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A Comparative Study on Two Infection Models of Colibacillosis in Broilers: Clinical Features, Pathogenesis, and
A Saberi1, N Mosleh1, T Shomali2
1Avian Diseases Research Center, Department of Clinical Sciences, School of Veterinary Medicine, Shiraz University, Shiraz, Iran.
Avian Diseases
|August 10, 2024
Summary
Comparing avian colibacillosis models, intratracheal infection in broilers mimics field conditions better than subcutaneous infection, despite being more complex. Subcutaneous models show more severe disease but differ in pathogenesis.
Area of Science:
- Veterinary Microbiology
- Avian Pathology
- Infectious Disease Modeling
Background:
- Avian colibacillosis, caused by *Escherichia coli*, is a significant economic concern in the poultry industry.
- Reliable experimental models are crucial for understanding disease pathogenesis and evaluating treatments.
- Existing models for avian colibacillosis vary, necessitating a comparison of their characteristics.
Purpose of the Study:
- To compare the characteristics of two avian colibacillosis infection models in broilers: intratracheal (IT) and subcutaneous (SC) routes.
- To evaluate clinical signs, mortality, gross pathology, and bacterial load in broilers challenged via different routes.
- To assess the suitability of each model for simulating field conditions and testing therapeutic interventions.
Main Methods:
- 125 broilers were allocated to negative control, infection control (IT and SC), IT infection, IT infection with florfenicol (ITF), SC infection, and SC infection with florfenicol (SCF) groups.
- Birds were challenged at 35 days old, with clinical signs and mortality recorded.
- Gross examination and euthanasia of birds on days 3 and 5 post-challenge (PC) for further assessment.
- Bacterial cultures from heart blood samples were performed on day 3 PC.
Main Results:
- Both IT and SC infection routes showed similar early clinical signs and mortality.
- SC-infected birds exhibited lower body weight and more severe kidney damage and cellulitis compared to IT-infected birds.
- IT infection resulted in more prominent lung injuries.
- Florfenicol treatment reduced bacterial load in the IT model more effectively than in the SC model by day 3 PC.
- SC infection induced a more severe disease overall.
Conclusions:
- The subcutaneous route for avian colibacillosis infection leads to more severe disease manifestations.
- The intratracheal route more closely resembles field conditions regarding clinical presentation, pathogenesis, and therapeutic response.
- While more technically demanding, the intratracheal model is preferred for studies aiming to replicate natural colibacillosis outbreaks and evaluate treatments.
