosquito to be infected. This disease carries special risks for pregnant people who become infected. Zika virus can be passed to a fetus by the mother and result in birth defects and abnormalities.

In 2022, the CDC’s ArboNet system had no reports of locally transmitted Zika virus, but 3 travel-acquired cases were reported in the states listed below. This is a slight decrease from 2021 when 4 cases were reported.

U.S. states reporting travel-acquired Zika virus cases in 2022

State	Case Count
Illinois	1
Kentucky	1
New York	1

While these case counts are low, there is no way to predict when the U.S. could see a spike in activity like it did in 2015 and 2016. It is important for community leaders to help citizens understand the risks associated with Zika virus and to report any Zika symptoms to their doctors, especially if they or someone they are close with has recently traveled to an area where Zika virus is prevalent. It is also critical that individuals understand the risks and take action to protect themselves, especially while traveling.

Find out more about Zika virus, symptoms, and mosquito-bite protection on VDCI’s vector-borne disease resource website.

Other vector-borne diseases of concern

While this year-in-review focuses on 6 major mosquito-borne diseases, there are others that remain a source of concern in the U.S., including malaria, St. Louis Encelphalitis and Jamestown Canyon virus. And let’s not forget heartworm, which is spread by infected mosquitoes to our beloved pets.

There are also other vector-borne diseases, which encompass viruses and illnesses spread by other pests, such as rodents, ticks, and fleas. These include some common conditions that most people are familiar with, such as Lyme disease, and lesser-known diseases such as hantavirus, plague, Rocky Mountain Spotted fever, Powassan virus, and more.

Protecting your community from mosquitoes

Whether you are responsible for mosquito programs in your community or concerned about mosquito activity on your business property, having an in-depth knowledge of integrated mosquito management programs is critical to protecting those under your care from mosquito-borne disease.

VDCI is committed to mosquito surveillance and disease monitoring, developing robust integrated mosquito management programs for our clients, and educating the public on measures to protect themselves from vector-borne diseases. We also offer emergency response and drone and aerial application services to assist communities in preventing disease, especially following major weather events such as hurricanes and flooding.

If we can assist you or your community in mosquito prevention, please connect with us online or call (866) 977-6964.

*Results reported to U.S. Centers for Disease Control and Prevention as of January 12, 2023.

The key to limiting the spread of mosquito-borne diseases is monitoring and prevention. Municipalities and mosquito abatement districts often execute Integrated Mosquito Management (IMM) programs to help protect communities, but private citizens can support these efforts and empower themselves with disease tracking tools like the CDC’s ArboNet map. The map provides a live overview of reported mosquito activity and the most common vector-borne diseases, including:

West Nile Virus (WNV)
St. Louis Encephalitis (SLE)
Eastern Equine Encephalitis (EEE)
La Crosse (LAC)
Dengue (DEN) locally-acquired and travel-associated
Chikungunya (CHIK) locally-acquired and travel-associated
Zika Virus (ZIKA) locally-acquired and travel-associated

*ArboNet is designed to reflect real-time information, but there are times when it may not be in sync. This resource is easy to navigate and can be sorted by disease type, state, and year.

In addition to staying informed about the risks posed by mosquitoes in your community, it’s important to observe any travel warnings issued by the CDC, particularly when pregnant. It’s also essential to exercise personal protection measures like wearing insect repellent and exercising best practices around your property to reduce mosquito reproduction.

VDCI is committed to public education and spreading awareness throughout the U.S. about the dangers of mosquito-borne diseases and their preventability, with the overarching goal of reducing illness and fatalities. Our dedicated and experienced team works tirelessly with local governments to prevent the spread of mosquito-borne diseases in all of the contracts we service from coast to coast.

VDCI Wants To Make Your Community Safer. How Can We Help?

Speak to an expert about implementing an IMM program.

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Mosquito-Borne Disease

Mosquito-Borne Disease Year In Review – 2021

While the COVID-19 pandemic has captured the attention of the world’s leading infectious disease experts, the scientific community has continued to track the transmission of mosquito-borne diseases, including West Nile, Zika, Chikungunya, Dengue, and other dangerous illnesses. As of December 14, 2021, the Center for Disease Control (CDC) reports that more than 2,400 human infections of West Nile occurred in the United States in the past year, of which 165 resulted in death. Nearly every state in the country has been affected, with Arizona, Colorado, California, and Nebraska representing the most cases.

Quick Links:

West Nile Virus

This map from CDC shows West Nile virus activity across the U.S. in 2021.

As in years past, West Nile virus (WNv) continues to be the most reported and most deadly mosquito-borne disease in the United States. WNv is carried by over 150 species of mosquitoes, which usually pass the virus to humans after feeding on infected birds. Scientists have identified Culex pipiens, Culex tarsalis, and Culex quinquefasciatus as the primary vector species.

Approximately 20% of people infected with WNv experience flu-like symptoms such as nausea, headache, muscle pain, fever, and swollen lymph glands. These symptoms may also be accompanied by rashes, sleepiness, disorientation, and stiff neck. Among those infected, less than 1% will go on to develop West Nile Encephalitis or Meningitis. This can result in tremors, convulsions, paralysis, coma, and even death.

