1. Infection and Infectious disease

2. Pathology is the scientific study of disease. Etiology: Cause of disease. Infection: the invasion or colonization of the body by pathogenic microorganisms. 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. Disease: occurs when an infection results in any change from a state of health. Pathology: is the scientific study of disease. It is concerned with the structural and functional changes brought about by disease and with their final effects on the body. Pathogenesis: the manner in which a disease develops. Every disease that affects the body alters body structures and functions in particular ways, and these alterations are usually indicated by several kinds of evidence.

3. Signs: which are objective changes the physician can observe and measure. Frequently evaluated signs include lesions (changes produced in tissues by disease), swelling, fever, and paralysis. Symptoms: changes in body function, such as pain and malaise (a vague feeling of body discomfort ). These subjective changes are not apparent to an observer. Syndrome: A specific group of symptoms or signs may always accompany a particular disease; such a group is called a syndrome.

4. Normal Microbiota Animals are generally free from microbes in utero. After birth, microbial populations rapidly establish themselves in the newborn’s body. Vaginal lactobacilli colonize newborn’s intestine. Feeding and breathing introduce many more microbes. E. coli and other bacteria colonize large intestine. Candida albicans colonizes mucous membranes. Normal Microbiota or Flora: Microorganisms that remain throughout an individual’s life. Transient Microbiota: Microorganisms that are present for a certain time period and then disappear.

5. Microbial Antagonism: Normal flora inhibits overgrowth of harmful microbes. Mechanisms include competition for nutrients and affecting environmental factors such as pH, toxic substances, and oxygen availability. In mouth streptococci produce compounds that inhibit growth of many other cocci. In intestine E. coli produce bacteriocins, which inhibit growth of closely related bacteria. Relationships Between the Normal Microbiota and the Host

6. SYMBIOSIS: “Living together”. Relationship between the host and its normal flora. 1. Commensalism: One organism benefits, the other is not affected (+/0). Many microbes live off secretions and dead cells and do not benefit or harm host. 2. Mutualism: Both organisms benefit from living together (+/+). E. coli synthesizes vitamin K and some B vitamins. 3. Parasitism: One organism benefits, the other is harmed (+/-). Most disease causing bacteria.

7. Opportunistic Pathogens The nature of symbiotic relationships can change. Opportunistic Pathogens: Organisms that normally do not cause disease in their natural habitat in a healthy person. They may cause disease if the host is weakened or if they enter a different part of the body. Pneumocystis carinii pneumonia in AIDS patients. Tooth decay and gum disease caused by mouth flora. Neisseria meningitidis is usually harmless in respiratory tract, but can cause meningitis. E. coli can cause urinary tract infections, meningitis, pneumonia, and abscesses.

8. Diseases are often classified in terms of how they behave within a host and within a given population. Classification of Infectious disese: Communicable Contagious Non-communicable

9. Communicable disease :Any disease that spreads from one host to another, either directly or indirectly is said to be a communicable disease. Chickenpox, measles, genital herpes, typhoid fever, and tuberculosis are examples. Contagious diseases :Chickenpox and measles are also examples of contagious diseases, that is, diseases that are easily spread from one person to another

10. Noncommunicable disease: 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 or by microorganisms that reside outside the body and produce disease only when introduced into the body. An example is tetanus: Clostridium tetani produces disease only when it is introduced into the body via abrasions or wounds.

11. Occurance of a Disease Incidence: The incidence of a disease is the number of people in a population who develop a disease during a particular time period. It is an indicator of the spread of the disease. Prevalence: 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.

12. Depending on the occurance of the dieases, they are classified into 4 groups: 1. Sporadic disease: If a particular disease occurs only occasionally, it is called a sporadic disease; typhoid fever in the United States is such a disease. 2. Endemic disease: A disease constantly present in a population is called an endemic disease; an example of such a disease is the common cold.

13. 3. Epidemic disease: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. 4.Pandemic disease: An epidemic disease that occurs worldwide is called a pandemic disease. We experience pandemics of influenza from time to time. Some authorities also consider AIDS to be pandemic

14. Severity or duration of disease: Another useful way of defining the scope of a disease is in terms of its severity or duration. 1.Acute disease: An acute disease is one that develops rapidly but lasts only a short time; a good example is influenza. 2. Chronic disease: A chronic disease develops more slowly, and the body's reactions may be less severe, but the disease is likely to continue or recur for long periods. Infectious mononucleosis, and hepatitis B fall into this category.

15. 3. Subacute disease :A disease that is intermediate between acute and chronic is described as a subacute disease; an example is subacute sclerosing panencephalitis, a rare brain disease characterized by diminished intellectual function and loss of nervous function. 4. Latent 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, one of the diseases caused by varicella virus.

16. Extent of Host involvement: Local Infection: A local infection is one in which the invading microorganisms are limited to a relatively small area of the body. Some examples of local infections are boils and abscesses. Systemic Infection: In a systemic (generalized) infection, microorganisms or their products are spread throughout the body by the blood or lymph. Measles is an example of a systemic infection. Focal Infection: Very often, 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. This condition is called a focal infection. Focal infections can arise from infections in areas such as the teeth, tonsils, or sinuses.

17. Development of Diseases Once a microorganism overcomes the defenses of the host, development of the disease follows a certain sequence that tends to be similar whether the disease is acute or chronic. Incubation Period: 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. The time of incubation depends on the specific microorganism involved, its virulence (degree of pathogenicity), the number of infecting microorganisms, and the resistance of the host.

18. Prodromal Period: The prodromal period is a relatively short period that follows the period of incubation in some diseases. The prodromal period is characterized by early, mild symptoms of disease, such as general aches and malaise.

19. Period of Illness: 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 (lymphadenopathy), and gastrointestinal disturbances. During the period of illness, the number of white blood cells may increase or decrease. Generally, the patient's immune response and other defense mechanisms overcome the pathogen, and the period of illness ends. When the disease is not successfully overcome (or successfully treated), the patient dies during this period.

20. Period of Decline: 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.

21. Period of Convalescence During the period of convalescence, the person regains strength and the body returns to its prediseased state. Recovery has occurred.

22. Development & stages of Disease