Fowl typhoid

                  The disease usually occurs in flocks rapidly, where it runs its course within a week, but sometimes presents in chronic form where birds may take upto 5 weeks to recover .

• It is mostly similar to Pullorum disease ; except FT is more likely to occur in adult chickens, 12 weeks of age ( 3-6 months old).

Etiology:

     Salmonella enterica gallinarum

Transmission:

   S.gallinarum is most commonly transmitted to chickens vertically through carrier breeders to chicken through hatching eggs.

• Transmitted by fomites, rodents, contaminated dropping, wild birds, etc .

Clinical sign:

• Mostly common to PD
• Ruffled feathers
• Pale comb/wattles
• Sticky ( yellow – green ) diarrhoea
• Increased thirst , droopiness
• Pale, dehydrated
• Sudden death in per-acute cases
• Loss of appetite

Lesions:

1. Gross lesions :

1. Per-acute form : no lesion due to sudden death

a. Acute form:

• Liver:
• Hepatomegaly, liver gets a characteristic copper color, presence of necrotic  foci on liver.
• Swollen , friable and bile stained liver

• Splenomegaly
• GI tract :
• Catarrhal enteritis with or without ulcers
• White nodules on gizzard , caeca , large intestinal wall
• Caseous cores are seen in caeca
• Ovary: Deformed and discolored
• Enlarged kidney
• Anaemia
• Yolk sac retention may occur ; with yolk appearing creamy or caseous.

b. Chronic:

• Joints : Synovitis and arthritis ( joints may be swollen with yellow viscous fluid )
• Heart: Small, grey nodular granuloma, sometimes may show small necrotic, grey spots.
• Pericardium may be thickened with yellow or fibrinous exudate .
• Lungs: Greyish areas of consolidation.

      Fig: pale comb/wattle

  Fig : Synovitis

   Fig : hepatomegaly with necrotic foci on surface  and splenomegaly

2. Microscopic lesion :

a. Liver:

• Diffuse hepatitis and fatty changes in hepatocytes and focal necrosis.
• Diffuse infiltration of lymphocytes in liver

b. Heart:

• Necrosis of myocardium along with some fibrosis
• Infiltration of mononuclear cells around the necrotic muscles

c. Kidney:

• Interstitial connective tissue hyperplasia in medulla.

d. bursa

• Marked depletion of lymphocytes from the bursa.

  Liver of chick showing:

(a) diffuse hemorrhage and bacterial clumps (arrow) within the hepatic tissue,

(b) hyperplasia of bile duct represented by newly formed bile ductules (arrow)

(c) focal areas of mononuclear inflammatory cells (arrow) and multiple areas of fatty   degeneration

 (d) aggregation of inflammatory cells forming microscopic nodule (arrow)

 (e) focal area of coagulative necrosis (arrow)

 (f) severe perihepatitis (arrow) 

Diagnosis :

• History
• Clinical sign and lesion
• Postmortem finding
• Isolation and identification of organism
• Serological test : serotyping of S.enterica
• PCR assay
• Bacterial culture

DDx:

• Pullorum disease
• Fowl cholera
• Erysipelas