Difference between revisions of "Category:Spirochaetes"

Overview

• Two families exist, Category:Leptospiraceae and Category: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

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 dysentery
  • 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