Foot-and-mouth disease, salmonellosis, E. coli – these are but a few of the zoonotic pathogens that have frightened consumers and plagued livestock producers in recent years. As threats ebb and surge, local, state, national and international government agencies conduct research and continuously refine their regulations to mitigate disease spread. Standard testing procedures are in place to ensure early detection and elimination. However, what happens when testing supplies run out?
This concern hit the dairy and beef industries this spring as the USDA issued a nationwide shortage of commercially produced purified-protein derivative (PPD) tuberculin product. According to Joelle Hayden, public affairs specialist for USDA-APHIS, this scarcity was the result of company restructuring in 2013.
Zoetis Animal Health bought Synbiotics Corporation, suspending distribution of their Colorado Serum Company’s tuberculin product because of differences in quality control.
At the same time, the only other approved U.S. tuberculin producer, based out of New Zealand, assumed new ownership, shifting customers to a product licensed in Europe but not the U.S. This left a nine-month void in production until Zoetis resumed operations in 2014, resolving the shortage by mid-April.
“USDA-APHIS’s Center for Veterinary Biologics expedited testing so that once the product was produced, it could be available as soon as possible,” Hayden says.
The USDA currently holds a sole-source agreement with the Colorado Serum Company.
Why is TB testing so important? Bovine tuberculosis is caused by Mycobacterium bovis, a gram-positive, acid-fast bacteria.
It is mainly transmitted between cattle in aerosols, more readily in large, confined herds. The bacteria can also be contracted by other mammals, including humans, by inhalation of infected air or ingestion of unpasteurized milk.
Infected livestock may be asymptomatic, the only indication of disease being lesions in lymph nodes. Therefore, regulatory TB testing in herds is crucial, particularly prior to herd movements across state and international boundaries.
Tuberculin is typically injected as part of a caudal fold test, with any non-negative results requiring an additional confirmation test conducted by a regulatory state or federal veterinarian.
Either a comparative cervical test or interferon-gamma release assays can determine whether the positive reading was from mammalian or avian tuberculosis. This process may take from three days to two weeks, with the limited availability of tuberculin causing additional delays.
“My advice to veterinarians and livestock owners shipping cattle is to plan as far ahead as possible when TB testing is required,” says Dr. Andy Schwartz, assistant executive director of Epidemiology and Laboratory Systems at the Texas Animal Health Commission (TAHC).
Schwartz says the state laboratory took several measures to help state producers through the pinch. These included updates through social media, tapping into the agency’s own tuberculin supplies as well as those from the USDA in New Mexico and holding off on regulatory testing to ensure there was enough for movement.
“Because the shortage was short-lived, we were able to fill the gap and minimize the effect on the dairy and beef industries in Texas. Had the shortage gone on even a few weeks longer, the impact on interstate and international commerce would have been significant,” Schwartz says.
All states currently hold TB-free status except Michigan and California. After nearly 30 years without an incidence of bovine TB, a cow infected with a Michigan strain was discovered in a Saginaw County herd in March of 2013. The herd, in which 17 percent of animals responded to TB testing, was depopulated and the state has since been divided into three zones.
The four counties where the disease still occurs – Alcona, Alpena, Montmorency and Oscoda – qualify as modified accredited, with the state funding rigorous regulatory testing practices. These include an annual surveillance of all cattle 12 months or older and all non-natural additions as well as testing 60 days prior to shipment within or between states.
The ability to procure tuberculin is crucial for those whose livelihoods are rooted in the beef and dairy industries, according to Dr. Rick Smith, the bovine TB eradication program coordinator for the Michigan Department of Agriculture and Rural Development (MDARD).
Smith also explained that cervids are a major reservoir for bovine TB, and MDARD encourages farmers to make wildlife risk mitigation biosecurity plans that propose methods for reduction of cross-species water and food contamination. For those seven counties that reside in the modified accredited advanced (MAA) zone, developing an approved plan eliminates the requirement of movement testing.
Even in those states that are accredited free, the risk of disease re-emergence is ever-present. Schwartz expounded that in 2000, the threat of 12 dairies with reoccurring infections caused Texas to section off EL Paso into an MAA zone and ban dairies from being established in the area.
This precaution, in addition to a ban on dairy animals imported from Mexico, has helped the state remain TB-free since 2006, but international imports of feeder cattle still present a hazard.
Despite differences in exposure risk, regulatory TB testing remains a critical component of disease eradication programs across the country. Therefore, the USDA is exploring measures to minimize future tuberculin shortages.
“The primary option is to identify as many sources of tuberculin as possible to help avoid a sole-source situation,” Hayden says. “We are considering other sources and methods of tuberculin production including recombinant technologies.
We are encouraging attention to field inventory management, including careful consideration to volume ordered and redistribution prior to expiration, to avoid the amount of expired tuberculin that is discarded. We are also conducting product stability studies to determine options for extending the product shelf life. A longer shelf life would hopefully reduce the amount of product discarded.”
Although the 2014 shortage had minimal effects thanks to cooperative measures of national and state government agencies as well as private veterinarians and livestock owners, it did raise awareness about the need for a stable supply of testing products. PD
Holly Drankhan is a senior at Michigan State University with plans to attend vet school. She is a 2014 Progressive Dairyman editorial intern.
