Family Rickettsiaceae

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RICKETTSIACEAE

Part-1

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Family Rickettsiaceae

Genus Species

Rickettsia R.prowazekii

R.typhi R.rickettsii R.conorii R.australis R.sibirica R.akari

Orientia O.tsutsugamushi

Ehrilichia (Family: Anaplasmataceae) E.sennetsu E.chaffeensis

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• Howard Taylor ricketts- 1906

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Genus Rickettsia

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• Small obligate Intracellular parasites

• Gram-Negative bacteria

– Stain poorly with Gram stain (Giemsa, Giemenez and machiavello stains used)

• Reservoirs - Animals, insects and humans

• Arthropod vectors (except Coxiella)

• Multiply by binary fission

• Possess a trilaminar cytoplasmic membrane and a cell wall of bacterial type.

• Possess both DNA and RNA

• Respond to Tetracycline (and chloramphenicol)

• Do not grow on ordinary culture media

General Features

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• Obligate intracellular parasite

• Gram negative pleomorphic rods

• Parasite of arthropods – fleas, lice, ticks and mites.

• No Human to human transmission.

Rickettsia inside the host cell

0.25 u in diameter

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Rickettsial infections- classification

• Typhus fever group

- Epidemic typhus

(Louse born typhus/ classical typhus): R. prowazekii

- Brill-Zinsser typhus

(Recrudescent typhus): ………..,,

- Endemic typhus

(Murine typhus/ flea born typhus): R. typhi

• Spotted fever group

- Rocky mountain spotted fever- RMSF:

R. Rickettsiae

- Rickettsial pox:

^{R. akarii}

- Indian Tick Typhus :

^{R. Conorii}

-

Siberian tick typhus - Australian tick typhus

• Scrub typhus

-Orientia tsutsugamushi

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Antigenic structure

• Group specific soluble Antigen

• Species specific Antigen

• Alkali stable polysaccharide

• Endotoxin

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General Features

The rickettsia are bacteria which are obligate intracellular

parasites. They are considered a separate group of bacteria

because they have the common feature of being spread by

arthropod vectors (lice, fleas, mites and ticks). The cells are

extremely small (0.25 u in diameter) rod-shaped, coccoid and

often pleomorphic microorganisms which have typical

bacterial cell walls, no flagella, are gram-negative and

multiply via binary fission only inside host cells. They occur

singly, in pairs, or in strands.

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PATHOGENESIS

• Rickettsia are transmitted to humans by the faeces/bite of infected arthropod vector.

• Multiply at the site of entry and enter the blood stream.

• Localise in the vascular endothelial cells and multiply to cause thrombosis lead to rupture & necrosis.

RICKETTSIA INSIDE THE ENDOTHELIAL CELLS

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Replication of Rickettsia

• Infect endothelial cells in small blood vessels - Induced phagocytosis

• Lysis of phagosome and entry into cytoplasm - produce phospholipase

• Replication

• Release

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A] EPIDEMIC TYPHUS (CLASSICAL TYPHUS)

Louse Born Typhus

Cause: Rickettsia prowazekii

Vector: Human body louse ( Pediculus humanus corporis) Human head louse ( Pediculus humanus capitis) Incubation period – 5-21 days

Mortality rate is 20-30% in untreated cases.

1] Typhus Fevers

LICE

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SYMPTOMS

• Severe headache

• Chills

• Generalised myalgia

• High fever ( 39-41⁰C)

• Vomiting

• Macular rash after 4-7 days – first on trunk and spreads to limb.(Not on Palms & Soles)

• Lacks conciousness.

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• This occur after the person recoveres from epidemic typhus and reactivation of the Rickettsia prowazekii which remained latent for years.

• Mild illness and low mortality rate.

B] Brill –Zinsser/ Recrudescent typhus

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C] ENDEMIC TYPHUS (MURINE TYPHUS)

• R. typhi

• Vector: Rat flea (Xenopsylla cheopis)

• Reservoir: Rat

• Infection occurs after rat flea bite

• Presentation

• pathogenesis

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Rickettsial infections- classification

• Typhus fever group

- Epidemic typhus

(Louse born typhus/ classical typhus): R. prowazekii

- Brill-Zinsser typhus

(Recrudescent typhus): ………..,,

- Endemic typhus

(Murine typhus/ flea born typhus): R.`typhi

• Spotted fever group

- Rocky Mountain Spotted Fever- RMSF:

R. Rickettsiae

- Rickettsial pox:

^{R. akarii}

- Indian Tick Typhus : R. Conorii - Siberian tick typhus

- Australian tick typhus

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Rocky mountain spotted fever R. ricketsii Ixodid Tick

Rickettsial-pox R. akari Mite

Australian tick typhus R. australis Ixodid Tick

indian Tick Typhus R. conorii Ixodid Tick

Siberian tick typhus R.sibirica Ixodid Tick

DISEASE SPECIES VECTOR

Cont...

