28 Vector-borne infections - bacteria Flashcards
Rickettsiae are a group of intracellular gram negative rods, transmitted by arthropods.
Person-person transmission does not occur
multiply in vascular endothelium to cause vasculitis in skin/ liver/ CNS
What are general symptoms of rickettsial infection?
Fever
headache
rash
How to diagnose rickettsial infection?
Serology - look for increase in antibody titre. Antibodies present 7-15 days after onset of infection
Western blot - detect specific antibodies to certain parts of rickettsia, which undergoes gel electrophoresis
PCR
What is treatment of rickettsia infection?
All susceptible to tetracyclines
Prevention relies on reducing exposure to vector
What diseases are causes by these rickettsia?
R rickettsii
R akari
R conorii
R prowazekii
R typhi
Orientia tsutsugamushi
R rickettsii - RMSF
R akari - Rickettsial pox
R conorii - Mediterranean spotted fever
R prowazekii - Epidemic typhus
R typhi - Endemic typhus
Orientia tsutsugamushi - Scrub typhus
What are arthropod vectors for these rickettsia?
R rickettsii - RMSF
R akari - Rickettsial pox
R conorii - Mediterranean spotted fever
R rickettsii - RMSF - tick
R akari - Rickettsial pox - mite
R conorii - Mediterranean spotted fever - tick
What are arthropod vectors for these rickettsia?
R prowazekii - Epidemic typhus
R typhi - Endemic typhus
Orientia tsutsugamushi - Scrub typhus
R prowazekii - Epidemic typhus - louse
R typhi - Endemic typhus - flea
Orientia tsutsugamushi - Scrub typhus - mite
Which rickettsial diseases are transmitted by these vectors?
Tick
Mite
Louse
Flea
Tick -
RMSF
Mediterranean spotted fever
Mite -
Rickettsial pox
Scrub typhus
Louse -
Epidemic typhus
Flea -
Endemic typhus
Where is geographical distribution of Typhus?
Epidemic
Endemic
Scrub
Epidemic -
Africa
SA
Endemic -
Worldwide
Scrub -
Far East
RMSF has mortality of 10%. Incubation period for 1 week. Eschar may be seen
What are symptoms?
Early - Fever myalgia severe headache respiratory symptoms
Late -
maculopapular rash, which becomes petechial. Starts on hands/ feet, then moves central
clotting defects - DIC
neurological involvement
Epidemic typhus transmitted by body louse, so associated with poverty/ war.
Bacteria replicate in louse gut, and faeces excreted on wound. Scratching wound inoculates bacteria.
What are symptoms?
Bacteria infect vascular endothelium in skin, heart, CNS, muscle, kidney
fever
headache
flu-like symptoms
meningoencephalitis - 80% cases
mortality 20-60% untreated
mortality 4% if treated
Even after treatment, can live in lymph nodes. When immunocompromised, can reactivate many years later - Brill-Zinsser disease
How is endemic typhus different to epidemic typhus?
Milder disease
transmitted by rat flea
What is the cause of relapsing fever?
How is it transmitted?
Borrellia recurrentis - gram negative spirochete
Epidemic - louse
Endemic - tick
Relapsing fever - bacteria multiply locally, and enter blood. Incubate for 3-10 days
What are symptoms?
Fever for 3-5 days, then afebrile for a week
Keeps repeating, usually with diminishing severity
How is borrelia recurrentis able to repeatedly infect and cause fever?
Antibodies form to initial infection, suppressing fever
Borrelia species then adapt, via antigenic variation on bacterial surface. Similar mechanism to trypanosomes
Endemic mortality <5%
Epidemic mortality 40% untreated/ 4% treated
How to diagnose relapsing fever?
Antibodies present after 1 week
PCR
What is treatment of relapsing fever?
tetracycline
can cause Jarisch-Herxheimer reaction, with worsening of fever, rigors, hypotension. Treat with steroids/ paracetamol
Lyme disease cause by -
Borrelia burgdorferi - most common species USA
Borrelia afzelii/ garinii - most common species Europe
How is it transmitted?
