Scientists with the Agricultural Research Service (ARS), the scientific in-house research agency for the US Department of Agriculture (USDA), have developed a new experimental vaccine to protect cattle from the bacterium that causes Johne’s disease, Mycobacterium avium subspecies paratuberculosis (MAP).
Johne’s disease, also known as paratuberculosis, is a chronic intestinal disorder that can cause diarrhoea, weight loss, poor health and, sometimes, death in afflicted cattle.
In the US, Johne’s disease is most prevalent in dairy herds, costing the industry more than $220 million annually in losses.
The disease also affects other ruminant animals, including sheep, goats and deer.
Experimental Johne’s disease vaccine
Rather than using the cells of live but weakened or dead MAP, as has been done with past commercial vaccine formulations, ARS microbiologists Judy Stabel and John Bannantine set their sights on four proteins from the bacterium.
These proteins were discovered from prior research they carried out to sequence and characterise the bacterium’s genetic makeup.
In preliminary trials, vaccinating mice with the proteins reduced bacterial colonisation of the rodents’ intestinal walls and bacterial shedding in faeces, a major route by which other hosts become infected.
Cattle, e.g. can become infected while grazing pasture where MAP-contaminated manure is located.
Calves ingesting colostrum from an infected dam is another route of infection, noted Stabel, who along with Bannantine, is with the ARS National Animal Disease Center’s Infectious Bacterial Diseases Research Unit.
Scaling up the experiments
Encouraged by the results with mice, the researchers scaled-up their efforts, using standard laboratory procedures to produce the four proteins and combine them into a single, recombinant vaccine ‘cocktail’ that could be administered to calves at doses of 200 or 400 micrograms (mcg).
Trials with dairy calves, detailed in the April 2021 issue of the journal Vaccine, indicate the vaccine cocktail did not disappoint.
In addition to rendering the young animals immune to the disease over the course of a year of monitoring, the formulation showed little to no cross-reactivity with serological tests for both Johne’s disease and bovine tuberculosis (bTB).
Irish Johne’s Control Programme
In Ireland, Animal Health (AHI) Ireland leads the Irish Johne’s Control Programme (IJCP), which is developing a long-term approach to control Johne’s disease, within the Irish cattle industry.
According to AHI, the IJCP provides a pathway for test-negative herds to guard against entry of infection, and to demonstrate progress towards an improved herd assurance against Johne’s disease, and a pathway for test-positive herds towards reducing the spread and effects of infection.
Administering the vaccine cocktail also did not trigger blemishes at the injection site, Stabel reported – a potential benefit for animals raised for their meat and hides.