Tick Transmitted Diseases Flashcards
Severe thrombocytopenia is more likely to be caused by which of the 4 mechanisms? (decreased production, immune-mediated destruction, consumption, or sequestration)
decreased production or immune-mediated destruction
typically, consumption and sequestration cause more mild thrombocytopenias
What are 4 potential mechanisms for developing thrombocytopenia?
- decreased PRODUCTION of platelets
- Immune-mediated DESTRUCTION of platelets
- CONSUMPTION of platelets
- Sequestration of platelets
What are 4 etiologies for pancytopenia caused by bone marrow disease?
- infection (e. canis, histoplasmosis)
- neoplasia (multiple myeloma, lymphoma, leukemia)
- immune-mediated (aplastic anemia)
- toxins or drugs (estrogens, chemo, azathioprine, phenobarb, etc.)
T/F: if morulae are not present within monocytes on your blood smear, this rules out E. canis
false – morula are suggestive of E. canis but an absence of them does not rule out the disease. you must put into context the clinical picture (lethargy, weight loss, hyporexia, fever, anemia, lymphadenomegaly, petechiae, etc.)
The sensitivity of this also decreases with chronic infections.
You could increase the sensitivity by looking at a buffy coat smear, lymph node aspirate, or splenic aspirate.
which tick transmits canine monocytic ehrlichiosis?
brown dog tick (rhipicephalus sanguineus) which is found throughout the entire US
Describe the “acute phase” (8-20d after inoculation) of E. canis infection
fever, lethargy, inappetance
lymphadenomegaly, hepatosplenomegaly, peripheral edema
uveitis, retinal disease
thrombocytopenia and thrombocytopathia
neurological signs
T/F: patients in the acute phase of E. canis infection can spontaneously recover after 2-4 weeks
true – they can either completely eliminate the infection or remain subclinically infected.
if they do not clear the infection on their own and present to you, you can prescribe doxycycline.
What defines the “subclinical phase” of E. canis infection?
you will detect it on a test, but there are no clinical signs present.
Describe the chronic phase of E. canis infection
similar signs to the acute phase +
bone marrow hypoplasia (pancytopenia)
protein losing nephropathy
polymyositis
marked lymphocytosis
bone marrow plasmocytosis –> hyperglobulinemia
Which two clinical features of a chronic E. canis infection may make it look like the patient has cancer?
marked lymphocytosis can be confused for lymphocytic leukemia
bone marrow plasmacytosis –> hyperglobulinemia can lead to monoclonal gammopathy which can be confused for multiple myeloma.
When performing antibody testing, there is cross-reactivity between E. canis and what 2 other organisms?
- E. ewingii
- E. chaffeensis
What is your interpretation of a positive antibody test for E. canis?
indicates exposure to organism but not necessarily an active infection
if you got a negative test result, it can still be false negative if the infection is acute.
Indirect immunofluorescent antibody (IFA) tests are considered the gold standard serological test for E. canis. IgG antibodies are reliable indicators of E. canis exposure. If you suspect your patient has been acutely exposed to E. canis, what should you do in regard to testing?
you should perform TWO consecutive IFA tests (7-14 days apart).
If there is a 4-fold increase in the antibody titers, this is suggestive of acute and active infection.
T/F: IgG antibodies may persist for several months to years after treatment and elimination of E. canis
true
Which of the following statements is FALSE?
A. ELISA (SNAP4dx) tests can assess IgG antibodies against E. canis
B. ELISA (SNAP4dx) tests are quantitative
C. ELISA (SNAP4dx) tests have a 97% sensitivity
D. ELISA (SNAP4dx) tests are considered point of care
B. ELISA (SNAP4dx) tests are quantitative
they are QUALITATIVE – positive or negative.
PCR can detect E. canis as early as _____ post inoculation
4-10 days
T/F: a positive E. canis PCR test indicates true infection
true because PCR test is detect E. canis DNA
Which PCR is more sensitive for acute infections – whole blood or serology?
whole blood.
serology is more sensitive for chronic infections.
What could potentially cause false-negative results of a E. canis PCR test?
antimicrobial treatment at the time of blood collection.
how do you treat E. canis?
doxycycline
(or can also use minocycline or chloramphenicol)
note that dogs with severe chronic disease may not respond to tx or their cytopenias may take months to resolve.
which breed is more susceptible to E. canis infections and has a worse prognosis?
german shepherds
What tick transmits ehrlichia chaffeensis?
