INFECTIOUS DISEASEInfectious Disease Process

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)

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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 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

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Fungi: form spores Examples include ringworm and histoplasmosis Yeasts of Candida genus are opportunistic Antibiotics reduces normal flora, allowing yeast to

growProtoza: 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)

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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

Malaria

Giardia and Cryptosporidium

Helminths Worm

Prions-Creuzfeldt-Jakob disease

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

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