2] Spotted Fever Group

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A] Rocky mountain spotted fever

• Most serious form

• Cause – R. rickettsii

• Infection occurs after tick bite

• Incubation period – 1 week

• More similar to typhus fever but the rash appears earlier and is more prominent (Palms & Soles involved)

Rocky mountain spotted fever R. ricketsii Ixodid Tick

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• The clinical symptoms of other spotted fevers are very similar to Rocky mountain spotted fever

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The rash in a case of Rocky Mountain spotted fever

Figure 21.3

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Rocky Mountain Spotted Fever

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B] Rickettsial pox

• Patients develops a papulovesicular lesion at the site of the bite and the enlargement of lymph nodes.

• Followed by fever, chills, headache, malaise and myalgia.

• After 3-4 days, generalised papulovesicular rash appears.

• Recovery after 10-14 days.

Rickettsial-pox R. akari Mite

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3] Scrub typhus

Scrub typhus

Orientia

tsutsugamushi

Trombiculid mite (chigger)

Rodents Asia-Pacific region from

maritime Russia and China to Indonesia and North Australia to Afghanistan

DISEASE SPECIES VECTOR RESERVOIR(S) GEOGRAPHIC

DISTRIBUTION

Japanese “tsutsuga” = small and dangerous and “mushi” = creature

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Scrub typhus

• 2-3 weeks after chigger bite abrupt severe headache, chills,

fever, conjunctivitis, deafness and a characteristic eschar at the site of chigger bite.

• Spleen & lymph nodes proximal to eschar enlarge

• One week after fever, a maculopapular rash appears on the trunk which later becomes generalised.

• Case fatality rate 10-60%

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Complications of rickettsial diseases

• Bronchopneumonia

• Congestive heart failure

• Multi-organ failure

• Deafness

• Disseminated intravascular coagulopathy (DIC)

• Myocarditis (inflammation of heart muscle)

• Endocarditis (inflammation of heart lining)

• Glomerulonephritis (inflammation of kidney)

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Different Methods of LabDiagnosis

Specimen?

Biopsy PCR

“Does not grow on ordinary culture media”

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Laboratory Diagnosis

Presumptive laboratory diagnosis is based on the finding of

rickettsial-like organisms in tissue or blood. Although the organisms are gram-negative, they only weakly take the counter stain, safranin.

Therefore, special staining procedures are used. Infected tissue may be stained with:

• 1. Macchiavello stain--organisms are bright red against the blue background of the tissue.

• 2. Castaneda stain--blue organisms against a red background.

• 3. Giemsa stain--bluish purple organisms.

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Gimenez stain of tissue culture cells infected with Rickettsia rickettsii

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A Giemsa stain for visualizing Rickettsia rickettsii

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IMMUNOFLUORESCENT ANTIBODY TECHNIQUE – UTILISES FLUORESCENT ANTIBODY TO DETECT RICKETTSIAL

ANTIGEN IN INFECTED TISSUES

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Serological tests

• Weil-Felix reaction

• Complement fixation test

• Latex agglutination test

• Enzyme immunoassay

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• Weil-Felix reaction

–To diagnose rickettsial infections by the demonstration of agglutinins to proteus strains

• P.vulgaris ( OX 19, OX 2)

• P.mrabilis (OX K)

Basis of the reaction is the sharing of antigens between Rickettsia and proteus

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DISEASE WEIL-FELIX

OX19 OX2 OXK

Epidemic typhus ++ +/- -

Endemic typhus ++ - -

Scrub typhus - - ++

RMSF + + -

Rickettsial pox - - -

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4. Enzyme-linked Immuno-Sorbant Assay (ELISA)

Ag-coated well

Ag-Ab complex

Optical Density

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ELISA test is a technique for detecting & measuring antigen or antibody.

:-It is one of the most reliable techniques to detect antibody against scrub typhus infection.

:-Its procedure is the principal for development of recent rapid diagnostic kits.

:-This technique is widely used in laboratories & hospitals.

Immunological Assays

Newer Techniques

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• Male guinea pig inoculated intra

peritioneally with blood of patients –

• Fever, scrotal swelling, Enlarged testis, and

cannot be pushed back.-due inflammation and adhesions between layers of Tunica vaginalis

• Test Positive for R.typhi (Endemic typhus ) and Negative for R. prowazekii (Epidemic typhus)

Neill-Mooser Reaction

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ISOLATION ^{- culture}

• Blood is inoculated in guinea pigs/mice.

• Observed on 3^rd – 4^th week.

• Animal responds to different rickettsial species can vary

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Treatment

• Treatment should be started early in the first week of illness.

• Doxycycline (first choice)

• Tetracycline (alternate)

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