Lone Star Tick (amblyomma americanum)
T/F: Ehrlichia chaffeensis and Ehrlichia canis are difficult to distinguish in canine patients because they cross react on ELISA and they cause the same severity of clinical signs.
false – they do cross react, but Ehrlichia chaffeensis rarely causes clinical signs in dogs and if a dog does show clinical signs they are usually much more mild than E. canis.
T/F: dogs may serve as a reservoir for E. chaffeensis infection in humans.
true
When a dog presents with lameness, joint effusion, and pain (polyarthropathy), what are your main differentials?
- non-erosive polyarthritis (immune-mediated polyarthritis that is either infectious, neoplastic, or drug/vaccine induced OR septic arthritis)
- erosive polyarthritis
You look at a blood smear for a dog with polyarthritis and see morula inside of a neutrophil, what two organisms could be the cause?
- Anaplasma phagocytophilium
- Ehrlichia ewingii
they both cause polyarthritis
A. phagocytophilium and E. ewingii both cause polyarthritis and result in morulae within neutrophils. How would you further distinguish the two?
PCR and/or serology (IFA or ELISA)
Which tick transmits E. ewingii and causes granulocytic ehrlichiosis?
Lone Star Tick (amblyomma americanum) which is found in the south-central and south-eastern parts of the US
E. ewingii replicates within the neutrophils and delays neutrophil apoptosis
T/F: E. ewingii only causes acute disease
true – signs will develop 3-4 weeks after inoculation.
Some dogs dont show any clinical signs.
what are possible clinical signs of E. ewingii infection?
fever, lethargy, inappetance
lymphadenomegaly
peripheral edema
polyarthritis*
neurologic signs
thrombocytopenia
proteinuria
what is the treatment for E. ewingii infection?
doxycycline
(or minocycline or chloramphenicol)
although some dogs may spontaneously clear the infection.
T/F: both cats and dogs can be affected Anaplasma phagocytophilium
true this organism causes granulocytic anaplasmosis.
Which tick(s) transmit(s) anaplasma phagocytophilium?
Ixodes scapularis and Ixodex pacificus
T/F: It is common to see animals co-infected with anaplasma phagocytophilium and borrelia burgdoreferi
true – both of these organism are transmitted by Ixodes ticks.
Though majority of dogs infected with A. phagocytophilium do NOT show any clinical signs, what would be some potential clinical signs?
The most common are often non-specific such as fever, lethargy, and inappetance.
Others include: lymphadenomegaly, hepatosplenomegaly, polyarthritis**, thrombocytopenia, and leukopenia.
what is a reliable method to diagnose A. phagocytophilium?
- SNAP4dx Plus (sens 92%, does cross react with A. platys)
- morulae may be observed in granulocytes in blood smear (cannot distinguish from E. ewingii)
what is the treatment for A. phagocytophilium?
doxycycline
some dogs and cats may spontaneously clear the infection
Which tick transmits the organism that causes rocky mountain spotted fever?
bonus: what is the organism
Dermacentor andersoni (wood tick) and Dermacentor variabilis (american dog tick)
transmit Rickettsia rickettsii
What cell type does rickettsiae replicate in and what pathophysiology occurs as a result?
endothelial cells of smaller arteries and venules.
This initiates vasculitis, which activates platelets and the coagulation cascade leading to the consumption of platelets and coagulation factors.
As a result, patients experience thrombocytopenia, hemorrhage, and/or thrombosis
Which areas of the patient are MOST adversely affected by R. rickettsii?
skin
brain
heart
kidneys
What are clinical features of R. rickettsii?
- fever, lethargy, inapp., v/d
- lymphadenomegaly, hepatosplenomegaly
- arthralgia, spinal hyperesthesia*
- uveitis
- thrombocytopenia
- cutaneous edema and hyperemia (can progress to dermal necrosis)
- neuro signs (meningitis)
- pneumonitis
- renal failure
- cardiac arrhythmias
Diagnosis of R. rickettsii is primarily made by what test?
serologic testing (IFA)
PCR is not sensitive enough
T/F: mixed breed dogs are more likely to develop severe disease as a result of R. rickettsii
false – purebred
what is the treatment for R. rickettsii?
doxycycline
chloramphenicol or enro work too.
some dogs may clear the infection on their own, but early recognition and treatment is KEY to reducing mortality.
