When we think of bacterial infections in free-range poultry, E. coli comes to mind. This is the most common bacterium isolated from the all-too-common condition known as egg peritonitis.

However, there are also some less common but very severe bacterial diseases that can infect poultry. They are known as erysipelas, which is caused by Erysipelothrix rhusiopathiae and pasteurellosis, otherwise known as fowl cholera, caused by Pasteurella multocida. These two bacterial infections have very similar risk factors, clinical signs and methods of control.

This article will aim to explain the infection risk factors, clinical signs and control methods for each disease.

Pasteurellosis

Pasteurella multocida infection is one of the most virulent and highly infectious agents known to infect poultry, potentially causing rapid and high mortality and losses, with serious consequences for the future economic viability of the flock.

There are other types of Pasteurella, including P. haemolytica and P. gallinarum, which are occasionally isolated from poultry. These other species are more likely secondary, opportunistic infections following another infection.

Erysipelas

Erysipelothrix rhusiopathiae can cause serious acute mortality. It appears spontaneously in flocks, usually without warning.

Both erysipelas and pasteurella can potentially – but fortunately, rarely – infect humans. As with all dealings with your birds, you should observe the highest standards of personal hygiene, including ensuring that all cuts and grazes are well covered when handling the birds.

Risk Factors to Introducing Infections into the Flock

Erysipelas can infect a number of different animals, including man, many farm animals and wild as well as domestic birds. Vermin are a significant risk factor for introducing infection into a flock.

Amongst farm animals, pigs and sheep are most commonly infected. Turkeys are the most susceptible bird species. Mature flocks appear to be more susceptible to infection. It is suspected that the organism can survive for more than one month outside the host, especially in soil contaminated by previous livestock. It has been known for erysipelas to recur on a site that has not been used for livestock for several years.

Pasteurella can also infect all species of poultry. It can infect wild birds and vermin such as rats. The disease can spread easily via the oral route in drinking water systems and feed troughs. Heavy mite infestation in a flock can increase the speed of infection within an already infected flock.

The same is possible when injectable vaccines are used in an infected flock: the stress of vaccination and multiple use of the same needle are known to increase the spread of infection significantly, which highlights the need for good hygienic practices and careful handling when vaccinating poultry.

Again, mature or older flocks seem to be more susceptible to infection, and turkeys are more susceptible to infection than other species.

Neither Pasteurella nor Erysipelas is transmitted through the egg.

What are the Symptoms of these Diseases?

Erysipelas cause few signs of disease. Often, the first hint of a problem is a sudden increase in mortality. Birds may be found dead or dying and occasionally, darkened areas of skin can be seen. Mortality can range from one to 50 per cent.

In contrast, pasteurellosis can present in a number of ways, as an acute or chronic form. In the acute form, high numbers of birds die rapidly without showing any clinical signs. Following on from this – or developing in its own right – may be a more chronic form. With this, there is depression, anorexia and diarrhoea in the flock, and birds show swollen wattles, lameness, twisted necks and difficulty in breathing. The variation in signs can lead to confusion with many other diseases.

How Can We Diagnose these Diseases?

Due to the sudden onset of both diseases and the potential for high mortality, rapid diagnosis is essential. This requires a prompt post-mortem whenever there is a sudden jump in mortality or acute illness.

Diagnosis is based on the history of the site, production system, pattern of mortality, vaccination history and clinical signs. It is confirmed by isolation of the bacteria from fresh post-mortem material.

Treatment

Both erysipelas and pasteurellosis are caused by bacteria and so antibiotics can be used to treat the infections. It is crucial to act fast when such infections are involved as late administration of therapy can result in a poor response to treatment and poor prognosis.

Prevention of Disease

This can be achieved in a number of ways, in relation to some of the risk factors already discussed.

• Vermin are a significant risk for carrying and introducing Pasteurella and Erysipelas (as well as Salmonella), through contaminating bedding, the environment or water, therefore effective and professional vermin control is paramount.
• Stress levels in the flock should be minimised. Bugs can be carried 'silently' for some time in the flock and as stressed birds can have a poor immune system, this makes the individuals more susceptible to infection.
• Vaccination can be used as a preventative measure or, under certain circumstances, in the face of a severe outbreak. The vaccines are inactivated and must be injected into birds.
• Red mite levels should be monitored and controlled throughout the year to reduce general ill-health in the flock, as well as to reduce the risk of spread should the flock become infected.
• Carcasses of any dead birds should be removed from the house as soon as possible.
• Other animals, particularly pigs, should be kept well away from poultry flocks.

Vaccination

Two vaccinations are usually required, 3 or 4 weeks apart, to stimulate good protection. Current vaccines are inactivated and injectable.

Pasteurellosis is caused by many different strains of the bacterium and therefore, the vaccine contains a number of the most common strains. It is possible that a less common strain may affect a flock, in which case, the vaccine will not protect the birds. In this situation, an autogenous vaccine is used. This is a special vaccine that is made from the bacteria isolated from the particular flock, and this is injected into the birds to protect them. This approach may be used more in future following the loss of the combined vaccine.

Should some of the risk factors mentioned above be relevant to your flock, routine vaccination may be a consideration. You should discuss this with your veterinarian, who will advise you based on a risk assessment to our birds.

Summary

Pasteurellosis and erysipelas are significant bacterial infections of free-range poultry, and they can have devastating consequences. There are well-known risk factors, which should be avoided or controlled where possible.

Vaccination is a viable method of control for at-risk flocks.

Treatment with chlortetracyclines is possible but response to treatment is dependent on the speed of diagnosis as well as commencement of treatment, age of flock, stress levels in the flock and concurrent diseases.

Further Reading

-

Find out more information on erysipelas by clicking here.

Further Reading

-

Find out more information on pasteurellosis (fowl cholera) by clicking here.

Further Reading

-

You can contact Crowshall Veterinary Services by clicking here.

January 2009