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This article was published in 1976
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Fowl Plague - an Exotic Exercise
P.T. Gilchrist,B.V.Sc., Special Veterinary Officer (Poultry Health), Department of Agriculture, N.S.W.
Introduction
There have been few outbreaks of exotic disease in Australia in recent years and the recent outbreak of Fowl Plague in the Keysborough district about 25 miles east of Melbourne has been the only recent opportunity to observe in the real situation our preparedness for handling an exotic disease. A number of alarms have occurred necessitating action and, in some cases, slaughter but Fowl Plague is the only case of a positive diagnosis of an exotic disease since Swine Fever in N.S.W. in 1961.
Fowl Plague virus was identified by the Victorian Department of Agriculture on 19th January, 1976.
A Meeting of the Consultative Committee which comprises the Chief Veterinary Officers in each State was called for the afternoon of 20th January. A decision was taken at this meeting to declare that an outbreak of Fowl Plague, an exotic disease, had occurred and, thus, set in motion the necessary legal procedures for slaughtering the birds on the affected property and compensating the owner for the loss of the birds at the current market value. All birds on the property were slaughtered by the use of cyanide gas within 24 hours after this meeting had occurred. The bodies, droppings and other perishable material were buried on the property.
The initial outbreak occurred on two adjoining properties owned by brothers. One was a mixed-age layer farm and the other was a mixed-age broiler farm. Strict quarantine was placed on an area of about 1 km. diameter which included 14 other poultry farms. All eggs from this area have gone to the Victorian Egg Board for pasteurising. Processed poultry were being directed towards fresh markets.
The Victorian Department undertook extensive serological tests throughout the State of Victoria to determine whether the disease may have been present anywhere else. All tests were negative for Fowl Plague antibody. In addition, all disease outbreaks coming to the attention of the Department were investigated and swabs from these birds were tested for the presence of the virus. All the farms in the control area were placed under close quarantine and dead birds were picked up from each farm daily and tested for the presence of virus.
On 9th February, a second property (a duck farm) was slaughtered out because of the presence of the virus despite the absence of clinical signs of disease. Since that time, no other properties have been slaughtered out.
Serological Tests.
Extensive serological tests were subsequently undertaken by the other States, also with negative results. These tests could not be started immediately because it was not considered wise to move the live virus out of Victoria and while the Victorian Department had to use live virus in their testing procedures, other States chose to wait until the virus had been inactivated in a manner suitable for the conduct of tests.
Signs
Affected birds were depressed, not eating and showed swelling, Cyanosis and Necrosis of the unfeathered parts of the body, particularly the head. The resemblance to Fowl Cholera was noteworthy but the lesions were more extensive than usually occur in Fowl Cholera. Recovered birds showed Necrosis and sloughing of parts of the comb. Internal lesions were not consistent but the carcases were 'septicaemic' with darkening of the flesh and some cases of Peritonitis and some cases of Subserous Petechial Haemorrhages. The blue oedematous head was the most significant sign. The cut surface in dead birds oozed straw-coloured fluid.
The Virus
Fowl Plague virus is a member of the avian influenza virus group. Avian influenza viruses belong to the Type A, Orthomyxoviruses, which includes some human and other mammalian influenza viruses. All the Type A Orthomyxoviruses share a common ribonucleoprotein and some tests, e.g. the agar gel diffusion precipitin test, can be used for detection of the group. Different members of this group of viruses, however, possess characteristics such as haemagglutinating activity and neuraminidase enzyme activity which vary from one virus to another. There is now a considerable body of evidence suggesting that genetic re-combinations of different Type A Orthomyxoviruses may occur when two different types infect a cell at the same time.
This can occur because the ribonucleoprotein of each infecting virus splits up into at least six separate parts and when the virus is reforming after finishing its activities in the cell, it is possible for a mixture of the parental ribonucleoprotein segments to occur in the newly-formed virus. In some cases, such re-combinations may include a new pathogen. The fact that this can occur is used to explain a number of the human pandemics of influenza and may also explain the Fowl Plague outbreak in Victoria.
Transmission Experiments
The Victorian Department of Agriculture, in co-operation with the C.S.I.R.O., have infected fowls, turkeys and ducks with the outbreak virus in the high-security facilities at the C.S.I.R.O. Division of Animal Health, Parkville.
These trials indicated that the virus produces a high morbidity but only about a 20% mortality in chickens and an even lower mortality in turkeys. Ducks do not show any signs of disease. The virus is capable of growing in all three species and producing antibodies but, again, ducks are less susceptible than turkeys which are less susceptible than chickens. Almost all infected fowls showed positive titres by two weeks post-infection. Despite the absence of frank disease in the ducks in the slaughtered out property the negative results of extensive testing carried out throughout Australia seems to justify the wisdom of applying the slaughter policy as an attempt to eradicate the virus and not just the clinical signs of the disease.
The original outbreak property in Victoria housed birds which were suffering from other diseases at the time of the outbreak and it is not sure how much of the 25% mortality reported at the time was caused by Fowl Plague virus and how much by the intercurrent disease.
Quarantine Procedures
The outbreak properties were quarantined and guards placed at the gate until all birds were slaughtered and buried, together with, droppings and other perishable materials. A control area of approximately 1 kilometre diameter was also quarantined and the properties were monitored by attempted virus isolation from dead birds. All properties in the control area were serologically tested on several occasions. The infection on the duck farm was discovered by virus isolation and by an increase in the incidence and titre of antibody.
