Difference between revisions of "Spirochaetes"

From WikiVet English
Jump to navigation Jump to search
Line 99: Line 99:
 
**Caused by ''Borrelia burgdorferi''
 
**Caused by ''Borrelia burgdorferi''
 
**Reported in humans, dogs, horses, cattle, sheep
 
**Reported in humans, dogs, horses, cattle, sheep
 +
**Ticks are the vector, which acquire the infection from small rodents, the reservoir hosts
 +
**Ticks transmit the infection to large mammals such as deer and sheep
 +
**''Ixodes ricinus'' is the most common tick vector in Europe
  
 
   
 
   
 
[[Brachyspira hyodysenteriae]]
 
[[Brachyspira hyodysenteriae]]
 
[[Leptospira]]
 

Revision as of 10:43, 31 December 2008

Infectious agents and parasitesWikiBugs Banner.png
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
  • May cause severe systemic disease, resulting in enteritis
  • 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-mediated 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, haemoglobin pigmentation, 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
      • L. icterohaemorrhagiae may cause hepatic jaundice
      • 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
    • Ticks are the vector, which acquire the infection from small rodents, the reservoir hosts
    • Ticks transmit the infection to large mammals such as deer and sheep
    • Ixodes ricinus is the most common tick vector in Europe


Brachyspira hyodysenteriae