Ixodes tick
More common to bite from spring-autumn
What are symptoms of lyme disease?
early
late
Multiply locally, and after a week cause -
fever
myalgia
lymphadenopathy
erythema migrans - immune complex deposition, appears 1-4 weeks after tick bite
meningitis/ encephalitis peripheral neuropathy heart block myocarditis arthralgia - immune complexes found infected joints
Later manifestations due to immune complex deposition, and borrelia species not detectable at this stage
How does lyme disease evade immune system?
antigenic variation
evade complement
How to diagnose lyme disease?
Serology ELISA 6 weeks after tick bite
Western Blot at reference lab to confirm all positive/ equivocal results
PCR only use for synovial fluid in lyme arthritis
What is treatment of lyme disease?
Doxycycline 21 days for early disease
amoxicillin/ azithromycin alternatives e.g children <9
Ceftriaxone IV 28 days if late disease
Patient tests negative at 6 weeks for lyme by ELISA.
What other testing should be offered?
If symptoms persist >12 week total, with negative ELISA, offer immunoblot
This in theory means most patients should be offered immunoblot
What symptoms should make us consider lyme as possibility?
Do not rule out the possibility of Lyme disease in people with symptoms but no clear history of tick exposure.
fever and sweats
swollen glands
malaise
fatigue
neck pain or stiffness
migratory joint or muscle aches and pain
cognitive impairment, such as memory problems and difficulty concentrating (sometimes described as ‘brain fog’)
headache
paraesthesia.
neurological symptoms, such as facial palsy or other unexplained cranial nerve palsies, meningitis, mononeuritis multiplex or other unexplained radiculopathy; or rarely encephalitis, neuropsychiatric presentations or unexplained white matter changes on brain imaging
inflammatory arthritis affecting 1 or more joints that may be fluctuating and migratory
cardiac problems, such as heart block or pericarditis
eye symptoms, such as uveitis or keratitis
skin rashes such as acrodermatitis chronica atrophicans or lymphocytoma.
Why are zoonotic diseases increasing?
Ecology change - deforestation/ mining/ global warming
urbanisation
travel
breakdown of public health services - increasing population
human behavior - food habits/ animal markets, religious practice, conflict
77 year old attends A+E following a dog bite. Wound not deep, no signs of local infection.
Which of following conditions does not require antibiotic prophylaxis?
prosthetic heart valve diabetes wound localised to hand wound >48 hours old devitalised tissue at wound site
Wound >48 hours old
antibiotic prophylaxis recommended for all cat/ dog bites
If no signs of infection at 48 hours, unlikely to become infected
Treatment options -
co-amoxiclav or
clindamicin + cipro or
co-trimoxazole
30 year old bitten by tick over weekend. Removed tweezers, and attended GP
What action do you advise? no action required reassurance, counsel on signs of lyme lyme serology doxycycline prophylaxis two week course doxycycline
reassurance, counsel on signs of lyme
serology may only be positive at 4-6 weeks
some studies suggest tick must be present >36 hours to transfer borrelia
42 year old farmer in SW England presents in April, three weeks fever, myalgia, dry cough, fatigue. Bloods show mild transaminitis and mild thrombocytopenia
What is most likely cause?
anaplasmosis bartonella brucellosis leptospirosis Q fever
Q fever
lambing season
Coxiella serology at NNUH
PCR for diagnosis at reference lab
Requires CXR/ ECHO
Rickettsia has small window of bacteraemia, how does this affect diagnostic testing?
After infection, approximate 2 day window of bacteraemia, which then subsides, as antibody levels begin to increase (but may be undetectable).
If check during window period, PCR may be negative, and antibody may be negative (as low levels).
If high suspicion, re-send antibody test a week later, and should see response
