28 – Rickettsiales Flashcards
Microbiological characteristics
- Obligate intracellular parasites
- ROD shaped
- Rickettsiacea family: Gram-negative
- Anaplasmataceae family; lack cell wall components of other Gram negatives
- Biocontainment levels depends
- Not possible to culture using ‘standard’ lab methods
Natural host or habitat
- Arthropod associated
- Replication of organism inside the TICK
- Sylvatic cycle: back and forth from vector and reservoir
- Tick to tick transmission
o Transstadial
o Verticel
o Horizontal - *ticks tend to be colonized with one species of Rickettsia
Virulence factors
- Not well described
- *more helpful to think about tissue tropisms
o Rickettsia: vascular endothelium
o Anaplasma: erythrocytes, platelets, leukocytes
o Ehrlichia: leukocytes
o Neorickettsia: leukocytes
What is the Rickettsia rickettsii the agent of?
- Rocky Mountain Spotted Fever
o First described in 1890s: ‘trail fever’
o *affects dogs and people
o IDed all over N. and S. America
o Increasing incidence since 1970s
What are the clinical signs of Rocky Mountain Spotted Fever in dogs?
- *fever
- Edema of extremities
- May develop petechial or ecchymotic haemorrhages (spots)
- Joint pain and swellings
- Myalgia
- Neurological signs
- can get necrosis associated with vasculitis
What is the seasonality of Rocky Mountain Spotted Fever?
- March to October
o Maybe different in SK, due to winter
What is the vector of Rocky Mountain Spotted Fever?
- Hard (Ixodidae) ticks
What is are the possible vectors of Rocky Mountain Spotted Fever in western Canada?
- D. andersoni: SK and AB
- D. variabilis: SK, MB, western ON
- *SK is a sympatric zone
What is the clinical significance of Rocky Mountain Spotted Fever in people?
- *RASH
- Fever, headache, nausea, vomiting, injected conjunctiva
- Long term consequences: vascular inflammation and thrombosis
o Hemorrhage or thrombosis of organs or brain - *not a reportable disease in Canada
o In US, it is increasingly common in people (incidence is up, but case fatality rate is DECREASED!)
o *me
Why decrease in Rocky Mountain Spotted Fever case fatality rate?
- Tetracyclines was invented in 1948
- *doxycycline in Rocky Mountain Spotted Fever
o NO tooth staining
What is Rickettsia prowezakii the agent of?
- Epidemic typhus
What is the clinical disease of epidemic typhus from Rickettsia prowezakii?
- Flu like symptoms
- Rash, neurological signs (headache to coma)
- Untreated takes 2-3 months to recover fully
- Mortality rate varies: up to 40%
What is epidemic typhus spread by?
- Pediculus humanus corporis=human body louse
- *human is reservoir
o Infected lice die within weeks - Associated with flying squirrels in southern USA
When does Epidemic typhus usually occur?
- Miserable conditions
o Filthy and HIGH density - Historical outbreaks: WW1 (Anne Frank)
Where does Bovine Anaplasmosis occur from Anaplasma marginale?
- Between 30 degree S and 40 degree N
o Not in SK
Bovine Anaplasmosis (Anaplasma marginale) in different aged animals
- Young animals (less than a year: subclinical
- *disease is more severe the older the animal is
o More than 2 years old=severe disease
What is seen in severely affected animals with Bovine Anaplasmosis (Anaplasma marginale)?
- Icterus, anemia (extravascular hemolysis)
- Fever
- Decreased milk production
- *can be RAPIDLY FATAL
- Bos indicus cattle may be more resistant?
How do you treat Bovine Anaplasmosis (Anaplasma marginale)?
- Tetracyclines!
- Supportive therapy may be necessary
Vaccination for Bovine Anaplasmosis (Anaplasma marginale) is possible
- Exact strategy depends on where you are
- Some regions: Anaplasma centrale
- *killed A. marginale vaccine in some to protect against severe disease
What does Anaplasma phagocytophilum cause in dogs?
- Canine granulocytotropic anaplasmosis
- *also reported in cats, small mammals, horses, mountain lions and coytoes
What is the vector for Anaplasma phagocytophilum in dogs?
- Ixodes ticks
o Minor distribution of Lyme disease
What are the clinical signs of Anaplasma phagocytophilum in dogs?
- Non-specific
- Pyrexia, lethargy, depression, anorexia
- Reluctance to move, soreness or weakness
- Joint pain
How do you treat Anaplasma phagocytophilum in dogs?
- Doxycycline
How do you control/prevent Anaplasma phagocytophilum in dogs?
- Avoiding exposure to ticks
- Acaricides
- NO vaccination available
Ehrlichia canis is a multi-systemic disease
- Depression, lethargy
- Bleeding and petechiation possible
- Lymphadenopathy and splenomegaly in 20-25% of affected dogs
- Ocular signs: change in eye colour, blindness
- Neurological signs
- Polyarthritis: lameness
What can Ehrlichia canis cause in dogs?
