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Mycoplasma haemofelis in cats: anemia, blood smear and PCR

Mycoplasma haemofelis is a tiny bacterium that sticks to the surface of a cat’s red blood cells. It was once called Haemobartonella felis, and the disease it causes is known as feline infectious anemia. The blood count shows the anemia; a PCR test on blood confirms the infection and names the species.

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

The essentials

Three main haemoplasmas infect cats. Mycoplasma haemofelis is the one most likely to cause disease, sometimes a severe anemia; the two others rarely do unless the cat has another illness. The anemia is usually regenerative, with large red cells and reticulocytes. Looking for the organisms on a blood smear misses most infections and gives false positives, so PCR on EDTA blood, taken before antibiotics, is the test of choice. Many cats stay carriers after treatment. With prompt treatment the outlook is generally good, but severe cases can be fatal.

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Three species, not equally harmful

All three can be carried without any signs [2]. Up to 10% of healthy cats are infected at any time, so a positive test does not by itself prove that the bacterium is the cause of a cat’s illness [3].

Figures vary widely because studies tested very different groups of cats, healthy or sick, owned or stray [1].
SpeciesHow often foundWhat it does
Mycoplasma haemofelis0.4–27.0% of cats tested by PCR [1]The most pathogenic: can cause anemia in otherwise healthy cats, sometimes severe or fatal [1].
‘Candidatus Mycoplasma haemominutum’The most common: 4.4–46.7% [1]Anemia is uncommon unless the cat has another problem, such as FeLV, chemotherapy or immune suppression [1].
‘Candidatus Mycoplasma turicensis’0–26.0% [1]Anemia is uncommon; other diseases and immune suppression seem to play a role [1].

What the blood work shows

  • Red cells (PCV or hematocrit): low. The anemia is typically regenerative, macrocytic (large red cells) and hypochromic, although some cats show little or no regeneration [1, 3]. See anemia in cats.
  • Reticulocytes and MCV: in a US study of 310 cats, those infected with M. haemofelis had higher reticulocyte counts, more nucleated red cells and a higher MCV than uninfected cats [5].
  • Coombs test and agglutination: red cells coated with antibodies can make the Coombs test positive or cause clumping. In infected cats these antibodies appear after the anemia starts and go away with antibiotics and supportive care alone [1, 6].
  • White cells and platelets: low lymphocytes or eosinophils, more monocytes, or mildly low platelets can be seen; their meaning is unclear [1].
  • Chemistry: bilirubin is occasionally high from red cell breakdown, ALT can rise when the liver lacks oxygen, and globulins can be high or albumin low [1, 3]. See high liver enzymes in cats.

Dehydration concentrates the blood and can hide how severe the anemia really is, so the count is checked again once the cat is rehydrated [3]. For the whole panel, see cat blood work explained.

How to read the hematocrit line

Here is an example line, taken from a published case of a young outdoor male cat with M. haemofelis [3].

An annotated line from a lab report · Illustrative example
AbbreviationResultUnitLaboratory intervalFlag
PCV Packed cell volume (hematocrit)16%25–45L
  1. Abbreviation PCV, HCT or Ht: the share of the blood made of red cells.
  2. Result 16% in this case: a moderate anemia [3].
  3. Unit Percent; some machines print a fraction (0.16 L/L).
  4. Laboratory interval 25–45% was the reference range in this case; each laboratory sets its own [3].
  5. Flag L: below the interval. The reticulocyte count tells whether the marrow is answering: here 380 ×10⁹/L aggregate reticulocytes (380,000/µL), a strong regeneration that points to red cells being destroyed or lost [3].

How the infection is confirmed

  • Blood smear: the organisms can be seen as small dots on red cells, but only when very many are present. Sensitivity was just 0–37.5% in studies, and ‘Ca. M. turicensis’ has never been seen on a smear [1].
  • Smear pitfalls: stain precipitate, Howell-Jolly bodies and artefacts from slow drying are common causes of false positives, and a smear cannot tell the species apart [1, 3].
  • PCR on EDTA blood: the diagnostic method of choice. It is far more sensitive and specific than the smear, and species-specific assays name each species and detect co-infections [1, 11].
  • Timing: blood for PCR should be taken before antibiotics, because effective treatment can make organism numbers fall within days. Numbers of M. haemofelis can also swing widely on their own over a few days [1, 3].
  • Coombs test: a positive result is also seen in primary immune-mediated hemolytic anemia, which vets consider when the diagnosis is uncertain or the cat does not respond to antibiotics [1, 3]. For how the Coombs test works, see IMHA in dogs.

Vets also test for FeLV and FIV, since retrovirus infection is a risk factor in many studies [1, 5].

Which cats get it, and how it spreads

Male cats with outdoor access are infected more often in many studies, and older age is sometimes a risk factor [1, 4]. In Japan, fight wounds and FIV infection were risk factors among 1,770 outdoor cats [10]. FeLV or FIV infection was linked to M. haemofelis in a US study [5].