WNv transmission is cyclical in nature, with 2021 data showing a significant increase in both total cases and death:

2021: Cases

2,445 Cases

2021: Deaths

165 Deaths

This chart reflects data taken on December 14, 2021.

2020 – 28 cases in citizens returning from travel, 0 cases in U.S. territories

2019 – 192 cases in citizens returning from travel, 2 cases in U.S. territories

2018 – 116 cases in citizens returning from travel, 8 cases in U.S. territories

To learn more about the symptoms, treatment, and mosquito species that vector this virus, visit our educational page on West Nile virus.

Zika Virus

This map from CDC shows Zika virus activity around the world.

Zika is a dangerous virus that primarily affects Africa and South America. Historically, U.S. citizens have become infected while traveling abroad, but warming climates have allowed the presence of Zika in the southern United States as well. Unlike other types of viruses, which require an animal reservoir host, mosquitoes are able to transmit Zika by simply feeding on the blood of an infected person. This can increase the spread very quickly during the summer months.

In the United States, Zika is typically transmitted by Aedes aegypti, but growing evidence suggests that the Asian Tiger Mosquito (Aedes albopictus) could also be a vector. Common symptoms of infection include fever, rash, headache, joint pain, muscle pain, and Conjunctivitis (red eyes). Zika very rarely results in death; however, it can cause serious congenital disabilities when an infection occurs during pregnancy. These typically manifest as microcephaly (collapsed skull), decreased brain tissue, eye tissue damage, and joint or muscle tone complications.

After an alarming peak in 2016, when the CDC reported more than 40,000 cases in the U.S. and its territories, Zika cases have decreased to remarkable lows. This may, in part, be due to pandemic-related travel restrictions:

2021: Cases in the United States

28 Cases

2021: Returning From Travel

1 Case

This chart reflects data taken on December 14, 2021.

2020 – 4 cases in citizens returning from travel, 57 cases in U.S. territories

2019 – 27 cases in citizens returning from travel, 74 cases in U.S. territories

2018 – 73 cases in citizens returning from travel, 148 cases in U.S. territories

To learn more about the symptoms, treatment, and mosquito species that vector this virus, visit our educational page on Zika virus.

Chikungunya Virus

This map from CDC shows Chikungunya virus activity around the world in 2020.

Chikungunya (chik-en-gun-ye) is less well-known than other mosquito-borne diseases, but has become more widespread among American citizens, most often when traveling abroad. Like Zika, Chikungunya virus can spread when mosquitoes feed on a person who is carrying the infection. Chikungunya is also primarily transmitted by Aedes mosquitoes.

Those infected with Chikungunya virus may experience painful and even disabling symptoms that appear 3-7 days after transmission. These most often include fever, severe joint pain, and rash. Death is very rare and, in fact, infected individuals tend to develop immunity from future infections.

Annual U.S. Chikungunya cases have dropped dramatically in recent years - reaching a record low in 2021. This may, in part, be due to pandemic-related travel restrictions and effective mosquito control interventions:

2021: Cases in the United States

0 Cases

2021: Returning From Travel

21 Cases

This chart reflects data taken on December 14, 2021.

2020 – 28 cases in citizens returning from travel, 0 cases in U.S. territories

2019 – 192 cases in citizens returning from travel, 2 cases in U.S. territories

2018 – 116 cases in citizens returning from travel, 8 cases in U.S. territories

To learn more about the symptoms, treatment, and mosquito species that vector this virus, visit our educational page on Chikungunya.2018 – 116 cases in citizens returning from travel, 8 cases in U.S. territories.

Dengue Virus

This map from CDC shows Dengue activity across the U.S. in 2021.

While many people think of Dengue as a disease we don’t need to worry about in the United States, mosquitoes capable of transmitting this virus are abundant in many areas of the country and quickly expanding their range. Characteristic symptoms of dengue include high fever, rash, in addition to muscle and joint pain. In severe cases there can be serious bleeding or shock, which is life threatening.

In 2021 there were 86 human cases of Dengue diagnosed in 23 states across the continental United States.

To learn more about the symptoms, treatment, and mosquito species that vector this virus, visit our educational page on Dengue.

Human Cases (2021)

States Affected Across the U.S. (2021)

Monitoring Real-Time U.S. Mosquito-Borne Disease Activity

West Nile Virus (WNV)
St. Louis Encephalitis (SLE)
Eastern Equine Encephalitis (EEE)
La Crosse (LAC)
Dengue (DEN) locally-acquired and travel-associated
Chikungunya (CHIK) locally-acquired and travel-associated
Zika Virus (ZIKA) locally-acquired and travel-associated
Powassan Virus (a tick-borne disease)

*ArboNet is designed to reflect real-time information, but there are times when it may not be in sync. This resource is easy to navigate and can be sorted by disease type, state, and year.

VDCI Wants To Make Your Community Safer. How Can We Help?

Speak to an expert about implementing an IMM program.

Fill out the information below, and one of our experts will follow up with you shortly.

Mosquito-Borne Disease