Virulent L. interrogans serotypes have been shown to adhere to and penetrate cultured endothelial and kidney epithelial cells in vitro. The proximal renal tubules may be the natural habitat for these organisms. The mechanisms by which leptospires cause multiorgan system dysfunction and, occasionally, diffuse vasculitis remain largely unknown. Direct spirochetal invasion of tissues may be one mechanism of cellular injury. The major impact of severe infection is on the liver and kidneys.
Aseptic meningitis is also common.
Occasionally, myocarditis or hemorrhagic pneumonitis occurs. Histologic changes in the liver are not often striking, and such changes are not diagnostic. Jaundice is often observed without hepatocellular necrosis. The most common renal lesions in patients with leptospirosis are interstitial nephritis and tubular epithelial necrosis. The pathophysiology of these lesions may, in some cases, be a direct toxic effect by the leptospires as well as immune-mediated injury.