Medical Microbiology Lecture 1 PDF

Medical microbiology lecture 1 **Pathology:** is the scientific study of disease. Primary **concerns/objective of pathology** regarding diseases Pathology is first concerned with the cause, or etiology, of disease. Second, it deals with pathogenesis, the manner in which a disease develops. Third,...

Medical microbiology lecture 1 **Pathology:** is the scientific study of disease. Primary **concerns/objective of pathology** regarding diseases Pathology is first concerned with the cause, or etiology, of disease. Second, it deals with pathogenesis, the manner in which a disease develops. Third, pathology is concerned with the structural and functional changes brought about by disease and their effects on the body. **Etiology** : Etiology refers to the study of the causes or origins of diseases. **Infection:** Infection is the invasion or colonization of the body by pathogenic microorganisms;. **Disease** :Disease is an abnormal state in which part or all of the body is incapable of performing its normal functions. disease occurs when an infection results in any change from a state of health. [The presence of a particular type of microorganism in a part of the body where it is not normally found is also called an infection---and may lead to disease.] For example, although large numbers of E. coli are normally present in the healthy intestine, their infection of the urinary tract usually results in disease. **Koch postulates:** Koch's postulates. 1\. The same pathogen must be present in every case of the disease. 2\. The pathogen must be isolated from the diseased host and grown in pure culture. 3\. The pathogen from the pure culture must cause the disease when it's inoculated into a healthy, susceptible laboratory animal. 4\. The pathogen must be isolated from the inoculated animal and must be shown to be the original organism. **Exception of Koch** postulates**:** 1. microbes having unique culture requirement.certain microbes may have specific nutritional, environmental, or growth requirements that are not easily met using standard laboratory culture methods. This can hinder the successful isolation and cultivation of the microbe. Example: The bacterium [Treponema pallidum] is known to cause syphilis, but virulent strains have never been cultured on artificial media. The causative agent of leprosy, [Mycobacterium leprae,] has also never been grown on artificial media. 2\. some infectious diseases are not as clear-cut and provide another exception to Koch's postulates. EXAMPLE: nephritis (inflammation of the kidneys) can involve any of several different pathogens, all of which cause the same signs and symptoms. Thus, it is often difficult to know which particular microorganism is causing a disease. 3.Ethical consideration : Fulfilling Koch\'s postulates may not always be feasible or ethical, especially in cases where experimentation on humans or animals is required. An example is HIV, the cause of AIDS. This poses the ethical question of whether humans can be intentionally inoculated with infectious agents. **communicable from a noncommunicable disease** A **communicable disease** is a disease in which an infected person transmits an infectious agent, either directly or indirectly, to another person who in turn becomes infected. Chickenpox, measles, influenza, genital herpes, typhoid fever, and tuberculosis are [examples]. Chickenpox and measles are also examples of contagious diseases, that is, diseases that are very communicable and capable of spreading easily and rapidly from one person to another. A **noncommunicable disease** is not spread from one host to another. These diseases are caused by microorganisms that normally inhabit the body and only occasionally produce disease. An [example] is tetanus: Clostridium tetani produces disease only when it is introduced into the body via abrasions or wounds. **Categorize diseases according to frequency of occurrence** If a particular disease occurs only occasionally, it is called a **sporadic disease**; typhoid fever in the United States is such a disease. A disease constantly present in a population is called an **endemic disease**; an example of such a disease is the common cold. If many people in a given area acquire a certain disease in a relatively short period, it is called an **epidemic disease**; influenza is an example of a disease that often achieves epidemic status. An epidemic disease that occurs worldwide is called **a pandemic disease**. **Categorize diseases according to severity** **acute disease** is one that develops rapidly but lasts only a short time; a good example is influenza A **chronic disease** develops more slowly. The body's reactions may be less severe, but the disease is likely to continue or recur for long periods. Example