Infectious Disease BMT Mrs. Cavanaugh
Disease • Condition that impairs normal tissue function. Examples include: • Cystic Fibrosis • Atherosclerosis • measles • Infectious Disease • Caused by the invasion of a host by agents whose activities harm the host’s tissues (cause disease) and can be transmitted to other individuals (they are infectious)
Microorganisms • Capable of causing disease and are called pathogens. • Usually disease causing m/o’s get the most attention, however, it’s important to note that most m/o’s do NOT cause disease. • Many provide protection.
Opportunistic Pathogen • Potentially infectious agents that rarely cause disease in individuals with healthy immune systems. • Typically found among groups such as • Elderly (immune systems are failing) • Cancer patients (chemotherapy and radiation) which affect immune systems • HIV positive or AIDS (altered immune system)
True Pathogen • Infectious agent that causes disease in virtually any susceptible host.
Two terms not synonymous • Infection • Results when a pathogen invades and begins growing within a host. • Disease • Results only if and when, as a consequence of the invasion and growth of a pathogen, tissue function is impaired.
Our bodies have defense mechanisms to prevent infection. If the defense mechanisms fail, we have the ability to prevent disease after infection occurs.
Infectious agents that are easily transmitted are considered contagious. • Infectious agents that easily cause disease are said to be virulent.
The most worrisome infectious agents are those that are both very contagious and very virulent.
For disease to occur, pathogens must • Enter the host body • Adhere to specific host cells • Invade and colonize host tissues • Inflict damage on those tissues
Pathogen typically enters the host through natural orifices such a the mouth, eyes, or genital openings • Or through wounds that breach the skin barrier to pathogens
Some pathogens can grow at the initial entry site, however most must invade areas of the body where they are not typically found to grow.
6 major types of infectious agents • Bacteria • Viruses • Fungi • Protozoa • Helminths • Prions – most recently recognized
Bacteria • Unicellular prokaryotic organisms • They have no organized internal membranous structures such as nuclei, mitochondria or lysosomes • Most reproduce by growing and dividing into two cells • Much diversity among bacteria
Most common are • Bacillus (rod-shaped) • Coccus (spherical) • Spirillum (helical rods) -Some bacteria obtain energy from the sun. • Others oxidize inorganic compounds to supply their energy needs. -Still other bacteria generate energy by breaking down organic compounds such as amino acids and sugars.
2 broad classes of bacteria • Gram-negative bacteria • Appear pink after a staining process • Example – Samonellatyphi which causes Typhoid Fever • Yersinipestiswhich causes plague • Gram-positive bacteria • Appear purple after staining process • Example –Staphyloccusaureus which cause skin, respiratory and wound infections • Clostridium tetaniwhich produces a toxin that could be lethal
Viruses • Can infect all organisms • Including plants, animals, fungi and bacteria • Cause disease like other infectious agents by disrupting normal cell function. • Viruses are not organisms themselves. • They have no metabolism and can not reproduce without a host cell.
Classified according to shape, size and type of genome • DNA viruses • herpes viruses that cause chicken pox, cold sores and genital lesions • Poxvirus that cause smallpox • RNA viruses • Rhinovirus that cause most common cold • Myxovirus and paramyxovirus that cause influenza, measles and mumps • Rotavirus that cause gastroenteritis • Retrovirus that cause AIDS and several types of cancers
Fungi • Most are multicellular • Yeast is type of fungus that is unicellular • Also infect plants and animals • Example of dz caused by fungi • Ringworm • Histoplasmosis (lung infection transmitted by bat or bird droppings)
Yeast • Type of fungi (Candida genus) • Opportunistic pathogen • Causes thrush in mouth and throat and common vaginal infections in people who are immunocompromised or undergoing antibodic therapy • Antibiotics reduce the bacterial population normally present in the throat and vagina, allowing yeast to grow
Protozoa • Unicellular • Amoeba and paramecium • No cell wall making them capable of rapid and flexible movements • Acquired through contaminated food or water or by the bite of infected anthropod such as a mosquito
Diarrheal disease in the US caused by • Giardia lamblia • Cryptosporidium parvum • Malaria • Tropical illness that causes 300-500 million cases annualy, caused by Plasmodium
Helminths • Complex reproductive cycles with multiple stages, many or all of which require a host • Schistosoma • Flatworm that causes swimmers itch • Trichinellaspiralis • Roundworm - ingested in improperly cooked pork from infected pigs. • Early sxincude vomiting, diarrhea, and fever • Later sx include intense muscle pain as larvae grow and mature in the tissues • Fatal cases often show congestive heart failure and respiratory paralysis.
