Thrombocytopenia and nonregenerative anemia in a 5-month-old Rottweiler

Jacqueline Nunnelley College of Veterinary Medicine, Michigan State University, East Lansing, MI

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Cheryl L. Swenson Department of Pathobiology and Diagnostic Investigation, College of Veterinary Medicine, Michigan State University, East Lansing, MI
Veterinary Diagnostic Laboratory, College of Veterinary Medicine, Michigan State University, East Lansing, MI

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Nyssa Levy Department of Small Animal Clinical Sciences, College of Veterinary Medicine, Michigan State University, East Lansing, MI

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Steven Bolin Department of Pathobiology and Diagnostic Investigation, College of Veterinary Medicine, Michigan State University, East Lansing, MI
Veterinary Diagnostic Laboratory, College of Veterinary Medicine, Michigan State University, East Lansing, MI

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History

A 5-month-old sexually intact male Rottweiler was presented to the Michigan State University Veterinary Medical Center for acute abdominal discomfort and diarrhea following 3 days of lethargy and anorexia. The dog was recently imported from Siberia and fully vaccinated with no history of dietary indiscretion.

Clinical and Clinicopathologic Findings

Hyperthermia (rectal temperature, 39.7 °C; reference interval, 37.8 to 39.2°C), tachycardia (160 beats/min; reference interval, 60 to 120 beats/min), tachypnea (80 breaths/min; reference interval, 10 to 30 breaths/min), hypersalivation, and orange, liquid diarrhea were documented on physical examination. Cranial abdominal palpation elicited signs of pain, and abdominal radiography revealed an enlarged hepatic silhouette and moderate splenomegaly. A CBC revealed moderate nonregenerative anemia characterized with Hct of 23% (reference interval, 43% to 59%) and reticulocyte count of 21,800 cells/μL (reference interval, 12,000 to 76,000 cells/μL) combined with marked thrombocytopenia (26,000 cells/μL; reference interval, 180 to 366 cells/μL), monocytosis (1,400 cells/μL; reference interval, 0 to 800 cells/μL), and mild neutropenia (2,000 cells/μL; reference interval, 2,700 to 7,800 cells/μL) with a left shift (200 band neutrophils/μL; reference interval, 0 to 100 cells/μL). Serum biochemical abnormalities included mild hyperbilirubinemia (0.8 mg/dL; reference interval, 0.1 to 0.3 mg/dL), hypoproteinemia (4.9 g/dL; reference interval, 5.4 to 6.7 g/dL), hyperphosphatemia (6.8 mg/dL; reference interval, 2.7 to 5.4 g/dL), and hyponatremia (134 nmol/L; reference interval, 139 to 151 nmol/L).

Additional Clinicopathologic Findings

The modified Wright-stained blood smear had individual, paired, or multiple (4 to 8+) pleomorphic (pyriform, round, ovoid, polygonal), 2- to 6-μm-diameter, pale blue intraerythrocytic inclusions with a thin dark blue outer membrane. The round to polygonal forms commonly had an approximately 2- to 3-μm thin blue cytoplasmic projection, while pyriform-shaped inclusions infrequently contained a small, pink, round, eccentrically located dot. There also were extracellular 4- to 6-μm rounded structures with stippled blue internal material. Small numbers of intraerythrocytic and extracellular structures were present throughout the body of the blood smear while large numbers of these forms were seen along the feathered edge (Figure 1). This case underscores that microscopic review of a stained blood smear is an essential component of a CBC, as automated analyzers do not detect hemoparasites.

Figure 1
Figure 1

Photomicrograph of the feathered edge of a blood smear showing pleomorphic RBC inclusions in a sample from a 5-month-old sexually intact male Rottweiler with lethargy, anorexia, and diarrhea. Modified-Wright stain; bar = 10 μm.

Citation: Journal of the American Veterinary Medical Association 261, 11; 10.2460/javma.23.04.0202

Two PCR assays (Babesia/Theileria spp and general apicomplexan) targeting the 18S ribosomal RNA gene showed 99% to 100% homology with comparable nucleic acid sequences from Babesia canis canis (GenBank). The next closest homology was 94% to 95% with Babesia canis vogeli.

