The role of an early Salmonella Typhimurium infection as a predisposing factor for necrotic enteritis in a laboratory challenge model.

Necrotic enteritis (NE) caused by Clostridium perfringens (CP) in poultry is an important bacterial disease in terms of economic implications. The disease is multifactorial and is invariably associated with predisposing factors. In the present experiments, we investigated the potential predisposing role of neonatal Salmonella Typhimurium (ST) infection for NE-associated mortality in a laboratory challenge model. In two experiments, day-of-hatch chicks were randomly assigned to four groups: Group 1, nonchallenged control; Group 2, chickens received Eimeria maxima (EM) and CP; Group 3, chickens received EM and CP and were also challenged with ST at day 1 of age; Group 4, chickens received EM and CP and were also challenged with ST at day 17 of age. Challenged groups received an oral dose of EM at 18 days of age and CP (10(8) colony-forming units/chick) at 22-23 days of age. When compared to EM and CP, chicks challenged with ST (day 1) had increased NE-associated mortality and CP-associated lesion scores (P < 0.05) in both experiments. Furthermore, body weight and body weight gain were lower (P < 0.05) in chicks infected with ST (day 1) in the first experiment, even though no differences (P > 0.05) were observed in weight gain in the second experiment. Chicks challenged with ST (day 17) were similar to the EM and CP group in all of the above-mentioned parameters, indicating that a paratyphoid infection in younger chicks remarkably alters the susceptibility to secondary bacterial infections. Based on this work, the authors suggest that an ST infection early in the age of a chick may be important for altering susceptibility to NE, an observation that may be useful from the perspective of experimental reproduction of this disease and, perhaps, as an economically important reason to address the problem of paratyphoid Salmonella infections in young chicks.