Which serovar of Leptospira is most virulent to humans?

The serovar of Leptospira most virulent to humans is L. interrogans, serovar icterohemorrhagica. This particular serovar is associated with severe forms of leptospirosis, which can lead to significant morbidity and mortality in infected individuals.

Icterohemorrhagica is known to produce a more severe clinical presentation in humans, characterized by symptoms such as jaundice, bleeding, and liver damage, often referred to as Weil's disease. This virulence is attributed to the ability of L. interrogans to evade the host's immune system and establish persistent infections, which enhances its pathogenicity.

In contrast, other serovars, such as L. biflexa, generally do not lead to serious disease in humans and are often considered non-pathogenic. Similarly, L. noguchii and L. interrogans, serovar grippotyphosa, do not exhibit the same level of virulence in humans as icterohemorrhagica. These differences highlight the significance of specific serovars in terms of their impact on human health and the need for targeted prevention and treatment strategies for leptospirosis.