Pathogenic microbes challenge the immune system in many ways. Viruses make us sick by killing cells or disrupting cell function. Many bacteria make us sick in the same way that viruses do, but they also have other strategies at their disposal. Sometimes bacteria multiply so rapidly they crowd out host tissues and disrupt normal function. Sometimes they kill cells and tissues outright. The protozoa that cause malaria , which are members of the genus Plasmodium, have complex life cycles.
Sporozoites, the stage of the parasite that infects new hosts, develop in the salivary glands of Anopheles mosquitos. Cells infected with sporozoites eventually burst, releasing another cell form, merozoites, into the bloodstream. A doctor can treat bacterial infections with antibiotics. However, some strains become resistant and can survive the treatment.
A fungus is often a multicellular parasite that can decompose and absorb organic matter using an enzyme. However, some types, such as yeasts, are single celled. Fungi almost always reproduce by spreading single celled spores. The structure of a fungus is usually long and cylindrical, with small filaments branching from the main body. There are approximately 5. Many fungal infections develop in the upper layers of the skin, and some progress to the deeper layers.
Inhaled yeast or mold spores can sometimes lead to fungal infections, such as pneumonia, or infections throughout the body. These are also known as systemic infections. The body usually has a population of good bacteria that help maintain the balance of microorganisms.
These line the intestines, mouth, vagina, and other parts of the body. Examples of fungal infections are:. A prion is a protein that contains no genetic material and is usually harmless. Scientists do not class prions as living microorganisms. However, if a prion folds into an abnormal shape, it can become a rogue agent and cause infection. Prions can affect the structure of the brain or other parts of the nervous system. They do not replicate or feed on the host.
Prions cause degenerative brain diseases, all of which are rare but progress rapidly and are currently fatal. 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.
Your family and friends can play a role in recognizing if you have caught an infection while in the How does fever help fight infection? Anthony L. Komaroff, MD. Fever, a common symptom of infection, can leave you feeling hot, achy and miserable. But it serves a What is a contagious disease?
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