Which tick transmits hepatozoon americanum and what is unique about transmission?
amblyomma maculatum (gulf coast tick)
the tick must be INGESTED
A dog presents to your clinic with fever, lethargy, anorexia, severe muscle wasting, generalized hyperesthesia, a stiff gait, and some purulent ocular discharge. The owners state that they didnt bring him in sooner because sometimes he just gets better, but then gets worse again. He is not on any flea/tick prevention.
What is your PRESUMPTIVE diagnosis?
H. americanum
A dog presents to your clinic with fever, lethargy, anorexia, severe muscle wasting, generalized hyperesthesia, a stiff gait, and some purulent ocular discharge. The owners state that they didnt bring him in sooner because sometimes he just gets better, but then gets worse again. He is not on any flea/tick prevention.
Your presumptive diagnosis is H. americanum, what would you expect your CBC and Chemistry to report?
CBC: severely elevated leukocytes, normocytic, normochromic non-regenerative anemia
Chem: increased ALP, hypoglycemia (glucose metabolized by WBCs in vitro), hypoalbuminemia
A dog presents to your clinic with fever, lethargy, anorexia, severe muscle wasting, generalized hyperesthesia, a stiff gait, and some purulent ocular discharge. The owners state that they didnt bring him in sooner because sometimes he just gets better, but then gets worse again. He is not on any flea/tick prevention.
Your presumptive diagnosis is H. americanum. Your CBC showed marked elevation of leukocytes, non-regenerative anemia, increased ALP, and hypoglycemia.
You decide to take radiographs of the limbs. What would you expect to see?
periosteal bone proliferation (more frequently occurs at proximal bones of limbs)
(this is why the ALP is elevated)
Looking at a blood smear, you see gamonts in leukocytes. What organism is associated with this finding and is this sensitive?
H. americanum
this has very low sensitivity. you can look at a buffy coat smear to increase sensitivity.
What is the MOST reliable way to confirm a diagnosis of H. americanum?
skeletal muscle biopsy – muscle lesions consist of onion cysts and pyogranulomatous myositis
What is the LEAST invasive way to diagnose H. americanum?
whole blood PCR
What is the treatment for H. americanum?
Combination therapy for 2 weeks:
1. Trimethoprim-sulfonamide
2. clindamycin
3. pyrimethamine
After combination therapy, give Decoquinate (anticoccidial) for 2 years
T/F: TCP combination therapy is effective in clearing H. americanum
false – no treatment eliminates the tissue stages of H. americanum. Clinical relapses are pretty common, but giving decoquinate for 2 years after combo therapy helps to prevent these relapses.
Which tick transmits Babesia canis?
Brown dog tick (rhipicephalus sanguineus)
what cells do Babesia canis invade once an animal is infected?
erythrocytes
on blood smear, they appear as large piriform-shaped protozoa within the red cells
How can you distinguish B. canis and B. gibsoni on blood smear?
B. canis: large, piriform shaped protozoa within the red cells.
B. gibsoni: little ring-like configurations within the red cells.
what are clinical features of UNCOMPLICATED canine babesiosis?
- fever, inappetance, lethargy
- lymphadenomegaly, splenomegaly
- thrombocytopenia*
- hemolytic anemia (extravascular and intravascular)*
what are features of COMPLICATED canine babesiosis?
Similar to uncomplicated PLUS…
- acute renal failure
- neuro signs
- hepatic injury
- acute respiratory distress syndrome
- pancreatitis
- “red biliary” syndrome (congested mucous membranes, hemoglobinemia, hemoglobinuria, elevated hematocrit, intravascular hemolysis, hemoconcentration)
Which species of babesia is more commonly associated with complicated babesiosis?
B. canis rossi (found in south africa)
which dog breed have a high seroprevalence of B. canis vogeli but rarely show clinical signs?
greyhounds
which dog breed has a high prevalence of B. gibsoni but rarely show clinical signs?
american pit bull terriers
T/F: blood smears are insensitive but highly specific for diagnosing canine babesiosis
true
What diagnostic is MOST sensitive for diagnosing canine babesiosis?
PCR
IFA has higher sensitivity for chronic infections but there is cross reactivity for B. gibsoni and B. canis
PCR may be most ideal in diagnosing canine babesiosis because it helps with species differentiation which is important in this disease because treatment differs between the species. How does treatment differ for B. canis versus B. gibsoni?
B. canis: imidocarb diproprionate
B. gibsoni: atovaquone + azithromycin
