ARS | Publication request: AIRBORNE HORIZONTAL TRANSMISSION OF SALMONELLA ENTERITIDIS IN MOLTED LAYING CHICKENS

Submitted to: Avian Diseases
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: May 28, 1997
Publication Date: N/A

Interpretive Summary: Induced molting is a procedure used by greater than 60% of the layer industry nationwide to achieve a second egg lay from their older hens. The primary method of inducing a molt is through a 10-14 day feed-removal protocol which causes the hens to cease lay for a certain period of time. We previously found that this procedure increases the severity of an infection by Salmonella enteritidis (SE) in these birds, substantially decreases the numbers of organisms necessary to infect the birds, and causes the rapid spread of the SE to uninfected birds in adjacent cages. SE became a major problem for the egg industry due to the large number of people getting sick from SE-contaminated eggs. The question we asked was: because SE spreads so readily to molted hens in adjacent cages, can it also spread through the air. The answer was yes, it can spread by this route although to a much lesser degree than through direct contact. These e results are important to the layer industry since they show that a prevalent industry procedure can have an effect on the spread of SE to members of the flock in different areas of the house. This could change the SE situation of a flock from a minor one to one where a large number of birds are infected. Such a situation might lead to an increased production of SE-contaminated eggs with the consequent risk to consumers and also increase the chance of passing the infection to future flocks.

Technical Abstract: Salmonella enteritidis is currently thought to be transmitted principally through contact with infected individuals and ingestion of fecally- contaminated materials. The present study was undertaken to determine if S. enteritidis could be spread in chickens by the airborne route and if induced molting could affect this mode of transmission. Hens were placed in 2 rows of cages, the rows separated from each other by 1 meter. One row of hens was challenged with S. enteritidis, while the other row remained unchallenged but exposed to the room air. In Expt. 1, 4 of 12 and 9 of 12 exposed molted hens became infected with S. enteritidis after 3 and 8 days of exposure, respectively, compared with 1 of 12 and 0 of 12 unmolted hens sampled on the same days. Experiments 2 and 3 examined airborne transmission in molted hens only. In Expt. 2, 2 of 12 exposed hens became infected with S. enteritidis 3 days post challenge and this increased to 12 of 12 one week later. In Expt. 3, exposed hens were agai housed in cages 1 meter from challenged hens, but were placed in every other cage to prevent transmission through contact with hens in adjacent cages. Day 3 post challenge, 0 of 12 exposed hens were culture positive for S. enteritidis and this increased to only 3 of 10 positive hens at day 10. These results indicate that airborne transmission of S. enteritidis occurred and induced molting increased the incidence of this event.