Scientific name

Aspergilla flavus

Description

The disease aspergillosis is caused by a fungus from the genus Aspergilla. Aspergilla has the potential to infect a wide range of mammalian, avian and reptilian species including man and is probably the most common fungal infection found in birds.

The most common species of Aspergilla causing disease in birds are A. fumigatus, A. flavus and A. niger. There are numerous other species of aspergilla present in the environment but these rarely appear as a cause of the disease.

A. flavus has been isolated as a cause of aspergillosis in emus in Queensland.

How the disease occurs

Aspergilla is widespread throughout the environment and where conditions are suitable it will grow and multiply to give a localised high concentration of the fungus.

Favourable conditions include:

1. warm, moist areas eg in litter around waterers and in some types of deep-litter and
2. mouldy or rotting areas eg spoiled or damp feed, rotting vegetation.

As with other fungi, aspergilla has a growing phase where hyphae (appearance of white strands/lumps) grow. This is followed by the production of spores. Spores are resistant to environmental conditions and are very small, allowing them to be easily transported by wind and in dust particles. Where conditions are favourable large numbers of spores are produced.

Birds get infected usually through inhalation of spores. The infection is not transferred from bird to bird. The bird's immune system is able to control infection where relatively small numbers of spores are inhaled. Infection results if the immune system is deficient eg in very young chicks where the immune system is still developing or in birds that have been stressed through other disease problems, overcrowding, insufficient food and water etc. Infection can also result in normal birds where massive numbers of spores are inhaled and the immune system is overwhelmed.

In Queensland at the time of writing, aspergillosis has only been found in young chicks and has caused deaths in the 3-8 week age group. There appears to be a strong association between infection and the presence of dust from the litter in the atmosphere of the brooder shed. This dust can be raised when the litter is shovelled out or raked over or even where the passage of older chicks raises dust from the litter.

Clinical signs

In Queensland the disease has only been seen in emus as a rapidly progressing respiratory condition that continues to worsen until the chick dies.

The chicks appear to get infected in the brooder house very early in life. Initially no signs will be seen but gradually affected chicks will appear unthrifty and less active than other chicks in the group and show signs of gasping and respiratory distress if forced to exercise. In the final stages the chick is obviously depressed, doesn't move much and shows laboured respiration which is seen as exaggerated movement of the ribs and chest in and out with each breath, possibly combined with open mouth breathing. This is the terminal stage and usually the chick will die soon after.

These signs are associated with the spores hatching and growing in the lungs. Firm, round, white nodules are formed in the lung tissue and these grow steadily. As they grow they occupy lung space and disrupt the normal functioning of the lung. This decreases the oxygen supply to the chick to the point where it can no longer survive. These nodules can also be found in other sites including the air sacs, attached to the rib cage, the liver and throughout the abdominal cavity.

Aspergillosis has not yet been recorded in Queensland in emus after 12 weeks of age. It has only been seen as an acute respiratory disease in young chicks.

This differs from the ostrich industry where reports indicate that as well as causing problems in chicks, aspergillosis can also infect the air sacs of older birds to cause a chronic debilitating disease.

Diagnosis

This is usually done by post-mortem of suspect birds with confirmation coming from specimens sent to a veterinary laboratory.

A blood test has been developed by Murdoch University for use in ostriches, however, I do not know if this test would work with emus. Given the difference in prices, diagnosis in emus is more likely to be done by post-mortem.

Treatment

There is no known effective treatment for clinically sick birds. A range of treatments has been attempted in the ostrich industry but to date a successful treatment regimen has not been found.

Prevention

At this stage, prevention is the only effective method of controlling aspergillosis in emus.
Prevention should be aimed at three broad areas:

1. Removal or control of favourable areas for fungal growth
This would include such things as removing wet litter, not using damp or mouldy straw/hay as litter or food, not using or removing spoiled grain and regular provision of fresh non-dusty litter.

2. Dust control in brooder sheds
This is an important area as dust in the air of brooder sheds appears closely associated with infection of young chicks.

Dust is most likely to be raised when litter is being removed or raked over. In these cases it would be worth lightly damping down the litter so dust is not raised when it is moved.

Good quality litter will also help. A coarse litter of wood chips or pine wood shavings appears to work well. Litter that is already dusty may only contribute to the problem.

3. Hygiene
Attention to hygiene can prevent aspergilla numbers building up to a point where problems occur. This needs to be done in all stages to the end of the brooder stage.

Eggs should be fumigated and/or washed in a recognised egg sanitiser used according to directions.

The cold storage room, the incubator and the hatcher should be fumigated or cleaned regularly with a recognised disinfectant active against fungi.

The brooder house should be cleaned and disinfected before the hatching season begins. If individual pens are cleaned out during the breeding season they should be disinfected as well each time.

Disinfectants that are active against aspergilla include those containing gluteraldehyde as an active constituent, Antec Virkon S and Antec Farm Fluid S.

The above procedure will also control other diseases that may cause problems during incubation, hatching and brooding.

Summary

In summary, aspergilla has a potential to cause severe problems. Efforts to control this problem should be directed at prevention as there is no effective cure at this point in time.

Scientific name

Salmonella spp

Description

Salmonellosis can be caused by any one of the salmonella group of bacteria. There are a large number of salmonella species spread widely throughout the environment.

Two individual salmonella species S. pullorum and S. gallinarum cause pullorum disease (S. pullorum) and fowl typhoid (S. gallinarum) in poultry. In the past these two diseases have caused significant problems, and both diseases are now very well controlled in the poultry industry. However, these diseases may still exist in backyard poultry. It would appear that there is little risk of emus being exposed to these two types of salmonella.

