Prevention of disease requires the application of a coordinated program of –
• Biosecurity
• Vaccination and
• Hygiene
Mechanisms of Disease Transmission
Biological transmission- occurs when the pathogen multiplies in the infected host which then transmits the agent when placed in contact with susceptible flocks.
Mechanical transmission- involves transfer of a pathogen from an infected source or reservoir host to a susceptible flock by contaminated personnel, equipment, insect vectors, rodents, wild birds, or dust carried by wind.
Mechanisms of transmission are-
Transovarial Route
Pathogens may be transmitted by the vertical route from hen to progeny via the egg. Examples are-
• Mycoplasmosis
• Pullorum disease (Salmonella pullorum)
• Reoviruses
• Adenoviruses
• Salmonella enteritidis (Se)
Transmission on the Egg Shell
Examples are-
• E. Coli
• Paratyphoid salmonella spp
Direct Transmission
Contact between susceptible flocks and clinically affected or asymptomatic reservoirs of disease results in infection. Examples are-
• Salmonellosis
• Coryza
• Mycoplasmosis
• Laryngotracheitis
• Pasteurellosis
Indirect Transmission
Contaminated transport coops, equipment or feed onto farms or movement of personnel between infected and susceptible flocks without appropriate biosecurity measures will effectively transmit disease.
Imperfectly decontaminated buildings which have housed infected flocks often contain pathogens including-
• Infectious bursal disease virus (IBDV)
• Salmonella spp
Dissemination by Wind
Infected flocks may excrete large numbers of viruses which can be entrained in dust and moved by wind for distances of up to 5km. Examples are-
• vvND
Biological Vectors
• Wild birds are reservoirs of avian influenza and Pasteurella spp.
• Rodents carry a wide range of diseases including pasteurellosis and salmonellosis.
• Insects are responsible for transmission of various diseases.
• Pox, West Nile and Highland J arbovirus may be transmitted by mosquitoes and spirochetosis by Argas ticks.
• Litter beetles (Alphitobius diaperinus) are reservoirs of a wide range of infections including Marek’s disease, IBD, salmonellosis, pasteurellosis and coccidiosis.
• House flies transmit campylobacteriosis. Argasid ticks (Argas spp) are vectors of spirochetosis.
Contamination of ingredients or manufactured feed with pathogens transmit-
• Salmonella spp
• Paramyxovirus
• Contaminated poultry vaccines
• Contaminated vaccination equipment or personnel used to administer vaccines
• Supervisors, and dealers in live poultry are significantly involved in transmitting disease
Biosecurity programs require a structured approach involving the following sequence:
1. Planning and evaluation of programs
2. Locating resources and training of personnel
3. Implementing including erection of facilities
4. Control involving review of results and analytical procedures
Conceptual Biosecurity
• Location of major and minor roads and the movement of commercial and backyard poultry in relation to company facilities
• Proximity to large lakes or waterways or migratory flyways
• For commercial egg production consider the implications of multi-age on-line units or single-age, company-owned or contractor-operated facilities
Structural Biosecurity
• Fenced farm area with notices to prevent trespass
• Fencing of house area, with secured gates
• Water supply free of pathogenic bacteria, and chlorinated to a level of 2 ppm
• Farm service module comprising an office, storage, and change room shower facilities
• Concrete apron with a suitable water and power supply to permit decontamination of vehicles entering the farm
• All-weather roads within secured perimeter to facilitate cleaning and to prevent dissemination of disease agents by vehicles and footwear
• Appropriate location of bulk bins or secure, vermin-free storage areas for bagged feed
• Installations for disposal of dead birds (incinerators, composters, pits)
• Secure housing with appropriate bird and rodent proofing
• Concrete floors
• Correct positioning of extractor fans to prevent airborne transmission of pathogens to flocks in adjacent houses
• Impervious apron adjacent to the door of each house and installation of drains
• Feed, unused litter and cleaned equipment should be stored separated from the live-bird area of the house
Operational Biosecurity
• Operational manuals should be developed for routine procedures carried out in feed mills, hatcheries, breeding and grow out facilities
Decontamination of Housing and Equipment
Thorough decontamination is necessary to achieve effective disinfection.
• A number of compounds are available commercially,
• Cresols, applied to buildings and soil. These compounds should not be used in the presence of live poultry, eggs, or processed meat.
• Organic phenols are suitable for use in hatcheries to decontaminate equipment.
• Quaternary ammonium compounds (QATs) are highly recommended to decontaminate housing, equipment, and in hatcheries provided that an anionic detergent precedes application of a QAT.
