Page 9 - Medical Parasitology_ A Textbook ( PDFDrive )

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Introduction

Medical Parasitology is the study of organisms that parasitize humans. According to
the definition, parasites include the viruses, bacteria, fungi, protozoa and metazoan
(helminths and arthropods). Since viruses, bacteria and fungi are not categorized as
animals, they have been incorporated into the discipline of Microbiology.
The discipline of Parasitology includes protozoa, helminths, and arthropods
whose existence depends on the availability of hosts and these are obligate para-
sites. Those which can survive and reproduce without a host are facultative para-
sites. Very few of these facultative parasites infect humans (e.g. the free-living
amoebae). Ectoparasites are referred to as parasites living on the host body surface
while endoparasites live inside the body of host. Entomology is the study of insects.
In Parasitology, insects play a role as vectors of several infections although several
are true parasites in their own right. On the other hand, acarology is the study of
ticks and mites. These are mainly ectoparasites.
Parasitic diseases have caused some of the most serious health problems in the
world today, particularly in the tropics and subtropics regions. One of the most sig-
nificant parasitic diseases, malaria, kills approximately half a million people each
year. Most of them are children under the age of 5 years in Sub-Saharan Africa.
The neglected tropical diseases (NTDs) include parasitic diseases such as
Chagas’ disease, cysticercosis, echinococcosis, human African trypanosomiasis,
schistosomiasis, leishmaniasis, soil-transmitted helminthiasis, lymphatic filariasis,
and onchocerciasis. These NTDs affect more than one billion people, mostly in
rural areas of low socio-economic countries, trapping one sixth of the world’s popu-
lation in a vicious cycle of poverty and neglect.
Though not in all cases, parasitic diseases are mostly confined to developing
countries. However, geographic distributions of parasitic diseases are evolving and
changing due to ease of international travel and influx of refugees and migrants to
developed countries for leisure, education, and economic reasons. Gastrointestinal
diseases, liver diseases, vector-borne diseases, scabies, and tuberculosis are com-
mon among migrants. Inbound migrants may harbour long-eliminated diseases in
the host country which may still be endemic in their country of origin and the

© Springer International Publishing AG 2017 1
R. Mahmud et al., Medical Parasitology,
https://doi.org/10.1007/978-3-319-68795-7_1