December 01, 2001

 

 New turkey virus identified, sequenced - December 1, 2001

Posted November 15, 2001

 

A unique strain of astrovirus associated with poult enteritis mortality syndrome has been isolated from the thymus of commercial flocks, and its genomic sequence deciphered by the Department of Agriculture's Agricultural Research Service.

PEMS is an infectious, transmittable disease that causes severe diarrhea, stunted growth, compromised immune systems, and high death rates in young commercial turkeys. PEMS was responsible for devastating financial losses to the turkey industry in the early 1990s.

Stacey Schultz-Cherry, PhD, a microbiologist for the Southeast Poultry Research Laboratory, Athens, Ga., was brought to the USDA-ARS to look for viruses associated with PEMS. Her unit identified the disease-causing organism in PEMS-infected turkey poults. The scientists are now focusing on how turkey astrovirus strain 1 affects the immune system. Mortality of up to 50 percent in flocks can result from secondary bacterial infections.

The ARS unit has developed a molecular-based diagnostic test to detect the astrovirus, which is serotypically and molecularly distinct from previously circulating strains of astrovirus in the United States. Diagnosis of astroviruses in turkeys has been made by electron microscopy in the past, yet the turkey astrovirus strain 1 does not look like other astroviruses.

"It's possible that there are a lot of flocks diagnosed as having enteroviruses based on electron microscopy that are really astrovirus positive," Dr. Schultz-Cherry said.

The astrovirus is stable and resistant to disinfection, and producers are advised to avoid contaminating other flocks.

"The astrovirus is incredibly difficult to inactivate and disinfect," said Dr. Schultz-Cherry. " Once it gets into a flock, it's going to be difficult to get rid of. The [turkey] producers need to keep that in mind and heighten biosecurity." Only formaldehyde, methanol, and the disinfectant Virkon S inactivate turkey astrovirus strain 1.

In the meantime, the research team is learning more about the virus, and how it is circulating in the flocks, before calling this outbreak a danger to food safety.

The researchers are planning on using the sequenced virus to do some molecular epidemiology and compare isolates across the United States, as well as trying to find the virus in other countries, and determine if it can spread to other avian species.

"We're making what we call an infectious clone, which means we're remaking the virus so we can manipulate it," Dr. Schultz-Cherry said. This will aid in the possible development of a vaccine.There is no vaccine available for PEMS or the new astrovirus.

"PEMS seems to be multifactoral disease," she said, "so it's going to be difficult to develop a magic bullet treatment. We really need to understand which viruses and bacteria are involved in PEMS before we can think about a vaccine."

Dr. Schultz-Cherry is pleased that the unit has a manageable animal model of the disease to study astrovirus infection.