Difference between revisions of "Spirochaetes"

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===Overview===
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#REDIRECT[[:Category:Spirochaetes]]
 
 
*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 [[Intestines Fibrinous/Haemorrhagic Enteritis - Pathology#Bacterial septicaemia and enteritis|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, [[General Pathology - Pigmentation and Calcification#Haemoglobin|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 [[General Pathology - Pigmentation and Calcification#Hepatic (Toxic) Icterus|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 [[Intestines Fibrinous/Haemorrhagic Enteritis - Pathology#Swine Dysentery|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]]
 

Latest revision as of 20:56, 14 May 2010