Syst Parasitol (2014) 88:181–184 DOI 10.1007/s11230-014-9489-0
A new species of Eimeria Schneider, 1875 (Apicomplexa: Eimeriidae) from the dusky rice rat Melanomys caliginosus (Tomes) (Mammalia: Rodentia) in Costa Rica Misael Chinchilla • Idalia Valerio • Ronald Sa´nchez • Antonieta Gonza´lez Donald W. Duszynski
•
Received: 7 January 2014 / Accepted: 7 April 2014 Ó Springer Science+Business Media Dordrecht 2014
Abstract We collected faecal samples from 24 dusky rice rats, Melanomys caliginosus (Tomes) (Rodentia: Cricetidae: Sigmodontinae), in a Biological Reserve in Costa Rica, and found three (12.5%) to be infected with a species of Eimeria Schneider, 1875, which we describe here as new. Sporulated oo¨cysts of Eimeria caliginosa n. sp. are almost spheroidal and measure 16–21 9 17–20 (mean 19.6 9 18.2) lm; micropyle, oo¨cyst residuum and polar granule are absent. Sporocysts are ovoidal, 9–13 9 6–8 (mean 11.2 9 6.7) lm, with small Stieda and sub-Stieda bodies present, but a para-Stieda body is absent; the sporocyst residuum is a compact mass of c.11–15 granules, c.5 lm wide. Sporozoites are crescent-shaped, 5–8 9 2–3 (mean 6.8 9 2.4) lm. This is the third species of Eimeria described from the genus Melanomys Thomas.
Introduction This study is a small part of an ongoing, collaborative effort between several Costa Rican academic institutions to study and protect our biodiversity. While M. Chinchilla I. Valerio R. Sa´nchez A. Gonza´lez Research Department, Universidad de Ciencias Me´dicas (UCIMED), San Jose´, Costa Rica D. W. Duszynski (&) Department of Biology, University of New Mexico, Albuquerque, NM 87131, USA e-mail: [email protected]
searching for the reservoirs of Leishmania spp., Trypanosoma cruzi Chagas, 1909 and Toxoplasma gondii Nicolle & Manceaux, 1908, we also examined the faeces of the wild rodents we caught for coccidian oo¨cysts. About 500 species of coccidia have been described from rodents to date (Duszynski et al., 2001, 2007) and within the subfamily Sigmodontinae (Rodentia: Cricetidae) there are 74 genera composed of 376 species (Musser & Carleton, 2005). To the best of our knowledge, prior to our work, coccidian species have been reported previously from only four of the genera in this subfamily (Akodon Meyen, Oryzomys Baird, Phyllotis Waterhouse and Sigmodon Say & Ord) and, in Costa Rica, eimerians are documented only in Sigmodon hispidus Say & Ord (see Castro et al., 1998; Rodrı´guez et al., 1999) and Melanomys caliginosus (Tomes) (Chinchilla et al., 2013). Thus, in our study of wild rodents, while looking for leishmaniosis and Chagas disease reservoirs and intestinal parasites, we sampled 24 additional M. caliginosus and a third species of Eimeria was discovered, that we describe herein and name as new.
Materials and methods Prior to collection, all necessary permits needed in Costa Rica for working with wild animals in the Reserva Biolo´gica Alberto Manuel Brenes (REBAMB) were obtained. All animals were collected in the protected REBAMB in San Ramo´n, Alajuela,
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182
Costa Rica, and our collections were all non-invasive with the least possible damage to the animals and to the Reserve. Dusky rice rats were captured with handmade wooden traps which were set in the afternoon and collected early the following morning. Spontaneously eliminated faecal samples were collected and stored in individual tubes, transported to the laboratory, and studied using routine laboratory examination for the presence of parasites. After collecting the faeces, the animals were released at exactly the same place where they were captured. It should be noted that oo¨cysts were so plentiful in the faecal pellets that we did not need to use any concentration techniques. Conventional methods for preservation and description of these coccidia were used (Bandoni & Duszynski, 1988; Duszynski & Wilber, 1997). Faecal pellets were placed in 2.5% (w/v) aqueous potassium dichromate (K2Cr2O7) and, after sporulation, the oo¨cysts were examined with an Olympus BX41 microscope and photographed with an Olympus C60 ZOOM camera. Photosyntypes (Duszynski, 1999) of sporulated oo¨cysts of the new eimerian were submitted to the United States National Parasite Collection (USNPC) in Beltsville, Maryland, U.S.A. (see Bandoni & Duszynski, 1988). All measurements are given in micrometres as the range followed by the mean in parentheses.
