Question

Identify at least 2 portals of entry and 2 portals of exits for microorganisms.

Bacteria possess various virulence factors. What is the definition of virulence?

What is antigenic shift? How or when does it occur?

Answer 1

• A portal of entry is the site through which micro-organisms enter the susceptible host and cause disease/infection.
  2 examples of portal of entry are - mucous membrane, gastrointestinal tract.
  A portal of exit is the site from where micro-organisms leave the host to enter another host and cause disease/infection.
  2 examples of portals of exit for microorganisms are - urogenital tract, respiratory tract (Coughing and sneezing can expel pathogens from the respiratory tract).
  
• Virulence is a pathogen's or microbe's ability to infect or damage a host. The virulence of a microorganism is a measure of the severity of the disease it causes.
  
  ( Explaination :  Ability of bacteria to cause disease can be described in terms of the number of infecting bacteria, route of entry into the body, effects of host defense mechanisms, and intrinsic characteristics of the bacteria which are called virulence factors. The virulence factors of bacteria are typically proteins or other molecules that are synthesized by enzymes.)
  
• Antigenic shift is the process by which two or more different strains of a virus, or strain of two or more different viruses, combine to form a new subtype having a mixture of the surface antigens of the two or more original strains.
  Antigenic shift is an abrupt, major change in an influenza A virus, resulting in new HA and/or new HA and NA proteins in influenza viruses that infect humans. Shift can result in a new influenza A subtype in humans.
  Antigenic shift occurs when a radical and abrupt change in influenza type A virus hemagglutinins occurs. In some cases, a 50% change occurs in the hemagglutinin structure. Antigenic shift can be the result of a direct jump from an unknown animal strain to humans or a reassortment of two or more influenza viruses within the same cell.
  One way shift can happen is when an influenza virus from an animal population gains the ability to infect humans. Such animal-origin viruses can contain an HA or HA/NA combination that is so different from the same subtype in humans that most people do not have immunity to the new (e.g., novel) virus. Such a “shift” occurred in the spring of 2009, when an H1N1 virus with genes from North American Swine, Eurasian Swine, humans and birds emerged to infect people and quickly spread, causing a pandemic. When shift happens, most people have little or no immunity against the new virus.