What is a parasite and host relationship

Host-Parasite Relationship (With Diagram)

what is a parasite and host relationship

A parasitic relationship is one in which one organism, the parasite, lives off of another organism, the host, harming it and possibly causing. Host and Parasite: A Mutual Relation: In the course of time a mutual adjustment or relation or tolerance frequently develops between the two which permits them . CHAPTER HOST PARASITE RELATIONSHIPS. INTRODUCTION: a) Healthy individuals are INFECTED and are being infected anew constantly. b) Some of.


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The benefited organism is called the parasite and the organism harbouring the parasite is called the host. Hosts are not hospitable to parasites. Instead they consider parasites as foreign bodies and want to exterminate or overpower them by operating various devices like: Parasitism is a very broad term and different types of parasites are recognised on different basis.


In the course of their life cycle, parasite may become associated with more than one host. In many cases the life cycle is characterised by numerous very rigid requirements. Host Specificity of Parasites: In mature condition a given parasite is quite often found in limited number of hosts.

In extreme condition, distribution of a parasite may be restricted to a single host—mono-specific parasite.

what is a parasite and host relationship

Even when poly-specific the different hosts are phylogenetically related. This host specificity is a function of physiological specialization and evolutionary age. It is broadly divided into two parts: The parasites are capable of making room in a foreign host but normally never reach another host due to ecological barriers.

The parasites are physiologically incapable of surviving and reproducing in a foreign host, e. If not, it is said to be incompatible. In the course of time a mutual adjustment or relation or tolerance frequently develops between the two which permits them to live together as a sort of compound organization without very serious effect or damage to either. The virulant types, however, try to eradicate the hosts.

But it is essential to keep the host alive and not to kill it by causing a high degree of pathogenecity. By killing the host it will ultimately lead to death of itself also. Accordingly Natural Selection leads to the elimination of most virulent species and maintains the less virulant ones. Effects of Parasites on Hosts: These effects depend on several factors, such as—age, diet, genetic factors, susceptibility of the hosts, the size, number and virulence of the parasites, their mortality, migration, and method of feeding.

what is a parasite and host relationship

Time and degree of damage vary greatly: Some inflict tissue damage after they have entered, e. Others induce to histopathology changes by eliciting cellular immunologic response to their presence, e. Types of cell damage: This type of damage is characteristic of liver, cardiac muscle and kidney cells. Fatty degeneration cells are filled with an abnormal amount of fat deposits, e. Necrosis means any type of persistent cell degeneration which finally die, e. Refers to an increased rate of cell division resulting from an increased level of cell metabolism.

Leads to a greater total number of cells but not in their sizes. This commonly follows an inflammation and is the consequence of an excessive level of tissue repair.

For example—thickening of bile duct in presence of Fasciola sp. Refers to an increase in cell size. Commonly associated with intracellular parasites.

  • The Relationship between Parasite Fitness and Host Condition in an Insect - Virus System

Spermatogonial cells of Polymnia nebulosum an Annelid when parasitized with Caryotropha mesnili a Protozoanare enlarged. Refers to the changing of one type of tissue into another without the intervention of embryonic tissue.

The encapsulating epithelial cells and fibroblasts of the fluke, Paragonimus westermani in human lungs are transformation of certain other type of cells in the lungs. This is the growth of cells in a tissue to form a new structure, e.

what is a parasite and host relationship

Neoplastic tumour is not inflammatory. This is not required for the repair of organs. It does not conform to a normal growth pattern. It may be benign or malignant.

what is a parasite and host relationship

Endoparasites with a great density causes nutritional deficiency in host by absorbing sugars, vitamins, amino-acids etc. Mal-nourished hosts are more proned to disease and infection.

Diphyllobothrium latum a fish tapeworm in human causes anaemia by absorbing profuse Vitamin B12 as much as 10 to 50 times more than do other tape-worms. Parasites in some cases also feed on host- substances, other than stored or recently acquired nutrients. Increased number of those adult worms in lymph vessels coupled with aggregation of connective tissue may result in complete blockage of lymph flow.

Excess fluid behind the blockage seeps through the walls of lymph ducts into the surrounding tissues, causing edema and ultimately with scar tissues—the elephantiasis of limbs, breasts, scrotum etc. Effects of toxins, poisons and secretions: Specific poisons or toxins egested, secreted or excreted by parasites cause irritation and damage to hosts, e.

what is a parasite and host relationship

Toxin of pathogenic Entamoeba histolytica produces toxic symptoms in parasitized mammalian hosts and creates ulcerations within the large gut of man. Schistosome cercarial dermatitis is the result of an allergin reaction against an irritating parasitic secretion from the fluke. Gonads of parasitized hosts may change, leading to sex reversals; e. Parasitized male crab acquired secondary female characteristics like broad abdomen, appendages modified to grasp eggs, chelae become smaller, testes with testicular cells at various stages of degeneration.

The mudflat snail—Ilyanassa obsoleta are directly castrated by the trematode— Zoogonus lasius. The freshwater snail, Lymnaea stagnalis is indirectly castrated by larvae Sporocysts of Trichobilharzia ocellata a trematode.

These larvae do not possess mouth and thus destroy the gonadal tissue by chemical means. An interesting aspect of parasite induced change in hosts is responsible for enhanced growth; e. Workers of the ant, Pheidole commutula become much larger when parasitized by the nematode, Mermis sp.

The Relationship between Parasite Fitness and Host Condition in an Insect - Virus System

Mice infected with larvae of Spirometra mansonoides a tapeworm grows faster than non-parasitized one. Rats when parasitized by Trypanosoma lewise increase their weight more rapidly than non-parasitized one. The enhanced growth of the host is due to stimulation of growth-promoting molecules secreted by the parasites.

In immuno-parasitology, the animal is the host and the parasite is either self by molecular memory or non-self foreign. When a host recognizes the parasite as non-self, it generally reacts against the invader in two ways: Cellular or cell mediated reactions: Where specialised cells become mobilised to arrest and eventually destroy the parasite as usual.

Innate or natural and II. Theoretically each of them again can be of two types—cellular and humoral.

Host-Parasite Relationship (With Diagram)

Innate internal defense mechanism: These includes the following chief categories: Phagocytosis consists of three phases: Attraction of phagocytes to the non-self material, commonly by chaemo-taxis. Internalization of the foreign substance i. Fate of phagocytosed parasites: May be degraded intracellularly. May be transported by phagocytes across epithelial borders to the exterior. May remain undamaged within the phagocytes and some may even multiply within host cells.