From a medical standpoint, parasites describe a number of multi-cellular organisms that are able to survive on or within the human body, but have side effects that are harmful to human health. Technically speaking, a parasite has two characteristics:
- Part of its life cycle must be spent within a host body; and
- It requires sustenance from the host in order to survive during this period.
However, the term 'parasite' is usually used to refer to any organism that meets either of these characteristics.
Parasites do not include single-celled organisms, such as bacteria, amoeba or viruses that can cause disease. It also excludes multi-cellular creatures that normally inhabit the human body and rarely have harmful side effects, like dust mites.
Parasites cause more disease related deaths than any other type of infection. Malaria, which is transmitted largely by mosquito bites, is the leading cause of death by disease. Leishmaniasis, transmitted by the bite of a sandfly, is second. Tapeworms, which are transmitted by eating parasitic cysts in undercooked food, typically fish and pork, can cause neurocysticercosis, the most common neurological disease in the world. However, it is very rare for parasitic diseases to be transferred from person to person. Schistosomiasis, which is rarely fatal, has the second highest economic impact on the developing world after malaria and is a much bigger health problem in Africa than AIDS.
Parasitic diseases are rare in North America and Europe, although they are very common in the developing world. Most Western patients who develop parasitic infections were exposed while traveling. As such, it is usually vital for a medical history to contain a patient's full travel itinerary for the past several years. However, there are a few parasitic diseases that are endemic to North America.
Monsters Inside Me, a series that focusses primarily on parasitic diseases.
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