12
MARINE MOLLUSCS AS HOSTS FOR SYMBIOSES
predatory molluscs such as the oyster drills, Urosalpinx cinerea,
Eupleura caudata and Thais haemastoma, may be utilized as biological
control agents. Until now, only limited and preliminary studies of this
nature have been conducted (Cooley, 1958, 1962), and hence the
effectiveness of these parasites as control agents remains unknown for
for the most part (Carriker, 1955).
A third reason why parasites of marine molluscs are of importance
to fisheries biologists is because many of them, especially the helminths,
develop to their infective larval forms in molluscs and later, as adults,
are parasitic in various fish, including the economically important
species. Although many of these parasites are essentially non-injurious
to their piscine hosts, they can be utilized as biological markers to trace
their hosts' migrations.
11. IMPORTANCE TO PUBLIC HEALTH
I n both North America and Europe there has been a concern over
the possibility of shellfish serving as carriers of human pathogens. The
correlation between typhoid and the eating of raw or poorly cooked
shellfish from polluted waters in China and elsewhere in Asia is a wellknown public health problem. If viruses and bacteria can be transmitted by shellfish, there is no reason not to believe that zooparasites
could also be transmitted. It is known, for example, that in the
Philippines the intestinal trematode Echinostoma ibocanum is transmitted to man through the ingestion of metacercariae-harboring snails
and corbiculid pelecypods. It is also known that in the Lake Lindoe
district of the Central Celebes the population is heavily infected
( 2 6 9 6 % ) with Echinostoma lindoensis which is contracted through
the ingestion of the clams Corbicula lindoensis and C. subplanata, and
other metacercariae-harboring molluscs.
Relative to zooparasites of marine molluscs transmissible to man,
Vogel (1933) has reported that a German became infected with the
intestinal trematode Himasthla muehlensi after eating several raw
" littlenecks " (Mercenaria mercenaria) on the half-shell in New York.
Recently, Cheng and Burton (1965a) have demonstrated that the
nematode Angiostrongylus cantonensis can develop to the infective
third-stage larva in both Crassostrea virginica and Mercenaria
mercenaria, and hence these pelecypods, which are commonly eaten
raw, could serve as potential transmitters. Although Knapp and
Alicata (1967) have reported that they were unable to infect Crassostrea
virginica and the clam Venerupis philippinarum experimentally, as
will be discussed later (p. 270), their negative results are questionable
in view of their experimental procedures, especially in the case of the
MARINE MOLLUSCS AS HOSTS FOR SYMBIOSES
predatory molluscs such as the oyster drills, Urosalpinx cinerea,
Eupleura caudata and Thais haemastoma, may be utilized as biological
control agents. Until now, only limited and preliminary studies of this
nature have been conducted (Cooley, 1958, 1962), and hence the
effectiveness of these parasites as control agents remains unknown for
for the most part (Carriker, 1955).
A third reason why parasites of marine molluscs are of importance
to fisheries biologists is because many of them, especially the helminths,
develop to their infective larval forms in molluscs and later, as adults,
are parasitic in various fish, including the economically important
species. Although many of these parasites are essentially non-injurious
to their piscine hosts, they can be utilized as biological markers to trace
their hosts' migrations.
11. IMPORTANCE TO PUBLIC HEALTH
I n both North America and Europe there has been a concern over
the possibility of shellfish serving as carriers of human pathogens. The
correlation between typhoid and the eating of raw or poorly cooked
shellfish from polluted waters in China and elsewhere in Asia is a wellknown public health problem. If viruses and bacteria can be transmitted by shellfish, there is no reason not to believe that zooparasites
could also be transmitted. It is known, for example, that in the
Philippines the intestinal trematode Echinostoma ibocanum is transmitted to man through the ingestion of metacercariae-harboring snails
and corbiculid pelecypods. It is also known that in the Lake Lindoe
district of the Central Celebes the population is heavily infected
( 2 6 9 6 % ) with Echinostoma lindoensis which is contracted through
the ingestion of the clams Corbicula lindoensis and C. subplanata, and
other metacercariae-harboring molluscs.
Relative to zooparasites of marine molluscs transmissible to man,
Vogel (1933) has reported that a German became infected with the
intestinal trematode Himasthla muehlensi after eating several raw
" littlenecks " (Mercenaria mercenaria) on the half-shell in New York.
Recently, Cheng and Burton (1965a) have demonstrated that the
nematode Angiostrongylus cantonensis can develop to the infective
third-stage larva in both Crassostrea virginica and Mercenaria
mercenaria, and hence these pelecypods, which are commonly eaten
raw, could serve as potential transmitters. Although Knapp and
Alicata (1967) have reported that they were unable to infect Crassostrea
virginica and the clam Venerupis philippinarum experimentally, as
will be discussed later (p. 270), their negative results are questionable
in view of their experimental procedures, especially in the case of the