Fowl typhoid may not make headlines like avian influenza, but it remains one of the most economically significant bacterial diseases affecting poultry across the globe. Though eradicated from commercial poultry systems in many developed countries, it still lingers in backyard and non-commercial flocks—especially in parts of Asia and Africa. This article dives into the causes, clinical signs, pathology, and diagnosis of fowl typhoid, with a focus tailored for B.Sc. Agriculture and B.V.Sc. & A.H. students preparing for competitive exams like Master’s entrance or Public Service Commission (PSC) exams. If you’re looking for a strong foundation in poultry disease management, you’ll find this guide incredibly valuable.
Fowl typhoid is primarily caused by Salmonella gallinarum, a gram-negative, rod-shaped bacterium belonging to the Enterobacteriaceae family. This pathogen primarily targets mature and growing chickens, but it can also infect turkeys, ducks, guinea fowl, and pheasants. Transmission occurs horizontally through contaminated feed, water, and feces, as well as vertically via transovarian passage. This dual mode of transmission makes the disease particularly hard to eradicate in uncontrolled settings.
Once ingested, S. gallinarum invades the intestinal lining, survives within mononuclear phagocytes, and spreads systemically via the bloodstream. The bacteria localize in vital organs such as the liver, spleen, lungs, and reproductive tissues. Depending on the immune status of the bird and bacterial load, the infection may lead to acute mortality or evolve into a chronic carrier state. The typical incubation period ranges from 4 to 6 days.
Clinically, young chicks may present with somnolence, poor appetite, slow growth, and a white pasty vent, often followed by rapid death. In mature birds, acute outbreaks manifest as sudden drops in feed consumption, greenish-yellow diarrhea, pale combs, and a sharp decline in egg production and fertility. Deaths can occur within days, often without much warning.
Post-mortem findings depend on the stage of infection. In chicks, liver and spleen enlargement, congestion, and occasional caseous yolk sacs are observed. In older birds, the liver may appear copper-colored with white necrotic foci, and the heart and ovaries may show nodular lesions. Microscopically, hepatocellular necrosis, interstitial fibrosis, and lymphoid depletion in the bursa are common findings.
Diagnosing fowl typhoid involves a combination of clinical observation, flock history, necropsy findings, and most importantly, laboratory culture of the pathogen—typically from the liver, spleen, or cecum. Since its signs overlap with other conditions like Mycoplasma synoviae, Staphylococcus aureus, or even Marek’s disease, definitive bacterial isolation remains the gold standard.
Understanding fowl typhoid isn’t just academic—it’s foundational for disease management and biosecurity in poultry production. Whether you’re preparing for competitive entrance exams or strengthening your veterinary knowledge, mastering this topic is crucial.
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