Eimeria caliginosa n. sp. Type-host: Melanomys caliginosus (Tomes), dusky rice rat. Type-locality: Reserva Biolo´gica Alberto Manuel Brenes, 42 km NE of San Ramo´n, Alajuela, Costa Rica (10°130 4900 N, 84°360 1000 W; elevation 600-1,640 m, mean temperature 21 °C, relative humidity 98%, rainfall 3,461 mm/yr; see Sanchez, Sa´nchez, 2000). Type-material: Photosyntypes of sporulated oo¨cysts, IB-1-R-4, 5, are deposited in the Department of Parasitology Research, Universidad de Ciencias Me´dicas, San Jose´, Costa Rica, and in the USNPC (Accession No. 105608). Symbiotype host (see Frey et al., 1992), skin and skeleton, are deposited in the Museo Nacional de Costa Rica (adult male, MNCR No. 861). Prevalence: 12.5% (in 3 out of 24 hosts examined) Sporulation: Exogenous.
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Syst Parasitol (2014) 88:181–184
Fig. 1 Eimeria caliginosa n. sp. from Melanomys caliginosus in Costa Rica. A, Photomicrograph of a sporulated oo¨cyst; B, Line drawing of a sporulated oo¨cyst. Scale-bars: 3 lm
Site of infection: Unknown, oo¨cysts recovered from faeces. Pathology: Unknown, but none was observed in the three hosts examined and found to be discharging oo¨cysts. Etymology: The specific epithet is derived from the specific epithet of the host, M. caliginosus.
Description (Figs. 1A, B) Sporulated oo¨cyst Oo¨cyst (n = 25) spheroidal to slightly sub-spheroidal, 16–22 9 17–20 (19.6 9 18.2); length/width (L/W) ratio 1.1. Oo¨cyst wall bi-layered, c.2 thick; outer layer clear, smooth, c.2/3 of total wall thickness. Micropyle, oo¨cyst residuum and polar granule all absent.
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Table 1 Key quantitative and qualitative characters of sporulated oo¨cysts of species of Eimeria described from rodents in the Tribe Orizomini (Cricetidae). Abbreviations: L/W ratio; Length/Width ratio; OR, oo¨cyst residuum; PG, polar granule; SB, Stieda body; SR, sporocyst residuum; SSB, sub-Stieda body Species
Host
Oo¨cyst mean size (L/W ratio)
OR &/ or PG
Sporocyst mean size (L/W ratio)
SR, SB, SSB
E. couesii Krudienier, Levine & Ivens 1959
Oryzomys couesi (Alston)
21 9 18 (1.2)
? & ?a
12 9 8 (1.5)
?/2, ?, 2
E. kinsellai Barnard, Ernst & Roper 1971
O. palustris (Harlan)
27 9 17 (1.6)
2b & 1
14 9 8 (1.7)
?, ?, 2
E. ojasti Arcay-de-Peraza, 1964
O. albigularis (Tomes)
17 9 13 (1.3)
2&2
8 9 6 (1.3)
?, 2, 2
E. oryzomysi Carini, 1937
Oryzomys sp.
23 9 18 (1.3)
?&2
11 9 8 (1.4)
?, ?, 2
E. palustris Barnard, Ernst & Stevens 1971 E. melanomytis Chinchilla, Valerio, Sa´nches, Gonza´lez, Martinez & Duszynski, 2013
O. palustris (Harlan)
24 9 18 (1.3)
2&?
