Unit 4 - The Order Rickettsiales Flashcards
What is the morphology of organisms in the order Rickettsiales?
rod shaped, coccoid, and often pleomorphic
Are organisms in the order Rickettsiales gram negative or positive?
gram negative - but stain poorly
What stains help visualize organisms in the order Rickettsiales?
Giemsa, Macchiavello, and Gimenez stains
What type of organisms are Rickettsiales?
obligate intracellular parasites
How do Rickettsiae enter the host cell?
by parasite-induced phagocytosis
How do Rickettsiae escape digestion?
in the phagolysosome by either escaping into the cytoplasm or remaining in the phagocytic vacuole and resisting digestion
How do rickettsiae multiply?
by binary fission
How are rickettsiae released?
by cell lysis or exocytosis
What organisms in the family Rickettsiaceae associated with?
nucleated host cells
What genera are included in the tribe Rickettsieae?
those that are pathogenic primarily for humans
When released from cells, what can the bacteria in the tribe Rickettsieae do?
infect vertebrate hosts when the vectors obtain a blood meal
What are the three distinct biotypes of the genus Rickettsia?
Typhus group (A), Scrub Typhus group (B), and Spotted fever group ©
What are two species belong in the typhus group?
Rickettsia prowazekii and Rickettsia typhi
What does Rickettsia prowazekii the cause of?
epidemic typhus - a louse-borne disease seen in conditions of war, poverty, and famine
How does clinical disease from Rickettsia prowazekii progress?
headache, fever, skin rash, and if untreated death
Is there an animal intermediate host for Rickettsia prowazekii?
no
What does Rickettsia typhi cause?
mouse typhus
How do humans get mouse typhus?
by accidental exposure to the rat flea or louse
What species belongs in the scrub typhus group?
Rickettsia tsutsugamushi
What does Rickettsia tsutsugamushi cause?
srub typhus or chigger-borne typhus
What are the vectors for Rickettsia tsutsugamushi?
mite larvae or chiggers
What species belings in the spotted fever group?
Rickettsia rickettsii
What does Rickettsia rickettsii cause?
Rocky-Mountain spotted fever
What transmits Rickettsia rickettsii?
ticks
What ticks are important vectors for Rickettsia rickettsii?
The Rocky mountain wood tick and the american dog tick
What serves as carriers of infected ticks for dogs and humans?
dogs
What is happens after Rickettsia rickettsii invades the body?
After gaining access to the body through a tick bite, the rickettsiae invade vascular endothelium causing widespread endothelial damage
What results from the endothelial damage that Rickettsia rickettsii does?
occlusion of small vessels, microthrombi, microhemorrhages, vasculitis, and in severe cases necrosis, shock, and death
When do clinical signs from a Rickettsia rickettsii infection typically appear?
2-3 days after a tick bite
What clinical signs are associated with Rickettsia rickettsii infections?
anorexia, fever, vomiting, diarrhea, depression, and petechial hemorrhages on the skin, mucous membranes, and retina
What are the most consistant causes of death associated with Rickettsia rickettsii infection?
cardiovascular, neurologic, and renal complications
What is the most common way to diagnose a Rickettsia rickettsii infection?
indirect FA
What other ways can you test for Rickettsia rickettsii infection?
PCR and immunohistochemical staining (post-mortem)
What treatment can be used for a Rickettsia rickettsii infection?
early treatment with tetracycline
When is transmission from dogs to humans of Rickettsia rickettsii assumed to occur?
when removing ticks from the dog
What genera are of importance in the family Anaplasmataceae?
Ehrlichia, Neorickettsia, and Anaplasma
What do organisms in the genus Ehrlichia infect?
circulating leukocytes but some can infect vascular endothelial cells
What are the vectors for Ehrlichia?
ticks
What does Ehrlichia ruminantium cause?
heartwater disease in ruminants
Where is heartwater disease an economically important disease?
in Africa and the Caribbean
What type of cells does Ehrlichia ruminantium prefer to infect?
vascular endothelial cells
What clinical signs are associated with an Ehrlichia ruminantium infection?
high fever, depression, anorexia, and neurologic signs
What is a common lesion associated with an Ehrlichia ruminantium infection?
hydropericardium
What do Ehrlichia bovis and Ehrlichia ovina cause?
a tick-borne disease that causes a fever of several weeks duration in bovine and ovine in Africa
What does Ehrlichia canis cause?
canine ehrlichiosis
Where is Ehrlichia canis prevalent?
in tropical and subtropical areas
What cells does Ehrlichia canis infect?
only circulating leukocytes
What is the life cycle of Ehrlichia canis?
It enters the leukocyte cytoplasm where it divides inside a membrane-bound vesicle to form a morula. Organisms leave the cell when the cell ruptures or by exocytosis
What is the primary reservoir for Ehrlichia canis?
the brown dog tick
What are the three stages of Ehrlichia canis infection?
acute, subclinical, and chronic
How long does the acute phase of Ehrlichia canis last?
