Cow Conundrum

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http://abcnews.go.com/sections/living/SecondOpinion/secondopinion010409.html

 

Cow Conundrum

Could Microbe in Dairy Cattle Be Found in Milk?

 

Commentary

By Nicholas Regush

 

 

April 9 — Here is a widespread farm animal disease to think about. This one

causes diarrhea, wasting and death, primarily in dairy cattle. Some scientists

are raising the alarming possibility that the microbe causing the illness may be

passed on to humans via milk.

 

 

The controversy about possible animal-to-human transmission of the microbe even

extends, on the basis of scientific theory, to ground beef and tap water.

The contagious animal disease is called Johne’s (pronounced “Yo-nees”).

There has been accumulating evidence in recent years that the bacterium causing

the disease, known as mycobacterium avium subspecies paratuberculosis, or MAP,

has some association with Crohn’s disease and may play some role in its

development.

Crohn’s is an often severe gastrointestinal illness affecting at least a half

million Americans. It causes symptoms such as abdominal pain, disabling

diarrhea, and loss of appetite. Drug treatments are limited and there is no

cure.

Complex, On the Rise

An extensive search of the literature on Johne’s disease and Crohn’s, and

interviews with experts reveals that the issues surrounding the possible animal

link to human disease are, to say the least, complex.

What is very clear is that Johne’s disease, which also affects sheep, goats,

deer, antelope and llamas, is on the rise, and that infected cattle continue to

be used for milk production and are then slaughtered, mainly for ground beef,

according to the dairy and beef industries, and veterinarians studying the

disease.

While the full extent of the disease is difficult to assess because of limited

testing for it, federal officials and the dairy industry estimate on the basis

of a 1996 national survey that some dairy cattle are infected in about 22

percent of herds across the country.

Dr. Michael Collins of the School of Veterinary Medicine at the University of

Wisconsin, on the basis of discussions with key researchers across the country,

including those at a meeting held in Colorado Springs late last month of a

national Johne’s monitoring group, estimates that the number of herds affected

is much higher.

“Most veterinarians and scientists that I speak to about this now believe that

the figure is at least 50 percent, if not higher, in many regions across the

country,” he says.

He emphasizes that “Johne’s has become common, and since there are no adequate

control mechanisms in place it will become even more common.”

Vaccines Ineffective, No Cure

Anti-microbial treatments for Johne’s do not cure the disease and a vaccine is

not a reliable way to stop it.

Chris Galen, vice president of communications at the National Milk Producers

Federation, said the disease costs farmers about $200 million each year. His

group asked Congress last week to allocate $1.3 billion over seven years to test

for Johne’s and to reimburse farmers for their losses.

“Right now, there is not a lot of incentive to test animals because of the

losses to farmers,” he said.

While Galen believes that “Johne’s is certainly a concern to the domestic cattle

industry because cattle lose weight and their milk production drops,” he

emphasizes that “milk is totally safe.”

As evidence, for example, he cites a recent federal study concluding that

pasteurization of milk kills the bacteria that dairy cattle excrete into the

milk.

Not so fast, says Collins. “The dairy industry takes a hard line on this, and

it’s certainly not that black and white.”

Collins recently headed a task force of 30 experts on Johne’s disease from 18

countries that was sponsored by the International Dairy Federation. One chapter

of its 61-page report that was published in January focuses on milk

pasteurization.

The report states that “it is difficult to come to any definitive conclusions

based upon the relatively few heat inactivation laboratory studies that have

been performed with MAP so far.” One reason is that “methods among labs have

varied widely.”

Does Pasteurization Work?

The scientists on the task force particularly note that pasteurization certainly

“produces a significant killing of [MAP],” but that finding needs to be

reconciled with research in Britain.

A preliminary British report issued in September 2000 by the

government-appointed Advisory Committee on the Microbiological Safety of Food

showed that live cells of MAP were found in 1.9 percent of raw milk samples and

2.1 percent of pasteurized retail milk samples tested. The study reaffirmed

conclusions from an earlier British report.

