Tick transmitted diseases

Question 1

What are 3 mechanisms for a fever and lymph node enlargement?

Answer 1

Infection, Neoplasia, Autoimmune

Question 2

What can cause pale mucous membranes?

Answer 2

Poor perfusion, Anemia

Question 3

What etiologies can result in petechiae?

Answer 3

Thrombocytopenia, Thrombocytopathia, Endothelial dysfunction (vasculitits)

*Coagulopathy more likely to cause large bruises or cavitary bleeding

Question 4

How low does a platelet count need to be before you see petechiae?

Answer 4

<50,000
-varies a bit from case to case, but generally this is the range that you worry about spontaneous bleeding

Question 5

What abnormalities are most likely to be seen on the chemistry of a patient with systemic inflammation?

Answer 5

Hypoalbuminemia and hyperglobulinemia

Question 6

What are the main mechanisms that can result in thrombocytopenia?

Answer 6

Sequestration, Consumption, Decreased production, Destruction (IMTP)
- severe thrombocytopenia more likely to be due to destruction or decreased production

Question 7

What would make you put bone marrow disease higher on your differential list for a patient with thrombocytopenia?

Answer 7

If the other cell lines are also reduced (pancytopenia)

Question 8

What are the main causes of thrombocytopenia due to decreased production (bone marrow disease)?

Answer 8

-infection (ehrlichia canis or histoplasmosis)
-neoplasia (multiple melanoma, lymphoma, leukemia)
-immune mediated (aplastic anemia)
-toxins or drugs (estrogens, chemotherapy drugs, azothiaprine, phenobarbital)

Question 9

What tick borne disease is the most likely to target the bone marrow?

Answer 9

Ehrlichia canis

Question 10

What abnormality can be seen on a blood smear of a patient with ehrlichia canis?

Answer 10

A morulae in the cytoplasm of monocytes
- specific but not very sensitive - cant rule out the disease if you don’t see this
-evaluation of buffy coat smears, lymph node aspirates or splenic aspirates increases sensitivity

Question 11

What is the other name for infection with Ehrlichia canis? What is the tick that transmits this disease?

Answer 11

Also known as canine monocytic ehrlichiosis
-primarily transmitted by the brown dog tick
-found throughout the US but prefers warm climates (southeastern and southwestern states)

Question 12

Describe the 3 potential phases of ehrlichia canis infection

Answer 12

Acute phase (8-20 days after innoculation): patients often will be febrile, lethargic, innapetant, with potential lymphadenopathy and hepatosplenomegaly. There may be peripheral edema present (due to vasculitits), as well as potentially uveitis and retinal disease. Thrombocytopenia/pathia are common findings. More rarely there may be neuro signs (meningeal inflammation and or CNS hemorrhage). May spontaneously recover after 2-4 weeks without vet intervention, or may become subclinical

Subclinical phase: will show up positive on snap test, but will have no appreciated clinical signs

Chronic phase: similar signs to acute phase plus maybe bone marrow hypoplasia (pancytopenia), protein losing nephropathy, polymyositis, marked lymphocytosis (can look like lymphoma or lymphocytic leukemia) and bone marrow plasmacytosis leading to hyperglobulinemia (can look like multiple myeloma)

Question 13

What are the downsides to antibody testing for E canis?

Answer 13

-there is cross reactivity with ehrlichia ewingii and e chaffeensis
-indicates exposure to the organism but not necessarily active infection
-potential for false negative results with acute infections

Question 14

What is the serological gold standard for Ehrlichia testing?

