Rickettsiales

Question 1

Characteristics of Rickettsiales

Answer 1

Obligate intracellular or epicellular organisms
Gram-negative bacteria
LPS has weak endotoxin activity
Do not stain well in the Gram reaction
Intracellular parasitism
Depend on host cell for the synthesis of macro-molecules
Synthesize own ATP or utilize cellular ATP
Long generation time: 9-12 hour

Question 2

Rickettsiaceae Reservoirs

Answer 2

Rodents; arthropod vectors

Question 3

Risckettsiaceae Pathogenesis

Answer 3

Invasion of host cells
Receptor-mediated endocytosis
Release from phagosome; mediated by phospholipase
Release from cell
Cell lysis or through cytoplasmic projections

Question 4

Riskettsiaceae Replication in Endothelium

Answer 4

Vasculitis

Question 5

Labortatory Diagnosis of Riskettsiaceae

Answer 5

Direct examination
Giemsa stain; Macchiavello stain; Gimenez stain; fluorescent antibody technique
Isolation
Tissue culture
Embryonated eggs [yolk sac route]
Nucleic acid tests
Serology—detection of serum antibodies
ELISA or IFA

Question 6

Rickettsia rickettssii

Answer 6

Rocky Mountain spotted fever [Tick fever]
Humans and dogs
Reservoir
Rodents and other wild mammals
Vectors
Eastern USA—Dermacentor variabilis [dog tick]
Western USA—Dermacentor andersoni [wood tick]

Question 7

Rocky Mountain Spotted Fever

Pathogenesis

Answer 7

Bacteremia

Multiplication in vascular endothelium

Question 8

Rocky Mountain Spotted Fever

Clinical Findings

Answer 8

Fever, dyspnea, abdominal pain, vomiting, diar-rhea, etc
Conjunctivitis, polyarthritis, lymphadenopathy, edema, DIC, hemorrhages, etc
Bleeding that occurs suddenly, most often from the nose, or in the stools etc
Discolored spots along the skin, often bruised or purplish in color

Question 9

Rocky Mountain Spotted Fever

Diagnosis

Answer 9

Clinical signs
Presence of ticks
Gross and clinical pathology
Rise in antibody titer

Question 10

Rocky Mountain Spotted Fever Treatment

Answer 10

Tetracyclines

Question 11

Ehrlichiaceae

Answer 11

Infection of leukocytes
Monocytes, macrophages, and granulocytes
Infection of erythrocytes
Replication in phagocytic vacuoles
Inhibition of phagosome-lysosome fusion
Binary fission and formation of microcolonies called morula[e]
Lysis of host cells and release of organisms

Question 12

Canine Monocytic Ehlichiosis

Pathogenesis

Answer 12

Replication in macrophages
Bacteremia
Further replication in endothelial cells of multiple organs
Thrombocytopenia—bleeding tendencies

Question 13

Genus Ehrlichia

Answer 13

Organisms infect granulocytes, monocytes, macrophages, and platelets
Hosts
Humans
Dogs
Horses
Ruminants

Question 14

Ehrlichia canis

Answer 14

Canine monocytic ehrlichiosis [Tropical canine pancytopenia]

Question 15

Canine monocytic ehrlichiosis [Tropical canine pancytopenia]

Answer 15

Transmission
Brown dog tick, Rhipicephalus sanguineus
Transstadial transmission
Iatrogenic transmission via blood transfusion

Question 16

Canine Monocytic Ehrlichiosis

Pathogenesis

Answer 16

Replication in macrophages
Bacteremia
Further replication in endothelial cells of multiple organs
Thrombocytopenia—bleeding tendencies

Question 17

Canine Monocytic Ehrlichiosis

Clinical Findings

Answer 17

Acute
Fever, weight loss, dyspnea, lymphadenopathy, oculo-nasal discharge, etc
Severe thrombocytopenia, leukopenia, anemia
Subacute—organisms may be carried in the spleen for years [antigenic variation]
Chronic
Pancytopenia—2o infections; sudden uncontrollable bleed-ing
CNS signs—hysteria, ataxia convulsion, paraparesis

Question 18

Ehrlichia ruminantium

Answer 18

Causes Heartwater [cowdriosis

Question 19

Heartwater [cowdriosis of Ruminants]

Answer 19

Amblyomma variegatum [tropical bont tick]
Amblyomma habraeum
Trans-stadial transmission
Cattle egrets—possible inter-island spread of infected vectors

Question 20

Heartwater (Cowdriosis) Pathogenesis

Answer 20

Replication in regional lymph nodes
Bacteremia
Replication in vascular endothelium
Vascular permeability, edema, hemorrhage, etc

Question 21

Heartwater (Cowdriosis)

Clinical Findings

Answer 21

Peracute: High fever, convulsions, etc, and death
Acute: Fever, dysentery, convulsions, and death
Subacute: Transient illness

Question 22

Heartwater (Cowdriosis)

Pathology

Answer 22

Ascites, hydropericardium, hydrothorax, pulmo-nary edema, hemorrhages, etc

Question 23

Heartwater (Cowdriosis)

Diagnosis

Answer 23

Giemsa-stained smears

PCR—detects E. ruminantium DNA in tissues

Question 24

Heartwater (Cowdriosis)

Treatment

Answer 24

Tetracyclines