14 9 8 (1.7)
?, ?, 2
Melanomys caliginosus (Tomes)
20 9 13 (1.5)
2&?
11 9 7 (1.6)
?, ?, 2
E. rebambensis Chinchilla, Valerio, Sa´nches, Gonza´lez, Martinez & Duszynski, 2013
M. caliginosus (Tomes)
21 9 17 (1 3)
2&?
12 9 7 (1.7)
?, ?, ?
E. caliginosa n. sp.
M. caliginosus (Tomes)
20 9 18 (1.1)
2&2
11 9 7 (1.6)
?, ?, ?
a
Present;
b
Absent
Sporocyst and sporozoites Sporocyst ovoidal (n = 72), 9–13 9 6–8 (11.2 9 6.7); L/W ratio 1.5–1.6 (1.7). Stieda body present, as a small rounded extension of the sporocyst wall; subStieda body present, tiny; para-Stieda body absent; sporocyst residuum present as several large globules forming spheroidal mass c.5 wide. Sporozoites appear to have a homogeneous or finely granular cytoplasm, but refractile bodies and a nucleus are not visible. Remarks The genus Oryzomys (Cricetidae: Tribe Oryzomyini) is known to be the most closely related host genus to Melanomys Thomas (see Musser & Carleton, 2005). Thus, the metrical characteristics of the sporulated oo¨cysts of the new species are compared with the five eimerians (see Levine & Ivens, 1990) known from Oryzomys spp. as well as with Eimeria melanomytis Chinchilla, Valerio, Sa´nches, Gonza´lez, Martinez & Duszynski, 2013 and E. rebambensis Chinchilla, Valerio, Sa´nches, Gonza´lez, Martinez & Duszynski, 2013 recently described based on material from M. caliginosus (Table 1). The sporulated oo¨cysts of E. caliginosa n. sp. are similar in size to those of E.
couesii Krudienier, Levine & Ivens 1959 from Oryzomis couesi Alston (19.6 9 18.2 vs 21 9 18 lm) but differ in lacking both an oo¨cyst residuum and a polar granule, both present in E. couesii. The sporulated oo¨cysts of the new species are most similar to those of E. rebambensis, but differ in many ways; those of E. caliginosa are more spheroidal with a smaller L/W ratio (1.1 vs 1.3), they have a smooth outer wall, whereas those of E. rebambensis have a brown, striated outer wall, and the new species is slightly smaller (16–22 9 17–20 vs 19–23 9 14–18 lm; means 19.6 9 18.2 vs 21.2 9 17.0 lm); the oo¨cysts of E. caliginosa also lack a polar granule that is present in E. rebambensis. Oo¨cyst dimensions of all other eimerian species from these two host genera, Melanomys and Oryzomys, are distinctly different and have length/width indices that are all higher than in E. caliginosa. Thus, we believe the form we have described here is a new eimerian from the dusky rice rat. In Costa Rica, only a few species of Eimeria (i.e. E. sigmodontis Barnard, Ernst & Dixon, 1974, E. tuskegeensis Barnard, Ernst & Dixon, 1974, E roperi Barnard, Ernst & Dixon, 1974 and E. webbae Barnard, Ernst & Dixon, 1974) have been found in the cotton rat Sigmodon hispidus Say & Ord (see Castro et al., 1998;
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184
Rodrı´guez et al., 1999). Although both hosts may live in the same ecological niche, there are important differences in oo¨cyst morphology between the coccidia from these hosts. The animals examined by us were captured close to a house near the Biological Station, where these rice rats inhabit burrow systems and all probably eat the same food. Under these burrow conditions the oo¨cysts should be quite resistant to environmental factors and the communal living of the rats makes the transmission of oo¨cysts easier between them. It is likely that these environmental parameters help these rats become infected, even when the prevalence of this eimerian is lower (12.5%), compared with the high prevalence (89%) found for the other two eimerians from the same host species in nearly the same locality (Chinchilla et al., 2013). In surveys for Eimeria spp. in S. hispidus, carried out in a pineapple plantation where animals are more dispersed (Castro et al., 1998; Rodrı´guez et al., 1999), the prevalence of infections was always lower (e.g.,\28% for E. sigmodontis). Acknowledgements We thank Laura Valerio Jose Bolan˜os, Luis Gonzalez and Hugo Pe´rez for handling of the animals and logistic support. This work was partially funded by the Universidad de Ciencias Me´dicas (UCIMED), Ministerio de Ciencia y Tecnologı´a (MICIT), and Consejo Nacional de Ciencia y Tecnologı´a (CONICIT).
