308 
PACIFIC SCIENCE, Vol XII, October, 1958 
titis have been based upon circumstantial 
evidence. The urgent need in diagnosing the 
cause of naturally occurring dermatitis is a 
technic (e. g., biopsy tests) which would 
yield direct evidence about the infective 
agent, so that proper control methods could 
be formulated. 
3. Australia 
Bearup (1955, 1956) showed that schisto- 
some cercariae occurred in a marine snail, 
Pyrazus australis Quoy and Gaimard, in Nar- 
rabeen Lake, near Sydney, N. S. W. The cer- 
caria was first identified as Cercaria variglandis 
later Miller and Northup, subspecies pyrazi , 
but was determined to be the cercaria of Aus- 
trobilharzia terrigalensis Johnston, 1917. The 
seagulls ( Larus novae-hollandiae) from the Syd- 
ney district were heavily infected. 
The incidence of schistosome infection in 
P. australis from Narrabeen Lagoon was 4-6 
per cent, the higher level occurring during the 
hot months at the end of the year. Cercariae 
from these infected snails would infect young 
seagulls, budgerigars (Melopsitacus undulatus ') , 
and pigeons ( Columba livia ), but not domestic 
ducks or mice. 
From Florida, U. S. A., several marine 
schistosome cercariae have been described 
(Hutton, 1952; Leigh, 1955; Penner, 1953^). 
These species are distinct from one another 
and different from A. variglandis. However, 
the extreme similarity in morphology of the 
three species, namely, (1) A. variglandis from 
the Atlantic, Pacific, and Hawaiian areas, (2) 
A. littorinalinae from southern California and 
Mexico, and (3) A. terrigalensis from Aus- 
tralia, raises the interesting question of 
whether or not they are actually one species 
with minor variations because of adaptation 
to the intermediate and definitive hosts in 
widely separated geographical areas. 
DISCUSSION 
Cercarial dermatitis is of worldwide distri- 
bution, and probably there are other areas 
where suspected cases of swimmer’s itch occur 
but where no investigations have been made. 
In the Pacific Ocean area, many islands in the 
Polynesian, Micronesian, and Melanesian 
groups are worthy of exploratory studies for 
the presence of bird schistosomiasis. Like- 
wise, other geographical areas such as China, 
Formosa, Indonesia, Viet Nam, the Philip- 
pines, and Thailand have yet to be investi- 
gated fully. 
In the North American continent, swim- 
mer’s itch has been widely studied, yet data 
on schistosome infections in migratory birds 
are still limited. Most of the information on 
definitive hosts has been obtained through 
experimental infection. As a result, the ques- 
tion is frequently asked as to the degree of 
natural infection with schistosomes in other 
types of birds. In this connection, the prob- 
lem of host susceptibility has been studied by 
many investigators. In our own experience, 
the marine schistosome adults found in the 
ruddy turnstone developed well in the sooty 
and noddy terns, but in chicks and ducks the 
adults did not remain viable for an extended 
period and the pathology was not entirely 
comparable to that in the natural host. This 
differential susceptibility between species and 
subspecies (or strains) of the birds is a chal- 
lenging problem to workers who are inter- 
ested in immunology. Such a study is impor- 
tant in relationship to speciation and distribu- 
tion of both the fresh-water and marine 
schistosomes in birds. 
Specificity of a trematode parasite for a host 
may be directly correlated with the host diet. 
An example of this correlation was reported 
by Oguri and Chu (1955) for the infection of 
domestic ducks by the cloacal trematode 
Parochis acanthus (Nicoll, 1906) Nicoll, 1907. 
The natural definitive hosts for this parasite 
are sea birds. When the infectious cysts of 
P. acanthus were given orally to mash-fed 
ducks, there were no infections in these ex- 
perimental hosts. However, if the ducks were 
fed with squids from the sea, instead of the 
mash diet, it was possible to establish the 
