Microbiology E

Question 1

what are zoonoses

Answer 1

Non human animal source

Humans usually ‘dead end host’ following contact with infected animals

Question 2

Describe the epidemiology, clinical effects, microbiology and treatment of Malaria.

Answer 2

epidemiology:
- Endemic in Africa, India, the Far East and South America.
- 35% of the world’s population is infected
10 million new cases annually and ~ 2 million deaths.
1792 cases (imported into) UK in 2017
- transmitted by:
o Mosquito vectors
o blood transfusion,
o needle accidents or,
o mother to fetus.

microbiology:
- 4 species of Plasmodium protozoa cause malaria in man, of which P. falciparum is the most virulent.
- most complex life cycles of any human infection:
o three quite distinct stages & alternating extracellular and intracellular forms.
o Affect RBCs
- P. Vivax, P. malariae and P Ovale
- slide 7 vector borne infections l

clinical features:

• fluctuating fever and drenching sweats
• Wide range of symptoms from fever to headache, muscle pains and vomiting
• Fatal cerebral or renal disease possible
• Fever follows rupture of erythrocytic schizonts and is mainly due to the induction of cytokines
• Synchronous parasitic life-cycles in red cells cause different species of malaria to have characteristic patterns of fever; for example a 48-hourly fever in P. falciparum
• Enlargement of the spleen and liver is common and anemia almost invariable.

Question 3

clinical complications associated with malaria

Answer 3

• Cerebral malaria
• Severe anemia
• Hypoglycemia
• Lactic acidosis
• Glomerulonephritis
• Complications most common in P. falciparum
• Complications most common in children aged between 6 months and 5 years, and in pregnant women. However occur at any age in the non-immune (e.g. tourists).

Question 4

how would you diagnose malaria

Answer 4

Microscopy of a ‘blood film’ :

• Parasites inside red cells
• can have low sensitivity (high false negative rate)
• Other antigen detection methods are available
• ‘thick films’- to detect the presence of parasitaemia
• ‘thin films’- to distinguish the different species of plasmodium in the red cells

Newer ways:
Antigen detection test:
- Quick, simple, relatively cheap screening test
- Low sensitivity in non falciparum malaria

PCR

Question 5

what are arboviruses and give some examples

Answer 5

Arthropod borne virus

• Any virus transmitted via an arthropod vector
• Mainly Flavivirus & Alphavirus
• Ticks, mosquitoes, & other arthropods
• Rashes, meningitis, encephalitis, hepatitis

Increasingly common in travellers returning to UK (especially Westnile virus, Chikungunya, Dengue) Zikavirus

EXAMPLES:

• Dengue virus/ Dengue fever
• Lyme disease (lyme borreliosis) - transmitted by exodus ticks - typically mice and deer - Borrelia burgdorferi

Question 6

describe dengue virus/dengue fever

Answer 6

• Flavivirus with 4 serotypes
• Mosquitoe vector- 50-100 million cases /yr.
• malaise, fever, headache, arthralgia, nausea and vomiting, rash
• Pathophysiology of thrombocytopenia/ leucopenia and vascular leakage

Question 7

describe lyme disease

Answer 7

• Borrelia burgdorferi (‘spirochaete’ or spiral bacteria)
• Transmitted by Ixodes ticks - Reservoir typically mice and deer
• no person-to-person
• fever, headache, myalgia, lymphadenopathy
• Characteristic erythema migrans rash at site of bite

Treatment:
Doxycycline or amoxicillin -effective in treatment of early disease.
Late disease requires more aggressive therapy, e.g. intravenous penicillin or ceftriaxone for 30 days

Question 8

describe Viral haemorrhagic fevers (VHF)

Answer 8

Various rare diseases: Ebola, Lassa, Marburg and others

Fever, hemorrhage, rash and disseminated intravascular coagulation

Question 9

List major viral haemorrhagic fevers including their geographic risk areas.

Answer 9

Various rare diseases: Ebola, Lassa, Marburg and others

Ebola ‘filovirus’ a long filamentous single-stranded RNA viruses. Animal reservoir is probably bat 
Fever, hemorrhage, rash and disseminated intravascular coagulation 
Specific treatments and vaccines under investigation- but public health controls most important
Big outbreaks ( e.g. 2014-2015 W.  Africa) involving urban and hospital transmission and HealthCare Worker (HCW) infection
UK cases of ebola (and other VHF) have been imported, often HCW

Question 10

Recognise the following key zoonoses: Q fever, anthrax, plague, leptospirosis, brucellosis and order these in terms of risk of acquisition in the UK.

Answer 10

slides 18-26

vector borne infections lecture