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By Dr. Ibne Ali, IMN PyrophosUpdated October 202614 min read

Pullorum Disease: A Major Threat to Poultry Health and Profitability

Pullorum disease (PD), also known as Bacillary White Diarrhea (BWD), is a serious bacterial infection that can devastate poultry flocks, especially young chicks. While it has been eliminated from commercial poultry in some developed regions like the United States, Canada, Australia, and Western Europe, it remains a common and economically important disease in many parts of the world, including India. This article explains what Pullorum disease is, how it spreads, its effects, how to diagnose it, and most importantly, how to prevent and control it, especially highlighting its impact in regions like India where it continues to pose a significant challenge.

Pullorum Disease in Poultry: Symptoms, Control & Economic Impact

What is Pullorum Disease?

Pullorum disease is a septicemic bacterial disease, meaning the bacteria spread throughout the bird's bloodstream. It is caused by the bacterium Salmonella Pullorum. This bacterium is highly adapted to poultry. While primarily affecting chickens and turkeys, other birds like quails, pheasants, ducks, peacocks, and guinea fowls are also susceptible.

Salmonella Pullorum is closely related to Salmonella Gallinarum, which causes Fowl Typhoid (FT). In fact, these two bacteria are now considered a single species, S. enterica serovar Gallinarum-pullorum. They are both Gram-negative, non-motile rods. A key biochemical difference is that S. Pullorum rapidly produces gas from ornithine, which S. Gallinarum does not.

How Does Pullorum Disease Spread? Epidemiology

Understanding how PD spreads is crucial for control. The bacteria can spread in several ways:

  1. Vertical Transmission (Egg-borne): This is considered the most important mode of transmission. Infected breeder hens can carry the bacteria in their reproductive organs, particularly the ovary and oviduct. The bacteria can infect the developing egg before the shell is formed, contaminating the yolk or albumen. Chicks hatched from infected eggs are already infected.
  2. Horizontal Transmission: The disease can also spread between birds through contaminated feed, water, and feces. Infected birds shed the bacteria in their droppings. Contact with contaminated litter, equipment, or even other birds (like cannibalism or mating) can spread the infection. Hatcheries are a common place for transmission, as chicks can be infected from contaminated eggs or from other infected chicks. Wild birds, rodents, insects, and contaminated vehicles or personnel can also introduce the bacteria into a flock.

Age and Susceptibility: Pullorum disease is usually most severe in young birds, typically under 3 weeks of age. Mortality can be very high, even up to 100% in young chicks. Older birds can become infected but often show less severe signs or may be asymptomatic carriers. These carriers are critical in spreading the disease, especially vertically through eggs. Lighter breeds, such as Leghorns, may be more resistant than heavier breeds.

Risk Factors: Several factors increase the risk and severity of PD:

  • Age: Younger birds are more susceptible and experience higher mortality.
  • Stress: Crowding, malnutrition, poor ventilation, and other stressful conditions can worsen the disease and increase mortality.
  • Hygiene: Poor sanitation in housing, hatcheries, and equipment facilitates horizontal spread.
  • Source of Birds: Obtaining chicks or eggs from infected flocks is a major risk.
  • Concurrent Infections: Other diseases can weaken birds and make them more susceptible.
  • Environmental Persistence: Salmonella Pullorum can survive in the environment for months or even years under favorable conditions, contributing to persistent infection issues.

Geographic Distribution, including India: While eliminated from commercial poultry in some developed countries, Pullorum disease is still widely distributed throughout the world, particularly in developing nations. Sources specifically mention Latin America, the Middle East, the Indian subcontinent, Africa, and other parts of the world where S. pullorum infections are common and Pullorum disease remains among the principal disease threats to poultry producers. In areas where it's absent from commercial farms, it may still be found in backyard flocks and wild birds. A study in Bangladesh, part of the Indian subcontinent, highlights local isolates and vaccine development efforts, suggesting the ongoing presence and impact in the region. Studies in Ethiopia also demonstrate high prevalence, indicating the challenges faced in African countries, which share similarities in disease persistence with other developing regions like India.

What Does Pullorum Disease Look Like? Clinical Signs

The signs of PD vary depending on the age of the bird:

  • Young Chicks (most commonly 2-3 weeks old): This is where the disease is often acute and severe.
  • Anorexia (loss of appetite)
  • Huddling together near heat sources
  • Droopy wings
  • Dehydration
  • Diarrhea, often appearing whitish
  • Pasted-down vent feathers due to diarrhea (bacillary white diarrhoea)
  • Increased mortality, which can be very high (up to 100%)
  • Other possible signs: Dyspnea (difficulty breathing), blindness, swelling of hock joints. Excessive numbers of dead embryos or dead-in-shell chicks may also be observed.
  • Older Birds (Growers and Adults): Signs may be less apparent or minimal.
  • Declining feed consumption
  • Droopy appearance and ruffled feathers
  • Pale and shrunken combs (especially in chronic Fowl Typhoid, which is clinically similar).
  • Decreased egg production
  • Poor fertility and hatchability

Birds that survive an infection, particularly mature birds, can become carriers and appear healthy while still harboring the bacteria.

