Vector-Borne Disease Resources | Center for Outbreak Response Innovation

About

Vector-Borne diseases encompass a wide range of illnesses transmitted by arthropods, including mosquitoes, ticks, and midges, many with potential for severe disease. They pose a significant public health challenge in the United States, with several, including West Nile Virus, Equine Encephalitis, St. Louis Encephalitis, and La Crosse Virus, endemic in the contiguous US, and Dengue and Zika Virus endemic in select US territories. Additionally, increased globalization has led to travel-related cases of Malaria, Zika, Dengue, and Oropouche across the US. Climate change and increased global travel are expanding the potential range of disease vectors in the US, prompting heightened surveillance and control efforts by public health agencies.

The following resources aim to inform and prepare public health agencies, governments, and the general public for vector-borne disease cases and outbreaks.

*The CORI research team is actively updating this page to include diseases transmitted by a variety of vectors, including mosquitoes, ticks, and midges. Please check back regularly as these updates are posted.

Table 1. Vector-Borne Cases US [for select diseases, 2024]

Disease	U.S. Cases 2024
Dengue	Over 5,600 cases of Dengue have been reported for 2024. Nearly 3,000 cases of dengue have been locally acquired so far in 2024, with over 36 cases from Florida, 130 from the Virgin Islands, and 3443 from Puerto Rico.4 locally acquired cases of Dengue have been reported in California.
Equine Encephalitis- Eastern (EEE)	15 case of EEE have been reported in 2024. The states affected include Wisconsin (1), Massachusetts (4), New Hampshire (5), New York (1), New Jersey (1), Vermont (1), Rhode Island (1), North Carolina (1). All 15 cases reported have been neuroinvasive.
Equine Encephalitis- Western (WEE)	No human cases of western equine encephalitis have been reported in the United States since 1999
Malaria	The total number of malaria cases reported in 2024 is over 1400. The last locally acquired cases of Malaria were in Florida and Texas in 2023. No locally acquired cases have been reported in 2024.
Oropouche	Over 90 travel associated cases have been reported in 5 US states and territories. None of the cases have been locally acquired. 95% of these cases were reported in the state of Florida.
West Nile Virus	CDC reports a total of nearly 1000 cases across 46 states.
St Louis Encephalitis	Nine cases were reported in 2023 and one case reported for 2024 to date.
Zika Virus	22 cases of Zika have been reported in 2024. 13 have been in the US territories and 9 in the continental US.

Resources

Vector-Borne Disease Summary Table

The diseases transmitted by arthropods vary significantly in symptoms, severity, diagnosis, treatment, prevention, and global distribution. See below for a summary table of the most common vector-borne diseases in the United States. For more information on each specific disease, see our main resources page.

Table 2. Summary of Disease Vector, Severity, and Global Distribution

Disease	Vector	Severity	Global Distribution
Dengue	Aedes mosquitoes, primarily Aedes aegypti	Mortality is < 1% in the US for travel associated cases but untreated dengue mortality can be as high as 13%.Most cases are mild, but severe dengue can be life-threatening. About 1 in 20 people with dengue develop severe, life-threatening disease.	Southeast Asia, the western Pacific islands, Latin America and Africa, particularly in urban and semi-urban areas.
Equine Encephalitis- Eastern (EEE)	Culiseta melanura mosquitoes (bird to bird), Coquilleta perturbans and various other species for transmission to humans.	Often severe when symptomatic. High mortality rate (approx. 30%) and significant brain damage in survivors (50%).	Eastern United States, particularly in Atlantic and Gulf Coast states.
Equine Encephalitis- Western (WEE)	Culex tarsalis mosquitoes	Generally much milder than EEE. Mortality is generally around 5%. Children under age 2 and adults over age 60 at highest risk for severe disease	Western United States (CO, TX, ND, CA), South America, Central America, and Canada
Malaria	Female Anopheles mosquitoes	Mortality is 2%. Can be severe and life-threatening if untreated, especially P. falciparum malaria. Severe symptoms include anemia and jaundice and severe disease can result in kidney failure, seizures, coma, and death.	Sub-Saharan Africa, South Asia, Southeast Asia, Oceania, parts of Central and South America.
Oropouche	Primarily Culicoides paraensis biting midges. Culex quinquefasciatus, Coquillettidia venezuelensis, and Aedes serratus mosquitoes also play a role in transmission.	Generally mild to moderate. Most patients recover fully within 2-3 weeks. Rare cases of meningitis reported	Central and South America, particularly in the Amazon region of Brazil, Peru, Panama, and Trinidad and Tobago
West Nile Virus	Culex species mosquitoes	Most infections are mild. 1 in 150 people who are infected develop severe illness (high fever, coma, vision loss, and paralysis). About 1 in 10 people who develop severe illness affecting the central nervous system die. Severe illness can occur in people of any age, although more likely in people over age 60.	United States, Africa, Europe, Middle East, West Asia, Australia
St Louis Encephalitis	Culex species mosquitoes, primarily Culex pipiens complex and Culex quinquefasciatus	Most infections are asymptomatic or mild. Severe disease is more common in older adults	United States, especially in eastern and central states
Zika Virus	Aedes species mosquitoes, primarily Aedes aegypti	Generally mild. Main concern is for pregnant people due to risk of congenital Zika syndrome.	Tropical and subtropical areas of Africa, the Americas, Southern Asia, and Western Pacific.