Of more significance to the emu industry are the large number of remaining salmonella species that are capable of infecting a wide range of hosts including man. Infection and disease caused by these salmonella is given the general term paratyphoid.

Distribution and transmission

Paratyphoid occurs worldwide.

Salmonella are widespread in the environment and a property can be infected from a number of sources including wild birds, other emus, feed sources and other animals.

The organisms are reasonably resistant and can survive for several weeks or months in the environment in favourable conditions. They are susceptible to sunlight and drying out.

In poultry, carrier birds are the main reservoir of infection once the organism has established in a flock. These birds have been infected and have survived but the organism has established itself in the intestine where it causes the bird little problem but is regularly passed out in faeces. This then acts as a source of contamination. Some rodents and insects also have a potential to act as reservoirs.

Paratyphoid has been detected on some emu farms in Queensland but the full extent of the problem is not known. Problems have occurred in young chicks less than 2 weeks of age, but further research is required to determine the full impact and size of the problem. It is not known whether adult emus can become carriers, but as it is known that paratyphoid affects a wide range of animals it is probable that infection could become established in emu flocks.

Transmission between birds occurs mainly by ingestion. Sick birds and carriers excrete salmonella in their faeces which then has a potential to contaminate food, water, litter etc.

Females can also lay eggs with contamination on the outside of the shell. The paratyphoid organisms are mobile and can penetrate the pores of the shell while it is still warm and moist. If these organisms are not killed during egg disinfection procedures, infected eggs will reach the hatcher. If these eggs hatch, large numbers of salmonella are released into the hatcher. Other chicks can become infected by inhalation of organisms or by eating contaminated fluff circulating round the hatcher. This can result in sickness, deaths and carrier birds from this batch of chicks.

Clinical signs

In poultry, mature and semi-mature birds rarely have problems even though they may be infected. However, if these birds are stressed the infection can flare up and cause clinical disease.

Most problems are seen in chicks and the disease has a potential to cause significant mortalities.

These mortalities may include a high proportion of dead embryos in-shell in both the pipped and unpipped stages.

After hatching, deaths may start after 2-3 days and continue for up to 3 weeks. The chicks will look depressed, lethargic and sit in one position with heads down for long periods. They stop eating but may increase their water consumption. A profuse watery diarrhoea develops. Paralysis, blindness, eye infections and joint problems have also been reported in poultry.

In Queensland, signs seen in young chicks include depression and weakness leading to death and also sudden death with few preceding signs.

Diagnosis

In the early stages after hatching, chicks sick from paratyphoid may show similar signs to those sick from yolk sac infections.

A field diagnosis should be confirmed by sending samples to a veterinary laboratory where the organism can be cultured and identified.

Freshly dead whole chicks can be sent to a laboratory for examination or specific samples can be taken from post-mortem. Samples should be kept chilled in a fridge and not frozen prior to dispatch.

Treatment

Paratyphoid will respond to antibiotic treatment. Drugs in the class nitrofurans are named in text books as the drug of choice for treatment, but these are no longer available having been withdrawn from the market.

This makes it important to consult your veterinarian regarding treatment and to get samples to a laboratory as soon as possible. If a salmonella organism is cultured then the laboratory can also carry out drug sensitivity tests to identify which drugs the organism is susceptible or resistant to. This information is valuable in formulating an effective disease control program.

Prevention

It is unlikely that salmonella paratyphoid could be eradicated from a property and it would not be worth trying.

If it becomes established on a property then a control program can be drawn up. This program would concentrate on the areas where this disease causes the most damage ie the incubation, hatching and brooder stages.

This program would require strict attention to hygiene and should include:

1. Daily collection and fumigation of eggs with formaldehyde gas which should eliminate or greatly reduce contamination on the outside of the shell.

Here it would be recommended that fumigation be used in preference to washing eggs. When eggs are washed the aim is to use a hot solution (43-49oC) so the egg contents expand and force air and hopefully any contamination out through the pores in the shell. The egg then needs to be dried using hot air before the egg contents shrink back to normal size. Problems can occur when the egg is not dried before the contents shrink as this may then suck fluid and contamination back through the pores in the shell.

2. Washing hands or wearing disposable gloves when handling eggs. As outlined, the salmonella is passed in the faeces and from there can spread to contaminate a wide range of objects including hands.

3. Fumigate the hatcher between batches with formaldehyde, virkon (s) gas or clean with a broad spectrum egg disinfectant (eg gluteraldehydes, orthosan etc.). Make sure all fluff, dust and egg shell remains are also removed.

4. Observe chicks closely. Send samples to a laboratory if chicks start dying, are not doing well or a high proportion of dead full-term embryos in shell are seen.

5. Use strategic antibiotic treatment to control infection in chicks.

6. Where a problem is identified additional precautions could be considered:
   • regular misting of the eggs stored in the cold room with a recognised disinfectant - eggs should not be handled or wiped until the surface has dried and/or fumigation of each batch of eggs just before they are put into the incubator.
   • fumigation of eggs as soon as they are put in the hatcher and before hatching begins. Advice should be sought if this option is used as the amounts of formaldehyde and condy's crystals are different to other fumigations and good ventilation is necessary.

Summary

In summary, paratyphoid appears to be a problem that could become established on emu farms. However, attention to hygiene and strategic use of antibiotics should control the disease if it occurs.