1. Infectious Disease Process

2. NATURE OF 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 tissue function is impaired (i.e. burns, skin lesions)

3. Continued… 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

4. MICROBES THAT CAUSE INFECTIOUS DISEASES
Bacteria: Salmonella typhi, Staphylococcus aureus
Morphology: bacillus, coccus, spirillum
Aerobes vs anaerobes
Gram-negative (salmonella) vs gram-positive (staphylococcus)
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

5. Continued… Fungi: form spores
Examples include ringworm and histoplasmosis
Yeasts of Candida genus are opportunistic
Antibiotics reduces normal flora, allowing yeast to grow
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)

6. … Helminths: simple invertebrate animals, some infectious parasites
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

11. Malaria

12. Giardia and Cryptosporidium

13. Helminths Worm

14. Prions-Creuzfeldt-Jakob disease

15. OCCURANCE OF INFECTIOUS DISEASES
Epidemiology: study of the occurence of disease in populations
Disease reservoirs: where the infectious agent survives (human, rodents)
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
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

16. HOST DEFENSES AGAINST INFECTIOUS DISEASES
Nonspecific mechanisms are the body’s primary defense against disease - anatomical barriers, physiological deterrents and presence of normal flora (skin, low pH and high salinity)
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
Specific mechanisms: immunity
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