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Medical Microbiology and Virology > 29 Multisystem Zoonoses > Flashcards

29 Multisystem Zoonoses Flashcards

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Biology 101 flashcards USMLE® Step 1 flashcards
1
Q

Zoonoses are animal diseases, which can incidentally infect humans. Most are poorly transmitted between humans

Which VHF belong to these classes?

Arenavirus

Bunyavirus

Filovirus

A 
Arenavirus -
Lymphocytic choriomeningitis
Lassa
Machupo
Junin

Bunyavirus -
Hanta

Filovirus -
Marburg
Ebola

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2
Q

Q fever caused by Coxiella Burnetti. Called this as unknown agent, and named “query fever”

Coxiella burnetti is a rickettsia - gram neg, non-spore forming bacteria

How does it differ from other rickettsiae?

A

No transmitted by arthropods

resistant to dessication/ heat/ sunlight, so stable enough to exist in dust, and infect via inhalation

main site of action is the lung, rather than vascular endothelium. So does not cause rash

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3
Q

Who is at risk of Q fever infection?

A

Exposure to domestic/ wild animals - cattle/ sheep/ goats

vets/ farmers/ abattoir workers

unpasteurised milk

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4
Q

What is life cycle of Q fever in human?

A

Inhaled - exposure to milk/ urine/ faeces
multiplies in terminal airways of lungs

3 weeks later presents with fever, headache, and features of atypical pneumonia

Can resolve spontaneously within 2 weeks.

Can become chronic - spread to liver causing hepatitis, or spread to heart causing IE

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5
Q

How to diagnose Q fever?

A

Serology - may need to check initial and convalescent samples

PCR

Does not grow in blood cultures

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6
Q

What is treatment of Q fever?

How to prevent?

A

Doxycycline or co-trimoxazole

Pasteurise milk
Vaccine available Australia

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7
Q

Anthrax caused by Bacillus anthracis. Gram-positive rod, which is spore forming, and can survive for years in the soil

Who is infected by anthrax?

A

Primarily herbivores who are exposed to infected soil

They secrete bacilli in faeces/ urine saliva

Humans infected with direct contact with infected animals, or by direct contact with spores in animal products

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8
Q

What are two clinical pictures of anthrax infection?

A

Cutaneous - eschar forms. Can then spread to lymph nodes, and cause septicaemia in 10% cases

Pulmonary - if inhaled. LEads to pulmonary oedema, mediastinal haemorrhage . Spreads to bloodstream cusing septicaemia and death. Cannot be spread person-person

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9
Q

How to diagnose cutaneous anthrax?

What is treatment?

A

film from skin lesion - gram positive bacilli

PCR of lesion

  • Ciprofloxacin
  • 20% fatality if untreated
  • anthrax anti-toxin if septic
  • cipro can be given as post-exposure prophylaxis e.g in bioterrorism
  • vaccine available
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10
Q

Yersinia pestis causes plague. Infects rodents (rats/ squirrels/ gerbils), and spread to humans by fleas.

Bacteria causes blood to clot in gut of flea, and eventually blocks gut lumen. So flea regurgitates infected material as it attempts to feed on human

What is structure of yersinia pestis?

How does it spread between humans?

A

Gram-negative rod
antiphayocytic capsule prevents phagocytosis

Usually not transmitted person-person. If high replication in lung and bronchopneumonia “pneumonic plague”, it can then be transmitted between humans

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11
Q

How does bubonic plague occur?

A

Infecting bacteria multiply at site of entry, spread to lypmh nodes which become necrotic

bacteria then spread to blood causing septicaemia, haemorrhagic illness, with multisystem involvement - spleen/ liver/ lungs/ CNS

bubonic plague has no person-person transmission

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12
Q

Plague has 50% mortality if bubonic, and 100% if pulmonary.

How to diagnose?

A

Gram stain - lymph node biopsy (bubonic) or sputum (pneumonic)

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13
Q

What is treatment of plague?

A

Streptomycin or
doxycycline or
ciprofloxacin

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14
Q

How to prevent plague?

A

quarantine ships at ports

rodent control

isolate patients with plague

doxycycline prophlyaxis during outbreaks

vaccination of military or certain groups in endemic areas

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15
Q

Franscisella tularanesis causes tularaemia.

What is gram stain?

How is it transmitted?

A

Gram negative rod

transmitted from rodents by ticks/ mites/ lice/ flies. Usually contact of human with infected carcass

Seen in USA/ Europe. Species in USA causes more severe disease

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16
Q

What are symptoms of tularaemia?

A

Multiplies at site of entry of vector bite, and forms skin ulcer after 3-5 days. Can form rash

If inhaled - causes pneumonia , most serious manifestation

lives intracellularly in macrophages, and moves to lymph nodes - which become painful and swollen

moves to bloodstream - febrile illness

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17
Q

How is tularaemia diagnosed?

A

IFA of tissue

serology

18
Q

What is treatment of tularaemia?

Vaccine exists for high risk groups e.g fur trapper. But is not 100% effective

A

Streptomycin is primary treatment or
doxycycline or
gentamicin

19
Q

Pasteurella multocida is part of normal flora of cats/ dogs. Transmitted by bite/ scratch. Worldwide distribution

What is gram stain?

A

Gram negative rod

20
Q

What clinical infection does pasteurella cause?