Interpretation and Case Summary

Interpretation: the morphologic appearance of the intraerythrocytic inclusions and extracellular structures were supportive for Babesia spp protozoa, with B canis canis considered most likely based on hemoparasite size and the dog’s presenting clinical signs, laboratory data, and travel history. Pending sequencing data, the dog was discharged on doxycycline, and the referring veterinarian administered imidocarb (6.6 mg/kg, SC) when the sequence data was available; however, scientific studies regarding treatment of babesiosis are sparse and poorly controlled.1

Case summary: babesiosis, supportive for B canis canis in a dog.

Comments

Babesiosis is caused by blood-borne protozoal organisms with a life cycle dependent on both invertebrate and vertebrate hosts. After inoculation into the vertebrate host, sporozoites rapidly penetrate erythrocytes, transform into trophozoites, and multiply by binary fission to produce merozoites that undergo additional divisions or become larger, variably shaped gametocytes.1 Pleomorphic organisms are most appreciable in large Babesia spp, including B canis canis, Babesia canis rossi, and B canis vogeli, and were a prominent feature of the present case. Large Babesia spp measure 2.5 to 7 μm in diameter with similar morphologies but differing vector specificity, geographic distribution, and clinical presentation. Small Babesia spp (Babesia gibsoni, Babesia conradae, and Babesia vulpes) are more challenging to discern by light microscopy at only 1.0 to 2.5 μm in diameter.1

Infection typically occurs via sporozoite transmission during tick feeding. However, other modes including vertical or horizontal merozoite spread (eg, blood transfusion/ingestion, wounds, or saliva) must be considered.1 Neonatal dogs infected with large Babesia spp typically present with severe acute babesiosis, making transplacental transmission unlikely in this case.1 Tick-borne transmission was considered probable, as this dog had been living in Siberia, where approximately 0.7% to 15% of Dermacentor reticulatus ticks reportedly are infected with B canis canis sporozoites. Moreover, B canis canis is prevalent in the European Union, and 4 genetic variants have been identified in Russia.2 Importantly, Babesia spp infection should be considered in young or immunocompromised dogs presenting with lethargy, fever, and anemia, especially those with a history of travel. Attempts were made to inform the breeder of the potential that other dogs housed in proximity may have Babesia spp infection, but it was unclear whether this information was successfully communicated due to distance and language barriers.

A wide variety of clinical signs including hypotension, fever, icterus, hematuria, lymphadenomegaly, and petechiae or epistaxis, have been described in dogs with babesiosis. Although dogs commonly present with mild to moderate nonregenerative anemia, some dogs have regenerative anemia or no anemia at diagnosis.1 Pathogenic mechanisms causing decreased infected RBC life span include asexual reproduction with intravascular hemolysis and expansion of RBC infection, increased osmotic fragility, oxidative damage, and secondary immune-mediated intra- and extravascular hemolysis.1 A systemic inflammatory response syndrome has been reported in some dogs with acute babesiosis and likely contributes to hematologic and biochemical changes, morbidity, and death.3 Notably, thrombocytopenia is reportedly the most common laboratory abnormality, found in 100% of infected dogs and considered a hallmark of B canis canis infection in Europe. Decreased platelet concentration may be due to consumptive and immune-mediated processes as well as splenic sequestration; however, evidence of hemorrhage is rare.4

Most observed laboratory abnormalities in the present case were attributed to the combination of diarrhea, dehydration, and hemolysis, similar to previous reports.1,5 The following pathophysiologic processes were supported by laboratory data: extravascular hemolysis; inflammation; and gastrointestinal protein, water, and electrolyte losses with decreased intake causing hypovolemia, which would stimulate antidiuretic hormone release causing water retention with resultant sodium dilution as well as additional contributions to decreased RBC indices.1,3,5 Decreased renal excretion, possible hemoconcentration, and the fact that this was a young, growing animal would contribute to the hyperphosphatemia.

While Babesia spp hemoparasites were easily seen at the feathered edge of the blood smear via light microscopy in this case, parasitemia at levels below the threshold of reliable visual detection has been reported in 30% of infected dogs; PCR assay is recommended to obtain a definitive diagnosis if there is a clinical suspicion of babesiosis.4 However, false negative PCR assay results are possible in dogs with minimal parasitemia. Serologic techniques such as indirect immunofluorescence antibody test and ELISA are generally ineffective when most animals develop clinical signs and are presented for veterinary care due to a 3- to 4-week lag between infection and antibody production.1 Therefore, results of confirmatory testing for babesiosis must be interpreted with caution and in the context of all relevant case information.