tuberculosis , and hepatitis B **subacute disease** A disease that is intermediate between acute and chronic ,an example is subacute sclerosing panencephalitis, a rare brain disease. A **latent disease** is one in which the causative agent remains inactive for a time but then becomes active to produce symptoms of the disease; an example is shingles. **Ques. how does herd immunity develops** ? Herd immunity develops when a sufficiently large proportion of a population becomes immune to a particular infectious disease, either through vaccination or previous exposure to the disease, thereby reducing the likelihood of the disease spreading within the population. outbreaks are limited to sporadic cases(unpredictable) because there are not enough susceptible(prone to ) individuals to support the spread of the disease to epidemic proportions. **Infection extent to which the host's body is affected** **local infection** is one in which the invading microorganisms are limited to a relatively small area of the body. a **focal infection** occurs when agents of a local infection enter a blood or lymphatic vessel and spread to other specific parts of the body, where they are confined to specific areas of the body. Focal infections can arise from infections in areas such as the teeth, tonsils, or sinuses. **Sepsis** is a toxic inflammatory condition arising from the spread of microbes, especially bacteria or their toxins, from a focus of infection**. Septicemia**, also called blood poisoning, is a systemic infection. **The state of host resistance** also determines the extent of infections. **A primary infection** is an acute infection that causes the initial illness. **A secondary infection** is one caused by an opportunistic pathogen after the primary infection has weakened the body's defense. **A subclinical infection**, also called inapparent infection, is one that doesn't cause any noticeable illness. **Ques. Distinguish the incidence from the prevalence of a disease** The incidence of a disease is the number of people in a population who develop a disease during a particular time period. It's an indicator of the spread of the disease. The prevalence of a disease is the number of people in a population who develop a disease at a specified time, regardless of when it first appeared. Prevalence takes into account both old and new cases. It's an indicator of how seriously and how long a disease affects a population. **Ques. Identify four predisposing factors for disease.** A predisposing factor makes the body more susceptible to a disease and may alter the course of the disease. 1.**Gender** is sometimes a predisposing factor; for example, females have a higher incidence of urinary tract infections than males, whereas males have higher rates of pneumonia and meningitis. 2. **genetic background** may play a role as well. For example, sickle cell disease is a severe, life-threatening form of anemia that occurs when the genes for the disease are inherited from both parents. Individuals who carry only one sickle cell gene have a condition called sickle cell trait and appear normal unless specially tested 3. **Climate and weather** seem to have some effect on the incidence of infectious diseases. In temperate regions, the incidence of respiratory diseases increases during the winter. 4. **vaccination and herd immunity** in decreasing the spread of diseases, age (the very young and elderly are more susceptible to infections), **Development of disease** 1**.The incubation period** is the interval between the initial infection and the first appearance of any signs or symptoms. In some diseases, the incubation period is always the same; in others, it is quite variable. 2. During **the period of illness,** the disease is most severe. The person exhibits overt signs and symptoms of disease, such as fever, chills, muscle pain (myalgia), sensitivity to light (photophobia), sore throat (pharyngitis), lymph node enlargement. If the disease is not successfully overcome (or successfully treated), the patient dies during this period. 3. During the **period of decline**, the signs and symptoms subside. The fever decreases, and the feeling of malaise diminishes. During this phase, which may take from less than 24 hours to several days, the patient is vulnerable to secondary infections 4. During the **period of convalescence,** the person regains strength and the body returns to its prediseased state. Recovery has occurred. **Reservoirs of Infection** organism needs adequate conditions for survival and multiplication and an opportunity for transmission. Such a source is called a reservoir of infection. These reservoirs may be human, animal, or nonliving. **1**.The principal living **reservoir of human** disease is the human body itself. Many people harbor pathogens and transmit them directly or indirectly to other. some people can harbor pathogens and transmit them to others without exhibiting any signs of illness. For [example,] immune adolescents and adults carry Bordetella pertussis and can transmit an infection to a nonvaccinated infant. **2**.