Page 1
1
Human Sarcocystosis: Current Status on Epidemiology and Diagnosis 1
2
3
Casper Sahl Poulsen and Christen Rune Stensvold# 4
5
Laboratory of Parasitology, Department of Microbiology and Infection Control, Statens Serum 6
Institut, Copenhagen, Denmark. 7
8
Running Head: Diagnosis and Epidemiology of Human Sarcocystosis 9
10
#Address correspondence to Christen Rune Stensvold, [email protected] . 11
12
13
14
15
16
17
18
19
20
21
22
23
24
JCM Accepts, published online ahead of print on 23 April 2014J. Clin. Microbiol. doi:10.1128/JCM.00955-14Copyright © 2014, American Society for Microbiology. All Rights Reserved.
on May 21, 2018 by guest
http://jcm.asm
.org/D
ownloaded from
Page 2
2
ABSTRACT 25
Species of Sarcocystis are Apicomplexan parasites requiring intermediate and definitive hosts to 26
complete their life cycle. Humans are one of many natural host species and may serve as both 27
intermediate and definitive hosts. However, the extent and public health significance of human 28
Sarcocystis infection is incompletely known. In this minireview we provide an update on the 29
epidemiology and diagnosis of human sarcocystosis, and propose some tools that could contribute 30
to a better understanding of the clinical significance and epidemiology of Sarcocystis infections. 31
32
33
34
35
36
37
38
39
40
41
42
43
on May 21, 2018 by guest
http://jcm.asm
.org/D
ownloaded from
Page 3
3
Introduction 44
Humans are natural hosts of multiple Apicomplexan genera and usually serve as either the 45
intermediate (e.g. Toxoplasma, Plasmodium) or definitive (e.g. Cryptosporidium (monoxenous life 46
cycle)) host. Meanwhile, Sarcocystis comprises Apicomplexan species with a two host life cycle 47
including an intermediate host (prey) and definitive host (predator), and humans may be both 48
intermediate and definitive hosts for some of these species (1-3) (Fig 1). In definitive hosts, 49
Sarcocystis undergoes sexual reproduction in the intestinal epithelium and oocysts are subsequently 50
shed in host stool, while in intermediate hosts the parasite forms the so-called ‘sarcocysts’ in muscle 51
tissue of distinct types, including striated, cardiac and smooth muscle. At least two species exist 52
with humans as definitive hosts and hence potential causes of human intestinal sarcocystosis, 53
namely Sarcocystis hominis and Sarcocystis suihominis with cattle and pigs as intermediate hosts, 54
respectively. Humans can also be accidental intermediate hosts and develop muscular sarcocystosis. 55
The importance of muscular sarcocystosis in the farming industry is a well-documented problem. A 56
high prevalence of Sarcocystis infection is seen in cattle, pigs, and sheep in both developing and 57
industrialized countries. Infection with Sarcocystis in the intermediate host is known to cause 58
mortality, morbidity, abortions, lower meat yield and meat condemnation due to visible sarcocysts 59
(1, 2). Meanwhile, the extent and importance of human sarcocystosis remains less well described 60
despite muscular or intestinal sarcocystosis potentially afflicting a large number of people (3-6). 61
In this minireview a short introduction to Sarcocystis taxonomy has been included. A systematic 62
literature search has been performed on the prevalence of both intestinal and muscular sarcocystosis 63
in humans. Lastly, diagnostic methods and their limitations are summarized with suggestions for 64
development and application of molecular diagnostic tools to facilitate detection and a better 65
understanding of the epidemiology and clinical significance of human Sarcocystis infections. 66
on May 21, 2018 by guest
http://jcm.asm
.org/D
ownloaded from
Page 4
4
67
Taxonomy 68
The taxonomy of Sarcocystis was updated in 1998 by Odening (7) who included 189 species. Since 69
then the number of species has increased, owing in part to an expanding interest in Sarcocystis in 70
wildlife. The taxonomy of Sarcocystis is currently under revision; a common source of confusion 71
has been the classification of identical Sarcocystis species from intermediate and definitive hosts as 72
separate species. Traditionally, a new species of Sarcocystis is accepted when described in a new 73
