Infectious Diseases
Pathogens: Microorganisms that are capable of causing disease Infection: Results when a pathogen invades and begins growing within the host Disease: Results only if and when normal tissue function is impaired The body has defense mechanisms to prevent infection (i.e. burns, skin lesions)
In order to cause disease, pathogens must be able to enter, adhere, invade, colonize, and inflict damage Entrance to the host typically occurs through natural orifices such as the mouth, eyes, genital openings, or through wounds that breach the skin barrier to pathogens Growth of pathogens or the production of toxins/enzymes cause disease Some normal flora prevent diseases
Infectious Disease a disease caused by the invasion of a host by pathogens causing impaired tissue function and can be transmitted to other individuals Five major types of infectious agents (microbes): bacteria, viruses, fungi, protozoa, and helminthes: Bacteria: They contain no organized internal membranous structures. Most reproduce by growing and dividing into two cells in a process known as binary fission.
Types of Bacteria: Salmonella typhi: a gram-negative organism that causes typhoid fever. Yersinia pestis- Causes plague The reservoir is rodents. *** Staphylococcus aureus- causes skin, respiratory and wound infections.
Viruses: Infect all organisms from plants and animals to fungi and bacteria. They are not organisms themselves because apart from a host cell, they have no metabolism and cannot reproduce.***
Types of viruses: Herpes viruses: cause chicken pox, cold sores, and painful genital lesions, and the pox virus that causes smallpox. Rhinoviruses: cause most common colds.
Viruses (continued) Myxoviruses and paramyxoviruses: cause influenza, measles, and mumps. Rotaviruses: cause gastroenteritis. Retroviruses: cause AIDS and several types of cancer.
Fungi: Reproduce primarily by forming spores. Types of diseases caused by fungi: Ringworm Histoplasmosis (a mild to severe lung infection transmitted by bat or bird droppings) Candida genus: opportunistic pathogens*** that may cause diseases such as vaginal yeast infections and thrush.
Protozoa: Do not have cell walls and are capable of a variety of rapid and flexible movements. Can be acquired by contaminated food or water or by the bite of an infected arthropod such as a mosquito.
Helminths: Simple, invertebrate animals, some of which are infectious parasites. Difficult to treat because the drugs that kill helminthes are frequently very toxic to human cells. Diseases caused by helminths: Trichinella Spiralis: occurs when improperly cooked pork from infected pigs is ingested. Symptoms include vomiting and diarrhea and fever*** Respiratory paralysis can occur in fatal cases of trichinella spiralis***
Prions: Infectious particles that consist of only protein. Diseases caused by Prions: Creutzfeldt-Jakob disease (in humans)*** Bovine spongiform encephalopathy (mad cow disease)
Epidemiology- the study of the occurrence of disease in populations. Disease reservoirs- The reservoir for a disease where the infectious agent survives (example: rodents, soil Modes of transmission: Infectious agents may be transmitted through either direct or indirect contact.
Host defenses against infectious diseases: Nonspecific mechanisms-the body s primary defense against disease these include anatomical barriers to invading pathogens, physiological deterrents to pathogens, and presence of normal flora. (skin, low ph and high salinity)
Specific mechanisms of host resistance- our immune system Immunity when a host encounters an antigen that triggers a specific immune response for the second time and the body responds quickly and produces antibodies Vaccination- produces immunity