GENERAL PARASITOLOGY LEARNING OBJECTIVES

Discuss the various types of parasites and hosts.
• Explain the relationship between a parasite and the host and their effects.
• Discuss in detail the classification of medically important parasites.
• Explain the difference between the Cestodes, Nematodes, Trematodes and Protozoa.
INTRODUCTION
Man and other living things on earth live in an entangling relationship with each other .They don’t exist in an isolated fashion. They are interdependent; each forms a strand in the web of life. Medical parasitology is the science that deals with organisms living in the human body (the host) and the medical significance of this host-parasite relationship.ASSOCIATION BETWEEN PARASITE AND HOST
A parasite is a living organism, which takes its nourishment and other needs from a host ; the host is an organism which supports the parasite. The parasites included in medical parasitology are protozoa, helminthes, and some arthropods. broader classification of parasites). The hosts vary depending on whether they harbor the various stages in parasitic development.
PARASITE NOMENCLATURE AND CLASSIFICATION
Kingdom: Protista *
Subkingdom : Protozoa
1- Phylum: Sarcomastigophora
Subphylum: Sarcodina
Class: Lobosea (amebas) i.e Entamoeba histolytica
Subphylum: Mastigophora
Class: Zoomastigophora flagellates/hemoflagellates i.e. Giardia lamblia and Leishmania spp.
2- Phylum: Ciliophora
Class: Kinetofragminophorea (ciliates) i.e. Balantidium coli
3- Phylum: Apicomplexa
Class : Sporozoa i.e. Toxoplasma gondii
Order : Blastocystida i.e Blastocystis
Subkingdom: Metazoa**
1- Phylum :Nemathelminthes
A-Class: Nematoda (roundworms) i.e. Ascaris lumbricoides
B-Class Filariae (tissue roundworms) i.e. Wuchereria buncrofti
2- Phylum :Platyhelminthes
A- Class Cestoda (tapeworms) i.e Echinococcus granulosus
B- Class:Trematoda (flukes) i.e Fasciola hepatica

DIFFERENT KINDS OF PARASITES
• Ectoparasite – a parasitic organism that lives on the outer surface of its host, e.g. lice, ticks, mites etc.

• Endoparasites – parasites that live inside the body of their host, e.g. Entamoeba histolytica.

• Obligate Parasite - This parasite is completely dependent on the host during a segment or all of its life cycle, e.g. Plasmodium spp.

• Facultative parasite – an organism that exhibits both parasitic and non-parasitic modes of living and hence does not absolutely depend on the parasitic way of life, but is capable of adapting to it if placed on a host. e.g. Naegleria fowleri

• Accidental parasite – when a parasite attacks an unnatural host and survives. e.g. Hymenolepis diminuta (rat tapeworm).

• Erratic parasite - is one that wanders in to an organ in which it is not usually found. e.g. Entamoeba histolytica in the liver or lung of humans.
Most of the parasites which live in/on the body of the host do not cause disease (non-pathogenic parasites). In parasitology we will focus on most of the disease causing (pathogenic) parasites. However, understanding parasites which do not ordinarily produce disease in healthy immunocompetent) individuals but do cause illness in individuals with impaired defense mechanism (opportunistic parasites) is becoming of paramount importance because of the increasing prevalence of HIV/AIDS in our country.