Alien E. coli: As Dangerous as STEC O157:H7

STEC serotype O165:H25 poses new hazard to humans
Cattle feeders and veterinarians should keep an eye out for E. coli O165:H25, an enterohemorrhagic strain that can cause disease in cattle and potentially poses a food-safety hazard for humans.

An Unexpected Death in the Family…

Russ Rice, a Veterinarian from Broken Bow, Nebraska, did not expect today to be the beginning of a saga that made him consider E. coli – certain STEC subsets, in particular – in a different way. He stood still as he observed the crew begin to pull some young female cows from a pen of 170 other heifers. Rice and his crew chose the cows based on their general demeanor and appearance, carefully selecting those that seemed to be lethargic, sick, or acting abnormally.

Today, he had noticed a number of heifers he felt were in need of respiratory disease treatment.

As the crew pulled the cows, Rice “noted that some bloody stools were present in the containment pen.” As a result, he also treated the animals for coccidiosism, a parasitic disease of the intestinal tract that manifest as bloody diarrhea. Despite the treatment, the cows’ bloody stools continued, and one of the animals died.

Rice examined the cow that died from what he had believed to be a fairly common intestinal ailment among young cattle. He immediately noticed abnormalities in the animal’s intestinal tract that were readily visible to the human eye.

He immediately submitted specimens from the heifer to the University of Nebraska diagnostic laboratory for testing.

…From an Unexpected Cause – Non-O157:H7 STEC (EHEC)

The test results came as more than a bit of a surprise: the laboratory found signs of attaching and effacing E. coli, and subsequently diagnosed the O165:H25 enterohemorrhagic, also known as Shiga toxin-producing (STEC) strain.

In humans, infections with some STEC serotypes “may result in hemorrhagic or nonhemorrhagic diarrhea, which can be complicated by” Hemolytic Uremic Syndrome (HUS), a potentially fatal complication that has the potential to lead to liver failure and death.

These specific STEC strains are known as enterohemorrhagic E. coli (EHEC) — EHEC strains are a subgroup of STEC with “high pathogenic potential for humans.”

Protecting the Herd

Rice recognized the need to take proactive measures to prevent the other heifers from contracting the potentially lethal disease. He added bovamine – essentially probiotics for cattle, or additional “good bacteria” to offset any STEC in the animals’ digestive tracts – to the cows’ food. He also decreased the amount of grain and increased the amount of hay the heifers were rationed each day.

A week following the change in diet, stool samples taken from the pen in question all tested negative for E. coli O165:H25.

At the same time, tests conducted on samples taken from the pen next to the one that had housed the E. coli-infected heifers tested positive for coccidia, the parasitic condition that Rice initially believed the animals infected with STEC had.

Rice drew two conclusions from the presence of coccidia in the adjacent pen:

First, he came to strongly suspect that coccidiosis initially infected the cows that later contracted E. coli O165:H25. The coccidiosis would essentially weaken the heifers’ immune system, making them more susceptible and less able to fight off the E. coli infection.

Second, Rice “also suggests that cases of STEC could be mistaken for coccidiosis, salmonella, BVD” (a diarrheal disease affecting bovine) or “other diseases” in the absence of laboratory diagnosis.

While his first conclusion helped explain the events of the past week or so, the second observation was more troubling. A potentially lethal strain of E. coli could easily be mistaken for a much more mundane condition. The second conclusion only led to more questions: how prevalent is this strain of E. coli? is it frequently detected in bovine? has it been detected in humans? how often is it tested for?…and the questions continued.

Future Ramifications

“Cattle feeders and veterinarians should keep an eye out for E. coli O165:H25, an STEC strain that can cause disease in cattle and potentially poses a food-safety hazard for humans.”

“The O165:H25 serotype,” Rice says, “is similar to E. coli O157:H7, and could be an emerging food-borne pathogen in cattle and beef.” He suggests that veterinarians include STEC in their list of differential diagnoses when they see enteric disease in feedlot cattle.”

Serotype O165 has now been associated with an outbreak in the Northwest US, and the complete whole-gene sequence for E. coli O165:H25 STEC was finally reported in December of 2015.

All that’s left to discover is how many other serotypes may be – or become – virulent to humans; and whether – or how much – they differ from O157:H7.

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