Ticks: The unwanted connection between people, pets and wildlife

Every time a person or pet is bitten by a tick there is a risk of disease transmission from the tick to the host. Ticks act as a link between species which may never interact and would be unlikely to share pathogens otherwise. You may never get a chance to snuggle a squirrel or wrestle a raccoon, but that doesn’t mean you cannot get diseases from them thanks to ticks.

Tick-borne diseases have increased in the U.S. in the last few decades. There are several ideas as to why these diseases have seen such a rapid growth. It boils down to more ticks, and therefore, more tick bites that could transmit pathogens. Tick populations are increasing in both numbers and geographic range. The Gulf Coast tick (Amblyomma maculatum) was once restricted to about 150 kilometers from the namesake Gulf of Mexico. The range of this tick has expanded northward and has now been found to be established in many counties in Illinois (the southernmost tip of Illinois to the Gulf of Mexico is around 800km). Another tick species, the lone star tick (Amblyomma americanum), named for the single white spot on the back of females, was once restricted to just the southern third of the state. Now the lone star tick ranges into southcentral Wisconsin. Both the lone star tick and the Gulf coast tick can transmit unique tick-borne diseases to humans and animals. Other ticks have become more numerous in locations where they were already present.

Ticks in Illinois can transmit several types of pathogens. These pathogens can be bacteria, viruses or protozoa. The type of pathogen does not necessarily indicate severity. Correct identification of the pathogen is important to ensure proper treatment.

Lyme Disease

Lyme disease is the most common tick-borne disease in humans in the U.S. Mice act as the reservoir host or wildlife host of Lyme disease. After a larval or nymphal tick has taken a blood meal from the mouse it becomes infective. If it bites a person, this tick can transmit the bacterium responsible for Lyme disease, Borrelia burgdorferi. The only tick species that transmits Lyme is the blacklegged tick (Ixodes scapularis). However, Lyme disease is not the only tick-borne disease threat to people and pets, every tick species in Illinois has the ability to transmit diseases. A selection of tick-borne diseases in people are described below.

Ehrlichiosis

Ehrlichiosis is a bacterial infection that can be caused by a few different bacteria species. Lone star ticks and blacklegged ticks can transmit ehrlichiosis. From 2000 to 2019 cases of ehrlichiosis have increased ten-fold in the U.S. The antibiotic doxycycline is used to treat ehrlichiosis.

Rocky Mountain Spotted Fever

Rocky mountain spotted fever (RMSF) is caused the bacterium Rickettsia rickettsii and is transmitted by the American dog tick (Dermacentor variabilis). Despite the name, this tick readily bites people as well. The lone star tick and the brown dog tick (Rhipicephalus sanguineus) are also known to transmit RMSF. RMSF can be fatal in up to 20 percent of people that are not treated. The treatment of choice is doxycycline.

Spotted Rickettsia Fevers

Spotted rickettsia fevers are a group of bacteria in the genus Rickettsia that all cause spotted fevers (this includes RMSF). The newly established Gulf Coast tick is the only known vector of a spotted fever called tidewater spotted fever. This new tick has already transmitted tidewater spotted fever to humans in Illinois. The treatment of choice for all spotted rickettsia fevers is doxycycline.

Anaplasmosis

Anaplasmosis is caused by the bacterium Anaplasma phagocyophilum. Anaplasmosis is transmitted by the blacklegged tick. Treatment for anaplasmosis is doxycycline.

Babesiosis

Babesiosis is cause by a protozoan parasite Babesia microti. Like Lyme disease, babesiosis is transmitted by the blacklegged tick. Babesiosis is not common but can lead to serious complications. Babesiosis is caused by a protozoan parasite and the treatment options differ from other tick-borne diseases. The recommended treatment choices are a combination of atovaquone and azithromycin or a combination of clindamycin and quinine.

Cytauxzoonosis

Cytauxzoonosis is a disease that affects domestic cats and some wild cat species. This disease is caused by a protozoan parasite related to Babesia. Cytauxzoonosis is a very serious disease that is almost always fatal to cats that are not treated. Even the best treatment option only has a 60 percent survival rate. This disease is most prevalent in southern Illinois but is moving north as lone star ticks move north. There is no vaccine for cytauxzoonosis. The best prevention is to use the best available tick preventatives.

Heartland Virus and Bourbon Virus

Heartland virus and Bourbon virus are rare but life-threatening tick-borne viruses in the Midwest. The lone star tick is thought to be a vector of Heartland virus, although it is unknown if other ticks may also transmit this virus. Heartland virus is rare and there are no specific treatments for this illness.

One Health is an approach widely adopted in public health sectors that recognizes that human health overlaps with environmental health and animal health. For ticks and tick-borne diseases this concept is especially true. Many environmental factors can impact tick populations. Invasive plants can lead to increased tick densities. Changes to the ecosystem can have significant impacts on ticks. Removal of large predators means that the density of deer increases, which leads to more ticks because deer are excellent “maintenance hosts” of ticks.

With One Health in mind, you can help reduce your risk, and your pet’s risk of tick bites and tick-borne diseases. It can be very challenging to completely prevent a tick from biting you, however you can take some precautions that may reduce your exposure.

• If a tick does bite you or your pet, it is very important to remove the tick as quickly as possible. Some tick-borne pathogens can take many hours to days to be transmitted, if you remove the tick promptly you can reduce the likelihood of becoming infected with a tick-borne disease.
• Pets should be on veterinarian-recommended tick preventatives year-round.
• Hunters and other outdoor enthusiasts are advised to take precautions when in the field. For tips on where ticks live, how to minimize the potential for tick bites, how to handle a tick bite and where to send a tick for analysis, review the OutdoorIllinois Journal article Staying Safe During Tick Season.

The rapid increase in tick-borne diseases across the U.S. requires vigilance from everyone. This means preventing tick bites and prompt removal of a tick from both people and pets. You also should familiarize yourself with the different tick species in order to know what disease risks there are and what symptoms to look for if bitten. The Illinois Lyme Association website is a good place to start your education on ticks and tick-borne diseases.

With a few precautionary measures we can still all enjoy all the outdoors have to offer.

---

Elliott Zieman is an assistant professor in the Department of Biological Sciences at Eastern Illinois University. Dr. Zieman grew up in the northwest suburbs of Chicago and went to Southern Illinois University for his bachelor’s and graduate degrees. He conducts research on several zoonotic tick-borne pathogens. Dr. Zieman and his students investigate the intersection of wildlife and domestic animal pathogens.