All States closed their borders to poultry and poultry products from Victoria. A number of overseas countries, (e.g. New Zealand, New Guinea, Fiji) prohibited importation from anywhere in Australia. It is fortunate that there is not a very large commercial dependence on export from Victoria to other States. However, a few organisations suffered from being unable to move day-old chickens and processed poultry into South Australia and N.S.W. The overseas prohibitions were also not severe but a number of State Egg Boards feared losing certain overseas markets and some poultry meat and day-old chick markets were affected.
If the event had occurred in N.S.V., the commercial effect would have been much more serious because most of the Australian poultry Industry is supplied by breeders from N.S.W.
Slaughter Techniques
The original two outbreak properties were slaughtered by the use of cyanide gas. In the case of the broilers on one property, the gas was pumped into the broiler sheds after ventilation had been sealed off. In the case of the layers which were in California-type sheds with a long central passage and two step-deck rows of birds on each side and no walls to the sheds, the operator, using a gas mask, backed through the shed and spread the cyanide gas over the birds. This method was effective for this type of shed. In the case of the ducks, the situation was extremely difficult and the ducks were rounded up into small yards in the corner of the property and killed by dislocation of the neck with a Burdizzo emasculator.
Disposal of Infected Material
In the case of the first two properties, everything was buried in 15 ft. deep pits. On the duck property, not only were the birds and faeces buried but, because of the difficulty of cleaning the sheds, everything including the sheds was bulldozed into the pits.
Disinfection
A number of quaternary ammonium compounds were used but frothing interfered with administration and after laboratory testing it was decided to use a 1% citric acid to disinfect the facilities. The internationally accepted period for leaving a Fowl Plague infected property empty of birds is 3 weeks and in Victoria 4 weeks had elapsed between burying the last birds and the second meeting of the Consultative Committee which reviewed the evidence and agreed that the emergency was over.
Cost
An agreement exists between the States and the Commonwealth to share the cost of eradication of exotic disease outbreaks. The cost of this outbreak was in excess of $200,000. This did not include the cost of any procedures other than those conducted in the control area, thus, serological testing elsewhere in Victoria and in other States was not included.
Lessons to be Learned
The Victorian Department of Agriculture is to be commended for its swift and effective handling of this outbreak but some problems which occurred without, in fact, interfering with the eradication effort may indicate lessons to be learned for application in future exotic disease situations.
1. Diagnostic Criteria
The establishment of clear diagnostic criteria for each possible outbreak situation is probably impossible to achieve in any absolute sense but it would seem reasonable to suggest that consideration should be given to wording exotic disease policies such that eradication applies to a specific organism and not to a disease. It would be possible at present to interpret the infection which occurred on the duck property as having been one which did not warrant eradication procedures. However, it was clearly a threat to surrounding chicken properties and was correctly slaughtered out. In the event that it is not possible to plan ahead for distinctive diagnostic criteria, then the criteria should be established very early in any exotic disease situation.
2. Shared Responsibility
In view of the implications of an exotic disease outbreak for the whole of Australia and in view of the financial contribution by each State, it would seem wise to establish a technical body with appropriate representation of experts from any part of Australia rather than to impose the full burden for technical decision making on the outbreak State. In this case, the Victorian Department made considerable effort to ensure that they had available the best expert opinion, but there is no formal provision for such consultation to be a necessary step. State Treasuries might also be expected to look askance at their money being spent by another State without formal consultation requirements.
3. Publicity
A press statement was issued by the Victorian Department at the commencement of the outbreak and a number of other communications to industry were maintained throughout the period involved. However it would seen desirable that a formal weekly, or, in some cases, even daily, press statement be issued. The U.S. Authorities in controlling the Newcastle Disease outbreak in California were very aware of the importance of public relations in their effort.
4. Expedition of Declaration of Eradication
There would appear to be no need to stress the importance of rapid action in establishing a diagnosis of an exotic disease but the present procedures for re-establishing normal commercial operations at the completion of an exotic outbreak appear to be cumbersome. Perhaps the Consultative Sub-Committee which is charged with the responsibility for the initial diagnosis could also be responsible for announcing publicly the end of the emergency rather then waiting for confirmation by a chain of superior Committees and, ultimately, Ministers of Agriculture.
5. Fowl Plague is Different from Newcastle Disease
At the present time, the policy for eradication of Fowl Plague is similar to that for Newcastle Disease, however present knowledge of the differences between the viruses should enable a re-evaluation of the situation. Fowl Plague virus is not as infectious as Newcastle Disease virus, and therefore probably requires less heroic efforts to control. With this in mind, a future Fowl Plague outbreak could possibly be controlled by application of quarantine to the immediate area without interfering with commerce by closing of State borders.
A number of outbreaks of poultry disease were investigated at Glenfield during and shortly after the Victoria Fowl Plague situation. One of these conditions led to the isolation of an organism which caused haemagglutination which could be inhibited by the outbreak serum from Victoria. The property was quarantined during investigation of this isolate which subsequently turned out to be bacterial. The Victorian Department also reported that they had experienced one property in which the bacteria, E. coli and Streptococcus faecalis, both produced a haemagglutinating effect neutralised by serum from the outbreak property.
Summary
The recent outbreak of Fowl Plague in Victoria is described and the steps taken principally by the Victorian Department of Agriculture to eradicate the conditions are discussed together with recommendations for future action in the event of further outbreaks of exotic disease.
Acknowledgements
Drs. B. Rushford, A. Turner, H. Westbury of the Victorian Department of Agriculture.