Avian Diseases: Infectious and Non-Infectious

Non-Infectious Diseases

• Non-infectious diseases cannot be passed from bird to bird and require a common experience for individuals to contract.
• These diseases are not caused by microorganisms.

Infectious Diseases

• Infectious diseases are caused by microorganisms such as parasites, fungi, protozoa, bacteria, mycoplasmas, chlamydia, and viruses.
• These diseases can be passed from one bird to another either directly or indirectly.
• Direct transmission occurs when a diseased bird passes the cause of the disease to a susceptible healthy bird via direct contact.
• Indirect transmission occurs when the causal organism is passed from one bird to another via an intermediate host or object.

Causes of Infectious Diseases

• Pathogens or disease vectors are organisms and microorganisms that have the potential to cause harm.
• There are many different types of pathogens that can be transferred from one bird to another or from one flock to another by various means.

Viruses

• Viruses are the smallest pathogens and can only be seen through an electron microscope.
• They consist of an outer layer surrounding special protein material similar to the genetic material of the cells they invade.
• Viruses can multiply and do harm only when inside the animal cell.

Mycoplasmas

• Mycoplasmas are single-cell organisms slightly larger than chlamydia.
• They have a cell wall and nucleus.
• The most commonly known disease caused by Mycoplasma is Mycoplasmosis or Chronic Respiratory Disease (CRD).
• Mycoplasma organisms respond to some antibiotics.

Fungi

• Fungi are organisms larger than bacteria and are considered to be members of the plant kingdom.
• They multiply by forming spores that are released and enter the local environment.
• Fungi harm birds in two ways: by direct invasion and by producing toxins.

Protozoa

• Protozoa are single-cell organisms larger than bacteria.
• They have a complex reproduction system that allows them to multiply quickly.
• Protozoa generally harm birds by destroying tissue.
• Chemicals can be used to treat birds infected by protozoa.

Internal Parasites

• Internal parasites are multi-celled organisms that live inside the bird.
• They are usually located in specific organs.
• Most internal parasites are visible to the naked eye.
• Only three internal parasites are likely to cause harm in poultry.

External Parasites

• External parasites live outside the bird.
• They can cause harm by irritating the bird or by being bloodsuckers that can cause anemia.
• Some external parasites can carry organisms that they inject into the bird while feeding.

Prevention of Disease

• Good hygiene practices are essential to prevent disease.
• Quarantine is necessary to maintain control over the means of entry by disease-causing organisms.
• Vaccination can be used to combat infectious diseases.
• Preventive medication may be necessary to combat infection by some organisms.

Resisting Disease

• Many disease outbreaks occur because of predisposing circumstances that ensure the success of the invasion by the causal organisms.
• Stress in the flock can reduce the bird's ability to fight disease.
• A primary infection can reduce the ability of the bird to fight invasion by secondary invaders.

Disease Severity

• Disease in poultry can be one of two levels of severity: catastrophic or chronic.
• In each case, affected birds and recovered birds are carriers that can transfer the causal organism to other stock.

Vaccination

• Vaccination triggers the bird's immune system to produce antibodies to fight infection.
• Not all diseases can be vaccinated against.
• A suitable vaccination program should be developed to combat identified disease threats.

Preventative Medication

• Preventative medication may be necessary to combat infection by some organisms.
• Veterinary advice may be necessary to determine an appropriate preventive medication program.

Monitoring Program

• A monitoring program is necessary to detect disease early.
• Techniques used in monitoring programs include laboratory tests, observation, and examination of bird behavior.

Recognising Healthy and Sick Birds

• A healthy bird will have a good appetite, be alert, and have a smooth, shiny plumage.
• A sick bird will show signs such as lethargy, loss of appetite, and changes in droppings.
• Early recognition of disease is essential to take appropriate action to prevent the spread of disease.