References Bandoni, S., & Duszynski, D. W. (1988). A plea for improved presentation of type material for coccidian. Journal of Parasitology, 74, 519–523.
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Syst Parasitol (2014) 88:181–184 Castro, A., Chinchilla, M., Guerrero, O. M., & Gonza´lez, R. (1998). Especies de Eimeria (Eucoccidia: Eimeriidae) en la rata de milpa Sigmodon hispidus de Costa Rica. Revista de Biologia Tropical, 46, 339–340. Chinchilla, M., Valerio, I., Sa´nchez, R., Gonza´lez, A., Martı´nez, L., & Duszynski, D. W. (2013). Two new Eimeria spp. (Apicomplexa: Eimeriidae) from the dusky rice rat, Melanomys caliginosus (Tome, 1860) in Costa Rica. Journal of Parasitology, 99, 82–84. Duszynski, D. W. (1999). Revisiting the Code: clarifying namebearing types for photomicrographs of protozoa. Journal of Parasitology, 85, 769–770. Duszynski, D. W., Lynch, A. J., & Cook, J. A. (2007). Coccidia (Apicomplexa: Eimeriidae) infecting cricetid rodents from Alaska, USA and Northeastern Siberia, Russia, and description of a new Eimeria species from Myodes rutilus, the northern red-backed vole. Comparative Parasitology, 74, 294–311. Duszynski, D. W., Upton, S. J., & Couch, L. (2001). Coccidia (Eimeriidae) of Rodentia: Muridae (rats, mice, hamsters, voles, etc.). http://biology.unm.edu/biology/coccidia/rodents. html. Accessed 9 Dec 2011. Duszynski, D. W., & Wilber, P. G. (1997). A guideline for the preparation of species descriptions in the Eimeriidae. Journal of Parasitology, 83, 333–336. Frey, J. K., Yates, T. L., Duszynski, D. W., Gannon, W. L., & Gardner, S. L. (1992). Designation and curatorial management of type host specimens (symbiotypes) for new parasite species. Journal of Parasitology, 78, 930–932. Levine, N. D., & Ivens, V. (1990). The coccidian parasites of rodents. Boca Raton: CRC Press, 228 pp. Musser, G. G., & Carleton, M. D. (2005). Superfamily Muroidea. In: Wilson, D. E. & Reeder, D. M (Eds) Mammal species of the world: a taxonomic and geographic reference, Vol. 2 (3rd edn). Baltimore: Johns Hopkins University Press, pp. 894–1531. Rodrı´guez, B., Gonza´lez, R., & Chinchilla, M. (1999). Fauna Parasitolo´gica de la rata de milpa Sigmodon hispidus, en un a´rea urbana-industrial de Alajuela, Costa Rica. Parasitologia al Dı´a, 23, 95–99. Sa´nchez, R. (2000). Reserva Biolo´gica Alberto Manuel Brenes. San Jose´: Editorial Toma´s Saravia, 50 pp.
