Tick-Transmitted Diseases

~~ by Kristen Thomas, Purdue College of Veterinary Medicine Class of 2020 and Dr. Magnusson, owner of Leo’s Pet Care ~~

As of spring 2018, Leo’s Pet Care is now recommending yearly screening blood tests for tick-transmitted diseases, and year-round tick prevention for dogs exposed to ticks or tick habitats.

None of these zoonotic diseases (“zoonotic”: affects both humans and animals) are transmitted directly from pets to humans; however, the same ticks that bite and infect dogs, can also bite and infect humans.

Therefore, screening dogs for tick-transmitted diseases isn’t just important to diagnose and treat disease in our companion pets. Testing dogs can also serve as an indicator of the potential for human infection in an area as well.

Since there has been a sudden rise in tick populations and now an incidence of clinical tick-transmitted diseases reported in Indiana, we are now recommending yearly blood screening for tick-transmitted diseases, and year-round prevention of ticks.

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Diagnosing tick-transmitted disease starts with a screening blood test run in the hospital

It is very important to understand what these tests check for, what they do not check for, and their limitations in screening.

Positive screening tests are common, and do not necessarily indicate your dog has an active disease.

Even if they appear healthy, your dog may come up “positive” for one of these tests if they have ever been exposed to a tick-transmitted disease. These in-house tests detect the presence of antibodies to tick-borne organisms, not the organisms themselves. Therefore, a “positive” test simply indicates your dog has been exposed to ticks and the diseases they carry, at some point in their lives. Additional tests will need to be performed if your dog is positive on the screening test, to determine if the infection is active, or long gone.

This additional testing to follow up on a positive screening test, will include a complete blood count with a slide review, serum chemistry profile and urinalysis, and possibly confirmatory tests for the tick organisms (Quant C6 or PCR testing).

90% of dogs with positive screening tests never show any symptoms, and do not need to be treated. A positive test in our hospital does not necessarily mean your dog has clinical disease, nor does it necessarily mean we need to initiate treatment, but it does mean we need to run the additional tests above to separate between non-clinical and clinically infected dogs.

Treatment is only performed if your dog is showing signs of disease, and/or has a positive confirmatory blood Quant C6 and/or PCR and/or urine protein test.

How are tick-transmitted diseases prevented in humans and animals?

The best way to protect yourself and your pets is to clear shrubbery around the house and avoid tick habitats which include tall grass, wooded areas, and marshes.

Products that can be used in dogs to prevent tick attachment and disease transmission include prescription veterinary oral tick preventives (Bravecto®), dusts, collars, sprays, or topical treatments.

To remove ticks, use tweezers and grasp the tick as close to the skin as possible, and pull straight out to remove the tick.

Prophylactic antibiotic treatment following a tick bite is not recommended as a means to prevent tick-transmitted disease. There is no evidence this practice is effective, and this may simply delay onset of disease.

Instead, humans and animals who experience a tick bite should be alert for symptoms suggestive of tick-transmitted illness as described above. Screening tests can be performed at the time of a tick bite and repeated 2-3 months later, or sooner if any of these symptoms of concern develop.

Clinical symptoms of tick-transmitted diseases in humans and animals

The clinical signs of tick-transmitted diseases are caused by the body’s reaction to the organism (immune-mediated hypersensitivity) and therefore can affect multiple systems in the body. Because each body will react differently, the same organism in different hosts can cause varying and completely different (and often very vague!) symptoms.

Most of these diseases look very similar clinically, and can be challenging to diagnose based on symptoms alone.

Lyme disease

Lyme Disease is an infection caused by bacteria called Borrelia bergdorferi, and is usually transmitted by the Deer tick (Ixodes scapularis).

• Symptoms of Lyme disease in DOGS may include lameness, joint pain, fever, lethargy, not eating (inappetance), occasionally redness and infection at the site of a tick bite (but not a “bullseye”), and rarely kidney involvement.
• Typical initial symptoms of Lyme disease in HUMANS include fever, headache, tiredness, and a characteristic “bullseye” skin rash around the site of a tick bite. If left untreated, Borrelia infection can spread to joints, the heart, and the nervous system.

Anaplasmosis

Anaplasmosis is caused by Anaplasma phagocytophilum or Anaplasma platus, most often transmitted by Deer ticks (Idoxes), Brown Dog ticks(Rhipicephalus sanguineus), or American Dog ticks (Dermacentor variabilis).

