Pesticide Exposure: Another Growing Hazard for Farmworkers in a Changing Climate
Climate change is altering many pest populations in the U.S., including via northern expansion of blacklegged tick populations, accelerated geographic spread and population growth of the spotted lanternfly, and increased duration of active periods of the codling moth, peach twig borer, and oriental fruit moth in California. This spread of agricultural pests, along with increased susceptibility of plants to invasive pests due to elevated CO2 and reductions in pesticide efficacy predicted with climate change, is increasing the use of pesticides—chemicals that are commonly used to manage pest populations.
Farmworkers, due to approximately 75% of pesticide use in the U.S. occurring in agricultural settings, and on the front lines of this increasing hazard. An estimated 10,000 to 20,000 pesticide poisonings among farmworkers are diagnosed in the U.S. annually. Workers applying pesticides face the highest exposure with their greatest exposure occurring during the mixing and loading processes (i.e., when the pesticides are in a concentrated state and there is a higher chance of spilling). Farmworkers working in sprayed fields are also at risk of high pesticide exposure and are less likely to use personal protective equipment (PPE) to protect themselves compared to those directly involved in the application process.
Acute health effects vary by pesticide type but can range from headache and dizziness to tremor and seizure. Acute occupational illnesses are tracked by the CDC-NIOSH Sentinel Event Notification System for Occupational Risk (SENSOR), a state-based surveillance program. In 2007–2011, 2,606 cases of acute occupational pesticide-related illness and injury were reported across 12 states. Of these cases, the rate of illness and injury among agricultural workers was 37 times greater than the rate for nonagricultural workers.
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.
Increasing Vibrio Threat with Warming Waters: Be Careful with Open Wounds
Vibrio vulnificus (V. vulnificus) are bacteria that live in coastal waters. They can get into an open wound of any size through salt water or brackish water (i.e., a mixture of fresh and salt water often found where rivers meet the ocean), or through drippings from raw seafood. Vibrio vulnificus wound infections are rare but serious. Treating these infections can require intensive care or limb amputations. About 1 in 5 people die from the infection.
V. vulnificus bacteria thrive in warmer waters—especially during the summer months (May to October) and in moderately salty environments like estuaries. Increasing water temperatures and extreme weather events (such as heat waves, flooding, and severe storms) associated with climate change create more favorable conditions for V. vulnificus. People at increased risk for V. vulnificus infection should takesteps to prevent an infection when enjoying coastal activities. CDC's Vibrio website provides additional information about Vibrio bacteria and the infections they cause.
Tickborne Diseases and Conditions
Tickborne diseases—when a person has been bitten by a tick and gets sick—are increasingly threatening the health of people in the U.S. Tickborne diseases include Lyme disease, anaplasmosis, babesiosis, ehrlichiosis, spotted fever rickettsioses (including Rocky Mountain spotted fever), and tularemia, as shown on the map below. Lyme disease is the most common tickborne illness in the U.S., with an estimated 476,000 Americans diagnosed and treated for Lyme disease and an economic burden between $345 million and $968 million each year (in 2016 U.S. dollars). Early localized symptoms can include a rash at the site of tick bite (occurring in 70–80% of infected persons), fever, chills, malaise, fatigue, headache, muscle aches, joint stiffness, and swelling of lymph nodes. Patients who have Lyme disease are often not even aware of a tick bite before getting sick. Untreated Lyme disease can progress to disseminated disease and produce a wide range of symptoms including additional rashes, facial paralysis, an irregular heartbeat, and arthritis.
