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Anaplasmosis in dogs: low platelets, PCR and antibody tests

Anaplasmosis is a tick-borne bacterial infection of the blood cells. A sick dog usually has a sudden fever and is tired and off its food, sometimes lame. The blood count gives the strongest clue, and the right test depends on how long the dog has been ill.

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

The essentials

Two species infect dogs: Anaplasma phagocytophilum lives inside neutrophils, Anaplasma platys inside platelets. Low platelets are the most common blood finding, seen in 86% of 63 sick dogs in one study. Bacteria (morulae) are not always visible on the smear. Early in the illness, PCR is the best test, because antibodies can still be missing. Most treated dogs recover, and platelets usually come back within about a week.

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Two Anaplasma species, two blood cells

Anaplasma phagocytophilum infects neutrophils and eosinophils, two types of white blood cell. It is spread by Ixodes ticks, the same ticks that carry Lyme disease [1, 6]. In Europe, the only known vector is Ixodes ricinus, and infections are reported mainly in northern and central Europe [5].

Anaplasma platys infects platelets and causes "infectious cyclic thrombocytopenia": the platelet count drops, recovers and drops again every 1 to 2 weeks [5, 6]. It is found especially around the Mediterranean, and its probable vector is the brown dog tick, Rhipicephalus sanguineus [5].

Signs start 1 to 2 weeks after infection [5]. Many dogs never get sick: there are far more healthy dogs with antibodies than dogs with the disease [5]. For the bigger picture, see tick-borne diseases in dogs.

Signs: fever, lethargy, lameness

  • Lethargy and reduced activity in 83% of 63 infected dogs, fever in 67% and poor appetite in 63% [4].
  • Lameness with swollen joints can come from an immune reaction in the joints (polyarthritis) [5, 6].
  • Bleeding signs such as small red spots on the gums, nosebleeds or black stools may occur [5].
  • A large spleen on X-ray or ultrasound is very common [2, 5].
  • Season: in a US study of 34 dogs, most were seen in May–June or October–November [3].

A. platys infection has been linked to fever, lethargy, weight loss, pale gums, small red spots and swollen lymph nodes, although some studies did not rule out other tick-borne infections [5].

What the blood count and chemistry show

Figures from dogs with confirmed A. phagocytophilum infection. With A. platys, the main finding is cyclic low platelets [5, 6].
TestTypical findingWhat it means
PlateletsLow, usually mild to moderate: about 90% of infected dogs [6]; 86% in 63 dogs [4]; 21 of 22 tested dogs [3]The most common finding in anaplasmosis [5]. It can be partly immune-mediated [2, 6].
Lymphocytes and neutrophilsLow lymphocytes; neutrophils low, normal or high [2, 5, 6]Part of the white cell response. See white blood cell count.
Red cellsMild, non-regenerative anemia [5, 6]; anemia in 70% of 63 dogs [4]An immune-mediated hemolytic anemia can occasionally be triggered [4, 5].
Albumin and globulinsLow albumin (62% of 63 dogs), sometimes high globulins [4, 6]Inflammation and immune stimulation [6].
Liver valuesHigh ALP; liver enzymes or bilirubin up in 77% of 63 dogs [4, 6]A high ALP may reflect stress hormones released during the illness [6].

More on the causes and next steps: low platelets in dogs.

How to read the platelet line

Here is an example from a dog with a sudden fever after a walk in the woods.

An annotated line from a lab report · Illustrative example
AbbreviationResultUnitLaboratory intervalFlag
PLT Platelets7210³/µL148–484L
  1. Abbreviation PLT or platelets.
  2. Result 72 × 10³/µL in this illustrative line: moderately low, the typical range for anaplasmosis [6].
  3. Unit 10³/µL, 10⁹/L or K/µL: the same number in all three.
  4. Laboratory interval An illustrative dog interval; each laboratory sets its own.
  5. Flag L: below the interval. With fever and tick exposure, vets think of anaplasmosis. On the smear, clumps of platelet granules can mimic A. platys morulae [6].

Which test, and when

  • Blood smear: morulae (small clusters of bacteria) in neutrophils are seen in up to 60% of clinical cases [5]. Other studies range from 36 to 100%, sometimes in very few cells, so a normal smear does not rule it out [6]. In platelets (A. platys), the smear has low sensitivity [5].
  • PCR detects the bacteria’s DNA in an EDTA blood sample. In experimental studies, it turns positive about a week before morulae appear [6]. A negative PCR means "not detected", not "free of infection" [5].
  • Antibody tests: antibodies appear about 8 days after infection [5, 7]. Early on, a dog can test negative: 6 of 18 sick dogs in a Berlin study were seronegative [2].
  • In-clinic tests (4Dx): detect antibodies to Anaplasma species. A. platys antibodies cross-react with the A. phagocytophilum test spot, so the result does not tell the two apart [6, 7]. A newer version has separate results, with a sensitivity of 93% for A. phagocytophilum and 89% for A. platys [8].
  • Paired tests 2 to 4 weeks apart: a rise in antibodies (seroconversion) confirms a recent infection [5]. A single positive result can reflect a past infection [5].