• Chlorine compounds are widely used in processing plants and to purify water on farms. Hypochlorite is only effective over a pH range of 6.5 to 7.5 in water free of organic matter and requires 10 – 20 minutes exposure to inactive bacteria
• Formalin is a corrosive and potentially carcinogenic compound suitable to fumigate eggs in purpose-designed cabinets. Use of formalin requires special precautions to avoid exposure and injury to applicators who must be provided with protective clothing, functional equipment and chemical monitors.
• In selecting a disinfectant, it is necessary to take into account the chemical characteristics, toxicity, and the cost of application.
Public Health Considerations
Recommendations concerning disinfection and pest control should always conform to statutory regulations and should be designed to limit possible contamination of the environment, flocks, and products.
Disinfection of Poultry Houses
• Complete depopulation of houses and decontamination of units and surroundings at the end of each broiler, rearing, breeder or layer cycle will contribute to enhanced liveability and performance in subsequent flocks.
• The following procedures should be followed;
• The surface of the litter and the lower side walls should be sprayed with a 2% carbamate insecticide.
• Litter should be graded to the center of the house for removal either manually or with a front-end loader. Litter should be either bagged or alternatively transported in bulk from the house to a central site for composting or disposal.
• Equipment should be disassembled and removed from the house for cleaning and disinfection.
• Electrical units, motors, and switch gear should be cleaned using a high-pressure air spray and then sealed to protect installations from water damage.
• The floor of the house should be swept to remove residual litter.
• The house should be decontaminated by spraying a non-ionic detergent at a concentration recommended by the supplier. Detergent should be applied to the exterior in the sequence of roof, exterior walls, drains, and service areas. Cleaning the interior should follow the sequence of ceiling, internal walls, and then the floor.
• The interior structure and equipment should be rinsed with water and remaining detergent solution should be allowed to drain.
• The interior of the house should then be sprayed with a quaternary ammonium or phenolic disinfectant solution. A cresolic disinfectant can be applied to earth floors.
• A 2% carbamate insecticide solution should be sprayed on the ceiling, walls, and floor to control litter beetles. (Alphitobius spp).
• Equipment should be reassembled and routine preventative maintenance completed. A clean, dry substrate (wood shavings, groundnut hulls, rice hulls, sawdust) should be spread to a depth of 3 – 10 cm, over the floor area.
• Water lines and drinkers should be drained and cleaned. A quaternary ammonium compound (1 – 2,000 dilution) or chlorine solution (1 liter of 6% sodium hypochlorite per 8 liters of water as a stock solution, proportioned at 1%) should be used to flush water lines.
• Rodent control measures should be implemented including sealing of burrows and baiting.
Control of Rodents
Rats and mice damage to building structures, including foundations, water lines, electrical cables, switch gear, and insulation.
Rodents are major vectors and reservoirs of poultry and zoonotic pathogens, including Pasteurella multocida, Salmonella typhimurium and S. enteritidis.
Rodents serve as mechanical transmitters of infectious agents such as influenza and infectious bursal disease viruses and Salmonella and Pasteurella spp.
The frequency of catching rodents in traps may also be used to assess the level of infestation.
A continuous integrated program to control rodents includes rodentproofing of buildings, elimination of nesting places, appropriate management and sanitation, and chemical and nonchemical elimination.
Preventing access to feed, water, and shelter is an important part of a rodent-control program.
Chemical methods to control rodents include bait and tracking powder. All rodenticides are poisonous at various levels for poultry, livestock, and humans. Caution in the use of rodenticides is required. Bait should be offered at stations located in the activity zone of rodents, in the routes between the nesting site and the common food source, and at the entrance to houses and near active burrows.
Control of Free-Living Birds
Free-living migratory and resident birds serve as reservoirs for Newcastle disease, avian influenza, duck viral enteritis, chlamydiosis, salmonellosis, and pasteurellosis.
The following precautions can be applied to reduce the probability of infection:
• Water obtained from lakes or ponds on which waterfowl accumulate must be filtered and treated with chlorine to a level of 2 ppm.
• Buildings housing flocks and warehouses should be bird-proofed. This includes netting over air inlets, exhaust openings, and screen doors.
Quality of Water
Water supply for farms and hatcheries should be clean and pure. Water containing mineral impurities can affect skeletal integrity, intestinal function and detract from optimal growth and feed conversion efficiency.
Microbiological contamination of water including fecal coliforms and viable Newcastle disease and avian influenza viruses can result in infection of flocks.
Water can be treated to purify by following measures-
• Chlorine can be added to drinking water at a level of 2 ppm
• pH of water should be within the range of 6.5 to 7.5

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