Sarcocystis-infected muscles from ducks, cowbirds, and grackles were fed to cats, opossums, rats, and a dog. Only the opossum (Didelphis virginiana) was a suitable definitive host. All opossums that were fed Sarcocystis-infected cowbirds (Molothrus ater) and grackles (Cassidix mexicanus and Quiscalus quiscula) passed sporocysts in their feces. Opossums that ate the cowbirds had prepatent periods of 5 and 10 days and remained patent for at least 105 days. Opossums that ate the grackles became patent on day 10 after the infective meal and remained patent for over 90 (Quiscalus) and 105 (Cassidix) days. A single opossum fed infected muscle from a pintail duck (Anas acuta) passed sporocysts in the feces from days 13 through 18 after infection. No sporocysts were passed by opossums fed infected muscle from the green-winged teal (Anas carolinensis) and shoveller (Spatula clypeata). Sporocysts of duck, cowbird, and grackle origin were structurally similar. Mean dimensions of sporocysts were: duck-origin, 11.2 by 8.2 μm; cowbird-origin, 11.4 by 7.8 μm; Cassidix-origin, 11.2 by 7.8 μm; and Quiscalus-origin, 11.6 by 7.7 μm. We designate the sporocysts of cowbird and grackle origin as Sarcocystis debonei Vogelsang, 1929 (Syn. Isospora boughtoni Volk, 1938)

Box, Edith D.

Duszynski, Donald

English

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University of Nebraska - Lincoln DigitalCommons@University of Nebraska - Lincoln Faculty Publications from the Harold W. Manter Laboratory of Parasitology Parasitology, Harold W. Manter Laboratory of 4-1978 The Opossum (Didelphis virginiana) as a Host for Sarcocystis debonei from Cowbirds (Molothrus ater) and Grackles (Cassidix mexicanus, Quiscalus quiscula) Donald Duszynski University of New Mexico, eimeria@unm.edu Edith D. Box University of Texas Medical Branch Follow this and additional works at: https://digitalcommons.unl.edu/parasitologyfacpubs  Part of the Parasitology Commons Duszynski, Donald and Box, Edith D., "The Opossum (Didelphis virginiana) as a Host for Sarcocystis debonei from Cowbirds (Molothrus ater) and Grackles (Cassidix mexicanus, Quiscalus quiscula)" (1978). Faculty Publications from the Harold W. Manter Laboratory of Parasitology. 129. https://digitalcommons.unl.edu/parasitologyfacpubs/129 This Article is brought to you for free and open access by the Parasitology, Harold W. Manter Laboratory of at DigitalCommons@University of Nebraska - Lincoln. It has been accepted for inclusion in Faculty Publications from the Harold W. Manter Laboratory of Parasitology by an authorized administrator of DigitalCommons@University of Nebraska - Lincoln. J. Parasitol., 64(2), 1978, pp. 326-329 ? American Society of Parasitologists 1978 THE OPOSSUM (DIDELPHIS VIRGINIANA) AS A HOST FOR SARCOCYSTIS DEBONEI FROM COWBIRDS (MOLOTHRUS ATER) AND GRACKLES (CASSIDIX MEXICANUS, QUISCALUS QUISCULA) Donald W. Duszynski* and Edith D. Boxt ABSTRACT: Sarcocystis-infected muscles from ducks, cowbirds, and grackles were fed to cats, opossums, rats, and a dog. Only the opossum (Didelphis virginiana) was a suitable definitive host. All opossums that were fed Sarcocystis-infected cowbirds (Molothrus ater) and grackles (Cassidix mexicanus and Quiscalus quiscula) passed sporocysts in their feces. Opossums that ate the cowbirds had prepatent periods of 5 and 10 days and remained patent for at least 105 days. Opossums that ate the grackles became patent on day 10 after the infective meal and remained patent for over 90 (Quiscalus) and 105 (Cassidix) days. A single opossum fed infected muscle from a pintail duck (Anas acuta) passed sporocysts in the feces from days 13 through 18 after infection. No sporocysts were passed by opos- sums fed infected muscle from the green-winged teal (Anas carolinensis) and shoveller (Spatula cly- peata). Sporocysts of duck, cowbird, and grackle origin were structurally similar. Mean dimensions of sporocysts were: duck-origin, 11.2 by 8.2 ,am; cowbird-origin, 11.4 by 7.8 ,um; Cassidix-origin, 11.2 by 7.8 tAm; and Quiscalus-origin, 11.6 by 7.7 tum. We designate the sporocysts of cowbird and grackle origin as Sarcocystis debonei Vogelsang, 1929 (Syn. Isospora boughtoni Volk, 1938). Sarcocystis species are ubiquitous parasites with an obligatory two-host cycle. The forms that parasitize muscles of mammals (cattle, sheep, pigs, rats, mice, horses, and deer) have recently been shown to be acquired by inges- tion of isosporan-like sporocysts shed by a host which had previously ingested infected muscle (for reviews, see Dubey, 1976; Kalyakin and Zasukhin, 1975; Levine, 1977). Macroscopic cysts of Sarcocystis are commonly seen in muscles of certain avian species (e.g., grackles and puddle ducks), but the definitive hosts for these forms, i.e., the hosts which discharge the infective sporocysts in their feces, are presently unknown. Results reported here show that the opossum (Didelphis virginiana) is a good host for the Sarcocystis of three species of icterid birds; it is also a possible host for one species of duck Sarcocystis, although apparently not the major one. Cats, rats, and a dog fed avian tissues infected with Sarcocystis failed to dis- charge sporocysts in their feces. MATERIALS AND METHODS Experimental definitive hosts Opossums were purchased from the University of Texas Science Park, Bastrop, Texas. They had Received for publication 27 May 1977. * Department of Biology, The University of New Mexico, Albuquerque, New Mexico 87131. t Department of Microbiology, The University of Texas Medical Branch, Galveston, Texas 77550. been trapped in the vicinity of Bastrop and were routinely held a minimum of 3 weeks before being sold for experimental use. During that time they were fed only dry commercial dog chow. After we received them, the opossums were kept in the University Animal Care Center, Galveston, Texas or in animal quarters of the University of Texas Medical School, Houston, Texas and were fed dry commercial dog chow. The cats were adult strays obtained from the University Animal Care Center and were main- tained there as part of a study on Brugia malayi infections. One stray dog and five adult Sprague- Dawley rats were also maintained at the Uni- versity Animal Care Center. Avian hosts Three species of ducks with muscle cysts were obtained during duck-hunting season from various donors, Anas acuta (pintail), Anas carolinensis (green-winged teal), and Spatula clypeata (shovel- ler). Infected breast and thigh muscles were removed and refrigerated from 1 to 15 days before being fed to animals. All were shot in Galveston County, Texas, except for the pintail and one green-winged teal, which were from Hudspeth County (near El Paso, Texas). Cowbirds (Molothrus ater) and grackles (Quis- calus quiscula and Cassidix mexicanus) were col- lected within or near the city limits of Houston by mist-net or live trap. All birds were skinned and examined for tissue cysts with a lighted magnify- ing lens. Particular attention was paid to tissues of the breast, thigh, calf, and back muscles (for incidence of infection, see Box and Duszynski, 1977). From one to seven infected, skinned (but not eviscerated) birds were fed whole to cats and opossums. Rats were fed muscle pieces containing cysts. All icterid birds had been dead and refrig- erated from 2 to 5 days when fed to experimental hosts. 326 DUSZYNSKI AND BOX-THE OPOSSUM AS HOST FOR SARCOCYSTIS DEBONEI FROM BIRDS 327 TABLE I. Predator-prey combinations for Sarco- cystis transmission experiments (- = 1 animal nega- tive for sporocysts; + = 1 animal positive for sporocysts; ND = combination not tried). Predator Prey Opossum Rat Dog Cat Ducks Shoveller, Spatula clypeata Pintail, Anas acuta + ND ND ND Green-winged teal, Anas carolinensis --- ND ND ND Cowbird Molothrus ater + - ND ---- Grackles Cassidix mexicanus + + ND ND - Quiscalus quiscula + ND ND ND Fecal examination All hosts tested as experimental definitive hosts were caged individually. The feces of each animal were examined by sugar flotation at least twice prior to feeding them infected tissues to check for extraneous coccidian infections. Feces were also examined daily or every other day beginning 3 to 5 days after an animal was fed infected meat, and continuing for 28 days in hosts that remained negative and for at least 100 days for hosts which passed sporocysts. Sporocyst measurements Sporocysts recovered from opossums were stored in 2% aqueous (w/v) potassium dichromate (K2 Cr2 07) solution at 4 to 5 C. They were con- centrated, washed, and measured at 1,000 X as described earlier (Duszynski and Marquardt, 1969). All measurements are in micrometers unless