The quarantine, which includes roughly 15,000 Nebraska cattle, is likely to continue growing in the weeks ahead, Nebraska Agriculture Director Greg Ibach said, because investigators are still tracking down all the animals that may have had contact with the infected herd over the last two years.
Ibach said the 10 herds added to the quarantine Tuesday included cattle bought from restricted herds before the quarantine was imposed. And Colorado and South Dakota officials have been alerted because animals from quarantined herds were sold to cattle producers in those two states.
Ten Nebraska counties now have quarantined herds, up from five last week.
Ibach said state and federal officials have confirmed only two cases of the disease in one Rock County herd. The other 41 quarantined herds either may have had fence-line contact with the infected herd or bought animals from a quarantined herd.
The 42 Nebraska herds are in Boyd, Brown, Cedar, Colfax, Gage, Holt, Keya Paha, Loup, Pierce and Rock counties.
None of the quarantined herds can sell cattle unless they obtain a special permit for immediate slaughter.
The U.S. Department of Agriculture is working with state officials to determine the source of the tuberculosis and how widespread the infection is.
The outcome of that investigation could create a significant disadvantage for Nebraska's roughly $10 billion cattle industry. If the state loses the tuberculosis-free label it has held for the past 17 years, Nebraska producers might have to pay to test their cattle and prove they are disease-free before shipping them to other states.
Last week, state officials estimated that 15,000 cattle were included in the quarantine when 32 herds were involved. Ibach said state officials did not increase the total number of cattle in their estimate Tuesday because the 10 new herds are relatively small and officials overestimated the size of the herds involved last week.
The number of cattle quarantined remains relatively small compared with the 6.35 million head of cattle and calves that federal officials estimate were in Nebraska at the start of 2009.
The disease is easily transmitted through a herd by nose-to-nose contact. It causes severe coughing, fatigue, emaciation and debilitation in the animals. Bovine TB is considered untreatable in cattle, so both infected and noninfected animals in a herd usually are killed when the disease is found.
Bovine TB can be transmitted from livestock to humans, but that's exceedingly rare. It can be transmitted to other animals.
Meanwhile, Texas officials quarantined a West Texas dairy herd and slaughtered several cattle that tested positive for tuberculosis. They have not yet identified the source.
The Texas Association of Dairymen says there is no public health concern from the detection since milk from commercial dairies is pasteurized, killing bacteria with heat.