1. Infection and Disease

2. Disease
Disease is any condition which prevents an organism from functioning efficiently.
There are two major groups of disease:
Non-infectious Diseases
Infectious Diseases

3. Non-Infectious Diseases
Can be caused by a number of factors including:
Environmental conditions
Nutrition
Breakdown of tissue, bone or muscle
Congenital
Genetic

4. Infectious Diseases
An infectious disease is a condition caused by the presence or growth of infectious microorganisms or parasites (macroorganisms).
Infectious diseases can be transmitted from one organism to another.
Can affect plants and animals.

5. Pathogens Pathogens are disease causing parasites.
Parasites can be grouped in different ways:
Microparasites: such as prions, viruses, bacteria, protozoa and fungi.
Macroparasites: such as parasitic worms, ticks and lice.
Endoparasites: live inside the host , for example, parasitic worms, prions, viruses, bacteria, protozoa and fungi.
Ectoparasites: live outside the host, for example, fleas, ticks, fungi and bacteria.

6. Pathogens The different types of pathogens are: Bacteria Fungi
Parasites
Protozoa
Arthropods
Non-cellular agents
Viruses
Prions
Viroids

7. Pathogens and Disease Pathogen Types Disease Agent That Causes Disease
Method of Transmission
Common cold
Rhinovirus
Two types (A, B), plus subtypes
Varicella
Paramyxovirus
Mycobacterium tuberculosis
Neisseria meningitidis
Vibrio cholerae
Clostridium tetani
Trypanosoma
Plasmodium
Entamoeba histolytica
Schistosoma
Taenia saginata
Imperfect fungi
Airborne; direct contact with infected person
Airborne; droplet infection; direct contact with infected person
Droplets in air; direct contact with secretions of infected person
Droplets in air; contaminated milk and dairy products
Direct contact with a carrier
Contaminated drinking water
Contaminated wound; usually puncture wound
Spread by tsetse fly
Spread by Anopheles mosquitoes
Freshwater streams and rice paddies
Contaminated meat
Contact with infected person
Exchange of hats, combs, or athletic head gear with infected person
Viruses
Influenza
Chickenpox
Measles
Bacteria
Tuberculosis
Meningitis
Cholera
Tetanus
Protists
African sleeping sickness
Malaria
Amoebic dysentery
Worms
Schistosomiasis
Beef tapeworm
Fungi
Athlete’s foot
Ringworm

8. Hosts
A host is an organism that supports a parasite to its own detriment. They can be:
Infected by the pathogen, displaying signs of its presence called symptoms.
Carriers of the pathogen, displaying no sign of its presence.

9. Portals of Entry Skin Gastrointestinal Tract Respiratory Urogenital
Via Placenta
Parenteral (injection, bite)

10. Vectors
A vector is an organism that transmits a disease-causing organism from one host to another.

11. Bacteria
Bacteria are classified by their shape, type of cell wall, nutrient requirements, and ability to grow in the presence or absence of oxygen.

12. Bacteria
Bacteria are single celled organisms that exist as free living cells or colonies.
Bacteria have both a cell membrane and a cell wall that protects them from their environment.

13. Bacteria Bacteria cells divide by binary fission.
First the chromosome is duplicated
As the cell grows, the two chromosomes are separated from each other.
The cell then divides and each daughter cell receives a single copy of the chromosome.

14. Bacillus anthracis
Gram positive rod
Survives in soil as spores
Infects hoofed animals
First bacterium proven to cause specific disease

15. Primarily a disease of domesticated and wild hoofed animals
Anthrax
Primarily a disease of domesticated and wild hoofed animals
Human infection arises from contact with diseased animals or carcasses

16. Anthrax in Herbivores May be listless or without appetite
After death, bleeding from body cavities
In US, incidence higher along old cattle drive routes

17. Human Anthrax Infections
Cutaneous
Respiratory
Gastrointestinal

18. Anthrax Disease Not spread person-to-person (not contagious)
Most common in countries without veterinary public health programs
NOW – biological warfare threat

19. Formation of bacterial endospores
Under adverse conditions, some species of bacteria can produce a highly stable, dormant cell called an endospore.
Bacterial spores can survive in extreme conditions.
General antiseptic chemicals and methods of disinfections are usually not sufficient to kill endospores.
Endospores can remain dormant for years.

20. Fungi
The Yeasts: Yeast cells look like little round or oval blobs under a microscope. Individual cells are too tiny to be seen with the naked eye, but you can see large clusters of them as a white powdery coating on fruits and leaves.
The Molds: Molds are described as filament-like, because they form long filament-like strands of cells called hyphae. These hyphae are what give mold colonies their fuzzy appearance.
The Mushrooms: Mushrooms are formed from the cells of the hyphae, such that mushrooms reflect a closer connection between the cells than in other multicellular creatures.

21. Fungi Fungi are eukaryotic organisms.
Their DNA is enclosed in a nucleus.
Many of them may look plant-like, but fungi do not make their own food from sunlight like plants do.
Fungi include single-celled organisms that exist individually) the yeasts( or in multicellular bunches (such as molds or mushrooms).
Fungi come in a variety of shapes and sizes and different types. They can range from individual cells to enormous chains of cells that can stretch for miles.

22. Parasites
Parasites are organisms that survive by living inside another, usually much larger organism (the host).
They include worms and single-celled organisms called protozoa.

23. Protozoa Protozoa are single-celled microorganisms.
Many protozoa benefit organisms by feeding on bacteria, others are parasitic to humans and animals and cause serious diseases.
The genetic material (contained in chromosomes) of protozoa is separated from the cytoplasm by a double membrane layer.  Also, the cytoplasm of protozoa is more highly organized, similar to the situation in animal cells.

24. Arthropods For example:
Ticks
Mosquitoes
Lice
Fleas
Pathogens that are capable of being transmitted by arthropods include protozoa, bacteria, viruses, helminths such as tapeworms, flukes, and roundworms.
The foremost disease carried by arthropods is malaria, involving a protozoan that is transmitted by mosquitoes. Malaria is the most deadly arthropod-borne disease in the world, affecting some 250 million people in the world, with as many as 2 million deaths annually.

25. Viruses
Viruses depend on the host cells that they infect to reproduce.
When found outside of host cells, viruses exist as a protein coat or capsid, sometimes enclosed within a membrane.
The capsid encloses either DNA or RNA which codes for the virus elements. While in this form outside the cell, the virus is metabollically inert.

26. Swine Flu

27. Prions Prions are naturally occurring
They are involved in myelin sheath repair
It is primarily composed of protein.
A modified form of prions is responsible for the diseases
A modified prion can alter a ‘normal’ prion by contact
All prion diseases discovered so far affect either the brain or the neural system.
Prion diseases are untreatable and always fatal.
E.g.: Creutzfeldt–Jakob disease, which causes brain tissue to break down.

28. Viroids
Viroids are a unique class of plant pathogens. They solely consist of a small, single-stranded, circular RNA.
These naked RNA molecules cause serious diseases among many crop plants, fruit trees and ornamentals, including potato, tomato, cucumber, chrysanthemum, avocado, and coconut palms.
The viroid induced diseases lead to dramatic economic losses in agriculture and horticulture worldwide.
Viroid RNA does not carry any protein specific genetic information. This means that its biological function is completely dependent on its interaction with target compounds of the host cell.

29. Viroids

30. Sexually Transmitted Disease (STDs)
Spread through sexual contact.
Large increases in STD cases with the introduction of the pill.
Can be caused by:
Bacteria
Viruses
Fungus
Protozoan
Arthropods

31. Control against pathogens
There are many reasons why pathogens need to be controlled:
Economic
Environmental
Public Health
Etc.

32. Quarantine
In Australia it is especially important that anything coming into the country is quarantined in order to stop any plant or animal diseases (pathogens) from being bought into the country.
Our quarantine measures in Australia have been successful in stopping many pathogens from entering the country, including:
Rabies
Foot-and-mouth disease