Infectious Diseases Part 3: The role of public health Flashcards
Learning objective 1:
Describe how infectious diseases are transmitted from person to person and in populations
pending
Learning objective 2
Describe the role of public health in controlling communicable diseases
eg controlling:
- Rubella
- Coliforms
- Plague
- HIV
- Influenza
- Rubella: Immunization
- Coliforms: Water and food testing
- Plague: Vector Control
- HIV: Contact tracing // Resistance transmission
- Influenza: Surveillance
8 ways in which a pathogen may be transmitted?
- Respiratory: incl droplet and airborne
- Fecal-oral
- Direct contact
- Blood and bodily fluids
- Sexual
- Fomites
- Arthropod vector
- “vertical” = infection of fetus in utero\
- Virus carried in germ cell line
- Infection of placenta
- infection in birth canal
Five features of a microorganism that would allow them to survive in a hostile environment?
- Multiple antimicrobial resistance
- A tough cell wall or capsule/envolope to resist phagocytosis
- Being an INTRACELLULAR pathogen
- Production of EXOTOXINS
- Adaptation to the environment
Rubella Story and the Role of Public Health:
- Infection during early pregnancy can lead to: (?)
Congenital Rubella Syndrome
- miscarriage
- microphthalmia
- chorioretinitis
- deafness
- limb aplasia
- cognitive impairments (eg microcephaly)
When is the risk of congenital rubella syndrome (CRS) the highest?
When Maternal infection occurs during the first 10 weeks of gestation the risk can be as high as 90%
CRS is rare now thanks to (?)
What does its occurance look like in
- Canada (1998-2010)
- US (2005-2011)
- Worldwide
CRS is rare now thanks to vaccination
What does its occurance look like in
- Canada (1998-2010): 0.69 cases/year
- US (2005-2011): 0.57
- Worldwide: ~100,000/year
Public Health: water testing
What is the goal of water testing? (ie what does it detect)
Water testing detects presence of fecal bacteria, parasites, or viruses in an effort to control of indirect transmission
Public Health: water testing
Two methods indirect transmission through water is controlled?
- Chlorination (con:some organisms are highly resistant to chlorine)
- Filtration
Public Health: food testing
Food testing detects presence of: (3)
Food testing detects presence of fecal bacteria, parasites, or viruses in potentially contanimated food sources
Public health: food testing
In food testing, how are each of the following identified?
- Bacteria
- Viruses
- Parasites
Collect food/water and feces from infected persons to identify source
- Bacteria: isolation and genotyping
- Viruses: detection and genotyping
- Parasites: detection and identification
Public health: food testing
In add’n to food testing, how does public health reduce the spread of disease through food?
Educate regarding proper food handling, storage, hand-washing, preventing infected persons from handling food etc
Public health: vector control
Role of public health in vector control:
Eradicate or prevent insents/vectors from contacting susceptible persons eg:
- Insecticides
- Rat patrol
Public health vector control
How is the plague in Madagascar an example of the role of public health in vector control?
(1): WHAT IS THIS PLAGUE? CAUSE? HUMAN TRANSMISSION?
Plague in Madagascar:
- Caused by Yersinia pestis bacteria
- Carried by small mammals and their fleas
- Humans can be contaminated by the bite of infected fleas through direct contact with infected materials or animals or by inhalation
How is the plague in Madagascar an example of the role of public health in vector control?
(2) RESPONSE TO THE PLAGUE
- 2017, Pasteur institute sent rapid diagnositic tests to outbreak hot spots and to health ministry
- Internationall Federation of Red Cross and Red Crescent Societies (IFRC) deployed its **1st ever plague treatment centre **
- Medicine du Monde set up 5 isolation and tx centres; Doctors w/out borders deployed 70 people to support the response
Public Health: contact tracing
What is contact tracing?
Who gets Quarantined?
- Identification, isolation and treatment of infected persons
- Only those with highest risk of transmission are quarantined
- Identify trasmission clusters and intervene to prevent more
- In some cases: Prophylaxis or vaccine given to close contacts
Public health: detection and diagnosis
What is HIV?
Target and action?
Human Immunodeficiency Virus
- HIV-1 (worldwide)
- HIV-2 (West Africa)
- Target is CD4 protein on cell membrane of helper T lymphocytes
- Action: DNA copy of RNA by reverse transcriptase; DNA inserts into host nuclein acid (HIV integrase)
- HIV protease cuts and assembles virus, then viral particles bud from infected cells
- Monocytes act as vehicle for viral spread b/c they are more resistant to killing by the virus
How does the Human Immunodeficiency Virus infect humans?
TARGET and ACTION
Human Immunodeficiency Virus
- HIV-1 (worldwide)
- HIV-2 (West Africa)
- Target is CD4 protein on cell membrane of helper T lymphocytes
- Action: DNA copy of RNA by reverse transcriptase; DNA inserts into host nucleic acid (HIV integrase)
- HIV protease cuts and assembles virus, then viral particles bud from infected cells
- Monocytes act as vehicle for viral spread b/c they are more resistant to killing by the virus
What is the role of the following enzymes in HIV infection and replication?
- Reverse Transcriptase
- HIV protease
- HIV integrase
- Reverse Transcriptase: create DNA copy of RNA
- HIV Integrase: inserts viral DNA into host nucleic acid
- HIV Protease: cuts and assembles virus, then viral particles bud from infected cells
Why are monocytes a vehicle for HIV transmission?
They are more resistant to killing by the virus
Controlling the spread of HIV:
Three ways HIV is detected?
- EIA (Enzyme immunoassay) - detects antibodies and antigens specific to HIV infection
- Ab Differentiation Assay: to differentiate between HIV-1/2
- NAT (nucleic Acid Test) - measure the amount of HIV RNA in the blood; can also be used for tx monitoring or for confirmation of initial infection
Why is a HIV NAT test performed if AD is negative?
Indeterminate or negative results from the differentiation test indicate either acute HIV infection (positive for p24 antigen or IgM antibody) or a biological false positive test; the presence of detectable HIV RNA on a subsequent nucleic acid test is the arbitrator
How reliable is HIV RNA test?
If taken at the recommended window period, the HIV RNA test is highly accurate, so you can have confidence in your results. The HIV RNA test is around 95-99% accurate starting around 9-11 days post exposure and will stand at about 99% accuracy around 28 days post exposure.
Limitations of HIV-1 p24 Antigen test
The HIV P24 antigen test is accurate, but it is dependent on when P24 is detectable in the bloodstream. The window period for a P24 antigen test is about one to two weeks. Meaning, if you take an HIV P24 antigen test seven to fourteen days after exposure to HIV, you will get an accurate test result.
What are three requirements for pandemic influenza?
- A new influenza virus subtype emerges
- It infects humans and causes serious disease
- It spreads easily and is sustainable among humans
All influenza A pandemics of the 20th century were from adaptation off (?) strains to allow for (?)
All influenza A pandemics of the 20th century were from adaptation off avian strains to allow for human-to-human transmission (1918) or reassortment of avian and human strains (1957 & 1968)
The 2009 H1N1 pandemic resulted from (?)
2009/H1N1 resulted from the recombination of two viruses
- American and Eurasian Swine
- The american swine virus itself was recombinant of three viruses established in 1998
- These viruses are gentically distinct from the seasonal human H1N1
