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Tuesday, December 4, 2012


The science which deals with the study of parasite is called Parasitology.


                Any living organism which draws its food and shelter from another living organism and also harming the host is called parasite.


                The parasite which live on surface of the host body e.g. parasites such as lice, bed bugs, leech and flies that live on the outer surface bodies.


                The parasite which live inside the body of host e.g. parasites the infect the internals parts of the body, such as trypanosomes or Ascaris worms, bacteria, tape worms etc

Temporary parasite:

                The parasite which lives on surface or inside the host but for short period time is called temporary parasite. Parasite that visits and leaves the host at intervals is also known
as Intermittent parasite.

Permanent parasite:

                The parasite which lives on surface or inside the host but for indefinite period of time is called permanent parasite. It is a parasite that lives its whole life (hatching until death) in a
single host but eggs or cyst is to be transferred to a new host before a second
generation develops.

Facultative parasites:

            An organism that may survive and dwell in the absence of a host but that occasionally infects a host organism is called facultative parasite. A parasite that may survive in a free living state or may become parasitic when the need arise is termed as facultative parasite e.g. lice and worms etc.

Obligatory parasites:

            A parasite that needs a host at some stages of its life cycle is called obligatory parasite. It must live as parasite without parasitism it cannot live.


            It is the living organism that harbors the parasite. The organism in, or on, which the parasite lives and causes harm is called host.

Definitive Host:

            It is the host in which sexual development and multiplication of the parasite takes place. It is the host in which adult form lives or sexual reproduction of parasite takes place. The organism in which the adult or sexually mature stage of the parasite lives is called definitive host.
Example: Female Anopheles (Mosquito) for plasmodium (Malarial parasite).

Intermediate Host:

            The organism in which the parasite lives during a period of its development only is called intermediate host. It is a host which harbors the larval stages of the parasites.


            In this type of host – parasite relationship, the parasite derives benefit and the host gets nothing in return but always suffers some injury.


            It is a type of host – parasite relationship in which the organisms live and eat together and are mutually beneficial to each other. They are so dependent upon each other that one cannot live without the help of the other.


            It is a type of host – parasite relationship in which the parasite only derives benefit without causing injury to its host.


            When the parasite establishes itself within the host, it is termed infection.


            The presence of animal parasites either on the skin (for example Ticks) or inside the body (for example tapeworms).

Medically Important Parasites:

·         Entameoba Histolytica
·         Plasmodium – Vivax, Ovale, Falciparum, Malariae
·         Toxoplasma Gondii
·         Trichomonas Vaginalis
·         Leishmania Donovani
·         Giardia Lamblia
·         Balantidium Coli
·         Diphyllobothrium Latum
·         Taenia Saginata
·         Echinococcus Granulosus
·         Hymenolepis Nana
·         Ascaris
·         Ancylostoma
·         Enterobius
·         Wuchereria Bancrofti
·         Loa Loa
·         Incocherea


                A natural home or environment of parasite is called as habitat of parasite.


                A supply or source of parasite is term as reservoir of that parasite. The starting point of the parasite is term as reservoir of that parasite.

Mode of transmission:

                The route by which the parasite passes from the source or reservoir to the host is called as Mode of Transmission.

Presentations of parasitic infestation:

                As most of the human parasites are intestinal, therefore the presentation are mainly intestinal which are as follow.
·         Anorexia or eating all the time but not gaining weight
·         Abdominal discomfort: dull to severe pain
·         Dyspepsia
·         Presence of blood in stool
·         Constipation and diarrhea or both alternatively
·         Salivation at night etc

Diagnosis of parasitic infestation:

·         Microscopy
·         Serology including CBC
·         Molecular diagnostics such as antigen detection and PCR
·         Radiology such as CT, MRI etc
·         Stool culture


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