Host-parasite relations in cotton rat filariasis. II: The quantitative transmission of Litomosoides carinii to Delhi and Carworth strains of white rats, including the effect of age.

Delhi and Carworth strains of white rats were exposed quantitatively to infection with Litomosoides carinii and their susceptibility compared. Liponyssus bacoti (= Ornithonyssus bacoti) mites of known (calculated) intensities of infection were used for transmission. The relation between the calculated exposure (= transmission intensity) and the number of adult worms recovered from each rat was established. Adults of both strains of white rat were much "poorer" hosts than cotton rats. All 24 Carworth white rats (100%) and 21/24 of Delhi white rats (87-5%) of differing ages and both sexes became infected. Carworth white rats were generally more susceptible. The susceptibility of newly born Carworth white rats was greatest and was similar to that of cotton rats. Young rats of the Delhi strain were more susceptible than older rats. This strongly suggests "age resistance". The degree of resistance may, however, differ in different species and strains of white rats and in individual rats of the same strain.