HOST-REACTION IN PARATENIC FISH HOSTS AGAINST 3RD STAGE LARVAE OF ANGUILLICOLA-CRASSUS

Many fish species of Lake Balaton (Hungary) serve as paratenic hosts f or the 3rd stage larvae of the eel parasite Anguillicola crassus. The incidence oi different phases of the host reaction varies with paraten ic fish host but its nature is basically the same. The appearance of m ononuclear cells around the larvae migrating in the tissues or in the abdominal cavity is regarded as a sign of cellular host reaction. The cells adhering to the surface of the larvae gradually assume an epithe lioid shape and form a granuloma. With the advancement of the process the larvae and the epithelioid cells surrounding them undergo necrosis , and the granuloma becomes surrounded by a connective tissue capsule. In more chronic cases, the inside of the parasitic nodule surrounded by several layers of connective tissue is filled out by amorphous tiss ue and parasite debris. In the 'suitable paratenic hosts' Anguillicola sp. larvae not affected by the host's cellular reaction outnumber tho se affected by it, whereas in the 'less suitable paratenic hosts' the cellular reaction very rapidly forces the larvae into foci and destroy s them.