Streptococcus gallolyticus in poultry
Emily Martin, Ðurđa Slavić, Tanya Rossi
Animal Health Laboratory, University of Guelph, Guelph, ON.
AHL Newsletter 2023;27(4):15.
Since the introduction of MALDI-TOF MS (mass spectrometry) for bacterial identification, there is an increased number of bacterial species reported as being associated with a variety of clinical conditions in birds. Starting in 2021, Streptococcus gallolyticus has been routinely identified from cases of meat turkeys, chicken broilers, chicken layers and waterfowl in mixed culture, and occasionally in pure cultures in meat turkey cases.
Streptococcus gallolyticus is a Gram-positive coccus that is arranged singly, in pairs, or short chains. It is part of the Lancefield group D streptococci having the subclassification of S. gallolyticus subspecies gallolyticus (formerly Streptococcus bovis biotype I). The Lancefield group D streptococci are considered part of the intestinal microbiota of wild animals, companion animals, farm animals (including poultry) and humans. They are also occasionally associated with opportunistic infections in humans and animals.
Turkey poults, broiler chickens, ducks and layer chickens are the avian species most commonly infected with S. gallolyticus. Turkeys and waterfowl are affected in the first 3 weeks post hatch, while chickens tend to be affected between 5-7 weeks or 44-55 weeks of age. The most common clinical signs are depression, listlessness, pasted vents, watery droppings, and dehydration. There is poor growth performance with increased culls and increased mortality in commercial flocks. In ducks, there is a drop in egg production and development of neurologic signs (i.e., fine head tremors, disorientation, dorsal recumbency, leg paddling). Chickens can also have lesions of vegetative valvular endocarditis, subclinical infection, or increased mortality with increased feed conversion.
The most common postmortem lesions include enlarged, congested, friable livers and spleens. The liver and spleen have multifocal necrotic foci (Fig. 1) and a marbled appearance. There is polyserositis as well as pale intestines that are segmentally distended with watery contents, and the cecal content appears frothy. The lymphoid organs are atrophied in individual birds that have not reached sexual maturity. Rule-outs for liver necrosis include E. coli septicemia, blackhead (histomoniasis), salmonellosis, pasteurellosis, clostridia-induced cholangiohepatitis, erysipelas, viral tumors, and tuberculosis.
There are multiple risk factors associated with development of S. gallolyticus infection, including immunosuppressive diseases (FAdV, IBDV, ALV-J-virus, HEV, circovirus), skin wounds, and other conditions causing loss of gastrointestinal tract integrity that can result in bacterial overgrowth, migration of bacteria, and septicemia. Environmental factors such as poor litter conditions, high stocking density, insufficient numbers of feeders and waterers, and inadequate lighting programs can result in competition, aggressive behavior, and stress which can all impair the immune response, resulting in a variety of infections, including S. gallolyticus. Poor hygiene levels and water quality can also play a role in the pathogenesis of disease.
As S. gallolyticus often presents in combination with other bacterial, viral and protozoal infections, its virulence potential remains to be established. AHL now routinely monitors all clinical cases for the presence of this bacterium, and reports it when isolated.
Figure 1. S. gallolyticus septicemia in 12-day-old meat turkeys.
A: Liver has numerous intravascular bacteria (basophilic stippling at arrow). H&E stain, 60x.
B: Spleen contains intravascular bacteria (arrow heads) with perivascular necrosis and fibrin deposition. H&E stain, 40x.
References:
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5. https://www.merckvetmanual.com/poultry/streptococcosis/streptococcosis-in-poultry