Rickettsia

I – CLASSIFICATION:

Rickettsia are obligate intracellular bacteria. They are almost as small as the largest viruses. However, it is indeed bacteria since these seeds divide by binary fission, they have both DNA and RNA, and are sensitive to antibiotics.

In the family of Rickettsiaceae four types are responsible for a disease to humans.

– Rickettsia, with several species responsible typhus and exanthematous fevers:

R. prowazekii, R. typhi, R. rickettsii, R. conorii, R. australis, R. akari, R. tsutsugamushi (R. orientalis), R. sibirica

– Coxiella, with one species, Coxiella burnetii, which causes Q fever

-. Ehriichia with several species responsible dog infections (E. canis), horse (. £ risticii and E. equi) and livestock (. I phagocytophila) Human ehriichîose is a rare disease described on the coast southern Japan and in Southeast Asia(E. sennetsu) and since 1986, the USA (as yet unidentified agent). It results in flu-like symptoms, fever, generalized lymphadenopathy and hepatosplenomegaly, and sometimes a rash. It is easily confused with infectious mononucleosis, but the patient often presents tick bite history, liver function tests disorders, fewer blood elements and a positive serological reaction with an antigen formed by E. canis. This germ is transmitted to humans by ticks.Germ reservoirs are still unknown.

– Rochalimaea quintana is responsible for febrile with a duration of 24-48 hours and separated by afebrile periods is trench fever (or Voihynie).

Leukocytosis and splenomegaly is observed. Recovery occurs within 5 to 6 weeks. This germ is transmitted to humans by the faeces of the body louse. Its ability to multiply in vitro cell-free medium justified the creation of the new genre.

Genetic studies in progress, analyzing the restriction profiles with pulsed field electrophoresis for example, should help in the near future to better understand the inter- and intra-specific species.

II – HABITAT:

Search Rickettsia in many arthropods shows that they are widespread; Infection usually occurs by ingestion. Some species remain localized in the digestive cavity, other invade the body of the animal; salivary glands may then contain the germ, which explains the transmission by bite.

They are also found in different reservoirs (human, rat, dog, wild rodent) and in vectors (lice, fleas, ticks, mites).

III – CHARACTER BACTERIOLOGICAL:

A – Body type:

These are cocco-bacillary elements very small, at the limit of visibility in optical microscopy, pale pink to the Gram stain, polymorphic intracellular most often Gram-negative. The Macchiavello amended by Gimenez staining (fuchsin – malachite green) allows to see the colorful rickettsial bright red on a pale green cytoplasmic background.

In electron microscopy, the structure of Rickettsia is that of Gram-negative bacteria.

B – Cropping characters:

Rickettsia multiply by binary division within the host cell.

Immediately after the division (microcinema) and when the conditions are good nutrition, rickettsiae are motivated by quick movements and travel the cytoplasm of the host cell in all directions. When the medium is depleted division stops, the bacteria grows and filamentous forms are obtained.

Rickettsia have intracellular multiplication of strategies that can be compiled into 3 groups:

– Bacteria of the genus Rickettsia live free in the cytoplasm after an extremely rapid escape of phagocytic vacuole.

– Bacteria of the genus Ehriichia inhibit (like Chlamydia and Legionella) the phagolysosomal fusion and multiply in the phagosome as morulae.

– Coxiella burnetii does not inhibit the phagolysosomal fusion, and multiplies in the acid pH phagolysosome.

Relations with the membranes of the host cell are important for the development of some species, especiallyR.tsutsugamushi requiring close membrane association for its metabolism while for R. prowazekii, there is a free development intracytoplasmic with the likely action of phospholipase A.

C – antigenic characters:

The study of antigens is difficult because of the fragility of Rickettsia and difficulties to separate the bacteria from the host cell.

Studies on the antigenic material were carried widely from crops grown on the membrane embryonated chicken egg yolk died 5-6 days after inoculation. The most important antigenic fraction is recovered in the ether lipid extract. This antigen can separate three groups:

– Group 1: R. prowazekii, R. typhi

– Group II: R. rickettsii, R. conorii. R. australis, R. sibirica. R. akari. R. japonica

– Group or R. tsutsugamushi

The different species may be separated by specific antisera. It is interesting to note that these groups separate species that have a common pathogenicity and so three groups are identified:

Group 1: Rickettsia typhus (louse, chip) with a 90% higher genetic homology (R. typhi, R. prowazekii) and a common lipopolysaccharide crossing with Proteus 0x19.

Group II: spotty fever transmitted by ticks: the pimply rickettsial group with LPS is also common, crossing with Proteus0x19 and 0X2 and having a greater than 90% genetic homology.

