Vector & Pathogen Ecology

The hierarchy of controls provides a method of prioritizing safeguards to protect workers from hazards. Primary exposure control methods are hazard elimination or substitution by a less toxic substance. For pesticides, this could entail substituting insecticides most commonly identified in cases of injury and illness and utilizing integrated pest management practices on farms to reduce the need for chemical pesticides. Methods with lower effectiveness include providing and encouraging the use of PPE. PPE can be effective, but only when workers use it correctly and consistently, including when using during hot weather (a time when there may be concern about the heat burden of the PPE wearer).

Currently, there is an Agricultural Worker Protection Standard (WPS), which requires that employers of pesticide handlers and agricultural workers receive annual pesticide safety trainings. The Pesticide Education Resource Collaborative provides a library of EPA-certified educational resources to help the agricultural industry comply with the WPS. EPA is working on other ways to protect workers from pesticide risk.

Healthcare providers can help by learning to identify symptoms and treat patients with pesticide exposure from EPA’s Recognition and Management of Pesticide Poisonings manual. Unfortunately, pesticide poisoning symptoms can often be confused with symptoms of heat exhaustion, so also check out EPA’s comparison chart.

NOAA and partners have developed predictive models for Vibrio that can provide early warning signs of potential coastal hazards. Several experimental models predict the presence of V. parahaemolyticus and V. vulnificus in the Chesapeake Bay based on data from the Chesapeake Bay Operational Forecast System. Although these models cannot determine individuals’ risk for infection, they demonstrate the association between environmental conditions like water temperature, salinity, and chlorophyll and presence of Vibrio.

Anyone can get a Vibrio infection, but some medical conditions and treatments can increase a person’s risk for infection and severe complications. These include:

• Having liver disease, cancer, diabetes, HIV, or thalassemia
• Receiving immune-suppressing treatments
• Taking medicine to decrease stomach acid levels
• Having had recent stomach surgery

People who enjoy seafood and coastal activities—including swimming, fishing, or wading—can take steps to prevent a Vibrio infection.

• Do not eat raw or undercooked oysters or other seafood. Cook them before eating.
• Do not let raw seafood, its drippings, or its juices contaminate other foods.
• Always wash hands with soap and water after handling raw shellfish.
• If you are at increased risk for infection, wear protective gloves when handling raw seafood.
• If you have an open wound, stay out of coastal waters, if possible. This includes wading at the beach.
• Cover your wound with a waterproof bandage if it could come in contact with coastal waters or drippings from raw seafood.
• Immediately wash wounds and cuts thoroughly with soap and clean running water after contact with coastal waters or drippings from raw seafood.
• If you are at increased risk for infection, wear clothes and shoes that protect you from cuts and scrapes when around coastal waters.

Healthcare providers can prevent infections from becoming more severe by considering V. vulnificus as a possible cause of infected wounds that were exposed to coastal waters, particularly near the Gulf of Mexico or East Coast, and during periods with warmer coastal sea surface temperatures. Early antibiotic therapy and early surgical intervention improve survival. Clinical guidance is provided on CDC’s Vibrio website.

Risk of tickborne disease varies based on time of year, time spent outdoors in tick habitat, and geographic region.

• Time of year: In areas of the eastern United States where Lyme disease is common, people are most likely to be bitten by blacklegged (deer) ticks during two times of the year: from April through July when nymphs are active, and again from September through November when adults are most active, though people can get bitten any time ticks are present.
• Time spent outdoors: Outdoor workers are at increased risk of tickborne diseases if they work at sites where ticks are common. Worksites with woods, bushes, high grass, or leaf litter are likely to have more ticks. Children ages 5 to 15 years are also at increased risk of tickborne diseases, especially if they play in tick-prone areas.
• Geographic region: Different climates throughout the U.S. support different species of ticks, which spread different diseases. Overall, the geographic range of infected ticks is expanding, putting an increasing number of communities at risk for tickborne diseases. Although the reported nationwide incidence of Lyme disease remained fairly stable from 2008 to 2019 at approximately 11 cases per 100,000 people per year, Vermont, Maine, Rhode Island, Pennsylvania, and West Virginia saw marked increases in Lyme disease incidence over the 10-year period. Data show that the majority of patients with AGS are adults living in the southern, mid-Atlantic, and midwestern regions.

WNV, primarily spread to people through bites of infected Culex mosquitoes, is the most common mosquito-borne disease in the continental U.S. Many U.S. counties now report West Nile cases, but the Great Plains and western states are more likely to have high incidence. Approximately 80% of people infected with WNV will not have any symptoms, 20% will experience flu-like symptoms, and less than 1% will develop severe West Nile neuroinvasive disease (WNND), a condition that can lead to death or long-term disability. Older adults and those with compromised immune systems are at higher risk for WNND. Currently, no medicines or vaccines are available for West Nile.

