Introduction To Parasitology 1

OPTOMETRY · SEMESTER 2

Microbiology and Parasitology

SESSION 1: concept of parasites and vector in detecting cause of diseases

Objectives

At the end of this course, you should be able to:
Define terminologies used in parasitology (Parasite, Endoparasite, Ectoparasite, Host)
Describe the concept of parasitism

Explain types of hosts

Classify parasites and Understand in detail the life cycles of parasites of medical importances List the parasites of medical importance depending on the site of infestation Explain characteristics of parasites of medical importance know organs commonly involved in the infection and infestation with the parasites

Important areas to be covered

As we study about the parasites (parasitology) the following parts will be discussed under every parasite Geographical distribution

Morphology of various stages
Life cycle
Transmission and epidemiology
Pathology
Diagnosis
Treatment/management

Control/prevention

Definitions

Parasitology is the scientific study of parasites, their hosts, and the relationship between them.

as a biological discipline, the scope of parasitology is not only determined by the organism and environment in question, but also by their ways of life.

Parasite is an organism that lives on or in another organism of different species known as host, from which it obtains food, shelter and protection.

Pathogen is any organism that can cause a disease.

Introduction To Parasitology 1

Parasitism is the association between two organisms of different species in which one organism (parasite) benefits while the other (host) is harmed.

example: ticks on the bodies of dogs, cattle etc.

Symbiosis is the association between two organisms living together either temporary or permanently.

It means living together in a close relationship
Example

Mutualism –both organisms in the association benefit e.g. gut bacteria , bees and flowers Commensalism –one organism benefit while the other do not, but not affected too e.g. the bird nests on tree and entamoeba coli in gut

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Definition of terms cont……

Parasitism –the association in which one organism (parasite ) benefit from the association or relationship while the host is affected , the parasite deprives the nutrients and shelter.

Plasmodium spp
Entamoeba histolytica
Ascaris lumbricoides
Necator americanus
Ancylostoma duodenale
Balantidium coli
Schistosoma mansoni

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Introduction To Parasitology 1

Phoresis is the association between two organisms of different species in which one organisms usually a smaller organism (phoront) is mechanically carried by another larger organism (the host), no dependency or physiological interaction in procurement of food by either partner.

Example: sedentary protozoans, attached on bodies of aquatic turtles.

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Endoparasite is the one that lives inside the host.

example:
ascaris lumbricoides
Plasmodium spp
Hookworms
Trichuris trichiura
A condition is called infection
Ectoparasite is the one that lives outside the host.
example:
pediculus humanus corporis
Tick infestation
Pediculus humanus capitis
Pthirus pubis
A condition is known as infestation

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Obligatory parasite is the parasite that can not survive without the host.

example plasmodium falciparum
Facultative parasite is the parasite which can survive in the absence of the host.
it is free living organism but is capable of becoming parasite in conducive situation.
example
Naegleria fowleri
Entamoeba coli
Candida albicans

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Introduction To Parasitology 1

Accidental or Incidental Parasites: these are not normal parasites of man but enter or attach to the body and cause parasitism in man.

For example, Toxocara Canis that causes visceral larva migrans in man.

Opportunistic Parasite: these are usually commensals or non-pathogenic organisms that invade the body and cause disease when the host’s immune status is compromised.

Examples toxoplasma gondii.

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Introduction To Parasitology 1

Larval Parasites: larval parasites are pathogenic parasites which infect man and cause pathology during their larval stage of development.

their adults may be parasites of other animals; man, or they may be free-living. e.g. echinococcus granulosa.

Zoonosis is any infection/disease that is naturally transmissible from vertebrate animals to humans and vice-versa.

Zoonotic disease is a disease that can be transmitted between vertebrate animals and humans.

For example, trichinella spiralis.

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Host: is an organism that harbours a parasite and provides the nourishment and shelter.

These hosts, in comparison to their parasites are (usually) relatively larger in size than the parasites.