Figure: Geographic distribution of select tickborne diseases. For more information, visit the interactive map at https://www.cdc.gov/ticks/data-research/facts-stats/geographic-distribution-of-tickborne-disease-cases.html
Tick bites can also lead to conditions such as alpha-gal syndrome (AGS), a potentially life-threatening allergy to red meat and consumer products made from mammals. Evidence suggests that AGS is primarily associated with the bite of a lone star tick (Amblyomma americanum) in the U.S., but other kinds of ticks have not been ruled out. People with AGS have delayed allergic reactions to a sugar molecule called alpha-gal, which can be found in pork, beef, rabbit, lamb, venison, gelatin, and dairy. Patients with AGS have varying tolerance and sensitivity to products containing alpha-gal, and AGS reactions can vary, ranging from mild to life-threatening. A 2023 CDC report investigating testing data showed that there were more than 110,000 suspected cases of AGS between 2010 and 2022. Additionally, suspected cases are on the rise—from 2017 to 2021, there were approximately 15,000 new positive test results for AGS in the U.S. per year. Another CDC report identified gaps in healthcare provider awareness of AGS, finding 42% of participating healthcare providers had never heard of AGS. Therefore, the number of identified suspect cases of AGS from 2010–2021 is likely an underestimate of the true burden of disease because the diagnosis of AGS requires a clinical exam and a positive diagnostic test.
The Role of Climate Change
Climate change is one of several factors that affect when and where tickborne diseases and tick-associated conditions can occur.
- Increasing temperatures from climate change can influence tick life cycles by increasing a tick’s ability to reproduce. This can lead to larger tick populations and greater risk of germs spreading from tick bites to people.
- Additionally, milder winters and warmer early spring temperatures expand the seasons when ticks are active, resulting in more weeks of the year that people in the U.S. are at risk of tick bites.
- Changing climate patterns can also alter the natural environment and longstanding ecological relationships. The distribution and density of the wildlife ticks feed on (e.g., deer and small mammals) is changing, which can lead to an expanded geographic distribution (e.g., latitude, altitude) of the diseases and conditions associated with these ticks.
- Expanding tick ranges and increasing cases of disease are also linked to changes in land use patterns, such as reforestation, forest fragmentation, and suburban development, which can lead to increased opportunities for humans to be exposed to ticks.
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.
How to Prevent Tickborne Diseases and Conditions
- Protect yourself from bites: Tick bite prevention is the first line of defense against tickborne diseases. Before you go outdoors apply EPA-registered insect repellents, treat clothing and gear with products containing 0.5% permethrin, and talk to your veterinarian about the best tick prevention products for your dog. Check out EPA’s webpage on Using Insect Repellents Safely and Effectively with extra guidance for applying repellents to children. If possible, when spending time outside, avoid wooded and brushy areas with high grass and leaf litter where ticks may live.
- Check for and remove ticks: After spending time outdoors, check your body for ticks, take a shower within 2 hours, and check your clothing, gear, and pets for ticks that may have caught a ride into your home. If you discover a tick on you or your pet, follow the recommended steps for proper tick removal as soon as possible. CDC’s Tick Bite Bot can assist you in removing attached ticks and seeking health care, if appropriate.
- Check your area’s risk: Check the current trends on tick exposure in your region at the CDC transmission website and the Tick Bite Data Tracker, which shows Emergency Department visits for tick bites on a weekly and regional basis. CDC has additional interactive maps displaying tick surveillance data of four tick species and surveillance of tickborne pathogens identified in blacklegged and western blacklegged ticks.
Help your patients: The CDC’s Ticks website and Tickborne Diseases of the U.S.: A Reference Manual for Healthcare Providers have information on specific tickborne diseases including information on how to avoid tick bites, common symptoms, and treatment. CDC has also issued guidance on caring for patients after a tick bite.
Figure. Places to check your body for ticks after being outdoors. Image from CDC.
Figure. How to remove a tick: (1) Use clean, fine-tipped tweezers to grasp the tick as close to the skin’s surface as possible. (2) Pull upward with steady, even pressure. Don’t twist or jerk the tick. (3) After removing the tick, thoroughly clean the bite area and your hands with rubbing alcohol or soap and water. (4) Dispose of a live tick by putting it in alcohol, placing it in a sealed bag/container, wrapping it tightly in tape, or flushing it down the toilet. (5) If you develop a rash or fever within several weeks of removing a tick, see your doctor. Image from CDC.
