3. UNDERSTANDING SYMBIONTS OF MARINE MOLLUSCS
13
oyster. Angiostrongylus cantonensis is the metastrongylid rat lungworm
that is believed to be the causative agent of one type of eosinophilic
meningoencephalitis in man in Asia and certain Pacific islands, including Hawaii (see review by Alicata, 1965).
Another aspect of the role of parasites of shellfish which is of
potential importance to public health is the possible role of parasites,
protozoa, helminths and arthropods, as carriers of pathogenic bacteria,
viruses and other microorganisms. This concept is not as far-fetched as
it would appear. Recently Moewus (1963) has reported that a holotrichous hymenostome ciliate, later named Miamiensis avidus by
Thompson and Moewus (1964), a facultative parasite associated with
skin tumors of seahorses, was experimentally found to be able to harbor
polio viruses of the Mahoney strain. Furthermore, it is well known
that the so-called “ salmon-poisoning fluke ”, Nanophyetus salmincola,
can harbor the rickettsia Neorickettsia helminthoeca, which is the
causative agent of salmon-poisoning disease in canines that have
ingested raw salmon parasitized by Nanophyetus salmincola.
In addition to serving as intermediate hosts of zooparasites, which
in turn may act as vectors for microorganisms, marine molluscs, as
the result of parasitization by otherwise medically unimportant
parasites, could cause temporary gastrointestinal disturbances resulting
from the presence of butyric and other toxic short-chain fatty acids
that accumulate in molluscs resulting from the degradation of the
molluscs’ neutral fats by parasite-secreted enzymes (Cheng, 1966a).
Thus, a more thorough understanding of both the types of parasites
found in commercially important and potentially important marine
molluscs and their metabolic effects on hosts are of importance to
medical and public health workers.
Another reason why certain parasites of marine molluscs are of
public health significance is associated with the ability of a number of
marine avian schistosomes to cause human cercarial dermatitis,
commonly referred to as “ clam-diggers’ itch ” or “ swimmers’ itch ”.
These schistosome trematodes develop to the cercarial stage in various
littoral gastropods that commonly share the same habitat as certain
commercially important shellfish. For example, the bird schistosome
Austrobilharxia variglandis is found along the Atlantic coast of the
United States in Nassarius obsoletus which shares the same mud flats
with the soft clam, M y a arenaria, and the quahaug clam, Mercenaria
mercenaria. Thus, individuals digging for clams in these areas may be
subjected to cercarial attack resulting in dermatitis on exposed skin.
Another group of marine trematodes that is of potential importance
in public health is represented by certain members of the genus
13
oyster. Angiostrongylus cantonensis is the metastrongylid rat lungworm
that is believed to be the causative agent of one type of eosinophilic
meningoencephalitis in man in Asia and certain Pacific islands, including Hawaii (see review by Alicata, 1965).
Another aspect of the role of parasites of shellfish which is of
potential importance to public health is the possible role of parasites,
protozoa, helminths and arthropods, as carriers of pathogenic bacteria,
viruses and other microorganisms. This concept is not as far-fetched as
it would appear. Recently Moewus (1963) has reported that a holotrichous hymenostome ciliate, later named Miamiensis avidus by
Thompson and Moewus (1964), a facultative parasite associated with
skin tumors of seahorses, was experimentally found to be able to harbor
polio viruses of the Mahoney strain. Furthermore, it is well known
that the so-called “ salmon-poisoning fluke ”, Nanophyetus salmincola,
can harbor the rickettsia Neorickettsia helminthoeca, which is the
causative agent of salmon-poisoning disease in canines that have
ingested raw salmon parasitized by Nanophyetus salmincola.
In addition to serving as intermediate hosts of zooparasites, which
in turn may act as vectors for microorganisms, marine molluscs, as
the result of parasitization by otherwise medically unimportant
parasites, could cause temporary gastrointestinal disturbances resulting
from the presence of butyric and other toxic short-chain fatty acids
that accumulate in molluscs resulting from the degradation of the
molluscs’ neutral fats by parasite-secreted enzymes (Cheng, 1966a).
Thus, a more thorough understanding of both the types of parasites
found in commercially important and potentially important marine
molluscs and their metabolic effects on hosts are of importance to
medical and public health workers.
Another reason why certain parasites of marine molluscs are of
public health significance is associated with the ability of a number of
marine avian schistosomes to cause human cercarial dermatitis,
commonly referred to as “ clam-diggers’ itch ” or “ swimmers’ itch ”.
These schistosome trematodes develop to the cercarial stage in various
littoral gastropods that commonly share the same habitat as certain
commercially important shellfish. For example, the bird schistosome
Austrobilharxia variglandis is found along the Atlantic coast of the
United States in Nassarius obsoletus which shares the same mud flats
with the soft clam, M y a arenaria, and the quahaug clam, Mercenaria
mercenaria. Thus, individuals digging for clams in these areas may be
subjected to cercarial attack resulting in dermatitis on exposed skin.
Another group of marine trematodes that is of potential importance
in public health is represented by certain members of the genus