A pathogen is an infectious agent; colloquially, a germ. The types of pathogens include prions, viruses, bacteria, fungi, and other parasites. Archaea, from which eukaryotic life arose, are the only microbial life form which is entirely benign.
Prions are misfolded proteins that propagate by transmitting their mangled state to other proteins. A prion acts as a template, inducing properly folded proteins to take the prion configuration.
One way that prions are transmitted to humans is by eating infected meat: cattle with mad cow disease (bovine spongiform encephalopathy), which causes Creutzfeldt–Jakob disease in humans.
Some fungi have proteins showing prion-like behavior, but fungal prions do not appear to harm their fungal hosts.
Viruses are stunningly cunning packages that hijack cells to reproduce. Viruses invade all organisms, including other viruses.
Viruses are major players in horizontal gene transfer, which greatly improves their adaptability. While this has had a major beneficial impact on evolution, it offers no consolation to the infected.
Bacteria comprise a huge domain of single cell prokaryotes, coming in a wide range of shapes and lifestyles. Bacteria are ubiquitous in every livable habitat on Earth, including some unlivable habitats where few other species care to dwell. Bacteria have cozied up to every multicellular life form, often symbiotically, though sometimes the occupation is less than cozy for the host.
The most common fatal bacterial diseases are respiratory infections. Tuberculosis is an airborne bacterial disease. The bacteria itself does not wreak havoc. Instead, a body’s immune system damages the lungs in an incessant war to purge the infection. 1/3rd of the world’s population may be infected with tuberculosis.
Human parasites include helminths (parasitic worms) and protists. Humans acquire helminths from contaminated water, fish, and meat. Mosquitoes are helminth delivery agents. However they enter the body – mouth, anus, nose or skin – most helminth species attach themselves to the intestinal tract.
Protists comprise a vast variety of unicellular eukaryotes that live anywhere that has water. When living as a colony, protists do not differentiate into tissues. Many protists, such as algae, are photosynthetic. Marine plankton are protists. Protists are typically vital primary producers in an ecosystem: the bottom of the food chain. The most notorious pathogenic protist delivers malaria.
Malaria is an ancient malady brought by mosquitoes bearing parasitic protists. The evolution of resistance is illustrated by human’s adaptive response to malaria.
Female mosquitoes pick up the microbe by feeding on the blood of an infected person. Male mosquitoes are not blood suckers, so do not transmit malaria.
2 genetic responses to malaria evolved that can themselves cause serious blood illnesses: sickle-cell anemia and thalassemia. If untreated, these mutations cause fatal red blood cell disorders in homozygotes: inheritors of the genetic mutation from both parents.
Over centuries carriers of these genetic anomalies survived while others died of malaria. This increased the frequency of the genetic variation until it became common among people living in areas where malaria was endemic.
Malaria remains prevalent in the sub-Sahara: killing 750,000 people each year, mostly young children. 40% of sub-Saharan Africans carry the sickle-cell anemia gene. 70% of Papua New Guineans inherit various thalassemia mutations.
Of the million or so types of microbes that exist, only 1,415 are known to manufacture human malady. Pathogens typically produce symptoms as a side effect of their lifecycle.
Each step of an infection is used to advantage by the invader. Pathogenic microbes assist each other to reproduce and spread: a cooperation honed over many generations.
Genetic mutations ratchet up during invasion. This alters the interface a pathogen presents to a host, raising the odds of a successful infection.
In an intricate life cycle of different lifestyles, many successful microbes ferry themselves between hosts using living vectors. To obtain optimal probability of distribution, those vectors often fly. Mosquitoes and birds have been common carriers of pathogens. The West Nile virus has managed worldwide distribution using both mosquitoes and birds as vectors.
Over time, evolution tends to mitigate devastation of a host. Virulence, in killing the victim outright, is disadvantageous, as the microbe is left homeless and is likely to die alongside/inside its host. With centuries of coexistence, there is the natural evolutionary tendency to optimize survival of both species, though the rapid adaptability of microbes generally puts them one step ahead of host response.
The carrier of a vector-based disease acts as passage but does not suffer the disease. The other route to human malady to is more direct and demonstrates another aspect of cleverness by microbes.
Corpuscular capitalists that they are, pathogens are constantly seeking new avenues for expansion. They rapidly adapting to exploit those opportunities. For a pathogen on the prowl, genic information from potential host cells allows a tweak to their own genes that makes a new host available for infestation.
Humans encourage many maladies by lifestyle choice, notably diet. Eating animals has been a particularly good formula for breeding disease and has successfully promoted cross-species contagion.
Humans give ambitious pathogens ample opportunity for entry by raising and slaughtering animals for food. Dipping one’s hands into the guts of an animal for meal preparation does wonders for maleficent microbes.
Animals have been the primary source of introducing infectious illness: 60% of human pathogens derive from animal contact, particularly mammals. Among new microbial maladies, the trouble transfer rate is ~75%.
Listeriosis is a most virulent foodborne illness, with a human kill-rate reaching 30%: around 500 deaths in the US per year. Listeria monocytogenes is the responsible bacteria. L. monocytogenes is commonly ingested along with dairy or other animal products, mostly raw, but including cooked poultry and smoked fish. The bacteria only rarely come from consuming raw vegetables.
Once inside, L. monocytogenes hijacks host cellular functions: subverting a body’s heterochromatin machinery and reprogramming the transcription of genes normally employed in innate immunity. The bacteria manipulate epigenetic regulation to wreak havoc.
Researchers spot a novel microbial nuisance about every 4 months. While most are trivial, a telling minority, such as HIV, avian flu, and SARS, pose grave threats.
Livestock cultivation promotes new vectors for pathogen victims. Congo fever comes from a tick-borne virus which is spread by many animals, including some birds as well as cattle. Incubation takes 1 to 3 days from a tick bite, and almost a week for exposure from the blood or tissue of someone infected. The malady made its way from Africa, where it was endemic to herding tribes, into the Middle East and elsewhere. With rising incomes comes opportunities for transmission. Importation of cattle into India has introduced Congo fever.
As people get a taste of prosperity via urbanization, they eat more animals. Prosperity is relative. Burgeoning slums are an ideal place to share disease.
Livestock not only pass new maladies to man and other species; they also help spread existing pathogens into new locales. While the market system shows no inclination to share the wealth, its practice is a paradigm for sharing ill health.
Sickness can result from an unhealthy microbiome, which practically invites infection by a badass bacterium. Researchers are only beginning to understand how changes in the microbiome inspire illness.
Chronic diseases are a dual phenomenon: hostile bacteria taking up residence alongside friends that have largely abandoned the neighborhood, or, worse, never moved in. Many diseases show a significant shift in the inner ecosystem. Not only is the onset of disease an invasion, it is an invitation for pathogenic low life to join the party. People with asthma have a different microbiome than healthy breathers.
Digestive disorders are disorder in the gut microbiome. Diabetes is directly related to the state of the gut microbiome.
Microbiome transfer can be beneficial. Gut infections have been successfully treated with fecal transplant: inserting feces from a healthy person into the colon of a sick person. That is a shotgun approach that offers only temporary relief unless the recipient changes dietary habits.
“Triclosan contributes to making bacteria resistant to antibiotics. Triclosan alters hormone regulation. Triclosan is not known to be hazardous to humans. FDA does not have sufficient safety evidence to recommend changing consumer use of products that contain triclosan at this time.” ~ US Food and Drug Administration (FDA) in 2010
Antibacterial soap is a supposed hygienic shotgun that one can point at oneself: killing microbes that may be beneficial, while infusing the skin with disruptive chemicals.
Triclosan, an antibacterial and antifungal agent, has been put into consumer products in the US since 1972. Triclosan is in liquid soaps, hand sanitizers, dishwashing liquids, shaving creams, toothpastes, and mouthwashes, as well as permeated into kitchen utensils, bedding, socks, shoe insoles, workout clothes, and toys. Any consumer product advertised as antimicrobial is infused with triclosan.
For lack of testing tykes, the US Centers for Disease Control and Prevention found triclosan in the urine of 75% of Americans over the age of 5.