Table 3. Summary of Disease Symptoms, Diagnosis, Treatment, and Prevention

Disease	Symptoms	Diagnosis	Treatment	Prevention
Dengue	About 1 in 4 people with dengue develop symptoms, including sudden high fever, severe headache, pain behind the eyes, muscle and joint pain, fatigue, nausea, vomiting, skin rash that appears 3 to 4 days after fever onset	Blood tests for virus or antibodies	No specific antiviral treatment. Supportive care includes fluid management. Non-steroidal anti-inflammatory drugs like ibuprofen and aspirin are avoided as they can increase the risk of bleeding.	Dengvaxia vaccine available in the US for individuals 9-16 years old with laboratory-confirmed previous dengue infection living in an area where dengue is endemic. This vaccine is currently available in Puerto Rico. Otherwise, prevention focuses on mosquito control and personal protection
Equine Encephalitis- Eastern (EEE)	Fever, chills, malaise. Severe cases: headache, irritability, restlessness, drowsiness, anorexia, vomiting, diarrhea, cyanosis, convulsions, coma.	Mainly cerebrospinal fluid tests for antibodies.	No specific antiviral treatment. Supportive care, includes hospitalization and possible ventilator support	No vaccine available in the US for general use. Prevention focuses on mosquito control and personal protection.
Equine Encephalitis- Western (WEE)	Fever, headache, nausea, vomiting, anorexia, malaise. Severe cases: neck stiffness, confusion, disorientation, seizures, coma	Blood or cerebrospinal fluid tests for antibodies	No specific antiviral treatment. Supportive case includes pain control, antiemetic therapy, and rehydration for associated nausea and vomiting.	No vaccine available in the US for general use. Prevention focuses on mosquito control and personal protection
Malaria	Fever, chills, headache, body aches, nausea and vomiting, fatigue	Blood smear microscopy, rapid diagnostic tests (BinaxNow is approved in the US), or PCR.	Various antimalarial drugs available in the US, including chloroquine, artemisinin-based combination therapies (ACTs), atovaquone-proguanil, and others. Choice depends on the species and drug resistance.	No vaccine available in the US for general use. Malaria chemoprophylaxis available. Prevention focuses on mosquito control and personal protection.
Oropouche	Sudden onset of fever, headache, muscle and joint pain, chills, sensitivity to light, nausea, vomiting, dizziness, and weakness	Blood tests for virus isolation or antibody detection	No specific antiviral treatment. Supportive care includes rest, hydration, and acetaminophen to reduce fever and pain	No vaccine available in the US or elsewhere. Prevention focuses on vector control and personal protection measures
West Nile Virus	Most people (8 out of 10) will not develop symptoms. The most common symptoms experienced are fever, headache, body aches, fatigue, skin rash, swollen lymph glands. Severe cases: high fever, neck stiffness, stupor, disorientation, coma, tremors, convulsions, muscle weakness, vision loss, numbness, paralysis	Blood or cerebrospinal fluid tests for antibodies	No specific treatment. Supportive care for severe meningeal symptoms often require pain control for headaches and antiemetic therapy and rehydration for associated nausea and vomiting.	No vaccine available in the US. Prevention focuses on mosquito control and personal protection.
St Louis Encephalitis	Fever, headache, nausea, vomiting, fatigue. Severe cases: neck stiffness, confusion, disorientation, tremors, seizures	Blood or cerebrospinal fluid tests for antibodies	No specific antiviral treatment. Supportive care for patients with severe meningeal symptoms often require pain control for headaches and antiemetic therapy and rehydration for associated nausea and vomiting. Patients with encephalitis require close monitoring for the development of elevated intracranial pressure, seizures, and inability to protect their airway.	No vaccine available in the US. Prevention focuses on mosquito control and personal protection
Zika Virus	Mild fever, skin rash, conjunctivitis, muscle and joint pain, headache. Many infections are asymptomatic	Blood or urine tests for viral RNA or antibodies	No specific treatment. Supportive care includes rest, fluids, and use of analgesics and antipyretics.	No vaccine available in the US. Prevention focuses on mosquito control and personal protection