2-4 weeks
What occurs during the acute phase of an Ehrlichia canis infection?
The organism multiplies in mononuclear cells which spread to tissues throughout the body. In these tissues, the mononuclear cells attach to the endothelium and produce a vasculitis or cause an inflammatory response as they migrate into the subendothelial tissue
What is a common finding with the acute phase of Ehrlichia canis infection?
thrombocytopenia and severe vasculitis which may result in disseminated intravascular coagulation and death
How long does the subclinical phase of an Ehrlichia canis infection last?
40-120 days after acute infection
What happens during the subclinical phase of an Ehrlichia canis infection and what does it cause?
Organisms persist and dogs can have thrombocytopenia, leukopenia, and anemia
If the infected dog is immunocompetent, what occurs after the subclinical phase of an Ehrlichia canis infection?
they can eliminate it - it is the last stage
What does the severity of the chronic phase of Ehrlichia canis depend on?
the strain variation, concurrent disease, and age
What breed is especially susceptible to the chronic phase of Ehrlichia canis infection and what do they get?
german shepards - terminal pancytopenia
True or False: Once an animal is infected with Ehrlichia they are immune to it.
False - Only if the animal still harbors the organism it is immune to reinfection, but if the organism is cleared then reinfection can occur
How is Ehrlichia canis infection diagnosed?
indirect fluorescent antibody test
How is Ehrlichia canis infection treated?
with tetracyclines
What does Neorickettsia risticii cause?
Potomac horse fever or equine monocytic ehrlichiosis
What time of year does Potomac horse fever typically present?
in the summer months
What cells does Neorickettsia risticii infect?
macrophages, mast cells, and epithelial cells of the intestinal tract as well as circulating monocytes
True or False: Neorickettsia risticii is the only rickettsial organism that grows in the intestinal epithelium of mammals.
TRUE
What carries Neorickettsia risticii?
a trematode that parasitizes snails, aquatic flies, and bat intestines
How do horses become infected with Neorickettsia risticii?
they eat or drink the fluke itself or the equatic insects, they ingest feces from bats or barn swallows that ate the organism, eat feces from infected horses, or direct transfer of blood
What is the major manifestation of Neorickettsia risticii?
gastrointestinal disease
How does acute onset of Neorickettsia risticii present?
as a sudden onset of depression, anorexia, colitis, laminitis, and fever with diarrhea starting 1-3 days after onset of clinical signs
How does subacute disease of Neorickettsia risticii present?
depression, anorexia, and fever but no diarrhea
How is the mild or inapparent form of Neorickettsia risticii diagnosed?
by seroligic studies
In general how is a Neorickettsia risticii diagnosed?
PCR on feces
How is a Neorickettsia risticii treated?
intravenous fluids and oxytetracycline - but it needs to be diagnosed as soon as possible
Is there an immunization for Neorickettsia risticii?
yes - there is a killed bacterin but due to different serologic variants it does not always confir protection
What does Neorickettsia helminthoeca cause?
salmon poisoning disease
Where is salmon poisoning disease prevalent?
from northwestern California to southwestern Washington
What cells does Neorickettsia helminthoeca typically infect?
cells of the mononuclear phagocytic system
What is the vector of Neorickettsia helminthoeca?
the trematode Nanophyetus salmincola
What hosts are required for complesion of the life-cycle of Nanophyetus salmincola?
snails, fish, and mammals or birds
What is the pathogenesis of Neorickettsia helminthoeca infection?
- Dogs ingest raw fish containing metacercariae 2. The fluke matures and attaches to the intestinal mucosa and somehow injects the rickettsiae 3. The rickettsiae enter the blood and spread throughout the body
What pathological findings are associated with Neorickettsia helminthoeca infection?
changes in the lymphoid tissue with edema, hemorrhage, and necrosis - there may be a meningitis or meningoencephalitis
What clinical signs are associated with Neorickettsia helminthoeca infections?
first sign is sudden fever then anorexia, vomiting, diarrhea, and enlarged lymph nodes
How is Neorickettsia helminthoeca infection diagnosed?
trematode eggs in the feces with fluid aspirated from enlarged lymph nodes to observe intracytoplasmic organism
How is Neorickettsia helminthoeca infection treated?
sulfonamides, penicillin, tetracycline, and chloramphenicol - fluid therapy to control vomitting and diarrhea
What does Neorickettsia elokominica known as?
the Elokomin fluke fever agent
What does Neorickettsia elokominica cause?
a disease similar to salmon poisoning disease but not as severe
Where are organisms in the genus anaplasma found?
within or on erythrocytes or free in the plasma of ruminants
How are organisms in the genus Anaplasma transmitted?
by any route whereby blood is transmitted including by arthropods, needles, surgical instruments etc.