otherwise stated. Mean values were compared using Student's t-test; differences were considered significant when probability values were <0.01. RESULTS Transmission experiments (Tcble I) The feces from nine cats, five rats, and one dog remained negative for sporocysts for at least 28 days after they were fed Sarcocystis- containing muscle from ducks, cowbirds, or grackles. One opossum discharged sporocysts in its feces 13 through 18 days after ingesting in- fected breast muscle from a pintail duck col- lected 15 days previously. However, heavily infected teal and shoveller muscle was fed to five opossums with negative results. Each of six opossums fed skinned, whole infected icterid birds became infected. One opossum was killed -38 hr after eating three infected cowbirds to collect intestinal tissue for histological examination of early endog- enous development. Fecal examinations of this animal had been negative for coccidia for 30 days prior to its eating the infected cow- birds. Tissue impression smears and sections showed developing gamonts throughout the length of the small intestine; these gamonts were presumed to be stages of Sarcocystis development. A second opossum became pat- ent 10 days after eating six infected cowbirds and was killed 2 days later to collect tissues for later study. A third opossum which ate seven infected cowbirds began passing sporocysts 5 days later and continued to pass large numbers of them daily for at least 105 days. Our fourth and fifth opossums were fed one and two grackles (Cassidix), respectively, and both began to discharge sporocysts 10 days later; one passed sporocysts for 20 consecutive days until it was killed for endogenous stages, and the other continued to pass sporocysts for at least 105 days. The opossum fed one grackle of the genus Quiscalus became patent 10 days later, and continued to pass sporocysts daily for at least 90 days. Sporocysts (Table II) Sporocysts of cowbird (N = 25) and grackle (N = 25, each species) origin differed sig- nificantly in size or length/width ratio from those of duck origin (N = 25) in six of nine possible comparisons; those of cowbird origin differed significantly from those of grackle origin in two of six possible comparisons (Table II). Residua in sporocysts of bird origin were highly variable and appeared either compact or as scattered granules. We designate the sporocysts of cowbird and grackle origin as Sarcocystis debonei Vogelsang 1929 (Syn. Isospora boughtoni Volk 1938) based on these criteria: (1) Vogelsang (1929) was the first to name a sarcocystid from cow- birds; thus, his name has priority over all later ones; (2) sporocysts of icterid bird origin are similar in four of six size and shape compari- sons (Table II); and (3) the prepatent and patent periods in the opossum are similar re- gardless of which icterid bird form is ingested. 328 THE JOURNAL OF PARASITOLOGY, VOL. 64, NO. 2, APRIL 1978 TABLE II. Mean dimensions (range) of sporocysts (N = 25) recovered from opossums fed Sarcocystis from avian hosts. Sporocyst Muscle source Length (/um) Width (,um) L/W ratio Anas acuta 11.2 (10-12) 8.2 (7-9) 1.37 (1.22-1.50) Molothrus ater 11.4 (11-12) 7.8 (7-8) 1.47 (1.38-1.57)? Cassidix mexicanus 11.2 (11-12) 7.8 (7-8): 1.44 (1.33-1.57) Quiscalus quiscula 11.6 (11-12)*t 7.7 (7-8)? 1.51 (1.38-1.71)?l1 * P < 0.025 when compared to Cassidix. t P < 0.01 when compared to Anas. : P < 0.005 when compared to Anas. ? P < 0.001 when compared to Anas. II P < 0.01 when compared to Molothrus. We choose not to name the sporocysts of duck origin at this time for reasons discussed below. DISCUSSION The American opossum was utilized in these studies because it is one of the few animals, other than cats and dogs, listed by Pellerdy (1974) as a host from which sporulated iso- sporan-like sporocysts have been recovered. These were described and named Isospora boughtoni by Volk (1938). Ernst et al. (1969), in the second report of its occurrence in an opossum, mentioned the presence of feathers of a brown-headed cowbird in the intestinal contents, indicating that birds are part of the diet of this omnivorous animal. Opossums in our experiments became in- fected in every case in which they ingested infected cowbirds or grackles and continued passing sporocysts for months. This suggests that they are