Bacteria 10 (intracell.): Rickettsial Infections Flashcards
Which different types of rickettsial infections are there?
Zoonoses caused by intracellular gram negative bacilli. There are many types of Rickettsiae that can infect humans causing typhus.
- Lice transmit Epidemic Typhus: Rickettsia Prowazekii 2. Mites transmit Scrub typhus: Orientia Tsutsugamushi 3. Ticks transmit Tick-typhus (Spotted Fever) e.g. Rickettsia Africae
- Fleas transmit Endemic Typhus: Rickettsia Typhi
Morphology of lice, flea, ticks and mites?
Summary epidemiology, transmission, clinical features, diagnosis, treatment and prevention of louse-borne epidemic typhus?
Louse-borne typhus (epidemic typhus, famine sickness, camp fever) is transmitted to man when the infected faeces of human lice, especially of P. humanus, are rubbed into broken skin or on to intact mucus membranes, e.g. conjunctiva. The louse deposits the faeces during the 15 minutes it takes to have a blood feed.
The disease is not transmitted by the bite of the louse.
Those with typhus seldom have lice on their body or clothes. This is due to the fact that once the Rickettsiae have multiplied sufficiently in the louse they rupture the intestinal epithelium and the louse dies in 8–12 days.
The Weil-Felix reaction (not the Widal Test) may be strongly positive in cases of typhus. This test relies on a cross-reaction between the O antigens of Proteus in the test reagent and generic rickettsial antibody. but the diagnostic standard is PCR.
Vector: human body louse – Pediculus Humanus Corporis • Mostly seen in Africa and South America
- Transmission via infected faeces of the louse is scratched into the bite.
- Seen in overcrowded, under-nourished populations e.g. refugees. Can cause epidemic outbreaks.
- Clinical features:
o No eschar
o Fever, myalgia, headache, conjunctivitis, delirium
o Rash appears on 3rd/4th day – usually central and macular o Subsequent pneumonia/meningitis/myocarditis o High untreated mortality
• Diagnosis
o PCR
- Treatment o Doxycycline 200mg OD for 1/52
- Prevention
o DDT disinfection in epidemics
o Prophylaxis Doxy 200mg stat
o Washing/boiling/disposing of clothes/bedding, etc.
Summary epidemiology, transmission, clinical features, diagnosis, treatment and prevention of Scrub Typhus?
Vector: Chiggers (larval Mites): Trombiculidae, seen in Asia/SE Asia/Oceania
• Clinical Features
o Small eschar at the site of the bite
o Abrupt fever, headache, myalgia, delirium as for louse-typhus
o Rash as for louse-typhus
o There may be hepatosplenomegaly and lymphadenopathy
o There can be pneumonia and myocarditis
o Lower mortality then for louse-typhus
- Diagnosis: clinical
- Treatment: as above but Doxy is the most effective and first line
The disease is transmitted by the bites of the larval stage of trombiculoid mites (chiggers). These mites live in scrub-land and in tall grassy plains and are mainly found in a triangle having as its base a line drawn from SE Asia to Australia and having the north of Japan as its apex.
Headache was present in 100% of cases in three series involving over 1000 patients from 1945 to 1998. Fever was the next commonest finding followed by adenopathy, hepatosplenomegaly and eschar.
Serology for Orientia tsutsugamushi, the causative organism, permits a definitive diagnosis*.
Clinically the presence of a painless eschar (3-6mm) and a transient rash are excellent pointers to the diagnosis. The Weil-Felix reaction is of little use in this regard.
Most cases of scrub typhus resolve spontaneously, and although fatalities are not unknown, it is a far less dangerous condition than louse-borne typhus.
Treatment with doxycycline or chloramphenicol is generally very successful.
* Orientia tsutsugamushi is an obligate intracellular gram-negative bacterium. It is the cause of scrub-borne typhus. It is no longer included in the genus Rickettsia but in the genus Orientia. Orientia tsutsugamushi was formerly called Rickettsia orientalis or R. tsutsugamushi.
