Introduction to PARASITOLOGY

Parasite:

An organism that depends on other organisms for its survival. OR A living organism that receives nourishment & shelter from another organism where it lives.

E.g., Entamoeba histolytica 

Parasitology:

It is the study of parasites.

Medical Parasitology:

It is the study of parasites that infect and cause diseases in human beings.

You can also watch this video to better understand the parasitology: 

Characteristics:

·       Each parasite has two names

·       Genus: that starts with an upper-case letter

·       Species: that starts with a lower-case letter

·       E.g., Entamoeba histolytia

·       If a parasite causes a disease, it is called Parastosis or Parastasis

·       E.g.; Giardia lamblia causes Giardiasis

Hosts:

An organism that harbors the parasite.

Classes or Classification of Host:

 

Definitive host – either harbors the adult stage of the parasite or where the parasite utilizes the sexual method of reproduction.

Intermediate host – harbors the larval stage of the parasite. In some cases, larval development is completed in two different intermediate hosts referred to as 1st and 2nd intermediate hosts.

Paratenic host – a host where the parasite remains viable without further development.

Host-Parasite Relationship:

Symbiosis is any type of close and long-term biological interaction between two different biological organisms, it can be mutualism, commensalism, or parasitism.

·       MUTUALISM

In this type of relationship, both partners get the benefit.

·       COMMENSALISM

In this type of relationship, the host is neither harmed nor benefited but the other organism gets the benefit.

·       PARASITISM

In this type of relationship, the parasite gets the benefit and in return harms the host.

CLASSIFICATION OF PARASITE:

Classification based on HABITAT: 

Obligate Parasite:

An obligate parasite or holoparasite is a parasitic organism that cannot complete its life cycle without exploiting a suitable host. If an obligate parasite cannot obtain a host it will fail to reproduce.

Facultative Parasite:

A facultative parasite is an organism that may resort to parasitic activity but does not rely on any host for the completion of its life cycle.

Accidental Parasite:

Also known as an incidental parasite, is a parasite that attacks or establishes itself in unusual hosts (hosts that they do not normally parasitize). Here, the host is referred to as an unnatural host.

Aberrant Parasite:

Parasites may enter aberrant hosts, in whom conditions are not adequate for survival, further development, or sexual maturity.

 

Classification based on DURATION:

 

Temporary Parasites:

Temporary parasites are organisms whose parasitic mode of life is limited to a few or even one stage of development. An example of this is the larval stage of harvest mites, while the adult stage is non-parasitic.

Permanent Parasites:

When a parasite is permanent, several generations occur in or on the host of an infested individual. Head lice are an example of this.

 

Classification of protozoa based on MEDICAL PURPOSES

Classification of Medically Important Parasites

PROTOZOA:

A- Sarcodina (Amoebas)

·       Genus Entamoeba (pathogenic Entamoeba histolytica)

·       Genus Endolimax (non-pathogenic)

·       Genus Iodameba (non-pathogenic)

·       Genus Dientameba (non-pathogenic)

B- Sporozoa (Sporozoans)

·       Genus Plasmodium (P.vivax, P.ovale, P.malariae, P.falciparum, and P.knowlesi)

·       Genus Toxoplasma (T.gondii)

C- Mastigophora (Flagellates)

·       Genus Giardia (intestinal flagellates – Giardia lamblia)

·       Genus Trichomonas (genital flagellates – T. vaginalis)

·       Genus Trypanosoma (blood and tissue flagellates – T. brucei, T. cruzi)

·       Genus Leishmania (blood and tissue flagellates – Pathogenic L. donovani, tropica, mexicana and braziliensis)

D- Ciliata (Ciliates)

·       Balantidium coli

METAZOA

A- Platyhelminthes

1- Trematoda

·       Genus Schistosoma (S.hematobium, S.mansoni, S.japonicum)

·       Clonorchis sinensis

·       Paragonimus westermani

·       Genus Fasciola (Fasciola hepatica)

2- Cestoda

·       Genus Diphyllobothrium (D. latum)

·       Genus Tenia (T. saginata, T. solium)

·       Genus Echinococcus (E. granulosus)

·       Genus Hymenolepsis (H. nana, H. diminuta)

B- Nemathelmenthies

1- Intestinal Nematodes

·       Ascaris lumbricoides

·       Ancylostoma dudodenale

·       Necator americanus

·       Enterobius vermicularis

·       Trichuris trichuria

2- Somatic Nematodes

·       Wuchereria bancrofti

·       Loa loa

·       Dracunculus medinensis

Author: Zukhruf 

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