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What is an example of direct transmission of disease?
What is an example of direct transmission of disease?
Which of the following is considered an indirect vehicle for disease transmission?
Which of the following is considered an indirect vehicle for disease transmission?
Which type of disease transmission involves water as a medium?
Which type of disease transmission involves water as a medium?
Which diseases are commonly transmitted through droplets from respiratory secretions?
Which diseases are commonly transmitted through droplets from respiratory secretions?
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What characteristic must organisms exhibit to survive in the air as droplets?
What characteristic must organisms exhibit to survive in the air as droplets?
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Which of the following methods can lead to the spread of infections through blood and body fluids?
Which of the following methods can lead to the spread of infections through blood and body fluids?
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What is a common way that salmonella can contaminate food?
What is a common way that salmonella can contaminate food?
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Which of the following diseases is NOT transmitted through sexual contact?
Which of the following diseases is NOT transmitted through sexual contact?
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What is an ideal medium for the growth of microorganisms found in saliva?
What is an ideal medium for the growth of microorganisms found in saliva?
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Which of the following best describes the defence mechanisms that deal with organisms after they have gained entry into the body?
Which of the following best describes the defence mechanisms that deal with organisms after they have gained entry into the body?
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What type of transmission is most commonly associated with the mosquito?
What type of transmission is most commonly associated with the mosquito?
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Which organisms are primarily responsible for causing diseases through soil transmission?
Which organisms are primarily responsible for causing diseases through soil transmission?
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What is a major health implication of filthy breeding habits in insects?
What is a major health implication of filthy breeding habits in insects?
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How can enteric pathogens reach humans from soil?
How can enteric pathogens reach humans from soil?
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Which disease is not transmitted by mosquitoes?
Which disease is not transmitted by mosquitoes?
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What common result can occur from ingestion of contaminated food or water?
What common result can occur from ingestion of contaminated food or water?
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Which of the following is a characteristic of mosquito-borne diseases?
Which of the following is a characteristic of mosquito-borne diseases?
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What percentage of the global burden of disease is attributed to typhoid infections?
What percentage of the global burden of disease is attributed to typhoid infections?
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Which type of T-lymphocyte is responsible for activating B-lymphocytes to produce antibodies?
Which type of T-lymphocyte is responsible for activating B-lymphocytes to produce antibodies?
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What is the primary function of polymorphonuclear leucocytes in the immune response?
What is the primary function of polymorphonuclear leucocytes in the immune response?
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What distinguishes natural immunity from acquired immunity?
What distinguishes natural immunity from acquired immunity?
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Which of the following is an example of passive artificial immunity?
Which of the following is an example of passive artificial immunity?
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Which type of T-lymphocyte functions to turn off the immune response?
Which type of T-lymphocyte functions to turn off the immune response?
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What is the primary function of the mucociliary escalator in the respiratory tract?
What is the primary function of the mucociliary escalator in the respiratory tract?
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Which component of the immune system primarily recognizes foreign antigens?
Which component of the immune system primarily recognizes foreign antigens?
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What role does the blood-brain barrier serve?
What role does the blood-brain barrier serve?
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Which of the following best describes the composition of saliva?
Which of the following best describes the composition of saliva?
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What triggers the rapid division of B lymphocytes upon encountering a foreign antigen?
What triggers the rapid division of B lymphocytes upon encountering a foreign antigen?
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Which part of the skin acts as a mechanical barrier to pathogens?
Which part of the skin acts as a mechanical barrier to pathogens?
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What function do the memory B cells serve in the immune response?
What function do the memory B cells serve in the immune response?
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What is the role of fatty acids and salts secreted by the skin glands?
What is the role of fatty acids and salts secreted by the skin glands?
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Which of the following statements about T lymphocytes is true?
Which of the following statements about T lymphocytes is true?
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What is the main purpose of gingival crevicular fluid in the body?
What is the main purpose of gingival crevicular fluid in the body?
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Study Notes
Transmission of Disease
- Transmission can be direct (physical contact) or indirect (through an object or vector).
- Transmission methods include kissing, touching, sexual contact, and air, water, food, oral secretions, body lesions, and vectors.
Indirect Transmission
- Vehicles: air/droplets, water, soil, food, fomites, blood, saliva.
- Vectors: insects, especially mosquitoes which transfer disease through saliva when withdrawing blood.
- Air/Droplets: droplets are too large to be airborne for long periods, but can survive outside the body and resist drying, allowing them to enter the respiratory tract.
- Waterborne: contaminated water by animal or human excreta, causing infections during bathing, washing, drinking, or food preparation.
- Soil: can transmit infections through contact, such as tetanus, and can contain enteric pathogens in high concentrations.
Food and Faecal-Oral Transmission
- Food: contaminated food/water can transmit infections that infect the digestive system.
- Faecal-Oral: organisms shed from the body in faeces can contaminate water supply or food, leading to infections.
Blood and Body Fluids
- Blood: infections can spread when blood/fluids from an infected person come into contact with mucous membranes or bloodstream of an uninfected person.
- Body fluids: infections can be passed by sexual contact through various routes, such as genital to genital, oral to genital, or oral or genital to anal.
Saliva
- Saliva: contains a balanced microflora (bacteria, fungi, and viruses) and acts as a medium for transmission from host to host.
- Infections can be spread by direct contact with saliva (kissing) or indirect contact with contaminated objects (children sucking toys).
Defence Against Disease
- Preventing Ingress: mechanisms that prevent entry of disease, such as tears, saliva, gingival crevicular fluid, stomach acid, skin, and blood brain barrier.
- Dealing with Ingress: defence mechanisms that deal with the micro-organisms after they enter the body, such as the immune response.
Preventing Ingress
- Mucociliary Escalator: the respiratory tract is lined with mucus and cilia, which trap microbes and sweep them up towards the epiglottis to be swallowed.
- Skin: has a tough outer layer of cells that produce keratin, serving as a mechanical barrier.
- Fatty acids and salts: glands in the skin secrete these, killing bacteria.
- Saliva: contains antibacterial agents and has a lavage effect.
- Gingival crevicular fluid: inflammatory exudate that contains antibacterial solutions and immunological defence mechanisms.
- Blood: flushing action of blood flow and clotting mechanisms prevent entry of infection.
- Blood brain barrier: specialized filter that surrounds the brain and spinal cord, acting as a physical barrier.
Dealing with Ingress
- Immune Response: involves the immune system recognizing and destroying foreign substances and organisms that enter the body.
- Lymphocytes: white blood cells that develop in the bone marrow and circulate throughout the body in the lymphatic system.
- B Lymphocytes: produce antibodies (humoral immune response). They differentiate into plasma cells that produce antibodies and memory cells that remember encountered antigens.
- T Lymphocytes: control immune response and destroy antigens directly (cell mediated immune response), including killer cells, helper cells, and suppressor cells.
- Phagocytosis: polymorphonuclear leucocytes engulf and destroy invading micro-organisms.
Immunity
- Immunity: condition of being protected against an infectious disease.
- Natural immunity: present from birth, inherited from mother to offspring.
- Acquired immunity: gained throughout life, developed in response to a disease, and may be temporary or permanent.
Acquired Immunity
- Active immunity: long-lasting immunity developed by having the disease, having a subclinical infection, or by inoculation with killed micro-organisms or detoxified toxins.
- Passive immunity: ready-made antibodies are injected into the human body to develop immunity.
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