Bacterial Diseases of Poultry

Bacteria are single-celled microbes that are abundant in the soil, water and in the air. Both human and livestock bodies also harbour large numbers of bacteria. Pathogenic bacteria enter the body through the digestive system, the respiratory system, or via cuts and other injuries. Bacteria can cause diseases either by creating mechanical damage to the body, and/or by generating toxins that are poisonous to the body.

Coliform Infections Salmonella Clostridial Diseases Pasteurella, or Fowl Cholera Mycobacterium (Avian Tuberculosis) Mycoplasmosis Infectious Coryza References and Further Reading

These are a group of infectious diseases caused by various strains of Escherichia coli. Commonly found in the environment worldwide, different strains of E. coli are normal inhabitants in intestinal tracts of chickens, as well as other livestock, and consequently are common organisms in the a chicken's environment. Whilst the majority of E. coli strains do not cause disease, some are capable of causing severe disease and a full range of pathogenicity exists between the two extremes.

All ages may be affected, but it is more common in young growing birds. The disease symptoms result from toxins produced by E. coli bacteria as they grow and multiply.

The primary routes of invasion by the organism are the respiratory system and the gastrointestinal tract. The symptoms vary with the different types of infections. In the acute septicemic form, mortality may begin suddenly and progress rapidly. Morbidity may not be apparent and birds in apparently good condition may die. However, in most cases, morbid birds are evident as listless birds with ruffled feathers and indications of fever. In the chronic infection, debilitation, and growth retardation are obvious. In the event of respiratory infection, additional symptoms of laboured breathing, occasional coughing, and rales may be apparent. In the case of enteritis, diarrhoea may be evident. Mortality may be high in recently hatched chicks and young growing birds as a result of omphalitis due to coliform infections.

Diagnosis by laboratory means is necessary since coliform infections in their various forms may resemble and be easily confused with many other diseases.

Management and sanitation practices designed to reduce the number of these types of organisms in the birds' environment are the preferred means of combating coliform infections. In addition, reducing stress factors and the presence of other disease agents can increase the ability of poultry to defend themselves against harmful infections. Providing adequate ventilation, good litter and good range conditions, properly cleaned and disinfected equipment and facilities and high quality feed and water will improve disease resistance. Avoid overcrowding and environmental stresses such as overheating, and avoid stress due to handling during periods when the birds are already subjected to other stressful conditions.

There are more than 2,000 species or serotypes of bacteria belonging to genus Salmonella; all are potential pathogens of poultry. However, most outbreaks of disease are caused by only a few species of Salmonella. It is also thought likely that a majority of chickens are infected with some form of Salmonella at some time during their lives. Chickens may therefore appear healthy, but can be carriers.

The bacteria are transmitted by carriers to offspring via the egg (transovarian transmission). Either the yolk is infected, or the shell is contaminated and bacteria enter the egg and then multiply. An infected embryo may die in the egg, or may hatch into an infected chick. Transmission may also be carried on shoes or on equipment, and may also originate from premises contaminated by previous outbreaks.

Salmonella generally enter the body via the mouth. The bacteria cause inflammation of the intestines (ulcerative enteritis) which is shown by watery diarrhoea in birds with acute symptoms. This may often smell bad and may also contain blood. Birds with chronic infections are likely to be emaciated and show persistent diarrhoea. The disease may become septicemic, in which case the birds wattles turn dark purple.

Salmonella survive and multiply in the environment and this makes control difficult. For example, they can survive in infected droppings for several years. They can also be found in feathers and in dust. Antibiotics can be used to control an outbreak, but this is generally not recommended, partly due to the possibility of causing antibiotic-resistant strains of Salmonella. In addition, the birds may become carriers and continue to spread the disease. Instead, a policy of culling is generally recommended in cases of Salmonella outbreaks in poultry.

See also the section on Salmonella

Clostridial Diseases

Clostridial diseases result from toxins produced by infections with Clostridium bacteria. They are not necessarily disease causing, and some Clostridia do not result in disease unless the animals resistance has been reduced by some other illness, by stress, or by some other factor such as a sudden change in diet.

Clostridium perfringens is commonly found in soil, water, faeces and in the air. This produces a toxin that causes necrotic ulceritis in young and growing birds, particularly in those raised under intensive conditions. The disease appears suddenly and may cause death within a few hours. As a result the most commonly seen symptom is often death. Avoidance is the best strategy, through ensuring good management practices, cleanliness, and making sure that any birds brought into the system are free from infection.

See also the section on Enterotoxaemia, Clostridial Diseases of the Stomach and Intestines of Sheep and Goats, where Clostridium perfringens may be responsible for rapid death.

