MLS 042 (INTRODUCTION TO PARASITOLGY)

Direct life cycle

When a parasite requires only single host to complete its development, it is called as

Indirect life cycle

When a parasite requires 2 or more species of host to complete its development it is called as 

1. Protozoology
2. Helminthology

WHAT ARE THE 2 DIVISIONS OF PARASITOLOGY

Ectoparasite

They inhabit the surface of the body of the host without penetrating into the tissues.

Aberrant or wandering parasite

They infect a host where they cannot live or develop further 

Biological Vectors

They are also known as "true vectors"

Rudolf Virchow in 1880

the word zoonosis was introduced by

Protozoa (unicellular organisms)
Helminths (multicellular organisms)

The term "parasite" is usually applied to

Carrrier

The person who is infected with the parasite without any clinical or sub clinical disease is referred to as a ____________. He can transmit the parasites to others.

Extrinsic Incubation period

The interval between the entry of the parasite into the vector and the time it takes to become capable of transmitting the infection is called______. 

Zoonoses

The infection which is transmitted from infected animals to humans is called as ________.

Accidental host 

The host, in which the parasite is not usually found

Intermediate host

The host, in which the larval stage of the parasite lives or asexual multiplication takes place

Definitive host

The host, in which the adult parasite lives and undergoes sexual reproduction is called

Disease

the clinical manifestation of the infection, which shows the active presence, and replication of the parasite causing damage to the host. It may be mild, severe and fulminant and in some cases may even cause death of the host.

Infestation

The infection by ectoparasites is called as

Ectoparasite

They are important vectors transmitting the pathogenic microbes.  

Mechanical Vector

refers to a vector, which assists in the transfer of parasitic form between hosts but is not essential in the life cycle of the parasite (e.g Housefly: Amebiasis) 

Biological Vector

refers to a vector, which not only assists in the transfer of parasites but the parasites undergo development or multiplication in their body as well.

Accidental parasite

Parasites, which infect an unusual host are known as

Ectoparasite & Endoparasite

Parasites can be classiffied as: 

Endoparasites 

Most of the protozoan and helminthic parasites causing human disease are

those diseases and infections, which are naturally transmitted between vertebrate animals and man.

Later, in 1959, the World Health Organization (WHO) defined zoonosis as

Free-living parasite 

It refers to nonparasitic stages of active existence, which live independent of the host,( e.g. cystic stage of Naegleriafowleri.)

Symbiosis

It is the close association between the host and the parasite. Both are interdependent upon each other that one cannot live without the help of the other. None of them suffer any harm from each other

Parasitism

It is an association in which the parasite derives benefit from the host and always causes some injury to the host. The host gets no benefit in return.

Commensalism 

It is an association in which the parasite only derives the benefit without causing any injury to the host. It is also capable of living an independent life.

Vectors 

is an agent, usually an arthropod that transmits an infection from man to man or from other animals to man, (e.g. female Anopheles is the vector of malarial parasite).

Infection

Invasion by the endoparasite is called as

Echinococcus granulosus

A parasite that infects man accidentally, giving rise to hydatid cysts.

Anthroponoses

Infections transmitted to man from lower vertebrate animals (e.g. cystic echinococcosis).

Zooanthroponoses

Infections transmitted from man to lower vertebrate animals 

Anton Van Leeuwenhoek of Holland in 1681

first introduced single lens microscope and observed Giardia in his own stools.

1) Malaria, filariasis
2) Kala-azar 
3) Sleeping sickness 
4) Chagas disease 
5) Babesiosis

EXAMPLES OF TRUE VECTORS: 
1) Mosquito- 
2) Sandflies- 
3) Tsetse flies-
4) Redwiid bugs- 
5) Ticks- 

1) Obligate parasites 
2) Facultative parasites
3) Accidental parasites
4) Aberrant parasites/Wandering parasites

Endoparasites can further be classified as:

Host

defined as an organism, which harbors (support) the parasite and provides nourishment and shelter to latter and is relatively larger than the parasite.

Medical parasitology

deals with the parasites, which cause human infections and the diseases they produce.

Reservoir host

A type of host which harbors (support) the parasite and act as an important source of infection to other susceptible host (e.g. dog is the reservoir host of hydatid disease)

Facultative parasite

A type of Endoparasite which may either live as parasitic form or as free-living form (e.g Naegleria fowleri & Acanthamoeba)

Obligate parasites 

A type of endoparasite that cannot exist without a host (e.g Toxoplasma gondii and Plasmodium).

Endoparasite (inside)

A parasite, which lives within the body of the host and is said to cause an infection is called an 

Paratenic host

A host, in which larval stage of the parasite remains viable without further development is referred as________. Such host transmits the infection to another host, e.g. fish for plerocercoid larva of D. lalum.

Spurious parasite

a free-living parasite that passes through the digestive tract without infecting the host 

Oral Transmission

The most common method of transmission is through __________ by contaminated food, water, soiled fingers, or fomites.

Oral Transmission

Many intestinal parasites enter the body in this manner; the infective stages being cysts, embryonated eggs, or larval forms. Infection with E. histolytica and other intestinal protozoa occurs when the infective cysts are swallowed.

Skin transmission

A type of mode of transmission where in the entry point is through the skin.

Hookworm & Strongyloides

What type of infection acquired, when the larvae enter the skin of persons walking barefooted on contaminated soil.

Schistosomiasis or Schistosoma

a type of infection acquired, when the cercarial larvae in water penetrate the skin.

Vectors

Many parasitic diseases are transmitted by insect bite

female Anopheles mosquito

malaria is transmitted by bite of

Culex mosquito

filariasis is transmitted by bite of

Direct transmission

Parasitic infection may be transmitted by person-to-person contact in some cases, e.g. by kissing in the case of gingivaJ amebae and by sexual intercourse in trichomoniasis.

Vertical transmission

Mother to fetus transmission may take place in malaria and toxoplasmosis.

Iatrogenic transmission

It is seen in case of transfusion malaria and toxoplasmosis after organ transplantation.

Pathogenesis

Parasitic infections may remain inapparent (no signs or symptoms) or give rise to clinical disease.

E. histolytica

A type of organism where it may live as surface commensals, without invading the tissues

1) Host factors

2) Parasitic factors

the immune response against the parasitic infections depends on two factors:

Host factors

Immune status, age, underlying disease, nutritional status, genetic constitution and various defense mechanisms of the host

Parasitic factors

Size, route of entry, frequency of infection, parasitic load and various immune evasion mechanisms of the parasites.

Innate immunity

the resistance which an individual possesses by birth, due to genetic and constitutional make-up

1) Age

2) Sex

3) Nutrients Status

4)Genetic constitution of the individuals

Factors influencing innate immunity: