Emerging & Re-emerging Infectious Disease. Infectious Diseases Disease: conditions that impair...
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Emerging & Re-emerging Infectious Disease Slide 2 Infectious Diseases Disease: conditions that impair normal tissue function Genetic or Metabolic diseases: ex Cystic Fibrosis Disease of aging: ex atherosclerosis Infectious Disease: caused by the invasion of a host by agents whose activities harm the hosts tissues Slide 3 Pathogens: microorganisms that are capable of causing disease Opportunistic pathogens are potentially infectious agents that rarely cause disease in individuals with a healthy immune system. Slide 4 The terms infection & disease are not synonymous An infection results when a pathogen invades and begins growing in a host Disease results only if and when, as a consequence of the invasion and growth of a pathogen, tissue function is impaired Slide 5 Contagious vs. Virulent Some infectious agents are easily transmitted (very contagious) but are not likely to cause disease (not very virulent) Example: Polio-probably infects most people it contacts, however only 5-10% actually develop the disease. Slide 6 Other infectious agents are very virulent, but not terribly contagious. Ex: Ebola hemorrhagic fever, virulence of the virus is 50-90% fatality among those infected, however the virus is not transmitted easily by casual contact. Slide 7 How do infections happen? In order to cause disease, pathogens must be able to enter the host body, adhere to specific host cells, invade and colonize host cells, invade and colonize host tissues, and inflict damage on those tissues Pathogens usually enter through natural orifices or through breaks in the natural skin barrier such as wounds. Slide 8 Corynebacterium diphtheria Bacteria that causes diphtheria Grows only on nasal and throat surfaces Damage to tissues is due to the production of enzymes or toxins Toxin is distributed to other systems via the circulatory system resulting in damage to the heart, liver and nervous tissues Slide 9 Streptococcus pyogenes Infectious agents associated with strep throat and flesh eating disease Produces enzymes that break down barriers between epithelial cells and remove fibrin clots, helping the bacteria invade tissues Slide 10 Microbes 5 major types of infectious agents Bacteria Viruses Fungi Protozoa Helminths In addition, a new class of infectious agents, the prions, has recently been recognized Slide 11 Bacteria Have no organized internal membranous structure such as nuclei, mitochondria, or lysomes. Most bacteria reproduce by growing and dividing into two cells (binary fusion) Slide 12 Variety of morphologies. 3 most common Bacillus (rod shaped) Coccus (round) Spirillum (helical rods) Slide 13 Some bacteria require oxygen aerobes Some bacteria can not tolerate oxygen anaerobes Some bacteria can grow either with or without oxygen facultative anaerobes Slide 14 Gram Stain Bacteria are generally divided into 2 broad classes based on their cell wall structure, which influences their Gram stain reaction Gram Negative bacteria appear pink after the staining procedure Slide 15 Gram Negative Bacteria Salmonella typhi (causes Typhoid Fever) Yersinia pestis (causes the plague) Slide 16 Gram positive bacteria Appear purple after gram stain procedure Staphylococcus aureus (causes skin, respiratory & wound infections) Clostridium tetani (produces a toxin that can be lethal for humans) Slide 17 Viruses Not organisms themselves, cannot reproduce apart from the host cell Cause disease by disrupting normal cell function Classified using a variety of criteria including shape, size, and type of genome. Slide 18 Viruses Examples of viruses: Herpes viruses that cause chicken pox, cold sores and genital herpes Poxvirus that causes smallpox Rhinovirus that causes the common cold Myxoviruses and paramyxoviruses that cause influenza, measles and mumps Rotaviruses that cause gastroenteritis Retroviruses that cause AIDS and several types of cancer Slide 19 Fungi Reproduce primarily by forming spores Together with bacteria, fungi work to be the decomposers in our environment Examples of diseases caused by fungi Ringworm Histoplasmosis (lung infection caused by bat or bird droppings) Slide 20 Fungi Yeasts of the Candida genus are opportunistic yeast infections and cause diseases such as vaginal yeast infections and thrush (a throat infection) among people who are immunocompromised or undergoing antibiotic therapy Slide 21 Protozoa Do have cell walls so are able to have rapid and flexible movements Can be acquired through contaminated food or water or by a bite of an infected anthropod such as a mosquito Slide 22 Protozoa Diseases Giardia lamblia & cryptosporidium parvum are two protozoa parasites that cause diarrheal disease in the US Malaria, a tropical illness, is caused by several species of the protozoan Plasmodium Slide 23 Helminths Are simple, invertebrate animals, some which are infectious parasites Because they are