So, obviously, more research is needed, and that is exactly the conclusion of

the International Dairy Federation task force.

And are there other ways that MAP can find its way from animals to humans? There

might be, but for now there is only theory, based on an understanding of how the

microbe infects dairy cattle and how it potentially can be transmitted.

Collins points out that MAP not only attacks the intestinal tract of dairy

cattle but that it is also present in blood and many organs of the body.

Therefore meat could theoretically contain MAP.

“When cows go to slaughter, there is also a risk of fecal contamination of the

meat,” he said, adding that while the slaughterhouses now take great precaution

in cleaning out carcasses of any potential contamination, it is not possible to

get rid of all microbes in fecal matter.

And he concludes: “Most dairy cows with Johne’s disease are used for ground

beef, so contamination of the ground beef is plausible.”

The appropriate research has not yet been done to test this theory and there are

no studies to determine whether cooking ground beef gets rid of any possible

MAP.

Questions About Ground Beef

“Ground beef is a question mark,” Collins said. Gary Weber of the National

Cattlemen’s Beef Association says his group “is aware of the issue,” and is

sponsoring a study at Cornell University in Ithaca, N.Y., to determine if MAP

can be found in ground beef. The focus, however, is not on fecal matter but on

lymph nodes of dairy cattle, where the bacterium can be concentrated.

“We’re looking to see whether these tiny lymph nodes could end up in ground

beef,” he said.

And there is evidence that they do but that the risk is low, according to Dr.

Donald Lein, head of the diagnostic lab at Cornell that conducted the

soon-to-be-published study. “In dairy cattle with end-stage Johne’s disease,

some of the lymph node can get in,” he said, referring to lymph nodes in the

knee and shoulder areas.

Weber says his group is also involved in the design of a study that will focus

on the types of cooking practices that might kill MAP in ground beef.

MAP in Water?

It is also plausible that MAP gets into in tap water. Cows excrete the bacteria,

and it can run into streams and city water supplies. In fact, the water supply

is thought to be the way that people with AIDS acquire intestinal infections

with a bacterium, mycobacterium avium, that is the most closely related cousin

to MAP. “Water is worth thinking about too,” Collins said.

The next big question is whether MAP is a trigger for Crohn’s disease. Here

again, there is considerable debate. A review of the peer-reviewed studies to

date shows that at least seven of 10 that involved testing for MAP in diseased

gut tissue obtained from surgery showed a statistically significant association

between a positive test and Crohn’s.

Some researchers who have tested only small samples of tissue from biopsies

didn’t find signs of MAP.

Others warn that any form of diagnostic tests for MAP may be limited in that

they may also be picking up signs of other biological materials.

Also, experts in Crohn’s disease have long taken the position that the disease,

whose cause is not clear, is set off by the body’s immune system attacking

itself, possibly due to a genetic factor, and that a microbial trigger is not

necessary.

However, those researchers who believe that MAP is likely linked to Crohn’s cite

preliminary studies showing there is an immune reaction in some Crohn’s patients

to MAP and that up to 40 percent of Crohn’s patients show signs of an antibody

response to the bacteria.

And some doctors like Florida gastroenterologist Ira Shafran, who have recorded

signs of MAP in their patients and published their data, are already treating

some successfully with antibiotics.

“Many of my patients on antibiotics do very well and some have remissions after

struggling with other medications for many years,” he said, adding that a lot

more research urgently needs to be done to explore the link between MAP and

Crohn’s.

Shafran, as others who believe that MAP is probably important in Crohn’s, also

suggests that this bacterium is not likely the only trigger. Other microbes may

be involved in setting off the disease.

So, in the end, there is much debate and uncertainty, as is often the case in

medical science. Johne’s disease and its possible link with Crohn’s reminds me

of how Australian researchers tried to convince their medical colleagues that

ulcers were not always caused by stress, but rather often by a microbe named H.

pylori.

In presenting their case, they often met with ridicule. Now, ulcers are commonly

treated for an H pylori infection. Could MAP and Crohn’s turn out this way too?

 

 

 

 

 

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