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الكلية كلية طب الاسنان
القسم العلوم الاساسية
المرحلة 3
أستاذ المادة علي زكي ناجي الاسدي
5/31/2011 7:31:59 AM
Infectious diseases:
Despite improved living conditions, widespread vaccination, and availability of effective antibiotics, infectious diseases continue to take a heavy toll in the United States among persons with acquired immunodeficiency syndrome (AIDS), debilitated with chronic disease, or treated with immunosuppressive drugs.
In developing countries, unsanitary living conditions and malnutrition contribute to a massive burden of infectious disease that kills more than 10 million persons each year.
Most of these deaths are among children, who suffer respiratory and diarrheal infections caused by viruses and bacteria. scientists established criteria for linking a specific microorganism to a specific disease:
(1) the organism is regularly found in the lesions of the disease,
(2) the organism can be isolated as single colonies on solid medium,
(3) inoculation of this culture causes lesions in an experimental animal, and
(4) the organism can be recovered from lesions in the animals.
Host organism interaction:
Commensals microorganism: These are microorganism that live on the expense of the host without harmful effects.
1- commensal bacteria of the skin.
2- Intestinal normal flora.
Pathogenic microorganisms: These microorganisms that live on the expense of the host producing harmful effect to the host; (viruses, bacteria, fungi,..).
Pathogenicity : it’s the capacity of particular microorganism to cause a disease.
Virulence: it’s the degree of pathogenicity.
Body defense mechanisms against infectious agents.
Non specific mechanisms: there are not depend on the nature of the pathogen.
1- mechnical barriers: integrity of the skin, and mucus secretion.
2- glandular secretion:
• Acidity of the gastric juice and sweat act as bactericidal.
• Secretion of mucous membrane of lacrimal and salivary glands contain a enzymes that able to kill bacteria by digesting the mucopeptide of bacterial cell wall.
• IgA antibodies found in tear, saliva milk can also protect the body from harmful effects of microorganism.
3- washing effect of secretion flow:
• Continuous tears flow.
• Respiratory ciliated epithelium.
Types of infectious agents:
A- Viruses All viruses depend on host cell metabolism for their replication, that is, are obligate intracellular parasites . They are classified by the nucleic acid content of their core (DNA or RNA) and by the shape of their protein coat or capsid. some are frequent causes of acute illness (colds, influenza). Others are capable of lifelong latency and of long-term reactivation (herpes viruses) or may give rise to chronic disease (HBV).
B- BACTERIA Bacterial cells are prokaryotes that lack nuclei and endoplasmic reticulum. Their cell walls are relatively rigid, composed either of two phospholipid bi-layers with a peptidoglycan layer sandwiched in between (gram-negative species) or of a single layer covered by peptidoglycan (gram-positive bacteria) . Bacteria synthesize their own DNA, RNA, and proteins but depend on the host for favorable growth conditions. Some thrive mainly on the body s surface layers on the skin, like Staphylococcus epidermidis and Propionibacterium acnes, the agent responsible for adolescent pimples. Many bacterial pathogens invade host tissue and are capable of extra-cellular division (e.g., pneumococcus) or of both extra-cellular and intracellular division (e.g., Mycobacterium tuberculosis). Next to viruses, bacteria are the most frequent and diverse class of human pathogens and include many of the major pathogens.
C- BACTERIOPHAGES, PLASMIDS: These are mobile genetic elements that encode bacterial virulence factors (e.g., adhesins, toxins, or enzymes that confer antibiotic resistance). They can infect bacteria and incorporate themselves into their genome thus converting an otherwise harmless bacterium into a virulent one or an antibiotic-sensitive organism into a resistant one.
D- CHLAMYDIAE, RICKETTSIAE, MYCOPLASMAS These infectious agents are grouped together because they are similar to bacteria in that they divide by binary fission and are susceptible to antibiotics but lack certain structures (e.g., mycoplasmas lack a cell wall) or metabolic capabilities (e.g., Chlamydia lack adenosine triphosphate [ATP] synthesis). Chlamydia, which are frequent causes of genitourinary infections, conjunctivitis, and respiratory infections of newborn infants, Most rickettsiae are transmitted by insect vectors, including lice (epidemic typhus), Rickettsiae are obligate intracellular agents that replicate in the cytoplasm of endothelial cells by injuring the endothelial cells, rickettsiae cause a hemorrhagic vasculitis often visible as a rash or injure the central nervous system and cause death, Mycoplasmas are the tiniest free-living organisms cause Mycoplasma pneumoniae spreads from person to person by aerosols, and causes an atypical pneumonia characterized by peribronchiolar infiltrates of lymphocytes and plasma cells.
