Ecology of Pathogenic Microbes

1. What is ¨pathogenic?”

2. “Life cycle” of pathogenic microbes

3. How do we know if microbe causes disease? (Koch’s postulates)

4. Epidemiology—population ecology of pathogenic micro-organisms: Tracking disease

1. What is pathogenic?

(Plasmodium protozoan lysing red blood cell)

Relationship between Us (host) and Microbe (symbiont)

• We always provide habitat and usually nutrition for microbe

• Microbe effect on us varies:Beneficial Neutral Deleterious

Mutualism(E. coli in gut)

Commensalism(Staphylococcus on skin)

Parasitism(Plasmodium)

Resident Microbes (are beneficial to neutral)

(Table 14.2 from Bauman text)

Resident microbes “gone bad”

• Sometimes resident or harmless microbes can become deleterious or harmful

• Depends on local conditions, immune health of person, micro-habitat and strain of microbe

• For example, E. coli in gut can be pathogenic elsewhere in body

• For example, resident fungal microbes can become pathogenic, especially with antibiotic treatment that kills bacteria which compete with fungus—vaginal yeast infection, thrush in mouth.

2. “Life cycle” of pathogenic microbes

Important events in life cycle or ecology of pathogen

Entry into host(INFECTION!!)

Exit from host

Transmission

(Cause Disease in host)

How does microbe enter human host—routes of infection

• Wiki Brainstorm (go to Wiki websites)• How do microbes enter or infect our the inside or

outside of our bodies?• Give route or mode of infection and an example if

you know one.

Portals of entry for pathogens

Exit portals for pathogens

Modes of Transmission

What is disease?

• Portals of entry (check)

• Portals of exit (check)

• Transmission (check)

• How do microbes cause disease? (coming up in Unit IV on immunity, but…)

• How do we know microbe is cause of disease?

3. How do we detect illness and determine if microbe is cause?

Robert Koch (1843-1910)

Signs and Symptoms

SIGNS (can be observed)

• Fever• Swelling• Rash, redness• Vomiting, Diarrhea• Cell counts• Pus formation• Change in heart rate

SYMPTOMS (felt by patient)

• Pain• Nausea• Headache• Chills• Soreness• Fatigue• Malaise• Itching• Cramps

Syndrome: a group of signs and symptoms that characterize a possible diseae (usually when disease cause is still poorly understood)

Koch’s postulates

Problems with Koch’s postulates

• Not always applied correctly or completely: example Haemophilus influenzae (bacteria originally thought to cause flu, later found in non-victim’s lungs)

• Not always possible to apply—require controlled laboratory conditions and usually culturable disease-causing microbe

• When can’t use Koch’s, use epidemiological data

4. Epidemiology

• Population dynamics of pathogens—how does disease spread through host population?

• Koch’s postulates—controlled laboratory “physiological” study

• Epidemiological data—observations, reporting, statistics from “wild” or general population

Goal of epidemiology is to track infection, transmission and efficacy of treatment to determine:

• How disease enters (mode of infection)

• How virulent or damaging is it?

• How does it exit?

• How is it transmitted?

• What is causative agent—is microbe involved?

• Spread of disease—epidemics and pandemics

London cholera epidemic—mapping cases traces to one water pump site

More on epidemiology:

• Center for Disease Control Mortality and Morbidity Weekly Report—principal national tool for tracking diseases

• World Health Organization Weekly Epidemiological Report—principal global epidemiological statistical report

• Web teaching Resources

• (see course website for links)

Review1. What is a pathogen—not all microbes that live in/on

us are pathogens (scale from mutualistic to parasitic)2. Life cycle of pathogens includes entry or infection

and exit with transmission to new host3. How do we determine if microbe causes disease?

Koch’s postulates are best proof, but…4. Epidemiology is powerful tool for tracking spread of

disease in host population and can also help to determine microbial causes.

COMING NEXT: Horror-Shop of Disease-causing microbes and their effects!!