Because Lyme bacteria (Borrelia) and A. phagocytophilum share the same tick, co-infections are frequent and may make each other worse [1, 5]. Antibodies to more than one infection were found in 354 of 1,195 samples tested with an in-clinic test [8]. See Lyme disease in dogs and ehrlichiosis in dogs, another cause of low platelets.

Outlook

The outlook is good with the right diagnosis and treatment, usually an antibiotic of the tetracycline family chosen by your vet [2, 6]. In a US study, fever and signs resolved within 3 to 5 days, and platelets returned to normal in a median of 7 days [3]. In Berlin, 59 of 63 dogs (97%) recovered; 2 died, one of them from an immune-mediated anemia [4].

After treatment, PCR and smear were negative in 14 tested dogs 2 to 8 weeks later [2]. Antibodies can remain positive for up to a year, so a positive test later on does not mean the disease is back [5]. It is not known whether a past infection protects against a new one, so tick control remains important [5].

Related articles

Tick-borne diseases in dogs

Lyme, Anaplasma and Ehrlichia: the overview.

Read the article

White blood cell count in dogs

Lymphocytes and neutrophils explained.

Read the article

When low platelets persist, vets also consider immune thrombocytopenia (ITP).

En français : l’anaplasmose du chien.

Questions to ask your veterinarian

  1. How low are the platelets, and was the count checked on a smear?
  2. Were morulae seen in the neutrophils or platelets?
  3. Should we run a PCR now, since antibodies may not have appeared yet?
  4. Is my dog also positive for Lyme or Ehrlichia?
  5. When should we recheck the blood count?
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Frequently asked questions

What is the difference between Lyme disease and anaplasmosis in dogs?

Both are spread by the same Ixodes tick, and dogs can have both [5]. Lyme disease (Borrelia) typically causes lameness with swollen joints, and most exposed dogs never get sick [9]. Anaplasmosis mainly causes a sudden fever and lethargy, with low platelets on the blood count [4, 6].

Is anaplasmosis in dogs contagious to humans?

People can get A. phagocytophilum, but from a tick bite, not directly from the dog. Infected ticks on a dog’s coat can reach people, and blood from an infected dog should be handled with care [5].

Does anaplasmosis ever go away?

In most dogs, yes. In one study, 97% of 63 dogs recovered [4], and in another, PCR was negative 2 to 8 weeks after treatment began [2]. Antibodies can stay positive for up to a year [5].

Is Anaplasma worse than Lyme?

No study compares them directly. Most dogs exposed to either never get sick [5, 9]. Sick dogs with anaplasmosis usually improve within days of treatment [3].

How long do platelets take to recover?

In a study of 34 dogs, the platelet count returned to normal in a median of 7 days after treatment started [3].

Sources

  1. Carrade DD et al. Canine granulocytic anaplasmosis: a review. J Vet Intern Med. 2009;23(6):1129-1141. doi.org/10.1111/j.1939-1676.2009.0384.x
  2. Kohn B et al. Clinical features of canine granulocytic anaplasmosis in 18 naturally infected dogs. J Vet Intern Med. 2008;22(6):1289-1295. doi.org/10.1111/j.1939-1676.2008.0180.x
  3. Granick JL et al. Anaplasma phagocytophilum infection in dogs: 34 cases (2000-2007). J Am Vet Med Assoc. 2009;234(12):1559-1565. doi.org/10.2460/javma.234.12.1559
  4. Chirek A et al. Granulocytic anaplasmosis in 63 dogs: clinical signs, laboratory results, therapy and course of disease. J Small Anim Pract. 2018;59(2):112-120. doi.org/10.1111/jsap.12787
  5. Sainz Á et al. Guideline for veterinary practitioners on canine ehrlichiosis and anaplasmosis in Europe. Parasit Vectors. 2015;8:75. doi.org/10.1186/s13071-015-0649-0
  6. eClinPath, Cornell University College of Veterinary Medicine. Anaplasma. eclinpath.com/hematology/infectious-agents/anasplasma
  7. Chandrashekar R et al. Performance of a commercially available in-clinic ELISA for the detection of antibodies against Anaplasma phagocytophilum, Ehrlichia canis, and Borrelia burgdorferi and Dirofilaria immitis antigen in dogs. Am J Vet Res. 2010;71(12):1443-1450. doi.org/10.2460/ajvr.71.12.1443
  8. Stillman BA et al. Performance of a commercially available in-clinic ELISA for detection of antibodies against Anaplasma phagocytophilum, Anaplasma platys, Borrelia burgdorferi, Ehrlichia canis, and Ehrlichia ewingii and Dirofilaria immitis antigen in dogs. J Am Vet Med Assoc. 2014;245(1):80-86. doi.org/10.2460/javma.245.1.80
  9. Littman MP et al. ACVIM consensus update on Lyme borreliosis in dogs and cats. J Vet Intern Med. 2018;32(3):887-903. doi.org/10.1111/jvim.15085

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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