UNIT 10PATHOGENS AND IMMUNITY

Today:• Pathogens and transmissible diseases• How pathogens are transmitted• Body defences against pathogens

Case Study• A British woman visited India, while there she was bitten by a dog.• The bite wasn't serious, so she didn't seek medical help.• 7 weeks later, back home in Britain, she felt ill and went to hospital.• Her symptoms were mild, so doctors were unable to diagnose. • She didn't mention the dog bite.• She eventually went to a specialist hospital for tropical diseases.• It was too late, she died a few weeks later, from a virus called Rabies.

Rabies

• A disease caused by a virus• What is a virus? • an infective agent that typically consists of a nucleic acid molecule in a

protein coat, is too small to be seen by light microscopy, and is able to multiply only within the living cells of a host.• What is an infective agent?• An infective agent is something that enters another living thing, like

you. When an infective agent enters, you have officially become an infected host. There are four main classes of infective agents: bacteria, viruses, fungi, and parasites.

Think• What could the woman have done in India?

• What could the doctors have done in Britain?

• What can be done to stop the spread of Rabies in animals?

Pathogens• Microorganisms that cause diseases.

• Viruses; Bacteria; Protoctists (Parasites); Fungi

• Pathogens can usually be passed from person to person• Transmissible diseases – "a disease in which the pathogen can be

passed from one host to another"

How do pathogens get into your body?• Direct contact - • Direct contact means that the disease-causing pathogen is passed

from one person (or animal) to another when their bodies touch in some way.

• Touching = bacterial gastroenteritis = chickenpox• Kissing = bacterial meningitis = glandular fever, cold sores• Sexual intercourse = gonorrhoea, syphilis = HIV, hepatitis B• Mother to unborn baby = german measles = HIV

• Indirect contact• Indirect contact happens when microorganisms are carried to a

person in some way, instead of by actual body to body contact.

Droplets in the air• When you cough, sneeze, or even speak, millions of viruses and sent

into the air on tiny droplets of moisture

• Some viruses can last outside the body on hard surfaces for up to 24 hours.

• Tuberculosis, cold, flu

Water and food transmission• If you eat or drink anything containing significant amouts of

bacteria/viruses. You may get sick.

• Water = cholera = polio

Food = Salmonella (food poisoning) = Hepatitus A

Vectors• What is a vector?• A vector is a an organism that carries a pathogen from one host to

another.

• Rabies = vectors are dogs, skunks, raccoons, bats• Malaria = mosquitoes• Plague = fleas

• Microorganism• A microscopic organism (only visible using a microscope)• Pathogen• Microorganisms that cause disease• Transmissible disease• a disease in which the pathogen can be passed from one host to another• Direct contact• pathogen is passed from one person (or animal) to another when their

bodies touch in some way• Indirect contact• pathogens are carried to a person in some way, instead of by actual body to

body contact. • Vector• A vector is a an organism that carries a pathogen from one host to another

Body defences• What can we do to stop pathogens entering into our bodies?

• Mechanical barriers - is the primary defense, structures which makes it difficult for the entry of pathogens into the body.

- Eg. Hairs in the nostril, thick outer layer of skin

• Chemical barriers – chemicals produced by the body that makes it difficult for pathogens to infect he body.

- Eg. Sticky mucus in respiratory passages, hydrochloric acid in stomach

Food hygiene• Keep bacteria away from food• Keep animals away from food• Do not keep foods a room temp for long periods • Keep raw meat away from other foods

• Personal hygiene, keep ourselves clean

Basic Hygiene Quiz

Waste disposal• Open landfill sites, may attract rats, dogs, houseflies. - carry harmful bacteria away• Dangerous chemicals• Methane from decomposers – can be flammable

Sewage Treatment

What do we know?• About pathogens and transmissible diseases• About indirect and direct methods by which pathogens can be transmitted• How mechanical and chemical barriers prevent pathogens entering the

body• How food hygiene and personal hygiene can reduce the risk of infection• The importance of hygienic waste disposal and sewage treatment