1. INFECTIOUS DISEASE Biomedical Technology
Objective: Discuss the infectious disease process

2. INFECTIOUS DISEASE PROCESS
Pathogen - microorganisms that are capable of causing disease
Infection – results when a pathogen invades and begins to grow within the host
Disease – results only if and when tissue function is impaired (i.e. burns, skin lesions) In order to cause disease the pathogens must be able to enter, adhere and invade, colonize and inflict damage.

3. INFECTIOUS DISEASE PROCESS
Growth of pathogens or the production of toxins/enzymes cause disease.
Entrance to the host comes from the mouth, eyes, genital openings, or wounds.
The body has defense mechanisms to prevent infection. Normal Flora

4. Microbes (infectious agents) cause infectious diseases: There are 5 with a 6th one emerging.
1. Bacteria: unicellular- no nuclei.
Salmonella typhi-causes typhoid fever-contaminated water.
Staphylococcus aureus-skin, wound infections
Yersinia pestis-bubonic plague
Clostridium tetani- found in soil and can cause Tetanus
Bacteria can be described in the following ways:
Morphology – bacillus (rod-shaped), coccus (spherical), spirillium (helical rods)
Aerobes-require oxygen vs. anaerobes-can’t tolerate oxygen
Gram negative ( salmonella) vs. gram positive acillus(staphylococcus).

5. 2. Viruses- have no metabolism and can’t reproduce apart from the host cell.
Retro viruses –HIV, some cancers
AIDS –a viral disease with a long latent period, it uses an enzyme to copy itself into a host cell-it is caused by the HIV virus.
Herpes viruses- chicken pox, shingles, cold sores, small pox
Rhinoviruses- common cold- mutation is so rapid therefore no vaccine available
Myxoviruses and paramysoviruses- influenza, measles, mumps
Rotaviruses- gastroenteritis

6. 3. Fungi Ringworm-most common in children
Histoplasmosis-lung infection from bat or bird droppings.
Yeast of Candida genus-opportunistic pathogens: lead to vaginal yeast infections, thrush
Why?? Because antibiotics reduce normal flora allowing yeast to grow making you more susceptible to an opportunistic infection

7. 4. Protozoa
Acquired through contaminated food or water or bite of arthropod ( mosquito)
Diarrheal disease in the US-Giardia lamblia and cryptosporidium parvum
Malaria- Plasmodium ( in tropical environment)

8. 5. Helminths
Simple, invertebrate animals-infectious parasites- like worms, larvae or slugs.
Because they are animals, their physiology is similar to ours so they are difficult to treat because meds can be toxic to us too.
Swimmers Itch in US flatworm, Schistosomiasis- symptoms abdominal pain and diarrhea
Trichinella spiralis- roundworm which is ingested in undercooked pork from infected pigs-symptoms are vomiting, diarrhea and fever. Fatal cases or the cause of death can be respiratory paralysis.
* show handwashing video clip

9. 6. Prions
Infectious particles that consist of only protein. The proteins are in a misfolded form.
Cretzfeldt Jakob Disease in humans or Mad Cow disease in cattle
Deteriorating mental capacity, loss of
coordination
All prion diseases result in brain tissue that is riddled with holes.
Some prion diseases are inherited, transmitted by eating infected tissue or through tissue transplants.

10. Occurrence of Infectious Diseases
Epidemiology- study of occurrence of disease in populations
Disease Reservoirs- where the infectious agent survives ( humans, rodents, soil)
Yersinia pestis (plague) – is a bacteria carried by rodents (reservoir)
Clostridium tetani is a bacteria causing tetanus- the reservoir is soil. It can be transmitted by stepping on a nail or metal and sustaining a puncture wound.

11. Occurrence of Infectious Diseases
Modes of Transmission:
Direct Contact – occurs when person is infected by contact with reservoir. Examples are rabies, malaria, influenza, ringworm, trichinosis, and AIDS
Indirect Contact – the pathogen is transmitted from contaminated substances such as food, soil, water, clothing, or equipment.
Example: Hepatitis A from fecal-oral route and food preparation, tetanus from soil

12. Host Defense Against Infectious Diseases
Non specific mechanisms are the body's primary defense against disease.
Anatomical barriers – nasal opening skull, vertebral column, skin
Physiological deterrents- tears, vaginal secretions, saliva, blood, sweat, and some tissue fluids.
Normal flora successfully compete with pathogens. Normal bacteria that is fighting germs.

13. Host Defense Against Infectious Diseases
Specific Defenses -Immunity
Cell mediated uses T-cells to destroy the pathogen or produce toxic molecules to kill the pathogen
Antibody mediated uses B-cells to produce antibodies
Vaccinations
Produce immunity-memory lymphocytes that will recognize the pathogen and prevent disease.

14. Opportunistic Infections
An opportunistic infection is an infection caused by pathogens (bacterial, viral, fungal or protozoan) that usually do not cause disease in a healthy host, i.e. one with a healthy immune system. A compromised immune system, however, presents an "opportunity" for the pathogen to infect.
Antibiotics can reduce normal flora-bacteria and put a host at risk for an opportunistic infection.

15. Review Questions
T/F Viruses have no metabolism and cannot reproduce apart from the host cell.
Which virus has a long latent period and replicates itself before showing signs and symptoms of the disease?
Which organism causes an opportunisitic infection? Yersinia Pestis or Candida
Antibiotics make you susceptible to opportunistic infections? True or False

16. Review Questions
What type of living environment do protozoan infections usually prefer?
What infectious agent causes Tetanus and what is the usual reservoir?
When you have been infected by a helminth, what are some symptoms you may have?
How is the rabies disease transmitted?

17. Answers True HIV virus leading to AIDS Candida
True; no matter how old or young you are.
Tropical
Clostridium tetani; soil
Diarrhea and abdominal pain
Direct contact by a bite from a rabid animal