important definitive hosts for Sarcocystis of these icterid birds. The two grackle species and the brown-headed cowbird are all members of the Family Icteridae, but they belong to different genera, whereas sporo- cysts of Sarcocystis species of dogs and cats, though varying slightly in size, have been found infective for, at most, a single genus of intermediate host (Levine, 1977). Although all sporocysts discharged by our experimentally infected opossums are within the size range reported for I. boughtoni (Volk, 1938; Ernst et al., 1969), we suspect we are dealing here with at least two species. There is sufficient precedent (Duszynski and Marquardt, 1969) to support the contention that exogenous stages of coccidians that differ in size, as do sporo- cysts from duck and icterid bird origins, are distinct species. We have tentatively desig- nated those sporocysts of cowbird and grackle origin as a single species, I. debonei, but con- firmation of this view must be dealt with later when cross-transmission studies can be made. Based upon appearance of muscle cysts, the duck Sarcocystis is not the same species found in icterid birds. Macroscopically, cysts from icterid birds were spindle-shaped and mea- sured up to 0.5 by 9.0 mm, whereas those from ducks were more round, had a rice-grain appearance, and measured up to 1.0 by 5.0 mm. Also, the mean size of Giemsa-stained zoites in dried, ethyl alcohol-fixed smears was 10.9 by 3.2 for the duck form and 6.5 by 2.1 for the icterid bird form. It is difficult to explain the light and tem- porary shedding of sporocysts by an opossum after feeding with muscles from a pintail duck when heavily infected teals and shovellers did not infect opossums. Possibly the parasite is evolving in a predator-prey relationship be- tween the opossum and pintail but with an- other major definitive host sustaining the duck infection. The fact that the pintail had been dead for 15 days before being consumed may have caused the infecting dose to be light, resulting in a shorter patency in the definitive host. ACKNOWLEDGMENTS Special thanks are due Mary Jenevein, Hous- ton Mosquito Control Board, for coordinating our efforts with her field personnel, Leon Pate and William Carter, who mist-netted cowbirds and grackles. We also thank Dr. Norman Weisbrodt, Department of Physiology, Uni- DUSZYNSKI AND BOX-THE OPOSSUM AS HOST FOR SARCOCYSTIS DEBONEI FROM BIRDS 329 versity of Texas Medical School, Houston, for use of the opossum to which we fed a pintail duck; Heidi Good, Department of Biology, Rice University, Houston, who live-trapped cowbirds; Mary Anne McCoy and Randall Gould, Galveston, and Drs. J. Bristol and A. Canaris, Department of Biology, University of Texas El Paso, for supplying the infected ducks; Drs. A. Ewert and W. Bosworth of this department for use of their experimental cats; and Dr. N. D. Levine, University of Illinois, for his helpful review of this manuscript. LITERATURE CITED Box, E., AND D. W. DUSZYNSKI. 1977. Survey for Sarcocystis in the brown-headed cowbird (Molothrus ater): A comparison of macro- scopic, microscopic and digestion techniques. J Wildl Dis 13: 356-358. DUBEY, J. P. 1976. A review of Sarcocystis of domestic animals and of other coccidia of cats and dogs. J Am Vet Med Assoc 169: 1061-1078. DUSZYNSKI, D. W., AND W. C. MARQUARDT. 1969. Eimeria (Protozoa: Eimeriidae) of the cotton- tail rabbit, Sylvilagus audubonii, in north- eastern Colorado with a description of three new species. J Protozool 16: 128-137. ERNST, J. V., C. COOPER, AND B. CHOBOTAR. 1969. Isospora boughtoni Volk, 1938 and Isospora sp. (Protozoa: Eimeriidae) from an opossum Didelphis marsupialis. Bull Wildl Dis Assoc 5: 406-409. KALYAKIN, V. N., AND D. N. ZASUKHIN. 1975. Distribution of Sarcocystis (Protozoa: Sporo- zoa) in vertebrates. Folia Parasitol 22: 289- 307. LEVINE, N. D. 1977. Nomenclature of Sarco- cystis in the ox and sheep and of fecal coccid- iosis of the dog and cat. J Parasitol 63: 36-51. PELLERDY, L. P. 1974. Coccidia and Coccidiosis, 2nd ed. Verlag Paul Parey, Berlin, 959 p. VOGELSANG, E. G. 1929. Beitrage zur Kenntnis der Parasitenfauna Uruguays. Sarkosporidien bei Vogeln. Z Bakt Parasitenkd I Orig 113: 206-208. VOLK, J. 1938. Isospora boughtoni n. sp., from the American opposum, Didelphis virginiana. J Parasitol 24: 547-548. 