Mosquito-Borne Diseases
West Nile Virus
West Nile virus (WNV) is the most common mosquito-borne disease in the continental United States, with a median of 2,205 cases reported each year (range: 712–9,862). People typically get infected following the bite of a mosquito carrying the virus. While uncommon, WNV has been spread through blood transfusion and organ transplantation, and from mother to baby during pregnancy, delivery, or breast feeding.
Approximately 80% of people infected with WNV will not have any symptoms. About 20% will experience a fever and other 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. There is currently no available treatment or vaccine for WNV disease. In severe cases, patients may need to be hospitalized to receive supportive treatment.
Most U.S. counties have reported WNV disease cases since its introduction into the U.S. in 1999. However, the incidence of WNV disease varies greatly. The Great Plains and western states are more likely to have high incidence of WNV (defined as more than 1.10 cases per 100,000 people). Six counties with both high incidence and large populations reported 23% of all WNND cases during 2009– 2018 (Cook County, IL; Dallas County, TX; Harris County, TX; Los Angeles County, CA; Maricopa County, AZ; and Orange County, CA). Although certain areas of the country are more likely to have higher WNV incidence, the number of cases reported in a given county varies greatly each year. This makes accurately predicting the number of WNV disease cases that will occur each year and in each county challenging.
West Nile virus human neuroinvasive disease average annual incidence per 100,000 population by county of residence, 1999–2022*
Source: https://www.cdc.gov/westnile/statsmaps/historic-data.html
Figure: Since 1999, WNND cases have been reported in the majority of counties in the continental United States. The counties with the highest incidence for WNND cases are mostly located in the Great Plains and western states.
The majority of WNV cases occur during mosquito season, which starts in the summer months and continues through fall. Cases of WNV are most commonly reported in August and September.
West Nile virus human disease cases reported by month of illness onset, 1999–2022, all disease cases
Source: https://www.cdc.gov/westnile/statsmaps/historic-data.html
Figure: WNV human disease cases reported by month of illness onset, 1999–2022.
Climate Change and West Nile Virus
Climate change has resulted in milder winters, earlier springs, longer and warmer summers, and changes in regional precipitation. These factors could potentially affect WNV transmission through changes in, for example, bird migration and breeding patterns, mosquito population size and biting rates, and human behaviors, such as spending time outdoors. While we do not fully understand how climate change impacts WNV transmission across the United States, seasonal weather patterns can have an effect. This was observed in 2021 in Maricopa County, AZ, when the county experienced the largest-ever WNV outbreak, resulting in a reported 1,487 WNV cases, 1,014 hospitalizations, and 101 deaths. Although the reasons behind this outbreak are likely multiple, one potential contributing factor was the increased rainfall that occurred during a wetter-than-average monsoon season in 2021. This change led to a longer duration and increased amount of moisture that likely resulted in the maintenance of mosquito larval habitat sites, leading to greater WNV transmission. To better understand the impact of climate on WNV and better predict WNV transmission, the Centers for Disease Control and Prevention (CDC) and the National Atmospheric and Oceanic Administration (NOAA) are partnering to develop models that can forecast WNV for the upcoming season.
In nature, WNV cycles between mosquitoes and birds. Some bird species develop high levels of the virus in their bloodstream, and mosquitoes can become infected by biting these infected birds, continuing the cycle. Humans are “dead end” hosts, meaning they don’t pass on the virus to other mosquitoes that bite them, because they do not develop high enough levels in the blood stream.
Malaria
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.
Dengue
Dengue viruses are spread to people through bites of infected Aedes species mosquitoes (Ae. aegypti or Ae. Albopictus). There are an estimated 400 million dengue infections each year, but only about 25% of people infected with dengue will get sick. Symptoms typically include fever with aches and pains, nausea and vomiting, or rash. Less than 5% of dengue infections will progress to severe disease, which can lead to hospitalization and death. Early diagnosis and supportive medical care are essential in cases of severe dengue, which can be life-threatening within a few hours. There are currently no medications available to treat dengue.
