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Mycoplasma spp. in Cats: Respiratory Infections and Anemia

Mycoplasma infections in cats can cause two very different clinical presentations — respiratory disease affecting the upper airways and lungs, and life-threatening hemolytic anemia. Despite being caused by bacteria, Mycoplasma species have an unusual biology that makes them behave quite differently from conventional pathogens, and their diagnosis and treatment require a specific approach.

This article covers both respiratory Mycoplasma infections and feline hemotropic mycoplasmosis (previously known as Haemobartonella infection), explaining what each condition is, how to recognise it, and how to treat it effectively.

What Are Mycoplasma Species?

Mycoplasma organisms are the smallest self-replicating bacteria known. They are unusual among bacteria in that they lack a cell wall entirely — a feature with direct clinical implications: beta-lactam antibiotics (penicillins and cephalosporins), which work by targeting the bacterial cell wall, are completely ineffective against them.

Several Mycoplasma species are relevant in cats, including Mycoplasma felis and Mycoplasma gateae (associated with respiratory and joint disease) and the hemotropic species — primarily Mycoplasma haemofelis, Candidatus Mycoplasma haemominutum, and Candidatus Mycoplasma turicensis — which infect and destroy red blood cells.

Respiratory Mycoplasma Infections in Cats

Respiratory Mycoplasma infections in cats are often underdiagnosed, partly because the signs overlap closely with those of feline herpesvirus and calicivirus, and partly because standard bacterial culture does not detect Mycoplasma organisms — specific PCR testing is required.

Clinical Signs

Mycoplasma felis has been associated with conjunctivitis, rhinitis, and tracheobronchitis in cats. Affected cats may show:

  • Serous to mucopurulent ocular and nasal discharge
  • Sneezing and coughing
  • Conjunctival redness and chemosis
  • In more severe cases, lower respiratory signs including dyspnoea and increased respiratory effort

Mycoplasma felis is often identified alongside other respiratory pathogens, particularly FHV-1 and Chlamydia felis, making it difficult to attribute disease severity to any single organism. Its independent pathogenicity in cats remains an area of ongoing research.

Diagnosis of Respiratory Mycoplasma

Standard bacterial culture will not detect Mycoplasma. Diagnosis requires PCR testing on conjunctival, nasal, or pharyngeal swabs. Commercial respiratory PCR panels that include Mycoplasma felis alongside FCV, FHV-1, Chlamydia felis, and Bordetella bronchiseptica are now widely available and provide the most efficient diagnostic approach in cats with upper respiratory signs.

Treatment

Because Mycoplasma organisms lack a cell wall, treatment requires antibiotics that target protein synthesis rather than cell wall construction. First-line choices include:

  • Doxycycline (5–10 mg/kg q12–24h for 4 weeks): The antibiotic of choice. Highly effective against all Mycoplasma species in cats. Tablet formulations should always be followed by water or a small amount of food to prevent oesophageal stricture formation.
  • Azithromycin: A macrolide alternative with good intracellular penetration. Useful when doxycycline is not tolerated.
  • Fluoroquinolones (pradofloxacin, marbofloxacin): Effective alternatives, particularly useful in cats with concurrent Chlamydia felis infection.

Feline Hemotropic Mycoplasmosis (FHM)

Feline hemotropic mycoplasmosis — formerly called haemobartonellosis — is a vector-borne infectious disease caused by small Mycoplasma organisms that attach to and damage the surface of red blood cells. It is one of the most important infectious causes of anemia in cats worldwide.

The Three Species and Their Significance

Three hemotropic Mycoplasma species infect cats, with markedly different levels of pathogenicity:

  • Mycoplasma haemofelis: The most pathogenic species. Capable of causing severe, regenerative hemolytic anemia in both immunocompetent and immunocompromised cats. Without treatment, anemia can become life-threatening.
  • Candidatus Mycoplasma haemominutum: More prevalent in the population but less virulent. Most often causes subclinical infection or mild anemia; may become clinically significant in immunosuppressed cats.
  • Candidatus Mycoplasma turicensis: Intermediate pathogenicity. Less commonly detected; may contribute to anemia particularly in cats with concurrent disease.

Transmission

The primary route of transmission for hemotropic Mycoplasma species in cats is via ectoparasites, particularly fleas (Ctenocephalides felis). Transmission via blood transfusion is also documented. There is some evidence for vertical transmission from queen to kitten, and bite wounds between cats may play a minor role. Strict flea control is therefore both a preventive and a management measure for FHM.

