March 27, 2024

Lily Sharkey

11th Grade

Dominican Academy

Scientists believe that about half of all human DNA descends from viruses that infect the germline of our ancestors with viral nucleic acid. Indeed, the human body contains ten times more bacterial cells than human ones. Microbes such as these exist all throughout our bodies and carry out processes that synthesize vitamins, digest food into nutrients, and stimulate immune systems. The ten trillion microbes found in the gastrointestinal tract protect the gut from disease-causing microorganisms, called pathogens. Chemicals produced by microbes have been used by researchers to create new medicines. Of the millions of species of microbes, less than one percent are pathogens- about 1,400 species. There are five kinds of pathogens: viruses, bacteria, fungi, protozoa, and helminths (worms). Protozoa and helminths are often collectively referred to as parasites.

Viruses are incredibly small, ranging in size from 20 to 400 nanometers (nm); a nanometer is equivalent to one billionth of a meter. For reference, the period at the end of this sentence is 350,000 nm in diameter. Viruses come in many shapes: some are rod-shaped, some are round, and some have multi-sided heads with cylindrical tails. They are made up of either DNA or RNA, encased in a protein shell and sometimes surrounded by fatty lipids. Viruses are dependent and cannot survive outside of a living cell as they do not have the materials for reproduction; in a cell, viruses are able to take over cellular metabolic capabilities and reduplicate. The common cold, measles, influenza, AIDS, and SARS (COVID-19) are some common virus-caused infectious diseases.

Bacteria are 10 to 100 times larger than viruses; they can often be seen under a low-powered microscope. Bacteria are single-celled and can thrive without a host. The shapes of bacteria are: spherical (coccus); rodlike (bacillus); and curved (vibrio, spirillum, or spirochete). They are made up of a singular ring of DNA, which allows the microbe to exist independently by encoding genes for necessary cellular functions, including reproduction. Some bacteria have additional rings of DNA, called plasmids, which allow for antibiotic resistance. Bacteria include only one pair of chromosomes instead of two; this means that they reproduce through binary fission, dividing into two genetical clones. Bacteria can evolve incredibly fast, which allows them to create toxins, suppress our bodies’ defenses, and resist drugs and immune system antibodies. They can receive genetic data from other bacteria, viruses, and plants which helps this speedy adaptation. It takes humans 20 to 30 years to produce a new generation while bacteria do so in only 20 to 30 minutes. Bacteria are responsible for strep throat, tuberculosis, and bloodstream infections.

Fungi are spore-forming organisms like mold, ringworm, and histoplasmosis. Protozoa are the microbes responsible for malaria and dysentery. Helminths are parasitic worms that cause trichinosis, hookworm, and schistosomiasis. Proteinaceous infectious particles (prions) are newly discovered infectious agents; they are abnormally folded proteins that, when they come into contact with them, turn other proteins into prions. Prions are commonly found in the brain and the spread of prions will eat holes into the brain. Diseases caused by prions, such as bovine spongiform encephalopathy (mad cow disease), progress rapidly and are always fatal.

Pathogens can infect a host through contact with an epithelial surface. Epithelial tissues make up the surfaces of organs; in this case, it can be the skin or the mucosal surfaces of the respiratory, gastrointestinal, and urogenital tracts. When infectious particles from an infected person make contact, they will penetrate the surface and replicate in the tissues. At this point, innate immunity will attempt to protect the body; innate immunity is the immune response that everyone is born with and the first line of defense in the immune system. This may involve a fever to kill pathogens or inflammation to carry immune system cells via blood to the impacted area. If these measures do not work, the pathogen will create a site of infection and the host will develop a disease. Diseases are often not dangerous unless they can spread via lymphatics or bloodstream or secrete toxins; if the pathogen remains at its point of origin then there will not be too much damage.