Results of PROHEALTH study on vertical transmission

Infections with Escherichia coli in avian species have been associated with several types of infections in organs other than the digestive systems. While the majority of E. coli strains are considered opportunistic pathogens, disease outbreaks are precipitated by predisposing factors such as concurrent virus infections or inappropriate husbandry practices. There is also the possibility that some types may act as primary pathogens.

Two major disease syndromes have been suggested, based upon the assumed routes of infection and lesions observed: (1) air-borne respiratory tract invasion followed by air sacculitis, polyserositis (inflammation of several serous membranes) and possibly septicaemia, and (2) an ascending invasion through the cloacae resulting in salpingitis (infection and inflammation in the oviduct) or salpingitis-peritonitis syndrome (SPS), which may progress to septicaemia and death. The respiratory type most often associated with broilers has received most attention, because of the heavy losses and predisposing factors involved, e.g. infectious bronchitis virus. However, outbreaks characterised by salpingitis in layers as well as broiler breeders are also economically devastating to the poultry industry, because of the decrease in egg-production as well as the increased mortality and the culling and treatment costs of both the breeders and their offspring. 

PROHEALTH has investigated the importance of E. coli infections in industrial broiler production. Because it has been suggested that chronic salpingitis in the breeders – an often unrecognized infection – represents a potential risk for transmission of E. coli to the broiler chicks and subsequent increased first week mortality, our investigations have focused on this aspect. We followed four parent flocks throughout the whole production period (20-60 weeks) by post mortem and bacteriological examination of randomly selected dead birds. Newly hatched chickens from each flock were swabbed in the cloaca (parent flock age 30, 40, 50, 60 weeks) and the bacterial flora analysed. Causes of first week mortality were determined pathologically and bacteriologically. E. coli isolates were selected for detailed characterisation, analysing the genome by different molecular methods e.g. Pulsed-Field-Gel-Electrophoresis (PFGE) and Multi-Locus-Sequence-Typing (MLST) enabling comparison of the isolates.

E. coli was the main cause of both salpingitis in parents and first week mortality in broilers, and E. coli dominated the bacterial flora of the cloaca of newly hatched chickens. PFGE of E. coli showed identical band patterns in isolates from the breeders, hatchery and broilers, indicating a potential vertical transmission of E. coli from parent birds to chickens. It is suggested that E. coli from salpingitis in broiler parents are transmitted vertically and subsequently spread in the hatchery. A single PFGE type dominated in one parent farm and this type was also found in the newly hatched chickens and was the cause of increased first week mortality. The PFGE type belonged to sequence type 131, commonly isolated from human urinary tract infections. Other commonly identified MLSTs included 95, 10 and 5217.

The results indicate that, besides general hygiene measures to prevent E. coli in the broiler flocks, attention should also be given to the broiler parents and possibly also to the grandparents. It appears that certain types of E. coli are highly capable of persistence and transmission through the production pyramid. However, further investigations are needed in order to identify specifically which subtypes of E. coli we should worry about most, and how best to intervene.