Paratyphoid infections are caused by non–host-adapted Salmonella spp. Clinical signs of paratyphoid infection occur in young birds but not usually in mature poultry. Hallmarks of the disease include lethargy, poor growth, weakness, diarrhea, and dehydration. Salmonella enterica serotype Enteritidis may cause diarrhea, decreased feed consumption, and decreased egg production in layers. Lesions in young birds may include an enlarged liver with focal necrosis, unabsorbed yolk sac, enteritis with necrotic lesions in the mucosa, and cecal cores. Isolation, identification, and serotyping of the causative agent are essential for the diagnosis of paratyphoid infections. Serological testing is not highly reliable. Treatment is not recommended. Control measures include biosecurity and sanitation measures at the hatchery and poultry houses; elimination of vectors such as wild birds, rodents, pets, and flies; feed management; vaccination; and the use of competitive exclusion products.
Paratyphoid infections caused by non–host-adapted Salmonella spp are of public health importance because of the contamination and mishandling of poultry products. Paratyphoids are usually present in the intestinal tract of poultry without causing any disease; however, a few serotypes have the ability to cause disease in poultry, particularly when they are vertically transmitted. For example, Salmonella enterica serotype Enteritidis is a major food safety concern in the egg-laying industry. Fecal contamination of the eggshell is the main mode of transmission from breeders to progeny; however, S Enteritidis is also transovarially transmitted. In addition, Salmonella enterica serotype Typhimurium could potentially cause disease in poultry.
Etiology of Paratyphoid Infections in Poultry
Paratyphoid infections can be caused by any one of the many non–host-adapted salmonellae. These Salmonella spp infect many types of birds, mammals, reptiles, and insects. Paratyphoid infections do not necessarily cause disease in poultry; however, they are of public health importance via contamination and mishandling of poultry products.
Salmonella enterica serotype Typhimurium, S enterica serotype Enteritidis, S enterica serotype Kentucky, and S enterica serotype Heidelberg are among the most common Salmonella infections in poultry. Some serotypes can be pathogenic to poultry as well. The prevalence of other species varies widely by geographic location.
Transmission usually occurs horizontally from infected birds, contaminated environments, or infected rodents. Transmission of most serotypes to progeny from infected breeders is mainly through fecal contamination of the eggshell; however, S Enteritidis and S enterica serotype Arizonae can infect the interior of the egg through transovarial transmission. Infected birds remain carriers.
Clinical Findings and Lesions of Paratyphoid Infections in Poultry
Clinical signs of paratyphoid infection are observed in young birds; however, clinical disease is not usually found in mature poultry. Death in young birds is most often limited to the first few weeks after hatch.
Although these clinical signs are not distinctive, the following are hallmarks of the disease:
depression
poor growth
weakness
diarrhea
dehydration
S Enteritidis may cause diarrhea, decreased feed consumption, and decreased egg production in layers.
Lesions in young birds 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 (see images of paratyphoid infection in the liver, hock joint, and cecal core of poultry).
Enlarged liver, with pinpoint necrotic foci, in a 6-month-old pigeon infected with a Salmonella sp.
Courtesy of Dr. Robert Porter.
Legs of two 1-week-old turkey poults: one infected with Salmonella enterica serotype Schwarzengrund (upper image), and one normal (lower image). Note the enlarged hock joint, indicating arthritis, in the infected leg.
Courtesy of Dr. Robert Porter.
Infection of a 20-day-old chukar partridge with Salmonella enterica serotype Typhimurium, with fibrinonecrotic exudate distending the ceca.
Courtesy of Dr. Robert Porter.
Enlarged liver, with pinpoint necrotic foci, in a 6-month-old pigeon infected with a Salmonella sp.
Courtesy of Dr. Robert Porter.
Legs of two 1-week-old turkey poults: one infected with Salmonella enterica serotype Schwarzengrund (upper image), and one normal (lower image). Note the enlarged hock joint, indicating arthritis, in the infected leg.
Courtesy of Dr. Robert Porter.
Infection of a 20-day-old chukar partridge with Salmonella enterica serotype Typhimurium, with fibrinonecrotic exudate distending the ceca.
Courtesy of Dr. Robert Porter.
Diagnosis of Paratyphoid Infections in Poultry
Isolation, identification, and serotyping
Rapid antigen tests and PCR assays
Isolation, identification, and serotyping of the causative agent are essential for the diagnosis of paratyphoid infections. Serological testing is not highly reliable. Rapid antigen tests and PCR assays have been used to identify Salmonella isolates such as S Enteritidis.
Treatment and Control of Paratyphoid Infections in Poultry
Control: biosecurity, sometimes including vaccination
Control measures for paratyphoid Salmonella include the following:
sanitation in the hatchery and poultry houses
elimination of vectors such as wild birds, rodents, pets, and flies
feed management
vaccination
use of competitive exclusion products
Due to transovarial transmission of S Enteritidis, additional control measures include depopulation of infected breeder flocks and refrigeration of eggs. Vaccination with killed or live commercially available or autogenous vaccines are commonly used in commercial layers to decrease egg contamination. Complete protection is not afforded by vaccination, and it should be used in combination with other control measures to decrease the incidence of Salmonella infection.
Treatment with antimicrobials is not recommended. Several antimicrobial agents help reduce mortality rate but cannot eliminate flock infection. Use may contribute to emergence of antimicrobial resistance.
S Enteritidisis a major food safety concern, primarily for the egg-laying industry. Possible sources in commercial layers include breeders, contaminated environments, infected rodents, and contaminated feed. Transmission to progeny from breeders is mainly through eggshell contamination, although, unlike other paratyphoid Salmonella spp, transovarial transmission may also occur.
The National Poultry Improvement Plan and the FDA's Egg Safety Final Rule specify 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.
Key Points
Paratyphoid infections are of public health concern and have been associated with foodborne disease outbreaks.
S Enteritidis is a major food safety concern for the egg-laying industry. Control measures for S Enteritidis are outlined in the National Poultry Improvement Plan.
Clinical signs, including weakness, poor growth, and diarrhea, are primarily observed in infected birds during the first few weeks after hatch. Lesions in young birds include enlarged livers with necrotic areas, yolk sac enlargement, enteritis, and cecal cores.
Control measures focus on breeders, hatcheries, and poultry houses and include sanitation, pest control, feed management, competitive exclusion products, and vaccination.
For More Information
Gast RK, Porter RE. Salmonella infections. In: Swayne DE, ed. Boulianne M, Logue CM, McDougald LR, Nair V, Suarez DL, associate eds. Diseases of Poultry, 14th ed. Wiley-Blackwell; 2020:719-753.
USDA Animal and Plant Health Inspection Service (APHIS). National Poultry Improvement Plan (NPIP)
Fulton RM. Bacterial diseases. In: Boulianne M, ed. Avian Disease Manual. 8th ed. American Association of Avian Pathologists; 2019:101-108.
