CLASSROOM EMBRYOLOGY PROJECTS:
HEALTH RISK FACTS
David C. Kradel (M.S., M.P.H., D.V.M),
Robert G. Elkin (B.S., M.S., Ph.D.) and
R. Michael Hulet (B.S., M.S., Ph.D.)
Department of Poultry Science
College of Agricultural Sciences
The Pennsylvania State University
213 William L. Henning Building
University Park, PA 16802-3501
THE FACTS
Avian Influenza (Al)

Chicks are never born with Al. In scientific terms, we say there is no “vertical
transmission” of the Al virus. This means that, even if it were present in a breeder hen,
the Al virus would not transmit through the fertile egg to the chick.

Most breeder flocks are tested monthly for Al and, if any are found positive, the flock
would be depopulated. In addition, even if eggs from such flocks were incubated, the
Al virus would not be vertically transmitted to the embryo (as state above). In addition
to breeder flocks, many states monitor commercial flocks for Al on a regular basis, and
active Al would never be allowed to remain in any flock.

Most strains of Al virus are species-specific and infect only one species. For instance,
human influenza only infects people, equine influenza only infects horses, avian
influenza usually only infects avians – with the one documented exception being the
Hong Kong strain of Al responsible for the 1997 outbreak.

It was purely coincidental that the first child to be found to have the Al flu in Hong
Kong had been in a classroom with chicks. The child involved was also suffering from
another severe disease and thus had a severely compromised immune system. Clearly,
there were other multiple opportunities for the child to be exposed to the virus.

The Al virus strain responsible for the 1997 Hong Kong problem is not present in the
U.S. Thus, in reality, American children are not at risk from this strain of Al.

THE BOTTOM LINE: The risk associated with newly-hatched chicks and Al is essentially
nonexistent for American children.
West Nile Encephalitis (WNE)

The only means by which the virus which causes WNE can be naturally transmitted to
people, horses, and other animals is from the bite of an infected mosquito.
Mosquitoes become infected by sucking the blood out of certain species of wild birds;
thus, the only effective preventative measure is mosquito control.

The virus that causes WNE is not vertically transmitted from the hen to the embryo.
Therefore hatching eggs or chicks cannot be a source of the virus.

There is no evidence that the virus that causes WNE is present in poultry in the U.S.
Experimental exposure of chickens did not result in illness. The chickens developed
antibodies but did not harbor the virus in their blood or tissues for an extended period
of time, as occurs in wild birds.

THE BOTTOM LINE: There is absolutely no evidence that newly-hatched chicks could
be infected with (and transmit to humans) the virus that causes WNE.
E. coli and Salmonella

The intestinal tracts of all mammals (including humans) and birds have various types
of E. coli, while some have Salmonella. Because E. coli and Salmonella often comprise
the natural intestinal microflora of many animal species, there are many opportunities
(such as pets, playmates, etc.) for young children to be exposed to these bacteria.

Some types of E. coli and Salmonella are more likely to cause disease in susceptible
humans. An example of this is the E. coli O157:H7, which is found in cattle intestines
(feces) but has not been generally found in poultry.

A small percentage (0.005%; or 1 in 20,000) of all eggs produced contain Salmonella
enteritidis (SE). Today all breeder flocks are tested monthly for SE and, if found
positive, are depopulated. All Midwestern breeder flocks have been negative for SE for
over six years.

Although most of the estimated 1.4 million human salmonellosis cases that occur
annually in the U.S. are caused by foodborne illnesses, direct contact with animals,
particularly reptiles and occasionally birds, may also be a source of infection (Source:
MMWR Weekly, April 14, 2000/49(14):297-299). Because Salmonella organisms are
shed in the feces, humans become infected when contaminated food, hands, or other
objects are placed in the mouth.

Hand washing is necessary to reduce any risk associated with Salmonella and E. coli
infections following direct or indirect contact with animals. This can significantly
eliminate any already minimal risk.

In general, any E. coli or Salmonella that may be present in a chick comes from
environmental exposure to fecal material that may have been present on the eggs
prior to start of incubation. Therefore the setting of very clean eggs in a well-sanitized
incubator can further reduce any potential for a problem with E. coli or Salmonella.

A recent large-scale epidemiological study of Salmonella infection in children showed
that the primary place of exposure was the home. Therefore, in order to prevent the
potential transmission of bacteria from children to the chicks, hand washing prior to
handling the eggs or bird would also be advised.

THE BOTTOM LINE: Exposure to chicken fecal material could, in rare instances, result
in infection from Salmonella and, less frequently, from E. coli. However, many other
bacterial and viral infections can result from poor hand sanitation. Thus, the teaching
of good hygiene (sanitation) habits can significantly reduce the already very small risk
of Salmonella or E. coli infections.