The Nature Of Disease What Is DiseasePresentation Transcript
To control infectious disease we must consider such aspects as:
The origin of the outbreak (especially the natural reservoir)
Its mode of transmission within the population
The possible methods that can be employed to contain it
Preventing the Spread of Disease
The best method of disease control is to prevent the disease spreading in the first place.
The four main methods by which the spread of infectious disease is controlled are through:
Behavioral control Modifying the environment Treatment Immunization Photo: CDC
Modifying the Environment
All pathogens require certain conditions for growth, reproduction, and transmission.
By modifying the environment to make it less suitable for pathogens, most infectious diseases can be controlled.
Draining swampy ground to eliminate breeding sites for mosquitoes carrying malaria and dengue fever .
Spraying disinfectants to sterilize potentially contaminated surfaces.
Photo: CDC Workers spray drainage ditches with insecticide to kill mosquitoes
The development of effective sanitation, sewage treatment , and the treatment of drinking water has virtually eliminated dangerous waterborne diseases from developed countries.
These practices disrupt the normal infection cycle of pathogens transmitted through the fecal-oral route , such as those causing typhoid fever and cholera .
Transmission of disease can be prevented or significantly reduced by adopting ‘safe’ behaviors.
Using condoms to reduce the spread of sexually transmitted diseases.
Establishing quarantine and isolation procedures to prevent the spread of disease from other countries.
Adopting appropriate personal hygiene practices, such as washing your hands after going to the toilet and before handling food.
Vaccination or immunization is a procedure that provides artificially acquired active immunity for the person receiving it.
A vaccine is a suspension of microorganisms (or portions of them) which protects people from disease by inducing immunity.
Vaccines that are effective against bacteria and viruses have been produced, but to date there are no useful vaccines for humans against protozoa, roundworms, flatworms, or fungi.
Photo: CDC/WHO Photo: CDC The last known person in the world to have smallpox, 23 year old Ali Maow Maalin (photo), from Merka, Somalia. Smallpox was eradicated due to a vigorous vaccination program.
Types of Vaccine
There are two basic types of vaccine: subunit vaccines and whole-agent vaccines .
Recombinant vaccines Toxoids Conjugated vaccines Acellular vaccines Attenuated (weakened) Inactivated (killed) Subunit Vaccine Contains some part or product of micro-organisms that can produce an immune response Whole-Agent Vaccine Contains whole, nonvirulent microorganisms Photo: CDC
Subunit Vaccines 1
Subunit vaccines contain some product of, or fragments of, microorganisms. These are capable of providing an immune response in the person receiving the vaccine.
Conjugated Vaccines Some pathogens produce polysaccharide capsules that are poorly antigenic, especially in young children. To enhance their effectiveness, they are combined with proteins such as toxoids from other pathogens. Recombinant Vaccines Produced using genetic engineering techniques when other microbes (bacteria and yeast) are genetically altered to make the desired antigenic fraction. Toxoid attached Polysaccharide from pathogen Yeast makes viral proteins Inactivated toxins
Subunit Vaccines 2 Toxoids Toxoids are bacterial toxins that have been inactivated by heat or chemicals. When injected, the toxoid stimulates the production of antitoxins. Acellular Vaccines These are produced by fragmentation of a conventional whole-agent vaccine and collecting only those portions containing the desired antigens. Heat, iodine or formaldehyde Antigenic fragments of bacterial cells
Whole Agent Vaccines
Whole agent vaccines contain complete microorganisms that are nonvirulent (not capable of causing disease).
They may be either inactivated whole or attenuated.
Many attenuated viruses provide recipients with life-long immunity (without the need for booster shots). An effectiveness of 95% is not unusual.
One danger of such vaccines is that these live viruses can back-mutate to a virulent form.
Inactivated : whole agent is inactivated by treatment with formalin or other chemicals Attenuated : The agent is alive, but has been significantly weakened. They are usually derived from strains where mutations have accumulated during long-term cell culture. Mutated DNA
Using genetic material to produce vaccines is one of the promising new fields of vaccine research.
Unlike traditional vaccines (which contain either whole or parts of a pathogen), genetic vaccines contain only the gene for producing an antigen from the pathogen.
When this gene is expressed in a patient the protein produced elicits an immune response.
Genetic vaccines are currently being developed and trialed to immunize people against:
HIV Cancer Hepatitis B Herpes simplex Malaria Rabies
Producing a DNA Vaccine 1 The recombinant bacteria are allowed to grow and reproduce on an agar plate. Antigen gene is spliced into the plasmid and the plasmid is inserted back into the bacterium. Gene for the antigen is removed from the pathogenic or cancerous cell Plasmid is isolated from a harmless bacterium.
Producing a DNA Vaccine 2 Expression of the gene in the patient produces a protein that elicits an immune response. The isolated antigen gene is delivered to the patient using direct injection or via a gene gun .
Antimicrobial drugs include synthetic (manufactured) drugs as well as drugs produced by bacteria and fungi, called antibiotics .
Antibiotics are produced naturally by microorganisms as a means of inhibiting competitor microbes around them (a form of antibiosis , hence the name applied to the drugs).
