“The numbers on some of these diseases have gone to astronomical levels,” says Lyle Petersen, MD, director of the division of vector-borne diseases at the Centers for Disease Control and Prevention (CDC). Tick-borne Lyme disease is a prime example: About 35,000 cases are reported each year, but the CDC estimates that the actual number could be more than 13 times greater. (2) Lyme disease and anaplasmosis are the most common diseases spread by ticks, while West Nile, dengue, and Zika are most frequently spread by mosquitoes. These illnesses can cause permanent disability or even death. For example, Zika infections in pregnant women have been linked to severe birth defects, such as microcephaly (an abnormally small head and brain size). (3) And about 1 in 150 people infected with West Nile virus develop severe illnesses of the nervous system, such as encephalitis (swelling of the brain) or meningitis (inflammation of brain and spinal cord membranes). (4) Just as alarming as the increase in known diseases is the fact that nine new germs spread by mosquitoes and ticks have been discovered in the United States and its territories since 2004. These include the Bourbon virus, a rare and deadly tick-borne disease that was first spotted in Bourbon County, Kansas, in 2014; and the Heartland virus, which is most likely transmitted by lone star ticks and is endemic to Midwestern and Southern states. Yet state and local health departments on the front lines may not be fully prepared to combat the rising epidemic. The CDC reports that more than 80 percent of organizations tasked with controlling these diseases need improvement in core competencies, such as routine mosquito surveillance, outreach and community education, and testing for pesticide resistance. (5) “People shouldn’t be afraid to go outdoors if they take prudent measures,” says Paul Auwaerter, MD, clinical director of the division of infectious diseases and a professor of medicine at Johns Hopkins University School of Medicine in Baltimore. “But we can do better.” “A lot of trends are driving the upsurge, all of these things working together: climate change, humans interacting differently with our environment, and some of the things we do in our households,” says Heidi Brown, PhD, an expert in vector-borne disease transmission at the University of Arizona in Tucson. Furthermore, regarding changes in deer populations, which carry the tick that spreads Lyme, or the distribution of the pathogens, she says that “teasing these apart is a challenge.” Hotter, wetter weather because of a changing climate fuels the spread of infectious diseases like Lyme, dengue, West Nile, and Rocky Mountain spotted fever, as mosquitoes and ticks move into newly warm habitats. International travel and commerce have facilitated increased transmission of lethal pathogens from the tropics to industrialized nations. Hitchhiking parasites and infected individuals who unknowingly transport microbes can now go anywhere in the world in less than 24 hours. This is how West Nile arrived in New York City in 1999, and why the United States has seen outbreaks of the Zika and chikungunya viruses for the first time in the past decade. (6) “As environmental conditions change, it is likely that certain diseases will occur in areas where they previously had not occurred,” says Dr. Petersen. “Climate is only one of several very important factors that influence the distribution and occurrence of vector-borne diseases.” Urban sprawl is upending natural habitats for animals that carry these vectors, like deer or mice, as humans increasingly move into once heavily forested regions. “When we fragment the forest to create housing developments, we are plunking down our home in the middle of harm’s way,” says Richard Ostfeld, PhD, a disease ecologist at the Cary Institute of Ecosystem Studies in Millbrook, New York. “We are creating the ideal living conditions for white-footed mice and other small mammals that are responsible for spreading infected ticks, and driving away predatory species, like foxes and owls, that feed on these small mammals,” says Dr. Ostfeld. “As a result, Lyme disease is now found in places that it never occurred in recorded history.” Improvements in surveillance and diagnosis have also contributed to the increase in reported cases of infectious diseases, even though much work remains to be done. “We’ve become much more adept at the molecular diagnostics that lead to pathogen discovery and securing a diagnosis faster,” says Dr. Auwaerter. However, the CDC believes that current surveillance data still substantially underestimates actual vector-borne disease occurrences. For example, insurance data suggests that Lyme disease infects approximately 476,000 Americans yearly, more than 13 times the number of cases reported by state and local health departments. (2) In the case of West Nile virus, the CDC estimates that the number of cases may be between 30 and 70 times what is actually reported. Part of the reason for the discrepancy is that people infected with these diseases who experience mild symptoms may not seek medical attention. Another factor is that many cases are misdiagnosed or simply never reported to the CDC in the National