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PACIFIC SCIENCE, Vol. XII, October, 1958 
seriform birds might be the natural definitive 
hosts for C. columbiensis. Goldfinches and 
cardinals are known to be the hosts for G. 
huronensis . 
2. Alaska 
Students interested in cercarial dermatitis 
have long suspected that the disease may be 
present in Alaska because this region is the 
home of many migratory water fowls (Ga- 
brielson, 1952). Harkema (1953, 1954, 1955, 
1957) reported in a series of papers that 
swimmer’s itch occurred in the Fairbanks and 
Yukon Flat areas in the Alaskan interior. He 
made a study of the life history of one of the 
two schistosome cercariae obtained from in- 
fected snails in this area. A total of 80 bodies 
of water was investigated during the sum- 
mers of 1952 and 1953, and 20 of these 80 
harbored infected snails of the species Lym- 
naea palustris , L. stagnalis , and L. auricularia. 
The incidence of the infection in snails 
seemed to vary according to location and 
time of the year. Additional localities having 
infected snails were reported in 1957. 
There were no extensive human infections 
derived from avian schistosomes in Alaska. 
Some cercarial dermatitis cases were observed 
in the Fairbanks area in the vicinity of Fort 
Yukon. Harkema (1957) used cercariae from 
the naturally infected Lymnaea stagnalis for 
experimental infections of ducklings, and the 
adult worm was identified as Trichobilharzia 
alaskensis Harkema, McKeever, and Becker. 
The other type of schistosome cercaria re- 
mains unidentified. However, two naturally 
infected baldpate ducks harbored adult schis- 
tosomes belonging to the genus Trichobil- 
harzia . So far there has not been an extensive 
study of the bird definitive hosts for schisto- 
somes in Alaska. 
Gabrielson (1952), in discussing Alaskan 
waterfowls and their management, stated that 
"Alaska has breeding populations of the 
Whistling Swan, Emperor Goose, White- 
cheeked Goose, Lesser Canada Goose, Cack- 
ling Goose, White-fronted Goose, and Black 
Brant. It also provides suitable nesting habi- 
tats for impressive numbers of Pintails, 
Mallards, Green-winged Teals, Baldpates, 
and Shovelers, among shallow water ducks.” 
He thinks that the Yukon delta is not only 
the most important breeding area in Alaska, 
but one of the great waterfowl production 
units of the continent. The green- winged 
teals, pintails, and baldpates, which have an 
extensive continental breeding range, are less 
affected by man-made changes in Alaskan 
topography than are the other species of wa- 
terfowls. Therefore in the future, the bald- 
pates, green- winged teals, and pintails are 
more likely to be implicated as reservoir hosts 
for the distribution of avian schistosomes. 
3. Mexico and El Salvador 
Possible fresh-water cercarial dermatitis 
from Lake Texcoco near Mexico City was 
reported by Cort (1950), but so far is uncon- 
firmed. As far as this reviewer is aware, the 
only cases of swimmer’s itch south of Mexico 
along the Pacific were those contracted from 
Lake Coatepeque, El Salvador, and reported 
by Reyes in 1944. According to Cort’s ac- 
count of the investigation by Reyes, the exact 
etiological agent was not identified. Jarcho 
and Van Burkalow (1952) reported that a 
blue-winged teal captured in this area had 
migrated from Douglas Lake, Michigan — the 
area where Professor W. W. Cort first found 
the cause of swimmer’s itch. These blue- 
winged teals, according to these authors, 
migrate along the Mississippi River and the 
Atlantic coast fly ways. The wintering grounds 
involved a large geographical area ranging 
from southern Florida, Texas, California, 
through Central America to parts of the north- 
ern South American continent, while the 
breeding grounds extend from the Great 
Lakes region westward to the Rockies and as 
far north as northwestern Canada. 
Gabrielson (1952) showed that certain spe- 
cies of migratory fowls did migrate as far 
south as Mexico and that they could be re- 
covered in British Columbia and the states of 