The first antibiotic, called penicillin , was discovered in 1928 by Alexander Fleming .
Since then, similar inhibitory reactions between colonies growing on solid media have been commonly observed.
Antibiotics are actually rather easy to discover, but few of them are of any medical or commercial value.
Agar plate with bacterial colonies and antibiotic discs Photo: CDC
Antimicrobial Effectiveness 1
To be effective, antimicrobial drugs must often act inside the host so their effect on the host’s cells and tissues is important.
The ideal antimicrobial drug has selective toxicity , killing the harmful organism without damaging the host.
Some antimicrobial drugs have a narrow spectrum of activity and affect only a limited number of microbial types.
The wrong antibiotic can allow infections such as this ulcer to get out of control Photo: CDC
Antimicrobial Effectiveness 2
Other drugs affect a large variety of microbes and are therefore called broad-spectrum drugs .
The identity of a pathogen is not always known. Therefore a broad-spectrum drug may be prescribed in order to save valuable time.
However there is a disadvantage with this practice. Broad spectrum drugs not only target the pathogen, but also the host’s normal microbial community (flora).
Staphylcoccus aureus infection The sticky looking substance is a polysaccharide biofilm, which protects the bacteria from antibiotics. Some strains of staph. have developed resistance to multiple antibiotics. The wide use of broad-spectrum antibiotics has contributed to this. Photo: CDC
Antimicrobial Activity Spectrum of antimicrobial activity of a number of chemotherapeutic drugs Streptomycin Prokaryotes Mycobacteria Gram-Negative Bacteria Gram-Positive Bacteria Rickettsias/ Chlamydias Penicillin Tetracycline Isoniazid Viruses Acyclovir
Antimicrobial Activity Spectrum of antimicrobial activity of a number of chemotherapeutic drugs Eukaryotes Fungi Protozoa Tapeworms/ Flukes Ketoconazole Nicosamide (tapeworms) Mefloquine (malaria) Praziquantel (flukes)
How Antimicrobial Drugs Work
Antimicrobial drugs disrupt the functioning of a bacterial cell in the following ways:
Inhibited Protein Synthesis Translation is disrupted. Examples: erythromycin, tetracyclines, chloramphenicol, streptomycin Damaged Cell Walls The synthesis of new cell walls during cell division is inhibited. Examples: penicillin, vancomycin, cephalosporins, bacitracin Damaged Plasma Membrane The plasma membrane may be ruptured. Examples: nystatin, miconazole, polymyxin B, amphotericin B Inhibition of Enzyme Activity The synthesis of essential metabolites is inhibited. Examples: sulfanilamide, trimethoprim Inhibit Gene Copying DNA replication and transcription are interfered with. Examples: Rifampin, Quinolones
A monoclonal antibody is an artificially produced antibody that neutralizes only one specific protein (antigen).
Monoclonal antibodies are produced by stimulating the production of B-cells in mice injected with the antigen.
These B-cells produce an antibody against the antigen.
B-cells can be isolated and made to fuse with immortal tumor cells. They can then be cultured indefinitely in a suitable growing medium.
Monoclonal antibodies are useful for 3 reasons:
They are totally uniform (i.e. clones).
They can be produced in large quantities .
They are highly specific .
Monoclonal antibodies chemically linked to a fluorescent dye to detect the presence of gonorrhea Photo: CDC
Making Monoclonal Antibodies Hybridoma cells Mouse cell and tumor cell fusing Unfused cell Pure tumor cells are harvested from culture A mouse is injected with a foreign protein ( antigen ). The mouse’s B-cells produce an antibody to recognize the antigen. A few days later, antibody-producing B-cells are taken from the mouse’s spleen. The mouse cells and tumor cells are mixed together in suspension. Some of the mouse cells fuse with tumor cells to make hybrid cells called hybridomas . Hybridomas are screened for antibody production. They are then cultured to produce large numbers of monoclonal antibodies. The mixture of cells is placed in a selective medium that allows only hybrid cells to grow.
The World Health Organization
Founded in 1948, the World Health Organization ( WHO ) is a specialized agency of the United Nations
WHO promotes technical cooperation for health among nations, carries out programs to control and eradicate disease, and strives to improve the quality of human life.
WHO has four main functions:
To give worldwide guidance in the field of health
To set global standards for health
To cooperate with governments in strengthening national health programs
To develop and transfer appropriate health technology, information and standards
A major event in WHO's first 50 years was the global eradication of smallpox.
The Role of the CDC
The Center for Disease Control and Prevention (CDC) is an agency of the US Department of Health and Human Services.
In today's global environment, new diseases have the potential to spread across the world in a matter of days, or even hours, making early detection and action more important than ever.
The CDC plays a critical role in investigating, monitoring and controlling these diseases, traveling at a moment's notice to investigate outbreaks worldwide.
CDC and Zairian scientists take samples from animals collected near Kikwit, Zaire, 1995. These samples were sent back to CDC in Atlanta for testing to search for the animal reservoir of the Ebola virus. Photo: CDC