The Opossum (\u3ci\u3eDidelphis virginiana\u3c/i\u3e) as a Host for \u3ci\u3eSarcocystis debonei\u3c/i\u3e from Cowbirds (\u3ci\u3eMolothrus ater\u3c/i\u3e) and Grackles (\u3ci\u3eCassidix mexicanus\u3c/i\u3e, \u3ci\u3eQuiscalus quiscula\u3c/i\u3e)

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University of Nebraska - Lincoln 
DigitalCommons@University of Nebraska - Lincoln 
Faculty Publications from the Harold W. Manter 
Laboratory of Parasitology Parasitology, Harold W. Manter Laboratory of 
4-1978 
The Opossum (Didelphis virginiana) as a Host for Sarcocystis 
debonei from Cowbirds (Molothrus ater) and Grackles (Cassidix 
mexicanus, Quiscalus quiscula) 
Donald Duszynski 
University of New Mexico, eimeria@unm.edu 
Edith D. Box 
University of Texas Medical Branch 
Follow this and additional works at: https://digitalcommons.unl.edu/parasitologyfacpubs 
 Part of the Parasitology Commons 
Duszynski, Donald and Box, Edith D., "The Opossum (Didelphis virginiana) as a Host for Sarcocystis 
debonei from Cowbirds (Molothrus ater) and Grackles (Cassidix mexicanus, Quiscalus quiscula)" (1978). 
Faculty Publications from the Harold W. Manter Laboratory of Parasitology. 129. 
https://digitalcommons.unl.edu/parasitologyfacpubs/129 
This Article is brought to you for free and open access by the Parasitology, Harold W. Manter Laboratory of at 
DigitalCommons@University of Nebraska - Lincoln. It has been accepted for inclusion in Faculty Publications from 
the Harold W. Manter Laboratory of Parasitology by an authorized administrator of DigitalCommons@University of 
Nebraska - Lincoln. 
J. Parasitol., 64(2), 1978, pp. 326-329 
? American Society of Parasitologists 1978 
THE OPOSSUM (DIDELPHIS VIRGINIANA) AS A HOST FOR 
SARCOCYSTIS DEBONEI FROM COWBIRDS (MOLOTHRUS ATER) 
AND GRACKLES (CASSIDIX MEXICANUS, QUISCALUS QUISCULA) 
Donald W. Duszynski* and Edith D. Boxt 
ABSTRACT: Sarcocystis-infected muscles from ducks, cowbirds, and grackles were fed to cats, opossums, 
rats, and a dog. Only the opossum (Didelphis virginiana) was a suitable definitive host. All opossums 
that were fed Sarcocystis-infected cowbirds (Molothrus ater) and grackles (Cassidix mexicanus and 
Quiscalus quiscula) passed sporocysts in their feces. Opossums that ate the cowbirds had prepatent 
periods of 5 and 10 days and remained patent for at least 105 days. Opossums that ate the grackles 
became patent on day 10 after the infective meal and remained patent for over 90 (Quiscalus) and 
105 (Cassidix) days. A single opossum fed infected muscle from a pintail duck (Anas acuta) passed 
sporocysts in the feces from days 13 through 18 after infection. No sporocysts were passed by opos- 
sums fed infected muscle from the green-winged teal (Anas carolinensis) and shoveller (Spatula cly- 
peata). Sporocysts of duck, cowbird, and grackle origin were structurally similar. Mean dimensions 
of sporocysts were: duck-origin, 11.2 by 8.2 ,am; cowbird-origin, 11.4 by 7.8 ,um; Cassidix-origin, 
11.2 by 7.8 tAm; and Quiscalus-origin, 11.6 by 7.7 tum. We designate the sporocysts of cowbird and 
grackle origin as Sarcocystis debonei Vogelsang, 1929 (Syn. Isospora boughtoni Volk, 1938). 
Sarcocystis species are ubiquitous parasites 
with an obligatory two-host cycle. The forms 
that parasitize muscles of mammals (cattle, 
sheep, pigs, rats, mice, horses, and deer) have 
recently been shown to be acquired by inges- 
tion of isosporan-like sporocysts shed by a host 
which had previously ingested infected muscle 
(for reviews, see Dubey, 1976; Kalyakin and 
Zasukhin, 1975; Levine, 1977). Macroscopic 
cysts of Sarcocystis are commonly seen in 
muscles of certain avian species (e.g., grackles 
and puddle ducks), but the definitive hosts for 
these forms, i.e., the hosts which discharge the 
infective sporocysts in their feces, are presently 
unknown. 
Results reported here show that the opossum 
(Didelphis virginiana) is a good host for the 
Sarcocystis of three species of icterid birds; 
it is also a possible host for one species of 
duck Sarcocystis, although apparently not the 
major one. Cats, rats, and a dog fed avian 
tissues infected with Sarcocystis failed to dis- 
charge sporocysts in their feces. 
MATERIALS AND METHODS 
Experimental definitive hosts 
Opossums were purchased from the University 
of Texas Science Park, Bastrop, Texas. They had 
Received for publication 27 May 1977. 
