Introduction

Salmonella Enteritidis and S.Typhimurium are presented separately from other sero-types of Salmonella because, on the one hand, these bacteria are often specifically cited in zoonosis control legislation, and, secondly, because there are differences in the epidemiology as compared to other salmonellae. These are the predominant sero-types associated with human disease in most countries.

Salmonella Enteritidis, especially phage type 4, has become much more common in both poultry and humans since the early 80s. The prevalence of S.Typhimurium has remained relatively stable though the spread of the highly antibiotic-resistant strain DT104 in various farmed species gives some reason for concern. Infections in chickens, turkeys and ducks cause problems worldwide with morbidity of 0-90% and a low to moderate mortality. Many infected birds are culled and others are rejected at slaughter. The route of infection is oral; many species are intestinal carriers and infection may be carried by faeces, fomites and on eggshells.

Vertical transmission may be either by shell contamination or internal transovarian contamination of yolk. Feed and feed raw material contamination is less common than for other sero-types. The bacteria are often persistent in the environment, especially in dry dusty areas, but are susceptible to disinfectants that are suitable for the particular contaminated surfaces and conditions, applied at sufficient concentrations. Temperatures of around 80°C are effective in eliminating low to moderate infection if applied for 1-2 minutes. This approach is often used in the heat treatment of feed. Predisposing factors include nutritional deficiencies, chilling, inadequate water and other bacterial infections.

Signs

• Dejection.
• Ruffled feathers.
• Closed eyes.
• Diarrhoea.
• Vent pasting.
• Lost of appetite and thirst.
• Stunting in older birds.

Post-mortem lesions

• In acute disease there may be few lesions.
• Dehydration.
• Enteritis.
• Focal necrotic intestinal lesions.
• Foci in liver.
• Unabsorbed yolk.
• Cheesy cores in caecae.
• Pericarditis.
• Perihepatitis.
• Misshapen ovules in the ovaries in S.E. infection

Diagnosis

Isolation and identification. In clinical cases direct plating on Brilliant Green and McConkey agar may be adequate. Enrichment media such as buffered peptone followed by selective broth or semi-solid media (e.g. Rappaport-Vassiliadis) followed by plating on two selective media will greatly increase sensitivity. However this has the potential to reveal the presence of salmonellae that are irrelevant to the clinical problem under investigation.

Differentiate from Pullorum/Typhoid, other enterobacteria such as E. coli. S.Enteritidis causes cross-reactions which may be detected with S.Pullorum serum agglutination tests. It is possible to detect reactions with specific antigens in agglutination tests but competitive and direct Elisa tests are more commonly used today.

Treatment

Sulphonamides, neomycin, tetracyclines, amoxycillin, fluoroquinolones in accordance with the sensitivity. Good management. Chemotherapy can prolong carrier status in some circumstances.

Prevention

Uninfected breeders, clean nests, fumigate eggs, all-in/all-out production, good feed, competitive exclusion, care in avoiding damage to natural flora, elimination of resident infections in hatcheries, mills, breeding and grow-out farms. Routine monitoring of breeding flocks, hatcheries and feed mills is required for effective control. Early depletion of infected breeding stock is required in some countries such as those of the European Union. Infection results in a strong immune response manifest by progressive reduction in excretion of the organism and reduced disease and excretion on subsequent challenge.

Vaccines are increasingly being used for S. Enteritidis and S. Typhimurium infection; both inactivated (bacterins) and attenuated live organisms.