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.

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.

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.