THE MERCK VETERINARY MANUAL
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Paratyphoid Infections in Poultry

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Paratyphoid infections can be caused by any one of the many non-host-adapted salmonellae. These Salmonella infect many types of birds, mammals, reptiles, and insects. Paratyphoid infections are of public health significance via contamination and mishandling of poultry products. S Typhimurium, S Enteritidis, S Kentucky, S Heidelberg, S Hadar, and S Saintpaul are among the most common Salmonella infections in poultry. Some serotypes are more pathogenic than others. The prevalence of other species varies widely by geographic location.

Transmission usually occurs horizontally from infected birds, contaminated environments, or infected rodents. Except for S Enteritidis and S Arizonae, transmission of most serotypes to progeny from infected breeders is mainly through fecal contamination of the eggshell. S Enteritidis and S Arizonae can infect the interior of the egg through transovarial transmission. Infected birds remain carriers.

Although not common, clinical signs are sometimes seen in young birds. Mortality is most often limited to the first few weeks of age. Depression, poor growth, weakness, diarrhea, and dehydration are hallmarks of the disease, although these clinical signs are not distinctive.

Lesions may include an enlarged liver with focal necrosis, unabsorbed yolk sac, enteritis with necrotic lesions in the mucosa, and cecal cores. Infections occasionally localize in the eye or synovial tissues. Conversely, there may be no lesions due to acute death caused by septicemia. Isolation, identification, and serotyping of the causal agent are essential for diagnosis. Serology is not highly reliable.

General control measures for the paratyphoid Salmonella include strict sanitation in the hatchery, fumigation of hatching eggs, pelleting of feed, cleaning and disinfection of poultry houses, rodent control, and use of competitive exclusion products. Maintenance of poultry in confinement and exclusion of all pets, wild birds, and rodents help prevent introduction of infection. The use of antibiotics is highly debated. Several antibacterial agents help prevent mortality but cannot eliminate flock infection and may lead to drug resistance. Vaccination with live or killed products has been used. Complete protection is not afforded by vaccination, and it should be used in combination with other control measures to reduce the incidence of Salmonella infection.

S Enteritidis (a paratyphoid Salmonella serotype) is a major food safety concern primarily for the egg-laying industry. Possible sources in commercial layers include transmission from breeders, contaminated environments, infected rodents, and contaminated feed. Transmission to progeny from breeders is mainly through eggshell contamination, although, unlike other paratyphoid Salmonella, transovarial transmission may also occur. The National Poultry Improvement Plan includes S Enteritidis control measures in breeders, including depopulation of infected breeder flocks, cleaning and disinfection of pullet and layer houses, rodent control programs, pest management, feed management, use of competitive exclusion products, vaccination, biosecurity, and proper handling and refrigeration of eggs.

Last full review/revision August 2013 by Sherrill Davison, VMD, MS, MBA, DACPV

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