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| + | #REDIRECT[[:Category: Rickettsiales]] |
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| − | {{toplink
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| − | |backcolour =
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| − | |linkpage =Bacteria
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| − | |linktext =BACTERIA
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| − | |pagetype=Bugs
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| − | <br>
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| − | ===Overview===
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| − | *Cause systemic diseases in animals
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| − | *Usually use arthropod vectors
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| − | ===Characteristics===
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| − | *Non-motile, pleomorphic Gram-negative organisms
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| − | *Obligate intracellular pathogens
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| − | *Require live cells for culture such as tissue culture cells or embryonated eggs
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| − | *Require Romanowsky stains
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| − | *Host and cell type specificity
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| − | *Include two families, ''Rickettsiaceae'' and ''Anaplasmataceae''
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| − | *''Rickettsiaceae'' have cell walls that contain peptidoglycan; they target endothelial cells and leukocytes
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| − | *''Anaplasmataceae'' lack cell walls; they target erythrocytes
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| − | *Q fever and Rocky Mountain spotted fever are zoonoses
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| − | ===Epidemiology===
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| − | *Rickettsiae replicate in gut epithelial cells of arthropod vectors and spread to other organs such as salivary glands and ovaries
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| − | *Transmission occurs during feeding on the animal host
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| − | *Transovarial or trans-stadial transmission occurs in the arthropod vectors
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| − | *Most ricketsiae have limited survival in the environment, apart from ''Coxiella burnetii'', which undergoes aerosol transmission
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| − | ===Pathogenesis and pathogenicity===
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| − | *Many rickettsiae target endothelial cells of small blood vessels; they produce phospholipase which damages phagosome membranes, escaping into the cytoplasm
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| − | *''Ehrlichia'' target leukocytes or platelets, and inhibit phagosome/lysosome fusion
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| − | *''Anaplasmataceae'' localise within vacuoles or on the surface of red blood cells; they may alter red cell antigens causing immune-mediated damage. Anaemia may result from haemolysis or removal of red blood cells
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| − | ===Identification===
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| − | *Giemsa-stained blood or tissue smears identify blue/purple organisms
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| − | *Fluorescent antibody technique for specific identification
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| − | *Isolation in embryonated eggs or tissue culture lines
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| − | *Nucleic acid probes and PCR
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| − | *Inoculation of susceptible animals
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| − | ===Rocky Mountain spotted fever===
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| − | *Caused by ''Rickettsia rickettsii''
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| − | *Affects humans and dogs
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| − | *Various tick vectors, which acquire the organism from small mammals
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| − | *Transovarial and trans-stadial transmission within the tick population
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| − | *Organisms replicate in endothelial cells of infected dogs, cause vasculitis, increased vascular permeability and haemorrhage
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| − | *Clinical signs
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| − | **Incubation period 2-10 days; course less than 2 weeks
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| − | *Fever, depression, conjunctivitis, retinal haemorrhage, muscle and joint pain, coughing, dyspnoea, oedema of extremities
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| − | *Neurological signs in dogs include stupor, ataxia, neck rigidity, seizures and coma
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| − | *Death from cardiovascular, neurological or renal damage in severely-affected animals
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| − | *Gross pathology includes haemorrhage, splenomegaly and lymphadenopathy
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| − | *Diagnosis
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| − | **Rising antibody titre during an indirect fluorescent antibody test or ELISA
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| − | **Thrombocytopenia and leukopenia during early phase
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| − | *Treatment and control
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| − | **Tetracycline therapy for two weeks
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| − | **Tick removal from dogs
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| − | ===Canine monocytic ehrlichiosis===
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| − | *Generalised disease of dogs in tropical and subtropical regions
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| − | *Caused by ''Ehrlichia canis''
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| − | *The brown tick, ''Rhipicephalus sanguineus'', is the main vector
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| − | *Dogs may carry the organism for 2 years after resolution of clinical signs
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| − | *Clinical signs
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| − | **Incubation period of 3 weeks
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| − | **Acute, subclinical or chronic phases
