Farmed deer are susceptible to Johne’s Disease, a chronic wasting condition that results in reduced meat yields, lower fertility and premature death. The condition is difficult to detect, but now a proof of concept study has shown that a new diagnostic, Actiphage, can directly detect the presence of the causal mycobacteria in cervid blood samples, offering clear potential for the control of this economically damaging disease.
Research published in Frontiers in Veterinary Science used a blind test of 132 animals from four production units to detect the carriers of the disease. Actiphage detected the presence of the causal bacteria, Mycobacterium avium subsp. paratuberculosis (MAP), mainly in one breeding unit and in a small number of animals in another.
When some of the MAP-positive animals were tested again one month later, the results were reproducible.
One of the authors, Cath Rees, associate professor of microbiology at the University of Nottingham, comments: “Early identification of carriers using Actiphage allowed the introduction of a disease management strategy on the farm.
“In addition, Actiphage was found to be a useful additional screening test before animals were moved to reduce the risk of spread of infection.”
In infected animals, MAP is shed in faeces as the disease progresses, with ingestion of contaminated faeces the main source of transmission.
Currently the main diagnostic for deer is an antibody ELISA, which detects the presence of MAP-specific antibodies produced by the animal in response to infection. There are a few commercially validated tests available that can identify high shedding animals, but these have a lower value in early stages of infection, before shedding occurs, and so are of limited use within a disease control program.
Actiphage directly detects the presence of the mycobacteria in blood or milk. It acts as a lysing agent, efficiently releasing genomic DNA from the MAP cells. Sufficient DNA can be released from just a few cells to enable detection by signature specific PCR assays.
Actiphage therefore enables the diagnosis of both Johne’s Disease and bovine TB (M. bovis) from a single blood sample even where just a few cells of mycobacteria are present.
The study also showed that a simpler method of blood preparation could be used to recover white blood cells, replacing the more complex Ficoll gradient method that has been previously used. This dramatically simplifies the assay procedure and produced cleaner samples with lower levels of red blood cell contamination which can inhibit the Actiphage reagent.
The study showed that Actiphage reliably identified Johne’s Disease at an early stage of infection and provided insights that enabled the farmer to isolate the infected animals to restrict the progression of the disease through the herd.
