Pathogens and Infectious Diseases
The word pathogen is a general term for any microbe (bacteria, virus, protozoan, prion, helminthes, or fungi) that causes disease within another organism. Each one of these microbes can affect their host which may or may not be beneficial to the organism. Microbes remain a threat to the health of humans worldwide.
When a disease is spread from one individual organism to another individual organism through various forms of direct contact, it is considered an infectious disease or a communicable disease. Infectious diseases still remains one of the leading causes of death in humans, primarily in babies, young children, elderly, and immunosuppresed and immunocompromised persons due to their vulnerable immune systems.
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Worldwide infectious diseases include but not limited to: HIV/AIDS, tuberculosis, H1N1, cholera, influenza, malaria, and African sleeping sickness. Emerging infectious disease can be defined as newly identified disease caused by a previously known organism; newly identified diseases caused by a previously unknown organism; the recognition of a new organism; a familiar organism whose geographic range has extended; whose host has changed, whose incidence has increased, or one that has changed to become more virulent or antibiotic resistant.
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Glossary terms: Host, pathogen, bacteria, virus, protozoan, prion, helminthes, fungi, immunosuppressed, immunocompromised, virulent, antibiotic
Transmission factors in the spread of infectious diseases
Factors that induce the emergence and reemergence of infectious diseases are: demographic factors, social and behavioral changes, changes in treatment and handling of water and food, climate changes, changes to environment, microbial evolution, human evolution, war, natural disasters (ex. hurricanes, tsunamis, flooding), and health care and technology advances.
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The transmission of infectious disease is through physical contact, sexual contact, food and water, blood transfusions, airborne/ droplet, insects and arthropods, and zoonoses.
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Glossary terms: evolution, arthropods, zoonosis
How pathogens affect human hosts
DNA and RNA Viral infections
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Viruses are nonliving particles that contain genetic material (nucleic acid) within protein layered coat (or lipid protein coat) called a capsid. Viruses are considered nonliving because of its inability to perform cellular functions. Viruses do not grow, do not move, cannot reproduce without a host cell (known as obligate intracellular parasites) nor can they metabolize. Viruses can affect both eukaryotic and prokaryotic celled organisms. When a virus enters the host, it will only be able to replicate once it finds and recognizes the host's cell receptors. The virus attaches onto the cell (similar to lock and key mechanism) and uses the enzymes and organelles within the cell to replicate; therefore, infecting the human host.
The method of for viral replication within the host's cell is different among the RNA viruses and the DNA viruses. Within the RNA virus replication process, the virus enters the host cell and translates new viral proteins immediately using the mRNA of the hot cell. Some viruses like HIV contain enzyme reverse transcriptase to make DNA from the RNA. Viruses that carry the enzyme reverse transcriptase are called retroviruses. On the contrary, the DNA viruses uses DNA to make mRNA, which is translated into viral proteins. The two methods of replication within a virus are the lytic cycle and the lysogenic cycle.
The lytic cycle is when the virus invades the host cell, produces new viruses, and immediately ruptures the host cell (lysis) when the viruses are released from the host's cell. The steps to the lytic cycle are as follows:
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The virus attaches to a cell and injects its DNA.
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The viral DNA circularizes.
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The viral DNA continues the lytic cycle or enters the lysogenic cycle.
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In the lytic cycle, new viruses are made.
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The cell lyses, which releases the viruses.
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The lysogenic cycle different from the lytic cycle because it allows the viruses to hide in the host cell for a period of time before the viruses emerges from the cell. The steps to the lysogenic cycle are as follows:
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The virus attaches to a cell and injects its DNA.
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The viral DNA circularizes.
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Viral DNA integrates into the host DNA.
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The viral DNA is replicated when the host cell replicates its own DNA and divides.
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The prophage may leave the host DNA and enter the lytic cycle.
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Major viral infections include: Herpes virus (HSV 1, HSV 2, chickenpox, shingles), Hepatitis (A, B, C, D, E), HIV/AIDS, influenza, polio, measles, West Nile Virus, HPV (Human Papillomavirus), HTLV (Human T-lymphotrophic virus), Epstein- Barr virus, SARS, Ebola virus, and Marburg virus.
Glossary terms: eukaryotic, prokaryotic, enzymes, DNA, RNA, prophage, retrovirus
Bacterial infections
Bacteria are living organisms that are single celled without a nucleus. The structure of bacteria varies depending on shape, size, and composition. Some bacteria are rod shaped bacteria (bacilli), sphere shaped (cocci), chains of cocci (streptococci), clusters of cocci (staphylococci) and spiral shaped (spirilla). Cell walls of the bacteria might consist of peptidoglycan, which creates a more complicated cell wall that may be difficult to penetrate. The genetic material within a bacterial cell is not encapsulated within a nucleus.
