Mosquito-borne Diseases

(This page is part of a series. For information on other illnesses that can affect NPS employees, volunteers, commercial use providers, and visitors, please see the NPS A–Z Health Topics index.)

Aedes aegypti adult mosquito

CDC/Amy E. Lockwood, MS

THE BASICS
There are over 200 species of mosquitoes across the U.S., and only a small number of these can cause disease in humans and animals. All mosquito species have similar life cycles: A mosquito egg hatches into a larva; a larva becomes a pupa; and an adult mosquito emerges from the pupa. Adult female mosquitoes need to feed upon blood to produce eggs and to continue the life cycle; thus, only female mosquitoes bite and transmit disease.

Humans: Pathogen transmission from mosquitoes to humans occurs when someone is bitten by a mosquito (most commonly Aedes, Culex, and Anopheles species). Cases of mosquito-borne disease are most common during warmer months (April to September) when mosquitoes are most active. West Nile Virus (WNV) is the leading cause of mosquito-borne disease in the U.S. Approximately 2,500 cases are reported to the CDC each year; however, this number represents only 1–2% of cases, as most infected persons do not have symptoms, do not seek medical care, or are not tested.

Malaria, which is caused by a parasite, is the most common mosquito-borne infection worldwide but is very rarely transmitted in the United States. However, in 2023, Florida and Texas have both reported locally-acquired cases, the first time locally-acquired cases have been reported in the U.S. since 2003. Dengue, Chikungunya, and Zika are globally common, and locally-acquired cases and outbreaks have occurred in the territories and some states (see CDC’s ArboNet for the data on location by year), although cases occur with much lower frequency than with WNV. St. Louis Encephalitis, Eastern Equine Encephalitis, Jamestown Canyon Encephalitis, and La Crosse Encephalitis are also viral mosquito-borne diseases that occur rarely in the United States. In humans, symptoms vary based on the pathogen but can, at the beginning, include fever, headache, body-aches, and rash and usually appear within a few days to a few weeks after a mosquito bite. Many can progress to more severe disease and even death. Although malaria is treatable, mosquito-borne viral diseases, like WNV, do not yet have specific treatment and involve mainly supportive care.

Animals: Mosquitoes feed on a variety of animals, which can provide a source of blood and maintain mosquito survival. Mosquito-borne diseases can pose a health risk to both domestic and wild animals. For example, some species of wild birds, as well as horses, are sensitive to fatal infections of WNV. Wildlife can also serve as a reservoir for mosquito-borne diseases, including Chikungunya, dengue, WNV, Zika, as well as other viral infections.

Environment: Mosquitoes are an important component of the environment and ecology of national parks, with many mosquitoes being native. Mosquitos eat algae, parasites, fungi, and other microorganisms, remove biological waste from the environment, and play an essential role as pollinators. Mosquitoes also serve as a food source for dragonflies, birds, fish, bats, reptiles, and amphibians. Different mosquito species have different habitat and behavioral preferences including floodwater, wastewater, aquatic plants, and containers. Mosquitoes can live indoors or outdoors and may feed on hosts during the day or at night. Mosquitoes are most active during warmer months (April-September), which corresponds to higher rates of mosquito-borne disease during the summer. Understanding mosquito behavior and habitat preference is critical for control and mitigation efforts.West Nile Virus, chikungunya, dengue, and Zika virus are all non-native diseases introduced by human activity. The non-native mosquitoes that spread dengue, chikungunya, and Zika virus prefer to feed on humans and breed in man-made habitats. Human impacts on the environment, including land development and climate change, are affecting mosquito habitats and development. Some of these changes to the land, air, and water promote the transmission and spread of mosquito-borne diseases. By protecting natural environments and their ecological properties and processes, we can help protect ourselves from mosquito-borne diseases – this is One Health in action.

PREVENTION

• Wear loose-fitting long-sleeved shirts and pants, high socks, and a hat/head net to help prevent mosquito bites.
• Use an EPA-registered personal mosquito repellent when working outside (see EPA’s “Find the Repellent that is Right for You.”) Read and follow the label directions to ensure proper use.
• Treat clothing and gear with products containing permethrin.
• If you are planning to be in a high-risk area (such as with international travel), talk to your doctor about vaccination or prophylaxis. For example, prophylactic medication to prevent malaria is recommended in many areas around the world, and vaccination against yellow fever is recommended, and sometimes even required, in some areas as well.
• Talk to your veterinarian about how best to protect your animals from mosquito-borne diseases.
• For NPS employees: Understand educational, behavioral, physical, chemical, and biological tools for mosquito management.
  • Provide training and resources to park staff, volunteers, and the general public on mosquito behavior, biology, potential diseases they may transmit, and how to reduce human exposure.
  • Avoid certain outdoor activities at dawn and dusk and use appropriate clothing, PPE, and avoidance mechanisms in areas with day-biting mosquitoes with the potential to transmit vector-borne disease.
  • Reduce viable breeding habitat, particularly in developed areas including removing standing or stagnant water.
  • Work with IPM to use EPA-registered larvicides and growth regulators in non-removable water bodies to reduce mosquito numbers in developed areas. Adulticides should only be used when there is a public health threat.

RESPONSE

• Consider utilizing an ice pack or an over-the-counter antihistamine cream to reduce swelling and itching from mosquito bites.
• Seek medical attention if you observe any symptoms of mosquito-borne illness. These vary based on the pathogen but may include fever, headache, body aches, and rash. It’s important to communicate the mosquito bite exposure and timing of symptoms to your medical provider.
• Please report any exposures or confirmed illnesses to the NPS Office of Public Health (e-mail us) as directed in the “Disease Reporting” guidance below.

(Last updated: 4/26/2023)

NPS

NPS RESOURCES:

• NPS Integrated Mosquito Management Manual (coming soon)
• NPS Integrated Pest Management Program Website (internal)

OTHER RESOURCES:

• CDC Mosquitoes webpage
• CDC Mosquito Bite Prevention Resources
• EPA: “Find the Repellent that is Right for You”

NPS-SPECIFIC PUBLICATIONS:

• Adjemian J, Weber IB, McQuiston J, et al. Zoonotic infections among employees from Great Smoky Mountains and Rocky Mountain National Parks, 2008-2009. Vector Borne Zoonotic Dis. 2012;12(11):922-931. doi:10.1089/vbz.2011.0917

Disease Reporting

Visitors: Please email us to report any disease or health concern you believe may be related to your visit. You should also contact your healthcare provider who will report any confirmed and reportable disease on your behalf to the local or state health department.

Concessioners & Partners: Please email us to report illnesses as defined in NPS guidance and policy and in the Concessions contract.

Employees & Volunteers: NPS staff should report all employee and volunteer incidents as defined in NPS guidance and policy by contacting your NPS Public Health Consultant (restricted access), or you can email us. All work-related exposures and illnesses must also be reported in the Safety Management Information System (SMIS) (restricted access). All known disease exposures should be reported in SMIS as well.