Answer 14

Indirect immunofluorescent antibody test (IFA)
-looks for IgG antibodies
-if acute exposure is suspected, take two consecutive tests 7-14 days apart- 4 fold increase is suggestive of acute and active infection (unlikely to change with chronic infection)
-be aware that IgG antibodies may persist for several months to years after treatment and elimination of E canis

Question 15

Describe the ELISA snap test for diagnosis of E canis

Answer 15

-point of care test that allows for a quick qualitative measurement of IgG antibodies against E canis
-sensitivity is 97% (great), comparable to IFA

Question 16

Describe PCR for diagnosis of E canis

Answer 16

-quantitative real time PCR that is frequently used
-detects E canis DNA as early as 4-10 days post inoculation (likely represents true infection and organism can be detected prior to seroconversion)
-whole blood PCR is more sensitive for acute infections but serology is more sensitive for chronic infections
-antimicrobial treatment at the time of blood collection may lead to false negative results
*take blood sample before starting antibiotics to avoid risk of false negative

Question 17

What are the treatment options for E canis?

Answer 17

-doxycycline, minocycline or chloramphenicol (risk of aplastic anemia) can be used alternatively
-most dogs with severe chronic disease may not respond to treatment or cytopenias may take months to resolve

Question 18

Which dog breed is the most susceptible to E canis?

Answer 18

German shepherds
- also cases are associated with a worse prognosis

Question 19

Describe some features of Ehrlichia chaffeensis

Answer 19

Spread via the Lone Star tick
-often causes no illness but potential signs include fever, lethargy, inappetence, lymphadomegaly, mild thrombocytopenia and monocytosis
-dogs may serve as a reservoir for human infections (humans have more severe infections)

Question 20

What are the different types of polyarthropathies?

Answer 20

Nonerrosive polyarthritis: immune mediated (primary or secondary- due to infection neoplasia or drugs) vs septic

Errosive polyarthritis

Question 21

What rickettsial agent should be suspected if you see morulae in neutrophils on a blood smear?

Answer 21

Anaplasma phagmacytophilium or Ehrlichia ewingii
- both can cause polyarthritis

Question 22

T/F: you always should perform PCR and/or serology to differentiate between anaplasma phagocytophilium and E ewingii

Answer 22

False- don’t necessarily need to as you will treat both infections the same way

Question 23

What is the other name for erlichia ewingii infection? What tick transmits it?

Answer 23

Granulocytic ehrlichiosis
- replicates in neutrophils and delays neutrophil apoptosis
-primarily transmitted by the Lone Star tick (found throughout south-central and southeastern parts of the US)

Question 24

Describe the signs associated with E ewingii

Answer 24

-only causes acute disease
-signs typically develop 3-4 weeks after inoculation
-some dogs may show no clinical signs but can develop fever, lethargy, inappetence, peripheral edema, polyarthritis, neuro signs, thrombocytopenia or proteinuria
-signs are milder than E canis

Question 25

What is the treatment for E ewingii?

Answer 25

-doxycycline (can also try minocycline or chloramphenicol alternatively)
-some dogs may spontaneously clear the infection

Question 26

What is the other name for anaplasma phagocytophilium? What tick transmits it?

Answer 26

Granulocytic anaplasmosis
-cats can be affected as well as dogs
-transmitted by ixodes scapularis (in northeast and upper midwest) and ixodes pacificus (in western US)
-coinfection with borriela burgdorferi is common

Question 27

How do you diagnose Anaplasma phagocytophilium? What is the treatment for this?

Answer 27

Diagnose through observing morulae on granulocytes on peripheral bloodsmear (indistinguishable from E ewingii)
-point of care ELISA, IDA or PCR can be used (be aware of cross reactivity with anaplasma platys which can cause cyclic thrombocytopenia)
-doxycycline can be used for treatment but some dogs and cats may spontaneously clear the infection

Question 28

What tick is responsible for the spread of rickettsia rickettsii aka Rocky Mountain Spotted fever?

Answer 28

Dermacentor andersoni (wood tick) in the west and dermacentor variabilis (American dog tick) in mid west to eastern US

Question 29

What are the clinical features of RMSF?