Clostridium colinum is another bacterium that causes ulcerative enteritis, and infection is spread by infectious droppings in the litter, in feed and in water. The bacteria can survive under wide range of conditions are contaminated premises are therefore difficult to clean. Best avoided by taking care not to bring a carrier into the flock, as well as good management practices and cleanliness. Birds with the acute form of this infection may die suddenly while in apparently in good condition. More chronically affected birds are listless, have ruffled feathers, whitish watery diarrhoea, and may develop a humped posture. Such birds usually die in an extremely emaciated condition.

Clostridium septicum is commonly found in soil and i the intestines of chickens. In combination with other bacteria it may cause infection when the bird's immunity has been reduced by other factors. This is characterised by necrotic dermatitis (the disease may be called "Gangrenous Dermatitis") which usually starts with the appearance of small pimples on the skin, soon progressing to involve large areas. The underlying muscles may also be exposed. Stress and injury may be important factors in this infection.

Clostridium botulinum commonly live in the intestines of chickens but are not themselves pathogenic. However, they are capable of multiplying in the carcasses of dead animals or in rotting vegetable matter and produce particularly virulent toxins. Birds may then become poisoned after pecking at rotting organic matter in which the toxins are present. A poisoned bird becomes gradually paralysed and then dies when the lungs or heart become paralysed. This disease can be avoided through good sanitation. Prevention should aim at eliminating sources of toxin production and preventing access of birds to any such materials. Prompt removal of all dead poultry from pens and poultry houses is required along with control of fly and insect populations and avoiding access by the birds to decaying organic material. Contaminated water supplies are particularly dangerous.

Fowl Cholera, or Pasteurella, is caused by a group of Pasteurella bacteria, the most common species responsible for the disease in chickens being Pasteurella multocida. The bacteria can survive in the droppings for at least a month, and for longer periods in moist soil. Spread and infection is largely through mucous discharge from the beak, nostrils and eyes of infected birds, as well as wild animal sand other livestock (humans may also act as carriers). Contaminated feed and water may also be involved in transmission.

Sanitation practices for prevention include:

• Complete depopulation each year with a definite break between older birds and their replacements. (this is only relevant to more intensive produciton systems).
• A good rodent control program.
• Proper disposal of dead birds.
• A safe, sanitary water supply.
• Adequate cleaning and disinfection of all houses and equipment on premises where outbreaks have occurred after disposal of affected flocks.
• Allowing contaminated areas to remain vacant for at least 3 months.

 

Avian mycobacteriosis (avian tuberculosis), a chronic disease that affects a wide range of birds, is caused by Mycobacterium avium. Mycobacterium avium is primarily transmitted via
the fecal-oral route. Avian mycobacteriosis in poultry is usually a chronic disease and is characterized by progressive loss of condition. Birds will continue to lose body weight despite having normal feed consumption. Mycobacterium avium has a long incubation period, and for that reason the disease is most commonly diagnosed in adult birds. It is considered relatively rare in most intensive systems of commercial poultry production, largely because of the limited life span of commercial poultry combined with management practices such as thorough cleaning and disinfection.

Mycobacterium avium also infects pigs and rabbits, and has zoonotic potential, based on the isolation of this agent from humans with HIV/AIDS (see in Porter 1998).

Prevention measures include replacing each year's breeding or laying flock with young birds, preventing birds from pecking in the droppings, and especially keeping birds away from any areas that may have housed previous infections.

The Mycoplasma bacteria are some of the smallest living organisms capable of free existence. Two important mycoplasmas affecting chickens are Mycoplasma synoviae, which causes air-sac disease in young birds and infectious synovitis in birds of all ages, and Mycoplasma gallisepticum, which also causes air-sac disease in young birds and chronic respiratory disease in growing and mature birds.

Diseases caused by Mycoplasma infections can be difficult to diagnose without laboratory work since they often occur alongside other bacterial and viral diseases. They are spread from infected breeding birds through hatching eggs as well as by direct contact with infected or carrier birds. However, the Mycoplasma bacteria are not able to survive long away from the bird's body. In commercial breeding flocks, management and biosecurity measures aim at eradication of the disease causing organisms, but this is difficult or impossible in freely ranging scavenging chickens.

Infectious Coryza is a respiratory disease caused by the Haemophilus paragallinarum bacteria. The disease resembles other respiratory diseases and can occur alongside them, so it may be difficult to recognise. The main symptoms are swelling of the face, and in chronic cases a characteristic odour of the nasal discharge. It is spread largely through contact with carrier birds. Survivors of the disease, including birds that were infected but which did not show any symptoms will become carriers. Outbreaks usually result from the introduction of infected or carrier birds into a flock. Once a flock is infected, all birds should be considered as carriers.

Prevention is considered to be the only effective method of control and is by eliminating contact between susceptible and infected birds.