Ovine Pneumonia Vaccine
Creating a vaccine to combat ovine pneumonia at the Hopkirk Institute
Pneumonia affects millions of lambs throughout New Zealand and costs the country millions of dollars. Building on years of research, AgResearch scientist Dr Natalie Parlane and her team are presently trialing new vaccines, with the hope of progressing to broader field trails in the 2017 season. At this stage there is no vaccine used in New Zealand and yet the illness causes significant losses for farmers. An economic assessment 10 years ago estimated that ovine pneumonia caused losses worth around $53 million, as a result of the death or retarded growth of lambs (resulting in lower carcass weights when delivered to the works).
AgResearch have been looking at ovine (sheep) pneumonia on and off for 20 years with Dr Tao Zheng and Dr Bryce Buddle contributing significant research into the organisms responsible. The disease is caused by a variety of organisms, notably the Mannheimia haemolytica bacterium. The wide variety of causes of pneumonia means that treatment is not an option and prevention is the only tool to manage it.
The Hopkirk Institute is an amalgamation of Massey University and AgResearch, where Dr. Parlane is working to create a vaccine for sheep pneumonia in association with Beef+Lamb New Zealand.
They are looking at the Mannheimia haemolytica bacterium and a mycoplasma bacterium. The two have been selected for their prevalence in cases of the disease and the fact that they’re from quite separate genera - the mycoplasma is a bacterium without a cell wall.
In 2016, Natalie’s team ran two trials. One trial looked at a vaccine for Mannheimia haemolytica and how the vaccinated lambs fared in terms of antibody immune response, weight gain and decreased death rate.
The second trial looked at three different adjuvants for the mycoplasma vaccine to identify the most effective one. An adjuvant is a component that assists and enhances the effectiveness and delivery of a vaccine antigen to the lamb. Importantly for their vaccines, they must not cause significant site reactions as these will mar the quality of the carcass and possibly need to be cut from the animal when processed, adding significant processing time.
The second trial was able to identify the best adjuvant but the data on the efficacy of the Mannheimia haemolytica vaccine was insufficient to assess the efficacy.
This year (2017) they’ve combined the Mannheimia haemolytica, the mycoplasma vaccine and the best adjuvant. This is known as a multivalent or polyvalent vaccine, that is, it is designed to immunize against two or more strains of the same microorganism, or against two or more bacteria and in this case be effective against pneumonia caused by either Mannheimia or the mycoplasma. After vaccinating, the animals are monitored regularly – with weighing, as well as blood tests and mouth swabs to check antibody levels.
The animals are then “challenged” by the introduction of the bacteria in question.
In post mortems, visual scoring of the lungs is done using a pre-determined lung map that rates the visual appearance of the lungs in terms of disease lesions. The lungs are then removed and washed in saline. Samples are prepared and cultured in an incubator. This can determine which bacteria caused the infection and the levels of the Mannheimia haemolytica.
A liquid medium is used that inhibits growth of all bacteria except the mycoplasma. The levels can be quantified to a degree, by colour changes over a course of weeks. The media colour changes are recorded. Also, a sample of the lungs is taken for histology, sectioned and stained and then viewed under the microscope to help with the diagnosis and help determine how the vaccine might have reduced the damage to lungs (pathology) particularly due to Mannheimia pneumonia.
These results will determine the next phase of the trials. If the vaccine is shown to be doing well, they will move onto bigger field trials on farms.
If the vaccine is not performing as desired, they’ll be looking at modifying the vaccine or the timing of vaccination. Natalie says they might find that the addition of the mycoplasma makes no difference or that the Mannheimia haemolytica vaccine is sufficient and all this will impact on the design of the next phase of trialing.
A vaccine will also need to meet New Zealand regulatory requirements – Mannheimia haemolytica vaccines have been used overseas but effective mycoplasma vaccines are yet to be developed.
Right now the best things a farmer can do to reduce ovine pneumonia within their flock are:
- Reduce heat stress – do work on sheep early in the day before it gets too hot. Avoid moving of animals on hot days/reducing long distance mustering of flock
- Cut down on dust – dust can aid the spread of the disease and exacerbate compromised airways in animals – this might be by setting up temporary yards in paddocks rather than the usual dusty yards.
- Assure good shade for animals