Mosquitoes in Maryland transfer several diseases, most notably West Nile Virus (WNV),
Eastern Equine Encephalitis (EEE), and La Crosse encephalitis.
While less common, localized risks for Dengue fever and Zika virus also exist, primarily driven by travel-associated cases and specific invasive mosquito species.
Public health surveillance by the Maryland Department of Health consistently monitors these threats, as the region’s unique geography along the Chesapeake Bay tidal wetlands creates ideal breeding grounds for disease-carrying mosquitoes.
The two primary species responsible for virus transmission in the state are the common house mosquito (Culex pipiens) and the Asian tiger mosquito (Aedes albopictus).
This guide walks through the major diseases carried by mosquitoes in Maryland, which species spread them, where disease pressure is the highest, and what you can do to reduce your exposure.
West Nile Virus in Maryland
West Nile Virus is the biggest mosquito-borne disease concern in Maryland. It is primarily spread by Culex pipiens, a dusk-to-dawn biting mosquito found statewide.
The Maryland Department of Health has documented West Nile-positive mosquito pools every year since 2001, making it a persistent health concern.
Culex mosquitoes commonly breed in storm drains, gutters, and any standing water found on residential properties.
Most West Nile infections are often mild. Most infected people develop no symptoms, with roughly 20% developing a fever, headache, body aches, and/or fatigue.
Fewer than 1% develop the severe neuroinvasive disease affecting the brain or nervous system.
Symptoms of West Nile neuroinvasive disease include:
- Encephalitis
- Meningitis
- Muscle weakness
- Paralysis
- Long-term neurological complications
Adults over 60 and immunocompromised individuals face the highest risk of illness. Unfortunately, there is no vaccine and prevention is the only reliable protection.
Eastern Equine Encephalitis in Maryland
Eastern Equine Encephalitis in Maryland is rare, but it is the most severe mosquito-borne disease present in the region.
It is transmitted by wetland-associated mosquito species, including Aedes and Culiseta, which maintain a bird-to-mosquito transmission cycle in swamp habitats.
According to the CDC, only a few cases in humans are recorded each year.
Still, it closely tracks EEE activity as outbreaks in the mid-Atlantic elevate regional risk. Even if it’s rare, EEE is extremely serious. It carries a 30 to 40% fatality rate, with high rates of permanent neurological damage in survivors.
Symptoms may begin with a sudden fever or severe headache and escalate to seizures, brain inflammation, and a coma.
Residents near wetland corridors must rely on professional mosquito-reduction efforts to reduce their exposure risk.
La Crosse Encephalitis in Maryland
La Crosse encephalitis is a lesser-known mosquito-borne disease, but is still documented by the CDC. It is primarily spread by Aedes triseriatus, a species that breeds in virtually any container or natural area that collects rainwater.
This disease commonly affects children under 16, with symptoms including:
- Fever
- Nausea
- Headache
- Fatigue
- Vomiting
In severe cases, symptoms can lead to encephalitis, seizures, and neurological complications.
According to the CDC, Maryland reports sporadic cases, with fewer than 250 cases reported nationwide in 2025. Still, it remains part of the state’s mosquito disease profile.
Dengue and Zika: How Much Are Maryland Residents at Risk?
Dengue fever and Zika virus are not established in Maryland, but they remain relevant because the Aedes albopictus, Asian tiger mosquito, is found in the state. This mosquito has the potential to help spread the disease.
The primary vector, Aedes aegypti, is not found in Maryland, which does limit outbreak potential.
However, imported travel cases still matter. When infected travelers return to Maryland, Aedes albopictus mosquitoes can bite them, making secondary transmission possible.
This is why it’s still important to control Aedes albopictus mosquitoes. The CDC urges travelers who are visiting areas with dengue fever and Zika virus to protect themselves from mosquito bites to prevent potential outbreaks.
Which Species of Mosquitoes Carry Diseases in Maryland?
In Maryland, the two primary disease-carrying species are the Culex pipiens (common house mosquito), a nighttime biter that transmits West Nile Virus, and the Aedes albopictus (Asian tiger mosquito), an aggressive daytime biter that spreads Dengue, Zika, and Chikungunya.
Since their offset activity patterns cover both day and night, residents face a continuous risk of transmission throughout the peak season.
