The spring season in Texas brings with it a return to warm weather, the beginning of seeding operations in many places, emerging plant life in the southern tier of the state, spring calving, and hope for a successful year for farm and ranch operations.
It also marks a time for longer days in the field and the many roadblocks of agriculture that return each year as spring quickly leads into the return of summer and the concerns brought about by rising temperatures on the farm and ranch.
A recent study led by the Cornell University College of Veterinary Medicine sheds new light on potential warm weather problems associated with livestock operations, indicating for the first time the possibility that water troughs on farms, and especially feed lots, can be a conduit for the spread of toxic E. coli in cattle, which can then spread the pathogen to humans through bacteria in feces.
Escherichia coli O157:H7 (E. coli O157:H7) is one of hundreds of types of the bacterium E. coli. Most types of E. coli are harmless and naturally live in the intestines of healthy humans and animals. However, E. coli O157:H7 produces a powerful toxin that can cause severe illness in humans.
Around 5 percent of E. coli O157:H7 infections lead to a severe complication called hemolytic uremic syndrome (HUS). HUS can stop a person’s kidneys from working properly and can destroy the person’s red blood cells, possibly requiring blood transfusions. About 5 percent of HUS cases are fatal. Even in non-fatal cases, the average hospital stay is 11 days, and health problems can continue for life.
Renata Ivanek, associate professor of epidemiology at Cornell and the paper's senior author, warns that the bacteria can easily be contracted by farm animals from contaminated water often found in watering troughs.
"Water troughs appeared in our mathematical model as a place where water can get contaminated and is where we could break the cycle," said Ivanek.
The hypothesis was tested in the field with surprising results.
Humans, often farm and ranch workers, commonly acquire infections from shiga toxin-producing E. coli through cow feces-contaminated beef and salad greens. The main shiga toxin-producing strain, E. coli 0157:H7, causes more than 63,000 illnesses per year and about 20 deaths, according to the Centers for Disease Control. Though cows carry and spread E. coli 0157:H7 when they defecate, the bacteria do not make them sick.
"Farmers do not see a problem because they see no clinical signs in cows; it is totally invisible," Ivanek said.
Symptoms of an E. coli O157:H7 infection include diarrhea and severe stomach cramps. Diarrhea usually starts out watery and then after one to three days turns bloody. People usually get sick two to five days after ingesting the bacteria. Their illness usually last for five to 10 days. Sometimes people infected with E. coli O157:H7 have no symptoms at all, but can pass the bacteria to others.
If a person develops HUS, on average it will occur within one week after their diarrhea started. Clues that a person is developing HUS include fatigue and decreased frequency of urination. HUS most commonly affects young children and adults over 60 years of age, but may affect any age group.
"A vaccine to reduce bacterial shedding in cows exists, but the beef industry has little incentive to use it, partly due to cost, and the industry does not benefit from labeling beef as E. coli safe," Ivanek said.
Ivanek and a research team of 20 co-authors conducted a study to identify other ways to reduce the bacteria's prevalence in cattle, which can vary over the year from zero to 100 percent of cows in a feedlot carrying the bacteria, with rates generally rising in the summer.
The group ran control trials in a feedlot over two summers. Trials involved reducing water volume in troughs in randomly selected treatment pens and leaving the volume unchanged in control pens. They expected that reducing water levels in troughs would prevent the spread of E. coli. Instead, they found reduced water levels increased spread; in the treatment pens, the odds of finding shiga toxin-producing E. coli in cows was about 30 percent higher than in the control pens.
"Our modeling studies did pick up the right parts of the system," Ivanek said, "but the mechanism that we postulated is the opposite from what we thought."
More research is needed to determine why more water in troughs reduced E. coli in cows, but Ivanek questions whether the lower volume made it easier for cows to swallow debris at the bottom of tanks, or whether a fuller tank reduced E. coli concentrations.
Next steps include repeating the results in other feedlots, evaluating the effectiveness and cost benefit of using more water to reduce E. coli, investigating how seasons and temperatures play a role in prevalence of E. coli, and understanding the actual mechanisms that led to the results.