Spirochaetes

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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
  • Cause systemic infections in many animals and humans
  • Slow growth in specialised culture media
  • 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
    • Pathogenesis
      • Virulence of the borreliae requires a change in expression of an outer membrane protein following ingestion of blood by the tick
      • Borreliae multiply in the blood stream of susceptible hosts and disseminate throughout the body
      • Localisation in joints, brain, nerves, eyes and heart can occur
      • The associated lesions may be in part caused by the host immune response
    • CLinical signs
      • May be subclinical in endemic areas
      • Clinical manifestation depends on the site of localisation of organisms
      • Disease in dogs may cause fever, lethargy, arthritis, cardiac, renal or neurological disturbance
      • Horses suffer similar clinical signs but also lameness, uveitis, nephritis, hepatitis and encephalitis
      • Cattle and sheep may suffer from lameness
    • Diagnosis
      • Laboratory confirmation difficult due to low numbers of organisms and fastidious growth requirements
      • History of exposure to ticks in an endemic region and clinical signs
      • Rising antibody titre to Borrelia burgdorferi detected by ELISA
      • Immunofluorescence
      • Culture in Barbour-Stoenner-Kelly medium for 6 weeks under microaerophilic conditions
      • PCR
    • Treatment and control
      • Amoxycillin and oxytetracycline in the acute phase; prolonged treatment in the chronic phase
      • Tick control and removal
      • Vaccines including whole cell bacterins and recombinant subunit vaccines available for dogs


Avian spirochaetosis

  • Caused by Borrelia anserina
  • Acute, endemic disease of birds in tropical and subtropical regions
  • Chickens, turkeys, pheasants, ducks and geese susceptible
  • Transmitted by soft ticks of the Argas family, but also via contact with infected material such as blood and tissues
  • Transmitted transovarially and trans-stadially via the tick population
  • Outbreaks during peak tick activity during warm, humid conditions
  • Fever, anaemia and wight loss occurs, with development of paralysis later
  • Immunity is serotype specific
  • Diagnosis using dark-field microscopy of buffy coat smears or immunodluorescence of blood or tissues
  • Giemsa-stained smears and silver impregnation of tissues
  • Isolation of borreliae by inoculation of embryonated eggs or chicks
  • Antibiotic treatment
  • Inactivated vaccines available


Brachyspira and Serpulina

  • Anaerobic, intestinal spirochaetes, found in normal and diseased pigs
  • Enterophogens of pigs
  • B. hyodysenteriae, B. pilosicoli, B. innocens, Serpulina intermedia and S. murdochii occur in pigs
  • Carrier pigs shed B. hyodysenteriae for up to 3 months, acting as a source of infection for healthy pigs
  • Demonstrated in stained faecal smears or silver-stained histopathology sections
  • Cultured anaerobically on selective blood agar
  • Spirochaetes differentiated by pattern of haemolysis on blood agar as well as molecular techniques
  • Pathogenesis
    • Motility in mucous allows colonisation of pig intestine
    • Haemolytic and cytotoxic activiity important for virulence
    • Attachment of B. pilosicoli to epithelial cells of colonic mucosa disrupts their function and leads to their shedding and oedema
  • Clinical infections
    • B. hyodysenteriae causes swine dysentry
    • B. pilosicoli causes porcine intestinal spirochaetosis
    • Infection is acquired via contaminated faeces
    • Disease spreads slowly through the herd
    • Dogs, rats, mice and flies may act as transport hosts
    • B. hyodysenteriae survives several weeks in moist faeces
  • Clinical signs
    • B. hyodysenteriae causes dysentry in weaned pigs 6-12 weeks old; pigs lose condition and become emaciated; appetite is decreased; large amount of mucous may be present in the faeces; low mortality; poor feed conversion ratio
    • B. pilosicoli causes less severe signs than swine dysentry; reduced feed conversion rates occur
  • Diagnosis
    • History, clinical signs and gross pathology
    • Anaerobic culture on blood agar with added antibiotics for at least 3 days
    • B. hyodysenteriae causes complete haemolysis whereas other spirochaetes cause partial haemolysis
    • Immunofluorescence, DNA probes and biochemical tests
    • Serology using ELISA can be used on a herd basis
    • PCR

Brachyspira hyodysenteriae