Respiratory Diseases in Livestock

Published on 29 September 2009 in Food, health and wellbeing

Introduction

Respiratory disease in sheep and cattle causes major welfare and economic problems for Scottish farms despite the widespread use of vaccines and antibiotics. Estimates of the financial cost run into millions of pounds per year, due to a combination of production losses, deaths, and veterinary bills.

Key Points

Infectious respiratory disease is a major welfare and economic problem on many farms. Carrier animals that may show no sign of disease, but are able to infect others, are difficult to identify and treat. Even with modern drugs, bacteria and viruses in the upper respiratory tract are difficult to remove, making sick animals difficult to cure and susceptible to secondary infections. There are vaccines against some respiratory diseases (e.g. infectious bovine rhinotracteitis [IBR], bovine respiratory syncytial virus [BRSV], bovine parainfluenza virus 3 [PI3] and pneumonic pasteurellosis caused by Mannheimia haemolytica), but not all; for example, Pasteurella multocida is now a major cause of cattle pneumonia. Livestock losses and welfare problems persist and we need a better understanding of the disease processes, the interactions between pathogens and how infectious diseases are carried over from year to year in order to develop better diagnostic tests and control measures.

Healthy lung - note healthy pink tissues Lung showing damage due to pneumonia - note dark patches of necrotic tissue

Research Undertaken

A recent Moredun on-farm survey of Scottish beef and dairy cattle found that 17% calves up to 8wk old had nasal infection with P. multocida, although most appeared healthy at the time of sampling. It was common for P. multocida to be associated with the detection of Mycoplasma spp. and bovine PI3 virus. Trials under standard farm conditions at Moredun with 40 newborn calves from 18 farms found that 10 were positive for P. multocida infection on arrival and that, by day 17, 29 naïve calves had become infected and many either treated with antibiotic or killed humanely to prevent suffering. Infection caused lung damage quickly (Fig), resulting in fever, breathing difficulties and dullness and spread easily and quickly from animal to animal, possibly via nasal secretions.

Calves with Pneumonia have difficulty breathing Sheep with OPA produce copious amounts of lung fluid containing JRSV

Ovine pulmonary adenocarcinoma (OPA) caused by Jaagsiekte sheep retrovirus (JSRV) is a transmissible lung cancer of sheep. A high proportion of sheep carry the virus without developing disease but, in affected flocks, up to 10% of sheep may die each year. A recent Moredun survey provided new data about the prevalence and distribution of OPA, finding that although 38% of flocks tested were positive for JSRV, many sheep farmers were not aware of the disease. Our research has shown there is no detectable immune response to JSRV in infected sheep but an immune response can be generated to parts of JSRV using a strong adjuvant. New knowledge about OPA will help develop a better test for diagnostic or eradication purposes and a better understanding of how the virus causes disease that may give insights also into certain aspects of human lung cancer.

Determining the infectious cause of respiratory disease in an individual or group of livestock is important to identify the correct treatment and management of the outbreak (antibacterials, anti-inflammatories) and for future stock management (vaccination, housing,). The bacteria and viruses involved are diagnosed by a number of methods, for example direct culture or antibody testing. Newer molecular methods based on the polymerase chain reaction have been developed to detect P. multocida and the viruses BRSV and bovine PI3 and a multiplex assay to detect these 2 viruses and IBR is in development. The potential to combine virus with bacterial molecular detection methods, allowing swift and accurate diagnosis of the cause of respiratory disease, is under investigation.

Policy Implications

Control of common endemic diseases, is important in increasing productivity and food security for Scotland. Reducing disease losses also increases efficiency and reduces the environmental impact of farming, whilst supporting the rural economy. Respiratory diseases have a large impact on farms and are a key target for improved control.

Disease control is best by vaccination, using up-to-date technology and exploiting genome information to identify novel vaccine components. Several commercially successful vaccines against respiratory disease originated from Moredun and more are in development. Improved diagnostic tests developed at Moredun have already had an impact for farmers and veterinarians and more are likely in the future.

New vaccines and tests benefit farm animal welfare and agricultural economics directly. In addition spin-out to biotech companies generates financial benefits to Scotland

Research on mechanisms, microbial characteristics and epidemiology of respiratory diseases provides the underpinning knowledge required for the development of new, improved control methods and is distributed to vets and farmers as soon as possible. Disease surveillance at Moredun is vital to detect emerging diseases and changing patterns of endemic diseases.

Author

Dr Chris Hodgson chris.hodgson@moredun.ac.uk

Topics

Food, health and wellbeing