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Disease
A disease is a deviation from normal health. The effects of disease can range from loss of appetite, loss of energy and may result in death. Diseases can be contagious or non-contagious. Contagious diseases are caused by germs (microscopic pathogens) and can be divided into classes: virus, bacteria, fungi and parasites. Parasites can be internal or external. See what they look like under a microscope in the illustrations below:
External Parasites
Poultry Mite
Mite


Poultry Louse
Louse

Internal Parasites
Tape Worm
Tape Worm
Protozoa
Protozoa can cause
diseases such as:
Coccidiosis
Round Worm
Round Worm
Microscopic Fungi
Microscopic fungi cause
diseases such as:
Aspergillosis
and Candidia
Microscopic Virus
Microscopic viruses cause
diseases such as:
Avian Influenza
Newcastle Disease
Avian Pox
Pacheco's Disease
Psitiacine Beak & Feather Disease
Microscopic Bacteria
Microscopic bacteria cause
diseases such as:
Colibacilosis (E-coli)
Tuberculosis
Psittacosis (Chlamydolphila psittaci)
 
One of the biggest obstacles to keeping germs away from birds is that we cannot see germs. To understand how small germs are, look at the head of this pin (1) as seen through a microscope (2). When we look close enough we can see how many germs can hide in just one very small place. Imagine how many germs are on our hands (3).
Thumb with a pin head

(1)
   
Pin head magnified 100 times

(2)
Germs magnified 300 times

(3)
Sample Question
Most disease germs are so small that they can only bee seen through a microscope.
a) True
b) False
 
Now that we have learned about disease causing agents lets' see how disease is recognized.