Salmonellosis in poultry
A wide variety of serovars are prevalent among chicken, turkeys, ducks and geese. The poultry is an important reservoir of salmonellae. The common diseases in poultry are pullorum disease or bacillary white diarrhoea due to infection with S. Pullorum, fowl typhoid due to S. Gallinarum, and fowl paratyphoid due to other serotypes. S. Gallinarum and S. Pullorum are considered to be identical in all respects except pathogenicity. Serologically both are identical.
Pullorum disease: The adult birds are symptomless carriers. The infection persists in ovaries. Some of the eggs laid by birds with infected ovaries carry the organisms in yolk. These infected eggs when hatched constitute the source of infection to other chicks in the incubator and hatcher. The faeces of infected chicks contaminate the environment thus spreading infection to other chicks. Some young chicks which survive infection may remain as symptom less carriers.In young chicks the disease is acute, septicaemic and highly fatal. When the disease is less acute the chicks appear sluggish; there is loss of appetite and thirst, drooping wings and ruffled feathers. Some chicks show nervous symptoms. Diarrhoea is generally present and vents of chicks are covered with whitish faeces. The duration of illness is 2 to 3 days. The disease in adult birds is of chronic type. The affected birds may not show any symptoms except lowered egg production. The lesions of dead chicks show congested spleen and yellowish liver streaked with haemorrhages. In adult hens the ovary is pedunculated and misshapen ovules are found detached in abdominal cavity. Adult birds died of acute disease show congested level with necrotic areas. Spleens and kidneys are also enlarged and congested.
Diagnosis: It can be arrived at by the history of disease in a flock, symptoms of ailing birds and lesions. A final diagnosis depends upon the isolation and identification of causal organisms. The diagnosis in carrier birds is made by various modifications of bacterial agglutination like tube-agglutination test and rapid whole blood test.
Control: To control the disease, serological tests like rapid whole blood test should be applied to detect carrier birds. The carrier birds as well as the survivors should be slaughtered. Incubators and hatchers should be fumigated with formaldehyde. In India, Salmonella Pullorum coloured antigen is used to identify the prevalence of the disease in young chicks and usually salmonella free chicks are distributed for commercial rearing.
Fowl typhoid: The infection of fowl typhoid also passes from hen to chick like pullorum disease. The common route of infection is by ingestion. The disease is of varying severity among growing birds. A high proportion of birds become carriers. They excrete S. Gallinarum intermittently in faeces. The disease in chicks is indistinguishable from pullorum disease. It is common among young stocks and adult birds causing a mortality up to 50% in acute outbreaks. The birds are listless and show diarrhoea with greenish faeces and purple discolouration of comb and wattles. The liver is congested and enlarged with multiple necrotic areas. Spleen also shows similar lesions. The small intestine may show catarrhal inflammation with petechial haemorrhages.
Diagnosis: The causal organism can be isolated from heart blood and visceral organs. The tube-agglutination test and whole blood rapid agglutination test can be used for detecting fowl typhoid in living birds.
Control: The measures to control the disease are similar to those used in pullorum disease. Vaccines have been developed using avirulent variants and rough variants such as 9R. Cross protection using S. Enteritidis has been reported.