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CLASSIFYING INFECTIOUS DISEASES

Symptom: A change in body function that is felt by a patient as a result of disease
Sign: A change in a body that can be measured or observed as a result of disease
Syndrome: A specific group of signs and symptoms that accompany a disease

Communicable vs. Non-communicable

vs. Contagious

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CLASSIFYING INFECTIOUS DISEASES

Communicable disease: A disease that is spread from one host to another
Contagious disease: A disease that is easily spread from one host to another
Noncommunicable disease: A disease that is not transmitted from one host to another

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OCCURRENCE OF A DISEASE

Incidence (заболеваемость): Fraction of a population that contracts a disease during a specific time
Prevalence (распространенность): Fraction of a population having a specific disease at a given time
Sporadic disease (единичное, отдельное): Disease that occurs occasionally in a population
Endemic disease: Disease constantly present in a population
Epidemic disease: Disease acquired by many hosts in a given area in a short time
Pandemic disease: Worldwide epidemic

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SEVERITY OR DURATION OF A DISEASE

Scope of disease can be defined as

Acute: disease develops rapidly
Chronic: disease develops slowly
Subacute: symptoms between acute and chronic
Latent: disease with a period of no symptoms when the causative agent is inactive

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EXTENT OF HOST INVOLVEMENT

Toxemia: Toxins in the blood
Sepsis: Toxic inflammatory condition arising from spread of microbes or their toxins, from a focus
Bacteremia: Bacteria in the blood
Septicemia: Growth of bacteria in the blood
Viremia: Viruses in the blood
Primary infection: Acute infection that causes the initial illness
Secondary infection: Opportunistic infection after a primary (predisposing) infection
Subclinical disease: No noticeable signs or symptoms (inapparent infection)

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EXTENT OF HOST INVOLVEMENT: AN INFECTION CAN BE

Local: limited to small area of body
Systemic: spread throughout body via
Focal: spread from local infection to specific areas o
Primary: acute infection causing initial illness
Secondary: occurs after host is weakened from primary infection
Subclinical (inapparent): no noticeable signs and symptoms

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PREDISPOSING FACTORS

Variable susceptibility due to

Genetics
Gender
Climate and weather
Age
Stress and fatigue,
Lifestyle
Chemotherapy

A predisposing factor makes the body more susceptible to a

disease and may alter the course of the disease

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DISEASE DEVELOPMENT

Incubation period: Time interval between initial infection and first appearance signs and symptoms

Prodromal period: Characterized by appearance of first mild signs and symptoms

Period of illness: Disease at its height: all disease signs and symptoms apparent

Period of decline: Signs and symptoms subside

Period of convalescence: Body returns to prediseased state, health is restored

The stages of disease

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THE COURSE OF DISEASE, AS TYPIFIED BY MEASLES

Period of illness

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THE SPREAD OF INFECTION: RESERVOIR

Copyri

For a disease to perpetuate itself, there must be a continual source of the disease organisms. This source can be either a living organism or an inanimate object that provides a pathogen with adequate conditions for survival and multiplication and an opportunity for transmission. Such a source is called a reservoir of infection.

Nonliving: Soil, e.g.: ??

Human: people with disease or asymptomatic carriers may have inapparent infections or latent diseases

Pathogen for some other species lives and multiplies in reservoir.

Zoonoses may be transmitted to humans.

Rabies (found in bats, skunks, foxes, dogs, and coyotes), and Lyme disease (found in field mice) are examples of zoonoses.

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DISEASE TRANSMISSIONS

CONTACT TRANSMISSION:

Direct: Close association between infected and susceptible host - person-to-person transmission. The most common forms of direct contact transmission are touching, kissing, and sexual intercourse.

Among the diseases that can be transmitted by direct contact are viral respiratory tract diseases (the common cold and influenza), staphylococcal infections, hepatitis A, measles, scarlet fever, and sexually transmitted infections (syphilis, gonorrhea, and genital herpes). Direct contact is also one way to spread AIDS, syphilis, and infectious mononucleosis.

Droplet: Transmission via airborne droplets from saliva or mucus (coughing or sneezing)

Disease Transmissions

TRANSMISSION OF DISEASE

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AIRBORNE TRANSMISSION: PATHOGENS CARRIED ON WATER DROPLETS OR DUST FOR A DISTANCE GREATER THAN 1 METER

VEHICLE TRANSMISSION: TRANSMISSION OF DISEASE AGENTS BY A MEDIUM, SUCH AS AIR, WATER, OR FOOD AND BLOOD, OTHER BODY FLUIDS, DRUGS, AND INTRAVENOUS FLUIDS

VECTOR TRANSMISSION: ARTHROPODS CARRY PATHOGENS FROM ONE HOST TO ANOTHER (MECHANICAL VECTOR VS. BIOLOGICAL VECTOR)

ARTHROPOD VECTORS TRANSMIT DISEASE BY TWO GENERAL METHODS.

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Congenital transmission is the transmission of diseases from mother to fetus or newborn at birth. This occurs when a pathogen present in the mother’s blood is capable of crossing the placenta or through direct contact with a pathogen in the mother’s blood or vaginal secretions during delivery.

Indirect contact transmission occurs when the agent of disease is transmitted from its reservoir to a susceptible host by means of a nonliving object. The general term for any nonliving object involved in the spread of an infection is a fomite.

Examples of fomites are stethoscopes, clothing from health care personnel, tissues, handkerchiefs, towels, bedding, diapers, drinking cups, eating utensils, toys, money, and thermometers.

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NOSOCOMIAL (HOSPITAL-ACQUIRED) INFECTIONS

Acquired as a result of a hospital stay.
5-15% of hospital patients acquire nosocomial infections.
Aseptic techniques can prevent nosocomial infections.
Hospital infection control staff members are responsible for overseeing the proper cleaning, storage, and handling of equipment and supplies.

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