animals, their physiology is similar to humans, making this parasite difficult to treat because drugs that kill helminths are frequently very toxic to humans Slide 24 Helminths Have complex reproductive cycles and many require a host Examples: Schistosoma, Caused by a flat worm Results in diarrhea and abdominal pain Trichinella spiralis, caused by a roundworm Results in vomiting, diarrhea and fever, later symptoms include muscle pain, congestive heart failure and respiratory paralysis Slide 25 Prions Infections particles that consist only of proteins Pronounced (pree-ons) Linked to some CNS degenerative disorders in humans and animals Slide 26 Prions Examples of diseases: Creutzfeldt-Jakob disease in humans Scrapie in sheep Bovine spongiform encephalopathy (mad cow disease) in cattle Some prion diseases are inherited, others are caused from eating infected tissue Slide 27 Epidemiology Defined as the study of the occurrence of diseases in populations Epidemiologist are concerned not only with infectious disease but also with non- infectious disease such as cancer and environmental diseases such as lead poisoning Slide 28 Disease reservoirs The reservoir for a disease is the site where the infectious agent survives Example: Humans are the reservoir for the measles virus because it does not infect other organisms Wild rodents are the reservoir for Yersinia pestis, the bacteria that causes the plague Soil is the reservoir for the bacteria Clostridium tetani which causes tetanus Slide 29 Modes of transmission Transmitted by either direct or indirect contact Direct contact is when an individual is infected by contact with the reservoir Example: touching an infected person, eating infected meat, being bitten by an infected animal, inhaling infectious droplets from a sneeze or cough, intimate sexual contact Slide 30 Direct contact diseases Some diseases spread by direct contact include: Ringworm AIDS Trichinosis Influenza Rabies Malaria Slide 31 Modes of Transmission Indirect contact occurs when a pathogen can withstand the environment outside its host for a long period of time before infecting another individual Examples: tissues or toys handles by sick people, ingesting food or beverages contaminated by contact with a disease reservoir Slide 32 Indirect contact Fecal-oral route is a significant form of indirect transmission for gastrointestinal diseases such cholera, rotavirus infection, cryptosporidiosis, and giardiasis. Also included in indirect transmission are diseases transmitted from parent to child such as AIDS and herpes encephalitis Slide 33 Role of research in prevention Understanding the infectious cycle is critical in order to identify accessible targets for control strategies Examples: Vector-borne diseases may be prevented by control methods that either kill the vector or prevent its contact with humans. Vaccines may prevent the development of a pathogen within a host, drugs may be used to prevent infections or suppress the disease process Slide 34 Host Defenses against Infectious Disease The humans body has several mechanisms for preventing diseases These include anatomical barriers to invading pathogens (skin, bone, nasal passage), physiological deterrents to pathogens (tears, sweat, blood, vaginal secretions), and the presence of normal flora (microorganisms present on and in the body) Slide 35 Immunity When a host encounters an antigen that triggers a specific immune response for the second or later time, the memory lymphocytes recognize it and quickly begin growing and dividing. The immune response occurs so quickly the second time that the pathogen does not have time to reproduce before the body has destroyed it. Slide 36 Vaccination A vaccine is either a killed or weakened strain of a particular pathogen The bodys immune system will respond to these vaccines as if they contain the actual pathogen. As a result, memory lymphocytes will rapidly respond when the actual pathogen is encountered, destroying the pathogen before it can reproduce Slide 37 Vaccination Many diseases are not easily prevented by vaccination Some pathogens have a way to evade the immune response either by not allowing antibodies to pass through their cells, by disguising themselves as a host cell or by mutating. Cold and influenza viruses are examples of rapidly mutating pathogens Slide 38 Public Health measures to prevent Infectious Disease Safe water: Many pathogens that cause gastrointestinal diseases (cholera & typhoid fever) are transmitted in water. Travelers to developing countries are asked to be immunized Unnecessary in the US and developed countries because the water used for drinking, washing and preparing food is purified before it goes into homes. Slide 39 Water purification Purification methods include settling, filtration and chlorination. Well water is usually safe if guidelines about distance from sewage disposal facilities is followed. When purification systems breakdown, such as with unusual flooding, drinking water may not be safe and should