E- FUNGI Fungi possess thick, ergosterol-containing cell walls and grow as perfect, sexually reproducing forms in vitro and as imperfect forms in vivo, which include budding yeast cells and slender tubes (hyphae), Some produce spores, which are resistant to extreme environmental conditions. Some fungal species, for example, those of the Tinea group causing "athlete s foot," are confined to the superficial layers of the human skin; other "dermatophytes" preferentially damage the hair shafts or nails. Certain fungal species invade the subcutaneous tissue, causing abscesses or granulomas. Opportunistic fungi (Candida, Aspergillus, Mucor), contaminants colonizing the normal human skin or gut without causing illness. Only in immunosuppressed individuals do opportunistic fungi give rise to life-threatening infections. In addition, AIDS patients, late in their course, are frequent victims of the opportunistic fungus-like organism Pneumocystis carinii.
F- PROTOZOA Parasitic protozoa are single-celled organisms endowed with motility, and complex cytoplasmic organelles. The intestinal protozoa (e.g., Entamoeba histolytica and Giardia lamblia) are spread by the fecal-oral route. Blood-borne protozoa (e.g., Plasmodium species, Trypanosoma species, and Leishmania species) are transmitted by blood-sucking insects, in which they undergo a complex succession of life stages before being passed to new human hosts.
G- HELMINTHS Parasitic worms are highly differentiated multi-cellular organisms. Their life cycles are complex; most alternate between sexual reproduction in the definitive host and asexual multiplication in an intermediary host or vector. Thus, depending on parasite species, humans may harbor either adult worms (e.g., Ascaris) or asexual larval forms (e.g., Echinococcus). Adult worms, once resident in humans, do not multiply in number but generate eggs or larvae destined for the next phase of the cycle. There are two important consequences of the lack of replication of adult worms:
(1) disease is often caused by inflammatory responses to the eggs or larvae rather than to the adults (e.g., schistosomiasis) and (2) disease is in proportion to the number of organisms that have infected the individual (e.g., 10 hookworms cause little disease, whereas 1000 hookworms cause severe anemia by consuming 100 ml of blood per day).
H- PRIONS Prions, which are apparently composed only of a modified host protein, cause transmissible spongiform encephalopathies Creutzfeldt-Jakob disease (associated with corneal transplants) bovine spongiform encephalopathy (better known as mad cow disease), and atypical Creutzfeldt-Jakob disease transmitted to humans from bovine spongiform encephalopathy
SPREAD AND DISSEMINATION OF MICROBES Once implanted, microbes spread on the surface of moist and warm mucosae faster than on cool and dry skin. Some of the superficial pathogens stay confined to the lumen of hollow viscera (e.g., cholera); others adhere to or proliferate exclusively in or on epithelial cells (e.g., papillomaviruses, dermatophytes). A variety of pathogenic bacteria, fungi, and helminths are invasive pathogens by virtue of their motility or ability to secrete lytic enzymes (e.g., streptococcal hyaluronidase, schistosome proteases). Spread through serosal cavities (pleura, peritoneum, meninges) is particularly fast and dangerous. Microbes may also ascend the lymphatics from their entry site to the regional nodes and hence into the bloodstream. Thus, untreated staphylococcal infections may progress from a localized abscess or furuncle to regional lymphadenitis followed by bacteremia, endocarditis, or formation of multiple pyemic abscesses in distant sites (brain, kidney, bone). Viruses may propagate from cell to cell by fusion or axonal transport (e.g., poliovirus), but like other intracellular pathogens (e.g., tubercle bacilli), they can enter the bloodstream and be carried to distant sites by migratory macrophages or by circulating red cells . The major manifestations of infectious disease may arise at sites distant from those of parasite entry. For example, chickenpox and measles viruses enter through the airways but manifest themselves first as rashes; poliovirus is ingested and multiplies inside the gut wall before proceeding to viremic invasion and killing of motor neurons. The placental-fetal route is an important mode of transmission. When infectious organisms reach the pregnant uterus through the cervical orifice or the bloodstream and are able to traverse the placenta, severe damage to the fetus may result. It may cause premature delivery or stillbirth. Treponema pallidum infecting the mother breaches the placenta by the end of the second trimester and causes manifestations of congenital syphilis in the infant, ranging from dental deformities to stillbirth. Central nervous system damage is particularly common in the so-called TORCH (Toxoplasma, rubella, CMV, herpesviruses, and other) infections. Fetuses infected late during pregnancy or during passage through the birth canal and infants receiving virus through maternal milk usually fare better than those infected during early embryonal life; their lesions may resemble those of adult patients. Maternal transmission of HIV results in opportunistic infections in 50% of untreated children during the first year of life..
المادة المعروضة اعلاه هي مدخل الى المحاضرة المرفوعة بواسطة استاذ(ة) المادة . وقد تبدو لك غير متكاملة . حيث يضع استاذ المادة في بعض الاحيان فقط الجزء الاول من المحاضرة من اجل الاطلاع على ما ستقوم بتحميله لاحقا . في نظام التعليم الالكتروني نوفر هذه الخدمة لكي نبقيك على اطلاع حول محتوى الملف الذي ستقوم بتحميله .
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