Vet Alan Pearson takes a look at Aspergillosis and other mouldy things
Aspergillosis is something we have probably all heard of, but few will have experience of. Unfortunately, when you do experience it you will know about it, because there is no medical cure
What then is Aspergillus? It is a family of moulds, about 200 in total, which are actually quite common. They grow in any oxygen rich environment. The main member of the family and the commonest disease causal agent is Aspergillus fumigatus. It rarely affects mammals or man but is more common in birds, probably because of the different nature of their breathing anatomy. It causes signs of pneumonia and gasping and can simply be seen as an increase in mortality in some cases. It affects ducks, geese, turkeys, laying hens and game birds and is particularly associated with straw which has become mouldy.
Any straw which has become wet and gone mouldy and black may contain the spores of the Aspergillus, which then become airborne and are inhaled by the birds. The disease is not thought to spread from bird to bird but to individuals from the environment. Once inhaled it grows in the lungs or in the air sacs of the birds restricting the efficiency of breathing resulting in signs of pneumonia and very often frank gasping for breath.
In young birds the infection can be associated with the hatchery where the mould has grown in the hatchery or the machines and has transmitted to the birds around the time of hatching. But it is not always the hatchery to blame.
I recall a case a few years back where a line of partridge huts were reported as having a high mortality at one week of age. Initial investigation had revealed nothing but on visiting the site I established that all the mortality was in the last two sheds furthest from the gate. On examining these sheds I discovered that they had been bedded with reed straw, whereas the rest were on the more common bed of chopped cardboard. Birds for the initial post mortem had not been submitted from the sheds bedded on cardboard – a reminder that it is always worth talking to the vet before you throw a bag of birds on his table and expect him to have a crystal ball. In this case, once we examined the relevant birds we picked up the classic signs of the disease, which are yellow to grey plaques in the lungs or air sacs. In other cases lesions may be found in the windpipe and in the eye, causing conjunctivitis and keratitis (a greying of the eye).
“Once inhaled it grows in the lungs or in the air sacs of the birds restricting the efficiency of breathing resulting in signs of pneumonia”
In life the birds may be quiet, weak, not eating but possibly thirsty and show rapid breathing and gasping. The number of birds affected will vary depending to some extent on the load of spores and the environmental conditions. Warm buildings at 25 degrees are ideal, particularly if they are slightly humid: mortality can vary from five to 50 per cent.
In older birds the signs are usually seen as gasping and sudden mortality in acute outbreaks. If the disease is mild and chronic, you will see simply wasting and a low grade mortality.