* Department of Biology, The University of New 
Mexico, Albuquerque, New Mexico 87131. 
t Department of Microbiology, The University of 
Texas Medical Branch, Galveston, Texas 77550. 
been trapped in the vicinity of Bastrop and were 
routinely held a minimum of 3 weeks before being 
sold for experimental use. During that time they 
were fed only dry commercial dog chow. After 
we received them, the opossums were kept in the 
University Animal Care Center, Galveston, Texas 
or in animal quarters of the University of Texas 
Medical School, Houston, Texas and were fed dry 
commercial dog chow. 
The cats were adult strays obtained from the 
University Animal Care Center and were main- 
tained there as part of a study on Brugia malayi 
infections. One stray dog and five adult Sprague- 
Dawley rats were also maintained at the Uni- 
versity Animal Care Center. 
Avian hosts 
Three species of ducks with muscle cysts were 
obtained during duck-hunting season from various 
donors, Anas acuta (pintail), Anas carolinensis 
(green-winged teal), and Spatula clypeata (shovel- 
ler). Infected breast and thigh muscles were 
removed and refrigerated from 1 to 15 days before 
being fed to animals. All were shot in Galveston 
County, Texas, except for the pintail and one 
green-winged teal, which were from Hudspeth 
County (near El Paso, Texas). 
Cowbirds (Molothrus ater) and grackles (Quis- 
calus quiscula and Cassidix mexicanus) were col- 
lected within or near the city limits of Houston by 
mist-net or live trap. All birds were skinned and 
examined for tissue cysts with a lighted magnify- 
ing lens. Particular attention was paid to tissues of 
the breast, thigh, calf, and back muscles (for 
incidence of infection, see Box and Duszynski, 
1977). From one to seven infected, skinned (but 
not eviscerated) birds were fed whole to cats and 
opossums. Rats were fed muscle pieces containing 
cysts. All icterid birds had been dead and refrig- 
erated from 2 to 5 days when fed to experimental 
hosts. 
326 
DUSZYNSKI AND BOX-THE OPOSSUM AS HOST FOR SARCOCYSTIS DEBONEI FROM BIRDS 327 
TABLE I. Predator-prey combinations for Sarco- 
cystis transmission experiments (- = 1 animal nega- 
tive for sporocysts; + = 1 animal positive for 
sporocysts; ND = combination not tried). 
Predator 
Prey Opossum Rat Dog Cat 
Ducks 
Shoveller, 
Spatula clypeata 
Pintail, 
Anas acuta + ND ND ND 
Green-winged teal, 
Anas carolinensis --- ND ND ND 
Cowbird 
Molothrus ater + - ND ---- 
Grackles 
Cassidix mexicanus + + ND ND - 
Quiscalus quiscula + ND ND ND 
Fecal examination 
All hosts tested as experimental definitive hosts 
were caged individually. The feces of each animal 
were examined by sugar flotation at least twice 
prior to feeding them infected tissues to check for 
extraneous coccidian infections. Feces were also 
examined daily or every other day beginning 3 to 
5 days after an animal was fed infected meat, and 
continuing for 28 days in hosts that remained 
negative and for at least 100 days for hosts which 
passed sporocysts. 
Sporocyst measurements 
Sporocysts recovered from opossums were stored 
in 2% aqueous (w/v) potassium dichromate 
(K2 Cr2 07) solution at 4 to 5 C. They were con- 
centrated, washed, and measured at 1,000 X as 
described earlier (Duszynski and Marquardt, 
1969). All measurements are in micrometers unless 
otherwise stated. Mean values were compared 
using Student's t-test; differences were considered 
significant when probability values were <0.01. 
RESULTS 
Transmission experiments (Tcble I) 
The feces from nine cats, five rats, and one 
dog remained negative for sporocysts for at 
least 28 days after they were fed Sarcocystis- 
containing muscle from ducks, cowbirds, or 
grackles. 
One opossum discharged sporocysts in its 
feces 13 through 18 days after ingesting in- 
fected breast muscle from a pintail duck col- 
lected 15 days previously. However, heavily 
infected teal and shoveller muscle was fed to 
five opossums with negative results. 
