Unit 10-Diseases and Epidemiology; Lesson 3-Classification, Transmission, and Patterns of Infection
Period of Decline
-signs and symptoms subside -fever decreases, feeling of malaise diminishes -patient is vulnerable to secondary infections during this time
Incidence
-the INCIDENCE of a disease is the # of ppl in a population who develop a disease during a particular time period. -an indicator of the spread of disease.
Prevalence
-the PREVALENCE of a disease is the # of ppl in a population who develop a disease at a specific time, regardless on when it first appeared. -prevalence- takes into account old and new cases. -its an indicator of how seriously and how long a disease affects a population. -ex- incidence of AIDS in US in 2007 was 56,300. Prevalence in that same year was estimated to be about 1,185,000.
Incubation Period
-the interval between the initial infection and the first appearance of any signs or symptoms -in some diseases, incubation period is always the same; in others its variable -Time of incubation- depends on specific microbes involved, its virulence, the number of infecting microbes, and the resistance of the host.
Contact Transmission (Direct Contact, Indirect Contact, and droplet transmission)
-the spread of an agent of disease by direct contact, indirect contact, or droplet transmission.
Epidemic
-when many people in a given area acquire a certain disease in a relatively short period (ex- influenza)
What are the categories that describe the severity and duration of disease?
Acute Disease Chronic Disease Subacute Disease Latent Disease
Put the following in the correct order to describe the pattern of disease: period of convalescence, prodromal period, period of decline, incubation period, period of illness.
Incubation period, prodromal period, period of illness, period of decline (may be crisis), period of convalescence.
Portal of Exit
The route by which a pathogen leaves the body
Systemic (generalized) Infections
- microorganisms or their products are spread throughout the body by the blood or lymph. (ex- measles)
Differentiate between communicable and non-communicable diseases.
-Communicable Disease: any disease that spreads from one host to another (either directly or indirectly)- ex. Chickenpox, measles, genital herpes, typhoid fever, tuberculosis -Nonommunicable Disease: not spread from one host to another. These diseases are caused by microorganisms that normally inhabit the body and only occasionally produce disease or by microorganisms that reside outside the body and produce disease only when introduced into the body (ex. Tetanus: Clostridium tetani produces disease only when introduced into body via abrasions or wounds).
Direct Contact
-Direct Contact Transmission- person-to-person transmission. The direct transmission of an agent by physical contact between its source and a susceptible host- no intermediate object is involved. - touching, kissing, sexual intercourse -Viral respiratory tract diseases (common cold and influenza), staphylococcal infections, hep A, measles, scarlet fever, and STIs (syphilis, gonorrhea, genital herpes) -one way to spread AIDS and infectious mononucleosis. - health care workers use gloves and other protective measures -potential pathogens can also be transmitted by direct contact from animals (or animal products) to humans (rabies and anthrax)
Droplet Transmission
-Droplet Transmission- microbes are spread in droplet nuclei (mucus droplets) that travel only short distances -discharged into air by coughing, sneezing, laughing, or talking -travel less than 1 meter from reservoir to the host - one sneeze can produce 20,000 droplets -disease agents that travel such short distance are not regarded as airborne -ex: influenza, pneumonia, pertussis (whooping cough)
Other definitions not in study guide
-Focal Infection-agents of local infections can enter a blood or lymphatic vessel and spread to other parts of the body) - can arise from teeth, tonsils, or sinuses -Toxemia- presence of toxins in the blood (as occurs in tetanus) -Viremia- presence of viruses in the blood -Subclinical (inapparent) infection- one that does not cause any noticeable illness (Poliovirus, Hep A virus- can be carried by people who never develop the illness.)
What are the three reservoirs of infection?
-Human Reservoirs -Animal Reservoirs -Nonliving Reservoirs
The Stages of a Disease
-INCUBATION PERIOD, PRODROMAL PERIOD, PERIOD OF ILLNESS, PERIOD OF DECLINE, PERIOD OF CONVALESCENCE
Indirect Contact
-Indirect Contact Transmission-occurs when the agent of disease is transmitted from its reservoir to a susceptible host by means of a nonliving object. -Fomite- any nonliving object involved in the spread of an infection -ex- tissues, handkerchiefs, towels, bedding, diapers, drinking cups, eating utensils, toys, money, thermometers, contaminated syringes (transmitting AIDS and hep B)
Vector
-animals that carry pathogens from one host to another. -Arthropod vectors- transmit disease by 2 methods: Mechanical transmission or Biological transmission
Period of Illness
-disease is most severe -person exhibits overt signs and symptoms- fever, chills, muscle pain (myalgia), sensitivity to light (photophobia), sore throat (pharyngitis), lymph node enlargement (lymphade-nopathy), and GI disturbances. -during this period- WBCs may increase or decrease -partients immune response and other defence mechanisms overcome the pathogen and period of illness ends. -if disease is not overcome- patient dies during this period
Period of Convalescence
-person regains strength -body returns to prediseased state- RECOVERY
Human Reservoirs
-ppl w/ signs and symptoms may transmit disease -Carriers- ppl can harbor pathogens and transmit to others w/o having signs and symptoms (Carriers- important living reservoirs of infection) --Human carriers play an important role in the spread of such diseases as AIDS, diphtheria, typhoid fever, hepatitis, gonorrhea, amebic dysentery, and streptococcal infections.
