THE BEHAVIOR AND PATHOGENICITY OF TOXOCARA-CANIS LARVAE IN MICE OF DIFFERENT STRAINS

In the present study the behavior and pathogenicity of second-stage la rvae of Toxocara canis were examined in different mouse strains with s pecial emphasis on the major histocompatibility complex (MHC). Mice of the inbred strains BALB, C3H, C57BL, and DBA and the outbred strain N MRI were infected orally with 1000 second-stage larvae of T. canis. Th e clinical behavior of the animals; the numbers of larvae detected in the liver, lungs, brain, and musculature; the hematological and serolo gical parameters; and histological sections were examined. In mice of the BALB strain, no death occurred during the entire period of the inv estigation and the pattern of body-weight development of infected and uninfected animals was almost identical. The highest larval counts in the brain of all strains were found in BALB mice. The percentage of eo sinophils in the blood of BALB mice increased after the 8th week posti nfection, whereas it decreased in the other strains. Histological and pathophysiological changes developed to a lesser extent in this strain than in the other strains. In mice of the strains C3H, C57BL, DBA, an d NMRI, deaths occurred from the 4th week postinfection onward. The in fected animals lost weight in comparison with the uninfected controls; the numbers of larvae found in the brains of infected mice of the abo ve-mentioned strains were lower than those detected in the BALB strain . There is no evidence that mechanical damage caused by migrating larv ae in the brain tissue is mainly responsible for symptoms of central n ervous toxocariasis. Likewise, the assumption that the MHC is involved in the allergic-inflammatory response in the brain could not be prove n: infected mice of the BALB and DBA strains reacted completely differ ently, although both are equipped with the same MHC haplotype.