Ch 7 The Etiology of Disease

Any negative change in a person's health

The cause of a disease

Symptoms develop quickly but infection lasts only a short time

Symptoms develop slowly and disease can last a long time

Symptoms are between those of acute disease and those of chronic disease

Symptoms can continue to reappear long after initial infection

Confined to a small body area

Initial site of a spreading infection

Pathogens use blood or lymph to move around body

Organisms multiplying/growing in blood

Presence of bacteria in the blood

Presence but not multiplication of viruses in blood (and moving through blood)

Presence of toxins in blood

Initial infection

Immediately follows primary infection; can be more dangerous than initial infection

• Microorganism: Benefits
• Host: Neither benefits nor is harmed
• Example: Soprophytic bacteria that live ff sloughed-off cells in the ear and external genitalia

• Microorganism: Benfits
• Host: Benefits
• Example: Bacteria in colon

• Microorganism: Benefits
• Host: Is harmed
• Example: TB in lungs

• The same pathogen must be present in every case of the disease
• The pathogen must be isolated from the sick host and purified
• The pure pathogen must cause the same disease when give to uninfected hosts
• The pathogen must be re-isolated from these newly infected hosts

• Microo are isolated from a dead mouse Microo are grown in pure culture and identified
• Microo are injected into a healthy mouse
• Disease is reproduced in the 2nd mouse; micro are isolated; pathogenic microo are grown in pure culture; identical microo are identified

The time between initial infection and the 1st symptom of disease. The length depends on the virulence of the pathogen: the lower the virulence, the longer the period will last.

First mild symptoms appear

Symptoms begin to subside (period of time when 2nd infections are acquired, they can be more dangerous than initial illness)

Patient regains strength and proceeds to full recovery

Develop quickly but last for only a short time (ex: chickenpox/meseals)

Develop slowly but remain for long periods of time (ex: hepatitis, mononucleosis, and tb)

Insidious onset that can take 6-12 months to develop and can be fatal (ex: sclerosing panencephalitis)

Diseases that remain in the host after the initial signs and symptoms disappear and can become reactivated after long periods (ex: herpes, chickenpox). seen in survival viral diseases (ex: chickenpox--> shingles)

The proportion of individuals in a population who are immune to a particular disease. Can be conferred through vaccination or developed after infection. It is a major and fundamental parameter for infectious diseases.

• there is a massive leakage of plasma from the circulation that causes the blood pressure to plummet.
• Fatal for 30-70% of patients, caused by the activation of neutrophils, which occurs when the neutrophils come in contact with bacterial surface protiens like M protiens found on streptococcal species; the pahtogens reproduce in the blood which can cause Streptococcal toxic shock syndrome (STSS).

• Sysemic infections occur when pathogens move away from initial infection. Presence of microo in blood or their toxins (out of control infection).
• 2 categories = severe sepsis and acute septic shock

• Signs of systemic inflammation (low but widespread) and organ dysfunction accompanied by abnormal temp, HR, RR, and leukocyte count as well as elevated levels of liver enzymes and altered cerebral function (decreased once in the process of sepsis).
• Kills slowly over several weeks with minimal tissue inflammation or damage at time of autopsy.

Occurs suddenly, and patients can die w/in 24-48 hours. widespread tissue inflammation (necrosis) and cellular death at autopsy.

An infection causing the initial acute onset of symptoms

An infection in which symptoms do not appear even though the infection is ongoing. Examples of this are polio and hep A. Although people with subclinical infections don’t show/feel symptoms, they are still carriers for the disease and can infect others.

• An infection that establishes itself in a host weakened by some primary infection.
• An example of this is pneumocystis pneumonia which is seen in connection with AIDS. It is more dangerous than the primary infection as it is able to take advantage of the weakened state of the host (which is weakened BECAUSE OF the primary infection). weak immune systems.
• Most dangerous. No symptoms.

When normal microbial flora fight to prevent pthogens from taking up residence