Classroom Embryology Projects: Health Risk Myths and Facts

The Myths

Recently, People for the Ethical Treatment of Animals (PETA) sponsored a full-page advertisement entitled: "Chick-hatching experiments are a shell game for children's health and for the chicks". In their ad, PETA stated that newly-hatched chicks place children at risk for contracting Avian Influenza, West Nile Encephalitis, or E. coli and Salmonella infections. This type of deplorable, self-serving information is replete with misinformation, and we would like to refute their claims by providing science-based, factual information.

The Facts

  • As we will subsequently discuss, it is blatantly false to say that baby chicks put children at risk for contracting Avian Influenza and West Nile Encephalitis.
  • The risks of becoming infected by E. coli and Salmonella are minimal.
  • Although E. coli and Salmonella can be found in young fowl, transmission from chicks to humans can be essentially eliminated through careful hand washing with soap and water.
  • To deprive students of the numerous real-life lessons that can be gleaned from embryology projects (e.g., reproduction, growth, development, and even death [i.e., non-hatching eggs]), while emphasizing the importance of sanitation after handling any animal, is certainly difficult to rationally defend.
  • Very few things in life are completely risk-free and the many health risks that children face each day are far greater than the extremely small risk associated with a well-controlled chick embryology project.

The Details

Avian Influenza (AI)

  • Chicks are never born with AI. In scientific terms, we say there is no "vertical transmission" of the AI virus. This means that, even if it were present in a breeder hen, the AI virus would not transmit through the fertile egg to the chick.
  • In Pennsylvania, all breeder flocks are tested monthly for AI and, if any are found positive, the flock would be depopulated. In addition, even if eggs from such flocks were incubated, the AI virus would not be vertically transmitted to the embryo (as stated above). In addition to breeder flocks, Pennsylvania monitors commercial flocks for AI on a regular basis, and active AI would never be allowed to remain in any flock.
  • Most strains of AI 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 AI responsible for the 1997 outbreak.
  • It was purely coincidental that the first child to be found to have the AI 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 AI 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 AI.
  • The Bottom Line: The risk associated with newly-hatched chicks and AI 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.
  • Pennsylvania is presently participating in an intense WNE monitoring study. To find out how the State of Pennsylvania, Penn State, and other governmental agencies and universities are responding to the current WNE situation, or to find out more about WNE, check out the following two websites: http://www.westnile.state.pa.us/ and http://www.pested.psu/edu/spwestnile.html.
  • 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 Pennsylvania 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 birds 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.

For more information, please contact any of the following individuals:

Prepared by 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.)