- Canine monocytotrophic ehrlichiosis
o gained attention during Vietnam war: American’s used German shepherds=increased susceptibility to infectious diseases
What is the vector of Ehrlichia canis?
- Dermacentor variabilis
- Rhipicephalus sanguineous
What is the treatment for Ehrlichia canis?
- Doxycycline
- Chloramphenicol
What does Neorickettsia helminthoeca cause in dogs?
- Salmon poisoning
- Highly fatal disease of dogs in California to BC
What are the clinical signs of Salmon poisoning (Neorickettsia helminthoeca) in dogs?
- Sudden terrible illness 5-7 days after eating parasitized fish
- Gradually become hypothermic 4-8 days after signs begin
- Marked anorexia and wasting
- Develop diarrhea and vomiting 14 days after signs begin
o Hematochezia may occur before death
What is the life cycle of Nanophyteus salmincola (flukes) in dogs?
- Adult flukes in dog intestine
- Eggs in feces
- Cercaria infect fish
- Metacercaria in fish muscle
- *as fluke matures it inoculates dog with Neorickettsia helminthoeca
How do you treat Salmon poisoning (Neorickettsia helminthoeca) in dogs?
- Tetracyclines
- Praziquantal: anti-trematode therapy
- Supportive therapy
o Fluids
o Anti-emetics
How do you prevent Salmon poisoning (Neorickettsia helminthoeca) in dogs?
- Vaccines NOT effective
- Prevent exposure=IMPORTANT
o Organism survives in rotting fish carcases for months
What are the clinical signs of Potomac Horse Fever (Neorickettsia risticii)?
- Mild colic
- Fever
- Diarrhea: watery
- Abortion in pregnant mares
- *case fatality is 5-30%
What is the epidemiology of Potomac Horse Fever (Neorickettsia risticii)?
- Thought to involve a yet to be IDed trematode
o Infection believed to occur following ingestion of insects infected with trematode metacercaria
o Has been ISOLATED from freshwater snails
What is the treatment for Potomac Horse Fever (Neorickettsia risticii)?
- OXYTETRACYCLINE
- Supportive care
o NSAIDs?
o Fluid therapy
How do you control Potomac Horse Fever (Neorickettsia risticii)?
- Inactivated vaccines are available
o Shown to be marginally protective in field trials - Heterogeneity in N. risticii strains may complicate vaccination
Sample collection and handling
- Blood
- Blood smears
- Acute and convalescent serum
- Feces
- Biopsies of lesions (R. rickettsii)
- *unless sending to specialized lab, culture is not a concern
- *freezing samples for preservation is OK
How can you Lab ID R. rickettsii?
- Serology
- Direct immunofluorescence
- PCR
How does serology work for Lab ID of R. rickettsii?
- Acute and convalescent serum
o Want to see a 4x increase in Ab titre=indicates response
o Send at same time! (freeze)
o Cross reactivity Ab among spotted-fever group
o Takes time
Lab ID for Anaplasma spp.
- ID of circulating morulae in blood
- PCR on blood
Lab ID for Neorickettsia helminthoeca
- Fecal flotation: N. salmincola eggs in feces
- Seroconversion: acute vs. convalescent
Lab ID for Neorickettsia risticii
- Seroconversion: acute vs. convalescent
- PCR on feces or blood
Ehrlichia spp.
- ID of morulae on smears of buffy coat
- PCR on blood
Zoonotic/interspecies transmission
- Many Ricetsiales have BROAD host range
o Particularly Rocky Mountain Spotted Fever - *Transmission to people via vectors AND contract with infectious material in hemolymph
- Do NOT squish, burn, scratch or rip off ticks
- Avoid exposure to hemolymph
- Wear gloves
- Fine forceps
- Disinfect wound
Client communication with zoonotic/interspecies transmission
- If concerned, GO to physician
- Don’t panic!
o Sick dog does NOT equal sick owner
o Prophylactic treatment not recommended
o *if signs=seek treatment immediately (Fever, severe headache, rash, nausea)
R. akaria: Rickettisalpox (zoonotic/interspecies transmission)
- House mouse reservoir
- Zoonotic via mites
- Urban areas
R. felis: cat flea typhus (zoonotic/interspecies transmission)
- Opossums IDed as one reservoir
- Worldwide distribution
- Zoonotic via cat flea
- Pathogenicity in cats unclear
Is a potential biological weapon due to
- Non-specific initial presentations
- High morbidity and mortality rate
- Ability to aerosolize
- Requires specialized lab to diagnose
- NOT notifiable disease in Canada
- Ex. R. prowazekii was weaponized by US, Japan and Soviet Union
Treatment options
- Not possible to do susceptibility testing on Rickettsiales
- *usually tetracyclines
- People: macrolides, penicillins and aminoglycosides NOT effective
- *intracellular pathogens
o Drugs don’t readily cross cell membranes
