Role of transmission and pathogen components in virulence and disease pathogenesis for important endemic diseases of livestock in Scotland

Challenges

For the important infections and diseases affecting Scottish livestock production, we do not have a full understanding of how the pathogens are distributed or transmitted to their host animal, what key pathogens and components are important for infection and disease, and how these components interact with the host immune system. Two major diseases affecting cattle production in Scotland are bovine pneumonic pasteurellosis and Johne’s disease.

Pneumonic pasteurellosis 

Pneumonic pasteurellosis is caused by P. multocida and results in significant production losses and mortality. No vaccines are available in Europe. Live vaccines in the United States provide a short duration of immunity and may exacerbate the disease. Extensive pulmonary damage occurs before clinical signs are evident. Therefore, an effective vaccine would offer more opportunities to instigate treatment to prevent lung damage.

John’s Disease

John’s Disease (JD) is caused by Mycobacterium avium subspecies paratuberculosis (MAP) and affects cattle, sheep, and goats. Ruminants often become infected in their first few months of life, via contaminated teats or the mother’s milk. MAP is shed in the faeces of infected livestock as well as wildlife reservoirs, contaminating the surrounding soil, water, and surfaces.

Infection can go undetected due to limited diagnostic testing. The current vaccine is only appropriate for sheep and does not stop infection or transmission. However, we can use it successfully as part of a JD control programme to mitigate introduction and spread in flocks. MAP is also controversially associated with Crohn’s disease in humans and so represents a potential public health threat.

Clinical mastitis 

Intramammary infections causing mastitis are other important production-associated diseases in ruminants. Clinical mastitis is an important animal welfare issue and can lead to death or premature culling. It causes a reduction in milk quantity and quality, which influences weight gain and lamb production. Another pathogen affecting sheep productivity is jaagsiekte retrovirus (JSRV), the cause of Ovine Pulmonary Adenocarcinoma (OPA), a contagious tumour of sheep. OPA remains a significant disease problem in the UK and worldwide. Disease control is problematic without a test for JSRV infection. Transthoracic ultrasound scanning (TUS) is an effective way to diagnose pre-clinical OPA, but it is expensive.

Questions

Solutions

This project focuses on four of the most important infections and diseases affecting Scottish livestock production. This project is improving our understanding of (i) the transmission of Mycobacterium avium subspecies paratuberculosis (MAP), mastitis and Ovine Pulmonary Adenocarcinoma (OPA) in cattle and sheep; and (ii) identifying the processes involved in the virulence and infection of Pasteurella multocida.

Identifying antigens and immune responses associated with bovine P. multocida strains that differ in virulence

Our previous research compared bovine strains isolated in the UK and US. We found differences in the severity of the pathology and published the full genome sequences of virulent UK strains. We are extending this work to determine whether genetic differences between these strains are associated with known expressed virulence-associated factors. This could provide the first step in the design of a novel vaccine.

Understanding the drivers of MAP Transmission in the environment to livestock

We are investigating the drivers of environmental MAP transmission in the spread of infection within farmed and wildlife reservoirs, potential transmission routes from the environment to healthy livestock and the effectiveness of control programs to mitigate the spread of JD. We are developing a baseline of MAP in the farm environment in Scotland and determining the effectiveness of current mitigation strategies.

Exploring mastitis and OPA

We are modelling OPA transmission and evaluating different control scenarios, exploring the duration of virus production through analysis of JSRV in exhaled droplets from sheep with various stages of the disease, and evaluating virus infectiousness using cell and lung slice cultures. From these studies, we are assessing the risk of aerosol transmission of JSRV at different disease stages. Lastly, we are sequencing samples of JSRV from different farms over time to explore the influence of virus strain on infectiousness.

Longitudinal study of mammary health in a genetically characterized sheep flock

We are studying the health of a genetically characterized sheep flock over time. This involves genotyping three hundred age-matched ewes to provide information on their genetic background and their overall health. The insights from our study are informing mastitis control and intervention strategies. It will also provide information on the incidence of antimicrobial resistance affecting treatment options.