Infectious Diseases

Sexually Transmitted Infection

What is a Disease?

• Disease = Any interference with the normal functioning of the body organs or systems

• Human Disease may be caused by• Environmental factors• Defects of body structures or functions• Activities of infectious microorganisms

Signs, Symptoms and Syndromes

• Signs – A more or less observable and obvious feature of

a disease• Includes things like diarrhia, a rash, peeling of the skin• Painless lesion of syphilis called a chancre

• Symptom– Any change in a body structure of function that

can be observed or felt by the individual• Asymptomatic

Signs, Symptoms and Syndromes

• Syndrome– A combination of signs and symptoms occurring in a

typical pattern• Etiology– The cause, set of causes, or manner of causation of a

disease or condition• Sequelae– Some diseases leave aftereffects

• Viral infections of the liver can result in the loss of functioning liver cells and interference with bloodflow through the organ

Signs, Symptoms and Syndromes

• The outcome of a disease depends on– Genetics– Age– Nutritional status– Prior exposure to the infectious agent– Resulting levels of body protection or immunity

• Prognosis– Predict the course and outcome of a disease

Types of Diseases

• Diseases can be placed in descriptive groups:– Hereditary and congenital– Degenerative– Neoplastic– Metabolic– Immunological– infectious

Hereditary and Congenital Diseases

• Hereditary Diseases– Caused by errors in the

information present in an abnormal gene or genes• May be abnormalities in

– The number and distribution of chromosomes

– Interaction of genetic and environmental factors

– Down’s Syndrome• Abnormal distribution of

chromosomes• Trisomy 21

Hereditary and Congenital Diseases

• Abnormalities that develop between the time of fertilization (conception) and birth are divided into two categories– Embryonic Period• First eight weeks of pregnancy

– Fetal Period• From the ninth week of pregnancy to birth

Embryonic Period

• Changes occurring produce visible deformities of organs or other body structures– Embryonic or congenital defects

• Are present at birth• Drugs, excessive X-ray exposure, or certain infections may

disrupt the developing embryo or fetus• The embryo is most vulnerable to injury during the 3rd to 8th

week of pregnancy

– Infections acquired by the mother may injure the developing fetus and cause congenital defects• Mental retardation, blindness, brain injury, even death

– German measles (rubella), Syphilis, Genital Herpes

Degenerative Diseases

• The breakdown of various body parts– Aging

• Chronic (long lasting) illnesses that can lead to death– Heart attack– Stroke (bleeding and/or blockages in blood vessels of the brain)

– Could occur even without aging• Hardening of the arteries• Certain forms of arthritis• Degenerating joints• Diverticulitis

Neoplastic Diseases

• Diseases associated with abnormal cell growth that leads to the formation of various types of tumors– Benign (harmless)– Malignant (cancerous)

• One in five persons die in the United States of some form of cancer– Human papilloma viruses cause genital warts• Has been associated with cervical cancer

Metabolic Diseases

• These diseases include a variety of disorders in which the body’s production of chemical products essential to its functioning either are nonexistent or defective– Hormones

• A chemical product body a body organ or gland, which is carried by the blood to another body site where it stimulates a particular function

• Endocrine

– Enzymes• A complex proteins produced by cells, that causes changes in

other substances without being changed in the process

Immunologic Diseases

• Diseases that result from the improper or impaired functioning of the body’s immune system– The immune system provides protection against various

disease agents and other factors in an individual’s environment• The immune system can destroy or neutralize disease agents

and factors considered to be foreign by the immune system

• Inflammation– A response to tissue injury

• Swelling, redness, local heat, pain, and abnormal functionin of the part involved

Immunologic Diseases

• Immunologic diseases are grouped into two categories:– Primary Immunodeficiencies• Arise from an inherited lack of development of one or

more parts of the immune system

– Secondary Immunodeficiencies• Occur more frequently than primary• Results from many factors that suppress an individual’s

immune responses to events such as infection– AIDS

Infectious Diseases

• Microbiota– Microscopic forms that live on the skin, in the mouth and the

large intestine– Most are harmless– Some, if given the opportunity can cause a disease

