Most virulent variety of shigellosis is caused by:

Ans. is 'a' i.e., Shigella dysenteriae(Ref: Ananthanarayan, 8th/e, p. 286 and 9th/e, p. 2851)Complications are most often seen in infection with Sh. dysenteriae type I and include arthritis, toxic neuritis, conjunctivitis, parotitis and in children, intussusception. HUS may occur in severe cases.