intermediate or definitive host (8). Sarcocyst wall structure is utilized for species identification due 74
to the variability between Sarcocystis species (2); however, the wall structure is subject to change 75
depending on the age of the sarcocyst (3), and may so have limited applicability as a morphological 76
criterion. Molecular characterization combined with phenotypic description is critical to the 77
ongoing revision of species in the genus Sarcocystis and is useful to study Sarcocystis transmission 78
patterns in intermediate and definitive hosts, circumventing the need for expensive and laborious 79
experimental infections (9, 10). This has been employed to some extent and recently led to the 80
division of Sarcocystis in cervids into multiple species (10). 81
82
With the utilization of molecular methods for species identification there is a need for guidelines as 83
to what genes are useful for this purpose. Currently, the small subunit (SSU) rRNA, cox1 and ITS 84
genes are used for species identification (9, 10). There appears to be no guidelines, however, as to 85
the amount of genetic diversity necessary to separate species, and how to best analyse genetic 86
diversity in terms of genetic markers, amount of DNA sequence data needed (e.g. sequence read 87
length), and phylogenetic models. Currently, however, Maximum Parsimony analysis of cox1 data 88
appears to be the best possible method for delineation of closely related species, which may in part 89
on May 21, 2018 by guest
http://jcm.asm
.org/D
ownloaded from
Page 5
5
be due to the fact that cox1 DNA sequences are less difficult to align than SSU rDNA sequences 90
(10). 91
92
With molecular confirmation pending, it is unknown whether Sarcocystis species other than S. 93
hominis and S. suihominis can cause intestinal sarcocystosis (3). Until recently, the Sarcocystis 94
species causing muscular sarcocystosis in humans were unknown (3, 5). Recently, 18S ribosomal 95
DNA sequencing performed on a human muscle biopsy containing Sarcocystis identified the 96
species as Sarcocystis nesbitti (11). S. nesbitti has been described in muscle tissue of non-human 97
primates (NHP) implying that indeed NHP may serve as reservoir hosts for Sarcocystis species 98
causing muscular sarcocystosis in humans. 99
100
Epidemiology and clinical significance 101
Natural enteric infections with S. hominis and S. suihominis are described mostly as asymptomatic 102
(4, 12, 13), although Yu (14) reported that 10% of infected individuals had symptoms associated 103
with Sarcocystis infection. Meanwhile, experimental infections have been associated with 104
gastroenteritis and eosinophilia (2, 3, 15, 16). 105
The prevalence of intestinal Sarcocystis infection in humans has been estimated to be between 1.1% 106
- 10.4% in Europe, between 0.4% - 23.2% in Asia, 0.5% in Australia, and 0% in Argentina (Table 107
1). In general, caution must be taken when comparing prevalence figures reported in these studies 108
due to the differences in diagnostic approaches. In addition, population bias may have been inferred 109
since individuals in the study groups were not selected randomly from the population. A relatively 110
high prevalence is observed in most of the studies indicating that a large population is infected but 111
there is a need for further studies to confirm this. There is tendency of recent studies reporting lower 112
prevalence figures compared to those reported in older studies (Table 1). 113
on May 21, 2018 by guest
http://jcm.asm
.org/D
ownloaded from
Page 6
6
Potential geographical variation in the prevalence of intestinal sarcocystosis is difficult to assess 114
due to many of the prevalence studies not being available in English and so the methodology cannot 115
be evaluated systematically. 116
Recent prevalence studies based on morphology and molecular data on S. hominis in cattle revealed 117
that the occurrence of S. hominis is rather common with a prevalence of 6.2% - 97.4% (17-19), 118
53.5% (20), and 94% (16) in Europe, Asia, and South America, respectively. However, no cases of 119
S. hominis were observed in a study from North America (21). Data on the prevalence of S. 120
