Molly

Photo by Kristin Laidre

After Molly, shown on a hike, was paralyzed by a tick bite, her owners in Seattle realized they didn't live and camp in the tick-free region they once imagined. As the disease-spreading arachnids expand their territories, pet owners and veterinarians are trying to keep up.

On a June morning two years ago, Kristin Laidre's dog, Molly, suddenly fell off her owners' bed.

"She just crashed to the ground," Laidre said. "She couldn't use her legs. They were basically like Jell-O."

Sitting beside her dog on the floor, Laidre and her husband watched with horror as Molly's chest cavity began to convulse, "like hiccups ... over and over again," Laidre said.

The Seattle couple rushed Molly to her veterinarian, Dr. Kristin Kemper. Laidre mentioned to the doctor that while trying to soothe Molly at home, she discovered an engorged tick behind one ear, likely picked up during a recent camping trip along the eastern Washington-Oregon border.

Kemper duly removed the tick, but neither she nor Laidre, a wildlife biologist, thought it relevant. Noting muscle weakness in Molly's limbs, delayed reflexes and anisocoria (a condition in which the eyes' pupils are different sizes), the doctor suspected Molly's condition was the result of a neurological disease. She ordered bloodwork and radiographs. But the results didn't shed light on a diagnosis.

Kemper's longtime office manager and veterinary assistant raised the possibility of tick paralysis. "As a veterinarian who had never seen tick paralysis, I'm like, 'OK, yeah, that's a zebra,' " Kemper said, using medical slang for a rare or unexpected disease.

But two hours after the tick was removed, a veterinary technician came to Kemper with a surprising update: Molly was stronger and could walk. "I thought, 'You have got to be kidding!' " Kemper laughed. "I give my wonderful, wonderful staff all the credit. [The tick] was the smoking gun the whole time."

As a veterinarian who has practiced throughout her 21-year career in western Washington, Kemper hadn't regularly encountered problems with ticks in the past. More recently, given shifting climate patterns and changes in land use, among possibly other factors, ticks are turning up in unfamiliar places, and new species are joining the scene, upending what used to be a common understanding about the nature and extent of tick-borne threats.

What's the deal with ticks?

Ticks are arachnids, like spiders and scorpions, with four pairs of legs (eight total). The parasites feed exclusively on blood throughout their life cycle, drawing nourishment from mammals, reptiles and birds.

Ticks can sicken their hosts — including people — in myriad ways. Molly's condition, tick paralysis, is caused by a neurotoxin released in the saliva of several species of female ticks as they feed. The toxin causes immobility, first in the limbs, then in the rest of the body. Molly's odd breathing indicated that the neurotoxin was beginning to affect the muscles involved in breathing. 

Treatment involves removing the tick and providing supportive care as needed, such as fluids, oxygen, antibiotics, assisted feeding and help in urinating. Having been diagnosed quickly, Molly was fortunate to recover by having the tick removed and receiving minor supportive care.

Tick paralysis is an outlier of sorts among tick-borne diseases in the United States. More commonly, ticks pick up bacterial, viral or protozoal pathogens from their various hosts and transmit the pathogens to new hosts. Once a pathogen is transmitted, merely removing the tick will not alleviate the condition.

Many of the infections transmitted by ticks result in fever, fatigue and muscle or joint pain. Some can affect red blood cells or platelets, resulting in anemia or bleeding or both. While cats can contract tick-borne diseases, dogs overwhelmingly are more likely to be diagnosed. Livestock, especially cattle, also can be infected.

Ticks familiar and unfamiliar

For many older Americans, awareness of the dangers of ticks came with the emergence of Lyme disease. Fifty years ago, an outbreak of illnesses in the seashore town of Old Lyme, Connecticut, initially thought to be juvenile rheumatoid arthritis, was confirmed as infections of the bacterium Borrelia burgdorferi. Now known as Lyme disease, it is transmitted by infected blacklegged ticks (lxodes scapularis and lxodes pacificus, also known as deer ticks and western blacklegged ticks, respectively).

