Rickettsia

The supervisors:Mr. Abed Elkader Elottol

Collected by:Ahmad al-Aswad

Content

Name of the pathogen DiscoveryGeneral characteristics ClassificationVirulence factors PathogenicityDiseases transmission routesCultural characters Weil-Felix test Sample collection Identification

world distribution Treatment Vaccine References

Name of the pathogen

the order Rickettsiales consists of three families:

1.Rickettsiaceae (genera Rickettsia, Coxiella, Rochalima,and Orientia)

2.Ehrlichiaceae (Ehrlichia, Anaplasma, Neorickettsia)

3.Bartonellaceae (genera Bartonella, Haemobartonella, Eperythrozoon, and Grahamella).

Discovery

Discovered form of tick-borne typhus first described in the Rocky Mountain section of the United States, caused by a specific microorganism (Rickettsia rickettsii). Discovery of the microbe of Rocky Mountain spotted fever in 1906 by Howard Taylor Ricketts led to the understanding of other rickettsial diseases.

General characteristics

• Highly pleomorphic bacreria that can present as cocci (0.1 μm in diameter), rods (1–4 μm long) or thread-like (10 μm long).

• Rickettsiaceae are Gram-negative, obligate intracellular bacteria (except Rochlimaea) that infect mammals and arthropods.

• Gram stain poorly, but appear to be G-• Stain readily with Giemsa .• Traditional biochemical tests are useless

because it can’t cultivated in ordinary medias.

Classification

• Usually rickettsia classified by the disease it cause to two groups :

1.Spott fever group (SFG)

Rickettsia prowazekiiRickettsia prowazekii , , R. mooseri R. mooseri , , R. felis R. felis

2.typhus group (TG)

R. rickettsiiR. rickettsii , , R. conorii R. conorii , , R. sibirica R. sibirica , , R. japonica R. japonica , , R. australis R. australis , R. akari, R. akari

RickettsiaRickettsia species species Disease Disease

Natural cycle Natural cycle

Geographic Geographic distribution distribution

Vectors Vectors Hosts Hosts

Typhus group: Typhus group:

Rickettsia Rickettsia prowazekiiprowazekii

Epidemic typhus Epidemic typhus HumaHuman body n body licelice

Humans Humans Worldwide Worldwide

Recrudescent Recrudescent typhus typhus

None None Humans Humans Worldwide Worldwide

R. mooseriR. mooseri Murine typhus Murine typhus Fleas Fleas Rodents Rodents Worldwide Worldwide

(Endemic typhus)(Endemic typhus) Fleas Fleas Opossums Opossums USA USA

R. felis R. felis Murine typhus Murine typhus like like

Fleas Fleas Opossums Opossums USA USA

Spotted Fever group: Spotted Fever group:

R. R. rickettsiirickettsii

Rocky Mountain Rocky Mountain spotted fever spotted fever

Ticks Ticks Small Small mammals, mammals, dogs, rabbits, dogs, rabbits, birdsbirds

North & North & South South America America

R. conoriiR. conorii Boutonneuse Boutonneuse fever fever

Ticks Ticks Rodents, dogs Rodents, dogs Africa, Africa, Southern Southern Europe, Europe, India India

R. sibiricaR. sibirica North Asia tick North Asia tick typhustyphus

Ticks Ticks Rodents Rodents Eurasia, Asia Eurasia, Asia

R. R. japonicajaponica

Japanese spotted  Japanese spotted  fever fever

TicksTicks Rodents, dogs Rodents, dogs JapanJapan

R. R. australis australis

Queensland tick Queensland tick typhus typhus

Ticks Ticks Rodents Rodents Australia Australia

R. akariR. akari Rickettsialpox Rickettsialpox Mites Mites House mice, House mice, rats rats

Worldwide Worldwide

Virulence factors

1. Group specific soluble antigens  compose from lipopolysaccharide and

consider from the major cell wall component, used in vaccine production. 

2. Species specific antigen  Used to differentiate between rickettsia

species, heat labile antigen.  

3. Alkali stable polysaccharide antigen Found in many rickettsiae and is shared

by certain strains of Proteus vulgaris. 

4. Endotoxin and the production of immune complexes and hypersensitivity reactions.

5. The enzyme phospholipase A may help penetration.

6. Induced phagocytosis and recruitment of actin for intracellular spread.

7. R. Canadensis haemolyses red blood cells, is susceptible to erythromycin.

Pathogenicity

On entry to human body

Organism multiplies locally & enters the blood stream

Invades the vascular endothelial cells.

