Mycoplasmas infections

Question 1

Give a brief description of Hemoplasmas

Answer 1

Hemoplasmas are small pleomorphic (rod, spherical or ring-shaped) bacteria that occur singly or in chains of three to six organisms on the surface of RBCs

These bacteria lack a cell wall, which is the reason why they have a negative reaction when Gram-stained and are resistant to penicillin-based antibiotics

Question 2

How many types of hemoplasmas are recognized in cats

Answer 2

There are three recognized hemoplasmas of cats:
- Mycoplasma haemofelis:
- it is generally associated with clinical anemia (although incidences of subclinical infection do exist)
- Other features of infection are lethargy, fever, jaundice and splenomegaly
- typically, infection with hemoparasites causes a regenerative anemia, however many animals present in the acute, pre-regenerative stage

- Candidatus Mycoplasma haemominutum
    - It tends to cause milder disease, often without overt anemia
    - Infections tend to be clinically significant if the host is immunocompromised (e.g., FeLV co-infection, undergoing chemotherapy for lymphoma)

- Candidatus Mycoplasma turicensis
    - It is present in cats with clinically significant hemolytic anemia
    - immunosuppression has been shown to increase the pathogenicity of this hemoplasma species

Question 3

What are the key epidemiological features of hemoplasma infections

Answer 3

Hemoplasma infections tend to occur much more commonly in male cats with outdoor access

Generally, cats tend to be infected with a single species
- co-infection with M. haemofelis and Ca. M. haemominutm or Ca. M. turicensis have been reported

Question 4

What is the mode of transmission for hemoplasmas

Answer 4

The flea has been suspected to be a vector but the mode of transmission is still somewhat of a mystery

As males are predisposed, direct inoculation via fighting has also been proposed, although levels of organism in saliva have been found to be low

Transmission between cats via contaminated blood transfusion has been documented, so cats should be screened by PCR prior entering into a blood donation program

Question 5

Explain how hemoplasmas can induce anemia

Answer 5

Hemoplasmas induce anemia by either:
- direct damage to the RBCs (intravascular hemolysis)

- or induction of immune-mediated mechanisms directed at either RBC antigen or the organism itself (extravascular hemolysis), which is thought to be the major pathogenic mechanism
    - it is thought that macrophages within the spleen can remove the organism and release the "cured" RBC back into circulation
    - this may account for the rapid clearance of parasites from RBC that can occur in the space of a few hours

Question 6

How a diagnosis of hemoplasma infection is done

Answer 6

Visualization of the parasite on RBCs via cytological examination of a blood smear is not very sensitive
- many false negative results occur due to the cyclical nature of the RBC parasitism
- false positive results may occur if Howell-Jolly bodies and stain precipitates are mistaken for hemoplasmas

PCR has superseded direct visualization
- PCR is extremely sensitive and specific if the laboratory utilizes positive and negative controls
- BUT the presence of hemoplasma organisms in a patient’s blood does not necessarily prove that this is the cause of the anemia
- it is helpful to know which species has been detected
- subclinical infection appears to be much more common with Ca. M. haemominutum
- M. haemofelis infection would be considered likely to be a cause of anemia

Question 7

What other laboratory findings could be seen

Answer 7

A positive Coomb’s test and persistant autoagglutination can occur in acute haemoplasmosis suggesting the presence of RBC-antibodies

Hyperbilirubinemia

Raised liver parameters (suspected secondary to hypoxic liver damage)

Polyclonal hypergammaglobulinemia

Question 8

What is the first line of treatment for hemoplsama infections

Answer 8

Antibiotic therapy is the mainstay of treatment for clinically affected cats
- Doxycycline (10 mg/kg, PO, q24h) is recommended
- Pradofloxacine is the preferred fluoroquinolone

It is recommended that cats remain on antibiotics for at least 2-4 weeks

The concurrent use of corticosteroids is controversial, and most cats will respond to doxycyline alone

Supportive therapy, such as blood transfusion may also be required

Question 9

What is the prognosis for hemoplasma infections

Answer 9

Cats may recover spontaneously and remain chronic carriers of unknown duration

Cats treated with antibiotic therapy may also remain carriers and relapses are reported