suihominis is scarce compared to S. hominis, and so recent prevalence studies estimating the 121
prevalence of S. suihominis in pigs appear not to be available. Again it should be emphasized that 122
studies vary with regard to the type of sample (processed or unprocessed meat for instance), type of 123
muscle tissue examined, animal age, and number of samples analyzed. The fact that S. hominis or S. 124
suihominis are regularly detected in intermediate hosts means that humans must be infected with 125
these parasites. 126
Possible risk factors associated with acquiring intestinal Sarcosystis infection include eating raw or 127
undercooked beef and pork and unsanitary disposal of human feces that can infect the intermediate 128
host and maintain the life cycle of Sarcocystis species causing intestinal sarcocystosis in humans 129
(4). 130
Symptoms of muscular sarcosystosis include acute fever, myalgias, myositis, vasculitis, 131
bronchospasm, and pruritic rashes (3, 5, 6, 22, 23). Muscular sarcocystosis has also been associated 132
with non-specific rheumatic diseases associated with myositis (24). No experimental infection 133
experiments have been performed with humans as intermediate hosts to the knowledge of the 134
authors. 135
Treatment with albendazole alone or in combination with prednisone may lead to improvement in 136
some cases (6, 22). However, as with intestinal sarcocystosis, there are currently no 137
on May 21, 2018 by guest
http://jcm.asm
.org/D
ownloaded from
Page 7
7
recommendations regarding treatment of muscular sarcocystosis despite the severity in some cases 138
mainly due to lack of experience (3, 5). 139
The prevalence of muscular sarcocystosis in humans has been estimated to range between 0% - 140
3.6% in western countries and 21% in Malaysia from post mortem examination (Table 1). The high 141
prevalence in Malaysia compared with western countries is likely due to NHPs being common in 142
Malaysia and humans can serve as intermediate host for Sarcocystis species found in NHPs (25). 143
Serological methods such as ELISA and indirect fluorescent antibody tests (IFAT) have also been 144
used to estimate the seroprevalence in Australia, former Social Federal Republic of Yugoslavia, and 145
Malaysia, producing seroprevalence figures of 34%, 22.5% - 44.4%, and 19.7%, respectively (Table 146
1) (26-28). The discrepancy between the higher prevalences observed in serological studies 147
compared with direct detection in post mortem studies might be explained by a low diagnostic 148
sensitivity of direct detection, and/or a low diagnostic specificity of serology. Another explanation 149
could be persistence of a serological response after clearance of infection. There is a need for 150
further studies to clarify this. 151
In 2004, Fayer (3) calculated the total number of muscular sarcocystosis cases described to be 92, 152
but that many cases were probably unreported. Recently, the largest outbreak of human muscular 153
sarcocystosis with 100 people infected has been investigated on Tioman Island, Malaysia (5). The 154
outbreak has received attention due to the severity of disease and since infected individuals were 155
almost exclusively European tourists (5, 6). Also supported by the prevalence studies in Malaysia 156
(26, 29) this indicates that the indigenous population is at substantial risk of contracting disease. In 157
addition, an outbreak of muscular sarcocystosis was observed in 89 Malayan college students that 158
visited Pangkor Island (23). 159
on May 21, 2018 by guest
http://jcm.asm
.org/D
ownloaded from
Page 8
8
Little is known about the risk factors associated with acquiring muscular sarcocystosis. Humans are 160
most likely infected consuming water or food contaminated with oocysts/sporocysts from definitive 161
hosts (5, 6). 162
163
Diagnosis of intestinal sarcocystosis 164
A suspicion of intestinal sarcocystosis may be based on a history of gastroenteritis combined with 165
habits of eating raw or undercooked meat that might contain infective Sarcocystis. The ‘diagnostic 166
window’ is limited to the time of oocyst/sporocyst excretion. The pre-patent period for S. hominis 167
and S. suihominis is 14-18 days and 11-13 days, respectively, and oocyst/sporocyst excretion can 168