The method in which bacteria reproduce is through a process called binary fission. Bacteria reproduce asexually in which the DNA replicates itself and the two strands separate from one another to create two identical daughter cells. In some cases, a bacterial cell can take in DNA from its outside environment through a process called transformation. In other instances, bacteria can undergo a process called conjugation where bacteria bind together and transfer DNA from one cell to another cell using sex pilli.
Glossary terms: conjugation, transformation, asexual reproduction
Prion infections, Protozoan infections, Helminths infections, Fungal infections
Other infections include prion infections, protozoan infections, helminth infection, and fungal infections. Prions are protein particles that do not have a genome and can cause fatal neurological degenerative diseases. Example prion diseases are Creutzfeldt-Jakob disease, otherwise known as CJD. Protozoans are parasitic organisms such as amoebae, flagellates, and ciliates that can cause disease in humans. Protozoans can remain in the soil and water for long periods of time and later be digested by humans. An example protozoan disease is malaria. Helminths are parasitic worms that consume nutrients within the body of the person infected. Helminths include roundworms, hookworms and guinea worms to name a few. An example helminth infectious disease is uncinariasis. Funis are not all harmful. However, fungi can cause infectious diseases such as athlete's foot and yeast infections. Fungi reproduce by spores and people who suffer from a weakened immune system are at a greater risk of infection.
Evolution and genetic variability
The origins of viruses are unknown but there are a few hypotheses that exist on its evolutionary development and genetic variability. One hypothesis is that viruses were naked pieces of nucleic acid that could enter a cell through damaged cell membranes and later, due to evolution, developed a protein coat to bind to healthy. Many viruses evolve rapidly and spread quickly due to the simple design of the viruses. Due to the rapid evolutionary process among the virus, the immune system of individuals cannot always recognize the new invader due to slower evolutionary response. However, the immune system can recognize older viruses that have existed and the body has its line of defense for protecting the individual based upon gene selection.
Bacteria also evolve rapidly to adapt to its environment through mutations of the genetic material. Humans undergo mutations as well but not as frequently as bacteria mutations. It is important to have mutations so that the less favorable traits within the organism are slowly eliminated, while the preferable traits remain allowing genetic variability. The goal in preserving the most preferable traits is to help a population reproduce and sustain. Within the human population, while there are still some traits that are not favorable, the human body has evolved significantly to keep the traits that allow humans to become more successful in reproduction and survival.
Human Body Line of defense
Immune Response
The human body has two forms of immune protection: innate and acquired immunity. Innate immunity is a nonspecific defense mechanism that consists of skin, mucous, cilia, sneezing, and diarrhea as the first line of defense. Other defenses include endocytosis, inflammation, and antimicrobial proteins. On the other hand, acquired immunity consists of production of antibodies and immune memory, where cells specialize in helping the body create proteins that defends the body against invaders.
Glossary: endocyosis, innate immunity, acquired immunity, antibodies
Fever
Through research, it has been suggested that fevers are evolutionary responses of the human body to fight infections. Fever is an example of human adaptation to its environment. Fever is considered to be a primitive immunological response
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which allows the body temperature to increase slightly to kill any infectious microbe. The body has the ability to go back to normal temperature.
Iron Withholding
Iron is an important part of the blood in humans. However, iron is also an important part in the survival of pathogens. Pathogens will obtain iron from the host to maintain its survival. The body can prevent the pathogens from obtaining the iron within the human system. The human body is able to bind the iron to iron binding proteins, which will in turn lower the amount of free iron available to pathogens. Lowering the iron levels will keep low levels of infections.
Diarrhea and vomiting
Connections have also been made that diarrhea and vomiting are also evolutionary responses to eliminate toxins from the body. Diarrhea and vomiting are the body's first line of defense within the immune system. Through diarrhea and vomiting, water is lost from the body, in addition to healthy calories. Although, these essentials are lost, harmful toxins are forcefully flushed out of the system to prevent infection.
Medicinal treatment of infectious diseases
Antibiotics and vaccines
Antibiotics affect only bacteria by inhibiting cell activities. The first antibiotic discovered was penicillin, which is naturally created from fungi and bacteria. Although, antibiotics are beneficial in killing bacteria, they are able to respond to environmental changes through genetic mutations, and develop new strains that are resistance to the antibiotic administered. Antibiotics can interfere with the body's natural abilities to prevent infection and create harmful bacteria. Antibiotics are typically overprescribed to patients feeling symptoms of a cold or flu, which do not kill viral infections that may be the cause of the symptoms or discomfort. Thirty billion dollars are spent in the United States for the treatment of antibiotic resistant infections.
