INTRODUCTION
Avian colibacillosis called to the any localized or systemic infection that caused entirely or partly by avian pathogenic Escherichia coli (APEC), including colisepticaemia, coligranuloma (Hjarre’s disease), air sac disease, swollenhead syndrome, venereal colibacillosis and coliform cellulitis, peritonitis, salphingitis, orchitis, osteomyelitis/synovitis, panopthalmitis, omphalitis/yolk sac infection and enteritis as there are different pathotypes. Avian colibacillosis is an infectious and economic threat disease of birds caused by Escherichia coli (E. coli) which is considered as one of the major causes of morbidity and mortality, associated with heavy economic losses to the poultry industry by its association with various disease conditions, either as primary pathogen or as a secondary pathogen like Mycoplasma spp., and various fungi.
Host
Clinically defined disease is reported most often in chickens, turkeys and ducks only. colibacillosis form of disease is most commonly seen in broiler chickens. It is majorly responsible for both embryo as well as early chick mortality even in breeders, too.
Risk factors
Factors associated with occurrence of avian colibacillosis are many Age is major factor of causing diseases. All age birds are susceptible to colibacillosis, but young birds are more frequently affected and severity of the disease is greater noticed in young birds. Most of the outbreaks of colibacillosis occur around the period of peak production even sometimes at early age due to environment and water. Environment is one of the major crucial role for poultry rearing and its management. Similarly, water supply to birds is major risk factor, as it directly caused the disease.
Clinical signs
Although, with the technically, death is not a clinical sign in colibacillosis, this may be the main indication of an outbreak of colibacillosis in a flock. But it can caused the death due to the septic cause which may callled as colisepticemia. Clinical signs of predisposing or compounding factors are seen concurrently with signs of E. coli infections.
Gross lesions
Gross lesions can be found after post mortem examination are characteristic of colisepticaemia/colibacillosis in birds inclusive of fibrinous perihepatitis, pericarditis, congestion and regression of ovarian follicles with thicked tracheal and bronchial plug deposition.
Diagnosis
Collection of samples
The diagnosis of colibacillosis iscan be done by isolation of E.coli from cardiac blood and affected tissues like liver, spleen, pericardium, bone marrow. Bone marrow cultures are easy to obtain it and are generally free of contaminating bacteria. Swabs collected from liver, oviduct and body cavity were also used for isolation of E. coli from colibacillosis infected birds.
Isolation and identification
E.coli can be identified primarily as gram negative rods by Gram staining technique. Selective media like MacConkey, eosinmethylene blue (EMB) and HiChrome E. coli agar(HiMedia, India) are used for isolation of E. coli. A presumptive diagnosis of E. coli infection can be made if most of the colonies are characteristically dark with metallic sheen colour on EMB agar, bright pink with precipitate surrounding colonies on MacConkey agar, greenish colour colonies on Hichrome agar. Further identification of the isolated colonies is based on biochemical reactions like, indole production, fermentation of glucose with gas production, presence of betagalactosidase, absence of hydrogen sulphide production and urease, and the inability to utilize citrate as carbon source. Molecular confirmative diagnosis can be made by the E.coli 16S rRNA based Polymerase chain reaction.
Economic losses
Colibacillosis is one of the major causes of economic loss in the poultry industry worldwide. Despite being known for its impact, avian colibacillosis remains one of the major endemic diseases of poultry resulting in decrease in productivity, mortality and economic losses. About 5.5 per cent mortality and 10-20 per cent drop in eggs was observed with E. coli infections in egg type layers reared in cages. Heavy economic loss occurs in colibacillosis affected broilers and layers due to morbidity and mortality, which reduced production and poor chick quality. It has reported by Omer et al. that colibacillosis in layers caused 1.9 per cent mortality, results in 824.6 US $ economic loss in layers.
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