Microbiology

Question 1

mode of infection of parvovirus B19

Answer 1

• by respiratory secretions, blood and blood products of infected patients
  -from mother to fetus

Question 2

what types of cells are affected by parvovirus B19

Answer 2

1) RBC precursors in the bone marrow, causing aplastic anemia
2) Endothelial cells in the blood cells, accounting for the rash associated with erythema infectiosum

Question 3

clinical manifestations of parvovirus B19

Answer 3

1) TAC (transient aplastic crisis):
-temporary arrest of RBC production
- this becomes apparent only in patients with severe hemolytic anemia

2) PRCS (pure red cell aplasia):
- persistent infection in immunocompromised patients leading to severe aplastic anemia and the patient is dependent on blood transfusions.

Question 3

Laboratory diagnosis of Parvovirus B19

Answer 3

Specimens: serum, blood cells

1) Direct detention:
a) ELISA for detection of viral antigen
b) PCR for detection of viral antigen. It is the most sensitive assay

2) Serology:
ELISA is used to detect B19 IgM antibodies, which indicates recent infection

Question 4

Treatment of B19 virus

Answer 4

symptomatic treatment

Question 5

Prevention of B19 virus

Answer 5

1) Screening of blood donors
2) Standard infection control precautions

There is no vaccine available

Question 6

What are Marburg and Ebola?

Answer 6

-They are severe and highly fatal diseases
-caused by viruses from the Filoviridae family.
• Though caused by different viruses, the two diseases are clinically almost indistinguishable
-Both diseases are rare but have a capacity to cause dramatic outbreaks with high fatality

Question 7

Reservoir of African Hemorrhagic fevers

Answer 7

Bats may be the reservoir
– monkeys are susceptible to infection but are not considered viable RH

Question 8

Mode of Transmission of AHF

Answer 8

These are highly communicable diseases.
- Person to person transmission by intimate contact is the main route of infection

Question 9

Fatality of Marburg and Ebola

Answer 9

• Marburg 25%
  -Ebola 50-90%

Question 10

Laboratory diagnosis of AHF

Answer 10

Based on symptoms and demonstration of filovirsuses in blood by ELISA and PCR

Question 11

Treatment of AHF

Answer 11

Supportive care - fluid, electrolytes and sometimes anticoagulants
- No antiviral drugs

Question 12

Incubation period of AHF

Answer 12

2-21 days

Question 13

Methods of controlling EVD

Answer 13

1) Reduce bat, monkey, pig contact by handling animals with gloves
2) cook food thoroughly before consumption
3) rapid and safe burial of the dead

Question 14

Diseases presenting hemorrhage

Answer 14

Flaviviruses - yellow fever, dengue fever

Bunya viruses - rift valley fever

Arenaviruses - Lassa Fever

Question 15

what is yellow fever?

Question 16

Reservoir and MOT of yellow fever

Answer 16

Jungle yellow fever:
- Primarily a monkey disease
- monkey-to-monkey transmission occurs by forest Aedes mosquito
- Man is accidental host on visiting jungle

Urban yellow fever
- involves person-to-person transmission by domestic Aedes mosquito
- It occurs when an infected person from the jungle returns to urban areas

Question 17

clinical manifestations of yellow fever

Answer 17

may be mild and unrecognized or severe and fatal
- fever, chills, headache, dizziness, jaundice or renal dysfunction

severe case - black vomititus with high mortality rate (20% or more)

Question 18

diagnosis of yellow fever

Answer 18

1) Detection of viral antigens in the blood by ELISA
2) Viral nucleic acid detection by PCR

Question 19

treatment of yellow fever

Answer 19

Supportive, depends on system involved

Question 20

General preventive measures of yellow fever

Answer 20

• Control of Aedes aegypti in urban yellow fever.
• Vector control measures:
(see Malaria)
• Aircrafts leaving an infected
area to receptive area should be disinfected
• Quarantine measures for imported monkeys at receptive areas.
• Periodic spraying of airports and surrounding receptive areas.

