Productivity and profitability in poultry farming are enhanced by application of sound principles of bio-security, vaccination and management. Improving efficiency increases the availability of eggs and poultry meat, which leads to increase in profits of the farmers. Improved bio-security and an awareness of the need for appropriate vaccination programs reduces the potential losses caused by both catastrophic and erosive infections in commercial scale farms.

Prevention of Diseases
Prevention of disease in commercial poultry operations requires the application of a coordinated program of biosecurity, vaccination, medication and improved hygiene.

Mechanisms of Disease Transmission: in order to develop control procedures it Is Important to understand the mechanisms by which disease causing pathogens are introduced into commercial poultry farms and how disease agents are disseminated among units.

There are two types of transmission of disease in poultry
Biological transmission and mechanical transmission

Biological transmission: This occurs when the pathogen multiplies in an infected host which transmits the agent when placed in contact with susceptible flocks.

Mechanical transmission: It 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

Routes of Disease Transmission:

• Aerosol transmission (through air)
• Direct contact (biting)
• Fomite transmission (Through contaminated objects, like feeders, drinkers etc. )
• Vector-borne transmission (Transmission by vectors like ticks, flies, mosquitoes etc.)
• Zoonotic transmission (Transmission from Animals to humans )

Mechanism of Disease Transmission

For an animal to come down with an infection, after the causative organism has gained entrance through any route (oral, aerosol direct contact, fomite etc), the microorganism has to:

• Reach an ineffective dose
• Overwhelm or subdue the host Immune system (both passive V and acquired immunity, after which the livestock will come down with the infection.

There are five stages of infection process

• Point of entry
• Incubation period
• Prodromal period (Shows Early Symptoms of diseases)
• Manifestation period
• Final period (recovery/death) Vaccination
  
  Vaccination also known as immunization is the administration of a vaccine to stimulate the immune system of an animal in order to produce specific antibodies against viral, bacterial and protozoan diseases. Vaccines are biologicals capable of stimulating immune response towards the production of antibodies. Vaccine confers immunity/protection upon flocks over a specified period of time. Vaccination is a protective device used to prevent the outbreak of many poultry diseases if it is well done. It confers protection upon the flock over a specified period of time.
  
  Vaccination program or schedule/table helps to know when vaccines will be administered, but in drawing vaccination program the following factors must be considered.
• Disease prevalence in area of operation.
• Risk of exposure.
• Immune status of parent stock (maternal Immunity)
• Cost of buying and administering vaccine
• Consequences of adverse vaccine reaction.
• Availability of specific vaccines.
  
  However, there is no permanent vaccination schedule suitable for all places and time because of existence and virulence of diseases and availability and use of vaccines.
  
  There are different types of vaccines e.g. (Gumboro vaccine, Lasota vaccines) Some School of thought will classify vaccines based on the nature of the pathogen from which they are derived, that is viral, bacterial or parasitic. However this does not really give us the understanding of how, vaccines work or should be used.
  
  Types of Vaccines:
  
  Based on their mode of action or how they Work, it is more useful to categories vaccines into:
  
  Attenuated live vaccines: this contain a modified live disease causing agent or antigen, usually adapted from the field for administration either individually ( Mareks disease vaccine, fowl pox Vaccines, etc.) or by mass application (HB1 vaccine, Gumboro vaccine, Lasota vaccines, usually oral preparation)
  Killed or inactivated vaccines: this is mostly used in poultry, it is oil emulsion based. The antigen is suspended in the oil. E.g. ND+ EDS oil vaccine, ND + lBD Oil vaccine etc.
  
  Routes of Vaccine Administration i.e how vaccines should be administered
  
  A Wide range of methods of administration of poultry vaccines is available for use both in the hatchery and on farms. All vaccines are approved for use by specific routes and doses. The routes of administration include the following:
  
  In ovo vaccination at 18 days of incubation to administer Mareks vaccine (advance technology).
• Post-hatch spray vaccination, in cabinets for mass administration of aerosol vaccines to day old chicks.
• Parentheral vaccination which include subcutaneous and intramuscular injection, to administer either live or inactivated emulsion vaccines to chicks, growing stock and layers.
• Wing-web stab to administer live vaccines directly to each bird e. g fowl pox vaccine.
• Eye drop and intranasal routes suitable for hatchery administration and during brooding of chicks’ e.g HBI.
• Aerosol administration, using a knapsack or electric sprayer to deliver vaccines to flocks as a coarse spray.
• Oral or drinking water administration: can be implemented at low cost but is of limited effectiveness against some infections.
  
  Handling of Vaccines:
  
  This is an important aspect of vaccination in livestock, it entails how Vaccines are transported from the manufacturer to the end users, a cold chain must be maintained and also the person that is administering the vaccine. A well designed vaccination program will not be effective if vaccine is damaged by improper handling prior to administration. Live vaccines can be inactivated when exposed to adverse conditions. Always store and handle vaccines as recommended by the manufacturer.
  
  Factors Responsible for Vaccine Break/Failure
• Wrong Vaccination program
• Improper Administration and handling
• Vaccine administration deficiency
• Maternal antibodies
• Stress
• Timing
• Immunosuppression
• Management practices
• Vaccine quality
• Vaccine modifications
• Vaccine strains and serotypes

Why Vaccine Break Is a Threat to Biosecurity
Vaccines are supposed to protect animals against diseases, but when animals are not protected they get exposed to the wild organisms, and eventually come down with the infection, which IS likely to spread to in-contact animals and animals in that locality. Also vaccine break can lead to breakout of a more deadly diseases, the vaccine which is supposed to confer immunity will serve as source of infection to the flock or herd. This will in turn spread to livestock in that area.

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