Angiostrongylus Cantonensis Infection in Rats and Rhesus Monkeys, and Observations on the Survival of the Parasite in Vitro

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Abstract
Summary The slugs Limax maximus and Deroceras reticulatum were found to act as intermediate hosts for Angiostrongylus cantonensis. Infections in white rats were fatal when worm burdens reached 50 to 60 and above but became chronic and persisted for many months when 5 to 10 worms were present. Naturally-infected wild rats tend to have worm burdens which are similar to or somewhat higher than the latter. Discharge of first-stage larvae in feces of heavily infected white rats reached mean values of approximately 100,000 per ml of feces, whereas the mean for lightly infected rats ranged between 6,000 and 12,000 larvae per ml. One rat infected with 23 larvae developed paraplegia on the 31st day of infection. Experimental infections in monkeys with A. cantonensis did not give rise to overt symptoms. Four monkeys were necropsied, respectively, on days 17, 24, 32 and 69 after infection; fifth-stage worms were found in the brain of each except the last, in which there were, however, lesions consistent with the infection. The worms were retarded in development compared to those from rats sacrificed at similar time intervals and were also smaller than the ones recovered from a human brain. By day 17, parasites in the brain had elicited a diffuse and severe eosinophilic meningoencephalitis. The presence of foreign-body granulomas around dead parasites indicated that some must have entered the brain earlier. As the time interval between ingestion of the parasite and death of the animal increased, the inflammatory reaction changed from a diffuse eosinophilic to a more focal and granulomatous response. The latter was most frequently related to fragments of dead worm. Although lesions similar to those seen in the brain were found in the spinal cord of all monkeys, parasites were not found in the meninges and cord proper in any of the monkeys. Adult worms maintained in vitro survived best in medium NCTC 109 supplemented with serum. Maximum survival was 80 days for females and 64 days for males. Eggs deposited in vitro embryonated in 5 to 6 days, but only low percentages hatched. First-stage larvae cultured in vitro in various media showed no growth.