Question 21

specific preventive measures of yellow fever

Answer 21

-By active immunization. A single S.C. injection of a 17 D vaccine containing viable attenuated yellow fever 17 D strain virus.
Validity of the vaccine: It begins after 10 days and persists for at least 10 years. During this period of validation, no cases have been reported.

Applications:
1. Those who work in jungles.
2. Resident of endemic areas.
3. Travelers to endemic areas or between endemic and receptive areas.
-If a traveler arrives in a receptive area without a certificate, he is isolated for 6 days from the date of leaving the last infected area.
-If a traveler arrives in a receptive area before completing 10 days of vaccination, he is isolated until the certificate becomes valid, with maximum of 6 days.

Question 22

control measures for cases of yellow fever

Answer 22

-Isolation at any place (Blood and body fluid precautions). Prevent access of mosquitoes to patients for at least 3-5 days by screening the sick room, by spraying quarters with residual and insecticide, by using
insecticide-treated bed nets…

-Notification to local health office then to WHO.

-Disinfection is not required.
-Treatment is symptomatic and correction of complications.

Question 23

control measure for contacts of yellow fever

Answer 23

Family and other contacts not previously immunized should be vaccinated

Question 24

control measure of environment (yellow fever)

Answer 24

Search for source of infection i.e. areas visited by patient
3-6 days before onset to locate focus of yellow fever.

Question 25

epidemic measures of yellow fever control

Answer 25

• Determine the extent of the infected areas. in forest areas, restrict the movement Of animal reservoirs from the affected area.
  Use approved mosquito repellents
  for those exposed.
  ー
  Conduct a community survey to determine density of vector mosquitoes, their breeding places and effective control measures.
• Identity infected animal reservoirs, prevent mosquitoes from feeding on them

Question 26

clinical manifestations of dengue fever

Answer 26

Clinical manifestations:
1. Classical dengue fever (DF)

-characterized by acute onset of high-grade fever, frontal headache, myalgias, arthralgias, and often a maculopapular rash.
The illness may be clinically indistinguishable from influenza, measles.

2. Dengue hemorrhagic fever DHE
   -DHF is a potentially deadly complication of dengue.
   -It appears to be an immunopathological consequence of infection of a person who has already developed immunity to one serotype of Dengue virus with a virus of another serotype, although the mechanism is not fully understood.
3. Dengue shock syndrome (DSS)
   - The most common of these manifestations are skin hemorrhages such as petechia and purpura.
   -Most patients develop thrombocytopenia and hemo-concentration. These patients have DSS, which if not immediately corrected, can lead to profound shock and death.

Question 27

diagnosis of dengue fever

Answer 27

Diagnosed by antigen detection in blood

Question 28

prevention of dengue fever

Answer 28

a. Mosquito control is the most important strategy to prevent virus transmission to
humans
b. No specific treatment is available.

Question 29

what is rift valley fever

Answer 29

It is a mosquito-borne zoonotic disease caused by Rift Valley Fever (RVF) virus; a member of Bunyaviridae family.

Question 30

reservoir and MOT of rift valley fever

Answer 30

Primarily sheep, cattle, buffaloes, goats and camels leading to hepatitis, abortion and death

Humans are secondarily affected by infected mosquito bite or blood/body fluid exposure of infected animals.

Question 31

clinical picture of rift valley fever

Answer 31

-Most human cases are asymptomatic or relatively mild manifested as flu-like illness with complete recovery.
• A small proportion of patients develop a much more severe disease. This generally appears as one of several recognizable syndromes: retinitis with visual loss, meningoencephalitis or hemorrhagic fever.

Question 32

prevention of rift valley fever

Answer 32

Sustained program of animal vaccination. Both live attenuated and killed vaccines have been developed for veterinary use.