SALMONELLA ENTERICA SUBSP. ENTERICA IN CATTLE EGRET (BUBULCUS IBIS) CHICKS FROM CENTRAL TEXAS: PREVALENCE, SEROTYPES, PATHOGENICITY, AND EPIZOOTIC POTENTIAL David N. Phalen, 1,2,6 Mark L. Drew, 2,4 Bruce Simpson, 2 Kimberly Roset, 2,5 Kimberly Dubose, 2 and Miguel Mora 3 1 Wildlife Health and Conservation Centre, University of Sydney, Camden, New South Wales, 2570, Australia 2 Department of Veterinary Pathobiology, Texas A&M University, College Station, Texas 77843, USA 3 Wildlife and Fisheries Science Department, Texas A&M University, College Station, Texas 77843, USA 4 Current address: Idaho Department of Fish and Game, PO Box 25, Boise, Idaho 83707, USA 5 Current address: ABC Animal and Bird Clinic, 11930 Highway 6 South, Sugar Land, Texas 77478, USA 6 Corresponding author (email: dphalen@camden.usyd.edu.au) ABSTRACT: Cattle Egrets have a worldwide distribution, feed in proximity to cattle and other domestic animals, and often nest in large colonies in urban woodlots. Over a 3-yr period, nestlings from five Cattle Egret colonies from Central Texas, USA, were surveyed for salmonellosis. Prevalence of infection ranged from 29% to 95%. Seventeen Salmonella enterica subsp. enterica serotypes were isolated, of which the 4,5,12:i-monophasic serotype predominated in cultures of both the digestive tract and pooled spleen and liver. Of 11 4,5,12:i-monophasic isolates phage typed, eight were determinate type 193. The 4,5,12:i-monophasic isolates were susceptible to all antibiotics tested and were highly invasive in the day-old chick infection model. Microscopic lesions were found in the livers of Cattle Egrets with systemic infections with the 4,5,12:i- monophasic serotype, suggesting that infections with this serotype may often be fatal. Twenty-nine serotypes were identified in 179 S. enterica subsp. enterica isolates from horses admitted to the Texas A&M University Veterinary Teaching Hospital in 2 yr following the Cattle Egret study. The 4,5,12:i-monophasic serotype was not isolated from horses, but 12 serotypes were isolated from both horses and Cattle Egrets. The temporal distribution of the horse cases suggested that Cattle Egrets and horses may be exposed to similar sources of Salmonella, but provided no evidence of transmission between these two species. Similar conclusions were drawn when Cattle Egret isolates were compared to isolates from feedlot and dairy cattle from Texas and surrounding states. Given that the Cattle Egret 4,5,12:i-monophasic serotype was highly invasive and other isolates of this serotype have been associated with food poisoning, it is likely that Cattle Egret colonies pose a health risk to humans living near them. Key words: Bubulcus ibis, Cattle Egret, pathogenicity, prevalence, Salmonella enterica subsp. enterica, serotype, 4,5,12:i-monophasic. INTRODUCTION Salmonellosis in wild birds is a well- documented phenomenon that occurs in widely divergent gregarious species of birds, including gulls, ducks, and passerine birds such as the Cowbird (Molothrus ater) and House Sparrow (Passer domes- ticus; Tizard, 2004). Salmonella enterica subsp. enterica infections in birds can result in a transient colonization of the digestive tract, a carrier state, or disease. Carriers act to disseminate these bacteria and are thought to be sources of salmo- nellosis in livestock, pet cats and dogs, and humans (Williams et al., 1977; MacDonald and Bell, 1980; Benton et al., 1983; Coulson et al., 1983; Tauni and O ¨ sterlund, 2000; Tizard, 2004). Birds that are tran- siently infected or carry Salmonella are typically infected with a variety of sero- types that reflect the organisms that they are exposed to in the wild (Quessy and Messier, 1992). In some species, such as the Pigeon, specific species of Salmonella appear to be host adapted (Faddoul and Fellows, 1965). Even host-adapted Salmo- nella species, however, can cause signifi- cant disease in their host species. As an example, since the 1950s specific sero- types and determinate types of S. enterica subsp. enterica caused high mortality in the House Sparrow and may be responsi- ble for the decline of other passerine birds (Wilson and MacDonald, 1967; Prescott et al., 2000). Journal of Wildlife Diseases, 46(2), 2010, pp. 379–389 # Wildlife Disease Association 2010 379