Group III: fevers brush: Rickettsia in this group antigenic community with Proteus OX K but this group has a considerable antigenic heterogeneity and genetics.

Immunofluorescence allows to highlight different serotypes whose study is particularly interesting in the group II.

Most interesting rickettsial antigens immunogenically are membrane proteins. Two major proteins are known in R.conorii (115 kDa and 135 kDa thermostable) R. typhi and R. prowazekii (120 kDa). Analysis of the structure of the 120 kDa protein should help to distinguish epitopes, particularly T cell recognition sites of these studies and the construction of synthetic peptides suggest the possibility to exploit their immunogenic properties to manufacture vaccines.

D – resistance:

Rickettsia bacteria are very fragile, easily killed by heat 30 minutes at 56 ° C, the desiccation and most disinfectants: formaldehyde, phenol.

Viability within infected cells depends on the temperature.

E – Experimental pathogenicity:

The spectrum of Rickettsia pathogenic activity is very broad and very many animals were used for their study. The male guinea pig is the animal of choice because of its sensitivity to most rickettsial (and the Coxiella) and scrotal swelling is observed in animals infected. There is a dermonecrotic effect after intradermal injection and rapid lethal effect after IV injection. The mouse is less sensitive; However, it is preferable to the guinea pig for R. akari and R.

tsutsugamushi. Intraperitoneal injection of these animals allows multiplication and isolation of these germs.

IV – PATHOGENICITY NATURAL:

A – typhus group:

Typhus epidemics have been known for a long time but the importance of arthropods in their transmission was highlighted in 1909 by Nicolle.

Two species are involved:

R. prowazekii: Epidemic typhus or historical typhus; R. typhi: endemic typhus and murine typhus.

1. Epidemic typhus:

It occurs in epidemics especially during wars. The disease is characterized by:

– Fever 40 ° C to 41 ° C, remaining in tray 2 weeks,

– A rash from the 4th to 7th day observing the face,

– A syndrome typhoid, maximum 2 to 3 days after the eruption prostration, lethargy, stupor.

There is a dry cough and labored breathing. Severe forms are fatal, but if recovery occurs, there is no sequelae.Antibiotics have completely changed this trend.

The disease has become rare in epidemic form, but it was one of the great historical evils accompanying famines, wars and playing by the deaths it caused, a major political role. Thus, Napoleon, in 1812, lost half a million men and this was one of the reasons for his final defeat. Typhus was also important in Russia and Serbia during the First World War; during the Second World War he touched the prison camps, it spread to Korea and Japan.

The risk still exists and an outbreak can occur at various conditions are met: gathering of displaced populations in poor or no sanitation, accentuation by misery and cold.

R. prowazekii appears in the blood of the patient at the beginning of the febrile period. Body lice feed on blood and tend to leave to find another host that is contracting typhus. The louse leaves rich faeces rickettsiae on the skin and is scratching at the rickettsial can penetrate the skin and altered.

There are a few indigenous cases in the USA transmitted by ectoparasites flying squirrels: the sporadic typhus.

2. Brill-Zinsser disease:

Brill in 1898 in New York, noted the occurrence of sporadic cases of a disease resembling typhus in communities of emigrants from Central Europe, but is not vector.

Zinsser in 1937, argued that it was a resurgence of persistent rickettsiae in the skin in former typhoid. Later in 1951, Murray was able to isolate rickettsiae, R. prowazekii, in the blood of such patients.

Disease similar to typhoid, but is characterized by a less pronounced intensity of clinical manifestations.

3. Murine typhus or endemic typhus:

Long confused with the classical typhus, it is due to R. typhi and arthropod vector is not lice but the chip. The seed tank is the rat.

Disease comparable to classical typhus but less serious: less severe symptoms, rash least, the temperature curve has large oscillations, healing is without sequelae.

Murine typhus is exceptional in France and was able to meet in the ports or places where rats were infected.

Its distribution is poorly known. There is endemic in Texas and Greece (Evia island).

B – Group of purple and spotty fevers:

This group corresponds to many clinical pictures, each linked to a Rickettsia whose names are reminiscent particular geographic location where the disease has been described. They can meet in France in the form of Mediterranean spotted fever and America in the form of the dreaded disease of the Rocky Mountains.

1. spotted fever Rocky Mountain:

Described in 1899, it is characterized by a high temperature with delusions and eruption of red purple papules suggestive of severe measles. The beginning is marked by sudden severe headache especially in the frontal region, acute muscle pain. Before antibiotics, the prognosis was severe with 20% mortality especially among the elderly;Currently it is estimated at 4% in the US.

