Microbiology Chapter 2

Types of Infections

1. Primary infection - infection in a previously healthy individual. 2. Secondary infection - infection that follows a primary infection, damaged tissue(lung)is more susceptible to infection by a different organism. 3. Mixed infection - infection caused by two or more pathogens. 4. latrogenic infection - infection transmitted from a health care worker to a patient. 5. Nosocomial infection - infection acquired during a hospital stay. (hospital - acquired infection) 6. Community acquired infection - infection acquired in the community, not at the hospital.

Pathogen

any bacterium, virus, fungus, protozoan, or worm that causes disease.

Opportunistic pathogens

cause disease only in a compromised host.

Primary Pathogens

disease causing microbes with the means to breach the defenses of a healthy host.

Host Range

how readily a pathogen can infect different animals and cause diseases. *narrow host range* ie: only infect humans *broad host range* ie: infect many different animals

Parasite

include any organism that colonizes and harms its host. Disease causing protozoa and worms (single celled eukaryotic organisms.

Direct contact

intimate interaction between two people

immunopathology

its important to realize that many of the signs and symptoms of an infectious disease, including some sequelae, are actually caused by the host's response to the infection. Cells given the task of killing the microbe can also damage nearby host tissue.

Endoparasites

living inside the body. * pathogens and parasites infect their animal and plant hosts in a variety of ways and enter into different host-pathogen relationships, depending on the site of colonization and the capabilities of the organism.

Ectoparasites

living on the body surface (outside)

Vehicle

means of pathogen transmission, as by air, food, or liquid

Septicemia

presence and replication of bacteria in the blood (blood infection)

Bacteremia

presence of bacteria in the blood. usually transient, little, or no replication.

Toxemia

presence of toxins in the blood

Viremia

presence of viruses in the blood

Invasiveness

refers to the ability of a bacterial pathogen to rapidly spread through tissue.

Colonization

refers to the ability of a microbe to stay affixed to a body surface and replicate.

Zoonotic diseases

some infectious agents cross species barriers to infect humans. Infections that normally afflict animals but can be transmitted to humans are called Zoonotic diseases.

latent state

some microbes enter into a latent state during infection, where the organism cannot be found by culture. (Herpes Virus)

Sign

something that can be observed by a person examining the patient.

Symptom

something that can only be felt by the patient.

Attachment

specific proteins (adhesins) on the surfaces of microbes help them adhere to host cells.

Endemic

Disease (humans) is present in a specific geographic location, pathogen is usually harbored in an animal or human reservoir. always present in a community and seen at a low rate.

Stages of Infectious Disease

(phases) 1. incubation period - the time after a microbe first infects a person through a portal of entry, but before the first signs of disease. Depending on the disease patients, patients may be contagious during the incubation period even though they appear healthy. (the microbe is trying to replicate to higher and higher numbers). 2. prodromal phase - short and may not even be apparent. It involves vague symptoms, such as headache or general feeling of MALAISE (fatigue and mild body discomfort) that serves as a warning to more serious symptoms to come. In the prodromal phase can spread microbes to others. 3. illness phase - begins when typical symptoms and signs of the disease appear. The point at which disease symptoms are MOST SEVERE is called the ACME. The battle between microbe and host is at its peak during this time. 4. decline phase - begins as the symptoms subside. Host defenses have won. 5. Convalescence - the period after symptoms have disappeared and the patient begins to recover normal health.

Five Basic stages of infectious disease

1. Acute Infection - infection in which symptoms develop rapidly, its course can be rapid or protracted. 2. Chronic Infection - infection in which symptoms develop gradually, over weeks or months, and are slow to resolve taking 3 months or more. 3. Subacute disease - infection in which symptoms take longer to develop than in acute infection but arise more quickly than for a chronic infection 4. Latent Infection - a type of infection that may occur after an acute episode, the organism is present but the symptoms are not, after time the disease can reappear. 5. Focal infection - initial site of infection from which organisms can travel via the bloodstream to another area of the body. 6. Disseminated infection - infection caused by organisms traveling from a focal infection, when affecting several organ systems it is called "systemic" infection. 7. Metastatic Lesion - A site of infection resulting from dissemination.

