Host Specificity and Organ Specificity of Parasites

Definition: Host specificity is defined as the natural adaptability of a species of the parasite to a certain species or group of hosts. It is a general observation that the parasites, specially helminthes are highly selective in their choice of host, as they are adapted to parasitism in a particular species of hosts or in a single species. Of there are more number. Of hosts they are usually closely related. Very few parasites have the capacity to prasitize many hosts ever thought they are unrelated to each other. The parasite will not survive on a different host. For example the parasites of horses, cattle, dogs or human are most likely to be found in their respective host. Moreover, parasites of the intestine, the liver, or tissue specificity, as the case may be.

The mechanism of host specificity are not fully known and are undoubtedly complex. The specificity differs from species to species. Some of the parasites have adopted themselves to many varieties of hosts. For example: the members of genus trypanosoma parasitize large number of hosts. Similarly, imeria spE, Balantidium coli, Toxoplasma have a wide range of hosts. For example, malarian parasites of man are quite host specific. While some are not very limited but can infect more than one category of host and show some degree of host specificity. For example Toxocara canis found in small intestine of dog can also be found in foxes. This indicates that the degree of host specificity differs from species to species of the parasites.
All organs of the body are equally subjected to the attack from parasites but even then it is observe that the parasites migrate to a particular organ of the body wher they thrive, multiply, divide and spread. If by chance the parasite does not reach the organ in the very host, it will cease to live. This shows great organ specificity also. Generally, a parasite that can survive in one or in few species of hosts is more likely to rquire a more specific site within its host while a parasite that is less host specific can live in a wide variety of environments. For examples, a tapeworm Taenia saginata which is specific parasite of man, can only live in the small intestine, while the larvae of Trichinella spiralis which can infect variety of warm-blooded animals, is much less specific and can encysts in any area of the hosts body.