Infectious diseases can be a problem in any group of poultry, even those in the best managed backyards. It’s important to know what to look for so that you can separate off the sick birds at an early stage for euthanasia or treatment, and at the same time, take steps to prevent the disease moving through the flock.
Here we describe some of the most common infectious diseases that cause problems for the backyard poultry farmer.
Diseases caused by bacteria
Omphalitis or navel-ill Deaths of chicks within a few days of hatching are often caused by bacteria entering the navel and infecting the yolk sac soon after hatching. Poor hygiene in the nest or incubator is a contributing factor. Deaths in this early phase could also be due to chilling or overheating or starvation, although with starvation deaths are usually at 5 to 6 days of age and starved chicks weigh less than 35 gm.
Colisepticaemia Escherichia coli bacteria can cause septicaemia (where the bacteria enter the blood-stream and proliferate), usually when the birds are 3 to 10 weeks old. Stresses such another disease can predispose. Antibiotic treatment via drinking water is usually effective.
Bumblefoot When older birds are kept on hard ground or in muddy runs or when they have to jump heavily down from high perches, they can develop callouses under their feet, and if these become infected by bacteria the feet become swollen and painful. Keeping the birds on soft grass may be enough to allow early cases to recover but sometimes it is best to lance the swelling to release any pus contained in it.
Salmonella infections There are over 2000 types of Salmonella that can be carried by poultry, and some of them cause outbreaks of severe diarrhoea sometimes blood-stained and deaths. Some types of Salmonella can be carried in the birds without causing the birds any health problems, but the bacteria can contaminate the eggs and meat, and may cause food poisoning in humans. It can be difficult to deal with Salmonella in flocks where there are carrier birds of this type. If salmonellosis is suspected, a veterinarian should be consulted.
Tuberculosis Avian tuberculosis is not common but it can occur in some areas, usually in older birds. The signs are slow onset of weight loss and emaciation.
Other significant bacterial diseases in some countries include:
- infectious coryza (watery eyes, foul-smelling discharge and oedema or swelling of the face and wattles)
- fowl cholera (sudden deaths, breathing difficulties, bluish discoloration of the head, and diarrhoea)
- avian mycoplasmosis (depending on the type of Mycoplasma, the signs range from watery eyes, nasal discharge and breathing difficulty, especially in young birds, to lameness with swollen footpads, hock and wing joints and diarrhoea)
For effective treatment and control of these diseases, it’s important to consult a veterinarian or poultry expert.
Diseases caused by fungi
Aspergillosis This is a fungal infection that causes lesions in the air sacs and lungs causing gasping, and it is most common in birds less than 4 weeks old. The disease is more common when hygiene is poor, when straw or sawdust is used as bedding (wood shavings or shredded paper is better), and when there is concurrent Marek’s disease (lowering immunity). Mild infections may clear up when birds are allowed outdoors in good weather.
Thrush (or moniliasis or candidiasis) This is caused by a yeast in the crop and mouth. It is usually secondary to some other problem or over-use of antibiotics. Good hygiene and good management are important in prevention.
Treatment of fungal infections can be difficult, and it’s more likely to be effective if it’s started early in the course of the disease.
Diseases caused by viruses
There is a long list of nasty viral diseases that can affect poultry, and some of them are highly infectious. Some countries are free of some of these diseases, and when they occur as outbreaks, the authorities sometimes make a co-ordinated effort to get rid of them, usually by testing and culling strategies, and sometimes using strategic vaccination too. In countries where the diseases are already established, vaccination is sometimes an option for poultry farmers, and this generally provides good protection.
It is best to consult a veterinarian or a local poultry expert for advice on the pros and cons of vaccination for your backyard flock. In many cases it won’t be necessary.
Here is a list of some of the main viral diseases of poultry, with a brief description of their clinical effect. We urge you to consult a veterinarian at once if you suspect an outbreak in your flock. Fortunately for most relatively isolated and well-managed backyard flocks, the risk of this is low.
Avian influenza This is a very infectious disease that at its most virulent can cause outbreaks of rapidly spreading disease with loss of appetite, dullness, drop in egg production, signs of brain disease, coughing, sneezing and diarrhoea, and swelling and blueness of the combs and wattles, and many deaths. There are milder forms of the disease that cause only mild respiratory disease and a drop in egg production. The virus can be carried by wild birds without them becoming ill. When outbreaks of the severe disease occur, the authorities generally try to eradicate it by culling affected and at risk birds to stop the spread, and there is no vaccine available. There have been some well-publicised campaigns recently to eradicate avian influenza or ‘bird flu’ in south-east Asia following outbreaks caused by a strain that is highly pathogenic and is present over a wide area, with the potential to combine with human viruses to create a new influenza virus that would pose serious risks to human health.
For more information: www.who.int
Marek’s disease This is an infectious viral disease that causes tumours on nerves, and in the brain and other organs. The result may be “range paralysis” in birds from 6 to 12 weeks old (leg or wing paralysis), and tumours on internal organs in birds up to 20-weeks old. The disease also causes immunosuppression so there is increased susceptibility to diseases like coccidiosis.
Lymphoid leucosis This disease is similar to Marek’s disease but it affects older birds, from 16 to 30 weeks of age. Some types of bird are resistant, eg most brown-egg stocks and vent-sexed white leghorn stocks.
Fowl pox This slow-spreading disease can be passed from one bird to another by biting insects so it tends to occur in summer. It is characterised by warty growths on the featherless parts of the skin, and the lumps can also form in the mouth and in the upper windpipe (‘wet’ pox), where they can interfere with breathing. Antibiotic treatment to control secondary bacterial infection is important.
Infectious bronchitis This is a highly contagious rapidly-spreading disease that causes a mild respiratory disease that may become severe if there are secondary infections. It can affect the kidneys of older birds causing kidney damage (and very wet droppings), and gout, and oviduct damage in very young pullets and birds in lay (egg production falls). Damage to the shell gland results in soft and mis-shapen eggs.
Infectious laryngo-tracheitis This is another severe upper respiratory tract infection that results in runny swollen eyes and breathing difficulty and sometimes coughing up blood. Egg production drops. The ‘wet’ form of fowl pox can look similar.
Newcastle disease There are various strains of this virus, some causing mild coughing and sneezing, and others causing very severe respiratory distress with diarrhoea, a drop in egg production and soft-shelled eggs, and signs of brain disease with paralysis.