Each of six opossums fed skinned, whole 
infected icterid birds became infected. One 
opossum was killed -38 hr after eating three 
infected cowbirds to collect intestinal tissue 
for histological examination of early endog- 
enous development. Fecal examinations of 
this animal had been negative for coccidia for 
30 days prior to its eating the infected cow- 
birds. Tissue impression smears and sections 
showed developing gamonts throughout the 
length of the small intestine; these gamonts 
were presumed to be stages of Sarcocystis 
development. A second opossum became pat- 
ent 10 days after eating six infected cowbirds 
and was killed 2 days later to collect tissues for 
later study. A third opossum which ate seven 
infected cowbirds began passing sporocysts 5 
days later and continued to pass large numbers 
of them daily for at least 105 days. Our 
fourth and fifth opossums were fed one and 
two grackles (Cassidix), respectively, and both 
began to discharge sporocysts 10 days later; 
one passed sporocysts for 20 consecutive days 
until it was killed for endogenous stages, and 
the other continued to pass sporocysts for at 
least 105 days. The opossum fed one grackle 
of the genus Quiscalus became patent 10 days 
later, and continued to pass sporocysts daily 
for at least 90 days. 
Sporocysts (Table II) 
Sporocysts of cowbird (N = 25) and grackle 
(N = 25, each species) origin differed sig- 
nificantly in size or length/width ratio from 
those of duck origin (N = 25) in six of nine 
possible comparisons; those of cowbird origin 
differed significantly from those of grackle 
origin in two of six possible comparisons 
(Table II). Residua in sporocysts of bird 
origin were highly variable and appeared either 
compact or as scattered granules. 
We designate the sporocysts of cowbird and 
grackle origin as Sarcocystis debonei Vogelsang 
1929 (Syn. Isospora boughtoni Volk 1938) 
based on these criteria: (1) Vogelsang (1929) 
was the first to name a sarcocystid from cow- 
birds; thus, his name has priority over all later 
ones; (2) sporocysts of icterid bird origin are 
similar in four of six size and shape compari- 
sons (Table II); and (3) the prepatent and 
patent periods in the opossum are similar re- 
gardless of which icterid bird form is ingested. 
328 THE JOURNAL OF PARASITOLOGY, VOL. 64, NO. 2, APRIL 1978 
TABLE II. Mean dimensions (range) of sporocysts (N = 25) recovered from opossums fed Sarcocystis 
from avian hosts. 
Sporocyst 
Muscle 
source Length (/um) Width (,um) L/W ratio 
Anas acuta 11.2 (10-12) 8.2 (7-9) 1.37 (1.22-1.50) 
Molothrus ater 11.4 (11-12) 7.8 (7-8) 1.47 (1.38-1.57)? 
Cassidix mexicanus 11.2 (11-12) 7.8 (7-8): 1.44 (1.33-1.57) 
Quiscalus quiscula 11.6 (11-12)*t 7.7 (7-8)? 1.51 (1.38-1.71)?l1 
* P < 0.025 when compared to Cassidix. 
t P < 0.01 when compared to Anas. 
: P < 0.005 when compared to Anas. 
? P < 0.001 when compared to Anas. 
II P < 0.01 when compared to Molothrus. 
We choose not to name the sporocysts of duck 
origin at this time for reasons discussed below. 
DISCUSSION 
The American opossum was utilized in these 
studies because it is one of the few animals, 
other than cats and dogs, listed by Pellerdy 
(1974) as a host from which sporulated iso- 
sporan-like sporocysts have been recovered. 
These were described and named Isospora 
boughtoni by Volk (1938). Ernst et al. 
(1969), in the second report of its occurrence 
in an opossum, mentioned the presence of 
feathers of a brown-headed cowbird in the 
intestinal contents, indicating that birds are 
part of the diet of this omnivorous animal. 
Opossums in our experiments became in- 
fected in every case in which they ingested 
infected cowbirds or grackles and continued 
passing sporocysts for months. This suggests 
that they are important definitive hosts for 
Sarcocystis of these icterid birds. The two 
grackle species and the brown-headed cowbird 
are all members of the Family Icteridae, but 
they belong to different genera, whereas sporo- 
cysts of Sarcocystis species of dogs and cats, 
though varying slightly in size, have been 
found infective for, at most, a single genus of 
intermediate host (Levine, 1977). Although 
all sporocysts discharged by our experimentally 
infected opossums are within the size range 
reported for I. boughtoni (Volk, 1938; Ernst 
et al., 1969), we suspect we are dealing here 
with at least two species. There is sufficient 
precedent (Duszynski and Marquardt, 1969) 
to support the contention that exogenous stages 
of coccidians that differ in size, as do sporo- 
cysts from duck and icterid bird origins, are 
distinct species. We have tentatively desig- 
nated those sporocysts of cowbird and grackle 
origin as a single species, I. debonei, but con- 
firmation of this view must be dealt with later 
when cross-transmission studies can be made. 