Notifiable Diseases Surveillance System. Some cases are clinically diagnosed based on symptoms and a history of possible exposure to ticks, but not verified with blood tests. Consider this: Mosquitoes that transmit West Nile or dengue fever are very sensitive to temperature changes, and frost kills both adults and larvae. But warmer winters enable mosquitoes to survive in locales that were once too cold. Since the middle of the 20th century, two species of mosquitoes capable of transmitting West Nile or dengue, Aedes aegypti and Aedes albopictus (also known as the Asian tiger mosquito), have expanded their habitat range, spreading into newly temperate areas in at least 28 states and as far north as New York and New Hampshire. (7) Higher temperatures extend the mosquitoes’ season of infectious transmission because breeding cycles get shorter and yield more mosquitoes to spread disease. Heat speeds up the incubation of viruses inside the bugs, so they become infective much faster, and there are a greater number of days that the virus can infect someone during the mosquito’s three- to four-week lifespan. Female mosquitoes also bite more frequently in the heat, boosting their capacity to transmit the virus. A study linked increased drought severity to changes in mosquito infection prevalence. According to the researchers, drought conditions from climate change over the next 30 years could triple the number of West Nile cases in regions with low human immunity. (8) And it’s not just mosquitoes that are a growing concern. Ticks, mice, and other carriers of potentially deadly microbes are surviving milder winters and moving into increasingly warm regions. The hardy blacklegged ticks that spread the Lyme-causing bacteria have taken up residence as far north as Canada. Meanwhile, lone star ticks, southern natives that transmit diseases like tularemia and human granulocytic anaplasmosis, have been spotted as far north as Maine. (9) Lyme disease is so closely linked to climate change that the Environmental Protection Agency (EPA) added the disease to its list of indicators to track where the country is warming. (10) RELATED: Your Guide to Lyme Disease More than half of U.S. counties are now home to the blacklegged tick that spreads Lyme disease — double the number of counties in 1994. “Lyme disease lived quietly in the environment for many thousands of years, but something kicked it off,” says Mary Beth Pfeiffer, author of Lyme: The First Epidemic of Climate Change. “Its emergence coincides with the time climate change reached a critical mass in the late 1970s and ’80s.” (11) Congress established the Tick-Borne Disease Working Group to review federal efforts related to all tick-borne diseases and to better coordinate the federal response to outbreaks. Even so, budget cuts at the local and national levels over the past few years have hit prevention campaigns, as well as the ability to detect outbreaks and swiftly respond as needed. On the plus side, the Kay Hagan Tick Act, signed into law in the spring of 2022, earmarks $114 million for Lyme and tick-borne illness research. Still, Auwaerter says, “Public health agencies are woefully underfunded, even though they have great potential for keeping us safe.” Complicating matters further is the fact that there is considerable disagreement over the diagnosis and treatment of diseases like Lyme. “Some physicians and infectious disease scientists don’t accept the term chronic Lyme disease, and the term now generally being used is post-treatment Lyme disease syndrome for people who still show symptoms after a course of antibiotics,” says Ostfeld. “There is some opposition to extended treatment with antibiotics, especially intravenous treatment, but the opposition is by no means universal,” he says. “Two professional groups, the Infectious Diseases Society of America and the International Lyme and Associated Diseases Society, are at odds over diagnostic and treatment guidelines.” According to the CDC, the yellow fever vaccine is safe and effective. Because there is no treatment or cure for yellow fever, the vaccine is recommended for anyone ages 9 months to 59 years who’s traveling to an area of the world with active yellow fever infections. Those outside of that age range should consult their healthcare provider. (12) A dengue vaccine is available in several countries, including the Philippines and Brazil, but the World Health Organization has voiced concerns about the vaccine’s reliability and the risk of complications. (13) RELATED: What Is Dengue Fever? Experimental vaccines against Zika, chikungunya, and dengue show promise in clinical trials, but experts don’t expect them to be on the market for several years. Bacterial tick-borne diseases like Lyme are usually treated with antibiotics once diagnosed. But, as Pfeiffer points out, some Lyme specialists dispute the notion that short-course antibiotics can kill the pathogen. Testing for Lyme can be unreliable, so the disease is often not caught in the early stages, when treatment would be most effective. Currently, there is no Lyme disease vaccine; a previously available vaccine was discontinued in 2002. Here are some steps that you can take to protect yourself and your family.
