Canine Ehrlichiosis

Oliver Organista, LA

Ehrlichiosis (also known as canine rickettsiosis, canine hemorrhagic fever, canine typhus, tracker dog disease, and tropical canine pancytopenia) is a tick-borne disease of dogs usually caused by organism Ehrlichia canis.

Ehrlichia canis was first identified in 1935 in Algeria; dogs infested with ticks showed fever and anemia [1]. Later, during the Vietnam War, many military working dogs brought to Vietnam by the US army exhibited a severe disease called Tropical Canine Pancytopenia [3]. Later, it was renamed canine monocytic ehrlichiosis (CME).

Canine monocytotropic ehrlichiosis (CME), caused by the rickettsia E. canis, is an important canine disease with a worldwide distribution. Diagnosis of the disease can be challenging because of its different phases and multiple clinical manifestations. CME should be suspected when a compatible history (living in or traveling to an endemic region, previous tick exposure), typical clinical signs and characteristic hematological and biochemical abnormalities are present [4].

German shepherd dogs are thought to be particularly affected by the disease, other breeds generally have milder clinical signs. Cats can also be infected [2]

Figure 1a. Peripheral blood smear from a dog. On the feathered edge, monocytes rarely contain cytoplasmic morula (arrow) consistent with Ehrlichia canis. Source: https://tvmdl.tamu.edu/2019/10/01/ehrlichia-canis-discovered-in-dog/. 1b. Photomicrograph of an E. canis strain isolated from the leukocytes of a dog Uberlandia, Brazil. Andia,dia, , Brazil. Note the multiple mourale in the DH82 cell cytopolasm (arrows). Source: DOI:10.4142/jvs.2014.15.2.241

Ehrlichiosis symptoms in dogs can be classified into three stages: early disease (acute phase), sub-clinical (no outward appearance of disease), and clinical or chronic (long-standing infection) [5].

Acute Phase

The acute stage of ehrlichiosis can last 2 to 4 weeks, during which the infection is either eliminated or your dog will progress to the sub-clinical phase. Symptoms of the acute stage include:

• Swollen lymph nodes
• Weight loss
• Respiratory distress
• Bleeding disorders (spontaneous hemorrhage or bleeding)
• Fever
• Neurological disturbances (meningitis or unsteady on feet)

Sub-Clinical Phase

In the sub-clinical phase, the Ehrlichia organism is present but there may not be any outward signs of disease. This is often considered the worst phase of the disease because it is able to progress undetected.

In some cases the disease is detected when the vet notices prolonged bleeding from the injection site after taking a blood sample. If the organisms are not eliminated in this stage, your pooch’s infection may move to the next stage – clinical ehrlichiosis.

Clinical Phase

Clinical ehrlichiosis happens when the organism isn’t eliminated by the immune system in one of the previous stages. This stage can lead to several serious symptoms, including:

• Lameness
• Swollen limbs
• Neurological problems
• Bleeding episodes
• Anemia
• Eye problems (such as blindness or hemorrhage into eyes)

This phase becomes extremely serious if the bone marrow (where blood cells are produced) fails, meaning that your pup will be unable to create any blood cells he needs to sustain life (platelets, white blood cells and red blood cells).

Diagnosis can be performed using visual, serologic, or molecular methods. Erhlichia spp. replicate inside a membrane-bound vacuole (i.e., morula) that can sometimes be observed by light microscopic examination of stained blood smears inside either monocytes (E. canis and E. chaffeensis) or granulocytes (E. ewingii). A cross-reactivity between antibodies is possible when performing an immunofluorescent assay (IFA) or enzyme linked immunosorbant assays (ELISA) [7]. The most common molecular method used to diagnose an Ehrlichia spp. infection, particularly in dogs with acute illness where the onset of clinical signs may precede a measurable antibody response is by polymerase chain reaction (PCR) [8].

In Canines, blood counts and hematological tests are crucial to the diagnosis of Canine monocytic ehrlichiosis. Low blood counts or thrombocytopenia are often critical signs of ehrlichial infection. In a study conducted by Shipov et. al red blood cell count and hemoglobin were used as the diagnostic indicators for canine ehrlichiosis (2008). Within the study dogs were assigned to two categories: survivors and non- survivors. Within each group the prognostic indicators and treatment protocols were observed and compared. Most commonly the dogs under examination exhibited symptoms such as weakness pale mucous membranes, fever, and bleeding tendencies [9].

Ehrlichiosis is typically treated with a 28- to 30-day course of antibiotics, most often prescribing doxycycline [11,14]. Doxycycline tablets were administered orally once a day for 20 consecutive days, at a target dose level of 10 mg/kg. The actual dose administered was calculated as ranging between 10 mg/kg and 11.7 mg/kg [12] .Most dogs in the acute or subclinical phases will not require hospitalization and can be managed as outpatients at home with minimal supportive care (pain medications and appetite stimulants). Dogs with chronic ehrlichiosis may require hospitalization for aggressive supportive care that includes blood transfusions, steroids, IV fluids, and nutritional support [10].

Minocycline can be an effective alternative to doxycycline for clearing E. canis from the blood in nonacute infections [13].

Fortunately, most tick bites can be prevented through monthly flea and tick preventative care. There are plenty of options available, including topical, tablet, and chewable medications. Your veterinarian will be able to help you find the best option for your pet.

If you live near wooded areas where ticks are prone, it is best to keep your dog away from these areas, since there currently is no vaccine for ehrlichiosis. When your dog comes back from any outdoor adventure, it’s important to inspect them for any ticks or fleas and remove them safely. Early removal of ticks is the best defense against the spread of any infection [15].

Reference

1. Donatien, A., and F. Lestoquard. “Existence en Algerie d’une Rickettsia du chien.” Bull. Soc. Pathol. Exot 28 (1935): 418-419.
2. Eddlestone, S.M., et al., Doxycycline clearance of experimentally induced chronic Ehrlichia canis infection in dogs. J Vet Intern Med, 2007. 21(6): p. 1237-42.
3. Huxsoll DL, Hildebrandt PK, Nims RM, Walker JS. Tropical canine pancytopenia. J Am Vet Med Assoc. 1970;157(11):1627–32.
4. Harrus S, Waner T. Diagnosis of canine monocytotropic ehrlichiosis (Ehrlichia canis): an overview. Vet J. 2011 Mar;187(3):292-6. doi: 10.1016/j.tvjl.2010.02.001. Epub 2010 Mar 11. PMID: 20226700.
5. Veterinary Specialty Center Tucson (www.vscot.com), Ehrlichiosis in Dogs – Treatment & Prognosis
6. Beall, M.J., Alleman, A.R., Breitschwerdt, E.B. et al. Seroprevalence of Ehrlichia canis, Ehrlichia chaffeensis and Ehrlichia ewingii in dogs in North America. Parasites Vectors 5, 29 (2012). https://doi.org/10.1186/1756-3305-5-29
7. Hegarty BC, de Paiva Diniz PP, Bradley JM, Lorentzen L, Breitschwerdt E. Clinical relevance of annual screening using a commercial enzyme-linked immunosorbent assay (SNAP 3Dx) for canine ehrlichiosis. J Am Anim Hosp Assoc. 2009;45:118–124.
8. Beall MJ, Alleman AR, Breitschwerdt EB, et al. Seroprevalence of Ehrlichia canis, Ehrlichia chaffeensis and Ehrlichia ewingii in dogs in North America. Parasit Vectors. 2012;5:29. Published 2012 Feb 8. doi:10.1186/1756-3305-5-29
9. A. Shipov, E. Klement, L. Reuveni-Tager, T. Waner, S. Harrus, Prognostic indicators for canine monocytic ehrlichiosis, Veterinary Parasitology, Volume 153, Issues 1–2, 2008 https://doi.org/10.1016/j.vetpar.2008.01.009.
10. Ehrlichiosis and Anaplasmosis, Pedro P. Vissotto de Paiva Diniz DVM, PhD;  2020, Online ISBN: 9781119501237
11. Eddlestone SM, Diniz PP, Neer TM, Gaunt SD, Corstvet R, Cho D, Hosgood G, Hegarty B, Breitschwerdt EB. Doxycycline clearance of experimentally induced chronic Ehrlichia canis infection in dogs. J Vet Intern Med. 2007 Nov-Dec;21(6):1237-42. doi: 10.1892/07-061.1.
12. Fourie JJ, Horak I, Crafford D, Erasmus HL, Botha OJ. The efficacy of a generic doxycycline tablet in the treatment of canine monocytic ehrlichiosis. J S Afr Vet Assoc. 2015 Mar 25;86(1):1193. doi: 10.4102/jsava.v86i1.1193.
13. Jenkins S, Ketzis JK, Dundas J, Scorpio D. Efficacy of Minocycline in Naturally Occurring Nonacute Ehrlichia canis Infection in Dogs. J Vet Intern Med. 2018 Jan;32(1):217-221. doi: 10.1111/jvim.14842. Epub 2017 Dec 2.
14. Nicholson, W., Allen, K., McQuiston, E. “The increasing recognition of rickettsial pathogens in dogs and people.” Trends in Parasitology. 2010 http://www.sciencedirect.com/science/article/pii/S147149221000019X

15.    Veronica Higgs, DVM, Ehrlichiosis in Dogs, PUBLISHED: MAY 09, 2022, https://www.petmd.com/dog/conditions/infectious-parasitic/c_dg_ehrlichiosi