How cats catch it naturally is still not known. Fighting may pass infected blood, especially from cats with many organisms in their blood [1]. Fleas were long suspected, but a 2024 reinvestigation suggests that fleas are unlikely to play a significant role [1]. Transmission by blood transfusion is proven, so blood donors are screened by PCR [1, 4].

Indoor-only cats can still be infected: among 4,880 healthy indoor blood-donor cats in Spain and Portugal, 3.7% carried a haemoplasma [1]. Carrier cats can stay free of signs for a long time, and the infection can reactivate later [1, 7].

Carriers and outlook

Haemoplasmosis generally has a good outlook when treatment starts promptly, but mortality can be high in severe disease [1]. Acute cases often improve within 24 hours of antibiotics and fluids [3]. In a Turkish study of 25 sick cats with M. haemofelis, 14 (56%) survived [8]. In 22 anemic cats followed in Germany, the infection was often chronic, could reactivate months later and was rarely the reason for euthanasia [7].

Treatment improves the anemia but often does not clear the bacterium, and cats usually stay PCR positive while they are carriers [1, 3]. Carriers that show no signs are not generally treated [1]. There is no vaccine [1].

Related articles

Other causes of red-cell destruction: hemolytic anemia in cats.

En français : hémobartonellose du chat.

Questions to ask your veterinarian

  1. How low is the PCV, and is the anemia regenerative?
  2. What does the reticulocyte count show?
  3. Was a haemoplasma PCR sent before antibiotics, and which species was found?
  4. Has my cat been tested for FeLV and FIV?
  5. When should the blood count, and possibly the PCR, be checked again?
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Frequently asked questions

Can humans get Mycoplasma haemofelis?

Very rarely, if at all. One M. haemofelis-like infection was reported in a person with HIV who also had Bartonella [9]. The ABCD experts do not believe there is a significant risk of human infection with feline haemoplasmas; vets simply handle blood samples with care [1].

What is the survival rate for cats with Mycoplasma infection?

It depends on how sick the cat is. The outlook is generally good with prompt treatment, but severe disease can be fatal: in one study of 25 sick cats, 56% survived [1, 8].

How did my indoor cat get Mycoplasma?

Often nobody knows. The natural route is unproven, carrier cats can show no signs for a long time, and blood transfusion is a known route. Indoor-only cats can be infected too [1].

Can the blood smear rule it out?

No. A smear misses most infections and can show false positives; PCR is the test of choice [1].

Will my cat be cured after treatment?

The anemia usually improves, but the bacterium is often not cleared and the cat may stay a carrier [1, 3].

Sources

  1. ABCD Europe. Guideline for haemoplasmosis in cats. Last updated 24 March 2026. abcdcatsvets.org/guideline-for-haemoplasmosis
  2. Tasker S et al. Haemoplasmosis in cats: European guidelines from the ABCD on prevention and management. J Feline Med Surg. 2018;20(3):256-261. doi.org/10.1177/1098612X18758594
  3. Tasker S. Haemotropic mycoplasmas: what’s their real significance in cats? J Feline Med Surg. 2010;12(5):369-381. doi.org/10.1016/j.jfms.2010.03.011
  4. Willi B et al. Prevalence, risk factor analysis, and follow-up of infections caused by three feline hemoplasma species in cats in Switzerland. J Clin Microbiol. 2006;44(3):961-969. doi.org/10.1128/JCM.44.3.961-969.2006
  5. Sykes JE et al. Prevalences of various hemoplasma species among cats in the United States with possible hemoplasmosis. J Am Vet Med Assoc. 2008;232(3):372-379. doi.org/10.2460/javma.232.3.372
  6. Tasker S et al. Description of outcomes of experimental infection with feline haemoplasmas: copy numbers, haematology, Coombs’ testing and blood glucose concentrations. Vet Microbiol. 2009;139(3-4):323-332. doi.org/10.1016/j.vetmic.2009.06.028
  7. Weingart C, Tasker S, Kohn B. Infection with haemoplasma species in 22 cats with anaemia. J Feline Med Surg. 2016;18(2):129-136. doi.org/10.1177/1098612X15573562
  8. Ider M et al. Evaluation of endothelial glycocalyx injury biomarkers in feline hemotropic mycoplasmosis. Sci Rep. 2024;14(1):12931. doi.org/10.1038/s41598-024-62359-7
  9. dos Santos AP et al. Hemoplasma infection in HIV-positive patient, Brazil. Emerg Infect Dis. 2008;14(12):1922-1924. doi.org/10.3201/eid1412.080964
  10. Tanahara M et al. An epidemiological survey of feline hemoplasma infection in Japan. J Vet Med Sci. 2010;72(12):1575-1581. doi.org/10.1292/jvms.10-0143
  11. Sykes JE. Feline hemotropic mycoplasmas. J Vet Emerg Crit Care. 2010;20(1):62-69. doi.org/10.1111/j.1476-4431.2009.00491.x

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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