A new species of Eimeria Schneider, 1875 (Apicomplexa: Eimeriidae) from the dusky rice rat Melanomys caliginosus (Tomes) (Mammalia: Rodentia) in Costa Rica Misael Chinchilla • Idalia Valerio • Ronald Sa´nchez • Antonieta Gonza´lez Donald W. Duszynski
•
Received: 7 January 2014 / Accepted: 7 April 2014 Ó Springer Science+Business Media Dordrecht 2014
Abstract We collected faecal samples from 24 dusky rice rats, Melanomys caliginosus (Tomes) (Rodentia: Cricetidae: Sigmodontinae), in a Biological Reserve in Costa Rica, and found three (12.5%) to be infected with a species of Eimeria Schneider, 1875, which we describe here as new. Sporulated oo¨cysts of Eimeria caliginosa n. sp. are almost spheroidal and measure 16–21 9 17–20 (mean 19.6 9 18.2) lm; micropyle, oo¨cyst residuum and polar granule are absent. Sporocysts are ovoidal, 9–13 9 6–8 (mean 11.2 9 6.7) lm, with small Stieda and sub-Stieda bodies present, but a para-Stieda body is absent; the sporocyst residuum is a compact mass of c.11–15 granules, c.5 lm wide. Sporozoites are crescent-shaped, 5–8 9 2–3 (mean 6.8 9 2.4) lm. This is the third species of Eimeria described from the genus Melanomys Thomas.
Introduction This study is a small part of an ongoing, collaborative effort between several Costa Rican academic institutions to study and protect our biodiversity. While M. Chinchilla I. Valerio R. Sa´nchez A. Gonza´lez Research Department, Universidad de Ciencias Me´dicas (UCIMED), San Jose´, Costa Rica D. W. Duszynski (&) Department of Biology, University of New Mexico, Albuquerque, NM 87131, USA e-mail: [email protected]
searching for the reservoirs of Leishmania spp., Trypanosoma cruzi Chagas, 1909 and Toxoplasma gondii Nicolle & Manceaux, 1908, we also examined the faeces of the wild rodents we caught for coccidian oo¨cysts. About 500 species of coccidia have been described from rodents to date (Duszynski et al., 2001, 2007) and within the subfamily Sigmodontinae (Rodentia: Cricetidae) there are 74 genera composed of 376 species (Musser & Carleton, 2005). To the best of our knowledge, prior to our work, coccidian species have been reported previously from only four of the genera in this subfamily (Akodon Meyen, Oryzomys Baird, Phyllotis Waterhouse and Sigmodon Say & Ord) and, in Costa Rica, eimerians are documented only in Sigmodon hispidus Say & Ord (see Castro et al., 1998; Rodrı´guez et al., 1999) and Melanomys caliginosus (Tomes) (Chinchilla et al., 2013). Thus, in our study of wild rodents, while looking for leishmaniosis and Chagas disease reservoirs and intestinal parasites, we sampled 24 additional M. caliginosus and a third species of Eimeria was discovered, that we describe herein and name as new.
Materials and methods Prior to collection, all necessary permits needed in Costa Rica for working with wild animals in the Reserva Biolo´gica Alberto Manuel Brenes (REBAMB) were obtained. All animals were collected in the protected REBAMB in San Ramo´n, Alajuela,
123
182
Costa Rica, and our collections were all non-invasive with the least possible damage to the animals and to the Reserve. Dusky rice rats were captured with handmade wooden traps which were set in the afternoon and collected early the following morning. Spontaneously eliminated faecal samples were collected and stored in individual tubes, transported to the laboratory, and studied using routine laboratory examination for the presence of parasites. After collecting the faeces, the animals were released at exactly the same place where they were captured. It should be noted that oo¨cysts were so plentiful in the faecal pellets that we did not need to use any concentration techniques. Conventional methods for preservation and description of these coccidia were used (Bandoni & Duszynski, 1988; Duszynski & Wilber, 1997). Faecal pellets were placed in 2.5% (w/v) aqueous potassium dichromate (K2Cr2O7) and, after sporulation, the oo¨cysts were examined with an Olympus BX41 microscope and photographed with an Olympus C60 ZOOM camera. Photosyntypes (Duszynski, 1999) of sporulated oo¨cysts of the new eimerian were submitted to the United States National Parasite Collection (USNPC) in Beltsville, Maryland, U.S.A. (see Bandoni & Duszynski, 1988). All measurements are given in micrometres as the range followed by the mean in parentheses.
