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Babesiosis in dogs: signs, blood smear and blood work

Babesiosis is a tick-borne disease in which a parasite, Babesia, destroys the dog’s red blood cells. It can become serious within days. A simple blood smear often confirms it at the clinic, and a PCR test helps when the smear is negative.

Written by the AI DiagAnimals editorial teamReviewed by the AI DiagAnimals TeamUpdated Our editorial policy

The essentials

Babesiosis shows as fever, lethargy, poor appetite and sometimes red or rust-coloured urine, 1 to 3 weeks after a tick bite. Blood work typically shows an anemia and low platelets. The blood smear, ideally from a drop taken at the ear tip, is the first test; PCR follows a negative smear. Antibody tests are not useful in the acute phase. It is an emergency.

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A tick-borne disease

In Europe, babesiosis is mainly caused by Babesia canis, carried by the tick Dermacentor reticulatus [1, 2]. Adult ticks are most active from October to March [1], and a female tick usually needs to feed for 24 to 48 hours to transmit the parasite [2]. A survey of French clinics estimated an annual incidence of about 1% of dogs seen, up to 16% in some regions [1].

The signs

  • Fever, lethargy, loss of appetite, 1 to 3 weeks after infection [2].
  • Pale or yellow gums, vomiting [1, 2].
  • Red, dark or rust-coloured urine, a sign that red cells are being destroyed [2].
  • Swollen lymph nodes and spleen [1].

What the blood work shows

Typical findings are an anemia from red cell destruction, low platelets and sometimes low neutrophils [2]. Platelets are often low, but small bleeding spots are uncommon [1]. Bilirubin can rise, and the urine can contain hemoglobin [1, 2]. See anemia in dogs.

An annotated line from a lab report · Illustrative example
AbbreviationResultUnitLaboratory intervalFlag
PLT Platelets3810³/µL211–621L
  1. Abbreviation PLT or platelets.
  2. Result 38 × 10³/µL in this illustrative line: markedly low.
  3. Unit 10³/µL, 10⁹/L or K/µL: the same number.
  4. Laboratory interval The dog interval of the Merck Veterinary Manual; each laboratory sets its own.
  5. Flag L: below the interval. With fever during tick season, babesiosis is suspected; the smear also excludes platelet clumps. See low platelets in dogs.

Confirming babesiosis

  • The blood smear is the first test. Capillary blood from the ear tip or a nail contains more parasites [1].
  • PCR on EDTA blood is more sensitive, identifies the species and indicates an active infection. It is advised when the smear is negative [1].
  • Antibody tests are not useful in the acute phase, because antibodies appear 3 to 4 weeks after infection. A positive result only shows past or current exposure [1].

Complications

Babesiosis can be complicated by acute kidney injury, clotting disorders (DIC), jaundice, immune destruction of red cells or platelets, pancreatitis or shock [1, 2]. After treatment, improvement within 48 hours is typical with Babesia canis, but the parasite is probably never fully cleared [2]. See IMHA in dogs and kidney disease in dogs.

Related articles

En français : la piroplasmose du chien.

Questions to ask your veterinarian

  1. Does the smear show parasites? Do we need a PCR?
  2. How severe are the anemia and the low platelets?
  3. Are the kidneys, liver and bilirubin affected?
  4. When should the blood work be rechecked?
  5. Which tick prevention suits my dog, and is a vaccine useful?
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Frequently asked questions

What are the symptoms of babesiosis in dogs?

Fever, lethargy, loss of appetite, pale or yellow gums and sometimes red or rust-coloured urine [2].

Can humans catch babesiosis from dogs?

Canine Babesia species have not been reported in humans [2].

How long after a tick bite do signs appear?

Usually 1 to 3 weeks after infection [2].

Does the vaccine fully protect?

No. In Europe, a vaccine reduces the severity of the disease but does not prevent infection [1, 2].

Why can the antibody test be negative?

Because antibodies only appear 3 to 4 weeks after infection. In the acute phase, the smear and PCR are the right tests [1].

Sources

  1. Solano-Gallego L et al. A review of canine babesiosis: the European perspective. Parasit Vectors. 2016;9(1):336. doi.org/10.1186/s13071-016-1596-0
  2. ESCCAP. Guideline 05: Control of vector-borne diseases in dogs and cats, 5th edition, 2024. esccap.org/guidelines/gl5

Laboratory methods and reference intervals vary. This article explains; it does not diagnose. For a decision about your pet, use the original report and talk to your veterinarian. Our editorial policy.

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