Types of Diseases

There are four main types of disease affecting poultry: metabolic and nutritional diseases; infectious diseases; parasitic diseases; and behavioural diseases.


Metabolic and nutritional diseases

These are conditions caused by a disturbance of normal metabolic functions either through a genetic defect, inadequate or inappropriate nutrition or impaired nutrient utilisation. These include Fatty Liver Syndrome, Perosis (or slipped tendon), Rickets and Cage Layer Fatigue.


Infectious diseases

An infectious disease is any disease caused by invasion of a host by a pathogen which subsequently grows and multiplies in the body. Infectious diseases are often contagious, which means they can be spread directly or indirectly from one living thing to another. These include Avian Encephalomyelitis, Avian Influenza, Avian Tuberculosis, Chicken Anaemia Virus Infection (or CAV), Chlamydiosis, Egg Drop Syndrome (or EDS), Fowl Cholera (or Pasteurellosis), Fowl Pox, Infectious Bronchitis, Infectious Bursal Disease (or Gumboro), Infectious Coryza, Infectious Laryngotracheitis, Lymphoid Leukosis, Marek’s Disease, Mycoplasmosis, Necrotic Enteritis, Newcastle Disease and Salmonellosis.


Parasitic diseases

Parasitic diseases are infections or infestations with parasitic organisms. They are often contracted through contact with an intermediate vector, but may occur as the result of direct exposure. A parasite is an organism that lives in or on, and takes its nourishment from, another organism. A parasite cannot live independently. These include Coccidiosis, Cryptosporidiosis, Histomoniasis, Lice and Mites, Parasitic Worms (or Helminths), Toxoplasmosis and Trichomoniasis.


Behavioural diseases

Abnormal behavioural patterns can lead to injury or ill health of the abnormally behaving bird and/or its companions. These include Cannibalism (or aggressive pecking).

List of avian diseases

Poultry can be affected by many types of disease, and a wide variety of pests (and behavioural problems) including those in the list below:

Diseases caused by Viruses

  • Avian Influenza
  • Avian Encephalomyelitis
  • Big Liver and Spleen Disease
  • Chicken Anaemia Virus Infection (or CAV)
  • Egg drop syndrome (or EDS)
  • Fowl Pox
  • Inclusion Body Hepatitis (or Fowl adenovirus type 8 )
  • Infectious Bronchitis
  • Infectious Bursal Disease (or Gumboro)
  • Infectious Laryngotracheitis
  • Leucosis
  • Lymphoid Leukosis
  • Lymphoid Tumour Disease (Reticuloendotheliosis)
  • Marek’s Disease Virus or MDV
  • Newcastle Disease
  • Runting/stunting and malabsorption syndromes
  • Viral Arthritis (Tenosynovitis)

Diseases caused by Chlamydia

  • Chlamydiosis

Diseases caused by Mycoplasmas

  • Mycoplasmosis – MG (Mycoplasma gallisepticum; MG infection; Chronic Respiratory Disease)
  • Mycoplasmosis – MS (Mycoplasma synoviae; infectious synovitis)

Diseases caused by Bacteria

  • Botulism
  • Colibacillosis
  • Infectious Coryza
  • Fowl Cholera (or pasteurellosis)
  • Necrotic Enteritis
  • Paratyphoid
  • Pullorum
  • Spirochaetosis (Avian Intestinal Spirochaetosis)
  • Tuberculosis (Avian Tuberculosis)

Diseases caused by Fungi

  • Aspergillosis
  • Favus
  • Moniliasis (Candidiasis; crop mycosis)

Diseases caused by Protozoa

  • Coccidiosis
  • Cryptosporidiosis
  • Histomoniasis
  • Toxoplasmosis
  • Trichomoniasis

Diseases caused by Internal Parasites

  • Round worms
  • Caecal worms
  • Capillary worms
  • Tape worms

Diseases caused by External Parasites

  • Several types of louse (insect; plural – lice)
  • Stickfast flea (insect)
  • Fowl tick
  • Several types of mite (acarid)

Diseases caused by Metabolic Disorders

  • Ascites (waterbelly)
  • Cage Layer Fatigue and Rickets
  • Fatty Liver Haemorrhagic Syndrome

Diseases caused by environmental factors

  • Cannibalism (or aggressive pecking)


  • Darkling Beetles

Differences between avian influenza and pandemic human influenza

A few avian influenza viruses have been shown to also infect humans, but these strains do not spread easily from birds to humans. Effectively all human infections have come from contact with infected birds and no significant transmission between humans has been confirmed.


Types of influenza viruses found in birds

All influenza viruses ever found in birds have been influenza “Type A” viruses. Many different subtypes and strains occur, which have variable abilities to make birds ill. These subtypes are given names labelled with “H” and “N”, to reflect the genetic makeup of the virus and its ability to invade the birds’ cells. Some avian influenza viruses circulate naturally in wild birds, generally with little effect. When these viruses get into poultry (eg chickens, geese, quail), some are highly pathogenic and kill large numbers of birds.


Wild birds

Wild birds would not ordinarily present a threat to human health. The main threat to public health lies in a human “pandemic” of influenza that may have its origin in a bird. The virus will then be adapted to humans and unlikely to affect birds. Such an adaptation is highly unlikely to occur in Australia and would be brought here by the movement of humans rather than birds.


Human and Avian influenza viruses

  • In humans, influenza viruses can be of type “A” or “B”.
  • It is thought that all human influenza “A” viruses have originated from birds.

    Avian influenza causing swollen head Source: CSIRO
  • Seasonal influenza epidemics occur every year and result from minor changes to the make-up of existing viruses. The changes are minor but substantial enough to create new strains of influenza that are still able to continue to spread from person to person. Vaccines are produced each year to protect people from seasonal influenza and are produced with knowledge of what the seasonal influenza virus is like.
  • Health authorities generally believe that another pandemic is inevitable. The widespread nature and behaviour of H5N1 has set it as a likely candidate virus to change sufficiently to become a pandemic human virus. A pandemic arising from a different influenza virus is also possible.
  • Purely on mathematical grounds, such a change from an avian to a human virus is likely to occur within those Asian countries with very large human populations that have regular contact with very large poultry populations. By comparison, Australia would be an extremely unlikely place to be the origin of such a pandemic.
  • The possibility of change occurring in an intermediate species (like a pig) exists, especially if the pig were to be simultaneously infected with two influenza viruses.
  • This change of virus need only occur once. It will then be spread onwards by human to human transfer. It is likely that the virus will then no longer be capable of infecting birds.

The take home message is a human pandemic virus, if it were to arise, would come to Australia with a human and would not involve poultry.

Original author: Ron Glanville, QDPI&F

The Merck Veterinary Manual has a section dedicated to Poultry

View the manual

Rapid tests for poultry diseases

The Asia Pacific Centre for Animal Health provides serological and virological diagnostic services to the poultry industry.

Their diagnostic laboratories are based on the University of Melbourne, Werribee campus.

Asia Pacific Centre for Animal Health

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Dr Ben Wells, Poultry Veterinarian and Acting President, Australasian Veterinary Poultry Association

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