Chapter 2: Basic Concepts Of Infectious Disease PDF

Chapter 2: Basic Concepts of Infectious Disease 2.1 Normal Microbiota versus Pathogens many years of the human body are colonized with microbes. ◦ The collection of all microbes on the human body is called the human microbiota. ‣ Commensalism or mutualism ‣ Commensalism -...

Chapter 2: Basic Concepts of Infectious Disease 2.1 Normal Microbiota versus Pathogens many years of the human body are colonized with microbes. ◦ The collection of all microbes on the human body is called the human microbiota. ‣ Commensalism or mutualism ‣ Commensalism - only one benefits form the interactions ‣ Mutualism - both organism benefit from the interactions. Colonization refers to the ability of the microbe to stay attached to the body surface and replicate ◦ Adhesns = enable the microbiota to attach to host cells. ‣ The way a microbe colonize a certain part of the body. A pathogen is any bacterium, virus, fungus, protozoan, or worm (helminth) that causes diseases in humans. Pathogenicity - is the ability of the organism to cause disease/infection. Parasites are microbes that cause harm-inducing infections. They live on or within the host organism ◦ All parasites are pathogens but not all pathogens are parasites. ◦ Ectoparasites - lives on the surface of the host (trichophyton rubrum) ◦ Endoparasites - living inside the host’s body. (Elephantiasis) Lingo of Pathogenesis an infection occurs when a pathogen or parasite enters and begins to grow on the host. (We don’t have symptoms) disease occurs when the patient develops symtopms ◦ During an acute infection, symptoms develop and resolve rapidly ‣ The common cold (less than 2-3 weeks) ◦ A chronic infection involves symptoms that develop gradually and resolve slowly ‣ Tuberculosis (stay for a long period of time) ◦ Latent state = microorganism cannot be found in the culture. ‣ Ex. Herpes virus remains dormant for years until cold sores develope. Primary Pathogens are likely to cause disease after infection in a healthy host ◦ Ex. Tuberculosis ◦ Rapidly reproduce/increase in number ◦ Moderate to high virulence Opportunistic pathogens ◦ Less likely to cause disease in healthy host ◦ Low virulence ◦ Immunocompormised patients - playing around the microbiota Latent state HSV I it herpessimplex ◦ Ex. Retro virus can emmbened invirus I the genome of the host symptomswhenstress UV ‣ They are there but not showing symptoms willshow I unweliness ispresent ◦ Ex. Cold sore Tissue trophism = the characteristic of a microbe affecting one specific cell. in HSVI they prefer the cranial nerve (specifically the trigeminal nerve) - they have three branches that causes sensation in our face, eyes, cheek, surrounding our mount. The trigeminal nerve esp. the third branch will be affected bh HSVI. Virulence ◦ Describes the level of harm caused by a pathogen following infection (degree of the disease) ◦ Can be measured by ‣ Lethal dose 50% (LD50) - amount of particles necessary to kill 50% of the population ‣ Infections dose 50% (ID50) - amount of particles necessary to infect 50% if the population. canaffectblood sepsis Aspects of the pathogen that contribute to virulence Invasion - the entry of a pathogen into a living cell, where it then lives ex pneumonia morevirulent thatcommon ◦ Some pathogens live inside of vacuoles, while others prefer to live directly in the cytoplasm of the cold host cell commoncold Invasiveness - the ability of a bacterial pathogen to spread rapidly through tissues ◦ Ex. Streptococcus pyogenes feat infectingrespiratory ‣ Highly invasive because they secrete enzymes that degrade host tissues “flesh eating bacteria” tract UpperRT only the host range refers to the animals a pathogens can infect and produce diseas in notasvi.ruent ◦ Some organisms can infect inlet one type of host to produce disease. ‣ Narrow ‣ Broad How do we define Disease? disease is a disruption of the normal structure or function of any body part, organ, or system that can be recognized by a characteristic set of symptoms and signs. infectious disease ◦ A disease caused by a pathogen (bacterial, viral, or parasitic) that can be transferred from one host to another ◦ Can produce infection Diseases are identified by characteristic signs and symptoms Signs can be observed by examination (objective marker of disease) ◦ Fluid-filled rash ◦ Fever of 40 C Symptoms ◦ Are experienced by the person (subjective indicator of disease) ◦ Pain and Fatigue are an example Syndrome is a colllection of signs and symptoms that occur together and collectively characterize a condition. Many of the signs and symptoms of disease are cause by the host’s response to the infection, calledimmunopathology immune pathology cells damage nearby host tissue when killing the microbe After a disease is resolved , pathological consequences called sequelae may develope ◦ For example, the immune response to strep throat can cause heart damage weeks after the infection is resolve. ◦ When pathogens meets hosts: ‣ Attachment ‣ Immune avoidance ‣ Stealing nutrients from the host Attachment adhesins on the surface of the microbe help them to adhere to the surface of the host. They bind to the host cell surface structures called receptors. They have preference to attach to those cells that are decorated with the right surface receptors. Immune avoidance Different pathogens have different tools that they use to avoid the immune system. ◦ salmonella changes their molecular shape of their structure to confuse the immune cells. ◦ Some secrete all is well molecules that tells the cell that there is no infections that is happening. ◦ Some secrete proteins that tell the immune cells to kill themselves in the process of apoptosis. Stealing nutrients from other hosts they have siderophores that will allow the to steal iron that the body has evolved to keep those nutrients away. Characteristic stages of an acute infectious disease: Incubation Phase time after microbe first infect a person until the first signs appear. Maybe contagious, even though they appear healthy They try to replicate to large numbers before the immune system knows that they are under attack. Prodromal Phase short and may not be apparent Headache and general feeling of unwell mess (malaise) Can spread microbes to others. Illness Phase begins when typical signs and symptoms have appear. Pathogens reaches peak numbers Symptoms begin when immune system starts attacking Acme - period where the disease symptoms have reached its peak. Decline Phase begins as the symptoms subside Host defenses has won Body temperature regulates back to normal Blood vessels need to dilate (lose heat) pt. Will sweat. Convalescence Phase symptoms have completely dissappeared Begin to recover strength and health. Long term Public health agencies track disease rates and severity ◦ Morbidity is the rate of illness due to a disease = how many are sick from a disease ◦ Mortality is the rate of death due to a disease = how many dies from a disease. Modes of transmission The route of transmission from one person or animal to another is called an infection cycle horizontal transmission occurs when the infection agent is transferred from one person or animal to the next. vertical transmission occurs when the infectious agent is transferred from parent to offspring. Cycles of infection can be simple or complex. direct contact transmission ◦ Organisms may spread directly form person through person ◦ Touching, kissing, sex… Indirect transmission ◦ Pathogens may spread indirectly through an intermediary, which may be living or no living ‣ Airborne transmission ‣ Vehicles = any medium that can transport infectious agents such as food, water, or air. ‣ Fomites (inanimate objects) ‣ Vectors (ticks, mosquitoes) depends iftheyhaveit Reservoirs is an animal (inducing humans) or an environment that normally harbours the pathogen. It may or may not exhibit the disease. Asymptomatic carrier harbours the potential disease agent but does not have the disease. Neisseria meningitidis is an important cause of meningitis nosymptoms ◦ It has no animal reservoir and is maintained in the human population by asymptomatic hosts. if theymakecontactwithchildrentthathasnovaccine.si ecamevirulent  p inanimate objects Flu diseaseduringwinter lymedisease northernarea dengefeveryellowfever Endemic, Epidemic, or Pandemic endemic disease is one that is always present in a community at a low rate, often in an animal reservoir Epidemic disease is one in which the number of cases increase in a community in a short time. e m Pandemic disease is an epidemic that spreads worldwide ◦ Influenza ◦ HIV ◦ Covid-19 ▪ Zoonotic diseases are infections of animals that can be transmitted to humans. ◦ Pathogens may or may not cause the animal reservoir to have a disease. ◦ Transmission may be direct or indirect “spillovers” from animal to human. ― Lyme disease: Pathogen does not cause disease in the animal host but does cause disease when bacteria “spill over” tohumans. Directinfection ― Ebola: Virus does cause disease in the animal host and also in humans. bothresoviorsandhumanhavedisease ▪ Animal and insect reservoirs can also function as “incubators” for new infectious diseases yet to emerge in humans. Two different strains of influenza virus can infect the same animal (usually pigs) at the same time. The two viruses can exchange discrete chunks of their genomes, and a new virus—more infectious and deadly than either of the original forms—can emerge. 2viruses mixgenome to createnew disease How Do Infectious Agents Gain Access to the Body? ▪ From one host to the next: Portals (routes) of exit/entry Fecal-oral: Portal is the mucosa of the GI tract. Skin: Portal is the skin epithelium. Respiratory: Portal is the mucosa of the respiratory tract. Urogenital: Portal is the mucosa of the genital and urinary tracts. Parenteral: Portal is through breaks in the skin. Entry via the eye: Portal is conjunctiva.