WHAT DISEASE DOES SALMONELLA CAUSE IN POULTRY? SIGNS, LESIONS, AND DETAILED DIAGNOSTIC METHODS

Salmonella in poultry causes Pullorum disease, Fowl typhoid, and Paratyphoid. Join Fivevet to learn about the clinical signs, lesions, transmission routes, and diagnostic methods of Salmonella infections in poultry. I. What diseases does Salmonella cause in poultry?
Salmonella is a common group of intestinal bacteria in poultry, capable of causing serious infectious diseases, reducing productivity, and leading to significant economic losses. The bacteria can be transmitted vertically (through eggs) or horizontally via feces, feed, water, and the environment.
In chickens and turkeys, Salmonella mainly causes three important diseases:
- Pullorum disease
- Fowl typhoid
- Paratyphoid
Adult poultry may often show no clinical signs but can act as carriers, serving as a long-term source of infection within the flock.
II. Diseases caused by Salmonella in poultry
2.1. Pullorum disease Salmonella Pullorum (S. Pullorum) is the causative agent of Pullorum disease (bacillary white diarrhea) – a severe septicemic disease with high morbidity and mortality in young poultry.
This is an acute infectious disease commonly seen in chicks and turkey poults, mainly transmitted vertically through eggs. The most typical sign is white diarrhea accompanied by high mortality. When birds are infected at an older age, they often show no clinical signs but become carriers, serving as a long-term source of infection within the flock.
The highest morbidity and mortality rates occur at 7–10 days of age after hatching. Affected birds often show:
- Depression and drowsiness.
- Weakness and stunted growth.
- Pasted vents due to dried white diarrhea sticking to feathers around the cloaca.
In some cases, swelling of the hock joints (tibiotarsal joints) may be observed. The disease can occur at all ages in chickens and turkeys but causes the most severe losses in poultry under 4 weeks of age.
Characteristic lesions
Post-mortem examination typically reveals:
- Grayish-white nodules in the liver, heart, lungs, gizzard, intestines, and peritoneum.
- Multiple small gray-white necrotic foci in the liver.
In carrier hens, S. Pullorum is transmitted vertically through eggs to the next generation. Additionally, newly hatched chicks may become infected horizontally through contact with infected birds or via the digestive and urinary routes. Carrier adult birds continue to shed the bacteria through feces and excretions, allowing the disease to persist in the flock.
2.2. Fowl typhoid a. Acute fowl typhoid Fowl typhoid in chickens often begins with a sudden drop in feed intake and egg production. At the same time, fertility and hatchability decrease significantly, accompanied by diarrhea.
In the acute form, mortality is high, ranging from 10% to 90%. About one-third of chicks hatched from infected eggs may die early. The disease mainly affects breeder hens and turkeys, but it can also occur in other poultry species and wild birds.
Characteristic lesions
Liver
- Larger than normal.
- Characteristic bronze-green discoloration.
- May show scattered necrotic foci.
- In some cases, necrotic areas develop into nodules of 1–2 cm in diameter.
Spleen
- Enlarged to 2–3 times the normal size.
- Presence of raised grayish-white nodules (enlarged splenic follicles).
Digestive tract
- Enteritis, especially in the anterior small intestine.
- Possible ulceration.
Other organs
- Lungs with a characteristic brownish discoloration.
- May show necrotic foci and tumor-like nodules.
- Myocardial necrosis due to Salmonella toxins is rare.
b. Chronic fowl typhoid In the chronic form, lesions are mainly concentrated in the reproductive organs of laying hens.
Typical lesions:
- Ovaries become inflamed and progressively degenerate.
- Ovarian follicles are deformed, forming round masses with thick walls, soft and friable consistency.
2.3. Paratyphoid
Paratyphoid is an infectious disease that can occur in both acute and chronic forms in poultry, and is also found in some bird species and mammals. The disease is caused by motile Salmonella strains, which do not have a specific host.
The causative agents include around 10–15 Salmonella serotypes, with the most commonly isolated being:
- Salmonella Enteritidis
- Salmonella Typhimurium
The highest morbidity and mortality rates occur during the first 2 weeks after hatching.
In infected birds, the ceca often show hemorrhage with fibrin strands. Most organs are affected by endotoxins produced by the bacteria, leading to clinical signs such as diarrhea, dehydration, and sticky pasting around the vent.
Post-mortem findings may include:
- Enteritis with hemorrhage and inflammatory exudate.
- Ceca containing gelatinous material, fibrin strands, and caseous (cheese-like) contents - a fairly typical sign of Salmonella infection.
- Inflammatory exudate adhering to intestinal mucosal folds.
Note: Not all Salmonella strains produce these characteristic lesions.
- Occasionally, necrotic foci may also be observed in the liver. Transmission routes
Chicks are commonly infected through:
- Bacteria entering eggs when the eggshell is contaminated with feces.
- Contaminated feed, especially animal protein sources (meat meal, bone meal, etc.).
- Rodents carrying and spreading the pathogen within the poultry house.
Treatment considerations
Treatment can help reduce mortality and alleviate clinical signs, but it cannot completely eliminate Salmonella from the flock. When properly treated, the birds’ resistance may improve; however, the pathogen can persist and lead to recurrence within the farm.
