Download Infectious Diseases

Infectious Diseases
• Pathogens: Microorganisms that are
capable of causing disease
• Infection: Results when a pathogen
invades and begins growing within
the host
• Disease: Results only if and when
normal tissue function is impaired
• The body has defense mechanisms to
prevent infection (i.e. burns, skin
lesions)
• In order to cause disease, pathogens
must be able to enter, adhere,
invade, colonize, and inflict damage
• Entrance to the host typically occurs
through natural orifices such as the
mouth, eyes, genital openings, or
through wounds that breach the skin
barrier to pathogens
• Growth of pathogens or the
production of toxins/enzymes cause
disease
• Some normal flora prevent diseases
Infectious Disease – a disease caused
by the invasion of a host by pathogens
causing impaired tissue function and
can be transmitted to other individuals
Five major types of infectious agents
(microbes): bacteria, viruses, fungi,
protozoa, and helminthes:
• Bacteria: They contain no organized
internal membranous structures.
Most reproduce by growing and
dividing into two cells in a process
known as binary fission.
Types of Bacteria:
• Salmonella typhi: a gram-negative
organism that causes typhoid fever.
• Yersinia pestis- Causes plague The
reservoir is rodents. ***
• Staphylococcus aureus- causes skin,
respiratory and wound infections.
• Viruses: Infect all organisms
from plants and animals to fungi
and bacteria. They are not
organisms themselves because
apart from a host cell, they have
no metabolism and cannot
reproduce.***
Types of viruses:
• Herpes viruses: cause chicken pox,
cold sores, and painful genital
lesions, and the pox virus that causes
smallpox.
• Rhinoviruses: cause most common
colds.
Viruses (continued)
• Myxoviruses and paramyxoviruses:
cause influenza, measles, and
mumps.
• Rotaviruses: cause gastroenteritis.
• Retroviruses: cause AIDS and several
types of cancer.
Fungi: Reproduce primarily by
forming spores.
Types of diseases caused by fungi:
• Ringworm
• Histoplasmosis (a mild to severe lung
infection transmitted by bat or bird
droppings)
• Candida genus: opportunistic
pathogens*** that may cause diseases
such as vaginal yeast infections and
thrush.
Protozoa: Do not have cell walls and
are capable of a variety of rapid and
flexible movements.
• Can be acquired by contaminated
food or water or by the bite of an
infected arthropod such as a
mosquito.
Helminths: Simple, invertebrate animals,
some of which are infectious parasites.
Difficult to treat because the drugs that
kill helminthes are frequently very toxic
to human cells.
Diseases caused by helminths:
• Trichinella Spiralis: occurs when
improperly cooked pork from infected
pigs is ingested.
– Symptoms include vomiting and diarrhea and
fever***
– Respiratory paralysis can occur in fatal cases
of trichinella spiralis***
Prions: Infectious particles
that consist of only protein.
• Diseases caused by Prions:
• Creutzfeldt-Jakob disease (in
humans)***
• Bovine spongiform
encephalopathy (mad cow
disease)
• Epidemiology- the study of the
occurrence of disease in
populations.
• Disease reservoirs- The reservoir
for a disease where the
infectious agent survives
(example: rodents, soil
• Modes of transmission:
Infectious agents may be
transmitted through either direct
or indirect contact.
Host defenses against
infectious diseases:
• Nonspecific mechanisms-the body’s
primary defense against disease –
these include anatomical barriers to
invading pathogens, physiological
deterrents to pathogens, and
presence of normal flora. (skin, low
pH and high salinity)
• Specific mechanisms of host
resistance- our immune system
• Immunity – when a host encounters
an antigen that triggers a specific
immune response for the second time
and the body responds quickly and
produces antibodies
• Vaccination- produces immunity