Answer 29

-replicates in endothelial cells of smaller arteries and venules
-initiates vasculitis –> activation of platelets and coagulation system –> consumption of platelets and coagulation factors
-thrombocytopenia also occurs due to immune mediated platelet destruction
-patients may hemorrhage excessively or experience thrombosis (petechiae is common)
-the skin, brain, heart and kidneys are the most adversely affected
-signs progress rapidly
-incubation period between 2-14 days

Question 30

What are the clinical signs associated with RMSF?

Answer 30

-fever, lethargy, inappetence
-lymphadenomegaly and hepatosplenomegaly
-arthralgia and spinal hyperesthesia
-vomiting and diarrhea
-uveitis
-thrombocytopenia
-cutaneous edema and hyperemia (may progress to derma necrosis)
-neurologic signs (meningitis progressing to encephalomyelitis)
-pneumonitis
-renal failure
-cardiac arrythmias

Question 31

How do you diagnose and treat RMSF?

Answer 31

-cant use snap test
-diagnosis primarily made with serological testing
-PCR can be utilized as well but it is not considered highly sensitive
-early recognition and treatment is key to reduce mortality
-purebred dogs, such as german shepherds are more likely to develop severe disease
-treatment with doxy recommended can use baytril as well (enrofloxacin) or chloramphenicol
-some dogs can clear on their own

Question 32

What tick is responsible for transmission of Hepatozoon Americanum? What disease does it cause?

Answer 32

Spread by ingestion of amblyomma maculatum
- causes American canine hepatozoonosis

Question 33

What are the clinical findings associated with H Americanum infection?

Answer 33

Severe lethargy, inappetence and weight loss
-severe muscle wasting (pronounced along temporal muscles)
-generalized hyperesthesia (especially along paraspinal region)
-stiff gait
-purulent ocular discharge
-potentially fatal
-periosteal bone proliferation occurring along the proximal bones of the limbs

*signs often wax and wane in severity

Question 34

Describe some clinical laboratory findings of infection with H americanum

Answer 34

-elevated leukocyte count
-mild normocytic and normochromic non regenerative anemia
-normal to increased platelet count
-increased ALP activity due to periosteal inflammation
-hypoglycemia due to in vitro metabolism of glucose by WBCs
-hypoalbuminemia (proteinuria, chronic inflammation and/or reduced protein intake)

Question 35

How can you diagnose H americanum?

Answer 35

-blood smear may reveal H americanum gamonts in leukocytes (low sensitivity (buffy coat smear increases sensitivity))
-skeletal muscle biopsy (most reliable way of confirming diagnosis, muscle lesions consist of onion cysts and marked pyogranulomas myositis)
-whole blood PCR- non invasive

Question 36

What is the treatment for H americanum?

Answer 36

TCP combo therapy
- trimethoprim sulfa, clindamycin and pyrimethamine for 2 weeks
-after 2 weeks start decoquinate and continue for 2 years

No treatment is effective at eliminating the tissue stages of H americanum and clinical relapses are common (decoquinate helps prevent relapses)

Question 37

Describe infection with babesia canis

Answer 37

-large piriform shaped protozoa existing singly or paired within erythrocytes
-primarily transmitted by the brown dog tick (rhipicephalus sanguineus)
-greyhounds most affected by this

Question 38

What breed is most affected by babesia gibsoni?

Answer 38

Pit bulls

Question 39

What are the main clinical findings associated with canine babesiosis?

Answer 39

Uncomplicated form: fever, inappetence, lethargy, lymphadenopathy and splenomegaly, thrombocytopenia, hemolytic anemia (extravascular and intravascular)
-can look just like IMHA

Complicated form: similar signs plus acute renal failure, neuro signs, hepatic injury, acute respiratory distress syndrome, pancreatitis, red biliary syndrome (more commonly found with infection in South Africa)

Question 40

What is the best way to diagnose Canine babesiosis?

Answer 40

PCR testing

Question 41

What are the treatments for babesia canis? babesia gibsoni?

Answer 41

Canis: imidocarb dipropionate
Gibsoni: atovaquone, azithromycin