Search

Enzyme histochemistry has revealed that encapsulation reactions surrounding larvae of the nematode Angiostrongylus cantonensis 4 wk after infection of the gastropod Biomphalaria glabrata are the sites of highly localized acid phosphatase and nonspecific esterase activities. Lesser amounts of alkaline phosphatase and β-glucuronidase activities also occur within such capsules, but aminopeptidase activity cannot be demonstrated. In addition, it has been ascertained that acid phosphatase activity gradually increases as the encapsulation reaction progresses during the first to the fourth week postinfection.

Nearly 2% of the specimens of the mudflat snail, Nassarius obsoletus, collected during June and July of 1972 from southern New Jersey has been found to be parasitized by sporocysts of the trematode Zoogonus rubellus. This parasite causes what is essentially total parasitic castration of this estuarine mollusc. The gonads of the hosts are almost completely absent and in their place, large, vacuolated Leydig cells fill the spaces not occupied by parasites on the periphery of the digestive glands. There is no doubt that the snails would have been sexually mature at the time of collection since all noninfected specimens included either fully developed ova or sperm. It is postulated that the destruction of the host's gonad has resulted from what is being designated as “direct chemical castration,” i.e., the sex cells are destroyed by some substance secreted by the parasite rather than as the result of direct mechanical damage. Since N. obsoletus also serves as the intermediate host for the avian schistosome Austrobilharzia variglandis, the etiologic agent for “swimmer's itch” in the same area, the potential importance of Z. rubellus as a biological control agent against A. variglandis is raised.

The most common route of infection of Biomphalaria glabrata experimentally exposed to first-stage larvae of Angiostrongylus cantonensis is via penetration of the gastric and prointestinal walls after ingestion. Subsequently, most parasites migrate through the kidney and rectal ridge to the mantle collar and head-foot of the gastropod at which sites they become lodged. Nematodes are encapsulated in B. glabrata beginning by 24/2-48 h post-infection. Encapsulation occurs as a two-phase process involving (1) initial infiltration and aggregation of basophilic hemolymph cells around the parasite and (2) subsequent transformation of such cellular aggregates into more fibrous-appearing nodules. The small number of parasites which localize in such tissues as the rectal ridge, kidney, or vascular connective tissue near the gonad are similarly encapsulated.

The tegumentary ultrastructure of Leucochloridiomorpha constantiae metacercariae and adults has been described. A filamentous glycocalyx invests the tegument of metacercariae and large numbers of biconcave, disk-shaped secretion vesicles are found in its outer zone, cytoplasmic bridges and cytons. Mitochondria within the outer tegumentary zone of metacercariae are restricted to its basal half. The transformation of metacercariae to adults involves the loss of the glycocalyx, a decrease in the number of disk-shaped secretion vesicles, a more uniform distribution of mitochondria through the outer tegumentary zone, an apparent degeneration of cytons, a thinning of the fibrous basal lamina and a decrease in the number of visible cytoplasmic bridges traversing it. The significance of these events for a metacercaria which does not encyst within the molluscan host is discussed. In addition, crystalline, spine-like inclusions in the outer tegumentary zone of adult L. constantiae are described and their possible function discussed.

A review of literature dealing with neurosecretion in the Platyhelminthes is presented and presumptive neurosecretory cells associated with the cerebral ganglia and longitudinal nerve cords of Leucochloridiomorpha constantiae metacercariae and adults are described. Both the mean number of aldehyde-fuchsin stained presumptive neurosecretory cells and the intensity of staining are less in adults than in metacercariae. This suggests that maturation in this trematode may be directly or indirectly associated with a reduction in neurosecretion as in nereid annelids. Results of cytochemical studies indicate the neurosecretory product contains a glycoprotein.