Intro to Virology Pt 2 Flashcards
Encounter and Entry-Transmission
- Transmission of virus from infected host to susceptible individual
- Human to human transmission from acutely ill persons, chronic carriers,
mother to fetus - Direct contact - sexually transmitted diseases
- Environmental - fecal-oral route in diarrhea
- Aerosols – respiratory - Chickenpox
- Direct inoculation - infected needles or blood products
- Hepatitis C
chronic carriers like those who are infected with hepatitis B sheeding virus and at low levels.
Trace contacts, and involved public health to trace hep B
Vertical transmission to fetus
Respiratory route
Aerosol droplets, nasal secretions or saliva
* Via coughing or sneezing
* A sneeze may generate up to 2,000,000 aerosol particles, a cough
90,000
* Epstein-Barr virus spread by saliva
* Kissing disease
You don’t necessarily need to sneeze it out. But you know the touching or sharing of saliva or spreading by saliva
Common cold
Caused by rhinoviruses
* Not spread by aerosols
* Spread from hands to eyes, nose or mouth
* Cycle can be interrupted by hand washing
Gastrointestinal Route
- Viruses shed in feces contaminate food or water
- Ingested by a susceptible individual
- “Fecal-oral spread”
- Poor personal hygiene: stool-tainted hands
*Day care centers and institutions for mentally impaired have difficulty
maintaining hygiene - Examples: Norovirus, Hepatitis A/E, Rotavirus
Transcutaneous route
west nile virus
- Skin provides a physical and biological barrier and virus entry.
- Direct inoculation via insect or animal bites or via mechanical devices
such as needles - Animal/insect vectors
- Rabies or West Nile virus, complicated disease cycle
West nile virus
- the mosquito can then bite, you know.
- and other animals that can invite us in when it infects other animals say, for example, horses, the the virus replicates, but it doesn’t produce what we call varymia, or acute illness that we can physically see with our own eyes.
We can’t tell if this this animal is sick, for example. But essentially the virus is replicating, and that animal hosts Another susceptible mosquitoes say it doesn’t carry the muscle virus to bite that host, and then draw some of that
infected blood and carry the virus as well. And then humans essentially become infected when those mosquitoes come and bite us
Most often cases are asymptomatic patients, typically, you know, present with like a very short febrile illness, immunocomp or preg pt more at risk
animal host, like the horse or the humans as Dead End hosts meaning, we can’t pass on the virus from human to human, necessarily or animal to animal. You requires really that mosquito vector for it to transmit from one human to the next, unless
you have direct inoculation, sharing of needles,
Transcutaneous route
- Iatrogenic inoculation - induced by medical or diagnostic procedures
- Contaminated blood products: Hepatitis B, Cytomegalovirus, HIV
- Infected donor material in transplantation
- Pituitary tissues used to prepare growth hormone
- May be purposeful as in parenteral vaccination using live attenuated
virus: Measles or Sabin polio vaccines
Sexual Transmission
Entry across the genitourinary or rectal
mucosa
* Virus may be spread to other parts of the
body or remain near the site of entry
* Ex. HIV, Hepatitis B, Cytomegalovirus, Herpes
Simplex Type 2 (or HSV-1), Mpoxx
Types of transmission
- Horizontal
- Transmission of virus between members of a susceptible host population
- Vertical
- Infection of a fetus in utero through
- Virus carried in the germ cell line
- Virus infecting the placenta
- Virus in the birth canal
Multiplication and Spread
- For some viruses, entry, primary replication and tissue tropism all
occur at the same anatomic site - Rhinovirus – common cold
- Rotavirus – enteritis
- Papillomavirus – warts
- Other viruses enter at one site and spread to a distant area to
produce disease - Enterovirus – meningitis
- Varicella zoster – chickenpox
Host factors in defense and damage
- Age and genetic make-up
- Newborns are susceptible to severe disseminated herpes simplex virus infection
- Some infections are more severe in older individuals, Epstein-Barr
(mononucleosis), poliovirus - General health - nutritional status, stress
- Physical Barriers
- In-tact skin
- Cell-mediated immunity
Antibody response
- Do not usually play a primary
role in terminating acute viral
infections but are very
important in preventing reinfection - Neutralizing antibodies reduce
infectivity by inhibiting
attachment, penetration or
uncoating of virus
Complement
Viruses can trigger the activation of the alternative
and classic pathways of complement
* Activated complement enhances phagocytosis of
viruses
* Leads to lysis of enveloped viruses or virus-infected
cells
Cell-mediated immunity
- Major factor in the termination of viral infections and the
pathogenesis of these diseases - Infected cells are susceptible to the action of lymphocytes
that recognize viral antigens on their surface - Virus-infected cells can be lysed by several types of
lymphoid cells
Identification of viruses (3)
- Isolation of virus in animals or tissue culture
- Detection of virus-specific antigens or nucleic acids in tissues or
body fluids - Demonstration of specific serologic responses
* Identification requires appropriate specimen obtained during a suitable phase
of illness
* Specimens must be rapidly transported with clinical information to the
laboratory
Lab Diagnosis
Standard Culture
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