last for at least one month (1-3). Importantly, this may imply that Sarcocystis may not be shed in 169
feces in the acute stage of intestinal infection. 170
Methods for coprological examination include different flotation techniques (2, 3), modified Kato 171
thick smear, formalin-ether technique, and direct smear (30). The sensitivity of these methods is to a 172
large extent unknown due the lack of studies addressing this specifically, but it should be possible 173
to determine sensitivity by spiking samples with known amounts of oocysts/sporocysts. In animals, 174
intestinal Sarcocystis infection is often detected post mortem by examination of mucosal scrapings 175
rather than stool due to light fecal shedding (8). 176
Oocysts of S. suihominis measure 12.3—14.6 µm by 18.5—20.0 µm; less detailed information is 177
available for oocysts of S. hominis, which may measure 20—23 µm in diameter. Sporocysts of S. 178
hominis average 9.3 by 14.7 µm and those of S. suihominis average 10.5 by 13.5 µm (3, 31). Both 179
oocysts and sporocysts may be seen in faceal samples from definitive hosts; the oocyst wall may be 180
difficult to discern (Fig 2), but the use of stains such as periodic acid-Schiff may enable its 181
detection. Given the shape and size of the oocysts and sporocysts there should be little risk of 182
on May 21, 2018 by guest
http://jcm.asm
.org/D
ownloaded from
Page 9
9
confusing them with oocysts of Cryptosporidium, Cyclospora, and Cystoisospora. Still, a number 183
of predicaments may impede our ability to detect Sarcocystis in human fecal samples based on 184
traditional parasitological methods and conventional reasoning. The relatively long pre-patent 185
period has already been high-lighted and it is reasonable to believe that sometimes fecal samples are 186
being analyzed from patients with gastroenteritis before oocyst shedding commences. Moreover, 187
oocysts/sporocysts do not consistently take up acid-fast stain (Fig 2), and so they may be missed by 188
Ziehl-Neelsen staining commonly used for traditional parasitological detection of Apicomplexan 189
parasites in stool. Moreover, in a recent study we showed that none of 16/889 fecal samples positive 190
for Cryptosporidium by real-time PCR were positive by Ziehl-Neelsen staining, which was 191
probably due to the presence of only light infections, evidenced by high Ct-values (32). Since fecal 192
shedding of Sarcocystis is presumably usually light, the parasite may therefore easily be overlooked 193
in Ziehl-Neelsen preparations, and given the variability in uptake of acid-fast stain, the Ziehl-194
Neelsen method should not be recommended for detecting Sarcocystis. 195
To detect Sarcocystis in stool, a DNA detection based approach therefore appears relevant. Real-196
time PCR assays have been published for several intestinal protozoa, but so far, none has been 197
published for Sarcocystis. This may be due to a variety of reasons. Generally, if laboratory methods 198
fail to enable detection of a given parasite, the parasite will probably be thought of as rare, and so 199
the incentive to develop DNA-based methods for its detection may remain low. More specifically, 200
conserved regions of the small subunit (SSU) rRNA gene across the Sarcocystis genus may be so 201
genetically similar to those found in competing template in fecal genomic DNA that the 202
applicability of this marker in genus-specific PCR analyses performed on DNA extracted directly 203
from feces is reduced due to decreased PCR specificity and sensitivity. Nevertheless, the first 204
molecular diagnostic assay to diagnose DNA of oocysts/sporocysts of Sarcocystis in fecal samples 205
was developed only recently. The described method included semi-nested amplification of the SSU 206
on May 21, 2018 by guest
http://jcm.asm
.org/D
ownloaded from
Page 10
10
rRNA gene with subsequent RFLP analysis, making species differentiation possible in cattle (33). 207
The primers target conserved regions; however, the forward primer ‘18s 2L’ given in the paper by 208
Xiang et al. (33) and used in both first and second PCR reactions reads 5’-209
GGATAAACCGTGGTAATTCTATG-3’, while the SSU rDNA template reads 5’-210
