2. Topic Outline
•Overview of Infectious Diseases
•Classifications of Disease
•Pathogenicity and Virulence
•Primary Pathogens versus Opportunistic Pathogens
•Virulence Factors of Bacterial and Viral Pathogens
•How do Fungi Cause Disease?
•Classification of Fungal Diseases
•Major Fungal Infections of Humans
•Medical Application of Fungi
3. • An infection is the successful colonization of a host by a
microorganism. Infections can lead to disease, which causes
signs and symptoms resulting in a deviation from the normal
structure or functioning of the host.
• The signs of disease are objective and measurable, and can
be directly observed by a clinician. Ex: Vital signs
Signs and Symptoms of Disease
4. •The symptoms of disease are subjective. Symptoms
are felt or experienced by the patient, but they cannot
be clinically confirmed or objectively measured. Ex:
pain
•A specific group of signs and symptoms characteristic
of a particular disease is called a syndrome.
5. Some diseases may be asymptomatic or subclinical, meaning
they do not present any noticeable signs or symptoms.
For example, most individual infected with herpes simplex
virus remain asymptomatic and are unaware that they have
been infected for many years including the most recent
COVID-19.
6. •The World Health Organization’s International
Classification of Diseases is used in clinical fields to
classify diseases and monitor morbidity and mortality.
•Infectious disease is any disease caused by the direct
effect of a pathogen.
• Communicable - they are capable of being spread
from person to person through either direct or
indirect mechanisms.
• contagious diseases - easily spread from person to person.
Classifications of Disease
7. • Iatrogenic diseases - Diseases that are contracted as the result
of a medical procedure. Ex: after procedures involving wound
treatments and catheterization
• Nosocomial diseases - Diseases acquired in hospital settings.
Patients have weakened immune systems, making them more
susceptible to infections.
• Zoonotic disease (zoonosis) - Infectious diseases that are
transmitted from animals to humans. Ex. COVID-19
8. • Noncommunicable infectious disease - is not
spread from one person to another. Ex: tetanus
caused by Clostridium tetani
•Noninfectious diseases – disease NOT caused by
pathogens. It can be caused by a wide variety
factors, including genetics, the environment, or
immune system dysfunction.
10. The ability of a microbial agent to cause disease is
called pathogenicity, and the degree to which an
organism is pathogenic is called virulence.
Highly virulent pathogens will almost always lead to a
disease state when introduced to the body, and some
may even cause multi-organ and body system failure in
healthy individuals. Less virulent pathogens may cause
an initial infection, but may not always cause severe
illness.
Pathogenicity and Virulence
11. •primary pathogen can cause disease in a host
regardless of the host’s resident microbiota or
immune system.
•opportunistic pathogen can only cause disease in
situations that compromise the host’s defenses,
such as the body’s protective barriers, immune
system, or normal microbiota.
Primary Pathogens vs
Opportunistic Pathogens
14. •A local infection is confined to a small area of the body,
typically near the portal of entry.
•A focal infection, occurs when a localized pathogen, or
the toxins it produces, can spread to a secondary
location.
•When an infection becomes disseminated throughout
the body, it is called a systemic infection.
•Sometimes a primary infection, the initial infection
caused by one pathogen, can lead to a secondary
infection by another pathogen.
20. • acute disease -pathologic changes occur over a relatively short time (e.g.,
hours, days, or a few weeks) and involve a rapid onset of disease conditions.
• example influenza - incubation period is approximately 1–2 days. Infected individuals can spread
influenza to others for approximately 5 days after becoming ill. After approximately 1 week,
individuals enter the period of decline.
• chronic disease - pathologic changes can occur over longer time spans (e.g.,
months, years, or a lifetime).
• example Hepatitis caused by HB virus can cause a chronic infection after the acute illness. A
chronic infection with hepatitis B virus is characterized by the continued production of infectious
virus for 6 months or longer after the acute infection, as measured by the presence of viral
antigen in blood samples.
• latent diseases - the causal pathogen goes dormant for extended periods of
time with no active replication.
• Example herpes (herpes simplex viruses [HSV-1 and HSV-2]), chickenpox (varicella-zoster
virus [VZV]) the evade the host immune system by residing in a latent form within cells of the
nervous system for long periods of time, but they can reactivate to become active infections
during times of stress and immunosuppression.
Acute and Chronic Diseases
26. How do Fungi Cause Disease?
•Fungal cell walls contain chitin, as opposed to the cellulose found
in the cell walls of plants and many protists.
•Additionally, fungal cell membranes have different sterols
called ergosterols.
•Ergosterols are often exploited as targets for antifungal drugs.
• The tissue damage associated with fungal infections results
primarily from direct invasion of tissue, with subsequent
displacement and destruction of vital structures, coupled with
toxic effects of the inflammatory response.
27. Classification of Fungal Diseases
• Fungal infections (mycoses) can be classified into the
following 4 categories:
– Superficial mycoses – fungal infections of the outermost
areas of the body (outer surfaces of hair shafts, the
epidermis)
– Cutaneous, hair, and nail mycoses (tinea or
“ringworm” infections)
– Subcutaneous mycoses
– Systemic mycoses – the most serious types of fungal
infections
28.
29. Cutaneous Mycoses
•Dermatophytosis (Tinea
[“Ringworm”] Infections,
Dermatomycosis)
– Caused by various species of
filamentous fungi, including
Microsporum, Epidermophyton,
and Trichophyton spp.
– These fungi are collectively
referred to as dermatophytes.
30.
31.
32. Systemic Mycoses
•Coccidioidomycosis (Valley Fever)
– Coccidioides immitis, a
dimorphic fungus;
transmission occurs via
inhalation of arthrospores
•Histoplasmosis
– Histoplasma capsulatum var.
capsulatum, a dimorphic
fungus; transmission occurs
via inhalation of conidia from
soil
33. Cryptococcal Meningitis
• Can be caused by 3 subspecies of Cryptococcus
neoformans, an encapsulated yeast
• Cryptococcosis starts as a lung infection, but
spreads via the bloodstream to the brain
• Cryptococcal meningitis can be presumptively
diagnosed by observing encapsulated, budding
yeasts in CSF specimens examined by a India ink
preparation
34. Yeast Vaginitis
• Most cases are caused by the yeast, Candida albicans
• Can be diagnosed by microscopic examination of a saline wet mount of
vaginal discharge material, in which numerous yeasts and hyphae may
be observed
36. Medical Applications
• Penicillin interfere with the synthesis of peptidoglycan cell
walls, which effectively targets bacterial cells. These antibiotics
are useful because humans do not have peptidoglycan cell
walls.
• Fungi have ergosterols in their cell membranes, the different
enzymes involved in sterol production can be a target of some
fungicide medications.
• Some antifungal medications target the chitin cell walls of fungi.
37. References
• Burton's Microbiology for the Health Sciences
• https://openstax.org/books/microbiology/pages/5-3-fungi#OSC_Microbio_05_03_TaxaTable
• https://www.medicalnewstoday.com/articles/321031#risk-factors
• https://www.cdc.gov/fungal/diseases/coccidioidomycosis/index.html#:~:text=Valley%20fever%2C
%20also%20called%20coccidioidomycosis,found%20in%20south%2Dcentral%20Washington.
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