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Vaccines are effective in preventing a viral infection and are specific to certain viral infections. A vaccine is a harmless virus or toxin that triggers the immune system to respond by creating antibodies. The body creates antibodies against the weakened form of the virus so if the body does become exposed to the true virus, the body will be able to defend itself. There has been concern about the overuse of vaccinations and its connection to autoimmune diseases and humans' ability to fight other viral infections..
Prescription drugs
When prescription drugs are administered, it has the ability to interfere with the body's natural evolutionary response to its environment. The use of over the counter prescription drugs, like Tylenol or aspirin, to alleviate the symptoms of a fever can be extremely harmful. If it is recognized that the fever is a sign of infection and the body's way of fighting the infection, why would one want to reduce the fever? Using prescription drugs could be dangerous leading to secondary infections or dangerous health conditions particularly in pregnant women and children. Antipyretics are examples of harmful drugs administered to pregnant mothers and children.
Next, using iron pills could be harmful in some instances, although many may find iron pills beneficial for their health. It is important to respect the human body's response to lower the iron rate so that the body can naturally defend itself. If the body's process is interfered with, it could increase virulence levels of certain pathogens and allow bacteria to grow rapidly.
Overall, individuals should be able to recognize the body's evolutionary mechanisms for protection against illness and disease. Some of the body's natural defenses include mucous, anxiety, coughing, and sneezing. Our body's natural evolutionary responses to protect us against pathogenic organisms are often mistaken and treated using unnecessary medications. The use of medicines to prevent defensive responses like diarrhea or vomiting or coughing could be harmful in the process of eliminating toxins and/or pathogens from the human body. In other instances, medicines can be over prescribed, causing the pathogen to rapidly evolve into new strains with increased virulence levels.
Scientists who've contributed to microbiology and evolutionary biology
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Girolamo Francastoro (1478-1553) identified diseases as transmissible
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and invisible airborne particles; incorporated poetry with science
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Antoin Van Leeuwonhook (1632-1723) found bacteria in microscope with
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a simple lens (1676)
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Louis Pasteur (1822-1895) confirmed the Germ Theory and developed the
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pasteurization process (1862)
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Robert Koch (1843-1910) developed Koch's postulates by testing the blood
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and of cows and found rod shaped bacterium (Anthrax)
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Lady Mary Wortley Montagu (1689- 1762) developed variolization
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(engraftment) where the virus is taken and scraped onto the skin to create
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immunity
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Edward Jenner (1749-1823) developed vaccinations using cowpox microbe
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to help create human immunity
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John Snow (1813-1858) is known as father of epidemiology due to his
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work in solving the cholera outbreak in Soho, England
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Alexander Flemming (1881-1955) discovered penicillin from penicillium
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Martinius Beijerinck (1851-1931) isolated the first virus
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Ignaz Semmelweis (1818-1865) discovered hand washing as an important
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step in gynaecological examinations
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Joseph Lister (1827-1912) is known as the "father of antiseptics" for
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recognizing and introducing chemical sterilization and sterile surgery
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Florence Nightingale (1820-1910) recognized clean hospitals are necessary
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in preventing illness (sanitary design)
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Dimitri Ivanovski (1864-1920) discovered the tobacco mosaic virus that
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caused disease in plants
Rosalind Franklin(1920-1958) used x-ray crystallographer to understand the
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molecular structures of DNA, RNA, viruses, coal and graphite
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Charles Darwin (1809-1882) provided evidence that species evolved over time
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and from a common ancestor
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Jean Baptiste Lamark (1744-1829) supported the idea that evolution followed
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natural laws
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Ernst Mayr (1904-2005) renowned taxonomist, naturalist, and explorer who has
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contributed to evolutionary biology
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Barbara McClintock (1902-1992) known for her research in corn cytogenetics to
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demonstrate genetic fundamentals
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Ernest Everett Just determined the factors for successful fertilization an
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development of the ovum
Dr. James Earl King Kildreth identified cholesterol as allowing HIV to penetrate
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the cell
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Lynn Margulis biologist known for her theory of how eukaryotic cellular
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organelles developed and her ideas within the endosymbiotic theory
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Dr. Turner evolutionary biologist at Yale University
Dr. Eloy Rodriguez investigated self medication of primates and environmental
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biology
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Other current scientists who have contributed to the study of biology are: Rita Colwell, Susan Wessler, Susan Wiliams, Pedro Villegas, Nettie Marca Stevens, Guillermo Zavala, Kenneth Olden, Ida Stephens Owens, Clifton Doodry, Lydia- Villa-Komaroff, Martha Zuniga, George Langford, Cynthia Kenyon, James Hildreth, Carlos Bustamante, David Burgess, Kogo Mensa-Wilmot, and Mari Carmen Garica.