Signalment:  

2-year-old spayed female Boxer Dog (Canis familiaris)A 2-year-old female spayed Boxer presented to MSU CVM for chronic anemia. The referring veterinarian administered multiple blood transfusions, and initiated treatment with doxycyline, prednisone and vitamin K. On presentation, the dog was bright and alert. The mucus membranes were pale, and a grade 4/6 systolic heart murmur was auscultated. A complete blood count revealed severe anemia and mild thrombocytopenia. Serum chemistries, PT, PTT, radiographs and abdominal ultrasound were within normal limits. A direct Coombs test was positive. An echocardiogram revealed mild tricuspid regurgitation.

A blood smear was submitted for review.

Histopathologic Description:

A blood smear from a 2-year-old spayed female Boxer Dog is submitted for review. The red cell density is markedly decreased indicating a severe anemia. There is moderate polychromasia and anisocytosis suggestive of a regenerative erythroid response. Scattered Howell-Jolly bodies and metarubricytes are also observed. Small (1-2μm) signet ring-shaped organisms and larger (2-3μm) piriform-shaped organisms are seen individually within erythrocytes (Fig. 2-1). The platelets appear mildly decreased. However, moderate platelet clumping is noted. Many megaplatelets are observed suggestive of a regenerative response to platelet consumption or destruction. The leukocytes appear normal in morphology and a mild left shift is present and is suggestive of an inflammatory process.

Morphologic Diagnosis:  

Severe regenerative anemia; mild thrombocytopenia; intraerythrocytic organisms consistent with Babesia species

Lab Results:  

CBC-

DAY	1	2	3(post transfusion)
Hematocrit (34-60%)	18.5%	15.8%	30.2%
Platelet estimate	128 K/μL	48 K/μL	128 K/μL
Segmented neutrophils (3,000-11,500/ μL)	12,638/μL	NA	2,686/ μL

Chemistry no significant abnormalities
Prothrombin time 7.4 sec (5-12)
Partial Thromboplastin Time 7.8 sec (10-20)
Canine Direct Coombs test positive
Serology -
---- Babesia canis positive 1:320
---- Babesia gibsoni positive 1:640
---- Borrelia burgdorferi positive 1:640
PCR -
---- Babesia gibsoni positive for Asian genotype

Condition:  

Babesia sp.

Contributor Comment:  

Canine Babesiosis is a hemoprotozoan infection which is typically caused by Babesia gibsoni or Babesia canis. Babesia gibsoni is small (1 x 3.2μm), pleomorphic, signet ring-shaped, and is usually observed as a single organism within the erythrocyte. Babesia canis is larger (2.4 x 5μm), and is generally observed as a paired, pyriform structure within the erythrocyte. Both species have Ixodid tick vectors and are found throughout Africa, Asia, Europe, the Middle East, and North America. B. canis is typically more prevalent. However, there has been an increase in the frequency of B. gibsoni infections, particularly in North America.(1) The specific vector for B. gibsoni in the United States has not been established. Rhipicephalus sanguineus and Dermacentor variabilis are suspected as possible vectors, but transmission studies have been unsuccessful or inconclusive. 

The organisms are transmitted through the bite of an infected tick. Once inside the host, the organisms attach to the erythrocyte membrane and are endocytosed. While in the cytoplasm, the organisms undergo binary fission resulting in the formation of merozoites. Ticks become infected during feeding by ingesting merozoites. Transtadial and transovarial (B. gibsoni) transmission result in the formation of sporozoites within the ticks salivary glands. While feeding, saliva and sporozoites from the infected tick are passed into the hosts circulation. For transmission to occur, the tick must remain attached for 2-3 days.(2)

Infected dogs may present with a variety of clinical signs, ranging from hemolytic anemia to multiple-organ dysfunction syndrome (MODS). Subclinical infection is common in American pit bull terriers, which have a strong breed predilection for B. gibsoni. The predominant feature of babesiosis is hemolytic anemia. Thrombocytopenia is also quite common. The anemia is a result of both extra- and intravascular hemolysis. Parasitemia results in increased osmotic fragility, shortened erythrocyte life span, and erythrophagocytosis. The infected erythrocytes have parasite antigens on their surface, which induce opsonization by host antibodies and removal by the mononuclear-phagocyte system. The induction of serum hemolytic factors and production of antierythrocyte membrane antibodies with resulting damage from the secondary immune system also contribute to the pathogenesis of this disease. Other factors thought to be involved include oxidative damage, impaired hemoglobin function, as well as sludging and sequestration of infected erythrocytes.

Diagnosis may be made by identifying the parasite on a blood smear, serology (IFA and ELISA), or PCR which can detect low levels of parasitemia. Coinfection with other tick borne pathogens occurs relatively often as a single vector can harbor several infectious organisms.(1)

JPC Diagnosis:  

Cytological specimen, peripheral blood smear: Moderate polychromasia and anisocytosis (regenerative anemia) with intraerythrocytic organisms consistent with Babesia species

Conference Comment:  

The proposed pathogenesis of babesiosis is as follows: tick transmission → parasitized erythrocytes → hemolysis (intravascular and extravascular) → anemia (hemoglobinemia, bilirubinuria, icterus) → decreased available oxygen for cellular machinery → anaerobic metabolism → acidosis → hypoxic cell damage → shock → death. DIC is often a sequelae of terminal babesiosis.(3)

Differential diagnoses for babesiosis include parasitic, immune-mediated, oxidative, and traumatic causes of hemolytic anemia.(3) Normally, infected animals present with anemia and thrombocytopenia. The anemia starts out as a normocytic, normochromic anemia and progresses to a macrocytic, hypochromic, regenerative anemia. Serum chemistries are generally within normal limits, with hypokalemia sometimes occurring in severely affected animals.(3)

Other intra-erythrocytic parasites of veterinary importance include:

Species affected	Parasite
Dogs	Babesia canis, Babesia gibsoni
Cats	Babesia cati, Babesia felis
Cattle	Anaplasma marginale, Anaplasma centrale, Babesia bovis, Babesia bigemina, Theileria mutans, Theileria annulata
Sheep	Babesia ovis, Babesia motasi
Horses	Babesia equi, Babesia caballi
Deer, Elk	Theileria cervi
Birds	Hemoproteus spp., Leukocytozoon spp., Plasmodium spp.Â

(2)

References:

1. Boozer L, Macintire D. Babesia gibsoni: An emerging pathogen in dogs. Compendium 27(1): 33-41, 2005
2. Brockus CW, Andreasen CB: Erythrocytes. In: Duncan & Prasses Veterinary Laboratory Medicine, Clinical Pathology, eds. Latimer KS, Mahaffey EA, Prasse KW, 4th ed., pp. 19-21. Blackwell Publishing, Ames, IA, 2003
3. Taboada J, Lobetti R: Babesiosis. In: Infectious Diseases of the Dog and Cat, ed. Green CE, 3rd ed., pp 722-736. WB Saunders, St. Louis, MO. 2006

Click the slide to view.

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2-1. Peripheral blood smear, dog

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