GGATAACCGTGGTAATTCTATG-3’. The two primer combinations used in the nested PCR 211
appear relatively non-specific, and in silico analysis suggests that they may amplify a variety of 212
Apicomplexan parasites. A different gene target, cytochrome oxidase 1 (cox1), exhibits extensive 213
genetic diversity and can be used to discriminate between even closely related species of 214
Sarcocystis (10). Unfortunately, cox1 DNA sequences are unavailable for the two species 215
commonly thought to be involved in human sarcocystosis, namely S. hominis and S. suihominis. 216
Once available, and given the amount of sequence data in GenBank available for multiple species of 217
Sarcocystis, it should be possible to develop diagnostic species- and group-specific PCRs based on 218
the cox1 gene in a real-time or nested PCR format to increase sensitivity. Relevant pre-treatment of 219
fecal samples could include purification and concentration of oocysts using gradient (zink sulfate, 220
sodium chloride, sucrose, etc.) methods, inherently increasing chances of detecting other single-221
celled parasites of similar densities as well, with subsequent microscopy and DNA extraction of the 222
meniscus. At present, nearly full-length SSU rDNA sequences (~1.9 kbp) and partial cox1 223
sequences (~1.0 kbp) of about 40 and at least 20 Sarcocystis species, respectively, are available 224
(10), potentially facilitating the design of relevant primers and probes for conventional or 225
quantitative PCR-based detection of oocysts/sporocysts in feces. 226
227
Diagnosis of muscular sarcocystosis 228
Muscular sarcocystosis is suspected when compatible symptoms are present and especially if 229
traveling to places where native wildlife includes NHPs has occurred. The identification of 230
on May 21, 2018 by guest
http://jcm.asm
.org/D
ownloaded from
Page 11
11
sarcocysts in muscle is considered the sole definitive diagnostic criterion (5). It is, however, rarely 231
possible to obtain a biopsy specimen containing sarcocysts both due to issues related to obtaining 232
consent from the infected individual and the low chance of retrieving a specimen that contains 233
sarcocysts. 234
ELISA and IFAT methods are used in serodiagnosis of muscular sarcocystosis (24, 34). There is no 235
reporting of cross-reactivity with e.g. Toxoplasma, indicating that methods in use have a high 236
specificity (34). One IFAT method showed complete agreement with morphological examination of 237
freshly slaughtered cattle (35). Similar prevalence figures in humans were also obtained in 238
Malaysia, where Wong & Pathmanathan (29) used microscopy to examine tongue tissue while 239
Thomas & Dissanaike (26) used IFAT reporting a prevalence of 21% and 19.7%, respectively. 240
However, the two studies were performed on two different groups of people. Ideally, ELISA and 241
IFAT methods should not be able to detect intestinal sarcocystosis and classify it as muscular 242
sarcocystosis (34); however, the high prevalence figures observed in the former Socialist Federal 243
Republic of Yugoslavia and Australia where no species of NHP is autochthonous indicate that this 244
may not be the case (28, 36). A Western Blot analysis for the confirmation of muscular 245
sarcocystosis is currently under development (5). 246
An inherent problem with the utilization of antibodies as principle of diagnosis is the lack of 247
differentiation between early and late stage infection (37). In humans this is of particular 248
importance in relation to development and clearance of sarcocysts. In animals, an ELISA assay 249
enabled detection of IgM in acute phase infections in mice and sheep; however, in pigs the IgG 250
response was detected earlier in infection compared to IgM (38). No data on IgM development in 251
humans are available. A different approach to detecting acute muscular sarcocystosis using nested 252
PCR on blood samples containing circulating merozoites has been developed for testing in sheep 253
(37). Molecular studies are warranted to identify the species that can cause muscular sarcocystosis 254
on May 21, 2018 by guest
http://jcm.asm
.org/D
ownloaded from
Page 12
12
