INFECTIOUS DISEASE Infectious Disease Process NATURE OF INFECTIOUS

INFECTIOUS DISEASE Infectious Disease Process

NATURE OF INFECTIOUS DISEASES l Pathogens: microorganisms that are capable of causing disease l Infection: results when a pathogen invades and begins growing within the host l Disease: results only if and when tissue function is impaired (i. e. burns, skin lesions)

Continued… l l l The body has defense mechanisms to prevent infection In order to cause disease, pathogens must be able to enter, adhere, invade, colonize, and inflict damage Entrance to the host: mouth, eyes, genital openings, wounds Growth of pathogens or the production of toxins/enzymes cause disease Some normal flora prevent diseases

MICROBES THAT CAUSE INFECTIOUS DISEASES l Bacteria: Salmonella typhi, Staphylococcus aureus Morphology: bacillus, coccus, spirillum ¡ Aerobes vs anaerobes ¡ Gram-negative (salmonella) vs gram-positive (staphylococcus) ¡ l Viruses: apart from the host cell, have no metabolism and cannot reproduce ¡ ¡ ¡ Retroviruses: HIV and certain types of cancer Herpes viruses: chicken pox, cold sores, smallpox Rhinoviruses: common colds – mutation (rapid) leads to no vaccine available Myxoviruses & paramysoviruses: influenza, measles, mumps Rotaviruses: gastroenteritis

Continued… l Fungi: form spores ¡ Examples include ringworm and histoplasmosis ¡ Yeasts of Candida genus are opportunistic ¡ Antibiotics reduces normal flora, allowing yeast to grow l Protoza: acquired through contaminated food or water, or bite of an arthropod (mosquito) ¡ Diarrheal disease in the US – Giardia lamblia and Cryptosporidium parvum ¡ Malaria – Plasmodium (in tropical environment)

… l Helminths: simple invertebrate animals, some infectious parasites ¡ ¡ ¡ l Symptoms: abd. pain and diarrhea Swimmer’s itch in US – flatworm, Schistosoma Trichinella spiralis – roundworm which is ingested in undercooked pork from infected pigs (Cause of death = respiratory paralysis) Prions-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

Malaria

Giardia and Cryptosporidium

Helminths Worm

Prions-Creuzfeldt-Jakob disease

OCCURANCE OF INFECTIOUS DISEASES Epidemiology: study of the occurence of disease in populations l Disease reservoirs: where the infectious agent survives (human, rodents) l ¡ l Example: yersinia pestis Modes of transmission ¡ ¡ ¡ Direct contact: occurs when a person is infected by contact with reservoir, inhaling infectious droplets – examples are AIDS, rabies, malaria, influenza, ringworm, trichninosis Indirect contact: the pathogen is transmitted from contaminated substances such as food, soil, water (Hepatitis A), clothing, equipment (example – tetanus) Horizontal vs vertical transmission l l Horizontal: transmission between individuals specifically who are not related as a parent is to its offspring Vertical: occurs from parent to offspring, e. g. , in utero, during passage down the birth canal, or in breast milk

HOST DEFENSES AGAINST INFECTIOUS DISEASES l Nonspecific mechanisms are the body’s primary defense against disease - anatomical barriers, physiological deterrents and presence of normal flora (skin, low p. H and high salinity) ¡ ¡ ¡ l Specific mechanisms: immunity ¡ ¡ ¡ l Anatomical barriers: nasal opening, skull, vertebral column, skin Physiological deterrents: tears, vaginal secretions, saliva, blood, sweat, and some tissue fluids Normal flora: successfully compete with pathogens Cell-mediated: uses T-cells; helper cells and killer cells; activate B cells Antibody-mediated: uses B-cells Both are lympatic cells Vaccination: produces immunity