Infectious Diseases Flashcards
What is a disease
An abnormal function of the body
- condition that impairs the normal functioning of an organism, leading to poor health
- each disease is associated with a set of symptoms
- infectious/non-infectious
Infectious diseases
• transmissible / communicable / contagious / transferable
• passed from one (infected) person / host / organism, to another
• caused by a pathogen / microorganisms / (x2) virus / bacterium / fungus / protoctist / worm
Modes of transmission of infectious diseases
• direct contact (if pathogen cannot survive outside the body)
• water
• food
• faeces
• animals e.g. insects
• indirectly from person to person
• symptomless carriers (spread pathogen even if don’t have disease)
Pathogen def
Examples
Organism that causes disease
e.g. virus, bacterium, fungi, protoctists
Examples of pathogens that cause diseases
• HIV —> virus that causes AIDS
• Mycobacterium tuberculosis —> bacterium that causes TB
Parasite
Organism that live on/in another organism (host) and causes damage to that organism
Some parasites can cause …
Disease
Therefore is a pathogen
Example of pathogen that can cause disease
Plasmodium species —> single-called parasite that causes malaria
Examples of infectious diseases
• cholera
• malaria
• HIV/AIDS
• tuberculosis (TB)
Causes of malaria
• by a protoctist / Plasmodium
• several different species - cause different types of malaria
• Plasmodium infects RBC and breeds inside them
• toxins released when Plasmodium bursts out of cell - causes fever
…
Key phrases - Malaria causes
• Plasmodium / falciparum / malariae / ovale / vivacité
• (only) female feeds on blood
• female requires blood (protein) for (development of) eggs
• (only) female carries pathogen / disease-causing organism / Plasmodium / parasite
• (only) female transmits the disease
• (only) female is vector
…
Transmission of Malaria
- Female Anopheles mosquito feeds on human blood to obtain the protein needed to develop they eggs
- If the person they bite is infected with Plasmodium, they will take up some of the pathogen’s gametes with the blood meal
- Gametes fuse and develop in mosquito’s gut to form the infective stages
- Infective stages move to the mosquito’s salivary glands
- When mosquito feeds again, it injects the anticoagulant that prevents blood meal from clotting so it flows out of host into the mosquito
- The infective stages pass out into the blood
together with the anticoagulant in the saliva - parasite enters the hepatocytes (liver cells) where they mature and multiply
- burst out of the hépatite and enter the RBCs, where they multiply
Prevention and control
• remove population of mosquitos
• prevent mosquitos biting people
• use Prophylactic drugs
Methods to remove population of mosquitos
• remove sources of water
• layer of oil on water
• stock ponds, irrigation and drainage ditches and other forms fo water, with fish
• spray a bacterium
Methods to prevent mosquitos biting people
• sleep under mosquito net soaked in insect repellent every 6 months
• wear long sleeves - especially at dusk
• insect repellent - some resistant to DDT and other insecticides
Drugs used to prevent malaria
Prophylactic drugs - prevent infection and breeding in a person
- take drug before, during and after visiting an area with high cases of Malaria
• chloroquine - inhibits protein synthesis and prevents parasite spreading inside the body
• proguanil - inhibits sexual reproduction of Plasmodium inside the biting mosquito (stops gametes fusing in gut)
Name and type of pathogen that causes cholera
Vibrio cholerae / V. Cholerae
Bacterium
Name and type of pathogen that causes Malaria
Plasmodium - malariae, falciparum, ovale, vivax
Protoctist
Name and type of pathogen that causes tuberculosis (TB)
Mycobacterium tuberculosis / Mycobacterium bovis
Bacterium
Name of pathogen that causes HIV/AIDS
Human Immunodeficiency Virus (HIV)
Transmission of cholera
Contaminated food and water
E.g. water/food in contact with untreated sewage
Transmission of malaria
• Female anopheles mosquito
• Blood transfusion and re-use of unsterile needles
• Mother to child across placenta
Transmission of TB
• airborne - infected people cough/sneeze
—> Mycobacterium tuberculosis bacteria enter the air in tiny droplets of liquid
—> uninflected people inhale
—> spread faster in overcrowded conditions
• Mycobacterium bovis occurs in cattle - spread to human through contaminated meat and unpasteurised milk
Transmission of HIV/AIDS
• retrovirus
• sexual contact
• infected blood / contaminated needles - e.g. IV drug users using the same needle
• mother to foetus in early stages of pregnancy, birth or breastfeeding
• promiscuous sex
—> mucus lining of rectum not as thick as vagina
—> less natural lubrication
—> damage occurs more easily during intercourse
—> virus pass from semen to blood
Retrovirus
Virus with the ability to make DNA from RNA because they have reverse transcriptase
Infectious diseases are caused by
Pathogens
Small pox pathogen
Variole virus
Small pox transmission
Inhalation of droplets of moisture containing the virus
Prevention and control of smallpox
Eradicated by a vaccination programme coordinated by WHO
Mode of action of penicillin
• penicillin inhibits a group of enzymes (glycoprotein peptidases) by blocking or altering the shape of the active site
• enzymes used by bacteria to form cross-links between the peptidoglycan molecules that make the cell walls
—> so, penicillin causes the peptidoglycan chains to not link up and stops cross-links from forming
• when a newly formed bacterial cell is growing, it secretes enzymes (antolysins), which make little holes in the cell wall
—> alone wall to stretch so a new reptidoghycan chain can link
• when penicillin present, cross-links can’t form, cell wall not made, but autolysins Keep making new holes
• bacteria takes up water by osmosis and the cell swells which then bursts due to the weakened cell wall which can’t withstand the increased pressure as the turgar of cells not resisted by cell walls
• penicillin doesn’t harm viruses or human cells
—> don’t have cell walls and don’t contain peptidoglycans
—> don’t have peptidase or cytoplasm
