Table of Contents:

• Taxonomy Information
• Lifecycle Information
• Genome Information
• Biosafety Information
• Culturing Information
• Epidemiology Information
• Diagnostic Tests Information
• Infected Hosts Information
• Phinet: Pathogen-Host Interaction Network
• Lab Animal Pathobiology & Management
• References
• Data Provenance and Curators

1. Species:
   1. Rickettsia prowazekii (Website 1):
      1. Common Name: Epidemic typhus, louse-borne typhus, classic typhus, sylvatic typhus
      2. GenBank Taxonomy No.: 782
      3. Description: Rickettsia prowazekii is the etiologic agent of epidemic typhus, which occurs in two clinical forms: the primary febrile illness and recrudescent infection (Brill-Zinsser disease). Epidemic typhus is transmitted by the body louse (Pediculus humanus corporis) and typically occurs during cold-weather months. Epidemic typhus is also known as louse-borne typhus, classic typhus, and sylvatic typhus(Baxter, 1996).
      4. Variant(s):
         • Rickettsia prowazekii str. Madrid E (Website 15):
           • GenBank Taxonomy No.: 272947
           • Parents: Rickettsia prowazekii
           • Description: Madrid E is an attenuated strain of R. prowazekii(Ge et al., 2004).

1. 1. Stage Information:
      1. Rickettsia prowazekii vegetative state:
         • Size: 0.2 to 0.3 by 1um
         • Shape: Intracellular rickettsia appeared as paired, lanceolate-to-ovoid bacilli.
         • Picture(s):
           • (Website 10)
             
             
             
             Description: Following the release from the phagosomes, rickettsia grow free in the cytoplasm of cultured cells, dividing by binary fission (seen at arrows). Inset highlights the outer and inner membranes of rickettsia(Website 10).
         • Description: Rickettsia prowazekii is a rickettsia-an obligate intracellular bacterium that is transmitted by an arthropod-vectored by the human body louse (Pediculus humanus subspecies P. corporis). The organisms are small (0.3-1.0 um) coccobacilli that have a typical gram-negative cell envelope in ultrastructural studies and also contain peptidoglycan and lipopolysaccharides. They are poorly stained by the Gram method and are better visualized using the Gimenez or Giemsa stains. Within the outer membrane are also found immunodominant surface-exposed proteins of the Sca family, which may provide structure or potentially contribute to host cell adhesion or other host cell interactions(Raoult et al., 2004).
   2. Description: The life cycle of epidemic typhus is believed to be initiated by a human case of primary epidemic typhus or by a case of recrudescent typhus, when the body louse feeds on an infected person. In the louse, the organism reproduces in the alimentary tract, yielding a large number of rickettsial organisms in its feces. The louse defecates while taking a blood meal, and the host then scratches the site, contaminating the bite wound with louse feces. Close personal or clothing contact is usually required to transmit lice from person to person. Infected lice usually die within 1 to 3 weeks from obstruction of the alimentary tract and do not transmit the organism to their offspring(Baxter, 1996).

1. Genome of Rickettsia prowazekii
   1. Description: The 1.1-Mb genome sequence of the aetiological agent of epidemic typhus, R. prowazekii, was published in 1998. One of the most controversial aspects of this genome sequence was its low coding content. Many scientists found it hard to accept that as much as 24% of this extremely small genome would be nothing but junk DNA. In total, only 834 protein coding genes were identified and these were sorted into their functional categories to provide a description of the R. prowazekii metabolism(Andersson and Andersson, 2000).
   2. Rickettsia prowazekii strain Madrid E(Website 6)
      1. GenBank Accession Number: NC_000963
      2. Size: 1111523 bp(Website 6).
      3. Gene Count: 834 protein-coding genes(Andersson et al., 1998).
      4. Description: The complete genome sequence (1,111,523 base pairs) of the obligate intracellular parasite Rickettsia prowazekii, the causative agent of epidemic typhus is described. This genome contains 834 protein-coding genes. The functional profiles of these genes show similarities to those of mitochondrial genes: no genes required for anaerobic glycolysis are found in either R. prowazekii or mitochondrial genomes, but a complete set of genes encoding components of the tricarboxylic acid cycle and the respiratory-chain complex is found in R. prowazekii. In effect, ATP production in Rickettsia is the same as that in mitochondria. Many genes involved in the biosynthesis and regulation of biosynthesis of amino acids and nucleosides in free-living bacteria are absent from R. prowazekii and mitochondria. Such genes seem to have been replaced by homologues in the nuclear (host) genome. The R. prowazekii genome contains the highest proportion of non-coding DNA (24%) detected so far in a microbial genome. Such non-coding sequences may be degraded remnants of 'neutralized' genes that await elimination from the genome. Phylogenetic analyses indicate that R. prowazekii is more closely related to mitochondria than is any other microbe studied so far(Andersson et al., 1998).
      5. Picture(s):
         • Rickettsia prowazekii strain Madrid E, complete genome (Website 11)
           
           
           
           
         • Rickettsia prowazekii strain Madrid E, complete genome (Website 11)
           
           
           
           

1. General biosafety information
   1. Level: 2 and 3.
   2. Precautions: Biosafety Level 2 practices and facilities are recommended for nonpropagative laboratory procedures, including serological and fluorescent antibody procedures, and for the staining of impression smears. Biosafety Level 3 practices and facilities are recommended for all other manipulations of known or potentially infectious materials, including necropsy of experimentally infected animals and trituration of their tissues, and inoculation, incubation, and harvesting of embryonate eggs or cell cultures. Animal Biosafety Level 2 practices and facilities are recommended for the holding of experimentally infected mammals other than arthropods. Level 3 practices and facilities are recommended for animal studies with arthropods naturally or experimentally infected with rickettsial agents of human disease(Website 12).

1. Shell Vial Cell Culture Assay (Vestris et al., 2003):
   1. Description: Over the last 7 years (from November 1995 to May 2002) our laboratory has adapted a centrifugation-cell culture system, the shell vial assay, for isolation of bacteria. This technique is used routinely in a biosafety level equipped laboratory for the isolation of rickettsiae and other strictly, or facultatively, intracellular bacteria from tissue biopsies, especially tick-bite eschars, and blood samples(Vestris et al., 2003). We received 490 clinical samples (273 blood samples and 217 cutaneous biopsies) from patients suspected of having a rickettsial disease. We have isolated and established by culture in shell vials 26 (5.3%) clinical isolates including 10 Rickettsia conorii, 9 R. africae, 1 R. slovaca, 4 R. mongolotimonae, 1 R. prowazekii, and a R. conorii new serotype. Rickettsiae were isolated more frequently from cutaneous biopsies (20, 9.2%) than from blood (6, 2.2%) (significant difference: P less than 0.05)(Vestris et al., 2003).
   2. Medium: Eagle's minimal essential medium with 4% fetal calf serum and 2 mM L glutamine(Vestris et al., 2003).
   3. Note: Detection of rickettsial organisms on the coverslip was carried out, while it remained inside the shell vial, by Gimenez staining and indirect immunofluorecence assay after 3, 6, and 14 days. If immunofluorescence was positive, the culture was reported as positive and culture supernatants were sampled in order to identify the isolate by a specific PCR assay. The remaining supernatants of positive shell vials as well as the third shell vial were inoculated on confluent layers of HEL cells in 25 cm(2) culture flasks in order to propagate isolates(Vestris et al., 2003).
2. Plaque Assay in Vero76 Cells (Policastro et al., 1996):
   1. Description: Typhus group rickettsiae, including Rickettsia prowazekii and R. typhi, produce visible plaques on primary chick embryo fibroblasts and low-passage mouse embryo fibroblasts but do not form reproducible plaques on continuous cell culture lines. We tested medium overlay modifications for plaque formation of typhus group rickettsiae on the continuous fibroblast cell line Vero76. A procedure involving primary overlay with medium at pH 6.8, which was followed 2 to 3 days later with secondary overlay at neutral pH containing 1 microgram of emetine per ml and 20 micrograms of NaF per ml, resulted in visible plaques at 7 to 10 days postinfection. A single-step procedure involving overlay with medium containing 50 ng of dextran sulfate per ml also resulted in plaque formation within 8 days postinfection. These assays represent reproducible and inexpensive methods for evaluating the infectious titers of typhus group rickettsiae, cloning single plaque isolates, and testing the susceptibilities of rickettsiae to antibiotics(Policastro et al., 1996).
3. R. prowazekii in Mouse L929 cells (Turco and , 1989):
   1. Description: L929 cells were harvested from monolayer cultures by incubation with 0.5% trypsin and 0.02% disodium EDTA in a salt solution. After being washed, the cells were suspended in serum-supplemented medium (MS) at a concentration of 2 x 10(6) viable (trypan blue excluding) cells per ml. Rickettsiae were diluted in Hanks balanced salt solution supplemented with 5 mM L-glutamic acid (monopotassium salt) and 0.1% gelatin (HBSSGG), and an equal volume of rickettsiae (approximately 2 x 10(8)/ ml) was added to each cell suspension.-(Turco and , 1989).
   2. Medium: MS medium(Turco and , 1989).
   3. Optimal Temperature: 34 C(Turco and , 1989).

