Difference between revisions of "Rickettsiales"

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#REDIRECT[[:Category: Rickettsiales]]
 
 
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===Overview===
 
 
 
*Cause systemic diseases in animals
 
*Usually use arthropod vectors
 
 
 
 
 
===Characteristics===
 
 
 
*Non-motile, pleomorphic Gram-negative organisms
 
*Obligate intracellular pathogens
 
*Require live cells for culture such as tissue culture cells or embryonated eggs
 
*Require Romanowsky stains
 
*Host and cell type specificity
 
*Include two families, ''Rickettsiaceae'' and ''Anaplasmataceae''
 
*''Rickettsiaceae'' have cell walls that contain peptidoglycan; they target endothelial cells and leukocytes
 
*''Anaplasmataceae'' lack cell walls; they target erythrocytes
 
*Q fever and Rocky Mountain spotted fever are zoonoses
 
 
 
 
 
===Epidemiology===
 
 
 
*Rickettsiae replicate in gut epithelial cells of arthropod vectors and spread to other organs such as salivary glands and ovaries
 
*Transmission occurs during feeding on the animal host
 
*Transovarial or trans-stadial transmission occurs in the arthropod vectors
 
*Most ricketsiae have limited survival in the environment, apart from ''Coxiella burnetii'', which undergoes aerosol transmission
 
 
 
 
 
===Pathogenesis and pathogenicity===
 
 
 
*Many rickettsiae target endothelial cells of small blood vessels; they produce phospholipase which damages phagosome membranes, escaping into the cytoplasm
 
*''Ehrlichia'' target leukocytes or platelets, and inhibit phagosome/lysosome fusion
 
*''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
 
 
 
 
 
===Identification===
 
 
 
*Giemsa-stained blood or tissue smears identify blue/purple organisms
 
*Fluorescent antibody technique for specific identification
 
*Isolation in embryonated eggs or tissue culture lines
 
*Nucleic acid probes and PCR
 
*Inoculation of susceptible animals
 
 
 
 
 
===Rocky Mountain spotted fever===
 
 
 
*Caused by ''Rickettsia rickettsii''
 
*Affects humans and dogs
 
*Various tick vectors, which acquire the organism from small mammals
 
*Transovarial and trans-stadial transmission within the tick population
 
*Organisms replicate in endothelial cells of infected dogs, cause vasculitis, increased vascular permeability and haemorrhage
 
 
 
*Clinical signs
 
**Incubation period 2-10 days; course less than 2 weeks
 
*Fever, depression, conjunctivitis, retinal haemorrhage, muscle and joint pain, coughing, dyspnoea, oedema of extremities
 
*Neurological signs in dogs include stupor, ataxia, neck rigidity, seizures and coma
 
*Death from cardiovascular, neurological or renal damage in severely-affected animals
 
*Gross pathology includes haemorrhage, splenomegaly and lymphadenopathy
 
 
 
*Diagnosis
 
**Rising antibody titre during an indirect fluorescent antibody test or ELISA
 
**Thrombocytopenia and leukopenia during early phase
 
 
 
*Treatment and control
 
**Tetracycline therapy for two weeks
 
**Tick removal from dogs
 
 
 
 
 
===Canine monocytic ehrlichiosis===
 
 
 
*Generalised disease of dogs in tropical and subtropical regions
 
*Caused by ''Ehrlichia canis''
 
*The brown tick, ''Rhipicephalus sanguineus'', is the main vector
 
*Dogs may carry the organism for 2 years after resolution of clinical signs
 
 
 
*Clinical signs
 
**Incubation period of 3 weeks
 
**Acute, subclinical or chronic phases
 
**Acute phase: fever, thrombocytopenia, leukopenia and anaemia
 
**Subclinical phase: low blood cell numbers but minimal clinical signs; can progress to a severe disease, tropical canine pancytopenia
 
**Chronic phase: bone marrow depression, haemorrhages, neurological disease, peripheral oedema, emaciation and hypotensive shock
 
 
 
*Diagnosis
 
**''E. canis'' morulae present in mononuclear cells in Giemsa-stained blood smears
 
**Rising antibody titre detected by indirect immunofluorescence
 
**Culture in canine macrophages
 
 
 
*Treatment and control
 
**Doxycycline for 10 days
 
**Fluid therapy or blood transfusion
 
**Prophylactic tetracyclines
 
 
 
 
 
===Canine cyclic thrombocytopenia===
 
 
 
*Caused by ''Ehrlichia platys''
 
*Affects platelets
 
*Recurrent thrombocytopenia, but dogs usually asymptomatic
 
*Seroconversion detected by indirect immunofluorescence
 
 
 
 
 
===Potomac horse fever===
 
 
 