Bacteremia
-presence of bacteria in the blood
Vehicle Transmission
-the transmission of disease agents by a medium such as water, food or air -other media include: blood, body fluids, drugs, IV fluids -waterborne transmission-pathogens are spread by water contaminated w/ untreated or poorly treated sewage. -diseases: cholera, waterbone shigellosis, leptospirosis. -foodborne transmission- pathogens are generally transmitted in foods that are incompletely cooked, poorly refrigerated, or prepared under unsanitary conditions. Diseases: food poisoning, tapeworm infestation -Airborne transmission- spread of agents of infection by droplet nuclei in dust that travels more than 1 meter from reservoir to the host -ex-microbes are spread by droplets, discharged during coughing and sneezing. -droplets are small enough to remain airborne for prolonged periods. -virus that causes measles and the bacterium that causes tuberculosis can be transmitted via airborne droplets. --dust particles- can harbor various pathogens. -staphylococci & streptococci- can survive on dust and can be transmitted airborne route -spores produced by certain fungi are transmitted by airborne route- can cause diseases such as histoplasmosis, coccidiodomycosis, and blastomycosis
How can a local infection become a systemic infection?
When microorganisms causing a local infection enter a blood or lymph vessel and are spread throughout the body, a systemic infection can result.
Indicate whether each of the following conditions is typical of subacute, chronic, or acute infections •a. )The patient experiences a rapid onset of malaise; symptoms last 5 days. •b.) The patient experiences cough and breathing difficulty for months. •c.) The patient has no apparent symptoms and is a known carrier.
a. Acute b. Chronic c. Subacute
Name the method of transmission of each of the following diseases: • a.malaria • b.tuberculosis • c.nosocomial infections • d.salmonellosis • e.streptococcal pharyngitis • f.mononucleosis • g.measles • h.hepatitis A • i.tetanus • j.hepatitis B • k.chlamydial urethritis
a.malaria-transmitted by a Vector- the Anopheles mosquito bite b.tuberculosis-Droplet Transmission c.nosocomial infections-Droplet Transmission, Direct and Indirect Contact. d.salmonellosis-ingestion of contaminated food and water, putting hands in mouth e.streptococcal pharyngitis -Droplet transmission, Indirect and direct contact. f.mononucleosis-Contact (Direct Contact (kissing disease- though saliva)) g.measles-Contact (Direct, Indirect, Droplet) Transmission h.hepatitis A- faecal-oral route; that is when an uninfected person ingests food or water that has been contaminated with the faeces of an infected person i.tetanus- direct contact through wound j.hepatitis B-spread when blood, semen, or other body fluid infected with the Hepatitis B virus enters the body of a person who is not infected k.chlamydial urethritis- sexually transmitted infection
Biological Transmission
an active process (more complex) -arthropod bite infected person or animal, and ingests some of the infected blood -pathogens then reproduce in the vector -some parasites reproduce in the gut of the arthropod- passed with feces -if arthropod defecates or vomits while biting a potential host- parasite can enter the wound. -Other parasites- reproduce in vectors gut and migrates to salivary glands- directly injected into a bite -Some protozoan and helminthic parasites use the vector as a host for a developmental stage in their life cycle
Chronic Disease
develops more slowly, and the body's reactions may be less severe, but the disease is likely to continue or recur for longer periods. (ex- infectious mononucleosis, tuberculosis, and hep B)
Secondary Infection
one caused by opportunistic pathogen after the primary infection has weakened the body's defenses. (secondary infections of the skin and respiratory tract are common- sometimes more dangerous than the primary infections) -Pneumocystis pneumonia as a consequence of AIDS- example of a secondary infection -streptococcal bronchopneumonia following influenza- an example of a secondary infection that is more serious than the primary infection.
Mechanical Transmission
the passive transport of the pathogens on the insects feet or other body parts. -insect can make contact w/ host food (houseflies- can transfer pathogens of typhoid fever and bacillary dysentery (shigellosis) from feces of infected ppl to food)
The Spread of Infection Reservoirs of Infection
• 1. A continual source of infection is called a reservoir of infection. • 2. People who have a disease or are carriers of pathogenic microorganisms are human reservoirs of infection. • 3. Zoonoses are diseases that affect wild and domestic animals and can be transmitted to humans. • 4. Some pathogenic microorganisms grow in nonliving reservoirs, such as soil and water.
