February 14, 2008

New discovery in poultry disease to change vaccine development
 

Poultry scientists are taking a new look at the lethal poultry bacterial disease, necrotic enteritis, after a discovery that alpha-toxin protein is not the main cause of the disease.

Anthony Keyburn, who works at the Australian Animal Health Laboratory (AAHL), made the discovery.

According to Keyburn, necrotic enteritis is one of the world's most common and financially crippling poultry diseases, costing global poultry industries an estimated US$2 billion ever year.

Keyburn and a team of scientists had found that the disease is caused by clostridium perfringens, a bacterium found in soil, litter, dust and in small quantities in the intestines of healthy chickens.

The bacterium only causes disease when it multiplies to high numbers, producing extracellular toxins that attack the bird's intestines, causing lesions, Keyburn said.

Poultry producers use antibiotics to treat and prevent the disease, which can cause up to 50 percent of mortality rate when triggered.

Alpha-toxin has long been thought to be the major causative factor and requirement for necrotic enteritis even though there was no concrete proof, and all vaccine development for the last 30 years have been based on this assumption.

The involvement of alpha-toxin was questioned when a survey revealed that there are low levels of alpha-toxin in local disease-causing bacterial strains. Keyburn and his team performed tests, and found that disease still occurred in chickens even without the presence of alpha-toxin.

This finding led the team to search for the disease's real cause, and they found a novel toxin - NetB - that is involved in disease-causing potential of a high proportion of virulent clostridium perfringens strains.

The discoveries have led to a new project established within the Australian Poultry CRC that investigates NetB and other proteins produced by clostridium perfringens, with the aim of developing effective vaccines against necrotic enteritis.