Infectious Diseases

Nature of infectious diseases

Pathogens Infection Disease In order to cause disease, pathogens must

be able to enter, adhere, invade, colonize, and inflict damage

Growth of pathogens or the production of toxins/enzymes cause disease

Microbes that cause infectious diseases

Bacteria Viruses Fungi Protozoa Helminths Prions

Picture of Health??

Occurrence of infectious diseases

Epidemiology –study of the occurrence of disease in populations

Disease reservoirs-where the infectious agent survives (humans, rodents) Example = yersinia pestis (plague)

Modes of transmission ingestion, inhalation, casual contact, intimate

contact, bites/animals

History

Emerging infectious diseases-Have not occurred in humans before,Have occurred previously but affected only

small numbers, Or have occurred throughout human

history, but only recently recognized as disease due to infectious agent

Re-emerging infectious diseasesOnce were major health problems globally

or in a particular country, then declined dramatically, but are again becoming health problems for a significant proportion of the population.

Prevention

Safewater Purification methods Testing against contamination

Sewage Treatment Waste water plants separate components of

sewage and treat them Chlorination

Food Safety Inspections Pasteurization Regulations

Prevention

Animal Control Domestic inspections Vaccinations Sanitation

Vaccinations Pre-school Threshold proportion Herd immunity

Public Health Organizations

NIH – supports health-related researchCDC – investigates disease outbreaks,

informs the publicFDA – monitors safety of foods and medicinesWHO – coordinates health/vaccine programs

internationally

Treatment

Bacteria (prokaryotes) Antibiotics “destroyer of life” Inhibit cell wall, protein, lipid, or RNA synthesis Penicillin was the first – interfers with cell wall Chloramphenicol, tetracycline – protein synthesis Rifampicin – prevents RNA from being made

Treatment

Viruses Non-living; uses cell materials to replicate Highly toxic to host cells Target virus-specific enzymes involved in making

DNA/RNA Acyclovir – herpes Amantadine – influenza AZT - AIDS

Treatment

Fungi, protozoans, helminths Highly toxic because also eukaryotes Target reproduction, cell membrane, or other

necessary functions Choroquinine - malaria

Resistance

Resistance the ability of the pathogen to survive treatment by a

particular drug Growing problem

Mechanism change in genes that allows them to evade the action of

the drug Stuctural changes in proteins, receptors

Transfer of anti-microbial genes Don’t mutate but acquire it from others Transformation – taking up free-floating DNA plasmids Transduction – virus carries resistant gene to other

bacteria Transposons – small “rogue” sections of DNA Mutations and genetic exchange is rare; but bacterial

growth is high

The body’s defense mechanisms

First Line of DefenseSkinSecretions Non-specific defenses -

macrophagesNormal Flora

The body’s defense mechanisms

Immune Systemhttp://highered.mheducation.com/

sites/0072507470/student_view0/chapter22/animation__the_immune_response.html

Humoral (antibody) response – B-cells

B-cell, plasma cell, antibodies, memory B-cells

Cell-mediated response – T-cells helper T-cells, killer T-cells,

memory T-cellsVaccination produces immunity An inside look at the flu

Need for Vaccines

Spanish flu killed millions during WWIStill kills today but generally in the 100sEndemic – local, normal, baseline diseaseEpidemic – widespread and in large numbers at

same timePandemic – world-wideProtects individualLowering occurrence in population can protect

those who can’t get vaccine (herd immunity)Threshold response - percent of people who need to

be vaccinated for herd immunity to work

Types of vaccinations

Live but weakened disease agents Good but higher mutations, can cause illness,

refrigeration

Inactivated or killed disease agents Less effective but safer, need boosters

Subunit vaccines – use only subunits of antigens

Toxoid vaccines - against toxins made by bacteria

Conjugate vaccines – helps infants recognize antigens

DNA vaccines Recombinant vector vaccines

Vaccine Production

Tested in cells and in animalsEggs – virus injected into fertilized eggs to

reproduce and then protein coats isolated and tested; takes up t0 6 months

Cell Culture – grown in confined cells; cells die and viral coats are isolated and tested, quicker

Pharming - tobacco plant infected with Agrobacterium that has gene for viral coat antigen inserted; virus-like particles of protein then isolated; no DNA so more safety.

Issues with Vaccines

Public perception Myths (autism) Makes me sick or allergies Government intrusion Religious freedom

Challenges Speed of production Safety and stability Storage and distribution Changing pathogen landscape

Bioterrorism

Violent acts or acts dangerous to human life that…appear to be intended:

1. To intimidate or coerce a civilian population; 2. To influence the policy of a government by

intimidation or coercion; or 3. To affect the conduct of a government by

assassination or kidnapping.

Bioterrorism

Biological weapons used in bioterrorism are living microorganisms such as bacteria, viruses, fungi, that can kill or incapacitate.

Health care facilities may be the initial site of recognition and response to bioterrorism activity. Because of this, the names and telephone numbers for internal and external departments or agencies that need to be contacted should be kept by each facility in its bioterrorism readiness plan.

Bioterrorism

Response to bioterrorism agents:Internal reporting requirements (within a

facility): Infection control personnel Epidemiologist (local and state) Administration (health care facility and health

department) Office of public affairs in the health facility

Bioterrorism

External contacts (outside of facility) Local health department State Health Department FBI CDC Local police EMS

Bioterrorism

Agents Bacterial- Anthrax and Plague Viral- Small Pox

Toxins- Botulism and Ricin