Unit 2 Topic 2 Biology

Infectious disease vs non-infectious disease

Infectious - invasion by a pathogen and can be transmitted from one host to another

Non-infectious - genetic and lifestyle diseases

Pathogens

Prions - cause host to misfold it own normal prion proteins, which hurt immune system, no treatments. Eg CJD (brain disease can caught from eating beef with ‘mad cows disease’)

Viruses - can only replicate inside cells, not made out of cells, need host to replicate, is genetic material encased in capsid protein coat, cannot be treated with antibiotics. Eg Influenza, chicken pox

Bacteria - can be treated by antibiotics, have many different types and features. Eg salmonella, E.coli

Fungi - can secrete enzymes and other chemicals into the environment to break down organic matter so it can be absorbed. These secretions act as an agent of disease in the host. Eg mold, true yeasts

Protists - can be pathogenic to plants and animals. Eg plasmodium which causes malaria, root rot in plants

Parasites - get their nutrients from the host, thus harming the host. Eg worms (pinworm, threadworms)

Virulence Factor

how effective a pathogen is against an organism’s defences depends on this factor

Capsule - coating around a bacterium, making it less vulnerable to elimination by the host

Adherence factors - proteins or carbs on the surface of the pathogen that allow it to stick to the host cells

Invasion Factors - surface components that allow it to invade the host cells

Toxins - substances the pathogen can excrete to damage the host cells

Modes of Disease transmission

Direct contact - poor hygiene, touching contaminated surfaces

contact with body fluids - contact with saliva, blood, semen

contaminated food/water - resulting from chemicals, pesticides, animal waste, industrial waste

disease-specific vectors - mosquitos carry malaria

Immune responses

pathogens (bacterial and viral) can cause both physical and chemical changes in host cells that stimulate the host immune responses. Eg introduction of foreign chemicals via the surface of the pathogen, production of toxins, recognition of self and non-self.

all plants and animals have innate immune responses (general/non-specific) and vertebrates also have adaptive (specific) immune responses

innate immune response in vertebrates comprises surface barrier (skin, mucus and cilia), inflammation and the complement system

Inflammatory response

The complement system

is made up of a large number of distinct plasma proteins that react with one another to opsonize pathogens and induce a series of inflammatory responses that help to fight infection.

adaptive immune response

Its key features include its ability to act automatically in response to microbial invasion, generate resistance proportional to the threat, and improve with experience.

Humoral vs cell-mediated immunity

Humoral immunity produces antigen-specific antibodies and is primarily driven by B cells.

Cell-mediated immunity does not depend on antibodies for its adaptive immune functions and is primarily driven by mature T cells, macrophages and the release of cytokines in response to an antigen.

Both responses produce memory cells that stay in the body for a period of time and ‘remember’ the pathogen if it enters the system again.

Transmission and spread of disease

transmission is facilitated by regional and global movement of organisms

factors that affect immunity are - persistence of pathogens within a host, transmission mechanism (ie direct/indirect contact/contaminates), proportion of the population that is immune or has been immunized, mobility of the individuals in the affected community.

Factors to predict potential outbreaks

persistence of pathogens within a host, transmission mechanism (ie direct/indirect contact/contaminates), proportion of the population that is immune or has been immunized, mobility of the individuals in the affected community.

Strategies to control the spread of disease

personal hygiene,

contact tracing,

school and workplace closures,

reduction of mass gatherings,

temperature screening,

travel restrictions