Bacterial and Viral Infections

Bacterial and Viral Infections

Bacterial Infections

  • Bacteria are prokaryotic microorganisms that carry out vital roles in nature but can also cause disease.
  • When bacteria invade a host, they can cause harm by continuing their biological functions, such as production of harmful enzymes and toxins.
  • Bacterial infections can be localised or systemic. Localised infections are restricted to one area, while systemic infections are spread via the bloodstream.
  • Some bacteria form biofilms, complex communities of bacteria adhered to a surface, which are difficult to cleanse and treat.
  • Bacteria susceptibility to antibiotics varies. Some have evolved resistance, resulting in antibiotic resistance, a major healthcare issue.
  • The rate at which bacteria reproduce, their mutation rates, and the probability of a beneficial mutation all factor into the speed at which antibiotic resistance can develop.
  • Many different factors can affect the spread of bacterial infection, including poor sanitation, overcrowding, and decreased immunity.

Viral Infections

  • Viruses are obligate parasites, which means they must invade a host cell to reproduce.
  • Viruses consist of genetic material (DNA or RNA) encased in a protein coat called a capsid.
  • Adhesion to a host cell is the first step in a viral invasion. Viruses bind to specific receptor proteins on the host cell’s surface.
  • Once inside, the virus uses the host’s cellular machinery to replicate its genetic material and produce more virus particles.
  • Viruses can cause disease by directly damaging or killing cells, or by causing immune responses that harm the host.
  • Antiviral drugs block key points in the viral life cycle, but antiviral resistance is a growing concern analogous to antibiotic resistance.
  • Vaccines are a critical tool in preventing viral infections and spreading it. They stimulate the immune system to recognise and combat viruses.
  • Influencing factors in the spread of viral infections include vaccination rates, population density, sanitation levels, and individual immunity.

Immunity to Infections

  • The human immune system is divided into two main types: the innate immune system, which acts quickly and non-specifically, and the adaptive immune system, which is slower but more specific and can confer long-term immunity.
  • Innate immune responses include physical barriers (like skin), phagocytosis, and inflammation.
  • Adaptive immunity relies on B cells and T cells. B cells can differentiate into plasma cells that produce antibodies, while T cells can directly kill infected cells or help other immune cells.
  • Antibodies bind to pathogens and neutralise them, mark them for destruction, or cause them to clump together (agglutination).
  • Vaccines work by stimulating the adaptive immune response, leading to the production of memory cells that can respond rapidly to future exposure to the pathogen.
  • Problems can occur with the immune system, such as allergies, where the immune system over-responds, and autoimmunity, where the immune system attacks the body’s own cells.
  • Immunodeficiency disorders, such as HIV/AIDS, can result in the immune system being less able to fight off infections.