to be able to make epidemiological inferences that can be used to assess the extent and importance 255
of human muscular sarcocystosis plus modes of transmission. 256
257
Concluding remarks 258
Diagnostic limitations have impeded our ability to increase our understanding of the epidemiology 259
and public health significance of Sarcosystis infections in humans. Due to light shedding, PCR-260
based methods for detection of DNA from oocysts/sporocysts in feces appear relevant and multiple 261
species of Sarcocystis have now been molecularly characterized, and available sequence data 262
should greatly enhance possibilities for development of relevant diagnostic PCR assays and assays 263
serving to map host specificity and transmission modes. Meanwhile, direct detection of the parasite 264
in cases of human muscular sarcocystosis is hampered by the apparent absence of a predilection 265
site, and so indirect detection by serological methods is preferred over testing of tissue biopsies. 266
267
268
269
270
271
on May 21, 2018 by guest
http://jcm.asm
.org/D
ownloaded from
Page 13
13
Legends to figures 272
FIG 1: Life cycle of Sarcocystis. Intermediate hosts ingest oocysts/sporocysts which release 273
sporozoites (A) that enter endothelial cells (B) with a varied number of merogony generations 274
eventually releasing merozoites. In muscle cells (myocytes), and inside a parasitophorous vacuole, 275
merozoites develop into sarcocysts containing infective bradyzoites (1 and C). Definitive hosts 276
ingest meat containing infectious sarcocysts (1 and C) which in turn release the bradyzoites that 277
invade gut epithelial cells and perform gametogony in the lamina propria or goblet cells producing 278
micro- and macro gametes (E). The gametes fuse and develop into oocysts (F and 2). 279
Oocysts/sporocysts are excreted in feces and may be distributed in water and food potentially 280
immediately infectious for the intermediate host (G and 3). 281
282
FIG 2: Sarcocystis oocysts in a Ziehl-Neelsen preparation; two sporocysts are seen in each oocyst. 283
Note that only one of the two oocysts has taken up stain. 284 on May 21, 2018 by guest
http://jcm.asm
.org/D
ownloaded from
Page 14
14
Table 1: Prevalence data of intestinal and muscular sarcocystosis in humans. Reference Country and study group Prevalence / % (Number
examined) Method
Intestinal sarcocystosis (39)
Poland
10.4 (125) Kato-Miur
(13) France S. hominis: 2.0 (3500) S. suihominis: 0.7 (700)
Ether treatment followed by flotation
(40) Germany, routine fecal samples from hospitals and clinics from patients with intestinal complaints
2 (403) Modified hematoxilin dye, Kato and sodium-nitrate flotation
(14) Tibet in 3 counties S. hominis: 20.5, 22.5 & 22.9 (926) S. suihominis: 0, 0.6 & 7.0 (926)
Zinc sulfate flotation
(41) Laos 7.9 (767) Kato-Katz & Merthiolate-Iodine-Formaldehyde concentration
(12) Central Slovakia, workers from Vietnam
1.1 (1228) Fecal smear
(42)
Western Australia, Aboriginal communities
0.5 (385) Direct microscopy
(4)
Thailand, Thai labourers 23.2 (362) Formalin-ether concentration
(43)
Argentina, children 0 (69) Modified Telemann and the Fülleborn methods
on May 21, 2018 by guest
http://jcm.asm
.org/D
ownloaded from
Page 15
15
(30) Thailand, rural communities 7.0 (1603) Kato thick smear & direct smear
(44) Northeast Thailand, rural communities 0.4 (253) Formalin-ethyl acetate
Muscular sarcocystosis (45) USA, California, autopsy samples 0 (297) Pepsin digestion, sieved and
centrifuged followed by microscopical examination
(26) Malaysia, blood samples from blood donors
19.7 (243) IFAT, 1:64 sera dilution considered positive
(28)
Yugoslavia, blood samples obtained from cases suspected to be infected with T. gondii
44.4 (341) IFAT, 1:40 sera dilution
(46) Denmark, autopsy samples 3.6 (112) Trichinoscopical examination of crus diaphragmatica
(27) Australia, blood samples
34 (50) ELISA
(29) Malaysia, autopsy samples 21 (100) Examination of formalin-fixed, paraffin embedded sections of tongue tissues
(47) Australia, Sydney, autopsy samples 0 (50) Two methods. 1: Examination of formalin-fixed, paraffin embedded sections from the psoas and diaphragm. 2: Pepsin digestion, sieved and centrifuged followed by microscopical examination.