“Triclosan is very stable. It lingers in the body and in the environment for a long time.” ~ American microbiologist Petra Levin
Companies insist that “there was no real evidence showing that triclosan was dangerous for humans,” but that triclosan had been proven effective “in killing germs.” Alas, those supposed “germs” are what keeps a body healthy.
Triclosan is a bacteriostatic agent that targets bacteria by inhibiting their microbial fatty acid synthesis, a process necessary for reproducing and building cell membranes.
As with many agents used to scour the microbe population, bacteria adapt to develop resistance. Rather than killing bacteria, triclosan actually helps staph pathogens infect nasal passages. Triclosan has been found to promote liver tumors and cancer in mice through molecular mechanisms relevant to humans.
“Triclosan has a dramatic protective effective effect on bacteria, increasing survival by several orders of magnitude in the presence of bactericidal antibiotics.” ~ American microbiologist Corey Westfall
“There is a rule in medicine that you don’t give drugs that slow cell growth before drugs that kill cells. Triclosan violates that rule.” ~ Petra Levin
The FDA, which is responsible for safeguarding the safety of personal-care products, medical devices, and products that come into contact with food, did nothing to regulate triclosan except shuffle papers, and write a tart letter to an inquiring Congressman who read studies on triclosan that “raise valid concerns about the effect of repetitive daily human exposure to these antiseptic ingredients.”
Triclosan is in so many products that it has been under studious neglect by 3 US federal regulatory agencies: the FDA, the Environmental Protection Agency (EPA), and the Consumer Product Safety Commission.
Triclosan is a polychloro phenoxy phenol: a highly reactive compound containing trace amounts of dioxins. Triclosan degrades to produce more dioxins. Dioxins are by-products of various industrial processes. As such, dioxins can be found throughout the world: in the soil, sediment, and the fatty tissues of animals, including those eaten by humans, as well as trace amounts in the air and water. Dioxins have no known use except act as a biological detriment.
Dioxins are commonly regarded as highly toxic compounds, but scientific proof of that is surprisingly scarce, for humans at least. Animal studies demonstrate a more dismal prospect: damage to the liver, thymus, and other organs. There is no reason to think that human infusion would be innocuous.
Dioxins are a family of chemical compounds. The American Chemical Council, a chemical industry political lobbyist, kindly reminds that only 17 of the 75 dioxins are “considered to pose a potential public health concern.”
For lack of research, the toxicity of triclosan’s dioxins are uncertain. But triclosan produces abundant dioxins.
The American Chemistry Council wants you to know that the breakdown of triclosan into dioxins “are generally not considered to be toxic to humans or wildlife.” So much for cause of death.
As always true of chemical contamination, children are more susceptible than adults. Triclosan incites and aggravates allergies and hay fever, especially in youngsters. Exposure in infancy degrades survival prospects.
As triclosan indiscriminately affects bacteria, its detrimental effects on the microbiome are widespread. This has numerous cascade effects on health.
Triclosan mucks up sewage treatment. Its presence in wastewater sabotages sludge-processing microbes while promoting resistance evolution in undesirables.
Some 100 tonnes of triclosan enter US sewage plants each year. Treated wastewater and sewage-based fertilizers are used on croplands, where triclosan promotes antibiotic resistance among microbial soil residents and accumulates in crops.
Scientists have expressed concerns for decades about triclosan, which not only has its dioxin impact, but also has been shown to disrupt hormonal balances (the endocrine system), muscle performance, reduce blood flow, and negatively impact the immune systems of animals. But industry apologists are having none of that naysaying.
“It’s a time of increased threats from disease and germs. These products and ingredients have been reviewed, regulated and researched for decades. The science strongly supports the safety and efficacy of these products.” ~ Shruti Sansoni of the US Soap and Detergent Association
In 2016 the FDA stunningly reversed itself, banning antibacterial soaps, including triclosan. The reversal was narrow. Triclosan is still allowed in other consumer products.
“Consumers may think antibacterial washes are more effective at preventing the spread of germs, but we have no scientific evidence that they are any better than plain soap and water. In fact, antibacterial ingredients may do more harm than good over the long term.” ~ FDA