Streptococcal infection, also referred to as avian streptococcosis, presents as an acute septicemia or a subacute or chronic infection, with mortality rates of 11% to 80%. Streptococci (genus Streptococcus
) are Gram-positive, catalase-negative, chain-forming, coccus-shaped bacteria. Most streptococci are considered opportunistic pathogens which are ubiquitous in nature and often part of the normal intestinal and mucosal flora of humans and animals. In animals, the main habitats of streptococci are the skin and mucous membranes of the respiratory, gastrointestinal, and urogenital tracts.
Chronic and subacte streptococcal infection can affect the reproductive system (salpingitis and peritonitis), their cardiovascular system (pericarditis, necrotic myocarditis, and bacterial or vegetative endocarditis), legs and joints (osteomyelitis, arthritis and/or tenosynovitis), skin (cellulitis), eyes (conjunctivitis), or liver (perihepatitis). Endocarditis occurs when septicemic streptococcal infection progresses to a subacute or chronic stage.
The genus Streptococcus
consists of more than 60 species, but only S. equi
, S. gallolyticus
, S. gallinaceus
, S. suis
, S. dysgalactiae
, S. mutans
and S. pleomorphus
have been isolated from poultry.
- Streptococcus gallolyticus subsp gallolyticus (SGG): Formally known as S. bovis, is a zoonotic pathogen which can be part of the normal gut microbiota of wild animals, dog and cats, and humans. It is an opportunistic bacteria which causes several diseases in animals, including chickens. Prevalence of shedding SGG in the fecal droppings in turkey flocks reached up to 100% on most farms, and 80% of crop and cloaca samples from pigeons. In laying hens, colonization of non-carrier birds introduced into an SGG-positive flock took approximately 35 weeks and occurred likely via feed and feces.
- Streptococcus equi subspecies zooepidemicus: Has been isolated from chicken crops, but less frequently and not as a predominant bacteria. Aerosol transmission of S. zooepidemicus results in acute septicemia in chickens.
- Streptococcus suis: Is a zoonotic pathogen which is a normal inhabitant of the tonsils of pigs, cattle, dogs, and cats. It has been diagnosed infrequently in birds. Previous cases described in birds resulted in birds showing a good appetite until shortly before death and some died with a full crop.
The acute septicemic form of streptococcosis presents as lassitude, bloodstained tissue and feathers around the mouth and head with blood coming from their mouth, yellow droppings, reduced egg production in hens, emaciation, and pale combs and wattles. Cyanosis (blue-purple comb) occurs in the terminal stages. The clinical signs observed in subacute and chronic streptococcal infections will vary depending on the location and severity of the infection.
Streptococci are transmitted to chickens most commonly via oral, and aerosol routes. It is less frequently transmitted through skin injuries. In order for it to cause infection via fecal-oral or food-oral route it requires the bacteria to survive the gastric passage to colonize the gut. Survival depends on the strain of streptococci, gastric pH, and amount ingested. Sources of infection can be wild birds, newly introduced poultry (pigeons, ducks, chickens, geese, and turkey), dogs, cats, humans, rodents (mice), and rabbits.
The incubation period for streptococcal infections range from 1 day to several weeks. 5–21 days is most common.
Gross lesions of S. zooepidemicus
in the acute septicemic presentation consist of splenomegaly, hepatomegaly (with or without miliary to 1 cm red, tan, or white foci), enlarged kidneys, congestion of sub-cutaneous tissue, and peritonitis.
Differential diagnosis for acute septicemic streptococcal infection include other bacterial septicemic diseases such as staphylococcosis, colibacillosis, pasteurellosis, and erysipelas. For subacute and chronic infections, the differential diagnosis include other bacterial-caused localized infections.
Treatment for streptococcal infections include the use of antibiotics including penicillin, erythromycin, novobiocin, oxytetracycline, chlortetracycline, and tetracycline in acute and subacute infections. Clinically affected birds respond well early in the course of the disease. As the disease progresses within a flock, treatment efficacy decreases. Antibacterial susceptibility should be performed on bacterial isolates in any clinical cases of streptococcosis. There is no treatment for chickens who develop bacterial endocarditis.