NY Vet: Growing Risk of Tick-Borne Diseases

It is important for veterinarians to remain aware of tickborne diseases and how they manifest in pets. In a presentation at the NY Vet conference in New York City, Dr. Mary Anna Labato, DVM, DACVIM (SAIM), discussed evidence of conditions spread by ticks and how the risk of disease has increased for dogs and cats.

Dr. Labato, who is a clinical professor and associate department chair for Graduate Programs at the Cummings School of Veterinary Medicine, Tufts University, explained that there are 850 tick species around the world, and 90 of those species live in North America. Tick species vary by region in the United States, as well as the diseases they carry. Furthermore, Labato said, there is evidence that the prevalence of ticks is increasing, and the diseases they carry are becoming more widely distributed.

“They’re spreading across the North American continent,” said Dr. Labato, in her presentation. “Ticks are active at different points of the year. They’re associated with different hosts and carry different diseases.”

Data from the CDC show tickborne diseases are on the rise in humans.¹ In 2017, state and local health departments reported a record number of cases of tickborne disease to CDC. Cases of anaplasmosis/ehrlichiosis, Lyme disease, spotted fever rickettsiosis (including Rocky Mountain spotted fever), babesiosis, tularemia, and Powassan virus disease all increased—from 48,610 cases in 2016 to 59,349 cases in 2017. These 2017 data capture only a fraction of the number of people with tickborne illnesses. Under-reporting of all tickborne diseases is common, so the number of people actually infected is likely higher.

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Disease-carrying ticks in North America include Amblyomma americium (Lone Star tick), Amblyomma maculatum (Gulf Coast tick), Dermacentor variabilis (American Dog tick), Dermacentor andersoni (Rocky Mountain Wood tick), Ixodes pacificus (Western Black-legged tick), Ixodes scapularis (Black-legged tick), Otobius megnini (Spinose Ear tick), and Rhipicephalus sanguineus (Brown Dog tick), as well as Haemaphysalis longicornis (Long Horned tick), which is native to Asia.

Anaplasmosis

Black-legged, Western black-legged and Brown Dog ticks are known to cause anaplasmosis in pets. The Black-legged and Western black-legged ticks are most prevalent in the Northeast and upper Midwest. The Brown Dog tick is most common in the Southeastern states, West Coast, Texas and Oklahoma, although it also is found throughout North America and Hawaii. “(The Brown Dog tick) is the only tick that lives in human homes and in kennels,” said Dr. Labato.

Clinical signs of anaplasmosis in dogs include fever, lethargy, anorexia, lameness and thrombocytopenia. It may be diagnosed with clinical signs, direct blood smear, serologic testing, polymerase chain reaction (PCR), serologic testing, and identification of morulae on blood smears.

Cats with anaplasmosis show similar clinical signs, according to Labato. Seroconversion has also been documented in cats.

Lyme disease

Lyme disease is caused by Borrelia burgdorferi, and transmitted by Black-legged and Western Black-legged ticks. This condition is most often found in the Northeast, Midwest, and West Coast, and is reportedly increasing in the Mid-Atlantic, Great Lakes, southern Appalachia, and southern Canada regions.

Clinical signs develop in only 10-20% of dogs. Clinical signs include fever, lethargy, shifting leg polyarthritis, and immune-complex glomerulonephritis.

According to Labato, diagnosing an active case of Lyme disease in a dog is challenging. A variety of tests on the market can help.

“Once you’re looking at it, you’re already in the chronic stage,” said Dr. Labato.

Healthy dogs that live in areas with ticks that carry Lyme disease should be screened, Dr. Labato said. Cats should also be tested for Lyme disease, she added, especially if they’re not behaving well.

Cytauxzoonosis

Most prevalent in the South and Mid-Atlantic states, cytauxzoonosis is transmitted by the Lone Star and American Dog ticks. The condition is especially harmful to cats, Dr. Labato said, and some felines will require blood transfusions.

Clinical signs of this illness can include lethargy, anorexia, dyspnea, fever, icterus and anemia. Cytologic examination and PCR assays can diagnose the condition.

“These cats are really sick. They die easily,” she said. “It’s the supportive that really matters.”

Other notable diseases transmitted by Black-legged ticks include Human babesiosis, a malaria-like infection that can be fatal; and tick paralysis caused by a neurotoxin in the insect’s salivary gland.

In addition to cytauxzoonosis, the Lone Star tick can transmit human monocytic ehrlichiosis, canine granulocytic ehrlichiosis, Southern tick-associated rash illness, and tularemia.

According to Dr. Labato, tickborne diseases are being brought to new areas as these insects increase their geographical distribution. Dr. Labato credited the expansion of tick activity to multiple factors, including climate changes, migratory birds, increased human contact with nature, reforestation, wildlife conservation, and housing developments in forested areas.

The decreased use of environmental pesticides also is a factor. “That’s good for us, but it’s also good for the ticks,” said Dr. Labato.

According to Dr. Labato, early recognition of tickborne diseases is recommended for treating pets. While the reason for this increase in tickborne illnesses is unclear, a number of factors can affect tick numbers each year, including temperature, rainfall, humidity, and host populations such as mice and other animals. Good tick control also helps avoid the spread of tickborne illnesses to pets.

Reference

1. Record Number of Tickborne Diseases Reported in U.S. in 2017 [news release]. CDC website. https://www.cdc.gov/media/releases/2018/s1114-record-number-tickborne-diseases.html Accessed Nov. 14, 2018.