Leading to proliferation of cells, and perivascular infiltration

Resulting in thrombosis of vessels

Rupture and necrosis

Diseases and transmission routes

• Typhus fever Group:1. Epidemic typhus

(Classical typhus)

R.prowazekii.

2. Recrudescent infection (Brill–Zinsser).

R.prowazekii

3. Endemic typhus (murine typhus)

R. mooseri (R.typhi).

• Spotted fever group: 1. Rocky mountain

spotted fever (RMSF) R. rickettsii.

2. Other tick borne diseases

R. siberica, R. conori, R. australis .

3. Rickettsial pox R. akari .

•Causative organism: R.prowazekii .Vector: Pediculus humanus corporis (human body louse).Transmission: Autoinoculation by the person while scratching the bite of infected body louse –produce abrasion- which is portal of entry for the organisms.Incubation Period: 6-15 days.It is associated with wars & poverty.It is found in Africa & South America but not in United States.Symptoms: Chills, fever, headache, pain, stupor and delerium. Signs of severe meningoencephalitis, begin with rash. If untreated - death occurs due to peripheral vascular collapse or due to bacterial pneumonia.R. prowazekii is the agent of epidemic typhus. During World War I, approximately 3 million deaths resulted from infection by this bacterium. In World War II, the numbers were similar. This agent is carried by the human louse; therefore, disease is a consequence of overcrowding and poor hygiene.

Epidemic typhus

Rocky mountain spotted fever (RMSF)

• Causative organism: R. rickettsii .• Vectors: Dermacentor variabilis (dog tick).• Reservoirs: Dogs & rodents .• Transmission: is via tick bite .• The organism is passed by the transovarian route from tick to tick.• Humans are accidental hosts.• Incubation Period: 3-14 days.• Mainly seen in children during spring & early summer – ticks are

active.• Symptoms: Sudden onset of fever, severe headache, mayalgia. In 2-6 days, a typical rash is seen. It begins with macules and

progress to petechiae. The rash appears on the hand and feet & spreads inwards to the

trunk. It can be fatal if untreated

Cultural characters

• Do not grow on cell-free media.• They can be cultivated in the yolk sacs

of embryonated eggs.• Can be cultivated on cell cultures –HeLa,

HEp2, Detroit 6 etc.• Laboratory animal like mice is used for

primary isolation .• The following nutrients are added to cell

media : serine , glycine , Other nonessential amino acids, additional glucose, and potential products.

Weil-Felix test

• Weil-Felix test is based on cross reaction of the rickettsial antigen with the O antigen polysaccharide found in Proteus vulgaris OX-19, OX-2 and OX-K.

• The test measures the antiricketssial Ab in patient’s serum.

Sample collection

• Coetaneous lesions are the symptoms which is in common between all rickettsial diseases, so, sample obtain mainly from skin lesions.

Identification

• If you do a skin biopsy, you can make a diagnosis in a day or so. Some people don’t bother to do a biopsy. Although the biopsy is 100% specific, it sometimes gives dangerous false negative reports.

• Later, you can confirm your diagnosis by doing tests for antibodies, or serology.

• The old tests, the Weil-Felix tests, are now archaic.

• Laboratories now have immunofluorescent antibody (IFA), or ELIZA assays.

• The problem is that you have to wait a couple weeks before you can expect the antibodies to develop and draw the blood for the convaslescent titers.

world distribution

R. rickettsii

R. africae

R. conorii

R. conorii

R. slovaca

R. conorii Astrakhan

R. conorii Israël

R. australis

R. honeiR. honei

Indian tick typhus Rickettsia

R. japonica

R. mongolotimonae

R. helvetica

R. mongolotimonae

R. sibirica

R. conorii

R. conorii Israël

« R. heilongjiangii »

R. helvetica

Treatment & VACCINES

• Treatment Tetracycline and chloramphinicol is

the antibiotic of choice (because of the small molecule size and the ability to penetrate infected cells).

• VACCINES Killed or attenuated live vaccines for

epidemic and endemic typhus, Rocky Mountain spotted fever and scrub typhus have been available for many years. Recombinant DNA methods are now being investigated.

References

• MIMS: chapter 21.• Levinson: chapter 26.• Bairley: chapter 39.• Emanuel: chapter 28.• Jawetz: chapter 27.• Kayser: unit 4.• http://www.textbookofbacteriology.net/Rickett

sia_2.html.

• http://en.wikipedia.org/wiki.• http://www.cehs.siu.edu/fix/medmicro/ricke.ht

m.

• others.