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| − | **Acute phase: fever, thrombocytopenia, leukopenia and anaemia
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| − | **Subclinical phase: low blood cell numbers but minimal clinical signs; can progress to a severe disease, tropical canine pancytopenia
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| − | **Chronic phase: bone marrow depression, haemorrhages, neurological disease, peripheral oedema, emaciation and hypotensive shock
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| − | *Diagnosis
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| − | **''E. canis'' morulae present in mononuclear cells in Giemsa-stained blood smears
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| − | **Rising antibody titre detected by indirect immunofluorescence
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| − | **Culture in canine macrophages
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| − | *Treatment and control
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| − | **Doxycycline for 10 days
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| − | **Fluid therapy or blood transfusion
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| − | **Prophylactic tetracyclines
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| − | ===Canine cyclic thrombocytopenia===
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| − | *Caused by ''Ehrlichia platys''
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| − | *Affects platelets
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| − | *Recurrent thrombocytopenia, but dogs usually asymptomatic
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| − | *Seroconversion detected by indirect immunofluorescence
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| − | ===Potomac horse fever===
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| − | *Caused by ''Ehrlichia risticii''
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| − | *Occurs during the summer
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| − | *Fluke vector
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| − | *Infects epithelial cells of colon and monocytes, macrophages and mast cells
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| − | *Clinical signs
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| − | **Fever, anorexia, depression, diarrhoea, colic, leukopenia, laminitis
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| − | *30% mortality
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| − | *Can cause abortion
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| − | *Hyperaemia of large intestine at post mortem
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| − | *Diagnosis
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| − | **Seroconversion detected by indirect immunofluorescence or ELISA
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| − | *Treatment and control
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| − | **Oxytetracycline for 1 week
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| − | **Inactivated vaccines
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| − | ===Equine granulocytic ehrlichiosis===
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| − | *Caused by ''E. equi''
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| − | *Clinical signs: fever, depression, ataxia, limb oedema, icterus and petechial haemorrhages
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| − | *Low mortality
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| − | *Diagnosis: presence of morulae in neutrophils during early disease; seroconversion; leukopenia
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| − | *Treatment: tetracyclines
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| − | ===Bovine petechial fever===
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| − | *Caused by ''E. ondiri''
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| − | *Disease of cattle in Kenya and other countries of East Africa
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| − | *Tick vector
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| − | *Clinical signs: intermittent fever, depressed milk yield, petechiation of mucous membranes and conjunctiva
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| − | *Death from pulmonary oedema
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| − | *Diagnosis: presence of organisms in Giemsa-stained blood smears
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| − | *Treatment: tetracyclines
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| − | ===Tick-borne fever===
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| − | *Caused by ''E. phagocytophila''
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| − | *Affects ruminants in Europe
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| − | *The tick ''Ixodes ricinis'' is the main vector
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| − | *Animals remain carriers for up to 2 years, but are immune to reinfection
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| − | *Clinical signs
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| − | **Incubation period of 2 weeks; recovery in 2 weeks
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| − | **Fever, anorexia, reduced growth rates in young animals
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| − | **Reduced milk production, abortion, still birth
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| − | **Leukopenia and thrombocytopenia
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| − | **Causes immunosuppression in young lambs causing susceptibility to tick pyaemia and louping ill
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| − | *Diagnosis
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| − | **Intracytoplasmic morulae in neutrophils of Giemsa-stained blood smears during acute phase
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| − | **Seroconversion detected by immunofluorescence
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| − | *Treatment and control
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| − | **Oxtetracycline
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| − | **Tick control
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| − | **Prophylactic tetracyclines for lambs during first few weeks of life
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| − | ===Heartwater===
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| − | *Severe disease of ruminants in sub-Saharan Africa caused by ''Cowdria ruminantium''
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| − | *Vectors include ''Amblyomma'' ticks
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