*Caused by ''Ehrlichia risticii''
 
*Occurs during the summer
 
*Fluke vector
 
*Infects epithelial cells of colon and monocytes, macrophages and mast cells
 
 
 
*Clinical signs
 
**Fever, anorexia, depression, diarrhoea, colic, leukopenia, laminitis
 
*30% mortality
 
*Can cause abortion
 
*Hyperaemia of large intestine at post mortem
 
 
 
*Diagnosis
 
**Seroconversion detected by indirect immunofluorescence or ELISA
 
 
 
*Treatment and control
 
**Oxytetracycline for 1 week
 
**Inactivated vaccines
 
 
 
 
 
===Equine granulocytic ehrlichiosis===
 
 
 
*Caused by ''E. equi''
 
*Clinical signs: fever, depression, ataxia, limb oedema, icterus and petechial haemorrhages
 
*Low mortality
 
*Diagnosis: presence of morulae in neutrophils during early disease; seroconversion; leukopenia
 
*Treatment: tetracyclines
 
 
 
 
 
===Bovine petechial fever===
 
 
 
*Caused by ''E. ondiri''
 
*Disease of cattle in Kenya and other countries of East Africa
 
*Tick vector
 
*Clinical signs: intermittent fever, depressed milk yield, petechiation of mucous membranes and conjunctiva
 
*Death from pulmonary oedema
 
*Diagnosis: presence of organisms in Giemsa-stained blood smears
 
*Treatment: tetracyclines
 
 
 
 
 
===Tick-borne fever===
 
 
 
*Caused by ''E. phagocytophila''
 
*Affects ruminants in Europe
 
*The tick ''Ixodes ricinis'' is the main vector
 
*Animals remain carriers for up to 2 years, but are immune to reinfection
 
 
 
*Clinical signs
 
**Incubation period of 2 weeks; recovery in 2 weeks
 
**Fever, anorexia, reduced growth rates in young animals
 
**Reduced milk production, abortion, still birth
 
**Leukopenia and thrombocytopenia
 
**Causes immunosuppression in young lambs causing susceptibility to tick pyaemia and louping ill
 
 
 
*Diagnosis
 
**Intracytoplasmic morulae in neutrophils of Giemsa-stained blood smears during acute phase
 
**Seroconversion detected by immunofluorescence
 
 
 
*Treatment and control
 
**Oxtetracycline
 
**Tick control
 
**Prophylactic tetracyclines for lambs during first few weeks of life
 
 
 
 
 
===Heartwater===
 
 
 
*Severe disease of ruminants in sub-Saharan Africa caused by ''Cowdria ruminantium''
 
*Vectors include ''Amblyomma'' ticks
 
*Carrier status can occur for up to 8 months in adult cattle and wildebeest
 
*Clinical disease in calves and lambs
 
 
 
*Clinical signs
 
**Incubation period 4 weeks
 
**Acute fever
 
**Neurological signs including chewing, twitching of eyelids, circling, high-stepping gait, convulsions and recumbency; can be fatal
 
**Subacute cases suffer from hydropericardium, hydrothorax and pulmonary oedema and congestion; splenomegaly and haemorrhages may occur
 
 
 
*Diagnosis
 
**Clinical and post mortem findings in endemic areas suggestive
 
**Orgnisms present in nuclei of endothelial cells in Giemsa-stained brain tissue
 
**PCR, indirect immunofluorescence, ELISA and western blot
 
 
 
*Treatment and control
 
**Tetracyclines during early disease
 
**Immunisation using infected blood
 
 
 
 
 
===Bovine anaplasmosis===
 
 
 
*Disease of cattle in tropical and sub-tropical regions caused by ''Anaplasma marginale''
 
*Carrier status in endemic regions with clinical disease occuring in times of stress
 
*High mortality rate in naive adult cattle
 
*Morulae localise inside red blood cells close to the cell membrane
 
*Transmitted via the ''Boophilus'' tick as well as flies and contaminated instruments
 
 
 
*Clinical signs
 
**Inculbation period 2-12 weeks
 
**Anorexia, fever, depression, reduced milk yield, weight loss
 
**Anaemia and icterus
 
**Sudden death from hypoxia can occur
 
 
 
*Diagnosis
 
**Clinical signs and haematology suggestive
 
**Organisms present in erythrocytes of Giemsa-stained blood smears
 
**Immunofluorescence of blood smears, PCR, serology
 
 
 
*Treatment and control
 
**Long-acting oxytetracycline or imidocarb early in the disease
 
**Supportive therapy
 
**Vaccination of animals being introduced into an endemic region
 
 
 
 
 
===Feline infectious anaemia===
 
 
 
*
 

Latest revision as of 20:15, 14 May 2010