Main Pathogens and Transmission Routes in poultry farms
Dr. Majed Hamed Al Saegh / poultry pathologist / Australia
22/ 7/ 2025
Airborne Transmission (Aerial):
• Coronaviruses: Avian Influenza Virus (AI), Avian Newcastle Virus (NDV), Infectious Laryngotracheitis (ILT), Marek’s Disease Virus (MDV), Avian Metapene Virus (aMPV), Avian Adenovirus (FAdV-4).
• Bacteria: E. coli, Pasteurella multocida, Staphylococcus aureus, Mycoplasma Synoviae (MS).
Risk factors: High bird density, poor ventilation, dry or dusty environments. Pathogens can travel long distances (meters to miles in ideal conditions such as AI).
Mitigation method: Use air filters, control humidity, and reduce air volume.
Transmission via contaminated equipment (fomites):
• Viruses: AI, NDV, Infectious Bronchitis Virus (IBV), ILT, extensively resistant Gambra disease virus (IBDV), MDV (long-lived in feather dust), Avian Reovirus (ARV), Chicken Anaemia Virus (CAV).
• Bacteria: Salmonella species (long-lived), Escherichia coli, P. multocida, Clostridium perfringens (C. perfringens – spores), Mycoplasma gallisepticum (MG), MS.
• Parasites: Histomonas meleagridis (via Heterox eggs), Eimeria oocysts (coccidia), and Dermanyssusgalinae.
Risk factors: Organic materials (bedding, feces, secretions) provide protection for pathogens. Poor cleaning and disinfection between flocks. Contaminated equipment, clothing, egg boxes, and trays.
Mitigation methods: “All in/All out” system, thorough cleaning and disinfection between flocks, rest periods, effective pest control, equipment allocation by house or age group.
Waterborne transmission:
• Viruses: AI, NDV, IBDV, IBV, ARV.
• Bacteria: Salmonella enteritidis (autotrophic), Escherichia coli, P. multocida, C. perfringens, Campylobacter jejuni (in cold-water equivalents), MG.
Risk factors: shared or contaminated water lines, biofilm formation (especially with nutrients and heat), poor water sanitation, fecal contamination.
Mitigation methods: regular cleaning and disinfection of water lines, monitoring water quality and sterilization, preventing biofilm formation.
Vector-Borne:
• Insects: Darkling beetle (Alphitobius Diaperinus – vector of ILT, Salmonella Typhimurium, E. coli, IBDV), mosquitoes (fowlpox).
• External parasites: Red avian tick (D. galinae – contacts Salmonella, E. rhusiopathiae, E. coli, AI viruses, and possibly P. multocida).
• Rodents: Asymptomatic Salmonella and C. jejuni contacts us, and contamination of feed/water/surfaces.
• Wild birds: Major reaper of AI, NDV, H. meleagridis, northern bird tick (Ornithonyssus sylviarum), aMPV. Environmental transmission occurs via feces.
Mitigation methods: strict pest control (insects, rodents), prevention of entry of wild birds (netting, protection of feed and water), management of vegetation around the barns.
Vertical transmission (from mothers to chicks):
• Viruses: Novel coronavirus and avian myeloid virus (AEV), CAV, Blue Egg Production Plant 76 (EDS ’76), FAdV, and possibly ARV.
• Bacteria: MG, MS (low incidence), Salmonella enterica, Salmonella infantum, E. coli.
Mitigation methods: importing chicks or eggs from disease-free and reliable farms, implementing strict biosecurity in parent flocks, vaccinating parent flocks, and conducting regular inspection and monitoring.
Biosecurity Considerations and Recommendations
A three-tiered sterilization system:
• External: Control of farm entry (house entry system, personal protective equipment, group disinfection), reliable feed/water/bird sources, prohibition of entry of wildlife and pests.
• Internal: Strict division within the farm, “all in/all out” production, separation of toys, separate equipment for each house, and inter-flock disinfection, cleaning of signage, humidity, and litter.
• Procedural/operational: Staff training, privacy strategies, health monitoring and surveillance, record keeping, adherence to instructions.
Necessary disinfection effectiveness: Disinfectants specific to the pathogen type must be used .
Basic points:
• Remove organic matter first.
• Adherence to the correct concentration, contact duration, and application method.
• An oxidizing agent (such as Virkon S, Accel) effective against viruses (AI, NDV, IBV).
• Ammonium complex formulations + aldehydes effective against ARV and MDV.
• Chlorine dioxide and dolomitic lime are effective against Salmonella.
• Glutaraldehyde + QAC are effective against P. multocida.
• Special agreements are required for highly resistant agents (such as IBDV, C. perfringens spores).
Environmental sustainability is a major challenge:
Some pathogens such as IBDV, Salmonella, MDV, Eimeria oocysts, and D. galinae persist in the environment for weeks, months, or even years, requiring strict disinfection and prolonged periods of inactivation.
Density and stress::
High density increases direct contact, airborne transmission, and environmental pollution, and causes bird stress and immunosuppression. It is essential to maintain optimal density and good ventilation.