Clinical Signs of Hemotropic Mycoplasmosis

The clinical presentation reflects the degree of anemia and whether the disease course is acute or chronic. Acute severe infection causes:

  • Profound lethargy and weakness
  • Pale or icteric (jaundiced) mucous membranes
  • Anorexia and weight loss
  • Tachycardia and tachypnoea as compensatory responses to anemia
  • Splenomegaly in some cases

Mildly or chronically infected cats may show few or no signs, with anemia detected only on routine blood testing. Immunosuppressed cats — including those with concurrent FIV or FeLV infection — are at higher risk of severe clinical disease even from the less pathogenic species.

Diagnosis of Hemotropic Mycoplasmosis

Blood smear examination was historically the primary diagnostic method, but it has low sensitivity — organisms are only visible on smears during periods of peak parasitemia, and they can be dislodged from red blood cells during sample preparation. PCR testing on EDTA blood is now the standard diagnostic tool, offering high sensitivity and the ability to differentiate between species. Key diagnostics include:

  • PCR on EDTA blood: Gold standard. Identifies and differentiates all three hemotropic species.
  • Complete blood count (CBC): Assesses anemia severity. Packed cell volume (PCV) below 20% indicates severe anemia requiring urgent intervention. Reticulocyte count helps determine whether the anemia is regenerative.
  • Blood smear: May show organisms on the surface of erythrocytes, but absence does not exclude infection.
  • Concurrent FeLV/FIV testing: Essential, as immunosuppression dramatically worsens prognosis.

Treatment of Hemotropic Mycoplasmosis

Treatment should be initiated promptly in all cats with confirmed or strongly suspected M. haemofelis infection.

  • Doxycycline (5–10 mg/kg q12–24h for a minimum of 4 weeks): First-line antibiotic. Reduces organism numbers rapidly but may not fully eliminate infection; some cats remain PCR-positive carriers.
  • Pradofloxacin: Shown to clear infection more completely than doxycycline in some studies; may be preferred in cats where carrier status is a concern.
  • Prednisolone (1–2 mg/kg/day initially): Indicated when immune-mediated destruction of infected red blood cells is contributing significantly to anemia. Taper once hematocrit stabilises.
  • Blood transfusion: Life-saving in cats with severe anemia (PCV < 10–12%). Compatible donor blood should be used.
  • Flea control: Essential to prevent reinfection and reduce transmission to other cats.

Prognosis

With prompt treatment, the prognosis for acute M. haemofelis infection in immunocompetent cats is generally good. Many cats respond well to doxycycline within the first week, with rising hematocrit values within 2 weeks. However, full PCR clearance may not be achieved, and relapses can occur, particularly during periods of stress or immunosuppression. Cats co-infected with FIV or FeLV have a more guarded prognosis.

Key Takeaways

  • Mycoplasma felis causes respiratory disease that mimics other common respiratory pathogens — PCR testing is required for diagnosis
  • Hemotropic Mycoplasma species cause infectious anemia; Mycoplasma haemofelis is the most clinically significant
  • Flea control is essential for preventing hemotropic mycoplasmosis
  • Beta-lactam antibiotics are completely ineffective; doxycycline is the treatment of choice for both forms
  • PCR on EDTA blood is more sensitive than blood smear for diagnosing FHM
  • Always test for concurrent FeLV and FIV in cats with hemotropic mycoplasmosis

References

1. Tasker S (2010). Haemotropic mycoplasmas: What’s their real significance in cats? J Feline Med Surg 12(5):369–81.

2. Sykes JE (2010). Feline hemotropic mycoplasmas. Vet Clin North Am Small Anim Pract 40(6):1157–70.

3. Dean RS et al. (2008). Use of real-time PCR to detect Mycoplasma haemofelis. Vet Microbiol 126(1-3):167–74.

4. Westfall DS et al. (2001). Inoculation of two genotypes of Haemobartonella felis in cats. J Clin Microbiol 39(8):2996–3001.

5. Sykes JE (2014). Canine and Feline Infectious Diseases. Elsevier Saunders.6. Lobetti R (2014). Feline haemotropic mycoplasmas. J S Afr Vet Assoc 85(1):Art#1148.