III. Diagnostic Methods for Salmonella in Poultry
3.1. Bacterial Culture and Isolation
Diagnosis of Salmonella in poultry is mainly based on bacterial culture and isolation from collected samples.
a. Types of Culture Media
General media:
- Blood agar
- Nutrient agar
- Brain Heart Infusion (BHI) broth
Selective media:
- Brilliant Green (BG) agar
- MacConkey agar
- Xylose Lysine Deoxycholate (XLD) agar
Enrichment media:
- Selenite cysteine broth
- Tetrathionate broth
- Rappaport–Vassiliadis (RVS) broth
b. Sampling and Culture by Specimen Type
The isolation and culture of S. pullorum and S. gallinarum depend on the type of specimen, with different procedures applied accordingly:
Feces, intestines, intestinal contents, ceca
- Homogenize the sample in sterile physiological saline or process using a stomacher (1:10 ratio).
- Inoculate a loopful of the suspension onto selective media.
- Incubate at 37°C for 24–48 hours.
- Simultaneously inoculate into enrichment media (selenite cysteine) at a 1:10 ratio, then subculture onto selective media.
Organs (liver, spleen, heart, etc.)
- Homogenize the sample at a 1:10 ratio in sterile physiological saline.
- Inoculate onto general media and selective media.
- Incubate at 37°C for 24–48 hours, then subculture onto selective media.
Cloacal swabs and rectal feces
- Streak the sample (using a swab from cloaca/rectum) onto selective media.
- Then place the swab into enrichment media (selenite cysteine).
- Incubate at 37°C for 24–48 hours and subculture onto selective media.
Egg yolk and yolk sac of chicks
- Use a sterile pipette or syringe to collect 100 µL of yolk and inoculate into 100 mL of peptone water or BHI broth.
- Mix well and incubate at 37°C for 24–48 hours.
- Subculture onto blood agar, selective media, and enrichment media.
- Incubate at 37°C for 24–48 hours.
- Then subculture onto selective media.
Embryo samples
- Homogenize embryonic organs.
- Inoculate onto blood agar, selective media, and enrichment media.
- Incubate at 37°C for 24–48 hours (selenite cysteine medium).
- Subculture bacteria onto selective media.
Eggshell samples
- Crush the eggshell into small pieces.
- Inoculate into enrichment media (selenite cysteine).
- Incubate at 37°C for 24–48 hours, then subculture onto selective media.
Salmonella Colony Morphology
Colony characteristics on isolation media after 24–48 hours of incubation:
- Blood agar or nutrient agar: Round, smooth, convex colonies, slightly opaque white, 1–2 mm in diameter.
- MacConkey agar: Round, smooth, convex, slightly opaque white colonies.
- Brilliant Green (BG) agar: Round, smooth, deep pink colonies.
- XLD agar: Round, smooth, red colonies with black centers.
After selecting colonies with typical morphology, subculture onto nutrient agar, blood agar, or BHI broth and incubate at 37°C for 18–24 hours for further biochemical testing and serological typing of Salmonella.
3.2. Bacterial Identification
a. Biochemical Identification
The biochemical characteristics of the bacteria can be determined using commercial biochemical test kits according to the manufacturer’s instructions or by using the following test media:
- Triple Sugar Iron (TSI) agar
- Lysine iron agar or lysine decarboxylase broth
- Urease medium
- Ornithine decarboxylase medium
- Media for fermentation of maltose and dulcitol
- Motility test medium
The obtained biochemical reactions are compared with standard reference tables for bacterial identification.
b. Serological Identification
The O (somatic) antigen is identified using a rapid slide agglutination test.
O antigen typing (O9 group or group D) is performed by mixing the bacterial suspension with:
- Standard O9 antiserum
- Group D antiserum
Observe the agglutination reaction and interpret the results according to the antiserum manufacturer’s instructions.
c. Serological Diagnosis
Serological diagnosis is used to assess the infection status of the entire flock.
To determine the prevalence of infection in a flock, an appropriate number of samples should be collected based on:
- Estimated prevalence rate
- Desired confidence level
Specialized software (e.g., Win Episcope 2.0) can be used to calculate the required sample size.
Common serological tests for antibody detection include:
- Rapid slide agglutination test (using whole blood or serum)
- Tube agglutination test
- Micro-agglutination test in 96-well plates
These tests use commercial antigens and are performed according to the manufacturer’s instructions.
This article was prepared by the Vaccine Research and Development Department – Central Veterinary Medicine Joint Stock Company No. 5 (Fivevet).
Frequently Asked Questions (FAQs):
1. How does Salmonella spread in poultry?
The bacteria spread through contaminated feces, drinking water, feed, infected eggs, and through rodents, wild birds, or farming equipment that has not been properly disinfected.
2. Why can eggs transmit Salmonella to chicks?
The bacteria can adhere to eggshells contaminated with feces or penetrate into the egg when it is stored under poor hygienic conditions, causing newly hatched chicks to already carry the pathogen.
3. How long can Salmonella survive in the environment?
The bacteria can survive for a long time in feces, moist litter, and drinking water. Wet and dirty conditions allow the pathogen to persist for several weeks to several months.
4. What samples should be collected for testing when the disease is suspected?
Samples may include liver, spleen, intestines, ceca, unabsorbed yolk sacs in chicks, or cloacal swabs and fresh feces for isolation and diagnosis.
5. Does Salmonella affect humans?
Yes. It is a zoonotic disease that can be transmitted to humans through contaminated food (meat and eggs). Therefore, food should be thoroughly cooked, and biosecurity measures must be followed in poultry farming.