While every dairy farmer has a unique affection dairy calves, the next great generation of his or her milking herd, it’s not a good idea to kiss them or allow farm visitors to smooch away.
The reason: The calves could transmit any number of diseases to their human handlers or those who pet them, and humans in turn can transmit diseases to the calves.
These animal-to-human transfer is known as zoonotic disease transmission, says Jeff Bender, a veterinarian and Director of the Upper Midwest Agricultural Safety and Health Center at the University of Minnesota. Bender presented a short podcast in August as part of the Dairy Producers of Wisconsin Dairy Signals video series.
The COVID-19 outbreak, if anything good can come of it, is a stark reminder of the impact infectious diseases can have on a population, be it human or bovine, says Bender.
The Centers for Disease Control reports that in 2017, there were 59 outbreaks of zoonotic diseases in humans in the United States. This led to 1,518 reported illnesses, 312 hospitalizations and 3 deaths. About two thirds of those outbreaks came from livestock or poultry operations, says Bender.
And there is a higher risk for people who live and work on farms. “The estimated incidence of zoonotic enteric infections for people who live and/or work on farms with food producing animals in Minnesota was 147/10,000 population versus 18.5/10,000 population for others not on farms,” he says. That’s an 8-fold increase in risk for farm residents and workers.
For calf-to-human transmission, Bender says there are four diseases (see below) that pose the most risk. “Hand-to-mouth transmission is primary for these four, and the infection dose is very low,” Bender says.
• Salmonella Heidelberg. An outbreak in 2018 of Salmonella Heidelberg occurred across 15 states, and bacterial isolates were drug resistant. There were 56 known human cases, and about a third were hospitalized. It can cause diarrhea, fever and stomach cramps.
• Campylobacter. Campylobacter is highly infectious in children less than a year of age, and can cause severe diarrhea. It has a low infectious dose level, and is most commonly associated with drinking raw, unpasteurized milk.
• E. coli 0157. E. coli can cause bloody diarrhea and kidney failure in children, and can be fatal to kids less than 5 years of age. The concern is that 15% to 20% of herds are positive for E. coli. In a survey done in 2006 of calves taken to Minnesota County Fairs, 75% of the Fairs had E.coli present. Typically, E.coli doesn’t cause disease in calves so they can be shedding the bacteria without handlers realizing it.
• Cryptosporidium parvum. “Newborns can excrete from 10⁶ to 10⁹/organisms (of Crypto) per gram of feces,” he notes, and it only take a few hundred to cause disease. Virtually all dairy farms have it, he says. Crypto can cause both acute and persistent diarrhea, particularly in children.
To prevent these diseases, hygiene is essential. Handwashing before and after handling calves, wearing gloves and having dedicated coveralls and boots while working with calves are all best management practices. Also work younger calves to older calves to help prevent disease spread.
For more tips on preventing zoonotic diseases, listen to Bender’s presentation here.