What is the most priminent clinical sign associated with the genus Anaplasma?
anemia
What is the pathogenesis of organisms in the genus Anaplasma forming an inclusion?
the organisms or initial bodies enter erythrocytes by invagination of the cytoplasmic membrane and formation of a vacuole. They multiply by binarry fission and form an inclusion
What is the most pathogenic Anaplasma species to cattle?
Anaplasma marginale
What age of cattle are typically affected by Anaplasma marginale?
young adult and older cattle (mortality increases with age)- cattle less than 6 months of age are relatively resistant
Where is Anaplasma marginale enzootic?
in southern states, lower plain states, and western states
Where are Anaplasma marginale organisms located?
in spherical inclusions near the periphery or margin of the erythrocytes - each inclusion contains one to eight initial bodies
What are the biological vectors of Anaplasma marginale?
with the pacific coast tick and the Rocky Mountain wood tick
How is Anaplasma marginale mechanically transmitted?
by other ticks, horseflies, mosquitos, other biting flies, and contaminated surgical instruments and needles
How does Anaplasma marginale cause regenerative anemia?
infected erythrocytes are removed by the mononuclear-phagocytic system resulting in regenerative anemia
What general clincical signs are associated with Anaplasma marginale?
fever, pallor, depression, anorexia, icterus, dehydration, and tachycardia
What are the four stages of Anaplasma marginale infection?
incubation stage, developmental stage, convalescent stage, and carrier stage
How long is the incubation stage of Anaplasma marginale?
3-8 weeks
What occurs during the developmental stage of Anaplasma marginale?
anemia develeps - the first clinical signs are noticed halfway through this stage: mortality mostly occurs in animals over 2 years of age
What occurs during the convalescent stage of Anaplasma marginale infection?
the reticulocytes return to normal - few weeks to few months
What occurs during the carrier stage of Anaplasma marginale?
the clinically recovered animals remain carriers with nondetectable lowe level parasitemia for life and act as reservoirs
What is conclusive to diagnose Anaplasma marginale?
demonstration of the marginal bodies in erythrocytes - which can only be found in the developmental and convalescent stages
What can be used to diagnose Anaplasma marginale in developmental, convalescent, and carrier stages?
serologic tests - rapid-card agglutination, CF, ELISA, competitive ELISA, and PCR testing
How is Anaplasma marginale treated?
with tetracycline
Is there a vaccine for Anaplasma marginale?
yes there is a killed product but it is considered experimental
What does Anaplasma centrale produce?
centrally-located inclusions in the erythrocyte
Where is Anaplasma centrale found?
in Europe, Africa, and Australia
What animals does Anaplasma ovis cause disease in?
sheep and goats
What does Anaplasma phagocytophilum cause?
human granulocytic ehrlichiosis
Where does disease from Anaplasma phagocytophilum occur?
upper Midwest, East, and Northeast US as well as the West Coast - disease also occurs in northern Europe and parts of Asia and South America
What is Anaplasma phagocytophilum transmitted by?
ixodid ticks
What species does Anaplasma phagocytopilum infect?
dogs, cats, human, horses, ruminants, and many wildlife species
What are considered to be the reservoir hosts for Anaplasma phagocytophilum?
whitetailed deer and several species of rodents
A high seroprevalence in endemeic areas indicates that disease caused by Anaplasma phagocytophilum is often _______ or at least not severe enough to warrant diagnosis.
subclinical
What vague clinical signs are associated with an Anaplasma phagocytophilum infection?
vague signs such as fever, lethargy, anorexia, and general muscle pain
What is clinical disease due to Anaplasma phagocytophilum most often associated with?
the acute, bacteremic phase of infection and can last from one to several days
What is the most frequent clinical sign is observed in dogs infected with Anaplasma phagocytophilum?
acute joint pain and lameness due to polyarthritis
At what age is clinical disease due to Anaplasma phagocytophilum most seen in dogs?
dogs 8 years or older
How is Anaplasma phagocytophilum diagnosed?
demonstration of morulae in WBC, ELISA, IFA, and PCR
How is Anaplasma phagocytophilum treated?
clinical infection can be treated with doxycycline - tick control to prevent infection is warranted
Is Wolbachia gram negative or positive?
negative
What percentage of insects are infected with Wolbachia pipientis?
twenty to seventy-five percent
How is Wolbachia pipientis most commonly transmitted?
from the female through the egg but horizontal transmission and cross-species transmission are also recognized
Wolbachia pipientis is required for fertility and _____ development in nematodes and is always present in _______ ______ in dogs and cats.
larval; Dirofilaria immitis
What is used to kill Wolbachia pipientis in concurrent with heartworm treatment?
doxycycline
What is reproductive infection of Wolbachia pipientis in arthropods characterized by?
the ability of the organism to override chromosomal sexxual determination, induce pathogenesis, selectively kill males, influence sperm competition, and generate cytoplasmic incombatibility