Primary host or Definitive host is the host that harbours parasite in adult/mature or sexual stage.

For example, man is definitive host for S. haematobium Secondary host or Intermediate host is the host that harbours the immature or asexual stage of the parasite.

for example, Bulinus spp is intermediate host for S. haematobium

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Natural host: is one which naturally infected with certain species of parasite.

example: mosquito is a natural host for plasmodium Reservoir host: is one which make parasites available for transmission to other hosts. Example dogs are reservoir for leishmania donovani an animal that harbors a parasite which is also infective to humans.

Accident host: is one which under normal circumstances is not infected with parasites.

Transport host: an animal that harbors a parasite that does not reproduce; it carries the parasite from one location to another to infect a new host

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Introduction To Parasitology 1

Vector: is an organism that transmit pathogens (parasites) from one host to another or from a source of infection to the susceptible host.

Mechanical Vectors

are vectors which assist in the transfer of parasite forms between hosts but are not essential in the life cycle of the parasite, i.e. no parasite development occurs in such vectors.

Examples of mechanical vectors are musca domestica which can transfer cysts of entamoeba histolytica from faces to food that is eaten by man.

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Introduction To Parasitology 1

Biological Vectors are vectors in which there is biological development of the parasite before it can be transmitted. for example, anopheles' mosquitoes are biological vectors of plasmodium spp.

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1. Helminthes

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PARASITIC HELMINTHES

These belongs to two phyla:
Platyhelminthes
Nemathelminthes

PLATYHELMINTHES

There are two medically important classes which include
1.Cestoda (tapeworms).
These are band-like and segmented

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1.CESTODES (tapeworms)

Taenia solium (Pork tape worm)
Taenia saginata (Beef tape worm)
Hymenolepis nana (Dwarf tape worm)
Diphyllobothrium latum (Fish tape worm)
Echinococcus granulosus (Dog tape worm)

Dipylidium caninum (dog tape worm)

2. Trematoda (flukes)

Flukes are typically leaf-shaped
Examples of trematodes of medical importance include
Blood fluke – Schistosoma spp ,
Lung flukes -Paragonimus spp
Liver flukes – Clonorchis sinensis ,fasciola hepatica, Opisthorchis spp
Intestinal flukes -Fasciolopsis, heterophyes ,metagonimus , echinostoma spp

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1.(a) Nematodes Nemathelminthes (round worms)

These have separate-sexes and unsegmented roundworms
They have body cavities
They have complete digestive, reproductive and nervous systems
They include many parasitic species that infect humans.
intestinal nematodes
Ascaris lumblicoides
Trichuris trichiura (Whip worm)
Enterobius vermicularis (Thread, pin or seat worm)
Strongyloides stercoralis
Hookworm

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Tissue nematodes

Loa loa spp
Wuncheleria spp
Onchcerca volvulus
Brugia spp
Trichnella spp

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2. Protozoa

Blood protozoan genera:
plasmodium, trypanasoma, leishmania , borrelia
Intestinal parotozoan genera:
entamoeba, giardia, cryptosporidium, balantidium,
Urirogenital protozoan genera:
trichomonas vaginalis
Tissue protozoan genera:

toxoplasma, acanthamoeba, naegleria

3. ENTOMOLOGY

Mosquito
Tsetse fly
Black fly
Housefly
Flea
Ticks
Cockroach
Lice

Mites

REFERENCE TEXT BOOKS

1. Manson’s Tropical Diseases 20th edition, Tokyo, WB Saunders Company Limited
2. Medical parasitology 3rd edition by S. C. Parija
3. Human Parasitology 3rd edition by Burton et al
4. Atlas of medical Helmithology and protozoology 3rd Ed by Hc.Jeffrey and R.leach
5. Medical laboratory manual for tropical countries-Vol ½ by Monica Cheesbrough

6. Human Parasitology 2nd Edition by Bogitsh, Thomas C. Cheng

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