Pasteurellosis is an infection caused by the bacteria Pasteurella multocida. This is a very severe infectious disease of poultry. In the days before antibiotics were available, this was a disease to be feared as it could result in massive losses in poultry flocks. These days, however, with better understanding of hygiene and biosecurity and the availability of vaccines and antibiotics which can treat/prevent infection, it is less of a threat although the risk should never be underestimated.
There are other types of Pasteurella bacteria which are not uncommonly isolated from free range layers, particularly Pasteurella haemolytica. Pasteurella haemolytica is usually considered to be much less harmful than Pasteurella multocida and is often a secondary opportunist infection where birds are already suffering from another disease.
Pasteurella multocida can affect all types of poultry with turkeys being particularly susceptible. The infection can be spread by wild birds which may carry the infection, and by rats and mice. The bacteria can persist on sites so if an outbreak has occurred on a farm, that farm remains at a higher risk of further outbreaks although this risk can be minimised by good biosecurity practice and vermin control.
What are the signs of Pasteurella infection?
Pasteurella may show up in a flock in a variety of ways. It can occur either as very sudden acute disease with an increase in mortality in birds in good condition with little in the way of symptoms. Sometimes birds found dead in the acute form show a blue-ish congested appearance to the head and may show some blood around the beak. It can also take a more chronic form where some birds in the flock may show lameness with swollen foot or hock joints or may show swellings of the wattles. Obviously it is not uncommon to see the occasional bird with swollen wattles due to traumatic damage but any unusual increase in the number of birds in a flock with swelling of the wattles or lameness should be promptly investigated as it could be an early sign of Pasteurella infection.
How do we diagnose the disease?
Diagnosis depends on the clinical history of the flock, for example a sudden increase in mortality with losses of birds in good condition would make one suspicious of Pasteurella infection. Prompt post mortem examination and isolation on culture of the Pasteurella bacteria will confirm the diagnosis. It is important to get a quick diagnosis of the problem as antibiotic treatment is most effective when implemented in the early stages of the condition. Once mortality in the flock is very high, the level of infection within the house is so high that antibiotic treatment may be less effective.
If there is a more chronic form of the disease where you are seeing increased numbers of lame birds or birds with swellings of the wattles or around the face, it is still important to have post mortem examinations undertaken to establish whether there is any Pasteurella infection present so that the flock can be treated appropriately to reduce the risk of a sudden flare up in mortality should the disease progress from a chronic to an acute outbreak.
Treatment and prevention
A single outbreak of Pasteurella in a flock where few birds are affected and treatment is started promptly, may respond to one course of antibiotic treatment without the need for further medication. Where there is a very heavy level of infection, initial antibiotic treatment via drinking water may be given followed by a longer period of follow up antibiotic treatment via feed with Tetracyclines. For flocks on farms where there seems to be an ongoing problem with Pasteurella infection, the birds can be vaccinated in the rearing period with an inactivated vaccine giving protection against Pasteurella. There are currently two commercial vaccines available, Pasteurella Erysipelas vaccine from Intervet and Pabac Pasteurella vaccine from Fort Dodge. These are given in the rearing period as two injections.
There are various different strains of Pasteurella multocida, the commonest of these are contained in the commercial vaccines available. In very rare cases, outbreaks may occur due to strains not in the vaccine and on these sites, emergency autogenous vaccines can be produced from bacteria isolated from particular sites for use only on those sites.
Prevention of disease
Reducing the risk of infection relies on good hygiene and biosecurity, good vermin control and ensuring, as far as possible, freedom from other diseases and parasites and ’stresses’. A flock which is ’stressed’ for whatever reason will be much more susceptible to bacterial and other infections.
If you suspect Pasteurella infection in your flocks, you should seek urgent veterinary advice to establish a diagnosis. If Pasteurella is diagnosed, you should discuss with your veterinary surgeon the most appropriate course of treatment for the affected flock and whether vaccination should be considered for future flocks.
Although fowl cholera is still a disease which should be taken seriously, good biosecurity and vermin control coupled with prompt diagnosis of any suspected infection should mean that it is not too much of a threat to your flock.