• These are known as opportunists• Can lead to opportunistic infections

– Pathogens• Microorganisms that cause severe problems upon gaining

entrance to the host tissues

– Pathogenesis• Eventual development of a diseases

Infectious Diseases

• Pathogenicity– The disease producing capability of a pathogen

• Virulence– The degree or intensity of pathogenicity

• Infectious Diseases are caused by infectious agents– Bacteria– Fungi– Protozoa– Viruses– Helminths (worms)

Infectious Diseases

• Communicable or Contagious– Certain infectious diseases can spread from

person to person• Flu or measles• Gonorrhea or syphilis

• Noncommunicable or not contagious– Caused by an infectious agent but does not spread

from person to person• Tetanus

The Course of an Infectious Disease

• Incubation Period– The time between the multiplication of the

pathogen and the appearance of signs and symptoms

• Prodromal Phase– The early stage of some diseases in which

nonspecific symptoms such as headache and general weakness appear

The Course of an Infectious Disease

• Invasive Phase– The period during which pathogens invade and

cause tissue damage• Signs and symptoms of the disease appear at the same

time

• Convalescence Phase– The time period during which recovery occurs and

includes healing and regaining strength• Even if signs and symptoms disappear individuals

may still be able to spread an infectious diseases

The Course of an Infectious Disease

• Acute– Disease occurs rapidly and sometimes with

intense symptoms• Chronic– Disease develops more slowly and lasts for a

longer, indefinite, period of time

The Concept of Infectious Disease

• Girolamo Fracastorius, a Franciscan monk in 1546– Distinguished several ways an infectious disease was able to

spread• Contact with the skin• Contact with objects close to a sick person• The air in a sickroom

• Anton VanLeeuwenhoek, late 1600s– Created the first real microscope– Discovered microorganisms with his microscope

• Rober Koch1876– Koch’s Postulate - “Germ theory of disease”

• Demonstrated a specific bacterium caused anthrax

Factors Contributing to the Success of an Infectious Disease

• Pathogens act in certain ways to cause diseases– Gaining access to the host– Attaching to and reproducing on the cell surface– Invading body tissues– Producing poisonous substances known as toxins

to breakdown the body’s defenses• Toxins may also cause allergic responses in some

people

The Microbial World

• Bacteria– Single-celled microorganisms• May be beneficial or harmful to the host

– Bacteria are differentiated from one another by several factors:• Shape• Color reactions• Chemical composition• Growth• Responses to chemicals such as antibiotics

Shape of Bacteria

• Coccus– Spherical form

• Bacillus– Rod

• Spirillum– Twisted or bent– Tight corkscrew known

as a spirochete

Isolating and Growing (Culturing) Bacteria

• Medium –– Nutrient used to grow

bacteria– Made from broth or

liquid, and solid or agar– Contains nutrients

• Sugar• Protein• Vitamins• Minerals

Fungi• Single- and multi-cellular forms of life

– Yeast– Molds– Mushrooms

• The majority of fungi are involved natural decomposition of rotting and decaying plant and related material

• Commercial production of some bakery goods, cheeses, antibiotics, alcoholic beverages and other chemicals

• Some fungi can attack the – Skin, nails and hair– Causes different forms of ringworm

• Athlete’s foot

– Some can form STD’s like a yeast infection• Fungi are opportunistic

Protozoa

• Single-celled animal-like microorganisms• Most are harmless and found in the soil and

water• Some causes diseases such as malaria, African

sleeping sickness and Amebic dsentery• Protozoa are opportunistic and cause STD’s

Viruses

• Cannot be seen by an ordinary light microscope– Must use an electron microscope– Viruses are therefore called submicroscopic• Chicken pox• HIV

• Viruses are not cells• Viruses vary in shape

Viruses

• Virions – Individual virus particles– Contain a single type of nucleic acid• Either DNA or RNA but never both

• Capsid– Protein coat encloses the nucleic acid component

• Culvitation– Viruses can only replicate in living cells

Helminths or Worms

• Helminths that cause most of human disease are – Flatworms– Roundworms