الطب البيطري veterinary medicine

The relationship between coccidiosis (caused by *Eimeria* spp.) and Salmonella infections in poultry is complex and synergistic, with coccidiosis often predisposing birds to Salmonella colonization and systemic spread. Here’s a breakdown of their interplay:

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### 1. Intestinal Damage and Barrier Disruption
- Coccidiosis destroys the intestinal epithelium (via *Eimeria* replication), compromising the gut barrier.
- Result: Increased gut permeability allows *Salmonella* to translocate from the intestines into the bloodstream (bacteremia) or internal organs.
- Damaged tissue also releases nutrients (e.g., iron, mucus) that promote *Salmonella* growth.

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### 2. Immune Suppression
- Coccidiosis triggers a strong but imbalanced immune response (Th2-biased, anti-parasitic), which may suppress Th1-mediated defenses critical for fighting bacterial infections like *Salmonella*.
- Inflammation from coccidiosis upregulates immunosuppressive cytokines (e.g., IL-10), reducing macrophage and T-cell efficiency against *Salmonella*.

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### 3. Gut Microbiota Dysbiosis
- *Eimeria* disrupts the normal gut flora, reducing competition for *Salmonella*.
- Opportunistic overgrowth: *Salmonella* thrives in the altered microbial environment, colonizing the gut more effectively.

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### 4. Enhanced Virulence of *Salmonella*
- The inflamed, oxygen-depleted gut during coccidiosis may activate *Salmonella* virulence genes (e.g., SPI-1 and SPI-2), enabling invasion and systemic spread.
- *Salmonella* can exploit immune cells (e.g., macrophages) to disseminate throughout the body.

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### 5. Clinical and Production Impacts
- Coinfection leads to:
- More severe diarrhea, weight loss, and mortality compared to either infection alone.
- Increased *Salmonella* shedding in feces, raising contamination risks for eggs and meat.
- Reduced vaccine efficacy (e.g., against *Salmonella*) due to immune exhaustion.

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### 6. Management Factors
- Anticoccidial drugs (e.g., ionophores like *Monensin*) may indirectly reduce *Salmonella* by controlling *Eimeria*.
- Overuse of antibiotics for coccidiosis can drive *Salmonella* antimicrobial resistance.
- Stress from coccidiosis increases corticosterone levels, further immunosuppressing birds.

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### Prevention Strategies
1. Coccidiosis control:
- Vaccination (live or attenuated *Eimeria* vaccines).
- Rotation of anticoccidials to prevent resistance.
2. Salmonella mitigation:
- Probiotics (e.g., *Lactobacillus*) to restore gut flora.
- Acidifiers or prebiotics in feed to inhibit *Salmonella*.
3. Biosecurity: Strict sanitation to limit fecal-oral transmission of both pathogens.

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### Key Takeaway
Coccidiosis creates a "gateway" for *Salmonella* by damaging the gut, suppressing immunity, and altering microbiota. Controlling *Eimeria* is critical to reducing *Salmonella* risks in poultry flocks and ensuring food safety.

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