Lecture 28 - Rickettsiales Flashcards
What type of pathogen is Rickettsiales?
Obiligate intracellular parasites
What animals do Rickettsiales prefer?
Vertebrates + Arthropods + pretty much all eukaryotes
What part of the Rickettsiales’ life cycle do ticks blood-feeding arthropod play?
Host
– and –
Vector
What is one of the most important reservoir host for Rickettsiales?
Ticks
What kind of host are humans in the Rickettsiales life cyle?
Accidental
What are the genera of Rickettsiales that we are concerned with?
Rickettsia + Anaplasma + Erlichia
How does rickettsia differ from anaplasma and erlichia?
Erlichia + Anaplasma are both in the family Anaplsmatacaea
What are the structural characteristics of Rickettsiaceae?
Gram- negative
Pleomorphic coccobacilli
How do Rickettsiaceae enter the host cell?
Induces phagocytosis
Escapes phagosome
Grows in cytoplasm and/or nucleus
What cell type does Rickettsiaceae prefer to invade and grow?
Endothelial cells
What happens when Rickettsiaceae takes up residence in the endothelial cells?
Necortizing vasculitis
What are the downstream effects of necrotizing vasculitis?
Increased vascular permeability
– leading to –
Edema + Hemorrhage + Hypovolemia
What are the major clinical problems seen with a Rickettsiaceae infection?
Encephalitis + Nephritis + Myocarditis
What disease does Rickettsia rickettsii cause?
Rocky mountain spotted fever
What ticks commonly carry Rickettsia rickettsii ?
American dog
Brown dog
Rocky mountain wood
What tick is present in AZ that carries Rickettsia rickettsii ?
Brown dog tick
When in the US are the most cases in dogs of RMSF seen?
March to October
How old are most dogs that come down with RMSF?
less than 3 years old
What parts of the US most commonly have RMSF?
South central + Southeastern
What are the mammalian reservoirs for Rickettsia rickettsii ?
Wild rodents + other small mammals
What are the early signs of Rickettsia rickettsii infection in a dog?
Fever + V/D + Achey + Edema + Coughing
What neurological disturbances are seen in dogs with Rickettsia rickettsii ?
Depression + Stupor + Ataxia + Tremors
What occurs in severe cases of Rickettsia rickettsii in dogs?
Acral necrosis
What is the treatment for Rickettsia rickettsii ?
Doxycycline
– or –
Tetracycline
When should treatment for Rickettsia rickettsii be started?
ASAP, do not wait for diagnostics
What are the structural characteristics of Anaplasmataceae?
Gram-negative
Pleomorphic coccobacilli
What types of cells do Anaplasmataceae bacterias tend to infect?
Ones of hematopoietic origin
What is the most common blood cell type that Anaplasmataceae grow in?
Leukocytes
Where do Anaplasmataceae multiply?
Within membrane-boudn structures called morulae
What are the three Anaplasmas that are important to us?
Marginale
Platys
Phagocytophilum
What does A. marginale like to infect?
RBC’s of ruminants
What does A. Platys like to infect?
Platelets of canids
What is unique about A. Platys?
ONLY PATHOGEN TO INFECT PLATELETS
What does A. Phagocytophilus like to infect?
Granulocytes + Monocytes of mammals
What animals can be infected with A. Marginale?
Domestic + Wild ruminants
What disease does A. Marginale cause in cattle?
Bovine anaplasmosis
Where in the US does A. Marginale tend to infect cattle?
Southeast
Midwest
Western mountain region
CA
What is the presentation of A. Marginale in a cow that is
Subclinical infection
What is the presentation of A. Marginale in a cow that is 6m to 3 years old?
Serious illness possible
What is the presentation of A. Marginale in a cow that is > 3 years old?
30 to 50% mortality rate
What are the two vectors most commonly spreading A. Marginale?
Black horse fly (Blood-feeding flies)
– and –
Tick ( Demacentor spp.)
What type of vector is the black horse fly?
Mechanical
What is seen in cattle that survive a A. Marginale infection?
Chronic, lifelong subclinical infections (carrier state)
What is the clinical presentation of A. Marginale in cattle?
Fever + Anemia + Icterus
Pregnant cows can abort
What is another name for A. Marginale infection in cattle?
Yellow bag
– or –
Yellow fever
What can be seen histologically that will hint at a A. Marginale infection?
Inclusion bodies in RBC’s
When is the only time a blood smear is successful at diagnosing a A. Marginale infection?
Early in disease
What is the antibiotic treatment for A. Marginale?
Tetracycline
– or –
Imidocarb