The challenge addressed by this project is to unravel the causes of stunting disease in UK broiler chickens. Stunting syndrome has been a production issue in commercial broiler flocks since they became industrialised after the second world war, but is also a problem for small producers in low and middle income countries, such as Nigeria, where women often raise small numbers of chickens to supplement the family income. The stunting problem has many names, including infectious stunting, runting stunting syndrome and malabsorption disease. It pertains to a failure to grow properly despite sufficient feed. Birds typically present with stunting problems around the second to third week post hatching, but clinical signs may be observable earlier. As well as the reduction in weight gain, which can be substantial with severely affected chickens only a fraction of their potential weight for age, there may be other signs such as altered appetite, watery droppings, abnormal feathering and enteritis. We and other groups have evidence that the stunting is caused by infectious agents: chiefly, viral aetiology is suspected and experimental infections at AFBI using specific strains of the endemic, enteric viruses, astroviruses and reoviruses separately have resulted in some of the signs observed during stunting, e.g., weight loss or lesions in the gut mucosa. Other groups have also demonstrated some of the signs of stunting from inoculating birds with single viral strains of these and other viral candidates, e.g., birnavirus; however, none have fully recreated the stunting syndrome, and co-infections with more than one viral agent are considered the more probable aetiology. Moreover, diverse strains of these viruses are in circulation which are known to vary widely in pathogenicity with the majority potentially of low or no pathogenicity and accordingly high levels of these virus may be detected in young, healthy, unaffected birds.
Other confounding factors in attributing disease aetiology includes the presence of maternally-derived antibodies, route of transmission (from the hen versus their environment) and the age at which birds become infected, since increasing age appears to confer resistance. All these factors have also hampered the identification of the virus(es) responsible for stunting diseases. The specific aims of the proposal are to: 1) identify a virus or viruses that are actively replicating within the lesions associated with stunting disease and that are present in many similar lesions from clinical cases. Histopathology and laser microdissection will identify and excise lesions from which nucleic acids will be sequenced to determine which virus strain(s) is present at levels indicative of an active infection. 2) confirm that the virus or viruses identified are aetiological agents of stunting; firstly, by cellular and tissue-based methods in the laboratory and secondly, by challenge studies of healthy chickens using purified isolates of the identified virus(es), which will demonstrate the development of hallmark lesions and associated clinical signs typical of stunting disease. These objectives will be achieved through the use of state-of-the-art imaging and genomic methodologies, and through collaboration with the Industry (Moy Park, which is one of UK’s top broiler meat producers and St David’s Poultry Team, the leading poultry veterinary practice in the country). Currently there are no commercial vaccines to prevent stunting or specific treatments for affected flocks so that affected birds are culled. The results of this project will provide evidence of the causal agents of stunting that will enable improved diagnostics and potential interventions for veterinarians, and for vaccine companies to develop appropriate vaccines.
Contact details:
Dr Victoria Smyth
Agri-food and Biosciences Institute