Host factors in Disease

1. Age 2. Host genetic makeup (genotype) 3. Host hygiene and behavior 4. Nutrition and exercise 5. Underlying noninfectious diseases or conditions 6. Occupation 7. Immune status and immunopathogenesis

Immune Avoidance

Different pathogens possess unique tools to avoid the immune system. Some periodically change the molecular shape of their surfaces to confuse the immune system. Others secrete molecules to tell the immune system all is well, no infection here.

Sequelae

Even after an infectious disease has resolved, pathological consequences called sequelae may develop. ie: step throat can result in heart or kidney damage.

Infectious Dose 50% (ID 50)

Infectious dose is measured by determining how many microbes are required to cause disease symptoms in half of an experimental group of hosts.

Receptors

Microbial adhesin proteins bind to structures called receptors on host cell surfaces.

How are disease spread?

Pathogens must pass from one person, or nonhuman animal, to another if a disease is to spread. The route of transmission an organism takes to infect additional hosts is called the infection cycle. These routes can be direct or roundabout.

Fundamental Host-Pathogen Interactions

Regardless of the pathogen-viral, bacterial, or eukaryotic-all must interact with a host in several ways to be successful. The pathogen must attach to a host tissue, avoid the host's immune system, and steal nutrients from the host.

Adhesins

To stay with us, members of our normal microbiota have proteins on their surface (called adhesins) that allow them to attach to and colonize epithelial cells lining mucous membranes (intestine, urinary tract, mouth, Nose)

Epidemic

When the number of disease cases rises above endemic level. When many cases develop in a community over a short time.

Pandemic

Worldwide Epidemic

Syndrome

a collection of signs and symptoms that occur together and signify a particular disease.

An Infectious Disease

a disease caused by a microorganism (bacterial, viral, parasitic) that can be transferred from one host to another.

How do we define a Disease?

a disease is the disruption of the normal structure or function of any body part, organ, or system that can be recognized by a characteristic set of symptoms and signs.

Vehicle transmission (fomites)

a form of indirect transmission whereby an infectious agent is transferred to an inanimate object (fomite) by the touch of one person and then transferred to another person touching the same object, or by ingesting contaminated food or water or by inhaling the agent in the air.

Vector

a living carrier of an infectious organism

Virulence

a measure of disease severity

Morbidity

a measure of how many are sick from an infectious disease.

Mortality

a measure of how many patients have died from a disease.

Mutualism

a mutualistic relationship win/win

Carrier

a person who harbors a potential disease agent but does not have the disease

Lethal Dose 50% (LD 50)

a way to measure Virulence. the number of bacteria or virus particles required to kill 50 % of an experimental group of animal hosts

Sign versus Symptom

most diseases are recognized by their signs and symptoms.

Reservoir

nonhuman animal, plant, human, or environment that can harbor the organism, a reservoir may or may not exhibit disease.

Infection

occurs when a pathogen or parasite enters or begins to grow on a host. The term infection does not necessarily imply overt disease. infection may be temporary if immune defenses kill the pathogen before noticeable disease results.

Transplacental transmission

organism transferred from mother to fetus through placenta

Aerosol

organisms in air suspension

Paternal route

pathogen enters body through insect bite or needle injection.

Respiratory route

pathogen enters the body through breathing

Urogenital route

pathogen enters the body through urethra or vagina.

Fecal - oral route

pathogen exits the body in feces, which contaminates food, water, or fomite. pathogen is introduced into a new host by ingestion

Invasion

the ability of some pathogens to actually enter (invade) and live inside a host human or nonhuman animal cell.

Pathogenicity

the ability to cause disease (depends on a combination of the organisms genetic makeup and the effectiveness of the hosts immune response). j

Normal Microbiota

the collection of bacteria, archaea, and eukaryotic microbes that call us home is our normal Microbiota. Most members of our microbiota both derive and give benefit to their hosts, which defines MUTUALISM.

Indirect contact or transmission

transmission of an infectious agent from one person to another by an insect vector or an inanimate object.