Poultry diseases and their causes

Many factors can contribute to diseases in your flock. By being aware of their causes and how they spread, you can put practices into place to reduce the risk of disease occurring.

Disease can often lead to reduced performance in areas such as breeding, growth rate, feed conversion and egg production. Disease can also affect appearance in show birds and racing ability in pigeon flocks.

Although there are many possible causes of disease, it is often a combination of factors that make birds sick.

Infectious agents

Infectious agents are living organisms that cause disease or illness and can be spread from bird to bird. These include 'germs' (bacteria, viruses, fungi), external parasites (lice and mites) and internal parasites (worms, coccidiosis, blackhead). Infectious agents that cause disease are also referred to as pathogens.

Environmental conditions

Some environmental conditions can also make birds sick. Unlike infectious agents, the illness is not spread between birds. When the environment affects the health of birds it is usually because the animals are unable to adapt to the conditions. Environmental factors that can cause disease include:

  • poisons
  • injury
  • nutritional deficiencies
  • poor air quality
  • temperature extremes
  • physical stress
  • exposure to disease carrying vermin and insects such as rodents and darkling beetles.


Severe physical stress can reduce the birds' ability to resist disease. Flocks rely on people to give them:

Without these, birds may suffer stress from fear, malnutrition, dehydration, over-crowding, dirty conditions and extremes in climatic conditions.

How infectious agents spread

Disease can be spread by new infectious agents entering your flock or by the spread of established infectious agents that are already in the flock.

Disease can be spread by:

  • people - including through clothing, hands and footwear
  • domestic and wild birds - through droppings, feathers and discharges from the nose and mouth
  • contaminated equipment and vehicles
  • eggs
  • air
  • feed and water
  • animals (e.g. dogs, cats, rodents)
  • insects (e.g. mosquitoes, flies, beetles) - through the transmission of diseases such as fowl pox, tapeworm, Newcastle disease and Salmonella.

In many cases of infection, birds (and other animals) keep illness at bay and do not appear sick. These so-called ‘carriers’ do not look sick but can spread disease, often without detection. This is often the case with the food safety pathogen Salmonella, where infected birds do not usually show visual signs of infection.

Specific classes of disease

Some poultry diseases are more serious due to their ability to spread quickly and their potential impact on commercial poultry industries. In Queensland, some poultry diseases are classified as prohibited or restricted matter, and must be reported to Biosecurity Queensland on 13 25 23. If you become aware of prohibited matter or category 1 and 2 restricted matter, you must report it within 24 hours.

Prohibited matter poultry diseases include:

  • avian influenza (highly pathogenic)
  • duck virus enteritis (duck plague)
  • duck virus hepatitis
  • infectious bursal disease (hypervirulent and exotic antigenic variant forms)
  • Newcastle disease (virulent).

Restricted matter poultry diseases include:

  • avian influenza (low pathogenic)
  • infectious laryngotracheitis virus
  • Newcastle disease (avirulent)
  • Salmonella enteritidis infection in poultry.

Find out more about prohibited matter, restricted matter and farm biosecurity.

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