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Medical Microbiology and Virology > 28 Vector-borne infections - bacteria > Flashcards

28 Vector-borne infections - bacteria Flashcards

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Biology 101 flashcards USMLE® Step 1 flashcards
1
Q

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?

A

Fever
headache
rash

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2
Q

How to diagnose rickettsial infection?

A

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

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3
Q

What is treatment of rickettsia infection?

A

All susceptible to tetracyclines

Prevention relies on reducing exposure to vector

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4
Q

What diseases are causes by these rickettsia?

R rickettsii

R akari

R conorii

R prowazekii

R typhi

Orientia tsutsugamushi

A

R rickettsii - RMSF

R akari - Rickettsial pox

R conorii - Mediterranean spotted fever

R prowazekii - Epidemic typhus

R typhi - Endemic typhus

Orientia tsutsugamushi - Scrub typhus

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5
Q

What are arthropod vectors for these rickettsia?

R rickettsii - RMSF

R akari - Rickettsial pox

R conorii - Mediterranean spotted fever

A

R rickettsii - RMSF - tick

R akari - Rickettsial pox - mite

R conorii - Mediterranean spotted fever - tick

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6
Q

What are arthropod vectors for these rickettsia?

R prowazekii - Epidemic typhus

R typhi - Endemic typhus

Orientia tsutsugamushi - Scrub typhus

A

R prowazekii - Epidemic typhus - louse

R typhi - Endemic typhus - flea

Orientia tsutsugamushi - Scrub typhus - mite

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7
Q

Which rickettsial diseases are transmitted by these vectors?

Tick

Mite

Louse

Flea

A

Tick -
RMSF
Mediterranean spotted fever

Mite -
Rickettsial pox
Scrub typhus

Louse -
Epidemic typhus

Flea -
Endemic typhus

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8
Q

Where is geographical distribution of Typhus?

Epidemic
Endemic
Scrub

A

Epidemic -
Africa
SA

Endemic -
Worldwide

Scrub -
Far East

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9
Q

RMSF has mortality of 10%. Incubation period for 1 week. Eschar may be seen

What are symptoms?

A 
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

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10
Q

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?

A

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

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11
Q

How is endemic typhus different to epidemic typhus?

A

Milder disease

transmitted by rat flea

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12
Q

What is the cause of relapsing fever?

How is it transmitted?

A

Borrellia recurrentis - gram negative spirochete

Epidemic - louse
Endemic - tick

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13
Q

Relapsing fever - bacteria multiply locally, and enter blood. Incubate for 3-10 days

What are symptoms?

A

Fever for 3-5 days, then afebrile for a week

Keeps repeating, usually with diminishing severity

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14
Q

How is borrelia recurrentis able to repeatedly infect and cause fever?

A

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

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15
Q

How to diagnose relapsing fever?

A

Antibodies present after 1 week

PCR

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16
Q

What is treatment of relapsing fever?

A

tetracycline

can cause Jarisch-Herxheimer reaction, with worsening of fever, rigors, hypotension. Treat with steroids/ paracetamol

17
Q

Lyme disease cause by -

Borrelia burgdorferi - most common species USA
Borrelia afzelii/ garinii - most common species Europe

How is it transmitted?

A

Ixodes tick

More common to bite from spring-autumn

18
Q

What are symptoms of lyme disease?

early

late

A

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

19
Q

How does lyme disease evade immune system?

A

antigenic variation

evade complement

20
Q

How to diagnose lyme disease?

A

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

21
Q

What is treatment of lyme disease?

A

Doxycycline 21 days for early disease
amoxicillin/ azithromycin alternatives e.g children <9

Ceftriaxone IV 28 days if late disease

22
Q

Patient tests negative at 6 weeks for lyme by ELISA.

What other testing should be offered?

A

If symptoms persist >12 week total, with negative ELISA, offer immunoblot

This in theory means most patients should be offered immunoblot

23
Q

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.

A

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.

24
Q

Why are zoonotic diseases increasing?

A

Ecology change - deforestation/ mining/ global warming

urbanisation

travel

breakdown of public health services - increasing population

human behavior - food habits/ animal markets, religious practice, conflict

25
Q

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
A

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

26
Q

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
A

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

27
Q

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
A

Q fever

lambing season

Coxiella serology at NNUH
PCR for diagnosis at reference lab

Requires CXR/ ECHO

28
Q

Rickettsia has small window of bacteraemia, how does this affect diagnostic testing?

A

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

Medical Microbiology and Virology (60 decks)

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