Solving the Campylobacter Mystery
|The age-old question of which came first, the chicken or the egg, is one scientists are pondering as they search for the source of Campylobacter, a foodborne bacterium that causes a human illness called campylobacteriosis. To find the answer, researchers from the Agricultural Research Service and the Canadian Food Inspection Agency traveled to Iceland. Why? Because Iceland has qualities that make such a study worthwhile. It has a closed agricultural system, meaning that almost all foods consumed by its inhabitants are produced within its borders. Poultry production in Iceland is no exception. It is an integrated approach with a high degree of control; breeder eggs are obtained from Sweden, hatched in Iceland, and quarantined at rearing farms. The birds at these farms are the breeders that lay eggs intended for broiler production. Access to poultry houses is limited to veterinarians and farmers. Additionally, water sources and nearby domestic livestock can be thoroughly investigated to assess their contributions to broiler flock infection.|
|| Iceland's poultry industry could be
seen as a smaller version of the industry in the United States, since they
operate in similar ways. "There is a thousandfold difference in the size
of the two countries, which translates the goals of the program from nearly
impossible in the United States to manageable in Iceland," explains Norman
J. Stern, research leader for ARS' Poultry Microbiological Safety Research
Unit. "Iceland's size allows researchers to exhaustively study the
Iceland also has one of the highest standards of public health in the world,
including monitoring its food supply. A zero-tolerance policy is in place for
Salmonella in the poultry population. If these bacteria are present, the
flock that harbors them is destroyed and the facility sanitized.
Campylobacter, however, has become a problem in Iceland as it is here in
the United States.
Because of its socialized system of health care, Iceland also monitors human
disease closely and keeps detailed records. The system allows a source of
illness to be traced back from the sick person more easily and quickly than in
the United States. Campylobacter is the most common bacterial cause of
diarrhea in the United States. The Centers for Disease Control and Prevention
estimates there are more than 2 million cases of campylobacteriosis each year.
Iceland, with its insulated poultry industry, was the ideal place to research
the source of Campylobacter.
The researchers in ARS' Poultry Microbiological Safety Research Unit believe
they have found one major source of Campylobacter: the fertile chicken
egg. Historically, possible sources of Campylobacter were thought to be
the feed, wild birds, well water, insects, and rodents. Through inoculation
studies, scientists showed that the bacteria couldn't survive longer than an
hour in dry conditions, eliminating bird feathers and hatchery transport paper
pads from the list of possible sources. Attention then focused on poultry
feces, which are moist and provide the environment needed for
Campylobacter to survive. By use of genotyping (DNA sequencing of
genetic material), a specific gene in Campylobacter was isolated from
fecal samples and used as a marker to identify identical Campylobacter
Microbiologist Kelli L. Hiett is conducting molecular analysis of broiler
production samples collected in the search for the source of
Campylobacter. "We can determine the genetic profile relationships
of the isolates," says Hiett. Campylobacter organisms from a
broiler-breeder flock and its broiler offspring were found to be identical,
even though the flocks were housed 20 miles apart. The two flocks had no
contact, other than that the eggs from the broiler-breeder operation were
transported 20 miles to the broiler hatchery.
Evidence suggests that the only way the same Campylobacter isolate could
have traveled from one location to the other is for it to have been in the
moist confines of the egg. Since previous studies showed Campylobacter
cannot survive in a dry environment, if the Campylobacter bacteria were
on the egg surface, it would dry out and perish during transport. Once the
organism dries out, it becomes undetectable by known methods.
The reproductive tracts of breeder hens were then tested, and
Campylobacter was present. Experiments are now under way to determine
whether breeder flocks are the most important source of these bacteria. Says
ARS microbiologist Nelson A. Cox, "Campylobacter was found all
through the egg-making machinery of the breeding hens, though we still don't
know the mode of action of the bacteria."
Three years ago, during discussions between scientists from the Poultry
Microbiological Safety Research Unit and various scientific agencies in
Iceland, it occurred to researchers that perhaps they could conduct
epidemiologic studies on Campylobacter in broiler operations and track
it through human incidences of campylobacteriosis. Iceland was an ideal
location to test sources of infection, since the country produces 100 percent
of the broilers consumed within its borders. Even though Icelanders consume
only about one-quarter the amount of poultry Americans do, campylobacteriosis
is much more prevalent in Iceland than in the United States. Human and chicken
biological samples were collected in Iceland and shipped to the United States
Through DNA sequencing of Icelandic poultry and human isolates, researchers
were able to prove the DNA sequence profiles of the isolates are identical.
"We can also see that the time from processing the poultry product to
consumption and onset of human illness is consistent with poultry being the
initial source of the human isolate," says Hiett. "Ninety percent of
human isolates of Campylobacter had genetic fingerprints identical to
those found in chickens," explains Stern.
Ultimately, the ongoing research may determine the major sources of
transmission and lead to a way to reduce the presence of Campylobacter
or prevent it from entering the marketplace. The Canadian researchers are
conducting risk analyses and developing models with varying parameters. But,
for the purposes of finding the source of Campylobacter, Cox says,
"Iceland was the research opportunity of a lifetime."By
Durham, Agricultural Research Service Information Staff.
This research is part of Food Safety, an ARS National Program (#108)
described on the World Wide Web at http://www.nps.ars.usda.gov.
Norman J. Stern is in the USDA-ARS Poultry Microbiological Safety Research Unit, 950 College Station Rd., Athens, GA 30603; phone (706) 546-3516, fax (706) 546-3771.
"Solving the Campylobacter Mystery" was published in the June 2001 issue of Agricultural Research magazine.