7.1.1 - Modes of transmission Flashcards
(14 cards)
1
Q
Infectious agent definition
A
Pathogen that is capable of infection and causes disease
2
Q
Virulence meaning
A
The ability of a pathogen to cause harm to its host. Greater virulence = greater effect on the health of the host
3
Q
Transmission definition and modes
A
Definition
- The way a pathogen spreads disease from one host to the next
Modes
- Direct contact: exposure to infected skin or body secretions enables pathogen transfer
- Indirect contact: transmission via a non-living object, e.g. contaminated grooming equipment in EID
- Vector transmission: transfer via another organism, like an arthropod
4
Q
Direct contact transmission
A
- Touching the affected area of the infected person passes the pathogen onto another person
- E.g. touching skin, sexual contact, kissing
- Diseases e.g. herpes simplex, ringworm, head lice
- Can be person-to-person or animal-to-person
5
Q
Person to person transmission
Direct transmission
A
- Physical contact with skin or mucous membranes of an infected person passes on pathogens, e.g. chickenpox, cold sores, glandular fever, headlice
- STDs are spread by direct sexual contact. As they are extremely sensitive to drying, eg. syphilis, gonorrhoea, indirect transmission e.g. via toilet seat is not possible
- Through infected blood or other body fluids (e.g. droplet sprays)
- Mother-to-child transmission can be via placenta during pregnancy (e.g rubella, hepatitis B), or during birth (e.g. HIV)
6
Q
Animal to person transmission
Direct transmission
A
- Pathogen transmitted via bites or scratches, e.g. rabies or cat scratch disease
- Can be transferred by contact with animal body fluids, e.g. dog or cat saliva, faeces, blood, urine of wild animals, or skin contact e.g. ringworm
7
Q
Indirect contact transmission
A
- Spread of disease through inanimate objects called fomites (passive vectors) that are contaminated by pathogens. E.g. bedding, clothes, and medical equipment
- Airborne diseases like common cold, influenza, whooping cough, and diphtheria, spread this way as they land on public spaces/objects e.g. bacterial spores on handrails, lightswitches
- Contaminated objects e.g. equipment used for cooking, eating, drinking, clothing, doorknobs etc.
- Nonsterile procedures: surgeries, tattoos, and dental work using non-sterilised equipment can spread diseases
8
Q
Vector transmission
A
- Transmission where another organism carries the pathogen from one person to another, or from an infected animal to a person. E.g. dogs, pigs, and birds are vectors
- E.g. the malaria protozoa, Plasmodium, is spread by the Anopheles mosquito, which acts as a vector for the transmission of the disease
- E.g. parrots can act as vectors for the transmission of psittacosis. Psittacosis spreads by inhalation of bacteria that are present in dried bird droppings and dust from the feather of infectious birds
- Biological vectors e.g. Anopheles mosquitoes transfer the pathogen from one individual to another, but the pathogen also undergoes part of its life cycle in the vector
- Mechanical vectors e.g. flies physically transfer the pathogen from one person to another wihtout being infected themselves
9
Q
Influenza A case study
Disease transmission: direcct + indirect
A
- Caused by Influenza Type A virus
Direct transmission
- Inhalation of water droplets containing the virus, which is expelled when an infected person sneezes or coughs. The droplets can enter the mouth or nasal passages of a healthy organism nearby
Indirect transmission
- The infected person’s hands can be contaminated with water droplets containing the virus during sneezing or coughing
- If the infected person touches an object, e.g. doorknob, the object can become contaminated with the virus
- A healthy, uninfected person who touches the object in the same spot later, and then places their hand on their nose or mouth, can also become infected as the virus enters their respiratory tract or mouth
Prevention measures
- Regular flu vaccines: ensures protection against the virus as it mutates frequently
- Wearing protectice face masks: reduces chances of inhaling the virus or inhaling water droplets from affected individuals
- Avoiding densely populated areas: minimises risk of obtaining the disease from affected people
- Hosting and running programs to educate people at risk of contracting the pathogen on preventative measures, e.g. vaccination
Control measures
- Follow international quarnatine procedures: stops transmission between regions
- Isolation of infected organisms from uninfected reduces incidence of the disease, e.g. employees who are affected can be ordered to remain at home and not commute to work
10
Q
Control vs prevention
A
- Prevention measures include preventing the occurrence of the disease
- Control meaures include reducing the incidence of the disease after it has occurred, lowering its duration (which decreases risk of spreading to healthy people because the number of affected people at a given time decreases), and reducing the financial burden to affected individuals, their families, and affected community
11
Q
Malaria case study transmission
Disease transmission: vectors
A
- Caused by the Plasmodium protozoan
Transmission:
- Plasmodium gametocytes infect Anopheles mosquito, a biological vector, by entering their stomach → gametocytes come together to form sporozoites (immature Plasmodium)
- Infected female mosquito bites a human, transferring the Plasmodium sporozoites into the human’s blood via their saliva
- Sporozoites are carried to the human’s liver, where they produce merozoites
- Merozoites develop and reproduce inside the liver cells → liver cells rupture due to amount of merozoites
- Merozoites then migrate and invade red blood cells, reproduce and rupture the cells again
- Some of the Plasmodium reproduce sexually to form male and female gametocytes
- When another mosquito bites the affected human, it becomes infected with the gametocytes
- Cycle begins again
**The symptoms of fever, nausea, headache and even anaemia (extreme) are due to the parasite’s ability to rupture liver and blood cells (vital for function)
**
12
Q
Malaria case study prevention
A
- Controlling the movement and population of the Anopheles mosquito vector is the primary mode of preventing malaria
- Indoor residual spraying prevents mosquitoes from resting on walls or roofs → effective for preventing mosquito bites
- Installing insecticide-coated mosquito nets and screens on doors and windows also reduces incidence of mosquito bites
- Adding larvicides and draining mosquito larvae breeding sites kills mosquito larvae and prevents more from accumulating in an area → less adult mosquitoes that can potentially become vectors
- Establishing effecting rainwater draininge systems prevents water from becoming stagnant, which makes for an ideal mosquito breeding site → less adult mosquitoes around
- Using antimalarial drugs to prevent contraction of malaria
- Educational programs to encourage people at risk of contracting malaria to take prevention measures e.g. taking antimalarial drugs, conducting regular draining of stagnant water and indoor residual spraying
13
Q
Malaria case study control
A
- Follow international quarantine procedures to stop the spread from one region to another: vector-borne diseases like malaria are usually limited to the vector’s geographical range, and generally only spreads beyond its usual range if the vector is introduced to another region
- Diagnostic testing for early detection, and prompt administration of antimalarial drugs can reduce the severity of the disease and prevent transmission
- Geographic information system (GIS) mapping can be used to identify areas with high transmission rates and target interventions effectively
- Make antimalarial drugs more accessible to affected individuals (preventative and control measure)
14
Q
Vehicle transmission
A
A classification of indirect transmission through vehicles of water, food, air - contamination can result in viable environments for contamination.
Transmission of pathogens through droplets can be vehicle (suspended in air) or direct (sneezed directly at someone’s face) or just indirect (contaminated doorknob, tissue)
