please give an example of avirulent strain
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Answer:
Pathogen Risk Factors
Strains of S. hyicus can be divided into virulent and avirulent strains with regard to ability to produce exudative epidermitis in experimental piglets; both types of strain can be isolated simultaneously from diseased piglets. It has been shown that different types of S. hyicus expressing different types of toxin may be present in the same diseased pig.
S. hyicus produces an exfoliative toxin that can be used to reproduce the disease. There are several toxins, including ExLA, ExLB, ExLC, ExLD, SHETa, and SHETb.4 Toxigenic S. hyicus is isolated more freely from diseases than healthy pigs.5 Strains of the organism isolated from a large number of Danish pig herds indicated different electrophoretic motility and plasma-mediated antibiotic resistance patterns. The antibiotic and plasmid profiles of strains isolated from pig herds may be a reflection of the use of antibiotics in those herds. Different types of toxin are produced.
Recently the genes encoding for the exfoliative toxins SHETb, ExLA, ExLB, ExLC, and ExLD have been identified and sequenced.
The condition has been seen more frequently in cases of PRRS and PCV-2 infections. It is very resistant to drying and can persist in the environment.
The organism has been found as a frequent inhabitant of the skin of cattle and has been isolated from cattle with skin lesions. Naturally occurring lesions of dermatitis of the lower limbs of horses and similar lesions over the neck and back of donkeys have been recorded. Experimentally, the organism can cause lesions in horses similar to those of exudative epidermitis. A concurrent infection with D. congolensis has also been reported.