Medical bacteriology Rickettsiaceae SlideShare

Medical bacteriology Rickettsiaceae

1. Vivekanandha arts and science college for women, veerachipalayam , sankagiri , salem – 637303. Affiliated to Periyar University , Salem; Recognised Under section 2(f)& 12(b) of UGC act,1956. SUBJECT INCHARGE , Dr. R.MYTHILI RAVICHANDRAN , HEAD OF THE DEPARTMENT , DEPARTMENT OF MICROBIOLOGY , VIIAS , SANKAGIRI. S UBMITTED BY , Ms.K.NATHIYA KUMAR , III Bsc . MICROBIOLOGY , DEPARTMENT OF MICROBIOLOGY , VIAAS , SANKAGIRI . SUBJECT : MEDICAL BACTERIOLOGY TOPIC : RICKETTSIAL

2. RICKETTSIACEAE - FAMILY ( Rickettsial )

3. FAMILY RICKETTSIACEAE The Rickettsiae are primarily parasitic in arthropods such as fleas,lice,ticks,and mites,in which the organisms propagate without producing any disease. Many rickettsial species are maintained in their natural hosts (arthropods) by transovarian transmission except in case of R.prowazekii , which kills its host –human body louse Pediculus humanus . The family Rickettsiaceae is named after Howard Ricketts who discovered spotted fever rickettsia (1906), who ultimately died of typhus in Mexico City during studies. The distribution of rickettsial diseases is dependent on distribution of arthropods host/vector. Tick-borne infections (spotted fevers) have a restricted geographical distribution, whereas infections transmitted with other vectors such as lice ( R.prowazekii ),fleas ( R.typhi ) ,and mites ( R.akari and O.tsutsugamushi ), are worldwide in distribution.

4. Major pathogenic species of Genera Rickettsiae and Table (Table 1)

5. It smears from infected tissues, Rickettsiae appear as pleomorphic cocobacilli either as short rods (0.3×1 to 2μm) non- mobile, noncapsulated and Gram- negative,through they stain poorly. The organisms stain bluish purple with Giemsa and Castaneda stains, while with Macchiavello and Gimnez stain they appear deep red in marked contrast to the blue staining of tissue cell cytoplasm. They are Gram negative rod. (Fig.1) Electomicrograph of R.prowazekii in experimentally infected tissue. Note The double –layered cell ( with Macchiavello stain) Morphology

6. Cultivation They grow readily in yolk sacs of embryonated egg and many strains also grow also on cell culture. The Optimum temperature for growth is 32°C-35°C 1.Yolk sac inoculation: They are cultivated in yolk sac of developing chick embryo. 2. Tissue culture : They grow on mouse fibroblast,Hela.HEp2,Detroit 6 and other continuous cell lines. Multiplication occurs by binary fission but slow (generation time,9-12 hrs at 34°C). The Rickettsiae continuous multiplying within the cell until it is copletely packed with organisms and bursts in contrast, O.tsutsungamushi are continually released from cells through long cytoplasmic projections.

7. Resistance Rickettsiae are readily destroyed at 56°C. They survive only briefly outside a host (reservoir or vector) and multiply only interacellularly . Rickettsiae become noninfectious with 1% Lysol, 2% formaldehyde,5% H2O2 , 70% ethanol and hypochlorite solution.

8. Antigenic structure Rickettsiae are prokaryotic cells having a typical double –layered Gram-negative cell wall. There are three types of antigens: 1.Surface protein antigens (SPA): SPA of R.prowazekii and R.typhi possess both species specific and cross-reactive antigenic epitopes. 2.Outer membrane protein: Rickettsiae of spotted fever group possess dominant outer membrane proteins (OMP)A and B.OMP-A is species –specific and act as adhesion. OMP-B exhibits limited cross –reaction with SPA of R.typhi . 3.Surface alkali-stable polysaccharide antigen: found in some rickettsial strains is the third surface antigen of Rickettsiae which is shared by certain strains of Proteus bacilli. This forms the basis of Weil- Felix reaction used for the diagnosis of rickettsial infections where the heterophile agglutinins are demonstrated by Proteus strains –OX19,OX2,and OXK.

9. Pathogenesis The Rickettsiae are generally transmitted to human beings, by infected arthropod vectors either through their bite or when the insect faeces is rubbed,or such insect is crushed into abraded skin at the site of bite. The organisms grow readily within the body of the vector ( louse,tick , and mite) after blood meal from infected men. Rickettsia species have an affinity for endothelial cells. The organisms appear to mobilise host cell actin fibrils which facilitate their exit into adjacent cells just like that of the genus Listeria.

10. Pathogenesis flow chart

11. Laboratory diagnosis of Rickettsiae Laboratory diagnosis of Rickettsiae : A. Bacteriological investigations: Laboratory diagnosis of rickettsial diseases is made either by isolation of the organisms,by detection of rickettsial antigen,or by serologic detection of antibodies. Specimen: Whole blood or emulsified blood clot in the early phase of disease. Culture and isolation: Isolation of Rickettsia is not only difficult and dangerous for laboratory personnel,but also cumbersome. The inoculated animal has to be observed for 3-4weeks. These methods are now supplanted by cell culture technique except for O.tsutsugamushi which is isolated by intraperitoneal inoculation of mice. The organisms grow well on Vero cell MRC 5 cell cover slip cultures within 3-5days. Direct detection of rickettsial antigen: Direct detection of antigen in clinical samples is is useful: (I) Direct immunofluorescent staining (ii) P.C.R

12. Cont . B.Serological tests: The serological test that has been most commonly commonly used in diagnosis of rickettsial diseases is the Weil-Felix test that relies on heterophile antigen. 1.Weil-Felix agglutination reaction : Table 2:

13. Cont. The agglutinins usually appear as early as 5 to 7 days after infection and generally reach peak titres of up to 1000 or 5000 by the end of second week or third week. 2.Specifc serological tests include : (a) Latex agglutination tests,now available commercially, are useful in diagnosis of Rocky Mountain spotted fever (RMSF). (b) Indirect immunofluorescence and complement fixation tests are most widely used. The rise of antibody titres should be demonstrated in paired samples. (c)PCR helps to diagnose RMSF and other diseases.

14. Control General measures Pasteurisation of milk Vaccination Chemoprophylaxis

15. Diseases Rocky Mountain spotted fever (RMSF)
Typhus (Epidemic and Endemic) Rickettsialpox Boutonneuse fever (Mediterranean spotted fever)
Queensland tick typhus
Japanese spotted fever
Oriental spotted fever

16. Common symptoms 1. Fever
2. Headache
3. Rash (often spotted or maculopapular )
4. Nausea and vomiting
5. Abdominal pain
6. Myalgia (muscle pain)
7. Arthritis

17. Treatment Since the infection is mainly intracellular, antibacterial agents must be able to penetrate mammalian cells . These drugs of choice in majority of rickettsial diseases are doxycycline. Tetracycline or chloramphenicol is an alternative drug for treatment.

18. Vaccines from rickettsial

19. Prevention Avoid tick, flea, and lice bites
Wear protective clothing
Use insect repellents Conduct regular tick checks

20. Reference Textbook of Microbiology – Chakraborty.