R. rickettsii agent spotted fever is transmitted by ticks: Dermacentor andersoni (Rocky Mountain Region), D.variabilis, Amblyomma americanum, Haemaphy soiled leporis-palustris Mexico, Rhipicephalus sanguineus which are found in wild animals, particularly rodents, but also among the cattle and in domestic animals. The infection can affect especially the loggers and walkers in the forest. It is not only found in the Rocky Mountains, but throughout the American continent after the tick development cycle. Currently this infection is more common on the East Coast than on the West Coast.

2. Mediterranean spotted fever:

It is due to R. . conorii The epidemiology of rickettsial disease is closely related to ticks that transmit it, Rhipicephalus sanguineus, normal parasite of the domestic dog Ticks become infected by biting infected mammals (domestic. dogs, cattle, sheep, goats and wild : rabbits and other rodents), and is itself a reservoir of the virus since it transmits Rickettsia his descendants transovarially.

The man contracted the disease especially in spring and summer in favor of a country walk. The Mediterranean basin is the largest homes, but other parts of France may be affected. Infection occurs through the saliva of the arthropod. Ocular mucosa shows another door.

From the clinical point of view, the incubation lasts 4 to 15 days. High fever associated with diffuse pain syndrome (headache, myalgia). The initial lesion is characteristic: black spot, small ulcer with a black necrotic center and erythematous border accompanied by lymphadenopathy. A generalized maculopapular rash affecting members with involvement of the palms and soles is also observed.

In the south of France this ancient condition called “Olmer of disease” had received the evocative name of “typhus harvest.” Malignant forms sometimes unfavorable changes have been described, marked by a purpuric rash and multiple organ damage, neurological complications, hepatic, cardiac, vascular and bronchopulmonary.

3. vesicular Rickettsiose:

It is due to R. akari. The epidemiological cycle includes the mouse and a mite (Dermanyssus sanguineus) who accidentally infects humans through bites. It is world distribution: Russia, America, Africa.

C – typhus Group Brousse:

The disease is limited to the Far East: Japan, Australia, New Guinea, India. It is due to R. tsutsugamushi (R. orientalis). It is transmitted by a Trombicula.

Japanese river fever and scrub typhus-Malaysia or scrub typhus typhus is a fever that appears ten days after being bitten by the larva of the mite which, at this stage of its development, must take a blood meal. The fever lasts for two weeks. Other signs include: pressure ulcer at the inoculation, satellite lymphadenopathy, frequent headaches and very strong, frequent coughing.

D – Pathophysiology:

The clinical expression of polymorphic rickettsial sometimes involves factors related to the host and bacteria. The severity of rickettsial diseases is variable and the same disease can be mild or fatal without that we can make differences between the strains responsible for these forms. Age, a congenital deficiency G6 – PD, alcoholism worsen rickettsial diseases, but the role of lower immune defenses has not been proven. Chemical mediators of the inflammatory response may play a role.

Rickettsial diseases are very virulent as some bacteria (about 10 / bite) are sufficient to induce disease. Generally they multiply locally earn satellite nodes and blood. They are then able to parasitize the vascular endothelial cells of all tissues: skin, central nervous system, myocardium, creating a vasculitis that explains the clinical signs of the disease: rash, headache, stupor, circulatory collapse, splenomegaly, pneumonia.

V – DIAGNOSIS OF BACTERIOLOGICAL RICKETTSIOSES:

A – Direct:

The isolation is by direct inoculation intraperitoneally to guinea pig blood or other medical products from the patient.Inoculation almost at the bedside because of the fragility of germs.

Isolation of blood R. conorii can be done quite easily by centrifugation technique on human fibroblasts (HEL MRC5).The risk of isolation of R. conorii is not higher than that of the influenza virus.

The culture of other rickettsial on different cell lines or embryonated egg, can be achieved in equipped laboratories (laboratory containment) Class 3. New diagnostic approaches make use of molecular probes and genomic amplification ( Polymerase Chain Reaction: PCR). The fertilized egg can also be used. The identification is carried out by immunofluorescence using specific antisera.

B – Indirect diagnosis:

1. Reaction Weil-Felix:

Weil and Felix had a Proteus isolated from the urine of a patient with typhus thinking they were dealing with the pathogen, they realized an agglutination reaction with the serum of the patient which proved positive. The old method was abandoned lacking sensitivity and specificity. It was based on the antigenic communities betweenProteus OX 19 – OX K – OX 2 and Rickettsia except Coxiella burnetii.

2. microscopic agglutination Giroud:

This technique consists in the presence of rickettsial suspensions with decomplemented serum of the patient. It tends to be abandoned.

3. Complement Fixation of reaction:

It uses a soluble antigen extracted with ether – specific and sensitive reaction performed with each of the groups typhus fever and Q fever spotty, sometimes low rates.

4. Indirect immunofluorescence:

Sensitive reaction and whose use is developed for the diagnosis of: Q fever, spotted fever, murine typhus. Rickettsial antigens ready marketed. It is currently the WHO reference method and requires systematic search for IgG and IgM antibodies. Cross-reactions giving false positives are found exclusively with IgM (Proteus, Legionella).

5. indirect hemagglutination – Latex Test:

The antigen is represented by R. carbohydrate-protein complex rickettsii heat treated in alkaline medium. Simpler and faster techniques, marketed.

VI – Q FEVER – Coxiella burnetii:

Rickettsia Coxiella differs from its greater resistance to external agents and different antigenic characters.

Coxiella have the structure of characters of Gram-negative bacteria.

The resistance is very large and Coxiella can survive several months at room temperature, on clothing or suspended in milk (straw, manure, dried placentas infected).

Q fever or Query fever is a zoonosis of worldwide distribution. C. burnetii is responsible for epizootic abortion and stillbirth in cattle. Rodents, sheep, goats, cattle are the reservoir of the virus. Humans are contaminated directly to their contact (milk, contaminated afterbirths) but also by dust. Transmission by arthropod vectors is quite negligible.

Contamination is by air or mucosal route. Exposed occupations: farmers, veterinarians, slaughterhouse workers, butchers.

A – Clinic:

After incubation for 2 to 3 weeks, the onset is abrupt. The disease has the following characters: headache, fever of 39 ° C tray, then curved sawtooth, frequent relapses, profuse sweating, asthenia, pleuropulmonary localization with signs of pulmonary infiltrates, pneumonia, and ill-defined, pace of SARS .

Complications are rare. Healing occurs around the third week, but fatigue and asthenia persist long. The Q fever endocarditis affects probably underestimated, presenting as subacute or chronic blood culture-negative endocarditis.

This nonspecific clinical picture may therefore evoke other atypical pneumonia or to think of a brucellosis given the epidemiological context.

The incidence of this zoonosis is unknown in France.

B – Pathophysiology:

The immune status of the host seems decisive in the clinical expression of Q fever Cases of Q fever have been reported in association with immunosuppression (blood disease, cancer, HIV infection, transplantation). LPS plays a role in the determination of the disease. C. burnetii is characterized by a phase change phenomenon.

Phase 1 is the wild and virulent form, Phase II is attenuated and obtained by successive passages in the laboratory.LPS stage 1 does not allow the attachment of the complement fraction € 3 and has a protective action of the lysis.

C – Diagnosis:

It is based on the demonstration of the germ. C. burnetii can be grown from biopsy products (liver, skin, valves) or blood. Possible methods are guinea-pig inoculation and culture on embryonated egg. Cell cultures are at risk of contamination of laboratory personnel and all this research should be reserved for specialized laboratories.However, the cell cultures are much less dangerous than animals that excrete C. burnetii.

C. burnetii can be revealed by direct immunofluorescence in pathological products.

PCR will also detect the bacterial genome and distinguish strains causing acute forms and chronic forms using two sets of primers, one detecting the DNA of C. burnetii, the other a plasmid sequence characteristic of the chronic form of strains.

Serology remains the most reliable and easiest way:

– Complement fixation test with both phase 1 and II antigens. The response is however late and lack of sensitivity, the anti-phase are not early antibodies but the existence of anti-Phase 1 antibody is useful in the diagnosis of endocarditis;

– Indirect immunofluorescence is sensitive and specific, separation IgG, IgM, IgA refines the diagnosis in particular an increase in IgA antibodies is often specific endocarditis;

– An ELISA technique is proposed.

VII – HANDLING AND FEVER RICKETTSIOSES Q:

A – Curative treatment:

It is based on intracellular penetration of antibiotics:

– Tetracyclines, especially doxycycline, minocycline;

– Chloramphenicol can also be used;

– Rifampicin, erythromycin and ciprofloxacin were advocated.

B – Preventive Treatment and prevention:

Pest Control Measures: different depending on the virus reservoir and vectors; in the presence of typhus, fight against lice, fleas and rats (rat control ports and vessels). There is still no effective vaccine for spotted fever. After a “historical” test succcession (White, Baltazard, Laigret, Giroud, Zinsser, Haagen, Cox), a vaccine for typhoid is derived Cox works, prepared from a grown egg rickettsial suspension embryonated and formalin.

For Q fever vaccination of livestock, but the diversity of sources contamination are that these measures may be insufficient.

For the Mediterranean spotted fever, knowing that the tick bites host a few hours after it be fixed, it is useful to inspect the body and clothing after crossing a endemically infested area and check if the tick contains blood in his abdomen, evidence of bite.