Today, Lyme is endemic in the U.S., common in humans and dogs and becoming more frequently diagnosed in horses. It usually causes fever, fatigue and joint pain and is treatable with antibiotics, although clinical signs may persist in some patients. Lyme nephritis, a kidney disease, has been reported in both dogs and humans as a severe outcome of infection.

This summer, ticks struck in Connecticut again. Public health officials in the city of Bridgeport closed a popular beach in early July for the rest of the season after discovering multiple tick species, including the longhorned tick (Haemaphysalis longicornis, also known as the Asian longhorned tick), according to a city Facebook post.

Ticks

Photos by KPixMining/Adobe stock, Clarence Holmes Wildlife/Alamy stock, ondreicka/Adobe and Doug Lemke/Adobe

Ticks with expanding ranges in the United States include (clockwise from top left) blacklegged ticks (lxodes), longhorned ticks (Haemaphysalis longicornis), lone star ticks (Amblyomma americanum) and American dog ticks (Dermacentor variabilis).

First detected in the U.S. on a New Jersey sheep farm in 2017, the longhorned tick has made rapid inroads in the country. It is now found in many states east of the Mississippi River, as well as several states west of the Mississippi — a total of 24 states, plus the District of Columbia.

Some key features aid its spread: It's tiny and plain-looking, blending easily into an animal's coat, and it reproduces through sexually and through parthenogenesis, meaning it doesn't need to mate. It is indiscriminate in its choice of hosts and will easily hitch a ride on migratory birds and other wildlife.

The longhorned tick commonly transmits the protozoan Theileria orientalis, currently considered to be most problematic for cattle (see sidebar). Laboratory studies and data from other countries where the tick is endemic demonstrate it can transmit a laundry list of potentially nasty diseases: anaplasmosis, babesiosis, rickettsiosis and ehrlichiosis.

Scientists reported in May that a longhorned tick collected in Connecticut was positive for Ehrlichia chaffeensis, a cause of ehrlichiosis, while two others in the same study were positive for the bacterium that causes Lyme.

E. chaffeensis is primarily a human pathogen, but it can sicken dogs, too. To date, most canine cases of ehrlichiosis in the U.S. are triggered by infection with E. canis, usually carried by the brown dog tick (Rhipicephalus sanguineus).

Dogs usually present with fever, swollen lymph nodes, difficulty breathing and bleeding disorders. Doxycycline is the treatment of choice for dogs in the acute phase. Dogs that aren't treated may appear to get better, but the bacteria lurk in the spleen, hiding out for months to years. Dogs that relapse or whose initial treatment wasn't sufficient may develop chronic infection, requiring another three to four weeks of antibiotics and supportive treatment. In these cases, dogs are more likely to die from the illness or be euthanized because they are so sick.

Extending their range

Unlike the longhorned tick, the lone star tick (Amblyomma americanum) is not a newcomer, but some 75 years ago, it was thought to live only in and south of Virginia. A specimen was collected in 1945 to the north, in Delaware, but it was considered an oddball, not part of an established population. Since then, the aggressive tick named for the white star-like pattern found on the back of its females has "invaded, established, and supplanted blacklegged ticks and American dog ticks (Dermacentor variabilis) as the most commonly encountered tick species in the state," according to a 2021 paper in the Delaware Journal of Public Health.

Today, lone star tick is fully established along the entire eastern coastline of the U.S. and north to Nova Scotia, Canada, along the Great Lakes and into Nebraska, and as far west as Saskatchewan, Canada.

It is perhaps best known for triggering alpha-gal syndrome in people, a curious and potentially life-altering allergy to mammalian meat (including pork) and sometimes dairy products. It is also a vector for ehrlichiosis and tularemia. Tularemia is primarily a disease of rabbits and rodents but can be transmitted by ticks to people, dogs and cats, as well. (Cats and dogs can also become infected by killing and eating infected animals.)

