A study by Amelia Woolums, DVM, University of Georgia College of Veterinary Medicine, showed that when they did PCR recovery out of the noses of beef cow herds, they found the cows free of Mycoplasma. “This tells me that an order buyer is buying a lot of seronegative naïve calves and running them together with a few, or perhaps many, infectious calves,” explains Rosenbusch. “That leads to an explosive situation.”
Transmission can also occur through a contaminated environment. Though research information is lacking, a French study of Mycoplasma synoviae, an arthritis-causing pathogen in chickens that produces a disease similar to that of Mycoplasma bovis, showed that environmental contamination resulted in a slow, simmering and late outbreak, whereas an infectious animal in contact with naïve animals resulted in an acute outbreak. “It’s been a concern for the poultry industry for years,” says Rosenbusch. “You’re looking at a lower dose presentation coming from the environment. It could be a feeder or the watering device. An operation may have had an outbreak last year, and the environment stayed contaminated. So when cattle are brought in, they may not show anything for two months because it takes a while to develop.”
It’s not known how hardy Mycoplasma is in the environment. Though it can live almost a year when mixed with manure under wet conditions in a lab refrigerator, it’s probably not that durable in the environment. However, Rosenbusch says there could be some significant environmental presence in the field. “In a feedlot where you empty one lot and refill it with cattle in three days or a week, the survivability of Mycoplasma is something to think about.”
He has looked at nasal secretions contaminating a feedbunk or waterer – primary sources of environmental contamination – but the organism could also be brought in on workers’ boots. “It would not necessarily infect just the feedbunk or the water source or the soil,” says Rosenbusch. “You can imagine a broader dissemination for some time.”
Grooms agrees that Mycoplasma can lurk in the environment. “In Michigan, a lot of our cattle are fed under roofs where they never see sunshine. I think the chances of environmental contamination with Mycoplasma is much greater.”
Whether it can infect calves through colostrum is unclear. Rosenbusch has not been able to demonstrate Mycoplasma bovis in colostrum, but he has evidence that colostrum can transmit the pathogen. “Calves given nothing but natural colostrum still are getting Mycoplasma bovis. Even if diseased milk is kept out of the equation, they still get Mycoplasma bovis in the first day of life. It has to be the colostrum, although we cannot detect it in the lab.”
Dan Grooms, DVM, PhD says Myco- plasma can be transmitted through aerosols, direct nose-to-nose contact and spread of discharge from the nasal passages from one animal to another.