Leptospira interrogans: Leptospira bacteria, Serovars (Serotypes) and Morphology

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Leptospira interrogans is the causative agent of a disease called Leptospirosis (also known as Weils Disease or Weils syndrome). These bacteria are spirochetes (spiral rods).

Leptospira spp

There are 2 species of Leptospira bacteria which include Leptospira biflexa and Leptospira interrogans. The most important that causes disease in humans is Leptospira interrogans.

Leptospira Classification

Leptospira belongs to a Family called Leptospiraceae and genus Leptospira. There are two species which are Leptospira biflexa (this does not cause disease) and Leptospira interrogans (the pathogenic specie that causes disease in humans). There are different serotypes (or serovars) of Leptospira interrogans based on their specific surface antigens variation this means they can trigger immunological response differently. There are more than 100 serovars of Leptospira interrogans but they have been group into 19 serogroups only the important ones are listed below.

Important Leptospira interrogans Serogroups

  1. Leptospira icterohemorrhagiae (the commonly isolated serotype in Weils disease)
  2. Leptospira canicola (affects dogs and pigs)
  3. Leptospira Pomona (affects pigs and cattle)
  4. Leptospira australis
  5. Leptospira grippotyphosa
  6. Leptospira hyos
  7. Leptospira sejroe
  8. Leptospira hardjo (affects cattle)

Because of the serological variations of Leptospira interrogans, it means developing immunity for one serovars does not confer immunity on other serovars this means when you survive one infection, you can still get infected by another serovars but cannot be infected again by the serotype that you have survived.

Leptospira bacteria Morphology and Characteristics

  1. Leptopsira spp are long, thin aerobic spirochetes that are wound up in a tight coil and have a hook on one or both ends which give them an “ice tongs” appearance
  2. Leptospirae bacteria are fine spirochetes that measure about 10 to 20 micrometer in length and 0.1 to 0.2 micrometer in diameter or thickness.
  3. Leptospirae have no flagella and only move by using their cell corpus to rotate.
  4. Leptospirae can best be visualized using dark field or phase contrast microscopy
  5. They are grown in special culture mediums under aerobic conditions at optimum temperature range of 27 to 30 degrees Celsius
  6. The organism can survive for many days in warm fresh water but only for up to 24 hours in sea water

Leptospira Pathogenesis

Leptospira spp damages the endothelial cells of the capillaries thereby leading to greater permeability and bleeding which subsequently interrupts the supply of oxygen to the affected body tissues. The jaundice seen in Leptospira infection is caused by a non-necrotic hepatocellular dysfunction. While lack of oxygen to the kidneys causes tubular damage and disturbs the renal function. There are two different types of Leptospira disease which are distinguished based on their clinical presentation: Anicteric leptospirosis (this is a milder form of the disease) and the severe form known as Icteric Leptospirosis (Weils disease). Although any of the serovars of Leptospira interrogans could potentially cause either the Anicteric Leptospirosis or Icteric Leptospirosis, this is not always the case in practical cases as the Leptospira icterohemorrhagiae is isolated more frequently in Weil disease.

Leptospira symptoms and signs

  1. Headache
  2. Fever
  3. Myalgias (muscle pains)
  4. Anorexia (loss of appetite)
  5. Malaise
  6. Vomiting
  7. Confusion
  8. Bleeding (extensive hemorrhage)
  9. Altered consciousness

The severe form of Leptospirosis known as Weils disease has life threatening symptoms such as hepatic and renal dysfunctions, extensive bleeding, cardiovascular symptoms, and clouding of the state of consciousness.

Leptospira diagnosis

Leptospira interrogans can be isolated by growing in special culture media by incubating the samples (such as blood sample, urine, cerebrospinal fluid or biopsies of affected organs). The samples should not be contaminated by any other bacteria and should be incubated at temperatures of 27 to 30 degrees Celsius for 3 to 4 weeks. The organisms should be visualized using a microscope over a dark field and this should be done weekly during the culture process to check if Leptospirae are proliferating. You can know the serovars or serotypes by in a lysis-agglutination reaction with specific test sera.

Another method of choice for a laboratory diagnosis of Leptospira is the use of antibody assay where quantitative lysis-agglutination test is used to detect the antibodies produced after the first week of the infection.

Leptospira Treatment

Treatment of Leptospira infections is by use of intravenous Doxycycline and Penicillin G in severe cases with supportive care.

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