Leptospirosis pathophysiology

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor(s)-in-Chief: Venkata Sivakrishna Kumar Pulivarthi M.B.B.S [2]


Leptospires shed in the urine of animals to the environment from where humans are infected by incidental hosts. In Carriers these bacteria harbor in the renal tubules and can persist in soil or surface water and then transmits to human hosts via mucous membranes or abraded skin.[1][2] Pathogen transmit through various mechanisms such as broken skin, mucus membranes and the conjunctivae, exposure to contaminated water are at risk of contracting leptospirosis.[3]


The disease leptospirosis involves a spectrum of symptoms ranging from subclinical infection to a severe syndrome of multiorgan infection with high mortality and Weil’s disease represents only the most severe presentation. Severe leptospirosis is frequently caused by serovars of the icterohaemorrhagiae serogroup. The presentation of leptospirosis is biphasic, with the acute or septicemic phase lasting about a week, followed by the immune phase, characterized by antibody production and excretion of leptospires in the urine.[4]


The major reservoir for leptospirosis is rat and small rodents that appear to harbour more virulent strains of the disease.[5]


Domestic animals such as dogs,cattle and pigs acts as potential carriers that increases the risk of leptospirosis in humans. These carriers are generally asymptomatic.[6][7]

Modes of transmission

  1. Direct contact with urine or tissue of infected animal: Through skin abrasions and intact mucus membrane
  2. Indirect contact: Broken skin with infected soil, water or vegetation, Through ingestion of contaminated food and water
  3. Droplet infection: Inhalation of droplets of infected urine

Infection can occurs either by direct contact with the carrier’s urine or through indirect transmission via urine-contaminated environment. Infection due to direct transmission through direct oral intake of contaminated drinking water or food is very rare.[8] Pathogenic leptospires live in the renal system and the genital tracts of domestic animals which act as sites of persistence.[9][10] Bacteria shed from the infected animals such as rodents and domesticat animals through urine. These animals may not show signs of disease but humans shows signs of illness after contact with infected urine, or through contact with water, soil or food that has been contaminated and the outbreaks are associates with floodwaters. The major route of infection by leptospires is probably by transmission through indirect contact with leptospires secreted into the environment. Humans are considered dead end hosts, but sometimes they also act as carriers. Mammalian species (e.g. rodents, insectivores, dogs, pigs and cattle) act as the main carriers of the disease.[11] Leptospires are excreted in urine into the environment, where they can survive for several months, depending on favourable environmental conditions such as humid and temperate areas. The pathogen may also be excreted in the products of abortion in mammalian animal species.[9]

Pathological findings of leptospirosis are due to the development of the following:[12][13][14][15]


Toxin production

Type of toxin production depends on the serovar

Damage to small blood vessels


• Direct cytotoxic injury or Immunological injury
• Fluid extavasation into the interstitial compartment due to vasculitis

Acute renal injury and vascular injury to internal organs

Gross Pathology

Gross findings of various organ systems are present as:[16]

  • Extensive petechial hemorrhages are common.
  • Discoloration of organs is seen in severe cases of icteric leptospirosis.

Microscopic Pathology




Leptospirosis is associate with interstitial myocarditis.[20][21][22][23]


Common pulmonary presentation in leptospirosis are pulmonary congestion and hemorrhage.[16][23][24][25]

Skeletal muscle



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