Acknowledgments

No third-party funding or support was received in connection with this study or the writing or publication of the manuscript. The authors declare that there were no conflicts of interest.

The authors thank Dr. Tiffany Scott, Michigan State University, for assistance with manuscript preparation.

References

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    Solano-Gallego L, Sainz Á, Roura X, Estrada-Peña A, Miró G. A review of canine babesiosis: the European perspective. Parasit Vectors. 2016;9(1):336. doi:10.1186/s13071-016-1596-0

    • Search Google Scholar
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  • 2.

    Rar VA, Maksimova TG, Zakharenko LP, Bolykhina SA, Dobrotvorsky AK, Morozova OV. Babesia DNA detection in canine blood and Dermacentor reticulatus ticks in southwestern Siberia, Russia. Vector Borne Zoonotic Dis. 2005;5(3):285287. doi:10.1089/vbz.2005.5.285

    • Search Google Scholar
    • Export Citation
  • 3.

    Zygner W, Gójska-Zygner O, Wędrychowicz H. Strong monovalent electrolyte imbalances in serum of dogs infected with Babesia canis. Ticks Tick Borne Dis. 2012;3(2):107113. doi:10.1016/j.ttbdis.2012.02.002

    • Search Google Scholar
    • Export Citation
  • 4.

    Turna H, Vichova B, Miterpakova M, Szarkova A, Baneth G, Svoboda M. Clinical and hematologic findings in Babesia canis infection in eastern Slovakia. Acta Parasitol. 2022;67(3):13291334. doi:10.1007/s11686-022-00584-8

    • Search Google Scholar
    • Export Citation
  • 5.

    Eichenberger RM, Riond B, Willi B, Hofmann-Lehmann R, Deplazes P. Prognostic markers in acute Babesia canis infections. J Vet Intern Med. 2016;30(1):174182. doi:10.1111/jvim.13822

    • Search Google Scholar
    • Export Citation
  • Figure 1

    Photomicrograph of the feathered edge of a blood smear showing pleomorphic RBC inclusions in a sample from a 5-month-old sexually intact male Rottweiler with lethargy, anorexia, and diarrhea. Modified-Wright stain; bar = 10 μm.

  • 1.

    Solano-Gallego L, Sainz Á, Roura X, Estrada-Peña A, Miró G. A review of canine babesiosis: the European perspective. Parasit Vectors. 2016;9(1):336. doi:10.1186/s13071-016-1596-0

    • Search Google Scholar
    • Export Citation
  • 2.

    Rar VA, Maksimova TG, Zakharenko LP, Bolykhina SA, Dobrotvorsky AK, Morozova OV. Babesia DNA detection in canine blood and Dermacentor reticulatus ticks in southwestern Siberia, Russia. Vector Borne Zoonotic Dis. 2005;5(3):285287. doi:10.1089/vbz.2005.5.285

    • Search Google Scholar
    • Export Citation
  • 3.

    Zygner W, Gójska-Zygner O, Wędrychowicz H. Strong monovalent electrolyte imbalances in serum of dogs infected with Babesia canis. Ticks Tick Borne Dis. 2012;3(2):107113. doi:10.1016/j.ttbdis.2012.02.002

    • Search Google Scholar
    • Export Citation
  • 4.

    Turna H, Vichova B, Miterpakova M, Szarkova A, Baneth G, Svoboda M. Clinical and hematologic findings in Babesia canis infection in eastern Slovakia. Acta Parasitol. 2022;67(3):13291334. doi:10.1007/s11686-022-00584-8

    • Search Google Scholar
    • Export Citation
  • 5.

    Eichenberger RM, Riond B, Willi B, Hofmann-Lehmann R, Deplazes P. Prognostic markers in acute Babesia canis infections. J Vet Intern Med. 2016;30(1):174182. doi:10.1111/jvim.13822

    • Search Google Scholar
    • Export Citation

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