Mosquito Vector Control Interventions

Table 4. Summary of Mosquito Vector Control Interventions: Description, Examples, and Best Target Vectors

Intervention	Description	Examples	Best Target Vector
Biological control	Using natural predators or pathogens to control mosquito populations	Introducing larvivorous fish, using Bacillus thuringiensis israelensis (Bti) or Wolbachia	Particularly effective against Anopheles and Culex species in larger water bodies; Bti and Wolbachia are effective against container-breeding Aedes species
Chemical larviciding	Using chemicals to kill mosquito larvae in water bodies	Applying insect growth regulators or other larvicides to breeding sites	Effective against various species breeding in accessible water bodies, including Anopheles (malaria vector), Culex species (West Nile and St. Louis Encephalitis vector), and Culiseta species (EEE vector).
Classical Sterile Insect Technique (SIT)	A biological method that involves releasing sterile male insects to mate with wild females, reducing the population over time	Irradiated Ae. aegypti mosquitoes are currently being evaluated as a control method in communities in Florida. This technique has been used to control other types of mosquitoes in Italy.	Species-specific. No chemical residues. Can lead to local elimination of pest populations
Fogging or spraying	Applying insecticides as a fine mist to kill adult mosquitoes	Truck-mounted or aerial spraying of adulticides	Targets multiple adult mosquito species in the treated area, including Aedes, Anopheles, Culex, Culiseta species
Genetic Modification	Altering the genome of mosquitoes to reduce their ability to transmit diseases or to suppress the population	Oxitec's OX513A Aedes aegypti mosquitoes	Currently Aedes aegypti. Additional CRISPPR techniques targeting Anophele gambiae are also promising.
Habitat modification	Altering the environment to reduce mosquito breeding sites	Draining standing water in artificial containers (flowerpots, cans, barrels, tires, water troughs, neglected swimming pools, ornamental ponds, etc), filling in low areas, maintaining proper drainage	Draining water in artificial containers is effective against container-breeding species like Aedes aegypti (zika vector) and species that breed in stagnant water (barrels, basins) such as Culex species. More extensive habitat modification such as draining swamps or ditching marshy areas is required to be effective against the anopheles species(malaria vector)

Table 5. Summary of Mosquito Vector Control Interventions: Benefits, Costs, Effectiveness, Public Opinion, and Special Planning Considerations

Intervention	Benefits	Monetary Costs	Effectiveness	Public Opinion	Special Planning Considerations
Biological control	Environmentally friendly, can be self-sustaining	Low to moderate	Moderate, varies by method and environment	Generally positive, seen as natural	May require ongoing management, potential ecosystem impacts
Chemical larviciding	Targets mosquitoes before they can fly and spread disease	Low to moderate	Moderate to high, depending on coverage and timing. May be difficult to identify and reach larval populations.	Mixed; concerns about chemical use	Need for regular reapplication, potential environmental impacts
Classical Sterile Insect Technique (SIT)	Irradiated mosquitoes cannot make people or animals (for example, fish, birds, pets) sick.	High initial costs for insect rearing facilities and irradiation equipment; Ongoing costs for continued releases	Highly effective when properly implemented, especially for isolated populations. SIT will not reduce numbers of all types of mosquitoes, only the type that has been irradiated and released into the wild.	Generally positive, seen as an environmentally friendly alternative to pesticides	Requires detailed understanding of target species biology. Need for continuous release of sterile males<br>- Effectiveness can be reduced by immigration of fertile insects
Fogging or spraying	Quick reduction in adult mosquito populations	Moderate to high	Short-term effectiveness, limited long-term impact	Mixed; concerns about chemical exposure	Timing critical, may affect non-target insects, requires public notification
Genetic Modification	No risk to people, animals, or the environment. Ability to reduce target mosquito population	High research and development costs; Regulatory costs for approval; Implementation costs vary	Promising in controlled trials, but long-term effectiveness in the field still being evaluated	Mixed; concerns about ecological impacts and unintended consequences	Regulatory approval processes. Public engagement and consent. Monitoring for unintended ecological effects. Potential for resistance development
Habitat modification	Long-lasting, environmentally friendly	Low to high, depending on scale	High, if done comprehensively. May be challenging if marsh or swamps are protected by conservation.	Generally positive, seen as eco-friendly	Requires ongoing maintenance, may affect other species

