More than 15 strains of avian influenza exist that are typically classified into two categories according to the severity of the disease in poultry:
Low pathogenic avian influenza, which is associated with no or hardly any signs of illness.
Highly pathogenic avian influenza, which is associated with severe signs of disease and high mortalities.
The H5N8 strain that broke out in South Africa in 2017 was not transferrable to humans but led to the deaths of close to two hundred thousands birds. Some of the affected producers reported that the birds did not show any signs of illness before, but merely dropped dead at a scary rate.
According to Lancet Laboratories and the Department of Agriculture’s Avian Influenza-Veterinary Fact Sheet, the disease in the mild form might be expressed as ruffled feathers, reduced egg production or mild respiratory symptoms, such as sneezing or snickering. In the severe form, it is not only the respiratory tract that it is affected but also other organs and tissues, which can result in internal haemorrhaging.
In the severe form symptoms may include some of the following:
The birds might be quiet, lethargic or seem depressed.
There might be a sudden drop in egg production, with many eggs being either soft-shelled or shell-less.
The wattles and combs of the birds might become swollen and congested.
The face or skin under the eyes might become swollen and bluish purple.
The birds might develop conjunctivitis (inflammation of the conjunctiva of the eye).
Respiratory symptoms may include coughing, sneezing and gasping.
Nervous symptoms might include tremors, twisted necks or paralyzed wings. Some poultry species might lose their balance and end up lying down while making pedalling movements with their legs.
The birds tend to suffer from diarrhoea.
There might be haemorrhages on the hocks of the birds.
A few deaths may occur over several days, followed by a rapid spread and a mortality rate that can approach 100% in 48 hours.