E coli

The Condition

Diseases caused by the bacteria species Escherichia coli (E. coli) are referred to generally as colibacillosis. E. coli are always found in the digestive tract of poultry and most strains are non-pathogenic. However, a small number of virulent serotypes of E. coli can cause poultry disease. Some of the more common of these diseases are colisepticaemia, egg peritonitis, Hjarre’s disease and mushy chick disease.

E. coli is also associated with other conditions, such as synovitis, arthritis, tracheitis, airsacculitis, panopthlmitis and localised abscesses. It has secondary associations with a number of other diseases, such as Swollen Head Syndrome (SHS) (White et al, 1990) and mycoplasmosis. Studies in the USA have shown that turkey flocks that have had a colibacillosis outbreak had increased odds of also having fowl cholera (Carpenter et al, 1988).

Cheville and Arp (1978) observed that, of the three respiratory tract disease syndromes associated with E. coli infection of birds, acute colisepticaemia, characterized by hyperaemic and swollen viscera, tends to occur in young birds. Subacute pericarditis, involving air sacs and pericardium, was more common in older birds. Chronic granulomatous pneumonitis was not seen as flock outbreaks but as chronic disease in birds dying in small numbers some time after one of the other forms of the disease.

Most of the E. coli serotypes that cause disease in poultry are pathogenic only to birds. However, there are a few that are also associated with disease of other animals, including humans. Whittam and Wilson (1988) concluded that only a relatively limited number of pathogenic clones cause colibacillosis within avian populations. Serotypes are normally classified by their O, H and K antigens. Types O1:K1, O2:K1 and O78:K80 are the most virulent, commonly producing disease in poultry (Nivas et al, 1977 and Cheville and Arp, 1978).

Piercy (1979) demonstrated a reduction in the iron-binding capacity of blood serum (hypoferraemia) in chickens exposed to E. coli infection, and a subsequent defence response of an increase in the concentration of the serum protein ceruloplasmin.

The main source of entry of E. coli pathogens is the respiratory tract. The entry of E. coli into eggs via faeces is also an important source of infection. The main predisposing factors are eggshell contamination, respiratory infections, infectious bronchitis, Newcastle disease and immunosuppression resulting from other infectious diseases, the presence of ammonia and dust.

Colisepticaemia

This condition, caused by E. coli, normally affects growing birds between 4 and 12 weeks of age. The E. coli serotype causing colisepticaemia is found in the upper trachea and throat. It has been shown that the serogroups O78, O2 and O8 are common serotypes usually associated with colisepticaemia in poultry (Wray, McLaren and Carroll, 1991). Most poultry species are affected, although it is most common in young broiler chickens.

There is no evidence to suggest any peculiar risks associated with organic and free-range conditions, and many of the risks associated with poor housing will be removed if organic standards are effectively applied. However, it should also be noted that the disease is closely linked with the health status of the flock, and hence precautionary health practices will also reduce disease risks.

The first indication of disease is a drop in feed intake, which may not be readily noticed in free-range systems. Symptoms include gasping and breathing difficulties, listlessness, reduced food consumption and ruffled feathers.

Post-mortem examination will reveal obvious gross lesions, air sacculitis, peritonitis, perihepatitis and pericarditis. The infected carcass will be septicaemic, with dark congested liver, spleen, kidneys and lungs. Air sacs and the surface of the heart will become thickened with caseous deposits. Mortality rates are normally no greater than 5%, although production losses in over 50% of flocks can occur. Infections in table bird flocks can result in a high proportion of carcass downgrading.

In a study in the USA, colisepticaemia was the primary cause of death associated with an early respiratory disease complex (ERDC) characterized by depression, respiratory distress, and increased mortality in 2-3 week old broiler chickens. Flock size was shown to be an important influential risk factor (Tablante et al, 1999).

It has been suggested that male turkeys may be more susceptible to colisepticaemia than female turkeys, especially when under severe stress (Huff et al, 1999).