What Do You See Inside the Bird? Lesions (Necropsy Findings)

Examining birds after death (necropsy) can reveal characteristic changes, although these can vary depending on the severity and duration of the disease.

Young Chicks:

  1. Enlarged and congested liver, spleen, and kidneys in acute cases. The liver may have white foci of necrosis (areas of dead tissue). Spleens may be enlarged and appear mottled white.
  2. Unabsorbed yolk sacs are common.
  3. Coagulated yolk sac contents with fibrinous exudate (a yellowish, sticky material) around the heart (pericardium), on the liver capsule, and in the abdomen (peritoneum).
  4. Grey-whitish nodules of various sizes may be found in organs like the gizzard wall, epicardium and myocardium (heart muscle), pancreas, lung, and muscle. In the heart, these can sometimes look like tumors.
  5. The ceca (two pouches off the intestine) may contain caseous cores (cheese-like material) in the lumen. Diarrhea and pasted-down vent feathers are also observed externally. Swelling of joints may be seen.

Adult Birds (often carriers or chronic cases):

  1. Lesions tend to be more localized, especially in the reproductive tract.
  2. Minimal lesions in some cases.
  3. Most prominent lesions are misshapen and discolored nodular ovarian follicles, sometimes attached to the ovary by a long stalk. These can appear like thickened, pendulous masses with a "cooked" aspect. Misshapen ovaries with atrophic (shrunken) follicles are common.
  4. The oviduct (tube carrying eggs) often contains caseous exudate.
  5. Fibrinous exudate in the peritoneum and on the liver capsule may also be observed.
  6. In males, the testes may have white foci or nodules.
Pullorum Disease in Poultry: Symptoms, Control & Economic Impact

Histologically (examining tissues under a microscope), acute cases show necrosis in the liver with inflammation and fibrin. Nodules in the heart contain macrophages, while ovarian nodules in adults show severe inflammation with many bacteria.

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How Do You Know It's Pullorum Disease? Diagnosis

Diagnosing Pullorum disease involves several steps, starting with what you observe on the farm and confirming with laboratory tests.

  1. Tentative Diagnosis: This is based on the flock history (e.g., source of chicks, recent introductions), the clinical signs observed (especially in young chicks), mortality rates, and post-mortem lesions seen during necropsy. However, these signs and lesions can be similar to other diseases, including Fowl Typhoid and even Marek's disease or Yersiniosis, so laboratory confirmation is necessary.
  2. Confirmatory Diagnosis: This requires laboratory work to identify the specific bacteria, Salmonella Pullorum.
  • Isolation and Identification: This is the definitive diagnosis. Samples like liver, spleen, yolk sac, and ceca from chicks are preferred for culture. In mature birds, reproductive organs, ovarian follicles, and testes can be cultured. The bacteria are cultured on specific media like Brilliant Green agar or MacConkey agar. S. Pullorum colonies are typically small and pale on Brilliant Green agar and small and colorless on MacConkey agar. They are non-motile. Biochemical tests are used to differentiate S. Pullorum from other Salmonella species and other bacteria like E. coli or Citrobacter. For example, S. Pullorum ferments dextrose and mannitol producing acid and gas, but does not ferment lactose or sucrose. It also produces rapid decarboxylation of ornithine, unlike S. Gallinarum.
  • Serological Tests: These tests detect antibodies against Salmonella Pullorum in the blood or egg yolk. They are very useful for screening flocks and identifying carriers, especially in breeding stock. Common tests include the Rapid Serum Agglutination Test, Stained Antigen Whole Blood Test, Microagglutination test, and ELISA. A crucial point is that antigens used in these tests can cross-react with antibodies from birds infected with other Salmonella species, especially Salmonella Enteritidis, so a positive serological test should ideally be followed by bacterial isolation for confirmation, particularly in eradication programs. Serological tests are considered satisfactory for establishing presence and estimating prevalence in a flock.

How Do You Deal with Pullorum Disease? Treatment and Control

Treatment should be the last option, and the primary goal is to eradicate the disease.

