Steps towards prompt diagnosis of feline haemoplasmas
What are feline haemoplasmas?
Feline haemoplasmas are small bacteria that cause haemolytic anaemia (destruction of red blood cells) in cats. Transmission is not fully understood but thought to involve blood-sucking parasites and/or aggressive contact. Haemoplasmas cannot be grown in the laboratory so studying their biology and interaction with the host immune system poses a unique challenge.
How are they diagnosed and treated?
As haemoplasma infections cannot be reliably diagnosed based on examination of blood smears, diagnosis currently involves specific polymerase chain reaction (PCR) assays. Haemoplasmosis can respond to antimicrobial therapy but severely affected cats may require blood transfusions and reoccurrence of disease is possible if the infection is not cleared.
Why are we working towards improving diagnosis of haemoplasma infections?
PCR testing cannot be performed patient-side and results may take up to a week to be reported. A rapid test using feline serum would allow specific treatment to be started straight away or similarly rule out haemoplasmas in other diseases causing haemolytic anaemia. Serologic tests are typically based on the host (the cat) producing specific antibodies to proteins, which can be found in the host serum, belonging to the pathogen. In haemoplasmas the nature of the antibodies produced by infected cats and haemoplasma immunoreactive proteins are largely unknown.
What are the steps involved?
In a previous project, the entire haemoplasma genome (where all its proteins are encoded) has been transformed into a library of E. coli bacteria. This means that each colony of E. coli bacteria contains a fragment of a haemoplasma gene/DNA (the ‘insert’) which may be stimulated to synthesise a piece of haemoplasma protein. This allows us to study haemoplasma proteins without growing the haemoplasma organisms themselves. Utilising this library, we can then use serum from cats with and without haemoplasma infection to screen for antibody binding to the haemoplasma proteins. Once positive binding has been identified, the original DNA insert can be removed from the bacteria and its sequence used to identify the encoded protein on the haemoplasma genome.
Another approach we have is to use advanced computer modelling software to predict haemoplasma proteins that should be immunoreactive; these will then be synthesised in E. coli bacteria and screened with feline serum from cats with and without haemoplasma infection to identify any that are immunoreactive.
Our immediate aim will be to optimise a serological assay for the diagnosis of haemoplasma infection which doesn’t include interference from feline antibodies cross-reacting to E. coli proteins.
Who is working on this project?
This study is being carried out at the University of Bristol by Serina Filler whose PhD is funded by the Langford T5rust for Animal Health & Welfare. Serina is supervised by the internationally well known and well respected Prof. Séverine Tasker along with Dr. Christopher Helps and Dr. Daryll Hill. The library was produced by Dr. Emily Barker, feline serum samples are remnant from previous studies and clinical samples at the Diagnostics Laboratory, Langford Veterinary Services.