178. General characterisation of rickettsiae, heartwater.

Question 1

Diseases caused by bacteria of the ordo Rickettsiales?

Answer 1

Diseases caused by bacteria of the ordo Rickettsiales

Occurrence:

• worldwide,
• some diseases regional,
• warm climate

Aetiology

• Small, coccoid rods
• Staining difficult (Giemsa)
• Propagation
• Cultured only in living cells: embryonated eggs, cell cultures, lab animals
• Some cannot be cultured (replicate only in infected animals)
• Replication in the cytoplasm or on the surface of cells (obligate intracellular)
• Ordo Rickettsiales
• Rickettsiaceae family: Rickettsia genus, Orientia genus (human pathogens)
• Anaplasmataceae family: Anaplasma genus, Ehrlichia genus, Neorickettsia genus
• Epidemiology
• Obligate cell pathogens
• Arthropods for transmission (ticks) – infected vertebrate: focal infection, seasonality
• Narrow host range

Question 2

Diseases caused by the bacteria of the genus Rickettsia Aetiology Epidemiology and pathogenesis?

Answer 2

Diseases caused by the bacteria of the genus Rickettsia

Aetiology:

• Intra cellular,
• cultured in living cells,
• nutrients are taken from the host cell,
• low resistance

Epidemiology

• Mainly tick vectors - Infection at blood sucking (faeces of the ticks)
• Seasonality
• Mainly humans have clinical signs

Pathogenesis

• Infection (blood sucking) → Septicaemia
• → Damage of the endothelial cells
• (vasculitis, perivasculitis, haemorrhages)

Question 3

Diagnosis treatment and prevention of Rickettsiae?

Answer 3

Diagnosis

• Epidemiology – clinical signs – pathology
• Detection of the agent: PCR, immunohistochemistry; culture of the agent (not possible)
• Detection of antibodies: CFT, IF immunoblot, ELISA, paired samples

Treatment, prevention

• Tetracyclines, doxycycline
• Repellents
• Human: inactivated & live vaccines (limited effect) – variable efficacy

Question 4

Diseases caused by Ehrlichia (Gram -ve)

Answer 4

Diseases caused by Ehrlichia (Gr -ve)

• No cell wall, no LPS
• Only intra cellular replication: endothelial, lymphoid, haemopoietic cells
• Immunosuppression
• Damage of BVs: haemorrhages, oedema

Question 5

E. ruminantium Heartwater occurence aetiology epidmeliogy

Answer 5

E. ruminantium: heartwater

Occurrence:

• Sub-Saharan Africa (in E. Africa the animal density is high), Caribbean

Aetiology:

• Ehrlichia ruminantium (Cowdria ruminantium)

Epidemiology

• Focal infection
• Ticks (Amblyomma: true vector),
• No transmission between animals
• Wild living animals can maintain (wildbeast)
• Clinical signs in small ruminants and cattle

Question 6

Pathogenesis and clinical signs of heartwater?

Answer 6

Pathogenesis

• Infection (tick bite) → regional lymph nodes → septicaemia
• Primary targets: Lymphoid tissue, endothelial cells
• Damage of endothelial cells: permeability increased, oedema, collapse of circulation (b/c so much
• fluid leaves the circulation)

Clinical signs:

• Differences btwn local breeds (less severe) & imported breeds (severe)
• Acute: fever, anorexia, depression; convulsions; nervous signs
• (hyperaesthesia, teeth grinding, spasms, opisthotonus)

Question 7

Pathology, diagnosis treatment and prevention of heartwater?

Answer 7

Pathology:

• oedema (hydrothorax, hydropericardium, oedema in lungs and brain, SC), haemorrhages,
• enlarged parenchymal organs (spleen, liver)

Diagnosis

• Epidemiology – clinical signs – PM lesions
• Detection of the agent: smear (Giemsa), IF, PCR; Isolation: endothelial cell culture
• Detection of antibodies: iIF, ELISA, immunoblo

Treatment: tetracycline, (rifampicin, fluoroquinolones)

Prevention

• Control of tick infestation
• Get over the infection (infection + antibiotics)
• Blood from infected animals artificially introduced to other animals, treat with ABs, then the
• immune system responds to the infection → immune
• Vaccines under development (attenuated) – not on the market