For more information on the costs, benefits, and logistics of each of these mosquito control interventions, review the practical guide for setting up a municipal mosquito control program.

Mosquito-borne Community Disease Prevention Messaging

Use insect repellent containing DEET, picaridin, IR3535 or oil of lemon eucalyptus on exposed skin and/or clothing. The repellent/insecticide permethrin can be used on clothing to protect through several washes. Always follow the directions on the package.
Wear long sleeves and pants when weather permits.
Have secure, intact screens on windows and doors to keep mosquitoes out.
Eliminate mosquito breeding sites by emptying standing water from flowerpots, buckets, barrels, and other containers. Drill holes in tire swings so water drains out. Keep children’s wading pools empty and on their sides when they are not being used.

Public Health Preparedness and Response Strategy

Prepare:

In advance of increased mosquito-borne illness in your jurisdiction, consider developing a mosquito-borne disease or arbovirus response plan or annex to your existing all-hazards plan. To the extent possible, consider which compounds are approved for mosquito control in your jurisdiction.
- Examples: Florida Mosquito-Born Disease Response Plan, Massachusetts Arbovirus Response Plan, California Mosquito-Borne Surveillance and Response Plan, Andover Town Response Plan.
Be sure to define response levels collaboratively and conduct exercises with partners, including the relevant state department of agriculture mosquito program, to ensure the effectiveness of the plan. [Example: Georgia Hurricane Response Hub Arbovirus Outbreak TTX]

2. Monitor:

Establish public-facing surveillance reports such as weekly updates on case data [Example: Florida Arbovirus Weekly Surveillance Report] and risk maps [Example: Massachusetts EEE Risk Level by Town], to the extent possible.

3. Respond:

Consider forming a mosquito control workgroup in your jurisdiction to bring together state/local leadership, public health leadership, and representatives from key partners (eg mosquito control program, board of education, directors of department of the environment or conservation, select residents, etc) to make key decisions about the public health response.
- Example: Andover Town Response Plan
Depending on the extent of the public health threat, consider publishing a Mosquito-Borne Illness Advisory [Example: Florida Advisory April 2024] or a Mosquito-Borne Illness Alert
- Example: Florida Alert June 2020
Depending on the circumstances, consider taking action by implementing mosquito control interventions (eg fogging or spraying).

4. Communicate:

Depending on the extent of the public health threat and actions being taken, consider publishing a press release to communicate the latest information and response activities.
- Example: Massachusetts Department of Agriculture Press Release on Plans to Spray for EEE
- Planning note: To improve community opinion of spraying, such press releases should include information on the spray being used, the impact to local fish and bee populations, guidance for ornamental pond owners, beekeepers, individuals with asthma or other respiratory illnesses, and safety information on the human consumption of any surface water or garden vegetables in the affected area.
In the event that spraying activities may be ongoing, consider regular situation updates to inform the public on the methods that are being used, the areas that are being targeted, and address any common questions or misconceptions [Example: Massachusetts Situation Update]
Consider publishing a clinician alert with specific reminders regarding main symptoms, diagnostic tests and specimen routing, treatment and supportive care, and key signs of severe disease.
- Example: Maine CDC Health Advisory
For EEE, WEE, and VEE, consider specific public communication related to vaccinating horses, limiting horse exposure to mosquitos, and reporting dead wild birds; consider communication to veterinarians about vaccination guidelines.
- See the USDA Animal and Plant Health Inspection Service for more information.

Sources