**Animal** **Reservoirs** Both wild and domestic animals are living reservoirs of microorganisms that can cause human diseases. Diseases that occur primarily in wild and domestic animals and can be transmitted to humans are called zoonoses. [example] Rabies (found in bats, skunks, foxes, dogs, and coyotes), and Lyme disease (found in field mice). **3**.The two major **nonliving reservoirs** of infectious disease are soil and water. [example] Clostridium botulinum, the bacterium that causes botulism; and C. tetani, the bacterium that causes tetanus. Water that's been contaminated by the feces of humans and other animals is a reservoir for several pathogens, notably those responsible for **gastrointestinal diseases**. [example] ,Vibrio cholerae, which causes cholera; Cryptosporidium, one cause of diarrhea; and Salmonella Typhi, which causes typhoid fever[. ] **Transmission of Disease** **Contact transmission** is the spread of a disease agent by direct contact, indirect contact, or droplet transmission. **1.Direct contact transmission**, also known as person-to-person transmission, is the direct transmission of an agent by physical contact between its source and a susceptible host; no intermediate object is involved ). The most common forms of direct contact transmission are touching, kissing, and sexual intercourse. Among few of them are viral respiratory tract diseases (the common cold and influenza), staphylococcal infections, hepatitis A, measles, scarlet fever, and sexually transmitted infections**. 2. Congenital transmission** is the transmission of diseases from mother to fetus or newborn at birth. This occurs when a pathogen present in the mother's blood is capable of crossing the placenta or through direct contact with a pathogen in the mother's blood or vaginal secretions during delivery. **Indirect contact transmission** occurs when the agent of disease is transmitted from its reservoir to a susceptible host by means of a nonliving object **[.]** The general term for any nonliving object involved in the spread of an infection is a fomite. Examples of fomites are stethoscopes, clothing from health care personnel, tissues, handkerchiefs, towels. **Droplet transmission** is a third type of contact transmission in which microbes are spread in droplet nuclei (mucus droplets) that travel only short distances.. These droplets are discharged into the air by coughing, sneezing, laughing, or talking.. Examples are influenza, pneumonia, and pertussis (whooping cough). **Vehicle transmission** is the transmission of disease agents by a medium, such as air, water, or food. **Airborne transmission** refers to the spread of agents of infection by droplet nuclei in dust that travel more than 1 meter from the reservoir to the host. **waterborne transmission**, pathogens are usually spread by water contaminated with untreated or poorly treated sewage. foodborne transmission, pathogens are generally transmitted in foods that are incompletely cooked, poorly refrigerated, or prepared under unsanitary conditions. **fecal-oral transmission** , some microbes are ingested contaminated in water or food. The pathogens usually enter the water or food after being shed in the feces of people or animals infected with them. **vectors**---animals that carry pathogens from one host to another. Arthropod vectors transmit disease by two general methods. **1**. **Mechanical transmission** is the passive transport of the pathogens on the insect's feet or other body parts. If the insect makes contact with a host's food, pathogens can be transferred to the food and later swallowed by the host example flies. **2. Biological transmission** by arthropod vectors involves active processes where the vector ingests infected blood, allowing pathogens to reproduce within it. These pathogens can be transmitted to another host through various mechanisms, including defecation, vomiting, or direct injection through a bite. Some parasites also use the vector as a host for their developmental stage.example malaria ,dengue. **ques.List several probable reasons for emerging infectious diseases, and name one example for each reason.** An emerging infection refers to a newly identified or reappearing infectious disease that is increasing in incidence or geographic range, posing a significant threat to public health. 1. **Biological factors**: Pathogens can undergo genetic mutations or recombination. New strains, such as E. coli O157:H7 and avian influenza (H5N1), may result from genetic recombination between organisms. 