Figure: Common symptoms of dengue.
Dengue viruses are common in most tropical and sub-tropical regions of the world, which experience year-round transmission with seasonal and intermittent major epidemics. Aedes mosquitoes have hitchhiked to most of the warm and wet areas of the world where people live. This includes many parts of the U.S., some of which have endemic dengue, including American Samoa, Puerto Rico, the U.S. Virgin Islands, and the freely associated states. In Puerto Rico, there were almost 30,000 confirmed cases reported between 2010 and 2020.
Figure: Map of areas with dengue risk, including frequent or continuous risk, sporadic or uncertain risk, and no evidence of dengue risk. Source: https://www.cdc.gov/dengue/areaswithrisk/around-the-world.html
Occasional dengue outbreaks can occur in non-endemic areas of the U.S. where Aedes mosquitoes live, but these outbreaks are rare. Outbreaks can happen when an infected traveler comes home and gets bitten by an Aedes mosquito. The mosquito gets infected and then bites healthy people, which can lead to an outbreak. Aedes mosquitoes require warm and humid environments for survival and reproduction, yet eggs can survive for up to 8 months in cold and dry conditions. This allows the species to persist through dry periods and winters in many parts of the continental U.S. and other temperate regions of the world. Recent local dengue transmission in the continental U.S. has occurred in Florida, Texas, and Arizona, but most dengue cases reported in the continental U.S. occur in travelers infected elsewhere. In 2019, there were 1,474 travel-associated cases reported in the U.S., but the true annual number of infected travelers is likely many times higher.
Figure: Maps showing the potential range of Aedes aegypti and Aedes albopictus in the U.S. as of 2017. These maps represent the CDC’s best estimate of the potential range of Aedes species mosquitoes in the U.S., but do not represent risk for spread of disease. Source: https://www.cdc.gov/mosquitoes/mosquito-control/professionals/range.html
Climate Change and Dengue
The impact of climate change on dengue is complex since many factors play a role in dengue transmission. Aedes species mosquitoes require warm temperatures for virus transmission, with optimal transmission estimated to occur at 77-86°F (25-30°C). Mosquitoes can alter their behavior to mitigate adverse environmental exposures, such as resting in shaded areas when temperatures are too high. The global increase in temperatures seems like a recipe for increased dengue due to better conditions for virus transmission.
Temperature is only one aspect of climatic suitability for Aedes mosquitoes. Extreme weather events that are increasing with climate change, such as floods and hurricanes, can also impact mosquito populations and dengue virus transmission. While Aedes species mosquitoes generally do not survive the high winds and flooding that hurricanes bring, mosquito eggs can survive. Natural and manmade containers filled with rain or used for water storage provide an excellent environment for eggs to hatch and larvae to grow. It is common for mosquito populations to decrease during and immediately after a hurricane, and then grow rapidly, as was seen approximately two weeks after Hurricane Maria in Puerto Rico in 2017. Increasing numbers of mosquitoes, combined with the destruction of housing and infrastructure, temporary or permanent human migration, and interruptions to mosquito control measures, can raise the risk of dengue transmission in the weeks that follow a hurricane.
Prevention of Mosquito-Borne Diseases
The best way to prevent any mosquito-borne disease is to protect yourself from mosquito bites. When outside, use an Environmental Protection Agency-registered insect repellent (follow these tips for applying insect repellent on children from the American Academy of Pediatrics) and wear loose-fitting, long-sleeved shirts and pants. Control mosquitoes in and around your home by installing screens on windows and doors and using air conditioning when available plus eliminating standing water (such as in outdoor buckets, planters, or bird baths) where mosquitoes breed. Children aged 9-16 years old who live in dengue-endemic areas and have laboratory confirmation of a previous dengue infection should get a dengue vaccine. For additional information, check out CDC’s Fight the Bite site with information on preventing bites from both ticks and mosquitoes, additional recommendations for if you are traveling to a place where a mosquito-borne disease is endemic, and recommendations for workers.
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).
Navigate to our other climate hazard pages below: