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Rickettsia
The disease and Panbio product training
Infectious Agent
• Rickettsia sp.
– Gram-negative coccoid or rod-shaped bacteria
– Obligate intracellular bacteria with an ability to grow in a
variety of eukaryotic cells
– Do not survive well outside their host environment
– Different species cause different diseases
Infectious Agent cont...
• The Rickettsia are subdivided into three groups of
species according to the type of clinical disease they
cause:
– Typhus Group
– Spotted fever Group
– Scrub typhus Group
• They are further subdivided according to host and
arthropod vector.
Infectious Agent cont...
• Spotted Fever Group
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–
–
–
R. australis
R. rickettsii (Rocky Mountain spotter fever)
R. conorii (Mediterranean spotted fever)
R. sibirica
• Typhus Group
– R. prowazekii (Louse-borne typhus)
– R. typhi (Murine typhus)
• Scrub Typhus Group
– Orientia tsutsugamushi
Epidemiology
• Occurrence worldwide
– Epidemic and endemic regions
• Mode of Transmission
– Ticks, mites, and fleas
Distribution: Spotted fever group
Distribution: Typhus group
Distribution: Scrub typhus group
Clinical: Scrub Typhus
• Clinical manifestations:
–
–
–
–
–
–
fever
headache
raised ulcer (eschar)
rash (later in illness)
myalgia
lymphadenopathy
Eschar
Clinical: Scrub Typhus
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•
•
•
•
•
Mortality rates 60% in untreated virulent strains
23% of all fever in endemic regions of Asia
Antigenic diversity of strains exists within this group
Vector - larval trombiculid mites (chiggers)
Host - native rat species
Incubation - 7 to 14 days
Chigger infected foot
Clinical: Spotted Fever
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•
•
•
•
Vector - predominantly tick borne
Host - rats, bandicoots
Incubation - 5 to 7 days
Common protein antigens with Typhus
Benign course of infection common, mortality rate of
35% for RMSF
• Reactivation may occur
Clinical: Typhus Group
• R. prowazekii
– Vector - body louse
– Incubation - 8 to 12 days
– Brill-Zinsser typhus (reactivation)
Clinical: Typhus Group
• R. typhi (Murine/endemic typhus)
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–
–
–
–
R. typhi also known as R. mooseri
Vector - oriental rat flea
Self-inoculation, flea faeces & bites
Non-specific clinical manifestations
Low mortality rate
Life cycle of Rocky Mountain spotted fever,
rickettsial pox and murine typhus.
•
A. Life cycle of Rickettsia
rickettsii in its tick and
mammalian hosts.
•
B. Rickettsia akari life
cycle.
•
C. Rickettsia typhi life
cycle.
Azad A.F. & C.B. Beard (1998) Rickettsial Pathogens and Their Arthropod Vectors. Emerg. Infect. Dis.4:179-186
Area where murine typhus is a
risk
Areas in which murine typhus poses a risk according to seroepidemiologic
studies, case series, or
imported cases in traveller.
Parola, P. (1998) Murine typhus in travelers returning from
Indonesia. Emerg. Infect. Dis. 4:677-680.
Clinical notes
• Prevention
– Use of mite repellents to exposed skin surfaces
– Elimination of mites from populated areas
– Doxycycline has been found to be an effective preventative
measure in a small Malaysian trial
– An effective vaccine is yet to be developed
• Treatment
– Doxycycline
Antibody response
• Antibody levels may be low or absent during early
infection.
• Antibody response may be delayed or eliminated in
some patients being treated with antibiotics.
• Elevated or rising IgM and/or IgG antibodies indicate
recent or active infection.
• Infection results in prolonged immunity to homologous
strain.
• During a period of months after primary infection,
infection with heterologous strain will result in mild
disease.
Diagnosis
• Weil Felix
– OX-19 (Typhus)
– OX-K strain Proteus mirabilis (Scrub Typhus)
• Dot blot EIA (Dip-S-Ticks from Panbio)
• IFA (Gold Standard)
• Agglutination based assays
– indirect haemagglutination (IHA)
– latex agglutination (LA)
• ELISA
Weil Felix
• Non-specific test that uses various Proteus spp.
• Test based on presence of common antigens in both
the Rickettsia and Proteus spp.
• Lacks both sensitivity and specificity & should no
longer be used as better methods available
• Leptospirosis and some other febrile illnesses may
cause a positive Weil-Felix reaction
• Re-infection does not always lead to a rise in WeilFelix agglutinins
Agglutination-based assays
• Indirect haemagglutination (IHA) & latex agglutination
(LA)
• Detect antibodies to Spotted fever and Typhus group.
• Uses solubilised antigen from purified rickettsiae
absorbed onto untreated red blood cells.
• Detects IgG and IgM
Panbio Dip-S-TickTM
• Panbio Dipsticks (Dot EIA) for:
– R. typhi (Murine typhus) Total IgG
– R. rickettsii (RMSF) Total IgG
– R. conorii Total IgG
• Principle:– specific antibodies if present in patient’s serum bind to the
antigen spotted on membrane
– reaction visualised by addition of alkaline phosphataseconjugated anti-human antibodies which is then reacts with
enzyme substrate reagent to form a spot.
Panbio IFA
• Excellent sensitivity & specificity
• Panbio has IFA slides for the following:– Typhus group
• Murine Typhus (R. typhi)
• Louse-borne typhus (R. prowazekii)
– Scrub Typhus Group
• Scrub Typhus (O. tsutsugamushi)
– Spotted Fever Group
• Rocky Mountain Spotted Fever (R. rickettsii)
• Mediterranean Spotted Fever (R. conorii)
Panbio IFA
Panbio Rickettsial ELISA kits
Scrub Typhus Group IgG
Cat # E-RST01G
Scrub Typhus Group IgM
Cat # E-RST01M
• Fast - 1.5 hours total assay time
Spotted Fever Group IgG
Cat # E-RSF01G
Spotted Fever Group IgM
Cat # E-RSF01M
• Fast - 1.5 hours total assay time
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