Airborne horizontal transmission of Salmonella enteritidis in molted laying chickens

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. To test for airborne transmission, hens were placed in two rows of cages, the rows separated from each other by 1 m. One row of hens was challenged with S. enteritidis, whereas the other row remained unchallenged but exposed to the room air. Ventilation delivered within the room provided an even air distribution within the area and minimized directional air flow toward any set of cages. In Expt. 1, 4 of 12 and 9 to 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. Similar S. enteritidis levels were detected circulating in the air in the two rooms housing the hens. Expts. 2 and 3 examined airborne transmission in molted hens only. In Expt. 2, 2 of 12 exposed hens became infected with S. enteritidis at 3 days postchallenge, and this increased to 12 of 12.1 wk later. In Expt. 3, exposed hens were again housed in cages 1 m from challenged hens but were placed in every other cage to prevent transmission through contact with hens in adjacent cages. At 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. Large numbers of S. enteritidis shed by the molted challenged hens were recovered from the floors beneath the cages. These results indicated that, contrary to the generally held beliefs regarding organism spread, airborne transmission of S. enteritidis can occur and induced molting can provide the impetus for this event. As was observed previously, rapid dissemination of the organism to other members of the flock resulted through bird-to-bird contact.