Deer ticks everywhere

Posted 5/29/19

REGION — A new study from Penn State shows that the ticks that cause most cases of Lyme disease, deer ticks or black-legged ticks, have become the most abundant type of tick in Pennsylvania. As …

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Deer ticks everywhere


REGION — A new study from Penn State shows that the ticks that cause most cases of Lyme disease, deer ticks or black-legged ticks, have become the most abundant type of tick in Pennsylvania. As recently as the 1960s, there were hardly any ticks in the state, according to the study.

One cause of the booming deer tick population is the regrowth of forests across the state that had been cleared more than a century ago to further agricultural interests, according to assistant research professor Joyce Sakamoto.

According to the Pennsylvania Department of Health in 2000, there were 2,271 cases of Lyme reported; by 2016, that number had jumped to 11,443. New York State also has a high number of cases with about 9,500 being reported in 2016.

The Centers for Disease Control and Prevention say there has been a 350% increase in vector-borne diseases, in the U.S. from 2004-2016, and more than 76% are caused by ticks; the majority of those are Lyme disease cases.

Deer ticks don’t get the Lyme disease from deer. Lyme disease is caused by a bacterium called Borrelia burgdorferi and it is transmitted to humans when an infected tick bites a human. According to the Northeast Wildlife Disease Cooperative (NWDC) (, “When the larvae hatch in the spring, they do not carry the B. burgdorferi bacteria. During the summer, the larvae feed on the blood of mice, squirrels, raccoons, rabbits and other small vertebrates. The larvae mature into nymphs in the fall and hibernate over the winter. The larval and nymphal ticks can become carriers of the Lyme bacteria by feeding on wildlife reservoir hosts. White-footed mice and eastern chipmunks are the most important reservoirs for B. burgdorferi in the Eastern and Midwestern United States. If they acquired the bacteria as larvae, the nymphs can transmit the bacteria to new vertebrate hosts when they feed the following spring or summer.”

“Deer are a dead-end host for the Lyme disease bacteria. They do not infect ticks with the bacteria that cause Lyme disease nor do they contract the disease when an infected tick feeds on them. They play no direct role in the transmission cycle,” according to the Pennsylvania Game Commission.

NWDC says that deer do not serve as reservoirs for B. burgdorferi, and that, while the bacteria are carried by the small mammals that the larvae and nymphs feed on, those mammals don’t seem to suffer any illness as a result.

Lyme disease can be successfully treated with antibiotics, especially if it is caught early on. Experts agree that the best way to avoid getting the disease is to check your body immediately after being outdoors in an area that might harbor ticks, and that includes grassy fields and wooded areas. Tuck socks into pants, wear white or light-colored clothing to make spotting ticks easier, and use repellents with picaridin or other ingredients.

Deer ticks can also carry a bacteria that causes tularemia or rabbit fever. As the common name suggests, it causes a fatal illness in rabbits and other wild rodents, and that illness can be spread to humans through tick bites or contact with an infected animal.

Symptoms include an ulcer on the site where the tick bite or contact took place, swollen glands, muscle pain and fever. The Mayo Clinic website says the disease is rare, but also, “highly contagious and potentially fatal,” but can be effectively treated with antibiotics, especially if caught early.

Deer ticks can also carry other diseases. Deer ticks and another species called groundhog ticks can carry the Powasssan virus and spread it to humans. It is still relatively rare in the United States, with only about six cases reported in 2018. Still, it’s a cause for concern among healthcare professionals because there is no vaccine to prevent or medicine to treat the Powassan virus. Some 10% of people who are infected with Powassan succumb to the disease and other must be hospitalized to receive support for swelling around the brain and breathing.


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