Eimeria caliginosa n. sp. Type-host: Melanomys caliginosus (Tomes), dusky rice rat. Type-locality: Reserva Biolo´gica Alberto Manuel Brenes, 42 km NE of San Ramo´n, Alajuela, Costa Rica (10°130 4900 N, 84°360 1000 W; elevation 600-1,640 m, mean temperature 21 °C, relative humidity 98%, rainfall 3,461 mm/yr; see Sanchez, Sa´nchez, 2000). Type-material: Photosyntypes of sporulated oo¨cysts, IB-1-R-4, 5, are deposited in the Department of Parasitology Research, Universidad de Ciencias Me´dicas, San Jose´, Costa Rica, and in the USNPC (Accession No. 105608). Symbiotype host (see Frey et al., 1992), skin and skeleton, are deposited in the Museo Nacional de Costa Rica (adult male, MNCR No. 861). Prevalence: 12.5% (in 3 out of 24 hosts examined) Sporulation: Exogenous.
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Syst Parasitol (2014) 88:181–184
Fig. 1 Eimeria caliginosa n. sp. from Melanomys caliginosus in Costa Rica. A, Photomicrograph of a sporulated oo¨cyst; B, Line drawing of a sporulated oo¨cyst. Scale-bars: 3 lm
Site of infection: Unknown, oo¨cysts recovered from faeces. Pathology: Unknown, but none was observed in the three hosts examined and found to be discharging oo¨cysts. Etymology: The specific epithet is derived from the specific epithet of the host, M. caliginosus.
Description (Figs. 1A, B) Sporulated oo¨cyst Oo¨cyst (n = 25) spheroidal to slightly sub-spheroidal, 16–22 9 17–20 (19.6 9 18.2); length/width (L/W) ratio 1.1. Oo¨cyst wall bi-layered, c.2 thick; outer layer clear, smooth, c.2/3 of total wall thickness. Micropyle, oo¨cyst residuum and polar granule all absent.
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Table 1 Key quantitative and qualitative characters of sporulated oo¨cysts of species of Eimeria described from rodents in the Tribe Orizomini (Cricetidae). Abbreviations: L/W ratio; Length/Width ratio; OR, oo¨cyst residuum; PG, polar granule; SB, Stieda body; SR, sporocyst residuum; SSB, sub-Stieda body Species
Host
Oo¨cyst mean size (L/W ratio)
OR &/ or PG
Sporocyst mean size (L/W ratio)
SR, SB, SSB
E. couesii Krudienier, Levine & Ivens 1959
Oryzomys couesi (Alston)
21 9 18 (1.2)
? & ?a
12 9 8 (1.5)
?/2, ?, 2
E. kinsellai Barnard, Ernst & Roper 1971
O. palustris (Harlan)
27 9 17 (1.6)
2b & 1
14 9 8 (1.7)
?, ?, 2
E. ojasti Arcay-de-Peraza, 1964
O. albigularis (Tomes)
17 9 13 (1.3)
2&2
8 9 6 (1.3)
?, 2, 2
E. oryzomysi Carini, 1937
Oryzomys sp.
23 9 18 (1.3)
?&2
11 9 8 (1.4)
?, ?, 2
E. palustris Barnard, Ernst & Stevens 1971 E. melanomytis Chinchilla, Valerio, Sa´nches, Gonza´lez, Martinez & Duszynski, 2013
O. palustris (Harlan)
24 9 18 (1.3)
2&?
14 9 8 (1.7)
?, ?, 2
Melanomys caliginosus (Tomes)
20 9 13 (1.5)
2&?
11 9 7 (1.6)
?, ?, 2
E. rebambensis Chinchilla, Valerio, Sa´nches, Gonza´lez, Martinez & Duszynski, 2013
M. caliginosus (Tomes)
21 9 17 (1 3)
2&?
12 9 7 (1.7)
?, ?, ?