1. Outbreak Locations:
   1. Between 1981 and 1997, epidemic typhus was predominantly thought of as a sporadic disease. However, in the last 25 years, intermittent outbreaks have occurred in Africa (Ethiopia, Nigeria, Burundi), Mexico, Central America, South America, Eastern Europe, Afghanistan, India, and China. There is a general lack of awareness that between 1993 and 1997, louse-borne typhus and 'sutama' (the abdominal pain manifestation of the disease) occurred in more than 45,000 Burundian patients with a case fatality rate of 15%, underscoring the woeful reporting and inattention of the western world. Thus it is highly likely that the prevalence and mortality of this important infection is significantly underestimated(Raoult et al., 2004).
2. Transmission Information:
   1. From: Rickettsia prowazekii is the causative agent of epidemic typhus, a severe reemerging disease. It is transmitted to humans by the body louse, Pediculus hominis corporis, and has the most serious epidemic potential among all rickettsiae(Fang et al., 2002). Man is the main host and seems also to be the natural reservoir for R. prowazekii(Andersson and Andersson, 2000). , To: The disease is transmitted among humans by the body louse, Pediculus humanus corporis. The lice are strict blood-sucking insects, depositing their infected feces near the bite lesion. The lice have a tendency to desert febrile hosts to seek new healthy individuals, which effectively spreads the disease in human populations. However, the louse also suffers from the rickettsial infection, and depending on the amount of bacteria in the gut, the louse may be killed within 12 weeks(Andersson and Andersson, 2000). , With Destination:Louse infestation always occurs in a blood meal, and the louse remains infected all its life(Roux and Raoult, 1999).
      Mechanism: Louse infestation always occurs in a blood meal, and the louse remains infected all its life, developing into an efficient epidemiological witness. The arthropod location, the effect of the location on louse survival, and microorganism transmission depend on the microorganism. After ingestion, R. prowazekii invades the midgut epithelium cells of the insect, in which they replicate, and a large number of infective organisms are released back into the gut. The organisms are then excreted with louse fecal matter and are thus transmitted to humans when a skin wound is scratched or scraped. The louse will then die as a result of the R. prowazekii infection(Roux and Raoult, 1999).
   2. From: The disease is transmitted among humans by the body louse, Pediculus humanus corporis. The lice are strict blood-sucking insects, depositing their infected feces near the bite lesion. The lice have a tendency to desert febrile hosts to seek new healthy individuals, which effectively spreads the disease in human populations. However, the louse also suffers from the rickettsial infection, and depending on the amount of bacteria in the gut, the louse may be killed within 12 weeks(Andersson and Andersson, 2000). , To: Rickettsia prowazekii is the causative agent of epidemic typhus, a severe reemerging disease. It is transmitted to humans by the body louse, Pediculus hominis corporis, and has the most serious epidemic potential among all rickettsiae(Fang et al., 2002). Man is the main host and seems also to be the natural reservoir for R. prowazekii(Andersson and Andersson, 2000). , With Destination:After ingestion, R. prowazekii invades the midgut epithelium cells of the insect, in which they replicate, and a large number of infective organisms are released back into the gut. The organisms are then excreted with louse fecal matter and are thus transmitted to humans when a skin wound is scratched or scraped(Roux and Raoult, 1999).
      Mechanism: Outbreaks of epidemic typhus can result from rapid transmission of R. prowazekii from human to human by infected lice(Azad and Beard, 1998). Inhalation and transdermal or mucous membrane inoculation of infected louse feces are well-established routes of pathogen transmission during epidemics of human louse-borne typhus(Reynolds et al., 2003).
