Pathogen
[2][3] Typically, the term pathogen is used to describe an infectious microorganism or agent, such as a virus, bacterium, protozoan, prion, viroid, or fungus.
The principal pathways have different episodic time frames, but soil has the longest or most persistent potential for harboring a pathogen.
[14] While the vast majority are either harmless or beneficial to their hosts, such as members of the human gut microbiome that support digestion, a small percentage are pathogenic and cause infectious diseases.
[17] Foodborne illnesses typically involve Campylobacter, Clostridium perfringens, Escherichia coli, Listeria monocytogenes, and Salmonella.
[18] Other infectious diseases caused by pathogenic bacteria include tetanus, typhoid fever, diphtheria, and leprosy.
Besides obtaining prions from others, these misfolded proteins arise from genetic differences, either due to family history or sporadic mutations.
[22] Additionally, wood, rocks, plastic, glass, cement, stainless steel, and aluminum have been shown binding, retaining, and releasing prions, showcasing that the proteins resist environmental degradation.
Many protozoans act as pathogenic parasites to cause diseases like malaria, amoebiasis, giardiasis, toxoplasmosis, cryptosporidiosis, trichomoniasis, Chagas disease, leishmaniasis, African trypanosomiasis (sleeping sickness), Acanthamoeba keratitis, and primary amoebic meningoencephalitis (naegleriasis).
[31] Helminthiasis is the generalized term for parasitic worm infections, which typically involve roundworms, tapeworms, and flatworms.
The bacteriophage life cycle involves the viruses injecting their genome into bacterial cells, inserting those genes into the bacterial genome, and hijacking the bacteria's machinery to produce hundreds of new phages until the cell bursts open to release them for additional infections.
[33] Streptococcus pyogenes uses a Cas9 nuclease to cleave foreign DNA matching the Clustered Regularly Interspaced Short Palindromic Repeats (CRISPR) associated with bacteriophages, removing the viral genes to avoid infection.
[38] The most common bacterial pathogens for plants are Pseudomonas syringae and Ralstonia solanacearum, which cause leaf browning and other issues in potatoes, tomatoes, and bananas.
They can cause a wide variety of issues such as shorter plant height, growths or pits on tree trunks, root or seed rot, and leaf spots.
[43] Humans can be infected with many types of pathogens, including prions, viruses, bacteria, and fungi, causing symptoms like sneezing, coughing, fever, vomiting, and potentially lethal organ failure.
However, for HIV, highly active antiretroviral therapy (HAART) is conducted to prevent the viral disease from progressing into AIDS as immune cells are lost.
For example, doxycycline inhibits the synthesis of new proteins in both gram-negative and gram-positive bacteria, which makes it a broad-spectrum antibiotic capable of killing most bacterial species.
[52] For example, a genetically distinct strain of Staphylococcus aureus called MRSA is resistant to the commonly prescribed beta-lactam antibiotics.
One target for new antimicrobial medications involves inhibiting DNA methyltransferases, as these proteins control the levels of expression for other genes, such as those encoding virulence factors.
Athlete's foot, jock itch, and ringworm are fungal skin infections that are treated with topical anti-fungal medications like clotrimazole.
The bacterial pathogens Helicobacter pylori, Haemophilus influenzae, Legionella pneumophila, Neisseria gonorrhoeae, and Streptococcus pneumoniae frequently undergo transformation to modify their genome for additional traits and evasion of host immune cells.
Examples of eukaryotic pathogens capable of sex include the protozoan parasites Plasmodium falciparum, Toxoplasma gondii, Trypanosoma brucei, Giardia intestinalis, and the fungi Aspergillus fumigatus, Candida albicans and Cryptococcus neoformans.
[59] These processes of sexual recombination between homologous genomes supports repairs to genetic damage caused by environmental stressors and host immune systems.