• DOGS with anaplasmosis often have many of the same symptoms as those with Lyme disease, and infection with both agents (co-infection) is not uncommon. Both Lyme disease and anaplasmosis are commonly found in the same geographic location and are transmitted by the same tick species.
• Infection with the more common form of anaplasmosis, A. phagocytophilum, often causes lameness, joint pain, fever, lethargy, and not eating (inappetance). Most infected dogs will have symptoms for 1 to 7 days; however, some will have no or only minor symptoms. Less common clinical signs include vomiting, diarrhea, coughing, and labored breathing. Rarely, neurological signs such as seizures have been reported.
• Infection with A. platys can cause low platelet counts, circulating cells that help in the blood clotting process. Clinical disease is often mild, but some dogs may develop bruising or bleeding (including nosebleeds), especially during the early stages of infection when platelet counts may be at their lowest.
• Symptoms of anaplasmosis in HUMANS may include fever, headache, muscle pain, chills, nausea/abdominal pain, cough, confusion, or rarely a rash.

Ehrlichiosis

Ehrlichiosis is caused by a Rickettsia type bacteria: either Ehrlichia canis, Ehrlichia chaffeensis, or Ehrlichia ewingii, and transmitted most often by Rhipicephalus sanguineus (Brown Dog tick), Dermacentor variabilis (American Dog tick), and Amblyomma americanum (Lone Star tick).

• The acute stage of Ehrlichiosis in DOGS, occurring most often in the spring and summer, begins one to three weeks after infection and lasts for two to four weeks. Depending which body system reacts most strongly to the organism, clinical signs might include fever, blood spots on the gums (petechiae), bleeding disorders, enlarged lymph nodes, discharge from the nose and eyes, joint swelling, or fluid swelling (edema) of the legs, face, scrotum, or prepuce.
• There are no outward signs of the subclinical phase. Clinical signs of the chronic phase include weight loss, pale gums due to anemia, bleeding (eg: nose bleed or bleeding from orifices) due to low platelet counts, tissue swelling, enlarged lymph nodes, breathing difficulties including coughing, drinking and urinating more than normal, lameness, eye changes including blood or cloudiness inside the eye, or mucus or pus discharge from the eyes, or neurological symptoms like a head tilt, tremors or seizures. Dogs that are severely affected can die from this disease.
• Symptoms of Ehrlichiosis in HUMANS may include fever, headache, chills, malaise, muscle pain, nausea / vomiting / diarrhea, confusion, conjunctival injection (red eyes), or rash (in up to 60% of children, less than 30% of adults)

Rocky Mountain spotted fever

Rocky Mountain spotted fever is caused by Rickettsia rickettsii, and most often transmitted by Dermacentor variabilis (American Dog tick).

• Symptoms of Rocky Mountain spotted fever in DOGS can be vague and non-specific. Typically, a dog that has become infected with Rocky Mountain Spotted Fever may have one or more of the following symptoms: poor appetite, non-specific muscle or joint pain, fever, coughing, abdominal pain, vomiting, diarrhea, swelling of the face or legs, or lethargy. Since these symptoms are non-specific, a history of tick exposure, or possible tick exposure, will help in the diagnosis of this disease.
• In severe cases where there are a lot parasites present in the body, extensive damage to blood vessels can cause necrosis (tissue death) of the extremities or ear tips.
• Symptoms of RMSF in HUMANS may include fever, headache, rash, nausea, vomiting, stomach pain, muscle pain, or lack of appetite

How are tick-transmitted diseases treated in dogs?

All four of the commonly diagnosed tick-transmitted diseases are usually treated with varying courses of the same first line antibiotic, doxycycline.

Anaplasma: Doxycycline 5-10mg/kg twice daily for 10 days
Ehrlichia: Doxycycline 5-10mg/kg twice daily for 28 days
RMSF: Doxycycline 10mg/kg twice daily for 14 days
Lyme: Doxycycline 5-10mg/kg twice daily for 28 days

Treatment of clinical tick-transmitted disease should result in resolution of symptoms within a few days.

However, resolution of clinical signs does not necessarily mean the body has been cleared of the causative organisms, and some treated dogs may remain reservoirs of tick-borne disease and remain potentially contagious to other dogs and humans through tick bites. Therefore, even dogs that are treated should be screened yearly for disease.