   3. From: 15 strains of R. prowazekii have been isolated, 10 from flying squirrels and the remainder from their ectoparasites (3 from lice and 2 from fleas). This rickettsial infection appears to be transmitted among the flying squirrel populations by their ectoparasites, primarily by squirrel lice, Neohaematopinus sciuropteri. The squirrel flea, Orchopeas howardii, is also implicated in the transmission cycle, but to a lesser degree(Azad, 1988). , To: Flying squirrel ectoparasites (lice and fleas) were implicated in the transmission of R. prowazekii between the squirrels and from squirrels to humans(Azad and Beard, 1998). , With Destination:After ingestion, R. prowazekii invades the midgut epithelium cells of the insect, in which they replicate, and a large number of infective organisms are released back into the gut. The organisms are then excreted with louse fecal matter and are thus transmitted to humans when a skin wound is scratched or scraped(Roux and Raoult, 1999).
      Mechanism: Inhalation and transdermal or mucous membrane inoculation of infected louse feces are well-established routes of pathogen transmission during epidemics of human louse-borne typhus. The mechanism by which R. prowazekii is transmitted from flying squirrels to humans is less well understood. Various routes have been hypothesized, but none have been empirically established. Plausible mechanisms include inhalation or direct introduction (through mucous membrane or dermal abrasion) of infected feces from louse or flea ectoparasites of flying squirrels or through the bite of infected flea ectoparasites of flying squirrels(Reynolds et al., 2003).
   4. From: 15 strains of R. prowazekii have been isolated, 10 from flying squirrels and the remainder from their ectoparasites (3 from lice and 2 from fleas). This rickettsial infection appears to be transmitted among the flying squirrel populations by their ectoparasites, primarily by squirrel lice, Neohaematopinus sciuropteri. The squirrel flea, Orchopeas howardii, is also implicated in the transmission cycle, but to a lesser degree(Azad, 1988). , To: Flying squirrel ectoparasites (lice and fleas) were implicated in the transmission of R. prowazekii between the squirrels and from squirrels to humans(Azad and Beard, 1998). , With Destination:After ingestion, R. prowazekii invades the midgut epithelium cells of the insect, in which they replicate, and a large number of infective organisms are released back into the gut. The organisms are then excreted with louse fecal matter and are thus transmitted to humans when a skin wound is scratched or scraped(Roux and Raoult, 1999).
      Mechanism: Inhalation and transdermal or mucous membrane inoculation of infected louse feces are well-established routes of pathogen transmission during epidemics of human louse-borne typhus. The mechanism by which R. prowazekii is transmitted from flying squirrels to humans is less well understood. Various routes have been hypothesized, but none have been empirically established. Plausible mechanisms include inhalation or direct introduction (through mucous membrane or dermal abrasion) of infected feces from louse or flea ectoparasites of flying squirrels or through the bite of infected flea ectoparasites of flying squirrels. At least one species of flea ectoparasite (Orchopeas howardii) of flying squirrels is known to opportunistically bite humans and could serve as a bridge vector for transmission from flying squirrel to human(Reynolds et al., 2003).
3. Environmental Reservoir:
   1. Currently no environmental reservoir information is available.
4. Intentional Releases:
   1. Intentional Release Information:
      1. Description: R. prowazekii was transformed into a battlefield weapon by the Red Army, and the Japanese Army successfully tested biobombs, containing R. prowazekii. So the precedent exists for using R. prowazekii as an agent of terror(Azad and Radulovic, 2003).
      2. Emergency Contact: .
      3. Delivery Mechanism: Dust containing infected louse excrement may transmit the organism by inhalation, an observation that lead to weaponization of R. prowazekii by the USSR in the 1930's and has raised recent fears of its use in bioterrorism(Raoult et al., 2004).
      4. Containment: Biosafety Level 2 practices and facilities are recommended for nonpropagative laboratory procedures, including serological and fluorescent antibody procedures, and for the staining of impression smears. Biosafety Level 3 practices and facilities are recommended for all other manipulations of known or potentially infectious materials, including necropsy of experimentally infected animals and trituration of their tissues, and inoculation, incubation, and harvesting of embryonate eggs or cell cultures. Animal Biosafety Level 2 practices and facilities are recommended for the holding of experimentally infected mammals other than arthropods. Level 3 practices and facilities are recommended for animal studies with arthropods naturally or experimentally infected with rickettsial agents of human disease(Website 12).