While tularemia in dogs usually isn't life-threatening, it can be fatal in cats without aggressive antibiotic treatment. Animals can also transmit the bacteria to humans, most commonly through bites or scratches. Signs include high fever, swollen lymph nodes, jaundice and, in severe cases, organ failure.

Another tick species to migrate beyond its customary territory is the Gulf Coast tick (Amblyomma maculatum), which has moved far beyond its namesake hot and humid habitat. A vector for the bacterium Rickettsia parkeri, known chiefly as a human pathogen, it's ranged north to the Mid-Atlantic states, into the Midwest and even emerged in pockets of arid southern Arizona.

One explanation for its spread may be its lack of fussiness in choosing a host — almost any ground-feeding bird or small mammal is suitable for the tick in its immature phase, while adults will feed on cattle, swine and white-tailed deer. As birds migrate and cattle move along production routes, the ticks are along for the ride.

As Daniel E. Sonenshine, an expert in ticks and tick-borne diseases at Old Dominion University, stressed in a 2018 paper published in the International Journal of Environmental Research and Public Health, all ticks have certain preferences for habitat and humidity as well as preferred hosts, but certain species are more flexible, enabling them to access a greater array of bodies on which to feed.

Patchwork tracking

Evolving weather conditions, including rising average temperatures, may account for the changing range of some tick species, as are factors such as how land is used — both increased building and development on previously wild lands, as well as reforestation projects, can bring ticks into closer contact with people and domestic animals.

While the U.S. Centers for Disease Control and Prevention tracks voluntary reports of human cases of tick-borne disease, there is no federal agency equivalent for other animals. Some specific tick-borne diseases are reportable to state and national authorities. For example, anaplasmosis (in cattle) and tularemia (in multiple species) are reportable to the U.S. Department of Agriculture. Certain strains of Babesia and Theileria in cattle and horses should be reported to the USDA through state veterinarians as "notifiable," meaning they are emerging diseases or emergency incidents. Some states have requirements for disease reporting within their borders.

Dr. David Needle, a senior veterinary pathologist at the state veterinary diagnostic laboratory at the University of New Hampshire, described the disparity in data collection for people versus other animals this way:

"If you go to your local hospital [system] and ask, 'How many people on December 12, 2011, had supplemental oxygen or were on a ventilator?' they could tell you exactly how many people and everything about them. ... But in a town with four veterinary hospitals, try asking how many dogs [on a particular date] were coughing at presentation. It's a completely different thing altogether."

The Companion Animal Parasite Council (CAPC), a nonprofit organization, maintains interactive prevalence maps of the tick-borne diseases Lyme, anaplasmosis and ehrlichiosis in dogs in the U.S. and Canada. The data are obtained by CAPC through agreements with the veterinary diagnostic laboratory companies Antech, Idexx and Zoetis. The maps date to 2012 and are updated monthly to help clinicians and pet owners track trends. CAPC also provides an annual pet parasite forecast.

For his part, Needle leads a multi-university tick surveillance study across northern New England. Ticks in Maine, New Hampshire and Vermont are collected from wildlife at hunter check stations and from animals involved in various research projects, including moose, fishers, foxes and deer. The labs identify and catalog the tick species and any pathogens they carry.

"We're really trying to get a handle on how tick-feeding ecology and environmental ecology relate to pathogen carriage," Needle said. The types of ticks Needle's project has captured so far were as expected; the pathogens they carried, less so. While Lyme is the most common tick-borne disease in people in the U.S., the bacterium that causes anaplasmosis was isolated most frequently.

The research also has found that even in New England, where ticks have long been commonplace, the bugs have forged new territories.

Needle said he knows long-practicing veterinarians from Maine, New Hampshire and Vermont who did not recommend tick preventatives to clients earlier in their careers because ticks were rare to nonexistent. "Now, it's constant," he said. "It's like watching parasites spread right in front of your eyes."