Parasites are microorganisms that live off of other organisms, or hosts, to survive. 

Some parasites don’t affect the host. 

Others grow, reproduce, or give off toxins that make the host sick resulting in a parasitic infection.

Parasitic infections are a large problem in tropical and subtropical regions. 

Malaria is one of the deadliest diseases caused by a parasite. 

There are also a number of parasitic infections that can occur in the U.S. Trichomoniasis, giardiasis, cryptosporidiosis, and toxoplamosis are the most common such infections that occur in the U.S.

Types of Parasitic Infections
Parasitic infections can be caused by three types of organisms: protozoa, helminths, and ectoparasites. 

Protozoa are single-celled organisms that can live and multiply inside of humans. Some infections caused by protozoa include giardiasis. 

This is a serious infection that can happen from drinking water infected with the protozoa. Helminths are multi-celled organisms that can live alone or in humans. 

These are commonly known as worms and include flatworms, tapeworms, ringworms, and roundworms. 

Ectoparasites are multi-celled organisms that live in or feed off of the skin of humans, such as mosquitos, fleas, ticks, and mites.

Causes
Parasitic infections can be spread in a number of ways. 

They can be spread through contaminated water, waste, fecal matter, blood, and through food that has been mishandled or undercooked. It can also be passed through sexual contact. 

Some infections are spread because an insect acts as a vector, or carrier, of the disease and transmits it while feeding on the host. Malaria, which is spread by mosquitos, is one such example.