1. Organism Detection Test:
   1. Gimenez or Giemsa stain for light microscopy :
      1. Time to Perform: unknown
      2. Description: The organisms are small (0.3-1.0 um) coccobacilli that have a typical gram-negative cell envelope in ultrastructural studies and also contain peptidoglycan and lipopolysaccharides. They are poorly stained by the Gram method and are better visualized using the Gimenez or Geimsa stains(Raoult et al., 2004). Giemsa or Gemenez staining is useful for identifying the organism in the cytoplasm of cells(Baxter, 1996).
   2. Immunofluorescence microscopy :
      1. Time to Perform: unknown
      2. Description: In order to identify Rickettsia prowazekii in lice, we developed a panel of 29 representative monoclonal antibodies selected from 187 positive hybridomas made by fusing splenocytes of immunized mice with SP2/0-Ag14 myeloma cells. Immunoblotting revealed that 15 monoclonal antibodies reacted with the lipopolysaccharide-like (LPS-L) antigen and 14 reacted with the epitopes of a 120-kDa protein. Only typhus group rickettsiae reacted with the monoclonal antibodies against LPS-L. R. felis, a recently identified rickettsial species, did not react with these monoclonal antibodies, confirming that it is not antigenically related to the typhus group. Monoclonal antibodies against the 120-kDa protein were highly specific for R. prowazekii. We successfully applied a selected monoclonal antibody against the 120-kDa protein to detect by immunofluorescence assay R. prowazekii in smears from 56 wild and laboratory lice, as well as in 10 samples of louse feces infected or not infected with the organism. We have developed a simple, practical, and specific diagnostic assay for clinical specimens and large-scale epidemiological surveys with a sensitivity of 91%. These monoclonal antibodies could be added to the rickettsial diagnostic panel and be used to differentiate R. prowazekii from other rickettsial species(Fang et al., 2002).
      3. False Negative: The negative predictive value of our test was 100%(Fang et al., 2002).
   3. Immunofluorescence :
      1. Time to Perform: unknown
      2. Description: The diagnosis of epidemic typhus was established by demonstrating increasing antibody titers from the acute to the convalescent-phase of illness, with the presence of immunoglobulin (Ig) M to R. prowazekii (micro-immunofluorescence titer IgG less than 1:80 and IgM less than 80 to IgG 1:4,096 and IgM titer 1:256) in serum samples collected 6 days apart(Niang et al., 1999).
   4. Microimmunofluorescence test :
      1. Time to Perform: unknown
      2. Description: A microimmunofluorescence test was used to study antibody responses to various spotted fever group and typhus group rickettsiae during Rocky Mountain spotted fever (RMSF) and epidemic typhus (ET). Patients with RMSF reacted most strongly to Rickettsia rickettsii; those with ET reacted predominantly to R. prowazekii. The degree of cross-reaction to other rickettsial strains varied from patient to patient, but a particular pattern of cross-reaction was consistently observed in serial sera from the same patient(Philip et al., 1976).
      3. False Positive: Cross-reactions of varying degree sometimes occurred to antigens both within and between the spotted fever and typhus group(Philip et al., 1976).
2. Immunoassay Test:
   1. Haemagglutination assay for endemic and epidemic typhus :
      1. Time to Perform: unknown
      2. Description: A latex test for assay of antibodies to endemic and epidemic typhus rickettsiae is simple, group-specific, sensitive, and reproducible. Cross-reactivity within the typhus group was extensive(Hechemy et al., 1981). Endemic typhus infection cannot be serologically differentiated from epidemic typhus by latex or micro-IF procedures(Hechemy et al., 1981).
   2. Complement-fixation :
      1. Time to Perform: unknown
