Canine Ehrlichiosis: The Complete Guide to This Tick-Borne Infectious Disease

ImmunityDiseasesMeongsiljang Veterinary Advisory Board

Canine ehrlichiosis is a bacterial blood disease transmitted through tick bites. It causes symptoms such as fever, bleeding, and anemia, making early diagnosis and long-term antibiotic treatment essential.

What Is Canine Ehrlichiosis?

A lethargic puppy lying on the examination table

Canine ehrlichiosis is a tick-borne infectious disease caused by the bacterium Ehrlichia, which infects white blood cells in the bloodstream after a bite from a tick. Early detection is key. If symptoms such as fever, loss of appetite, or nosebleeds appear within 1–3 weeks after a tick bite, seek veterinary care immediately. If the disease progresses to the chronic stage, bone marrow function can become severely compromised, making treatment much more difficult.

Causes and Transmission Routes

The primary causative agent is Ehrlichia canis, which is transmitted by the brown dog tick (*Rhipicephalus sanguineus*). As the tick attaches to your dog’s skin and feeds on blood, it introduces the bacteria into the bloodstream through its saliva. Once inside, the bacteria multiply within white blood cells such as monocytes, forming clusters called morulae, before spreading throughout the body. The incubation period is typically 2–3 weeks (approximately 15–18 days), and bacterial levels can rise even before symptoms appear. In Korea, the risk of exposure increases during the tick-active season from spring to autumn, making prevention and close monitoring especially important during these months.

Symptoms to Watch For

Symptoms of ehrlichiosis vary depending on the stage of the disease. If your pet shows two or more of the following signs, it’s a good idea to have them undergo a blood test.

Fever: Recurrent fever and reluctance to move

Nosebleeds or gum bleeding: Petechiae or purpura may appear due to low platelet count

Lethargy: Refusal to go for walks and lying down all day

Loss of appetite: Even their favorite food is turned down

Swollen lymph nodes: Lymph nodes under the jaw and in the armpits become noticeably enlarged, and the spleen may also swell

Weight loss: As loss of appetite continues, noticeable weight loss may occur over a few weeks

A veterinarian checking a puppy's gum color.

Emergency Signs Requiring Immediate Veterinary Care

If your pet’s nosebleed won’t stop, if you notice blood in their urine or stool, or if their gums turn pale, take them to a 24-hour emergency animal hospital immediately. In chronic ehrlichiosis, bone marrow suppression can lead to pancytopenia, which may require blood transfusions. If your pet has a history of tick bites, be sure to inform your veterinarian, as this will significantly influence the diagnostic approach.

How Is It Diagnosed?

Ehrlichiosis is confirmed through a combination of diagnostic tests. Relying solely on a basic blood test can lead to missed diagnoses in the early stages.

CBC (Complete Blood Count): Checks for non-regenerative anemia, thrombocytopenia, and changes in white blood cell counts.

Serology (IFA/ELISA): Detects Ehrlichia antibodies. Results typically turn positive 2–3 weeks after infection, once seroconversion has occurred.

PCR Test: Directly detects bacterial DNA, making it especially useful for early diagnosis before antibodies develop. However, results may be negative in the chronic stage.

Blood Smear: Examines for morulae (bacterial clusters) within white blood cells (monocytes).

Veterinary internal medicine textbooks recommend using serology or PCR tests in conjunction with clinical signs and abnormal blood findings for accurate diagnosis.

Treatment Protocol

The cornerstone of treatment is consistent administration of doxycycline-class antibiotics for at least 28 days. Stopping the medication midway, even if symptoms have resolved, can lead to relapse. In severe or chronic cases, additional therapies such as blood transfusions, immunosuppressants, and supportive fluid therapy may be necessary. Your veterinarian will determine the dosage schedule and duration based on your pet’s weight and stage of infection, so please do not adjust the medication on your own.

