INTO PARASITOLOGY

PARASITOLOGY is a science that studies a phenomenon of parasitism. PARASITISM is the association between a host and a parasite. PARASITE is a living organism (may be animals, plants, bacteria or viruses) which depends on other organism for food, shelter, protection and reproduction. HOST – an organism which harbours the parasite.

ANIMAL ASSOCIATIONS in nature Mutual cooperation Mutual antagonism Beneficial associations Neutral associations Neutral associations Harmful associations Harmful associations ● Mutualism ● Symbiosis ● Mutualism ● Symbiosis ● Commensalism ● Synoikia ● Commensalism ● Synoikia ● Parasitism

Beneficial associations When two different species of organisms live together and lead a mutually beneficial life, it is called mutualism or symbiosis. It is ‘an intimate association’ between two different organisms, in which each one derives benefit from the other. These animal associations are defined as synonymous. However, in symbiosis the relationship between the two partners is more intimate than in mutualism. When the symbionts are separated from each other, they cannot lead an independent life. On the other hand, the partners of mutualism can lead an independent life easily.

Beneficial associations symbiosismutualism Hermit crab and Sea anemone: A coelenterate called Sea anemone lives on the external surface of a gastropod shell occupied by an arthropod called Hermit crab. The crab carries Sea anemone to different places where food is available. In return, the Sea anemone gives protection to hermit crab. As Sea anemones are attached to the shell, the crabs are not detected easily by their enemies. further, due to the presence of cnidoblasts in Sea anemone, the enemies will not approach the crab. Lichens = green alga + colourless fungus The alga supplies carbohydrates formed during photosynthesis to the fungus. In turn the fungus gives water, mineral salts and protection to the alga.

Neutral associations When two organisms of different species live together in an association which is beneficial to one and neither beneficial or harmful to the other, it is called commensalism or synokia. In commensalism one organism gives shelter and food to the other species. For example, Entamoeba gingivales, protozoan of human mouth lives in oral cavity. Bacteria in pockets between the teeth and gums are food for amoeba. In synokia one organism receives only shelter from the another. It occurs intermittently between two organisms (the sucker fish, Echineis, is temporarily attached to the body of a shark and carried to different places).

CLASSES of HOSTS DEFINITIVE or primary host DEFINITIVE or primary host ADDITIONAL host INTERMEDIATE or secondary host INTERMEDIATE or secondary host PARATENIC or reservoir host PARATENIC or reservoir host

Generally, the parasites complete their life cycle in one or two hosts. In such a case, the first host where sexual reproduction or adult stage of the parasite takes place is known as the primary (definitive) host, the second one where asexual multiplication or development of larval stages occur – as the secondary (intermediate) host. When reproduction of parasite is absent and parasite only accumulates in host organism without further development, it is called as paratenic (reservoir) host. Additional host is the second intermediary host.

The fish tapeworm (Diphyllobothrium latum)

CLASSES of PARASITES EndoporasitesEctoparasites Coelozoic parasitesHistozoic parasitesIntracellular parasites Parasites I. Types of Parasites on Localization:

Temporary parasites Permanent parasites Parasites II. Types of Parasites on Time of parasitizing The parasites, which spend only a part of their life cycle on the host, are called temporary parasites or partial parasites. For example, the mosquito leads a free life during larval stage and parasitic life during adult stage. The organisms, which spend their entire life as parasites are known as permanent parasites. e.g. Ascaris and Taenia solium.

III. Types of Parasites on Character of parasitizing Parasites Facultative parasites Obligate parasites The parasites, which change their hosts frequently, are known as facultative parasites. They spend, part of their life cycle on the host and part of it independently. For example, Mycobacterium tuberculosis, whish causes tuberculosis in man is a facultative parasite. The parasites, which have to depend on definite hosts throughout their life, are called obligate parasites. They cannot live independently. Hence they will not leave their hosts. For example Taenia solium, which lives in the intestine of man, cannot survive if it resides somewhere else.

Effects of Parasites on Hosts

Parasitic Adaptation and Effects on Parasites

Feral nidal illness – the illness distributed in certain territory among wild animals. The doctrine about feral nidal diseases has been developed by Russian scientist E.N.Pavlovskii in For feral nidal diseases are characteristic the following components: ● areal with the certain complex of natural-climatic conditions; ● presence of the agent of disease; ● presence of the hosts among wild animals necessarily; ● presence of the person unessentially; ● presence of a specific carrier, if illness is obligate transmissible diseases. Thus, the disease circulating in the nature irrespective of the person on a certain area, which is determined by presence wild animals – reservoir hosts of the parasite, is called feral nidal diseases.