Dr. Pokyem Ering & Dr. Himani Ravi
Indian Veterinary Research Institute, Bareilly
Pullorum disease is a highly infectious and fatal bacterial disease of severe septicaemic nature, chiefly affecting newly hatched chicks up to 2-3 weeks and also been noted in turkeys, pheasants, ducks and other wild birds. This disease is highly prevalent and distributed worldwide, leading to severe economic losses in poultry industry due to high chick mortality up to 100%, reduced egg production, poor hatchability, fertility and the cost of medication, vaccination and eradication programs. Historically, pullorum disease was known as “bacillary white diarrhoea.” It is caused by Salmonella enterica serovar Gallinarum biovar Pullorum—a gram negative, non-motile and non-sporing rod-shaped organisms.
Modes of Infection
The principal modes of transmission include both vertically from infected eggs laid by carrier hens which survive the disease and become long-term asymptomatic carriers of Salmonella Pullorum and transmit it to their progeny in eggs, the organisms being in the yolk and horizontally by direct contact with infected birds, ingestion of contaminated feed and water can also amplify the outbreak after the chick’s hatch. Fomites such as Clothing, tools, equipment and machinery can carry the pathogen from one flock to another.
Clinical Signs
Pullorum disease usually affects chicks less than 3-4 weeks of age and are heaviest during 2-3 weeks. If birds are hatched from infected eggs, some chicks may die in the shell, and dead and dying chicks can be found soon after hatching. The clinical signs of Pullorum disease vary depending on the age of the bird. In young chicks, symptoms usually appear within the first few days after hatching such as lethargy and weakness, loss of appetite, huddling, drooping wings, ruffled feathers, respiratory distress, dehydration and chalky white and pasty diarrhoea leading to soiled vents. Adult birds may not show noticeable symptoms, and arthritis affecting various joints, especially the hock, has been described in some outbreaks. Birds that survive Pullorum disease may be underweight and they may not mature into fertile adults, result in decreased egg production, fertility and hatchability of eggs. Infections in poultry > 4 weeks of age are served as carriers, spreading the infection to their offspring and other flock members.
Post Mortem Lesions
Upon necropsy, recently hatched birds affected by Pullorum disease exhibit several characteristic lesions, particularly in the digestive, respiratory, and reproductive systems. These include enteritis, peritonitis, hepatomegaly, Splenomegaly, congested lungs and unabsorbed yolk sacs. Birds that survive pullorum disease often have typhlitis with hard, cheesy material in the cecum and small greyish-white necrotic foci in the liver, spleen, lungs, heart and other viscera. The anterior chamber of the eye contained exudates in birds with ocular lesions. Birds that die per-acutely may have no gross lesions. Infected hens may show ovarian regression, atrophied follicles, or caseous deposits.
Diagnosis
Pullorum disease can be diagnosed by isolating Salmonella Pullorum from dead or carrier birds. At necropsy, organisms consistently recovered from various internal organs, such as the liver, spleen, heart, kidneys, lung, yolk sac, cloacal contents and the ovary and oviduct. Salmonella Pullorum can be cultured on selective media such as MacConkey, brilliant green and xylose lysine deoxycholate agars. Isolated organisms can be identified and differentiated with biochemical and serological tests and PCR.
Serological test can be diligent as a flock test in control programs. Field testing of chickens is possible with the rapid whole blood plate agglutination test, rapid serum agglutination test, tube agglutination test, microagglutination, immunodiffusion, hemagglutination and ELISAs.
Specialized techniques including loop-mediated isothermal amplification assays, plasmid profile analysis, pulsed field gel electrophoresis, PCR-restriction fragment length polymorphism (RFLP), multi-locus variable-number tandem-repeat analysis (MVLA) may be useful in epidemiological investigations.
Treatment and Control
There is no effective treatment for Pullorum disease, making control and prevention essential for poultry management. Key strategies include reporting of the suspected infections with Salmonella Pullorum to the local or national authorities, purchased of live birds and eggs from certified Pullorum disease-free breeders, strict biosecurity measures and implementing hygiene protocols, disinfecting equipment, and restricting farm access are also important in excluding organism. Wild birds, rodents and poultry mites should be controlled and excluded from the facility. The infected flocks should be quarantined and repeatedly conducting serological tests in breeding flocks helps identify and remove carriers and infected individuals to prevents the spread of the disease. The entire flock should be depopulated and the premises are cleaned and disinfected before restocking. Vaccination with effective vaccines to the breeder flock is one of the most effective strategies to prevent the disease.
Conclusion
Pullorum disease is an important disease and remains a serious threat to poultry farming due to high morbidity and mortality rate, especially in regions lacking stringent disease control measures. Disease can transmit both vertically and horizontally. Antimicrobial treatment helps to reduce the mortality however, treated birds remain carriers. Therefore, treatment of Pullorum disease is not advisable. Farmers and poultry industry stakeholders must prioritize biosecurity, regular testing, and responsible breeding practices to mitigate the spread of this infectious disease. Continuous efforts in disease surveillance and poultry management are crucial in maintaining healthy flocks and ensuring sustainable poultry production.