What are Infectious Diseases?
Epidemic vs. Pandemic: Think about a panoramic picture. It covers a large area. A pandemic is larger than an epidemic.
Also, remember that animals and other humans don't directly make you sick with infectious diseases. It is the pathogens that they are carrying that might make you sick.
#1 Bacteria vs. Bacterium
Bacteria is the plural form. Bacterium is the singular form. It would be incorrect to say "I saw a bacteria walking down the street." It would correct to say either "I saw a bacterium walking down the street" or "I saw several bacteria walking down the street." Most likely, you will never see a bacteria walking down the street. We hope.
# 2 Not every bacteria wants to infect a human
Lots of bacteria prefer to infect other animals or plants or just the environment. In fact the human body can be a deadly place for many bacteria. Many of them think we are the bad guys.
All viruses don't look like a cartoon virus
Not all viruses look like a little robotic mosquito or a ball with spiky things. Some viruses are long and shaped more like a worm. Some viruses have tons of spikes like some medieval weapon (which are actually surface proteins) and some have none at all. They are very diverse in size and shape.
Fungi and Parasite Infections
Why don't we have Malaria in the United States?
Many people think that Malaria is not a problem in the United States because the special mosquitos that carry Malaria are not found here. This is not true, there are three species of mosquitos in the United States that can carry Malaria and have done so in the past. Malaria used to be a large problem in the United States all the way up until the 1950's when a chemical called DDT was used heavily to kill mosquitos. DDT has since been shelved because of unhealthy effects it has on humans and other species.