Bugs can carry pathogens such as bacteria, nematodes, protozoa, and viruses which transmit tricky-to-diagnose diseases to humans. Many of these illnesses (e.g., dengue fever, Lyme disease) can start with vague symptoms like a headache, fatigue, or fever—and there’s not always a telltale bite mark.

When travelers get sick, it’s understandable to want to get home immediately to familiar medical care, says William Spangler, an emergency medicine doctor and the global medical director with insurance company AIG Travel. “It’s likely better to seek treatment locally, where practitioners know the endemic disease and how to treat it.”

(Why bedbugs are everywhere—and what you can do about them.)

Before a trip, consider visiting a travel medicine clinic, which can tailor medications and vaccinations to your destination. And read on for intel on all the bugs you really want to avoid.

The culprit: Bedbugs

Including Cimex lectularius (common bedbug) and Cimex hemipterus (tropical bedbug).
Where they are Furniture, carpets, and suitcases around the world.
How they can hurt you and what to do “You don’t have to travel to get bedbugs,” says Keck. “You can get them from your school, sitting in a waiting room, or from a visiting friend.”
Though bedbugs can carry viruses, they rarely transmit pathogens to humans. Their bites are painless; clusters or zigzags of itchy welts are an allergic reaction that can appear up to nine days later. “The bites can really only be treated by antihistamines and the relief will be limited,” says Spangler.
The good news? Bedbugs can’t fly. When not sucking your blood, they prefer hiding in dark places like the creases of mattresses.
“To avoid bringing bedbugs home, place your bags in the hotel tub where they cannot climb,” says Keck. “Then inspect the bed by pulling the sheets and mattress pad up, looking at the elastic areas, and checking all around the bed.” If you see the apple seed-sized reddish brown bugs, their pale yellow eggs, or blood stains, Keck says to “ask for another room not touching the one you’re in,” meaning neither next door, above, nor below it.
Bedbugs prefer cloth luggage over plastic or metal, and it’s easier to spot them on light colors if you do an inspection with your phone flashlight. Rejoice if it’s cold when you return home: storing your suitcase outside for 80 hours below 32° Fahrenheit kills the pests. Washing your clothes in hot water followed by a half-hour high-heat tumble dry helps too.

The culprit: Mosquitoes

Including Aedes mosquitoes that transmit chikungunya, dengue, yellow fever, and Zika; Culex that cause West Nile fever; and the malaria-spreading Anopheles.
Where they are Around the world except Iceland and Antarctica; disease-carrying species prefer tropical, subtropical, and some temperate climates.
How they can hurt you and what to do “Mosquito-borne diseases kill approximately one million people worldwide every year,” says Spangler. Mosquitoes cause 200 million cases of malaria annually with about 625,000 deaths, and an estimated 100 to 400 million cases of dengue with about 40,000 deaths. While 80 percent of dengue infections have no symptoms, it’s nicknamed “breakbone fever” because it can cause such intense pain.
People living in countries with disease-carrying mosquitoes are most affected, but travelers aren’t immune. Plus climate change is expanding mosquitoes’ territory. The U.S., for example, has suffered cases of locally acquired malaria in 2023. And the World Health Organization warns that, within this decade, dengue will become a major threat to more places in Europe and the U.S.
When planning a trip, Spangler recommends checking the Centers for Disease Control and Prevention’s (CDC) maps, which provide travel information about illnesses like dengue and malaria. Travel medicine clinics can advise if you need malaria-prevention pills and vaccinations for yellow fever. A second malaria vaccine was approved in early October. It, and a limited-use dengue vaccine, hold promise for the future.
It’s best to prevent mosquito bites in the first place. Use insect repellent with picaridin or DEET and wear long sleeves and pants, ideally treated with permethrin. Sleep with a mosquito net, but note that new research counters previously held theories that malaria mosquitoes only bite at night. A 2022 study found that 20 to 30 percent of Anopheles mosquito bites happen during the day.

The culprit: Biting midges or no-see-ums 

About 4,000 species of Ceratopogonidae.