2. **Antimicrobial resistance**: use of antibiotics and pesticides encourages the growth of more resistant populations of microbes and the vectors (mosquitoes, lice, and ticks) that carry them. 3. **Globalization and travel**: Known diseases, such as Zika virus disease, chikungunya, dengue, and West Nile , may spread to new geographic areas by modern transportation. This was less likely 100 years ago, when travel took so long that infected travelers either died or recovered during passage. 4. **Global warming and changes in weather patterns :** may increase the distribution and survival of reservoirs and vectors, resulting in the introduction and dissemination of diseases such as malaria and Hantavirus pulmonary syndrome. 5. **Bioterrorism,** the use of pathogens or toxins to produce death and disease in humans, animals, or plants as an act of violence and intimidation, is another factor that could affect the occurrence of emerging infectious diseases **Ques.Give several examples of emerging infectious diseases**. 1. **COVID-19**: Caused by the novel coronavirus SARS-CoV-2, COVID-19 emerged in late 2019 in Wuhan, China, and quickly spread globally, leading to a pandemic. 2. **Ebola virus:** Ebola virus periodically emerges in outbreaks, primarily in Central and West Africa. The virus causes severe hemorrhagic fever with high mortality rates. 3. **Chikungunya:** virus, transmitted by Aedes mosquitoes, has caused outbreaks in various regions, including Africa, Asia, Europe, and the Americas. 4. **Severe acute respiratory syndrome :**The virus SARS-CoV emerged in China in 2002 and spread to several countries, causing a global outbreak. The disease primarily affects the respiratory system. **Ques.Define epidemiology, and describe three types of epidemiologic investigations**. **Epidemiology:** The science that studies when and where diseases occur and how they are transmitted in populations is called epidemiology. **1**.the cholera epidemic of 1848-1849 in London, Dr. John Snow conducted investigations and analyzed death records. He discovered that most victims who died of cholera had consumed water from the Broad Street pump. By mapping cases, he concluded that contaminated water from this pump was the source of the epidemic. After removing the pump\'s handle, cholera cases significantly decreased, confirming Snow\'s hypothesis and demonstrating the importance of clean water in preventing disease transmission. Snow's search for the cause of the cholera outbreak in London is an example of **descriptive epidemiology** collecting all data that describe the occurrence of the disease under study. **2**. Ignaz Semmelweis observed high maternal death rates due to puerperal sepsis in Vienna General Hospital\'s First Maternity Clinic compared to the Second Clinic. Wealthy women avoided the clinic, while poor women had better survival rates elsewhere. Semmelweis introduced handwashing practices among medical staff, leading to a significant reduction in puerperal sepsis cases, highlighting the importance of hygiene in healthcare. Semmelweis's use of handwashing is an example of **experimental epidemiology** ,that begins with a hypothesis about a particular disease; experiments to test the hypothesis are then conducted. **3**. Ignaz Semmelweis introduced handwashing with chloride of lime for medical students, reducing mortality rates to under 2%. Florence Nightingale\'s statistical analyses on epidemic typhus led to reforms in the British Army and her recognition as the Statistical Society\'s first female member. Together, their work pioneered epidemiology, emphasizing the importance of understanding disease transmission within population. Nightingale's work was an example of analytical epidemiology (analyzes and compare a particular disease to determine its probable cause)., in which she compared disease in soldiers and civilians. **The Centers for Disease Control and Prevention (CDC)** monitors the occurrence of diseases, identifies outbreaks, and investigates their causes. This involves collecting, analyzing, and interpreting health data to track trends and patterns in disease occurrence. **Morbidity:** Morbidity refers to the state of being diseased or unhealthy within a population. It encompasses the occurrence, frequency, and distribution of diseases, injuries, and other health-related conditions within a specific population over a particular period of time. **Mortality:** Mortality refers to the state of being subject to death within a population. It represents the number of deaths that occur within a specific population over a given period of time **Notifiable infectious**: Notifiable infectious diseases are diseases that are required by law to be reported to public health authorities when diagnosed.