  • Treatment (Antibiotics): Various antibiotics have been used to reduce mortality from PD, including sulfonamides, nitrofurans, furaltodone, furazolidone, chloramphenicol, biomycin, apramycin, and chlorotetracycline. However, antibiotic treatment does not eliminate the carrier state, meaning treated birds can survive but still carry and shed the bacteria, continuing to spread the infection. Resistance to some antibiotics has also been reported. Withdrawal of antibiotics can lead to a resurgence in bacterial shedding. Therefore, treatment is generally not recommended as a control strategy, and in many countries, it's not feasible or desirable. Antibiotic therapy should ideally follow an antimicrobial susceptibility test.
  • Control and Prevention Strategies: These are the most effective methods. The focus is on biosecurity, hygiene, testing, and elimination of carriers.
  • Establish Infection-Free Flocks: This is fundamental. Purchase poultry and hatching eggs only from sources certified to be free of Pullorum disease.
  • Routine Serological Testing: Regularly test breeding flocks and commercial layers using agglutination tests or ELISA to identify carrier birds.
  • Elimination of Carriers: Birds identified as carriers through testing should be removed (culled/slaughtered) from the flock immediately.
  • Strict Biosecurity: Prevent the introduction of the disease into the farm. This includes controlling access to the farm, using footbaths and clean clothing/footwear for personnel, disinfecting vehicles and equipment, and ensuring feed and water sources are not contaminated. Houses should be designed to exclude rodents, wild birds, and other animals that can carry the bacteria.
  • Cleaning and Disinfection: Thoroughly clean and disinfect poultry houses and equipment between flocks. Disinfectants effective against Salmonella should be used, ensuring they are not inactivated by organic matter.
  • Hatchery Hygiene: Since egg transmission and hatchery spread are critical, strict hygiene in hatcheries is essential. Only eggs from PD-free flocks should be incubated.
  • Vaccination: In countries where eradication is not practiced or where the disease is endemic, vaccination can be used to reduce clinical disease and mortality. Live attenuated vaccines (like the 9R strain for Fowl Typhoid, which offers some protection against PD) and killed vaccines have been developed. Vaccination of layer or breeder flocks is considered an important tool.

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Pullorum Disease in Poultry: Symptoms, Control & Economic Impact

Why is Pullorum Disease Important? Economic Impact

Pullorum disease causes huge economic losses in the poultry industry, particularly in countries where it is still prevalent.

  • High Mortality: The most significant economic loss is the high mortality rate, which can reach up to 100% in young chicks. This directly reduces the number of birds available for meat or egg production.
  • Reduced Production: In surviving birds, especially adults, the disease leads to a decrease in egg production, poor hatchability, and reduced fertility. This impacts the supply of chicks and marketable eggs.
  • Culling of Carriers: Eradication programs require the testing and slaughter of carrier birds, which represents a direct loss of valuable stock.
  • Cost of Control: Implementing biosecurity measures, routine serological testing, and cleaning/disinfection programs involves significant costs.
  • Medication Costs: While treatment is not ideal, attempts to reduce mortality using antibiotics add to the economic burden.
  • Trade Restrictions: Countries free of Pullorum disease may impose restrictions on the import of poultry and eggs from affected regions, impacting international trade.
  • Loss of Confidence: Outbreaks can damage the reputation of a farm or region, leading to reduced demand.

In regions like India, where backyard farming is common and intensive production is expanding, the disease remains a main problem causing heavy economic loss. The lack of consistent biosecurity, potential presence in backyard flocks and wild birds, and challenges in implementing widespread testing and culling programs contribute to its persistence and economic impact. Studies in Ethiopia highlight significant seroprevalence, demonstrating similar economic threats in other developing regions.

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Can Humans Get Pullorum Disease? Public Health Importance

While Salmonella Typhimurium and Salmonella Enteritidis are the most common causes of food-borne illness in humans related to poultry products, Salmonella Pullorum is not typically associated with human food poisoning. However, sources indicate that Salmonella Pullorum can occasionally cause acute, self-limiting enteritis in people who eat massively contaminated food. So, while less common than other Salmonella serovars, it still has potential public health relevance.

Conclusion and Recommendations

Pullorum disease is a serious and highly contagious bacterial disease caused by Salmonella Pullorum, primarily affecting young poultry and causing high mortality. It is transmitted mainly through infected eggs (vertical) and contact with contaminated sources (horizontal). The disease causes significant economic losses due to death, reduced production, and control costs, particularly in regions like India where it is still prevalent. Treatment with antibiotics is generally ineffective in eliminating the carrier state and is not a sustainable control strategy.

For farmers and field technicians, the key takeaway is that prevention and control through strict biosecurity, regular testing, and elimination of infected birds are the most effective ways to manage Pullorum disease.

Recommendations:

  • Source Birds Carefully: Always purchase chicks and hatching eggs only from certified Pullorum-free flocks.
  • Implement Strict Biosecurity: Prevent introduction and spread of the bacteria. Control access to your farm, use disinfectants, keep wild birds, rodents, and other animals out of poultry houses, and clean and disinfect equipment and vehicles regularly.
  • Regularly Test Your Flock: Participate in routine serological testing programs to identify and remove carrier birds, especially in breeding and laying flocks.
  • Cull Infected/Carrier Birds: Promptly remove and humanely cull birds identified as infected or carriers through testing.
  • Maintain Good Hygiene: Keep housing, feed, and water sources clean and sanitized. Hatchery hygiene is critical.
  • Optimize Management: Avoid overcrowding and minimize stress factors like poor ventilation or malnutrition to keep birds healthy and more resistant.
  • Consider Vaccination: In areas where the disease is common and eradication is not feasible, discuss vaccination options with your veterinary professional.
  • Avoid Relying on Antibiotics: Understand that antibiotics do not cure the carrier state and contribute to resistance issues. If treatment is necessary to reduce acute mortality, follow veterinary guidance and antibiotic susceptibility testing, but recognize the limitation.

By focusing on these preventative measures, farmers and field technicians can significantly reduce the risk and impact of Pullorum disease on their flocks and livelihoods.

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