Parasitic diseases are caused by organisms that live on or inside a host organism and obtain their nutrients from it. The organisms that cause parasitic diseases can be divided into two main categories: protozoans (single-celled organisms) and helminths (worms).
Protozoan parasites, such as those that cause malaria, are transmitted by vectors such as mosquitoes. When a person is bitten by an infected vector, the protozoan enters the body and reproduces within the host, eventually causing symptoms such as fever, chills, and joint pain.
Helminth parasites, such as those that cause schistosomiasis and ascariasis, are usually transmitted through contaminated water or soil. When an infected person comes into contact with water or soil containing the parasites, the parasites enter the body and cause symptoms such as abdominal pain, fatigue, and diarrhea.
In addition to these two main categories, there are also other types of parasites, such as ticks, fleas, and mites, that can cause parasitic diseases. These parasites are usually transmitted through contact with an infected animal or through contact with an infected person.
Overall, parasitic diseases are caused by organisms that live on or inside a host organism and obtain their nutrients from it. These organisms can be protozoans, helminths, ticks, fleas, or mites, and they are usually transmitted through vectors, contaminated water or soil, or contact with an infected person or animal.