Understanding Infectious Diseases: Paths & Prevention

1. Viruses Bacteria Worms About Infectious Disease • Infectious diseases are diseases that are caused by certain pathogens – microorganisms (microbes) also known as infectious agents or, more commonly, germs. • They are usually contagious, meaning that they can be transmitted from one person to another or from one species of plant or animal to another

3. The mechanisms by which they are transmitted are: Contact with aerosolized droplets – these droplets are spread by sneezing, coughing, talking, kissing and singing. Eating contaminated food and drinking contaminated water. Contact with bodily fluids Contact with contaminated objects, for example a coin passed from one person to another – some diseases penetrate the skin directly Biological Vectors (more later) Mechanical Vectors (more later) Infecting agents are transmitted by: Physical contact with an infected individual Liquids Food Body Fluids Contaminated objects Airborne inhalation Vector – borne spread. Infecting agents are transmitted by: • Physical contact with an infected individual • Liquids • Food • Body Fluids • Contaminated objects • Airborne inhalation • Vector – borne spread. The mechanisms by which they are transmitted are: • Contact with aerosolized droplets – these droplets are spread by sneezing, coughing, talking, kissing and singing. • Eating contaminated food and drinking contaminated water. • Contact with bodily fluids • Contact with contaminated objects, for example a coin passed from one person to another – some diseases penetrate the skin directly • Biological Vectors (more later) • Mechanical Vectors (more later) Infecting agents are transmitted by: • Physical contact with an infected individual • Liquids • Food • Body Fluids • Contaminated objects • Airborne inhalation • Vector – borne spread.

4. The mechanisms by which they are transmitted are: Contact with aerosolized droplets – these droplets are spread by sneezing, coughing, talking, kissing and singing. Eating contaminated food and drinking contaminated water. Contact with bodily fluids Contact with contaminated objects, for example a coin passed from one person to another – some diseases penetrate the skin directly Biological Vectors (more later) Mechanical Vectors (more later) Infecting agents are transmitted by: Physical contact with an infected individual Liquids Food Body Fluids Contaminated objects Airborne inhalation Vector – borne spread. Infecting agents are transmitted by: • Physical contact with an infected individual • Liquids • Food • Body Fluids • Contaminated objects • Airborne inhalation • Vector – borne spread. The mechanisms by which they are transmitted are: • Contact with aerosolized droplets – these droplets are spread by sneezing, coughing, talking, kissing and singing. • Eating contaminated food and drinking contaminated water. • Contact with bodily fluids • Contact with contaminated objects, for example a coin passed from one person to another – some diseases penetrate the skin directly • Biological Vectors (more later) • Mechanical Vectors (more later) Infecting agents are transmitted by: • Physical contact with an infected individual • Liquids • Food • Body Fluids • Contaminated objects • Airborne inhalation • Vector – borne spread.

5. Transmission of infectious diseases may also involve a vector. Vectors may be mechanical or biological: Image: “Mosquito” by tanakawho on Flickr.

6. Transmission of infectious diseases may also involve a vector. Vectors may be mechanical or biological: An example of a mechanical vector is a housefly, which lands on cow dung and then lands on food, which is then eaten. The bacteria travel from the dung to the food without ever actually entering the body of the fly. Image: “Mosquito” by tanakawho on Flickr.

7. Transmission of infectious diseases may also involve a vector. Vectors may be mechanical or biological: An example of a mechanical vector is a housefly, which lands on cow dung and then lands on food, which is then eaten. The bacteria travel from the dung to the food without ever actually entering the body of the fly. A biological vector has the pathogens within its body, and delivers them to new hosts in an active manner, usually a bite. Mosquitoes, ticks, fleas and lice are examples of biological vectors and are often responsible for serious blood-borne diseases, such as malaria. Image: “Mosquito” by tanakawho on Flickr.