      2. Description: Sera from patients suspected of having rickettsial infections were tested in the complement fixation test with antigens prepared from the rickettsiae of Rocky Mountain spotted fever (SF), rickettsial pox (RP), murine typhus, epidemic typhus, and from Rickettsia canada (RC). Eight units of antigen were used in all cases and two units in man. Only those patients with antibody titers of 1:16 or higher were included in the study. Largely on the basis of comparative titers, the patients were divided into two groups: 102 with SF and 35 with infections by one of the members of the typhus group. The antibody titers were higher with SF antigen than RP antigen in 72% of the SF patients, and in only two SF patients was the RP titer higher, and then by only one tube (twofold dilution). There seemed little advantage in including the RP antigen in the battery of rickettsial antigens. Cross-reaction with at least one of the typhus antigens was observed in the sera from 64% of the SF patients. It was extensive enough to be confusing (within one tube) in 17% with eight units of antigen, but the differentiation was more distinct with two units of antigen. The cross-reaction with typhus antigens was as frequent in children with SF as it was in adults; thus, it is unlikely that these cross-reactions resulted from previous typhus vaccination. The serological differentiation between murine typhus and epidemic typhus was frequently difficult, but the epidemiological background was distinct. Five patients had higher titers to RC antigen, and four of these may possibly have had RC infections(Shephard et al., 1976). Antibody titers obtained by the CF test correlate better with IgG titers than with IgM titers obtained by immunofluorescence assay. Results vary according to the method of antigen production and the amount of antigen used in the assay. The use of 8U of antigen increases the sensitivity of detection of the early IgM response but also increases the numbers of cross-reactions between antibodies to typhus and SFG rickettsiae(La Scola and Raoult, 1997).
   3. Enzyme-linked immunosorbent assay :
      1. Time to Perform: unknown
      2. Description: Enzyme-linked immunosorbent assay (ELISA) was first introduced for detection of antibodies against Rickettsia typhi and Rickettsia prowazekii. The use of this technique is highly sensitive and reproducible, allowing the differentiation of IgG and IgM antibodies(La Scola and Raoult, 1997).
   4. Western blotting :
      1. Time to Perform: unknown
      2. Description: Differentiation of murine typhus due to Rickettsia typhi and epidemic typhus due to Rickettsia prowazekii is critical epidemiologically but difficult serologically. Using serological, epidemiological, and clinical criteria, we selected sera from 264 patients with epidemic typhus and from 44 patients with murine typhus among the 29,188 tested sera in our bank. These sera cross-reacted extensively in indirect fluorescent antibody assays (IFAs) against R. typhi and R. prowazekii, as 42% of the sera from patients with epidemic typhus and 34% of the sera from patients with murine typhus exhibited immunoglobulin M (IgM) and/or IgG titers against the homologous antigen (R. prowazekii and R. typhi, respectively) that were more than one dilution higher than those against the heterologous antigen. Serum cross-adsorption studies and Western blotting were performed on sera from 12 selected patients, 5 with murine typhus, 5 with epidemic typhus, and 2 suffering from typhus of undetermined etiology. Differences in IFA titers against R. typhi and R. prowazekii allowed the identification of the etiological agent in 8 of 12 patients. Western blot studies enabled the identification of the etiological agent in six patients. When the results of IFA and Western blot studies were considered in combination, identification of the etiological agent was possible for 10 of 12 patients. Serum cross-adsorption studies enabled the differentiation of the etiological agent in all patients. Our study indicates that when used together, Western blotting and IFA are useful serological tools to differentiate between R. prowazekii and R. typhi exposures. While a cross-adsorption study is the definitive technique to differentiate between infections with these agents, it was necessary in only 2 of 12 cases (16.7%), and the high costs of such a study limit its use(La Scola et al., 2000).