on May 21, 2018 by guest
http://jcm.asm
.org/D
ownloaded from
Page 16
16
(48) Northern Ireland, autopsy samples 0 (50) Examination of formalin-fixed, paraffin embedded sections of tongue and diaphragm tissues
285
on May 21, 2018 by guest
http://jcm.asm
.org/D
ownloaded from
Page 17
17
References 286
287
1. Markus MB. 1978. Sarcocystis and sarcocystosis in domestic animals and man. Adv. Vet. 288
Sci. Comp. Med. 22:159-193. 289
2. Dubey JP, Speer CA, Fayer R. 1989. Sarcocystosis of Animals and Man. CRC Press, Inc., 290
Boca Raton, Florida. 291
3. Fayer R. 2004. Sarcocystis spp. in human infections. Clin. Microbiol. Rev. 17:894-902. 292
4. Wilairatana P, Radomyos P, Radomyos B, Phraevanich R, Plooksawasdi W, 293
Chanthavanich P, Viravan C, Looareesuwan S. 1996. Intestinal sarcocystosis in Thai 294
laborers. Southeast Asian J. Trop. Med. Public Health 27:43-46. 295
5. Esposito DH, Freedman DO, Neumayr A, Parola P. 2012. Ongoing outbreak of an acute 296
muscular Sarcocystis-like illness among travellers returning from Tioman Island, Malaysia, 297
2011-2012. Euro Surveill. 17. 298
6. Tappe D, Ernestus K, Rauthe S, Schoen C, Frosch M, Müller A, Stich A. 2013. Initial 299
patient cluster and first positive biopsy findings in an outbreak of acute muscular 300
Sarcocystis-like infection in travelers returning from Tioman island, Peninsular Malaysia, in 301
2011. J. Clin. Microbiol. 51:725-726. 302
7. Odening K. 1998. The present state of species-systematics in Sarcocystis Lankester, 1882 303
(Protista, Sporozoa, Coccidia). Systematic Parasitology 41:209-233. 304
8. Heckeroth A, R., Tenter A, M. 2007. Sarcocystiosis, p. 172-232. In Ortega-Mora LM, 305
Gottstein B, Conraths FJ, Buxton D (ed.), Protozoal Abortion in Farm Ruminants. 306
www.cabi.org, UK, Gateshead. 307
9. Stojecki K, Karamon J, Sroka J, Cencek T. 2012. Molecular diagnostics of Sarcocystis 308
spp. infections. Pol. J. Vet. Sci. 15:589-596. 309
on May 21, 2018 by guest
http://jcm.asm
.org/D
ownloaded from
Page 18
18
10. Gjerde B. 2013. Phylogenetic relationships among Sarcocystis species in cervids, cattle and 310
sheep inferred from the mitochondrial cytochrome c oxidase subunit I gene. Int. J. Parasitol. 311
43:579-591. 312
11. Lau YL, Chang PY, Tan CT, Fong MY, Mahmud R, Wong KT. 2014. Sarcocystis 313
nesbitti infection in human skeletal muscle: possible transmission from snakes. Am. J. Trop. 314
Med. Hyg. 90:361-364. 315
12. Straka S, Skraciková J, Konvit I, Szilágyiová M, Michal L. 1991. [Sarcocystis species in 316
Vietnamese workers]. Cesk. Epidemiol. Mikrobiol. Imunol. 40:204-208. 317
13. Deluol AM, Mechali D, Cenac J, Savel J, Coulaud JP. 1980. [Incidence and clinical 318
aspects of intestinal coccidiosis in a tropical medicine practice]. Bull. Soc. Pathol. Exot. 319
Filiales 73:259-265. 320
14. Yu S. 1991. [Field survey of Sarcocystis infection in the Tibet autonomous region]. 321
Zhongguo Yi Xue Ke Xue Yuan Xue Bao 13:29-32. 322
15. Chen X, Zuo Y, Zuo W. 1999. [Observation on the clinical symptoms and sporocyst 323
excretion in human volunteers experimentally infected with Sarcocystis hominis]. Zhongguo 324
Ji Sheng Chong Xue Yu Ji Sheng Chong Bing Za Zhi 17:25-27. 325
16. Pena HF, Ogassawara S, Sinhorini IL. 2001. Occurrence of cattle Sarcocystis species in 326
raw kibbe from Arabian food establishments in the city of São Paulo, Brazil, and 327
