Relationship between a parasite and its host

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

relationship between a parasite and its host

Parasitism is an association or a situation in which two organisms of different The parasites are capable of making room in a foreign host but normally never. Among such criteria the relationship of the parasite to the host takes pride of place for pathogenic micro-organisms and it is to aspects of this relationship that I . Research in host-parasite evolutionary ecology has demonstrated that environmental variation plays a large role in mediating the outcome of.

relationship between a parasite and its host

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. 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. Fate of encapsulated parasite: Nacrezation is another type of cellular defense mechanism, known in molluscs.


As certain helminth parasites, e. In so doing, a pearl is formed and the enclosed parasite is killed. The process involves deposition of the black-brown pigment, melanin around the invading parasite. Melanization is chemically the result of enzymatic oxidation of polyphenol by tyrosinase. This is detrimental to the parasite and may lead to its death by interfering with such vital activities like hatching, moulting or feeding.

relationship between a parasite and its host

Melanization of the nematode, Heterotylenchus autumnalis in haemocoel of larval house-fly—Musca domestica. These fall into two categories: These are two types: Those are directly parasitocidal, e. Those that enhance cellular reactions, e. These glycoprotein molecules enhance phagocytosis of the non-self-material.

relationship between a parasite and its host

These are also of two types: Immunity refers to resistance against disease caused by a foreign agent. Antigen is the only foreign substance Proteins, glycoproteins, nucleoproteins etc. These are chiefly of two types: Somatic antigens molecules comprising some of parasites. Mechanism of antigen-antibody interactions: Host lymphocytes are now stimulated to proliferate and differentiate.

Plasma cells are B-lymphocyte effector cells that secrete antibodies. The parasites try to establish itself within the host while the latter tries to destroy it which results in dynamic state of equilibrium. If resistance is sufficiently high to prevent parasite reproduction, it is known as absolute resistance and if parasite is able to overcome it and still reproducing it is called partial resistance.

The properties and number of antibodies vary from individual to individual parasitic infections.

relationship between a parasite and its host

These are known to operate in malaria and other viral reactions by rendering the host cells unfit for habitation by intercellular parasites. Categories of antigen-antibody interactions: These are of three types: This is referred to as agglutination reaction. Lysin and lysis reaction: Lysin antibodies dissolves or lyses antigens. The reaction occurs in the presence of complement, a substance in normal serum representing a system of enzymes.

In the second phase of reaction the fixation of complement by antigen-antibody occurs which is used for detecting many of the parasitological infections. This precipitin reaction is used for detecting infections like plague, anthrax, tularaemia etc. In vertebrates, this is introduced through the action of antigen, antibody and complement. This occurs in two ways: Opsonins are antibodies occurring in normal as well as in immune sera which inhibit microbes making them more amenable to phagocytosis.

This is usually of two types: Cattle infected with certain species of Babesia shows premonition. While cattle, long after Theileria parva has disappeared, shows sterile immunity. Abstract Research in host-parasite evolutionary ecology has demonstrated that environmental variation plays a large role in mediating the outcome of parasite infection. For example, crowding or low food availability can reduce host condition and make them more vulnerable to parasite infection.

This observation that poor-condition hosts often suffer more from parasite infection compared to healthy hosts has led to the assumption that parasite productivity is higher in poor-condition hosts.

However, the ubiquity of this negative relationship between host condition and parasite fitness is unknown.

Moreover, examining the effect of environmental variation on parasite fitness has been largely overlooked in the host-parasite literature. Here we investigate the relationship between parasite fitness and host condition by using a laboratory experiment with the cabbage looper Trichoplusia ni and its viral pathogen, AcMNPV, and by surveying published host-parasite literature. Our experiments demonstrated that virus productivity was positively correlated with host food availability and the literature survey revealed both positive and negative relationships between host condition and parasite fitness.

Together these data demonstrate that contrary to previous assumptions, parasite fitness can be positively or negatively correlated with host fitness.

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

We discuss the significance of these findings for host-parasite population biology. Introduction Parasites play a significant role in the ecology and evolution of their hosts.

Symbiotic Relationships-Definition and Examples-Mutualism,Commensalism,Parasitism

For example, parasites can regulate host population dynamics [1] — [3]drive the maintenance of host sexual reproduction [4] — [6]and shape the evolution of sexually dimorphic traits [7]. Environmental variation can play a large role in mediating the immediate outcome of parasite infection, as hosts that are reared in crowded conditions or with limited food can suffer greater morbidity or mortality from parasitism compared to hosts in better health [8] — [14].

Far less is known about how stressful conditions for the host such as crowding or food limitation affect the fitness of the parasites. Examining this question is a subtle but significant departure from most host-parasite studies, where the focus is primarily on host performance. Understanding how environmental factors affect parasite fitness might result in more accurate predictions regarding the number of parasite propagules available for subsequent infection.

Host Parasite Relationship | Global Events | USA| Europe | Middle East| Asia Pacific

Susch as when one sees peritonitis after a ruptured appendix. The agent must be observed in every case of the disease. The agent must be isolated from a diseased host and grown in pure culture. When purified agent is inoculated into a healthy but susceptible host, it must cause the same disease. The agent must be reisolated from the newly infected, diseased host, and be identical to the previously identified causative agent. Identification of disease agents, according to the postulates requires growing the organism; this can be difficult or impossible for some: Treponema pallidum, Mycobacterium leprae, and so this cannot be an inflexible approach.

How they behave within a population? NOT all communicable diseases are equally contagious. Contagiousness depends on several factors. II Frequency in a population: