What Causes Lyme Disease?

Infected blacklegged ticks, which typically live in grassy and wooded areas, spread Lyme disease.

During the warm months, you likely hear a lot about Lyme disease, a tick-borne illness that causes a "bulls-eye" rash, fever, headache, and fatigue. Infected blacklegged ticks spread bacteria through their bites, causing Lyme disease.

The Centers for Disease Control and Prevention (CDC) reports that 30,000 cases of Lyme disease occur yearly, with most infections from April through October. Though, that only includes cases that healthcare providers diagnose and confirm. Some estimates suggest that about 476,000 people get sick from Lyme disease yearly.

There is also a lot of misinformation about how people catch Lyme disease. Here, learn what to watch out for, risk factors, and how to protect yourself.

Alex Sandoval

What Causes Lyme Disease?

The bacteria Borrelia burgdorferi causes Lyme disease. The bacteria spread through the bites of infected blacklegged ticks, also known as deer ticks.

"Lyme disease transmission happens when an infected tick bites you and remains attached for long enough to have a blood meal and become fully engorged," Daniel Kuritzkes, MD, the division of infectious diseases chief at Brigham and Women's Hospital, told Health. Usually, ticks must attach to the skin for 36–48 hours to transmit Lyme disease.

"In the process of sucking the blood from the person, [the tick is] also releasing the bacteria from its salivary glands into the person's body," said Dr. Kuritzkes. "If you can discover and remove the tick before it's had a chance to do this for very long, you're much less likely to be infected."

A person with Lyme disease may show symptoms between three and 30 days after infection. One of the hallmark Lyme disease symptoms is a red, circular "bulls-eye" rash. Although, not everyone develops a rash.

Other Lyme disease symptoms include:

  • Fever
  • Chills
  • Headache
  • Muscle aches and pains
  • Fatigue
  • Swollen lymph nodes

A blood test can diagnose Lyme disease. Mostly, symptoms subside after taking antibiotics for two to four weeks. Lyme disease can cause severe complications if untreated. In that case, you may require a longer course of antibiotics.

How Else Do You Catch Lyme Disease?

Lyme disease is a tick-borne illness. Only infected blacklegged ticks can transmit the bacteria that causes Lyme disease. Still, some misconceptions about how Lyme disease spreads exist.

For example, a study published in 2014 found that the bacteria that causes Lyme disease may be present in semen and vaginal secretions. Still, no evidence suggests that Lyme disease passes between sexual partners, said Dr. Kuritzkes.

In rare cases, Lyme disease can transmit from a pregnant person to the fetus through the placenta. Though, pregnant people with Lyme disease can take antibiotics to protect the fetus from adverse effects. There is also no evidence that Lyme disease can be passed through breastfeeding.

Likewise, there have been no reports of transmitting Lyme disease through a blood transfusion. Still, some experts say it could happen and advise people with Lyme disease not to donate blood.

Is Lyme Disease Hereditary?

Lyme disease is not a heritable illness. Certain inherited genes may increase the risk of complications like Lyme arthritis. Lyme arthritis occurs if the bacteria that causes Lyme disease makes its way into joint tissues. The bacteria triggers inflammation and causes swollen and painful joints. Usually, Lyme arthritis symptoms come on within a few months of infection.

Certain genes, such as human leukocyte antigen (HLA), help guide the body's immune response to Lyme disease. Some people with variations in those genes are more likely to develop Lyme arthritis than others. 

Normally, HLA genes target proteins made by infectious bacteria. In contrast, people with specific variations in their HLA genes may mistakenly cause the body to target its normal proteins. That immune response may trigger Lyme arthritis.

Who Gets Lyme Disease?

Anyone can develop Lyme disease. Still, some evidence suggests that specific populations may have a higher risk than others.