E. caliginosa n. sp.
M. caliginosus (Tomes)
20 9 18 (1.1)
2&2
11 9 7 (1.6)
?, ?, ?
a
Present;
b
Absent
Sporocyst and sporozoites Sporocyst ovoidal (n = 72), 9–13 9 6–8 (11.2 9 6.7); L/W ratio 1.5–1.6 (1.7). Stieda body present, as a small rounded extension of the sporocyst wall; subStieda body present, tiny; para-Stieda body absent; sporocyst residuum present as several large globules forming spheroidal mass c.5 wide. Sporozoites appear to have a homogeneous or finely granular cytoplasm, but refractile bodies and a nucleus are not visible. Remarks The genus Oryzomys (Cricetidae: Tribe Oryzomyini) is known to be the most closely related host genus to Melanomys Thomas (see Musser & Carleton, 2005). Thus, the metrical characteristics of the sporulated oo¨cysts of the new species are compared with the five eimerians (see Levine & Ivens, 1990) known from Oryzomys spp. as well as with Eimeria melanomytis Chinchilla, Valerio, Sa´nches, Gonza´lez, Martinez & Duszynski, 2013 and E. rebambensis Chinchilla, Valerio, Sa´nches, Gonza´lez, Martinez & Duszynski, 2013 recently described based on material from M. caliginosus (Table 1). The sporulated oo¨cysts of E. caliginosa n. sp. are similar in size to those of E.
couesii Krudienier, Levine & Ivens 1959 from Oryzomis couesi Alston (19.6 9 18.2 vs 21 9 18 lm) but differ in lacking both an oo¨cyst residuum and a polar granule, both present in E. couesii. The sporulated oo¨cysts of the new species are most similar to those of E. rebambensis, but differ in many ways; those of E. caliginosa are more spheroidal with a smaller L/W ratio (1.1 vs 1.3), they have a smooth outer wall, whereas those of E. rebambensis have a brown, striated outer wall, and the new species is slightly smaller (16–22 9 17–20 vs 19–23 9 14–18 lm; means 19.6 9 18.2 vs 21.2 9 17.0 lm); the oo¨cysts of E. caliginosa also lack a polar granule that is present in E. rebambensis. Oo¨cyst dimensions of all other eimerian species from these two host genera, Melanomys and Oryzomys, are distinctly different and have length/width indices that are all higher than in E. caliginosa. Thus, we believe the form we have described here is a new eimerian from the dusky rice rat. In Costa Rica, only a few species of Eimeria (i.e. E. sigmodontis Barnard, Ernst & Dixon, 1974, E. tuskegeensis Barnard, Ernst & Dixon, 1974, E roperi Barnard, Ernst & Dixon, 1974 and E. webbae Barnard, Ernst & Dixon, 1974) have been found in the cotton rat Sigmodon hispidus Say & Ord (see Castro et al., 1998;
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184
Rodrı´guez et al., 1999). Although both hosts may live in the same ecological niche, there are important differences in oo¨cyst morphology between the coccidia from these hosts. The animals examined by us were captured close to a house near the Biological Station, where these rice rats inhabit burrow systems and all probably eat the same food. Under these burrow conditions the oo¨cysts should be quite resistant to environmental factors and the communal living of the rats makes the transmission of oo¨cysts easier between them. It is likely that these environmental parameters help these rats become infected, even when the prevalence of this eimerian is lower (12.5%), compared with the high prevalence (89%) found for the other two eimerians from the same host species in nearly the same locality (Chinchilla et al., 2013). In surveys for Eimeria spp. in S. hispidus, carried out in a pineapple plantation where animals are more dispersed (Castro et al., 1998; Rodrı´guez et al., 1999), the prevalence of infections was always lower (e.g.,\28% for E. sigmodontis). Acknowledgements We thank Laura Valerio Jose Bolan˜os, Luis Gonzalez and Hugo Pe´rez for handling of the animals and logistic support. This work was partially funded by the Universidad de Ciencias Me´dicas (UCIMED), Ministerio de Ciencia y Tecnologı´a (MICIT), and Consejo Nacional de Ciencia y Tecnologı´a (CONICIT).
References Bandoni, S., & Duszynski, D. W. (1988). A plea for improved presentation of type material for coccidian. Journal of Parasitology, 74, 519–523.
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