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Key takeaways

Canine ehrlichiosis, also known as hemorrhagic fever, is an infectious tick-borne illness that affects a dog’s blood cells.

  • Ehrlichiosis is caused by Ehrlichia bacteria and is transmitted via the bite of an infected tick
  • Common symptoms of ehrlichiosis include fever, lethargy, anemia, and weight loss
  • There are three stages of ehrlichiosis: acute, subclinical, and chronic phases
  • Initiating medical treatment prior to the chronic phase increases the chances of survival
  • Diagnosis requires specialized blood testing
  • Treatment involves a month-long antibiotic course
  • In some cases, blood transfusions are also required
  • Prognosis depends on how soon treatment is initiated; outcomes worsen as the disease progresses
  • Prevention of tick-borne diseases includes the immediate removal of ticks, the use of veterinarian-approved tick prevention products, and environmental controls to reduce exposure to ticks
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A closer look: Ehrlichiosis in Dogs

Ehrlichiosis is divided into three phases:

Acute phase: occurs 1 to 3 weeks after the infected tick bite. During the acute phase the animal starts to present symptoms:

  • Lethargy
  • Decreased appetite
  • Enlarged lymph nodes

In the first phase of infection, ehrlichiosis is rarely life-threatening.

Subclinical phase: If the animal receives no treatment during the acute phase, after 1 to 4 weeks it will enter the subclinical phase. During this second phase, the dog does not present any clinical signs.

Chronic phase: The chronic stage is the most dangerous stage of infection. During this stage the condition becomes life-threatening. Symptoms during the chronic phase result from:

  • Severe red blood cell destruction
  • Renal failure
  • Meningitis
  • Inflammation of the eyes

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Risk factors

Dogs living in suburban and rural areas are more likely to be exposed to ticks in general. Infections in North America are most common during spring and summer in the south central and southeastern US.

As ehrlichiosis becomes life-threatening once it reaches the chronic stage, early identification of infected dogs is essential. Routine screening of asymptomatic dogs for ehrlichiosis is common in endemic areas, often performed along with an annual heartworm test.

The chronic phase of ehrlichiosis caused by E. canis can develop in any breed, but german shepherds seem to be predisposed.

Ehrlichiosis is a potentially life-threatening condition in humans, especially for older or immune deficient patients. Ehrlichiosis is not spread directly from dog to human, but if a dog is diagnosed with Ehrlichiosis, the human might have been exposed (and vice versa).

Possible causes

The most common cause of ehrlichiosis is the Ehrlichia canis bacteria. E. canis is transmitted by the brown tick. The E. Canis bacteria is endemic to the southern US states.

Several other disease-causing Ehrlichia bacteria are transmitted by other kinds of ticks:

  • E. ewingii and E. chaffeensis are transmitted by the lone star tick, common thought the United States, especially in the South
  • E. muris eauclairensis is transmitted by the black-legged tick, common throughout the United States

Main symptoms

Many infected dogs remain asymptomatic. Dogs that develop symptoms usually do so 1 to 3 weeks after the bite of the infected tick.

Ehrlichia canis infection is also associated with eye symptoms and conditions.

Testing and diagnosis

Ehrlichiosis is diagnosed using specialized blood tests specifically for identifying this type of infection.

Steps to Recovery

Treatment strategies include:

  • Antibiotics
  • Blood transfusions: If enough red blood cells are damaged to cause life-threatening anemia, blood transfusions support recovery

Dogs in the acute or subclinical stage generally have a good prognosis. Dogs in the chronic stage have a very poor prognosis and a high mortality rate. **If left untreated, chronic ehrlichiosis has a very high mortality rate. **


Ehrlichiosis is not contagious, but ticks can transmit the bacteria to any animal they are attached to, including humans. External parasite control is the most useful prevention against ehrlichiosis and all tick-borne illnesses.

In addition to keeping up with vet-prescribed external parasite control medication schedules, general strategies to prevent tick-borne illnesses include:

  • Immediate removal of ticks when discovered
  • Daily inspection of exposed animals
  • Keeping dogs away from tick-prone areas
  • Reducing tick habitat, such as long grasses and shrubs in the dog’s living environment

Note: always consult a veterinarian before selecting external parasite control for pets and ensure treating vet staff are aware of any other animals or children in the home. Many available over the counter medications are toxic, especially to cats.

Is Ehrlichiosis in Dogs common?

Dogs living in rural areas are more likely to have contact with Ehrlichia canis infected ticks. Ehrlichiosis is common in endemic areas.

Typical Treatment

  • Antibiotics
  • Blood transfusion


- Writing for Centers for Disease Control and Prevention
Jenna R. Gettings,Stella C. W. Self,Christopher S. McMahan,D. Andrew Brown,Shila K. Nordone & Michael J. Yabsley - Writing for Parasites and Vectors
Becky Lundgren, DVM; Jacqueline Brister, DVM - Writing for Veterinary Partner
Wendy Brooks, DVM, DABVP - Writing for Veterinary Partner
- Writing for Cornell University of Veterinary Medicine
Jennifer H. McQuiston, DVM, MS - Writing for Merck Veterinary Manual
Janet E. Foley, DVM, PhD - Writing for Merck Veterinary Manual
- Writing for Companion Animal Parasite Council

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