• This year marks the 25th anniversary of the first detection of WNV in people in the U.S. WNV has caused 59,000 infections and 2,900 deaths between 1999 and 2023 (and likely more because many people don’t have symptoms).
• West Nile prevention depends on community-level mosquito control programs to reduce mosquito vector densities, personal protective measures to decrease exposure to infected mosquitoes, and screening of blood and organ donors. Despite progress in the fight against WNV, current prevention methods are not enough to reduce the burden. It is normal for West Nile cases to vary in number and location by year in the U.S., making it difficult to predict or identify any one reason for a higher-than-average year. Public health needs more ways to detect outbreaks early, control mosquitoes, and treat and prevent the disease to effectively protect people from WNV.

Dengue virus, spread to people through bites of infected Aedes species mosquitoes (Ae. aegypti or Ae. albopictus), is common in six U.S. territories and freely associated states, and outbreaks have recently occurred in Florida, Hawai’i, Texas, Arizona, and California. About 25% of people infected develop symptoms, including fever with aches and pains, nausea and vomiting, or rash. Less than 5% of dengue infections progress to severe disease, which can lead to hospitalization and death. Early diagnosis and supportive medical care are essential in severe cases, though no specific treatments are available. A vaccine is being implemented in Puerto Rico for children 9–16 years old who have laboratory-confirmed evidence of previous dengue infection.

• In 2024, there have been over 10 million dengue cases across the Americas, significantly surpassing the 4.6 million cases reported for the entirety of 2023—already a record year for dengue. After a decade of almost no dengue transmission, Puerto Rico is now facing an outbreak ahead of the typical dengue season (starting in August). The Puerto Rico population has limited immunity to the strains of dengue currently circulating, and repeat infections raise the risk for hospitalization and severe disease. The observed limited immunity, combined with a prolonged period of low transmission, could lead to an outbreak with greater magnitude and severity.
• As of July 2024, more than 50% of dengue cases in Puerto Rico have required hospitalization, with over 1,100 hospitalizations reported. The U.S. Virgin Islands have also reported dengue cases, and travel-associated cases in the continental U.S. are higher than previous years, increasing the risk of local transmission in areas wit Aedes mosquitoes and conducive climatic conditions.

For the first time since 2003, the U.S. has had locally acquired cases of malaria in Florida, Texas, and Maryland. Malaria is a serious mosquito-borne disease caused by different species of Plasmodium parasites that infect Anopheles species mosquitoes. People typically become infected with malaria following the bite of a mosquito carrying the parasite.

There are about 2,000 reported cases of malaria in the U.S. each year, mostly in travelers returning from other countries. Continuous spread of malaria was eliminated in the U.S. in the early 1950s through mosquito surveillance and control measures; however, as we’ve seen this summer, locally acquired malaria cases do still occur in the U.S.

Anopheles species mosquitoes can be found in much of the continental U.S., making local spread possible if people infected in a malaria-endemic country travel to the U.S. and are bitten by local Anopheles mosquitoes, which can then become infected and spread the parasite to people who have not traveled. The risk for local transmission is higher in areas where local climatic conditions allow Anopheles mosquitoes to survive during all or most of the year. Temperatures also need to be warm enough for the malaria parasite to develop in the mosquito. This summer, the U.S. has had plenty of the hot and humid conditions in which mosquitoes thrive, as well as increased international travel, potentially contributing to local spread.

While local malaria transmission in the U.S. is rare, it is possible that increased temperatures and altered precipitation patterns and humidity due to climate change may lead to increased mosquito populations, increased range of Anopheles mosquitoes, a greater number of mosquito biting days, and faster development of the malaria parasite in mosquitoes, all of which could impact local transmission in the U.S. in the future.

Climate change is one of several factors that can influence the distribution and prevalence of vector-borne diseases. Among vector-borne diseases in 2023, Lyme disease (tickborne) as well as West Nile virus, dengue, and malaria (mosquito-borne) were of public health concern in the United States. Lyme disease is the most common vector-borne illness in the United States, with an estimated 476,000 people diagnosed and treated each year. Traditional Lyme disease surveillance data  are available through 2021 from CDC. In 2023, 2,406 West Nile virus disease cases  were identified across 47 jurisdictions, including 1,599 neuroinvasive disease cases. There were also 2,556 dengue cases  across 52 jurisdictions, including locally acquired dengue cases in Florida (n=168), California (n=2), Texas (n=1), and Puerto Rico (n=933; where dengue is endemic). The vast majority of malaria cases  in the United States are travel-related, usually by people who travel to countries where malaria is endemic (regularly occurring). During May–October of 2023, though, the United States had a total of 10 cases of locally acquired malaria  reported in Florida, Texas, Maryland, and Arkansas (as of October 19, 2023).

Figure: Number of West Nile virus human disease cases in the United States over the past decade. Data from CDC (2023 data are preliminary and subject to change).

Figure: Number of locally acquired dengue cases in the contiguous U.S. over the past decade. Locally acquired cases occurred among people with no history of travel to a dengue-endemic region in the two weeks before illness onset. Data from CDC (2023 data are preliminary and subject to change).