A

after bite/ scratch - local multiplication causes cellulitis and lymphadenitis (also risk of anaerobe co-infection)

can become systemic and cause pneumonia

21
Q

What is treatment of pasteurella infection?

A

Co-amoxiclav
add metronidazole if concerned about anaerobe co-infection

need to clean wound first

22
Q

Leptospira interrogans is spirochete which causes leptospirosis. Have two flagella.

Many different species with many serotypes

Which animals are infected by it?

A

Rats/ mice/ voles

Can infect any mammal including dogs/ humans

23
Q

How are humans infected by leptospirosis?

A

Contaminated water/ food - usually rat urine

enter via breaks in skin or mucosa

at risk - swimmer, miners, farmer, sewage worker

bacteria present in human urine, but person-person transmission rare

24
Q

What are clinical features of leptospirosis?

A

fever and influenza type illness, which resolves spontaneously in 90% cases

can cause -
hepatitis
jaundice
AKI
aseptic meningitis

Weil’s disease - renal/ liver failure

severe cases due to damage to endothelium

25
Q

How to diagnose leptospirosis?

A

Clinical history of water exposure

serology

26
Q

What is treatment of leptospirosis?

A

Mild disease -
Doxycycline or
penicillin

Severe -
ceftriaxone

27
Q

What is cause of rat bite fever?

A

spirillum minus - gram neg spiral

streptobacillus moniliformis

both found in oropharyngeal flora of 50% healthy rats worldwide

28
Q

What are symptoms of rat bite fever?

A

incubates 7-10 days

fever
headache
myalgia
local lesion and also maculopapular rash
lymphadenopathy

Complications -
pneumonia
IE

fever may be recurrent if untreated

mortality 10% if untreated

29
Q

How to diagnose rat bite fever?

How to treat rat bite fever?

A

Culture from wound site/ lymph node/ blood

streptomycin or
penicillin or
ceftriaxone

30
Q

What is structure of bacteria which cause brucellosis?

A

Gram neg coccobacilli, adapted for itnracellular replication

Four species -
B abortus
B melitensis
B suis
B canis
31
Q

How are humans infected with brucella?

A

Consumption unpasteurised milk/ cheese

direct contact with infected animal - farmer/ vet/ abbatoir. Enters via abrasions in skin, or inhaled

Animals includes - cows/ goats/ sheep/ pigs/ dogs. Varies by country

no person-person spread

32
Q

What are clinical features of brucellosis?

A

Incubation period 2-6 weeks

Infects reticuloendothelial system - liver, spleen, bone marrow, lymphoid tissue. Bacteria survive for long time, and multiply, causing granulomatous reaction

can often be subclinical

fever - undulant
fatigue
night sweats

Rarer events -
hepatitis
osteomyelitis
IE
meningitis

long term sequale after >1 year -
fatigue
aches/ pains
anxiety/ depression

33
Q

How to diagnose brucellosis?

A

blood culture - although rare to isolate

biopsy lymph node/ bone marrow

serology - observe rising titre. Although weaker antibody response as intracellular bacteria

34
Q

What is treatment of brucellosis?

A

doxycycline + streptomycin for 6 weeks

brucella destroyed by pasteurisation

35
Q

Echinococcus are tapeworms of dogs. Eggs laid by worm are passed in faeces. Can be swallowed by sheep or humans, eggs hatch and release larvae which penetrate small intestine, and enter blood vessel. Larvae then move to liver or lung. Then grow slowly into large thick-walled fluid filled hydatid cysts

What two clinical pictures can they cause?

A

Echinococcus granulosus (cystic hydatid) - makes large cyst in liver

Echinococcus multilocularis (alveolar hydatid) - makes multilocular mass in liver, can spread to lung/ brain

36
Q

What is treatment of hydatid disease (cystic)?

A

If dead cysts - no need to aspirate

Aspirate cyst
Albendazole + praziquantel

If aspirate and fluid leaks, can cause severe anaphylactic reaction

37
Q

What is treatment of hydatid disease (alveolar)?

A

Surgically remove - can spread in liver and resemble HCC. May be inoperable

albendazole - may need lifelong therapy if inoperable

38
Q

What are symptoms of hydatid disease?

A 
Fever
abdominal bloating
diarrhoea
anaemia
cough

Symptoms may only occur 5-15 years after initial exposure

39
Q

Trichinella spiralis is transmitted in undercooked pork. Natural life cycle involves various mammals.

How are humans infected?

A

Undercooked meat (pork/ game/ horse) containing encysted infected larval stages.

Larvae multiply rapidly into adults in small intestine, then invade mucosa. Then spreads around blood stream to various organs

40
Q

What are symptoms of trichinella infection?

A

CNS - seizures

myocardium - heart failure

fever

arthralgia

eosinophilia

periorbital oedema

41
Q

How to diagnose trichinella infection?

what is treatment?

A

Muscle biopsy

serology

benzimidazoles + steroids

42
Q

38 year old welsh farmer presents 6 week history of fever, weight loss.

Blood culture neg x3
TTE - vegatite lesion

what is most likely cause?

Bartonella quintana
Chlamydia psitacci
Coxiella burnetti
Kingella
Streptococcus oralis
A

Coxiella burnetti

exposure to sheep/ cattle

kingella/ streptococcus are easily culturable, so would be positive.

bartonella quintana does not cause IE. Bartonella henselae can cause IE

Chlamydia does not cause IE

Medical Microbiology and Virology (60 decks)

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