Based upon appearance of muscle cysts, the 
duck Sarcocystis is not the same species found 
in icterid birds. Macroscopically, cysts from 
icterid birds were spindle-shaped and mea- 
sured up to 0.5 by 9.0 mm, whereas those 
from ducks were more round, had a rice-grain 
appearance, and measured up to 1.0 by 5.0 
mm. Also, the mean size of Giemsa-stained 
zoites in dried, ethyl alcohol-fixed smears was 
10.9 by 3.2 for the duck form and 6.5 by 2.1 
for the icterid bird form. 
It is difficult to explain the light and tem- 
porary shedding of sporocysts by an opossum 
after feeding with muscles from a pintail duck 
when heavily infected teals and shovellers did 
not infect opossums. Possibly the parasite is 
evolving in a predator-prey relationship be- 
tween the opossum and pintail but with an- 
other major definitive host sustaining the duck 
infection. The fact that the pintail had been 
dead for 15 days before being consumed may 
have caused the infecting dose to be light, 
resulting in a shorter patency in the definitive 
host. 
ACKNOWLEDGMENTS 
Special thanks are due Mary Jenevein, Hous- 
ton Mosquito Control Board, for coordinating 
our efforts with her field personnel, Leon Pate 
and William Carter, who mist-netted cowbirds 
and grackles. We also thank Dr. Norman 
Weisbrodt, Department of Physiology, Uni- 
DUSZYNSKI AND BOX-THE OPOSSUM AS HOST FOR SARCOCYSTIS DEBONEI FROM BIRDS 329 
versity of Texas Medical School, Houston, for 
use of the opossum to which we fed a pintail 
duck; Heidi Good, Department of Biology, 
Rice University, Houston, who live-trapped 
cowbirds; Mary Anne McCoy and Randall 
Gould, Galveston, and Drs. J. Bristol and A. 
Canaris, Department of Biology, University of 
Texas El Paso, for supplying the infected 
ducks; Drs. A. Ewert and W. Bosworth of this 
department for use of their experimental cats; 
and Dr. N. D. Levine, University of Illinois, 
for his helpful review of this manuscript. 
LITERATURE CITED 
Box, E., AND D. W. DUSZYNSKI. 1977. Survey 
for Sarcocystis in the brown-headed cowbird 
(Molothrus ater): A comparison of macro- 
scopic, microscopic and digestion techniques. 
J Wildl Dis 13: 356-358. 
DUBEY, J. P. 1976. A review of Sarcocystis of 
domestic animals and of other coccidia of 
cats and dogs. J Am Vet Med Assoc 169: 
1061-1078. 
DUSZYNSKI, D. W., AND W. C. MARQUARDT. 1969. 
Eimeria (Protozoa: Eimeriidae) of the cotton- 
tail rabbit, Sylvilagus audubonii, in north- 
eastern Colorado with a description of three 
new species. J Protozool 16: 128-137. 
ERNST, J. V., C. COOPER, AND B. CHOBOTAR. 1969. 
Isospora boughtoni Volk, 1938 and Isospora 
sp. (Protozoa: Eimeriidae) from an opossum 
Didelphis marsupialis. Bull Wildl Dis Assoc 
5: 406-409. 
KALYAKIN, V. N., AND D. N. ZASUKHIN. 1975. 
Distribution of Sarcocystis (Protozoa: Sporo- 
zoa) in vertebrates. Folia Parasitol 22: 289- 
307. 
LEVINE, N. D. 1977. Nomenclature of Sarco- 
cystis in the ox and sheep and of fecal coccid- 
iosis of the dog and cat. J Parasitol 63: 
36-51. 
PELLERDY, L. P. 1974. Coccidia and Coccidiosis, 
2nd ed. Verlag Paul Parey, Berlin, 959 p. 
VOGELSANG, E. G. 1929. Beitrage zur Kenntnis 
der Parasitenfauna Uruguays. Sarkosporidien 
bei Vogeln. Z Bakt Parasitenkd I Orig 113: 
206-208. 
VOLK, J. 1938. Isospora boughtoni n. sp., from 
the American opposum, Didelphis virginiana. J 
Parasitol 24: 547-548. 


https://digitalcommons.unl.edu/cgi/viewcontent.cgi?article=1137&amp;context=parasitologyfacpubs

The Opossum (\u3ci\u3eDidelphis virginiana\u3c/i\u3e) as a Host for \u3ci\u3eSarcocystis debonei\u3c/i\u3e from Cowbirds (\u3ci\u3eMolothrus ater\u3c/i\u3e) and Grackles (\u3ci\u3eCassidix mexicanus\u3c/i\u3e, \u3ci\u3eQuiscalus quiscula\u3c/i\u3e)

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