Get Rid of Standing Water
The Aedes aegypti mosquito that transmits Zika, dengue, and chikungunya is known as a container-breeding mosquito because it likes to lay eggs around standing water. A study conducted by researchers at the University of California, Davis, found that an economic downturn in Bakersfield, California, was associated with a 276 percent increase in West Nile virus cases. Aerial surveillance revealed that stagnant water sitting in swimming pools in abandoned foreclosed homes had become breeding grounds for mosquitoes. (14) Make sure there is no stagnant water in damp cellars, swimming pools, storm drains, flowerpots, garden fountains, or any moist places for mosquitoes to nest and reproduce.
Reduce the Risk for Mosquito Bites
The best protection against mosquito-borne illnesses is to avoid getting a mosquito bite in the first place. The CDC offers several tips: (15)
Use an effective insect repellent. The CDC recommends EPA-registered insect repellents that contain DEET, Picaridin, IR3535, oil of lemon eucalyptus, or 2-undecanone. When used as directed, these repellents are proven safe and effective, even for pregnant and breastfeeding women.Keep mosquitoes outside of your home. Make sure your windows and doors have screens. Inspect the screens and fix any holes.Treat clothing and gear with insecticide. You can spray boots, pants, socks, and tents with permethrin; or buy permethrin-treated clothing and gear.Wear long-sleeved shirts and long pants. These give you an extra layer of protection.
Know How to Avoid, Spot, and Remove Ticks
Ticks live in grassy wooded areas. They can also travel on animals like deer, mice, or the family pet. Any time spent outdoors — whether it’s gardening, walking the dog, or camping — can bring you in contact with ticks. If you’re walking outdoors, avoid wooded and brushy areas with high grasses and piles of leaves. Treat clothing and gear with permethrin. A study conducted by researchers at the CDC found the insecticide to be highly effective in incapacitating ticks and preventing bites. (16) Do a careful tick check when you come indoors. Check under the arms, around the ears, inside the belly button, between the legs, behind the knees, and in and around the hair on your head — all places where ticks like to hide. Tumble dry clothing on high heat for 10 minutes to kill any ticks. Shower within two hours of coming indoors. If you spot a tick, be careful how you remove it. The goal is to pull it out steadily and slowly so you remove all of it, including the head. The CDC advises using fine-tipped tweezers to grasp the tick close to the skin’s surface. Then pull upward with steady, even pressure. Once you’ve removed the tick, clean the bite area and your hands with rubbing alcohol or soap and water. “People should educate themselves, know what the ticks look like, know how to pull them out of your skin, and understand how to protect yourself from infection,” says Ostfeld.
Watch Out for Zika Hotspots
No mosquito-borne Zika virus transmissions have been reported in the continental United States since 2018. The CDC advises pregnant women, partners of pregnant women, and even couples considering having children to avoid travel to areas where Zika is endemic. Areas with a high risk of Zika include many nations in Africa, Asia, Central and South America, and the Caribbean. (18) Myron Cohen, MD, the director of the Institute for Global Health and Infectious Diseases at the University of North Carolina School of Medicine in Chapel Hill, believes the recent CDC data can help raise awareness and education about all of these diseases. The report, he says, “shines a light on the opportunity for acquiring a vector-borne disease that might not have been otherwise recognized, and on the opportunity for prevention.”