People who have a high risk for Lyme disease depend on factors such as:

  • Geographical region: Lyme disease most commonly spreads in the Northeastern United States, in states like Connecticut, Delaware, Maine, and Rhode Island. Although Lyme disease generally spreads in forested areas, cases are reported in suburban parts of Boston, New York, and Philadelphia. 
  • Occupation: Outdoor workers, such as construction workers, landscapers, farmers, and park and wildlife managers, have increased exposure to infected ticks. 
  • Age: Children and young adolescents aged 5–14 and adults aged 45–55 get Lyme disease more often than others.
  • Sex: Data shows that men make up about 56% of confirmed cases of Lyme disease. 

Risk Factors

Beyond people most likely to get Lyme disease, a few factors can increase your risk. Generally, risk factors include being outside, having a pet, and walking in grassy or wooded areas.

Spending Time Outdoors

In addition to having a job that requires working outdoors, spending time outside increases the risk of Lyme disease. Activities like gardening, hunting, and hiking, especially in warm, moist weather, boost exposure to infected ticks.

Although Lyme disease is most common in summer, infected ticks may come out during early fall and late winter if the temperatures are mild.

Having a Pet

You can not catch Lyme disease from eating infected animal meat or from being bitten or scratched by a pet. Though, pets can carry infected ticks that can latch onto your skin and transmit disease.

"The types of ticks that usually bite dogs, called dog ticks, aren't the type that carries Lyme disease. So, it's not likely that a tick attached to your dog would then go on to infect you," explained Dr. Kuritzkes. "It's worth noting that if you're outdoors somewhere where your dog is picking up ticks, it's likely that you could be picking up ticks, too."

Check your pets after spending time outdoors, and remove any ticks you find. Even though dog ticks don't carry Lyme disease, they can carry other illnesses. Talk to a veterinarian about preventive treatments, such as vaccines, to reduce the risk of your pets getting Lyme disease.

Walking in Grassy or Wooded Areas

Your risk of Lyme disease increases if you walk in or near places where blacklegged ticks typically reside. Those places include grassy or wooded areas, especially in humid weather. You can avoid infected ticks by steering clear of tall grasses and sticking to trails while walking outside.

How To Prevent Lyme Disease

To prevent bites from infected ticks that spread Lyme disease, take note of the following precautions:

  • Steer clear of grassy and wooded areas during warm months. Instead, stay in the center of trails while walking outside.
  • Wear long-sleeved shirts and pants, close-toed shoes, and a hat while outside. Choose light colors so that you can easily spot ticks.
  • Use insect repellent with DEET on your clothes and exposed skin.
  • Remove your clothes and wash them right away after returning inside. 
  • Carefully check your body, belongings, pets, and children after being outside. 

Ticks can be difficult to spot since they are so tiny. Mainly, immature ticks, called nymphs, transmit Lyme disease. Nymphs can be less than two millimeters in length. Adult ticks carry Lyme disease, too, but are more likely to be found and removed from people's skin before they're able to transmit the bacteria.

Remove ticks as quickly as possible using fine-tipped tweezers if you find one attached to your skin. Consult a healthcare provider if you suspect a tick may have been feeding for more than 24 hours. They may suggest you take a prophylactic course of antibiotics to prevent infection. Lyme disease is curable. Still, avoiding infection is key, said Dr. Kuritzkes.

"You can definitely get Lyme disease again, and we certainly see people with repeat infections. The antibodies you get from Lyme disease aren't like those you get from measles, which convey some immunity," added Dr. Kuritzkes. That's one reason it's been hard for scientists to develop an effective Lyme disease vaccine for humans. 

"Hopefully, someday, we will have [a vaccine]," said Dr. Kuritzkes. "For now, avoiding tick bites—and removing ticks as quickly as possible—is really the best defense."

A Quick Review

Lyme disease is a common tick-borne illness. Infected blacklegged ticks spread the bacteria that causes Lyme disease if they bite you and stay on your skin for at least 36 hours. 

To prevent Lyme disease, avoid places where ticks usually reside, such as grassy or wooded areas during warm months. Wear long-sleeved shirts and pants, close-toed shoes, and a hat while outside. Frequently check your body, belongings, pets, and children for ticks.

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