Rickettsiae

Question 1

General characteristics

Answer 1

• cytoplasmic membrane extremely permeable
• obligate intracellular parasites
• cannot live in artificial nutrient environments!! –> is grown in tissue, or chicken embryos
• reside in cytoplasm

Question 2

Transmission

Answer 2

Numerous types of arthropod

- chigger, ticks, fleas, lice

Question 3

Rickettsiae is responsible for

Answer 3

• Rocky Mountain Spotted Fever
• Ehrlichiosis
• Murine Typhus
• Salmon Poisoning Disease
• Elokomin Fluke Fever

Question 4

Rocky Mountain Spotted Fever

Answer 4

In dogs and people, caused by R. rickettsii

• dogs are sentinels of risk for infection in people due to higher rates of tick exposure
• transmitted thru bites of infected ticks

Question 5

What are the 2 primary vectors for RMSF?

Answer 5

American dog tick, Rocky Mountain wood tick

Question 6

Pathogen is acquired by _____ and _____ stages of ticks

Answer 6

Larval; nymph

- feeding on infected vertebrate hosts is passed from female ticks to progeny thru transovarial transmission

Question 7

R. rickettsii induce internalization into _______

Answer 7

Host endothelial cells via receptor mediated invasion
- cytosol of host endothelial cell contains nutrients, adenosine triphosphate, amino acids, nucleotides which are used by bacteria for growth

Question 8

Death occurs from

Answer 8

Damage of endothelial cells, leakage of plasma, decrease in blood volume = shock

Question 9

R. rickettsii is rarely diagnosed in ______

Answer 9

Cats

Question 10

Early signs in the dog

Answer 10

Fever (5 days post tick bite), lymphadenopathy, polyarthritis

• petechial hemorrhages of conjunctiva and oral mucosa
• thrombocytopenia is common with leukopenia in early stages
• vascular endothelial damage

Question 11

What is a consistent finding in the canine form?

Answer 11

Thrombocyopenia

Question 12

Treatment

Answer 12

Antibiotic treatment administered based on clinical suspicion without waiting for results of serologic tests
- doxycycline is drug of choice, regardless of age

Question 13

Salmon poisoning disease

Answer 13

Neorickettsia helminthoeca

• acute, infectious disease of canids
• signs appear suddenly, 5-7 days after eating infected fish –> culminate in death in up to 90% of untreated animals

Question 14

SPD clinical signs

Answer 14

Vomiting, diarrhea develop by day 5-7

- contains blood, may be severe

Question 15

Canine ehrlichiosis

Answer 15

Ehrlichia canis

- monocytic form of illness

Question 16

E. chaffeensis

Answer 16

Monocytic form, primary species causing human ehrlichiosis infection in the USA

Question 17

Monocytic ehrichiosis

Answer 17

Tick must feed for 48 hours before transmission occurs

- important virulence factor!

Question 18

Ehrlichia ewingii

Answer 18

Infects granulocytes of deer and dogs

Question 19

Anaplasma phagocytophilum

Answer 19

Anaplasmosis

- pathogen found predominantly in granulocytes

Question 20

A platys

Answer 20

Infects platelets

- cause of infectious cyclic thrombocytopenia of dogs

Question 21

E. canis is transmitted by the ________

Answer 21

Brown dog tick

Question 22

E. canis

Answer 22

Causes the most potentially severe clinical signs

- acute: reticuloendothelial hyperplasia, fever, lymphadenopathy, splenomegaly, thrombocytopenia, CNS signs

Question 23

What is a common finding in canine granulocytic ehrlichiosis?

Answer 23

Polyarthritis

Question 24

What is an important screening test?

Answer 24

Platelet count due to thrombocytopenia

Question 25

Drug of choice for Ehrlichia and Anaplasma

Answer 25

Doxycycline

Question 26

Heartwater or Cowdriosis

Answer 26

Affects cattle, sheep, goats, and antelope

• found in sub-Saharan Africa and Caribbean
• caused by E. ruminantium

Question 27

Clinical signs of Heartwater

Answer 27

Fever, nervous signs, hydropericardium, hydrothroax, ascites, edema of the lungs, high mortality
- seen within 14-28 days after an infected tick feeding

Question 28

Reason for concern of heartwater disease

Answer 28

Bont ticks have been identified in the US (Fl on imported tortoises)
- death rate reduced by early treatment with tetracyclines