Ehrlichiosis (Canine)

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Canine ehrlichiosis is an acute to chronic infectious disease that is transmitted to dogs by ticks. Ehrlichiosis can affect multiple organ systems and present with a variety of clinical signs.

Common name: Canine hemorrhagic fever, Tropical canine pancytopenia, Canine typhus
Scientific name:Ehrlichiosis, Ehrlichia canis (Canine moncytotropic ehrlichiosis), Ehrlichia ewingi (Canine granulocytotropic ehrlichiosis)

Diagnosis

Signalment
There is no age or sex predilection. German shepherd dogs are more susceptible than other breeds and have more severe disease and a poorer prognosis.

Incidence/prevalence
The exact incidence and prevalence of canine ehrlichiosis is not known because of the existence of chronic, subclinical carriers. The prevalence is dependent on the distribution of the tick vector, which is located primarily in the Southeast and Southwest regions of the United States.

Geographic distribution
Ehrlichia canis: worldwide distribution, including Asia, Africa, Europe, and the Americas, most common in the southwest and Gulf Coast areas of the United States. Ehrlichia ewingi: southern and southeastern United States.

Clinical signs (primarymost to least frequent, scientific term, synonyms)
The following is for E. canis: Fever, Depression, Bleeding disorders, Weight loss, Anorexia, Enlarged lymph nodes, Enlarged spleen, Nervous system signs (seizures, stupor, ataxia, tremors, hyperesthesia (increased sensitivity to touch), Ocular disease (hyphema (blood in the eye), retinal disease, corneal edema, uveitis), Lameness with a stiff gait. The following is for E. ewingi: Fever, Depression, Lethargy, Lameness, Neurologic signs.

Clinical signs (secondarymost to least frequent, scientific term, synonyms)
Secondary infections by opportunistic bacteria, Arthritis, Kidney disease (glomerulitis), Pneumonia.

Causes (scientific, common term)
Ehrlichia canis is transmitted by Rhipicephalus sanguineus (brown dog tick), Ehrlichia ewingi is transmitted by Amblyomma americanum (deer tick).

Organ system affected (most to least affected)
Blood, blood vessels, and bone marrow, Spleen, Lymph nodes, Liver, Central nervous system, Eyes, Kidney, Musculoskeletal.

Diagnostic tests
Indirect fluorescent antibody test, PCR (polymerase chain reaction), Cytology of blood, joint fluid, lymph node aspirate, Western immunoblotting.

Differential Diagnosis
Other tick-borne diseases (Rocky Mountain spotted fever, Lyme disease), Lymphoma (*The differentials will vary depending on the presenting clinical sign or signs.)

Overview

Canine ehrlichiosis is a disease caused by several Ehrlichia species of bacteria, most commonly E. canis and E. ewingi that infect white blood cells. The disease is transmitted by ticks, usually the brown dog tick, Rhipicephalus sanguineus, and is seen primarily in the United States in the Southwest and Gulf Coast. Ehrlichiosis affects many organs and causes a wide variety of symptoms such as fever, weight loss, hemorrhage, and ocular or nervous system disease. The severity of the disease varies based on the strain of Ehrlichia and the presence of other health problems in the affected dog. The severity of the disease, as well as the symptoms seen, also depends on the phase of ehrlichiosis ‚Äì acute, subacute, or chronic. If infection with Ehrlichia is suspected, several diagnostic tests are available, including an antibody titer and PCR (polymerase chain reaction). Treatment includes supportive care as needed for the variety of symptoms that can occur as well as antibiotic therapy. It is not known whether the infection is cleared by treatment. Dogs are monitored for improvement of clinical signs and laboratory values. Tick prevention is of primary importance to protect dogs from this disease, especially in endemic areas.

Treatment

Home Care
Tick prevention should be implemented in tick-infested areas, and both the dog and the environment should be addressed. A veterinarian can provide recommendations for appropriate tick prevention. Part of tick prevention is frequently checking the dog for ticks to attempt to remove them before transmission of Ehrlichia takes place, although it is not known how long a tick must be attached to transmit the disease.

Professional Care
The veterinarian will likely start a dog infected with Ehrlichia on several weeks of antibiotics, while providing supportive care and treating the secondary signs caused by ehrlichiosis. Blood work may be assessed before treatment and rechecked after treatment to look for improvement. In endemic areas, some vets may regularly screen healthy dogs with an indirect fluorescent antibody test; however, the treatment of healthy dogs based on a positive fluorescent antibody test is controversial.

Action
The clinical signs associated with ehrlichiosis are not specific to the disease, thus veterinary advice should be sought whenever one's dog is acting unusual or has any signs of ill-health. The veterinarian should be informed if the dog has traveled, especially if to an endemic area for ticks, or if the owner has noticed ticks on the dog.

Outcome
Most dogs experience clinical improvement 24 to 48 hours after beginning antibiotic therapy. Treatment of acute ehrlichiosis carries a good prognosis, whereas the chronic phase has a more variable to guarded prognosis. Dogs that recover from ehrlichiosis are not protected from re-infection, and it is not known if the infection is ever really cleared even when symptoms are resolved.

References/Additional Readings
Breitschwerdt, Edward B. Obligate Intracellular Bacterial Pathogens. In: Ettinger, Stephen J. and Feldman, Edward C., ed. Textbook of Veterinary Internal Medicine: St. Louis: Elsevier, Inc., 2005; 632-634.

Greig, Barbara, Breitshwerdt, Edward B., and Armstrong, P. Jane. Canine Granulocytotropic Ehrlichiosis (E. ewingii Infection). In: Greene, Craig E., ed. Infectious Diseases of the Dog and Cat. St. Louis: Elsevier, Inc., 2006; 217-219.

Lappin, Michael R. Infectious Diseases. In Nelson, Richard W. and Couto, C. Guillermo, ed. Small Animal Internal Medicine. St. Louis: Mosby, Inc., 2003; 1270-1267.

Neer, Mark T. and Harrus, Shirmon. Canine Monocytotropic Ehrlichiosis and Neorickettsiosis (E. canis, E., chaffensis, E. ruminatium, N. sennetsu, and N. risticii Infections). In: Greene, Craig E., ed. Infectious Diseases of the Dog and Cat. St. Louis: Elsevier, Inc., 2006; 209-216.

Author
Rachel DeBender, DVM

Editor
Sharon Gwaltney-Brant, DVM, PhD
DABVT, DABT

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