Where they are Worldwide (except Antarctica and the Arctic), especially near coasts, lakes, and rivers.
How they can hurt you and what to do Often as tiny as a pencil point but up to an eighth of an inch long, biting midges are a type of fly. Depending on where you live, you might call them no-see-ums, midges, punkies, or, in Florida and Alabama, five-O’s—a reference to 5 p.m., when they start feasting on humans.
Biting midges are more annoying than dangerous (although they can spread rare diseases like Oropouche fever in Central and South America). Keck says, “True no-see-ums or biting midges are actually very easy to spot because their bite is painful.” Some people get an allergic reaction that feels even worse, usually itchy red welts and swelling.
Bug spray, even with DEET, provides only limited protection. Wearing long sleeves and pants (consider tucking them into your socks), prevents bites. Hats with a fine net can protect your face.

The culprit: Ticks

Ixodidae (hard ticks) and Argasidae (soft ticks); about 60 of the 900 species can spread diseases to humans, including the “Lyme disease tick” Ixodes scapularis.

Where they are Grassy and bushy areas—even in cities—on every continent except Antarctica and in all U.S. states except Alaska.
How they can hurt you and what to do Technically an eight-legged arachnid, ticks are bloodsuckers. They can’t fly or jump, but some ticks wait on the tips of shrubs on well-used paths and can quickly climb onto a person (or pet) that brushes by.
While they eat, ticks hold themselves in place by stabbing a barbed harpoon into your skin. This makes them difficult to remove. It can take them a day or two to finish their meal, but tick bites are usually painless, often go unnoticed, or are mistaken for mosquito bites.
“Different infectious pathogens are carried by different species of ticks,” says Lin H. Chen, director of the Mount Auburn Hospital Travel Medicine Center and a professor at Harvard Medical School. About 476,000 people in the U.S. are diagnosed with Lyme disease every year. Other U.S. tick-borne diseases include Rocky Mountain spotted fever, tularemia, and anaplasmosis. Travelers doing extensive outdoor activities in Europe and Asia are at risk of tick-borne encephalitis and might consider a vaccine.
“There are a number of readily available repellents that have some effectiveness,” says Spangler, “but in tick-prone areas, you basically want to limit your exposed skin with good footwear, long pants, and long sleeves. If you’ve been outside near tall grass or other foliage, conduct a full-body inspection to look for ticks—it’s possible to spot one on your clothes (or even your skin) before they’ve latched on.” A shower within two hours can also help wash away any ticks that haven’t yet attached themselves.

The culprit: Parasitic worms

Including blood flukes (Schistosoma) and hookworms (Ancylostoma duodenale and Necator americanus).

Where they are Tropical and subtropical countries, especially where sanitation is poor, including on beaches where dogs and cats roam freely.
How they can hurt you and what to do While travelers rarely get infected with parasitic worms, it’s certainly something to avoid. Symptoms can be minor (stomach pain) or serious (seizures), though even the thought of a worm infection may make you nauseated. It’s possible to eat worms or their eggs, especially in undercooked meat or poorly washed vegetables. This can result in trichinosis (caused by roundworms), tapeworms, or even that headline-making worm found in an Australian woman’s brain. Kids, including in the U.S., are known for spreading pinworms, principally if they don’t wash their hands well after using the bathroom.
Travelers also need to be aware of “environmental exposures like wading in freshwater,” says Chen, which has “potential risks of schistosomiasis and leptospirosis” and of walking barefoot through soil and sand contaminated with hookworm or Strongyloides.
About 230 million people globally have flu-like schistosomiasis (also called bilharzia) and 200,000 people die annually from it, mostly, but not exclusively, in Africa. According to the CDC, malaria is the only parasitic disease that’s more devastating than schistosomiasis. Blood flukes (schistosomes) replicate in freshwater snails found in 78 countries; they mainly spread when infected people urinate or defecate. The parasite can survive for 48 hours after leaving the snail and can enter human skin that’s in contact with contaminated water.
Poor sanitation can also lead to worm infections through the soles of your feet, especially from soil and sand where cats and dogs defecate. Keeping your shoes on is the best way to avoid larvae such as hookworms and whipworms and the lesions, diarrhea, anemia, and rectal prolapse they can cause. Prescription medications are effective for many worms, assuming you get the right diagnosis.
Feeling grossed out? That might be okay, since it can remind you to take precautions like applying bug spray and keeping your skin covered in higher-risk areas. And, as Keck says, “Remember that there are far more beneficial insects than harmful [ones]. Most are not going to sting, bite, transmit a disease, or hurt you in any way.”