Prions • Evidence has linked degenerative disorders of the central nervous system to infectious particles that are made up only of protein. • Creutzfeldt-Jakob disease (humans) • Scrapie (sheep) • Bovine spongiform encephalopathy – also known as “mad cow disease” (cattle)
All known prion diseases frequently result in brain tissue that is riddled with holes. • Some are inherited • Others are apparently due to infection by eating infecected tissue or inadvertently through medical procedures such as tissue transplants.
Creuzfeldt-Jakob disease • A rare, degenerative, invariably fatal brain disorder; believe caused by an unusual "slow virus" or another organism • Typically, onset of symptoms occurs about age 60, and about 90 percent of individuals die within 1 year. • Characterized by rapidly progressive dementia and they eventually lose the ability to move and speak and enter a coma
Occurrence of Infectious Disease • Epidemiology • The study of the occurrence of disease in populations • Epidemiologist (specialist in this area) – work to prevent or minimize the impact of diseases in the population. • Work may include activities of identifying unusually high incidences of disease, determining the effectiveness of a vaccine and calculating the cost effectiveness of various means of controlling disease transmission. • Concern is with infectious and non-infectious disease • Non infectious includes cancer, atherosclerosis, lead poisoning
Disease Reservoirs • The site where the infectious agent survives • Humans • Measles virus because it does not infect other organisms • Animals • For diseases that infect humans • Ex – bacteria that causes plague (Yersinia pestis) • Rodents are the reservoir • Soil • Nonliving reservoir • Fungi and bacteria • Clostridium tetani– Causes Tetanus
Mode of Transmission • Direct Contact • Contact with the reservoir • Ex – touching infected person, ingesting infected meat, or being bitten by infected animal Also includes inhaling the infectious agent in droplets emitted by sneezing or coughing. • Indirect Contact • Occurs when pathogens can withstand the environment outside its host for a long period of time before infecting another individual • Ex- from toys, door knobs, contaminated water
Horizontal Transmission • Agent is passed from person to person in a group • Includes cholera and rotovirus • Vertical Transmission • Transmitted from parent to child during reproduction, fetal development or birth • Includes AIDS, Herpes encephalitis
Host defenses against infectious disease • Nonspecific mechanisms include the body’s primary defense against disease • Include anatomical barriers • Ex – skin, nasal openings, skull and vertebral column • Difficult to treat burn patient with tissue breakdown • Physiological deterrents • Tears, vaginal secretions, saliva and nasal secretions, blood, sweat • Inflammatory response • Normal flora • Microorganisms present on and in the body normally. • Typically do not cause disease in the body • Protect the host by competing with invading harmful bacteria
Breakdown in Normal Flora • Growth of normal flora is depressed during altered immunity • Sickness, antibiotic treatment, disease • Opportunistic infections can occur at this time
Immunity • When a host encounters an antigen that it recognizes. • Memory cells are present and begin to respond by producing antibodies to fight off the invading pathogen. • Usually a very rapid response. • Vaccinations cause this memory response and typically prevents first occurrences of many diseases.
Vaccination • Either a killed or weakened (attenuated) strain of a particular pathogen, or a solution containing critical antigens from the pathogen. • Body’s immune system will respond to these vaccines • As a result, memory lymphocytes will be present that respond rapidly if the actual pathogen is encountered. • The resulting rapid activation of immune cells prevents disease.