Rickettsiales

Question 1

Ehrlichia characteristics and important species

Answer 1

• Ehrlichia canis
• obligate intracellular in monocytes and lymphocytes (monocytic)
• transmitted by brown dog tick
• scarce in peripheral blood
• coyote, fox, feral dog reservoirs

Question 2

What are the 3 Rickettsial organisms?

Answer 2

• Anaplasma
• Ehrlichia
• Neorickettsia
• all blood cell pathogens
• ticks are most important vector

Question 3

Anaplasma marginale characteristics

Answer 3

• obligate intracellular bacteria (seen on margin of RBC’s)
• form membrane-bound inclusion bodies (bags of baby bacteria)
• cycle back and forth between vegetative and infective form

Question 4

Anaplasma marginale disease patterns

Answer 4

adult cows show anemia and other secondary signs (fever, weight loss, etc.)

Question 5

Anaplasma phagocytophilum characteristics

Answer 5

• obligate intracellular bacteria (seen on neutrophils)
• broad host range (zoonotic)
• seen where deer and ticks are prevalent

Question 6

Anaplasma phagocytophilum disease patterns

Answer 6

• can be chronic disease (signs 14 days after exposure)
• flu-like presentation in large animals (fever, coughing, increased respiration)
• vague signs of illness in dogs, lyme-like lameness
• seldom fatal

Question 7

Anaplasma treatment

Answer 7

• -A. marginale*: antibiotics allow time to survive acute infection (long acting oxytetracycline)
• A. phagocytophilum: short acting oxytetracyclines (large animals), doxycycline (dogs)

Question 8

What is the only intracellular organism known to infect platelets/thrombocytes?

Answer 8

A. platys

Question 9

Ehrlichia canis disease patterns

Answer 9

• acute: thrombocytopenia, non-regenerative anemia (mild non-specific signs)
• subacute: thrombocytopenia (few clinical signs)
• chronic: reappearance of signs

Question 10

Ehrlichia canis treatment

Answer 10

• diagnose with clinical signs/lab finidings, serology, PCR
• doxycycline, excellent prognosis controversial if infection can be completely cleared

Question 11

What is the species of Ehrlicia that is granulocytic?

Answer 11

E. ewingii (also causes thrombocytopenia)

Question 12

Neorickettsia characteristics and important species

Answer 12

• -N. risticii*
• common in horses
• infectious, but not contagious
• invertebrate (snail) intermediate host
• needs aquatic environment to become infectious

Question 13

Neorickettsia risticii disease patterns

Answer 13

• anorexia, fever, diarrhea, colic
• “Potomac horse fever”
• EME (equine monocytic ehrliciosis)

Question 14

N. ritsticii treament

Answer 14

• diagnosis with PCR
• treat with IV oxytetracycline
• supportive therapy