Isospora palustris Hertel and Duszynski, 1987
Type host: Sorex palustris Richardson, 1828, Northern water shrew.
Other hosts: Sorex pacificus Coues, 1877, Pacific shrew; Sorex
trowbridgii Baird, 1858, Trowbridge shrew; Sorex unguiculatus Dobson, 1890, Long-clawed shrew;
Sorex vagrans Baird, 1858, Vagrant shrew.
Type locality: NORTH AMERICA: USA, New Mexico, Santa Fe County, 8 km N,
12.9 km E, Santa Fe.
Geographic distribution: ASIA: Japan, Hokkaido; NORTH AMERICA: USA, California, New Mexico,
Description of oocyst:
Oocyst shape: subspheroid;
number of walls: 2;
wall thickness: <1.0;
wall characteristics: outer, generally with a few small bumps, irregularly spaced, ~1/2 of total thickness,
and with a striated appearance in optical cross section;
L x W: 17.6 x 16.7 (16-19 x 16-18);
L/W ratio: 1.1 (1.0-1.2);
PG: usually 1, but sometimes (30%) as 2-4 fragments of irregular size and shape.
Distinctive features of oocyst: subspheroid shape with striated outer wall.
Description of sporocysts and sporozoites:
Sporocyst shape: ovoid;
L x W: 12.8 x 8.3 (12-14 x 8-10);
L/W ratio: 1.6 (1.23-1.8);
SSB: present, almost spheroid, about the same width as SB;
SR characteristics: many small granules;
SP: probably have 1 large RB at rounded end, which was not reported in the original description, but is seen in the line drawing.
Distinctive features of sporocyst: spheroid SSB.
Prevalence: 2/12 (8%) S. pacificus; 3/41 (7%) S. palustris;
3/105 (3%) S. trowbridgii; 1/48 (2%) S. unguiculatus; 1/112 (<1%) S. vagrans.
Sporulation: Exogenous. Oocysts sporulated in 7-10 days in 2.5% aqueous (w/v) potassium
dichromate solution at ~23 C.
Prepatent and patent periods: Unknown.
Site of infection: Unknown. Oocysts recovered from feces and intestinal contents.
Materials deposited: Skin, skull, skeleton and tissues of the symbiotype host
are preserved in the Mammal Division of the Museum of SW Biology, UNM: MSB No. 41122 (NK 1002, male),
R.A. Hoyt #098, 6 July 1979. Photosyntypes in the USNPC No. 86357.
Remarks: Oocysts and sporocysts of this species are very similar to those
of I. brevicauda, but differ in 2 ways: 1) oocyst length, oocyst width, sporocyst length, sporocyst
width and oocyst L/W ratio of I. brevicauda from Blarina sp. were highly significantly
smaller (P<0.0001, Student's t-distribution) than those of I. palustris from Sorex spp.
even though the respective means and ranges are similar; and 2) the width of the SSB is about the same as the
SB in I. palustris, whereas it is 2 times wider than the SB in I. brevicauda; also, the shape of
the SSB is different between the 2 species.
References: Hertel and Duszynski (1987).