Parasites may be protozoa, fungi, or multi-cellular organisms. Many parasites have complex life cycles that insure their proliferation and survival.
As mentioned above, protozoa have a more complex organization than bacteria. Some protozoa form cysts that protect them from harsh conditions and enable them to live outside of a host for a long time. Some diseases caused by protozoans are:
Malaria (transmitted by mosquitos) is most prevalent in Sub-Saharan Africa
Leishmaniasis (transmitted by sandflies which are about one-third the size of mosquitoes)
African trypanosomiasis (sleeping sickness transmitted by the tsetse fly)
Amoebic dysentery – infection of the intestine caused by an ameba (Entamoeba histolytica), which causes severe diarrhea.
Coccidiosis – intestinal infection that causes bloody diarrhea.
Cryptosporidiosis – parasitic disease of the intestine caused by Cryptosporidium.
Giardial enteritis – an infection of the small intestine caused by Giardia lamblia.
Toxoplasmosis – a systemic parasitic infection transmitted by eating undercooked meat or contamination by cat feces.
Malaria, a debilitating disease that causes high fevers, is contracted through the bite of an infected mosquito. The parasite reproduces within the human liver and red blood cells (shown above), and it is transmitted back to other mosquitos when they feed on the infected person. Mosquitoes and flies are also vectors of parasitic diseases such as sleeping sickness and elephantiasis.
Fungi include one-celled yeasts slightly bigger than bacteria, and multi-celled mushrooms and molds. Fungi do not have chlorophyll to make their own food, so they get their nutrition as parasites or by breaking down remains of dead plants or animals. Some fungi are poisonous (e.g., Amanita mushrooms), but some have beneficial uses. For example, Penicillium notatum produces the antibiotic penicillin and Saccharomyces cerevisiae is the yeast used to make bread rise and to brew beer. Fungal diseases are called mycoses and include:
Aspergillosis – infection of sinuses and lungs
Blastomycosis – skin and pulmonary infections
Candidiasis – cutaneous and vaginal infections. Candida albicans is the most common cause of vaginal yeast infections.
Coccidioidomycosis – may cause cough, chest pain, shortness of breath
Cryptococcosis – may be transmitted in pigeon droppings
Multicellular parasites include various kinds of worms and fungi that cause diseases such as:
Lymphatic filariasis or elephantiasis (transmitted by mosquitos)
Schistosomiasis (liver or blood flukes)
Trichinosis – a disease caused by consumption of poorly cooked meat that contains cysts of Trichinella spiralis.
Tinea corporis, tinea pedis (ringworm, athlete’s foot)
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