SUSCEPTIBILITY OF PEROMYSCUS-LEUCOPUS AND MUS MUSCULUS TO INFECTION WITH BAYLISASCARIS PROCYONIS

In this study, we compared the susceptibility of Peromyscus leucopus ( white-footed mouse), a common natural intermediate host, and Mus muscu lus, a commonly used experimental model, to infection with larvae of t he raccoon ascarid, Baylisascaris procyonis. Three groups of 10 mice o f each species were given 50, 250, or 500 infective B. procyonis eggs by gavage. The mice were observed daily for clinical signs of central nervous system (CNS) disease and at necropsy the distribution of larva e in 10 body regions and organs was determined and compared. Clinical CNS disease developed in 57% of P. leucopus and 93% of M. musculus. Th e average clinical incubation period was significantly longer in P. le ucopus (20.6 days postinfection [PI]) than in M. musculus (10.7 days P I), and clinical disease progressed slower in P. leucopus. Significant ly fewer larvae were recovered from P. leucopus than from M. musculus. Most larvae were recovered from the anterior carcass and viscera of P . leucopus and from the carcass, head, and brain of M. musculus. CNS i nvasion was dose dependent in M. musculus but not in P. leucopus. Few or no grossly visible larval granulomas were present in P. leucopus bu t were abundant in M. musculus. We concluded that P. leucopus was less susceptible than M. musculus to B. procyonis infection, based on a de creased intensity of infection, longer clinical incubation period or l ack of clinical disease, slower progression of disease, different larv al distribution. and lower tissue reactivity to larvae.