      3. False Positive: When both IFA and Western blot results were considered, exposure to R. prowazekii or R. typhi was reliably determined for 10 of the 12 patients(La Scola et al., 2000).
   5. Immunoblotting :
      1. Time to Perform: unknown
      2. Description: In order to identify Rickettsia prowazekii in lice, we developed a panel of 29 representative monoclonal antibodies selected from 187 positive hybridomas made by fusing splenocytes of immunized mice with SP2/0-Ag14 myeloma cells. Immunoblotting revealed that 15 monoclonal antibodies reacted with the lipopolysaccharide-like (LPS-L) antigen and 14 reacted with the epitopes of a 120-kDa protein. Only typhus group rickettsiae reacted with the monoclonal antibodies against LPS-L. R. felis, a recently identified rickettsial species, did not react with these monoclonal antibodies, confirming that it is not antigenically related to the typhus group. Monoclonal antibodies against the 120-kDa protein were highly specific for R. prowazekii. We successfully applied a selected monoclonal antibody against the 120-kDa protein to detect by immunofluorescence assay R. prowazekii in smears from 56 wild and laboratory lice, as well as in 10 samples of louse feces infected or not infected with the organism. We have developed a simple, practical, and specific diagnostic assay for clinical specimens and large-scale epidemiological surveys with a sensitivity of 91%. These monoclonal antibodies could be added to the rickettsial diagnostic panel and be used to differentiate R. prowazekii from other rickettsial species(Fang et al., 2002).
      3. False Negative: 9%(Fang et al., 2002).
   6. Weil-Felix test :
      1. Time to Perform: unknown
      2. Description: The Weil-Felix test is based on the detection of antibodies to various Proteus species which contain antigens with cross-reacting epitopes to antigens from members of the genus Rickettsia with the exception of R. akari. Whole cells to Proteus vulgaris OX-2 react strongly with sera from persons infected with SFG rickettsia with the exception of those with RMSF, and whole cells of P. vulgaris OX-19 react with sera from persons infected with typhus group rickettsiae as well as with RMSF(La Scola and Raoult, 1997). By the Weil-Felix test, agglutinating antibodies are detectable after 5 to 10 days following the onset of symptoms, with the antibodies detected being mainly of the immunoglobulin M (IgM) type(La Scola and Raoult, 1997). The poor sensitivity and specificity of the Weil-Felix test are now well demonstrated for the diagnosis of RMSF, MSF, murine typhus, epidemic typhus, and scrub typhus. Although a good correlation between the results of the Weil-Felix test and detection of IgM antibodies by an immunofluorescence assay is often observed, with the development of techniques that are used to grow rickettsiae, this test should be used only as a first line of testing in rudimentary hospital laboratories(La Scola and Raoult, 1997). In most hospitals the laboratory diagnosis of RMSF is synonymous with the archaic, nonspecific, insensitive Weil-Felix test. Early in this century, the agglutination of certain strains of Proteus vulgaris by sera of patients convalescent from typhus fever was recognized. This phenomenon depends on antigens shared by P. vulgaris OX-19 and OX-2 and R. prowazekii, R. typhi, R. rickettsii, R. conorii, R. sibirica, and R. australis. Between 5 and 12 days after onset of symptoms, antibodies appear that agglutinate P. vulgaris OX-19 in 70% of patients and agglutinate P. vulgaris OX-2 in 47%. In addition to this poor level of sensitivity, another drawback is lack of specificity. Many healthy persons have agglutinating antibodies to P. vulgaris OX-19(Walker, 1989).
3. Nucleic Acid Detection Test: