TB source baffles Indiana researchers

COLUMBUS, Ohio — Indiana has been tuberculosis free since 1984, but in the last nine years cases keep cropping up in the southeastern part of the state.


“I can’t explain how this is moving around,” said veterinarian Bret Marsh of the Indiana State Board of Animal Health.


He described the recent history of the disease and how trace-outs have been conducted since it was found in cattle, white-tailed deer and a raccoon.


The source of infection is under investigation, and state officials suspect there has been a low level of the disease in the area for a long time, he told the National Institute of Animal Agriculture meeting held in Columbus April 3-6. 


“My concern is it is moving in something. I can’t tie these cattle herds by cattle contact,” he said. 


“We could not prove it is in the white-tailed deer population.” 


Genetic testing at the U.S. Department of Agriculture’s national laboratory shows that all the state’s deer and cattle were infected with the same strain of TB. This strain has been found in wildlife across the United States. 


The first case was found in late 2008 when inspectors at an out-of-state packing plant found lesions in a cow traced back to Indiana. 


The disease was found the following year at a nearby cervid farm, where the owner had about 100 fallow deer, red deer, elk and five white- tailed deer. The herd was destroyed.


A Pennsylvania slaughter plant discovered two more cases in 2010. Four loads of fed cattle went to that plant, but there did not seem to be any conclusive links. 


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“It was six years later before we ever found out where these steers came from,” he said. “If it had not been for whole genomic sequencing, we may never have found out.”


Another beef herd from the same region was infected in 2011, and a lack of identification created problems for investigators. 


“The reality is we worked hard on premises identification, but we need some ID on these animals,” Marsh said.


“It takes weeks to find these, and we spend a lot of time testing cattle that don’t need to be tested.” 


The most recent cases happened last year when six of 11 steers shipped to a packer tested positive. 


The buyer bought those steers from the farm and put a back tag on them. Those tags were still visible at the packing plant in Pennsylvania and they were able to find the owner within three hours. 


These cattle came from a farm that ran two sites: cows and heifers on one and market cattle at another. The entire operation was depopulated, and extensive testing was launched in a five kilo-metre radius. 


A river runs through the region where all the infected herds were found, so that area was also cordoned off for testing of cattle and wildlife. 


White-tailed deer surveillance has been ongoing since 2009, but none were found until last year when a positive diagnosis was declared in a two-year-old doe found on one of the infected farm sites.


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“That was the first positive wild species we have ever had in Indiana,” he said. 


The test area was expanded to a 16 kilometre radius. A positive raccoon was collected in that sweep, and another farm came up positive last December. 


“The encouraging side of finding a wild animal was that we put up a 10 mile (16 km) circle,” Marsh said.


“If we had not done that, we would have missed seeing it.”


A widespread public education program was launched and hunters were asked to submit deer heads, although no disease was found in the 2,000 samples. 


Testing involved a large group of officials. 


Private veterinarians can be en-listed to help test animals in Indiana, and about 14 local practitioners joined three federal teams. They tested 380 cattle herds with a total of 6,500 head of cattle. All the tested cattle have been tagged, and they will be tested again. 


Low-level offenders from a local jail were enlisted to help set up corrals, gates and chutes, which were taken to the farms because many did not have adequate facilities or equipment. 


Surveillance will continue this year in cattle herds and wildlife. 


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