Summary epidemiology, transmission, clinical features, diagnosis, treatment and prevention of flea-borne typhus?
similar to scrub typhus
Plague flea, rat flea: xenopsylla cheopis
Murine typhus is also called endemic typhus, jail fever and flea typhus. It is distributed widely throughout the world in conditions of poverty, overcrowding and unhygienic living standards. Rickettsia typhi is the causative organism.
Infection in man chiefly occurs infected rat fleas when their faeces are scratched into the skin or rubbed into the eye.
Cat and mouse fleas are sometimes responsible and occasionally fleas from opossums, raccoons and skunks are involved. It is also probably true, that on rare occasions, the bite of a rat can cause direct transfer of R. typhi to man.
Infected fleas do not die from R. typhi. Instead they transmit the organism to rats, in which they multiply enormously, so that a large rat reservoir is maintained.
Infected rats in turn transmit R. typhi to other fleas so contributing to an ever-increasing quantum of virulent organisms.
The clinical disease is generally mild, but on rare occasions, death can occur. This actually happened to a lady from the UK who, after returning from a holiday in Spain, complained of high fever, headache, photophobia and neck stiffness.
The diagnosis was only made at post-mortem.
Summary epidemiology, transmission, clinical features, diagnosis, treatment and prevention of tick bite fever?
Most common type is Rickettsia Africae
- Transmitted by various forms of hard tick (often amongst hikers/campers/safari)
- There are various forms: o Rocky Mountain spotted fever: rickettsia rickettsii (USA) – no eschar, can be severe with 25% mortality untreated.
o Mediterranean spotted fever: rickettsia conorii
o Siberian tick typhus
o Queensland tick typhus
- Clinical Features: like mild scrub typhus with eschar/fever/rash, complications and mortality are rare in most forms of tick typhus.
- Diagnosis: clinical usually, positive rickettsia serology usually after acute illness.
- Treatment: often not required but as for the others.
ATBT is far less serious than either louse-borne or mite-borne scrub typhus. Over 80% of cases occur in Africa with most of these south of the Sahara. Indeed several cases have been reported recently in Ethiopia.
Several hard-tick species, e.g. Amblyomma, Dermacentor spp. act as vectors*. Unlike Ixodes these species remain only a short time with the human host.
Fever and an eschar occur in over 90% of cases followed by rash, headache, regional lymphadenitis and arthralgia in that order.
Nowadays Rickettsia africae is the prime cause of African tick-borne typhus, displacing the closely related Rickettsia conori. Dogs, rodents and wild animals, e.g. hippopotamus, act as reservoirs.
* Like other hard-ticks they lack the coxal organs, which are so typical of soft ticks.
MCQ: Recognise pediculus humanus corporis
MCQ: Recognise hard tick vs soft tick
MCQ: Recognise Xenopsylla Cheopsis (orental rat flea; plague flea)
MCQ: Recognise Pulex irritans (human flea)
MCQ: Recognise Tunga penetrans
MCQ: Recognise dog vs cat flea
MCQ: recognise chiggers/trombiculidae mite (scrub typhus)
MCQ key words
The eschar caused by Rikettsial infections is photogenic for MCQs
- Remember Epidemic Typhus does not present with eschar – keep this infection in mind if the scenario is an outbreak with fever/rash in crowded populations.
- Don’t confuse Typhus and Typhoid.
Classical presentation of ricketssial disease and usual treatment?
Recommended treatments for rickettsial illnesses are tetracycline, chloramphenicol and doxycycline.
Doxycycline is the drug of choice; it is preferred over other tetracyclines for treatment of rickettsial infections and, at such low dose and short duration, is rarely associated with staining of teeth in children younger than 8 years
Summary of different types of rickettsial infections
Scrub typhus eschar
