Spirochaetes

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Leptospira

  • thin spiral organisms
  • stain poorly, better visualised by dark field microscopy 
  • persist in humid environments (water-saturated soil, pastures) 
  • host-adapted serovars - leptospires infect host and are not eliminated, induce asymptomatic or mild sometimes chronic disease, host becomes a reservoir for disease almost indefinitely 
  • non host-adapted serovars - leptospires infect host and can cause acute disease, not maintained in the host 
  • disease can be acute, sub-acute, chronic or asymptomatic 
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Clinical signs leptospira

  • Cattle Leptospira hardjo - may cause sudden drop in milk production 'milk drop syndrome', abortions, birth of weak calves or infertility 
  • Pigs - commonly infected with Leptospira bratislava in UK, causes reproductive disease 
  • Dogs - Leptospira canicola or Leptospira icterohaemorrhagiae - kidney failure or liver disease 
  • Rats - reservoir of infection for Leptospira icterohaemorrhagiae 
  • Horses - can be found positive for bratislava and icterohaemorrhagiae 
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Leptospira pathogenesis

  • Entry - through mucous membranes or damages skin via contact with urine or contaminated water, milk, genital secretions 
  • Spread - mainly haematogenous 
  • Localisation and proliferation - in lumen of proximal convoluted tubules in kidney, liver, spleen and occasionally brain in sheep and goats. penetration and multiplication in the foetus can lead to abortion 
  • Damage - of vascular endothelium, interstitial nephritis, production of haemolysin 
  • Haemorrhages, haemolysis with haemoglobinuria 
  • may be asymptomatic - shedding 
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Leptospira infection as zoonosis

  • first human lectospiral disease to be described was known as Weil's disease - febrile illness characterised by jaundice, haemorrhages, and involvement of the kidney - caused by L. icterohaemorrhagiae - transmitted to man by infected rats 
  • Leptospira serovars - associated with prevalence of infection with the animals with which people have contact 
  • Leptospiral infection in humans in the UK are mainly L. hardjo (cattle), L. icterohaemorrhagiae (rats, dogs) - about 50 cases per year in UK 
  • bacteria enter body through cuts/blisters in the skin and through mucous membranes - mouth, conjunctiva, nose 
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Brucella

  • gram -ve coocobacilli 
  • intracellular pathogens - persist very well in macrophages 
  • B. melitensis  isolated in 1887 - Bruce from spleens of British soldiers dying in Malta from disease known as Malta fever - 1904 cultured from milk and urine of sheep and goats 
  • B. abortus isolated in Denmark in 1897 from cattle suffering from infectious abortion - Bang's disease 
  • B. suis cultured in US in 1914 from foetus of a prematurely delivered sow 
  • transmitted by ingestion, penetration of skin and conjunctiva
  • organusms reach local lymph nodes and reach target organs via blood stream 
  • main diseases 
    • abortion
    • orchitis and epididymitis
    • synovitis and arthritis 
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Brucellosis in humans

  • Acquired - via raw milk, fresh cheese, handling of infected animals, exposure to contaminated aerosols 
  • Clinical forms 
    • asymptomatic
    • mild - tiredness, anorexia, muscle pains
    • acute - high temperature, hepato-splenomegaly, sweating, arthralgia, muscular pains, weight loss, jaundice, malaise 
    • chronic-relapsing - same as above but milder symptoms 
    • complications - epididymitis, orchitis, arthritis 
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Dermatophilus congolensis

  • first described by Sleghem in cattle in Belgian Congo as contagious dermatitis 
  • Transmission occurs via - contact, ticks and biting flies 
  • disease affects - areas vulnerable to abrasion and eposed to wetting (back, muzzle, feet)
  • areas infested by arthropods (axilla, ventral trunk, udder)
  • predisposing factors
    • rainfall and humidity - water can dilute inhibitory substances in skin, facilitate transport of spores from one area to another 
    • prescence of ticks, flies and biting flies - carry organism, local inflammation - predispose to skin site 
    • mechanical injuries - shearing, barbed fences, spines/branches
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Dermatophilus congolensis clinical signs

  • Cattle - small moist papules which become covered by progressively thickr hard crust and the hair appears as a paintbrush 
  • Sheep - animals often appear normal with evident lesions only on the ears and muzzle, careful examination reveals papules with moist exudate and crust, wool fibres become matted together with exudate 
  • Donkeys, Horses, Mules - areas of crust with localised tufts of matted hair
  • Man - pustules on hands and feet and scabs 
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Erysipelothrix rhusiopathiae

  • gram +ve bacillus 
  • recovered from sewage, soil, slurry from pig farms, faeces and tonsils of normal pigs, surface slime of fresh fish, numerous species of mammals and birds 
  • infection is acquired mainly by oral route 
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Erysipelothrix rhusiopathiae disease (1)

Pigs 

  • acute septicaemic form 
    • fever, anorexia depression, reluctance to walk, skin lesions usually present 
  • uticarial form - diamond skin disease 
    • usually accompanied by fever and signs of systemic illness 
  • vegetative endocarditis 
    • fibrin deposition and connective tissue proliferation 
  • arthritis and synovitis, erosion of joints 
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Erysipelothrix rhusiopathiae disease (2)

  • Birds (turkey and geese)
  • acute septicaemia
  • vegetative endocarditis 
  • arthritis 
  • Sheep 
  • polyarthritis in lambs - non suppurative polyarthritis with minor swelling of affected joints 
  • post-dipping lameness - infection occurs through skin abrasions 
  • Humans 
  • erysipeloid (infection of skin and subcut tissue) - occupational hazard in animal and fish handlers, septicaemia, endocarditis and arthritis are rare complications
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Listeria

  • gram +ve rods 
  • can grow between 4C and 45C - optimal 30-37C
  • widespread in the environment and in numerous animal species, poor silage with pH >5.5 is a common source of infection 
  • transmission mainly via oral route, penetration through damaged mucosal surfaces can occur 
  • L. monocytogenes and L. ivanovii two principal pathogenic species for animals and humans 
  • mainly in cattle and sheep - 2007 - VLA recorded 45 cases ain cattle and 87 in sheep/goats 
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Listeria - disease

  • L. monocytogenes
  • visceral (septicaemic) listeriosis, necrotic foci in liver and other abdominal organs - young animals of many species, can be birds 
  • neural listeriosis - circling disease - microabscesses in brain-stem and perivascular cuffing - sheep/goats/cattle sometimes other species 
  • abortion - sheep/goats/cattle 
  • iritis, with or without other signs, often associated with feeding big-bale silage - cattle 
  • L. ivanovii 
  • abortion - sheep and cattle 
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Listeriosis in humans

  • last decade - average of 180 cases reported anually 
  • individuals with impaired cell-mediated immunity and elderly people are most vulnerable 
  • infection is acquired by ingestion of raw vegetables, milk, fresh cheese, sliced meat, sandwiches, butter 
  • human infection usually involves 
    • bacteraemia - especially in older people
    • meningitis 
    • abortion, stillbirth or premature birth 
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