Spirochaetes

BACTERIA

Overview

• Two families exist, Leptospiraceae and Spirochaetaceae
• Leptospiraceae include the pathogens of the genus Leptospira
• Spirochaetaceae include the pathogens of the genera Borrelia, Brachyspira and Treponema
• Many cause zoonotic infections

Characteristics

• Spiral or helical Gram-negative bacteria
• Motile organisms via endoflagella
• Poor survival in the environment and sensitive to dessication
• Stain poorly with Gram stain
• Most require specialised media for growth
• Serology required for identification

Leptospira

• Motile, helical bacteria found in aquatic environments
• Require liquid media for culture
• Cause leptospirosis in all animals, which can range from mild urogenital tract infections to systemic diseases
• Organisms persist in kidney tubules or genital tract of carrier animals and are shed in urine
• Transmission via direct contact
• Serovars are fairly host-specific, causing mild disease in the maintenance host, with shedding in the urine
• Maintenance hosts may transmit the infection to incidental hosts, which are less susceptible to infection, but develop serious disease

• Pathogenesis and pathogenicity
  • Depends on virulence of the serovar and susceptibility of the host
  • Leptospires invade tissues through moist skin or via mucous membranes, aided by their motility
  • Leptospires may invade via receptor-mediatied endocytosis
  • They disseminate through the body via the blood stream
  • Antibodies clear organisms from the blood stream after about 10 days of infection
  • Organisms may persist in the renal tubules, uterus, eye or meninges
  • Evade phagocytosis possibly via macrophage apoptosis
  • Damage red blood cell membranes and endothelial and liver cells, leading to haemolytic anaemia, jaundice, haemoglobinuria and haemorrhage in acute leptospirosis

• Diagnosis
  • Clinical signs and history of exposure
  • Dark-field microscopy of urine may detect organisms
  • Isolation from blood or urine by culture or animal inoculation
  • Identificaiton or certain serovars using DNA probes and serology
  • FLuorescent antibody technique for identification in tissues
  • Silver impregnation
  • Molecular techniques such as PCR
  • Serology using microscopic agglutination test or ELISA

• Clinical infections
  • Cattle and sheep
    • Cattle are maintenance hosts for L. borgpetersenii serovar hardjo
    • L. interrogans serovar hardjo is host-adapted to cattle
    • Acute disease in susceptible heifers, with fever and agalactia of all quarters; abortion and stillbirth may occur
    • Diagnosed by rising antibody titre in paired serum samples
    • Infection in sheep may cause abortion and agalactia
    • Urinary excretion can be reduced by administering dihydrostreptomycin or amoxycillin
    • Incactivated vaccines are of questionable efficacy
    • Serovars pomona, grippotyphosa and icterohaemorrhagiae cause pyrexia, haemoglobinurea, jaundice, anorexia, uraemia due to renal damage and death in calves and lambs

• • Horses
    • Clinical disease rare
    • May be maintenance host of serovar bratislava, which causes abortion and stillbirth
    • Incidental hosts for serovar pomona, suffering from abortion and renal disease
    • Chronic leptospirosis may cause an immune-mediated anterior uveitis

• • Pigs
    • The rodent-adapted serovars icterohaemorrhagica and copenhagenii cause acute disease in pigs
    • Severe disease in young pigs
    • Serovar pomona is the host-adapted species, and may be shed in the urine
    • Infections may cause abortions and stillbirths
    • Pigs are maintenance hosts for serovars tarassovi and bratislava, which may cause reproductive failure

• • Dogs and cats
    • Serovars canicola and icterohaemorrhagica cause leptospirosis in dogs, but are vaccinated against
    • Serovars pomona and grippotyphosa are becoming important
    • The host-adapted serovar canicolar causes acute renal failure in puppies; a chronic uraemic syndrome may follow
    • Incidental infections with serovar icterohaemorrhagica or copenhagenii cause renal failure
    • Serovar bratislava causes abortion and infertility in dogs, which may be the maintenance host
    • Infections uncommon in cats

Borrelia

• Longer, wider, helical spirochaetes with a linear chromosome and linear and circular plasmids
• Obligate parasites transmitted by arthropod vectors

• Lyme disease
  • Caused by Borrelia burgdorferi
  • Reported in humans, dogs, horses, cattle, sheep

Brachyspira hyodysenteriae

Leptospira