Escherichia coli which causes cystitis. Breaks in the skin surface e. Clostridium tetani which causes tetanus. Immune system An infection can be seen as a battle between the invading pathogens and host. Routes of transmission Find out how you can pick up germs and pass them on to others. Vaccination Just a shot in the arm — what do vaccines do? While the forms of infection that we have listed above are the main types, there are others that can have an effect on the body.
A single celled organism with a nucleus can cause a protozoan infection. Protozoa commonly show features similar to those of animals, such as mobility, and they can survive outside the human body. They most commonly transfer to other humans through feces. Amebic dysentery is an example of a protozoan infection.
Helminths are larger, multicellular organisms that tend to be visible to the naked eye when fully grown. This type of parasite includes flatworms and roundworms. These can also cause infection. Finally, ectoparasites — including mites, ticks, lice, and fleas — can cause infection by attaching or burrowing into the skin. Ectoparasites can also include blood-sucking arthropods, such as mosquitoes, which transmit infection by consuming human blood.
The cause of an infection is whichever type of organism has entered the body. A specific virus, for example, will be the cause of a viral infection. A wound fills with pus , for example, when white blood cells rush to the site of an injury to combat foreign bacteria. The symptoms of an infection depend on the organism responsible, as well as the site of the infection.
Viruses target specific cells, such as those in the genitals or upper respiratory tract. The rabies virus, for example, targets the nervous system. Some viruses target skin cells, causing warts.
Others target a wider range of cells, leading to several symptoms. A flu virus can cause a runny nose, muscle aches, and an upset stomach. A person with a bacterial infection will often experience redness, heat, swelling, fever, and pain at the site of infection, as well as swollen lymph glands. A rash can indicate a fungal infection of the skin. However, viruses and bacteria may also cause skin conditions and rashes.
Common symptoms of prion diseases include rapid onset of brain damage, memory loss, and cognitive difficulties. They can also trigger the buildup of plaque in the brain, causing this organ to waste away. There is no single method for preventing all infectious diseases. However, people should take the following steps to reduce the risk of transmission:. Some infectious diseases can be passed from person to person. Some are transmitted by insects or other animals.
And you may get others by consuming contaminated food or water or being exposed to organisms in the environment. Signs and symptoms vary depending on the organism causing the infection, but often include fever and fatigue. Mild infections may respond to rest and home remedies, while some life-threatening infections may need hospitalization. Many infectious diseases, such as measles and chickenpox, can be prevented by vaccines.
Frequent and thorough hand-washing also helps protect you from most infectious diseases. Each infectious disease has its own specific signs and symptoms. General signs and symptoms common to a number of infectious diseases include:. An easy way to catch most infectious diseases is by coming in contact with a person or an animal with the infection. Infectious diseases can be spread through direct contact such as:. Person to person. Infectious diseases commonly spread through the direct transfer of bacteria, viruses or other germs from one person to another.
This can happen when an individual with the bacterium or virus touches, kisses, or coughs or sneezes on someone who isn't infected. These germs can also spread through the exchange of body fluids from sexual contact. The person who passes the germ may have no symptoms of the disease, but may simply be a carrier. Disease-causing organisms also can be passed by indirect contact. Many germs can linger on an inanimate object, such as a tabletop, doorknob or faucet handle.
When you touch a doorknob handled by someone ill with the flu or a cold, for example, you can pick up the germs he or she left behind.
If you then touch your eyes, mouth or nose before washing your hands, you may become infected. Some germs rely on insect carriers — such as mosquitoes, fleas, lice or ticks — to move from host to host. Your body can be more prone to bacterial infections when your immune system is compromised by a virus.
The disease state caused by a virus enables normally harmless bacteria to become pathogenic. Antibiotics are used to treat bacterial infections. Some strains of bacteria have become resistant to antibiotics, making them difficult to treat. This can happen naturally, but also happens because of the overuse of antibiotics, according to the World Health Organization WHO.
There are millions of different fungal species on Earth. Just or so are known to cause sickness. Fungi can be found just about everywhere in the environment, including indoors, outdoors, and on human skin. They cause infection when they overgrow. Fungi cells contain a nucleus and other components protected by a membrane and a thick cell wall. Their structure can make them harder to kill.
Some new strains of fungal infections are proving to be especially dangerous , such as Candida aurus , and have prompted more research into fungal infections. Parasites are organisms that behave like tiny animals, living in or on a host and feeding from or at the expense of the host.
Though parasitic infections are more common in tropical and subtropical regions, they can occur anywhere. They can be spread several ways, including through contaminated soil, water, food, and blood, as well as through sexual contact and via insect bites. Viruses can cause a number of infections, many of which are contagious. Examples of viral diseases include:.
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