A puppy taking medicine in its owner's arms

Comparison of Ehrlichiosis Stages

Item	Acute Phase	Asymptomatic Phase	Chronic Phase
Onset Timing	1–3 weeks after infection	1–4 months after infection	Several months to years after infection
Main Symptoms	Fever · loss of appetite · lymph node swelling	No outward symptoms	Bleeding · anemia · weight loss
Treatment Response	Good	Very good	Limited
Prognosis	Good	Good	Owner management is important

Treatment difficulty rises as the stage progresses, so early detection is important

Home Care Guidelines

During treatment, avoid strenuous exercise and administer medication at the prescribed times. Doxycycline can irritate the stomach if given on an empty stomach, so it’s best to give it with a small amount of food. Focus on maintaining your pet’s weight with a high-protein, high-calorie recovery diet, and schedule blood tests every two weeks to monitor platelet counts and liver enzyme levels. Since reinfection is common, continue using tick preventatives throughout the treatment period.

Breed-Specific Precautions — Shetland Sheepdogs and Collie Breeds

Certain breeds, such as Collies, Shetland Sheepdogs, and Australian Shepherds, may carry a genetic mutation that increases their sensitivity to certain medications. As a result, high doses of ivermectin-based tick preventives can cause adverse reactions. For these breeds, topical preventives containing fluralaner, afoxolaner (isoxazoline class), or fipronil are generally safer options. Always consult with your veterinarian before selecting a preventive treatment.

Prevention Is Key — Tick Management Principles

Since there is no vaccine for ehrlichiosis, preventing tick bites is the only way to protect your pet. Veterinary dermatology textbooks emphasize year-round prevention.

Monthly topical treatments: Ingredients like fipronil and fluralaner block ticks before they can feed.

Tick collars: Containing deltamethrin, these provide a repellent effect.

Full-body checks after walks: Carefully inspect ears, between the toes, and the groin area.

Avoid tall grass: Steer clear of grassy areas during early mornings and evenings from spring through autumn.

Indoor environment management: Wash your dog’s bedding at high temperatures once a week.

A pet owner carefully checking their dog’s fur after a walk

Reviewed by a veterinarian

Dr. Tony — Punnawat Phongkittirak

Veterinarian

A veterinarian who majored in veterinary medicine at Khon Kaen University, Thailand, and completed the IVSA program at North Carolina State University in the United States. Drawing on clinical experience at animal hospitals, he works in the pet healthcare field and is dedicated to building a digital care environment that connects pet parents with veterinarians.

Frequently Asked Questions

Can Ehrlichiosis be transmitted to humans?

Ticks don’t directly transmit from dogs to humans. However, since humans can also become infected if bitten by the same ticks, it’s a good idea to treat the surrounding environment as well when ticks are found on your dog.

Will my pet develop lifelong immunity after being fully cured?

No, immunity doesn’t last long, so reinfection is possible. Even after treatment is complete, you should continue using tick preventive medication consistently.

I found a tick on my pet. Can I just pull it out right away?

Using tweezers or a tick removal tool, grasp the tick as close to the skin as possible and pull it straight out slowly and steadily. Avoid twisting or crushing the tick, as this can force more bacteria into the bite site. After removal, disinfect the area and monitor for any abnormal symptoms over the next two to three weeks.

Can a single blood test provide a definitive diagnosis?

In the early stages, antibodies may not have formed yet, so the test could come back negative. If symptoms persist, it’s best to retest in 2–3 weeks or add a PCR test for more accurate results.

Can cats get ehrlichiosis?

While extremely rare, there have been reported cases. The incidence is much lower in cats than in dogs, and the symptoms and treatment principles are similar. However, cats are toxic to pyrethroid-based flea and tick medications, so you must never share dog medication with your cat.

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References

[1] Principles and Practices of Canine and Feline Clinical Parasitic Diseases, Chapter 13 — Tick-Borne Diseases

[2] BSAVA Manual of Canine and Feline Dermatology, 4th Ed — Tick Control and Prevention

[3] Shoorijeh S.J. et al., Seasonal frequency of ectoparasite infestation in dogs, Turkish Journal of Veterinary and Animal Sciences 32(4): 309–313, 2008

[4] 수의내과학 교과서 — 감염성 혈액 질환 챕터