8. Transmission of infectious diseases may also involve a vector. Vectors may be mechanical or biological: An example of a mechanical vector is a housefly, which lands on cow dung and then lands on food, which is then eaten. The bacteria travel from the dung to the food without ever actually entering the body of the fly. A biological vector has the pathogens within its body, and delivers them to new hosts in an active manner, usually a bite. Mosquitoes, ticks, fleas and lice are examples of biological vectors and are often responsible for serious blood-borne diseases, such as malaria. A common strategy used to control vector borne infectious diseases is to interrupt the life cycle of a pathogen by killing the vector. Image: “Mosquito” by tanakawho on Flickr.

9. The study of disease in a population is called epidemiology. • In the case of infectious disease, epidemiology is used to classify the type of disease outbreak: • Sporadic: occasional occurrence • Endemic: cases in a region are regular and often • Epidemic: unusually high number of cases in a region • Pandemic: global epidemic

10. The study of disease in a population is called epidemiology. • In the case of infectious disease, epidemiology is used to classify the type of disease outbreak: • Sporadic: occasional occurrence • Endemic: cases in a region are regular and often • Epidemic: unusually high number of cases in a region • Pandemic: global epidemic • Transmission of an infectious disease depends on a number of factors: • Virulence: the ability of a pathogen/infecting agent to cause disease • The distance that is travelled by infected people • How contagious the disease is

11. The study of disease in a population is called epidemiology. • In the case of infectious disease, epidemiology is used to classify the type of disease outbreak: • Sporadic: occasional occurrence • Endemic: cases in a region are regular and often • Epidemic: unusually high number of cases in a region • Pandemic: global epidemic • Transmission of an infectious disease depends on a number of factors: • Virulence: the ability of a pathogen/infecting agent to cause disease • The distance that is travelled by infected people • How contagious the disease is • Small-world Networks – how groups of people interact: a small, relatively isolated group of infected people could infect a large susceptible group of people even if there’s very little interaction between the two groups

12. Testing for infectious Disease • Microbial Culture – growth medium is provided for a specific agent, and a sample taken from potentially diseased tissue or fluid is tested for the presence of an infectious agent able to grow in that medium • Microscopy – can be a simple compound light microscope or an advanced electron microscope • Biochemical Tests – used to test for infections like strep throat • Molecular Diagnostics – used to test for infections like tetanus

13. Clearance • Immune mechanisms kill or inactivate the inoculums of the pathogen. • Antibodies and/or T lymphocytes mediate immunity against infectious diseases by having a direct effect on the pathogen • Neutralising viruses – they can no longer enter cells to cause harm • Kill the infected cell so that the disease cannot spread from this cell. • Testing for infectious Disease • Microbial Culture – growth medium is provided for a specific agent, and a sample taken from potentially diseased tissue or fluid is tested for the presence of an infectious agent able to grow in that medium • Microscopy – can be a simple compound light microscope or an advanced electron microscope • Biochemical Tests – used to test for infections like strep throat • Molecular Diagnostics – used to test for infections like tetanus

14. Clearance • Immune mechanisms kill or inactivate the inoculums of the pathogen. • Antibodies and/or T lymphocytes mediate immunity against infectious diseases by having a direct effect on the pathogen • Neutralising viruses – they can no longer enter cells to cause harm • Kill the infected cell so that the disease cannot spread from this cell. • Testing for infectious Disease • Microbial Culture – growth medium is provided for a specific agent, and a sample taken from potentially diseased tissue or fluid is tested for the presence of an infectious agent able to grow in that medium • Microscopy – can be a simple compound light microscope or an advanced electron microscope • Biochemical Tests – used to test for infections like strep throat • Molecular Diagnostics – used to test for infections like tetanus • Immunity: • Resistance to infection may be acquired: • Following a disease • Asymptomatic (symptom free) carriage of the pathogen • Harbouring an organism with a similar structure – cross-reacting • Vaccination

15. Infectious diseases: the biggest killers 2002 Source: http://en.wikipedia.org/wiki/Infectious_disease