SUMMARY! Classifying Infectious Diseases
• 1. A patient may exhibit symptoms (subjective changes in body functions) and signs (measurable changes), which a physician uses to make a diagnosis (identification of the disease). • 2. A specific group of symptoms or signs that always accompanies a specific disease is called a syndrome. • 3. Communicable diseases are transmitted directly or indirectly from one host to another. • 4. A contagious disease is one that is easily spread from one person to another. • 5. Noncommunicable diseases are caused by microorganisms that normally grow outside the human body and are not transmitted from one host to another.
Patterns of disease Predisposing Factors
• 1. A predisposing factor is one that makes the body more susceptible to disease or alters the course of a disease. • 2. Examples include gender, climate, age, fatigue, and inadequate nutrition.
Extent of Host Involvement
• 10. A local infection affects a small area of the body; a systemic infection is spread throughout the body via the circulatory system. • 11. A primary infection is an acute infection that causes the initial illness. • 12. A secondary infection can occur after the host is weakened from a primary infection. • 13. An inapparent, or subclinical, infection does not cause any signs of disease in the host.
Development of Disease
• 3. The incubation period is the interval between the initial infection and the first appearance of signs and symptoms. • 4. The prodromal period is characterized by the appearance of the first mild signs and symptoms. • 5. During the period of illness, the disease is at its height, and all disease signs and symptoms are apparent. • 6. During the period of decline, the signs and symptoms subside. • 7. During the period of convalescence, the body returns to its prediseased state, and health is restored.
Latent Disease
- one in which the causative agent remains inactive for a time but then becomes active to produce symptoms of the disease (ex. Shingles)
Local Infections
- one in which the invading microorganisms are limited to a relatively small area of the body. (ex- boils and abscesses)
Acute Disease
- one that develops RAPIDLY but only lasts a SHORT TIME (ex. Influenza)
Nonliving Reservoirs
-2 major nonliving reservoirs: SOIL & WATER -soil- harbors pathogens such as fungi- cause mycoses such as RINGWORM and systemic infections and systemic infections; Clostridium botulinum & C. tetani- -both species of clostridia are part of normal intestinal microbiota of horses and cattle- so their bacteria are found in soil where animal feces are used as fertilizer -Water that's been contaminated by feces of humans or other animals- reservoir for pathogens (esp those responsible for GI diseases) -these include: Vibrio cholera, Salmonella typhi -other nonliving reservoirs include foods that are improperly prepared or stored (may be sources of trichinellosis, and salmonellosis.
Sporadic
- a particular disease that occurs only occasionally (ex. Typhoid fever in the US)
Prodromal Period
- a relatively short period that follows period of incubation in some diseases. -characterized by early, mild symptoms of disease, such as general aches and malaise
Septicemia
- also called BLOOD POISONING, is a systemic infection arising from the multiplication of pathogens in the blood. (septicemia- common example of sepsis) -Sepsis- toxic inflammatory condition arising from the spread of microbes especially bacteria or their toxins, form a focus of infection.
Primary Infection
- an acute infection that causes the initial illness
Subacute Disease
- intermediate between acute and chronic (ex. Subacute sclerosing panencephalitis- a rare brain disease)
Animal Reservoirs
-Zoonoses- diseases that occur primarily in wild and domestic animals and can be transmitted to humans.- ex Rabies & Lyme disease -transmission of zoonoses to humans can occur via many routes: -direct contact w/ infected animals -direct contact w/ domestic pet waste contamination of food and water -air from contaminated hides, fur, or feathers -consuming infected animal products -insect vectors
Endemic
-a disease constantly present in a population (ex. The common cold)
List and describe the six forms of disease transmission
Contact Transmission: 1.Direct Contact, 2. Indirect Contact, and 3. Droplet Transmission 4.Vehicle Transmission Vectors 5. Mechanical Transmission 6. Biological Transmission
Pandemic
an epidemic disease that occurs worldwide (we experience pandemics of influenza from time to time.) (another example: AIDS)
Transmission of Disease
• 5. Transmission by direct contact involves close physical contact between the source of the disease and a susceptible host. • 6. Transmission by fomites (inanimate objects) constitutes indirect contact. • 7. Transmission via saliva or mucus in coughing or sneezing is called droplet transmission. • 8. Transmission by a medium such as water, food, or air is called vehicle transmission. • 9. Airborne transmission refers to pathogens carried on water droplets or dust for a distance greater than 1 meter. • 10. Arthropod vectors carry pathogens from one host to another by both mechanical and biological transmission.
Occurrence of a Disease
• 6. Disease occurrence is reported by incidence (number of people contracting the disease) and prevalence (number of cases at a particular time). • 7. Diseases are classified by frequency of occurrence: sporadic, endemic, epidemic, and pandemic.
Severity or Duration of a Disease
• 8. The scope of a disease can be defined as acute, chronic, subacute, or latent. • 9. Herd immunity is the presence of immunity to a disease in most of the population.
