‘Bac’ teria to Basics – Pasteurella and Erysipelas

When we think of bacterial infections in free range poultry E.coli comes to mind. This is the most common bacteria 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. These are 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 of each.

Pasteurellosis

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

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

Erysipelas


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

Both Erysipelas and Pasteurella can potentially, but fortunately rarely, infect humans, so as with all your 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 your birds.

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

Amongst farm animals, pigs and sheep are the most commonly infected and 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 over a 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 also vermin such as rats. The disease can spread easily via the oral route in drinking water systems and feed troughs. Heavy red mite infestation in a flock can lead to the increased spread of infection within an already infected flock. The same is possible when injectable vaccines are used in an already infected flock. The stress of vaccination and multiple use of the same needle are known to significantly increase the spread of infection, highlighting the need for good hygienic practices and careful handling whenever vaccinating poultry. Again, mature or older flocks appear to be more susceptible to infection. Turkeys are more susceptible to infection than other species. Neither Pasteurella or Erysipelas are transmitted through the egg.

What are the signs of infection of these two deadly diseases?

Erysipelas causes few signs of disease. Often the first hint of a problem is a sudden increase in mortality. Birds may be found dead or dying, occasionally darkened areas of skin can be seen. Mortality can range from 1 to 50 per cent.

In contrast, Pasteurella can present in a number of ways – an acute or more chronic form. In the acute form high numbers of birds die very rapidly and no clinical signs are observed. Following on from this, or developing in its own right, may be a more chronic form. Here there is depression, anorexia and diarrhoea in the flock leading to birds showing swollen wattles, lameness, twisted necks and difficulty in breathing. This variation in signs can lead to confusion with many other disease processes.


How do we diagnose these diseases?

Due to the sudden onset of both diseases and the potential for high mortality, rapid diagnosis is essential, again emphasising the need to seek a prompt post mortem whenever your birds show sudden jumps 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 offending bacteria from fresh post mortem material.

Treatment

Both Erysipelas and Pasteurellosis are caused by bacteria and therefore antibiotics can be used to treat the infections. Only one antibiotic is licensed for use in laying hens without the need for an egg withdrawal period. This is chlortetracycline or CTC. Fortunately most Pasteurella and Erysipelas isolates are sensitive to CTC.

Other antibiotics, such as amoxicillin, may be used in rearing birds not producing eggs. CTC can be given in the drinking water or in feed, which gives flexibility for treatment. In the short-term, drinking water medication is usually advised whilst waiting for the medicated feed. It is crucial to act very fast when such infections are involved as late administration of therapy can result in a poor response to treatment and poor prognosis.

Ongoing strategic use of in feed medication may be needed to prevent future flare-ups in mortality. Your veterinary surgeon will be able to develop a strategy tailored to your situation.

Prevention of Disease

This can be achieved in a number of ways. Some risk factors have already been discussed above.

Vermin are a significant risk for carrying and introducing Pasteurella and Erysipelas infection (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 a flock, and as stressed flocks can have a poorer immune system this can make birds more susceptible to infection.

Vaccination can be used as a preventive measure, or on some occasions in the face of a severe outbreak. The vaccine is inactivated and needs to be injected into birds (see below).

Red mite should be monitored and controlled throughout the year to reduce general ill-health in your flock and also the risk of spread should a flock become infected.

Carcases - Any dead birds should be removed from the house as soon as possible.

Other animals - Try to avoid placing flocks next to other types of stock, especially pigs.

Vaccination

Two vaccinations are required, 3 to 4 weeks apart, to stimulate good protection.

Vaccination can be used for both Erysipelas (Eryvac - Intervet) and Pasteurellosis (Pabac – Fort Dodge). There is currently a combined vaccination (Nobilis Pasteurella Erysipelas - Intervet). All vaccines are inactivated injectable vaccines. The combined vaccine is only available until the end of 2005.

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

Should some of the risk factors discussed above be relevant to your flock then vaccination may be a consideration - you should discuss the need for this approach with your poultry veterinarian, who will help to assess the risks to your birds.

In summary, Pasteurellosis and Erysipelas are significant bacterial infections of free range poultry which can have potentially devastating consequences. There are well known risk factors which should be avoided and controlled where possible. Vaccination is a viable method of control for at-risk flocks.<