When Are Mosquitoes Most Active in Maryland?
Mosquito activity in Maryland ranges from early spring to fall, with disease risks rising and falling at fairly predictable rates.
West Nile Virus transmission peaks July through September, when Culex pipiens populations are at their height and bird reservoir amplification is also at its peak.
EEE risks follow a similar pattern with Aedes albopictus populations active May through October.
How to Reduce Mosquito-Borne Disease Risk in Maryland
You can reduce mosquito-borne disease risk in Maryland by using EPA-registered repellents, wearing protective clothing, eliminating standing water weekly, and utilizing professional barrier treatments. Adopting these habits severely disrupts their breeding cycles and shields you from both day- and night-biting vectors.
- Apply Proven Repellents: Use EPA-registered formulas containing DEET (25% to 30%), Picaridin, IR3535, or Oil of Lemon Eucalyptus (OLE/PMD).
- Wear Protective Clothing: Cover up with long sleeves, long pants, and socks during peak mosquito activity at dusk, dawn, and during the day.
- Eliminate Standing Water Weekly: Tip and drain stagnant water from gutters, birdbaths, tarps, buckets, toys, planters, pool covers, and drainage areas to stop eggs from developing.
- Maintain Water Features: Properly chlorinate swimming pools, clean drainage systems, and use aerators in ornamental ponds to keep water moving.
- Apply Professional Barrier Sprays: Use targeted backyard sprays to eliminate adult resting sites and significantly reduce the local mosquito population.
Partnering with a professional pest control expert is the most effective way to drop local mosquito populations by 85% to 95%. This drastic reduction breaks the virus transmission cycle between local wildlife and humans, delivering the highest level of long-term protection for your family.
FAQ
What diseases do mosquitoes carry in Maryland?
Mosquitoes in Maryland carry West Nile Virus, Eastern Equine Encephalitis Virus, and La Crosse encephalitis virus. Asian tiger mosquitoes can also transmit dengue and Zika under the right conditions.
How common is West Nile Virus in Maryland?
West Nile Virus is common and the most consistently documented mosquito-borne disease in Maryland, with the state identifying positive mosquito pools every year. While most people show no or only mild symptoms, severe cases, albeit rare, can lead to neuroinvasive disease.
Should I be worried about Eastern Equine Encephalitis in Maryland?
Yes. You should take the proper precautions. EEE is rare, but extremely serious when it occurs, as it carries a high fatality rate and often causes neurological injury in survivors.
Do Maryland mosquitoes carry Zika?
Maryland mosquitoes do not carry Zika as the primary vector species is absent. However, Asian Tiger mosquitoes have the potential to carry it and are present statewide. Under the right circumstances, they are capable secondary vectors and travel-associated imported cases remain a relevant concern.
What kind of mosquitoes are in Maryland?
Maryland is home to multiple species of mosquitoes, with the most medically important species being Culex pipiens, or northern house mosquitoes, and Aedes albopictus, or Asian tiger mosquitoes. Northern house mosquitoes primarily spread West Nile Virus and bite at dusk and night, while Asian tiger mosquitoes bite aggressively during the day and are capable of spreading several tropical viruses.
Can mosquito repellent prevent disease transmission?
Yes. EPA-registered repellents reduce mosquito bites, which lowers disease exposure risk. Because disease-carrying mosquitoes are active at all times, consistent application is key.
Does eliminating standing water really reduce disease risk?
Yes. Mosquitoes breed in standing water and some species only need small amounts to complete development within seven to ten days. Weekly removal prevents the cycle from completing.
When is West Nile Virus most active in Maryland?
West Nile activity peaks between July and September when Culex mosquito populations are at their peak and virus amplification in bird populations is strongest. This is the highest-risk season for disease exposure in Maryland.
Does professional mosquito treatment reduce disease risk?
Yes. Professional mosquito treatments drastically reduce populations, in turn reducing exposure risk. Pairing them with regular removal of standing water and use of personal protection is the best way to lower risks.
What should I do if I think a mosquito bite made me sick?
Mosquito bites do not transmit disease, but exposure to mosquitoes can still pose a risk. If fever, severe headache, stiff neck, confusion, weakness, or neurological symptoms develop within days to two weeks after mosquito exposure during Maryland’s active season, contact a physician promptly and mention mosquito exposure history.