Rickettsiae
Introduction
- This family consist of 3 genera –
- Rickettsia
- Orientia
- Ehrlichia
Morphology
- Gram negative
- Pleomorphic coccobacilli
- Obligate intracellular organisms
- Non motile
- Non capsulated
- Stain bluish purple with Giemsa and Castaneda stains
- Stain deep red with Machiavella and Gimenez stains
Culture
- Rickettsiae are unable to grow in cell free media.
- Exception to this rule, R. Quintana
- Growth generally occurs in the cytoplasm of infected cells.
- In case of spotted fever, growth may take place in the nucleus as well.
Ricketsiae are cultivated in –
- Yolk sac of developing chick embryo.
- Mouse fibroblast
- Continous cell lines -4 HeLa, HEP-2, Detroid-6
- Tissue cultures are not satisfactory.
- Guinea pigs and mice are useful for isolation.
Rickettsial Diseases
| Disease | Rickettsial agent | Insect vector | Mammalian reservoir |
| Typhus group | |||
| Epidemic typhus | R. prowazekii | Louse | Human |
| Murine (Endemic)typhus | R. typhi | Rat flea | Rodent |
| Scrub typhus | R. tsutsugamushi | Mite’ | Rodent |
| Spotted fever group | |||
| Indian tick typhus | R. conorii | Tick* | Rodent , Dogs |
| Rocky mountain spotted fever | R. rickettsii | Tick* | Rodent , Dogs |
| Rickettsial pox | R. akari | Mite* | Mice |
| Others | |||
| Q fever | C. burnetii | Nil | Cattle, sheep, goat |
| Trench fever |
Rochalemaea
Quintana |
Louse | Human |
lmportant Points:
- Most severe
- Rocky mountain spotted fever
- Most mildSymptoms
- Rickettsia pox
- fever
- headache
- malaise
- Prostration
- skin rash
- (except in Q fever)
- hepatosplenogy
- Amongst the typhus group, lymphadenopathy is seen only in scrub typhus.
Rash is seen in
- Epidemic typhus
- Endemic typhus
- Scrub typhus
- Rocky Mountain spotted fever
- Indian tick typhus
Lymphadenopathy is seen in
- Scrub typhus
- Rickettsial pox
Eschar is seen in
- Scrub typhus
- Rickettsialpox
- Indian tick typhus
Mortality
- Associated with a high morbidity and mortality.
- 20% of Rocky Mountain Spotted fever
- 30% for epidemic typhus.
- Enter the human body
- Multiply locally and enter the blood.
- Become localized chiefly in vascular endothelial cells
- Which enlarge, degenerate and cause thrombus formation
- Partial or complete occlusion of the vascular lumen
- The overall pathological features of the rickettsial diseases are due to the damage of vascular endothelium.
Neil – Mooser or tunica reaction
| Positive | R. typhi, R. conori, R.akari |
| Negative | R. Prowazekii |
Weil felix reaction
- This reaction is an agglutination test in which sera are tested for agglutinins to 0 antigens of certain nonmotile proteus strains OX -19, OX – 2 and OX – K.
- The basis of the test is the sharing of an alkali – stable carbohydrate antigen by some rickettsiae and by certain strains of proteus, P. vulgaris OX – 19 and OX – 2 and P. mirabilis OX – K.
| OX 19 | ln epidemic and endemic typhus |
| OX-2 | In rocky mountain spotted fever |
| OKX | In scrub typhus |
| No value | Q fever, Trench fever, Rickettsial pox |
| False positive | Typhoid, liver diseases, Proteus infection Pseudomonas,Borelia,S. typhi |
Treatment
- Tetracyclines (e.g., doxycycline are DOCs)
Exam Important
Morphology
- Gram negative
- Pleomorphic coccobacilli
- Obligate intracellular organisms
Culture
- Rickettsiae are unable to grow in cell free media.
- Exception to this rule, R. Quintana
- Can be cultivated in Mouse fibroblast
Rickettsial Diseases
- Rickettsia tsutsugamushi is a small gram-negative, obligate intracellular organism causing scrub typhus
- Rickettsial pox is caused by Rickettsia akari
- ‘Louse’ is the insect vector for Rickettsia prowazekii.
- Rickettsial pox, caused by Rickettsia akari, is transmitted to humans by the house mouse mite Liponyssoides sanguineus.
Important Points:
- Most severe
- Rocky mountain spotted fever
- Most mildSymptoms
- Rickettsia pox
- fever
- headache
- malaise
- Prostration
- hepatosplenogy
Rash is seen in
- Epidemic typhus
- Endemic typhus
- Scrub typhus
- Rocky Mountain spotted fever
- Indian tick typhus
Lymphadenopathy is seen in
- Scrub typhus
- Rickettsial pox
Eschar is seen in
- Scrub typhus
- Rickettsialpox
- ndian tick typhus
Mortality
- 20% of Rocky Mountain Spotted fever
- 30% for epidemic typhus.
- Become localized chiefly in vascular endothelial cells
- The overall pathological features of the rickettsial diseases are due to the damage of vascular endothelium.
Weil felix reaction
- This reaction is an agglutination test in which sera are tested for agglutinins to 0 antigens of certain nonmotile proteus strains OX -19, OX – 2 and OX – K.
| OX 19 | ln epidemic and endemic typhus |
| OX-2 | In rocky mountain spotted fever |
| OKX | In scrub typhus |
| No value | Q fever, Trench fever, Rickettsial pox |
| False positive | Typhoid, liver diseases, Proteus infection Pseudomonas,Borelia,S. typhi |
Treatment
- Tetracyclines (e.g., doxycycline are DOCs)
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