Spirochaetes
Jump to navigation
Jump to search
|
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
- Cattle and sheep
- 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
- Horses
- 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
- Pigs
- 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
- Dogs and 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