experimental transmission to humans. J. Parasitol. 87:1459-1465. 328
17. Moré G, Pantchev A, Skuballa J, Langenmayer MC, Maksimov P, Conraths FJ, 329
Venturini MC, Schares G. 2014. Sarcocystis sinensis is the most prevalent thick-walled 330
Sarcocystis species in beef on sale for consumers in Germany. Parasitol. Res. (In press). 331
18. Domenis L, Peletto S, Sacchi L, Clementi E, Genchi M, Felisari L, Felisari C, Mo P, 332
Modesto P, Zuccon F, Campanella C, Maurella C, Guidetti C, Acutis PL. 2011. 333
on May 21, 2018 by guest
http://jcm.asm
.org/D
ownloaded from
Page 19
19
Detection of a morphogenetically novel Sarcocystis hominis-like in the context of a 334
prevalence study in semi-intensively bred cattle in Italy. Parasitol. Res. 109:1677-1687. 335
19. Vangeel L, Houf K, Chiers K, Vercruysse J, D'Herde K, Ducatelle R. 2007. Molecular-336
based identification of Sarcocystis hominis in Belgian minced beef. J. Food Prot. 70:1523-337
1526. 338
20. Jehle C, Dinkel A, Sander A, Morent M, Romig T, Luc PV, De TV, Thai VV, 339
Mackenstedt U. 2009. Diagnosis of Sarcocystis spp. in cattle (Bos taurus) and water 340
buffalo (Bubalus bubalis) in Northern Vietnam. Vet. Parasitol. 166:314-320. 341
21. Pritt B, Trainer T, Simmons-Arnold L, Evans M, Dunams D, Rosenthal BM. 2008. 342
Detection of sarcocystis parasites in retail beef: a regional survey combining histological 343
and genetic detection methods. J. Food Prot. 71:2144-2147. 344
22. Arness MK, Brown JD, Dubey JP, Neafie RC, Granstrom DE. 1999. An outbreak of 345
acute eosinophilic myositis attributed to human Sarcocystis parasitism. Am. J. Trop. Med. 346
Hyg. 61:548-553. 347
23. Abubakar S, Teoh BT, Sam SS, Chang LY, Johari J, Hooi PS, Lakhbeer-Singh HK, 348
Italiano CM, Omar SF, Wong KT, Ramli N, Tan CT. 2013. Outbreak of human infection 349
with Sarcocystis nesbitti, Malaysia, 2012. Emerg. Infect. Dis. 19:1989-1991. 350
24. Abdul-Rahman SM, Rashad SM, Doma MA. 2002. Human muscle sarcocystosis in 351
relation to non-specific rheumatic diseases and rheumatoid arthritis. Egypt. Rheumatol. 352
Rehab. 29:743-753. 353
25. Dissanaike AS. 1994. Human Sarcocystis infection. Trans. R. Soc. Trop. Med. Hyg. 354
88:364. 355
26. Thomas V, Dissanaike AS. 1978. Antibodies to Sarcocystis in Malaysians. Trans. R. Soc. 356
Trop. Med. Hyg. 72:303-306. 357
on May 21, 2018 by guest
http://jcm.asm
.org/D
ownloaded from
Page 20
20
27. Murrell TG, O'Donoghue PJ, Ellis T. 1986. A review of the sheep-multiple sclerosis 358
connection. Med. Hypotheses 19:27-39. 359
28. Sibalic D, Bordoski A, Conic V, Durkovic-Dakovic O. 1983. A study of Toxoplasma 360
gondii and Sarcocystis sp. infections in humans suspected of acquired toxoplasmosis. Acta 361
Vet. Yugoslav. 33:39-48. 362
29. Wong KT, Pathmanathan R. 1992. High prevalence of human skeletal muscle 363
sarcocystosis in south-east Asia. Trans. R. Soc. Trop. Med. Hyg. 86:631-632. 364
30. Tungtrongchitr A, Chiworaporn C, Praewanich R, Radomyos P, Boitano JJ. 2007. The 365
potential usefulness of the modified Kato thick smear technique in the detection of intestinal 366
sarcocystosis during field surveys. Southeast Asian J. Trop. Med. Public Health 38:232-238. 367
31. Bunyaratvej S, Bunyawongwiroj P, Nitiyanant P. 1982. Human intestinal 368
sarcosporidiosis: report of six cases. Am. J. Trop. Med. Hyg. 31:36-41. 369
32. Stensvold CR, Nielsen HV. 2012. Comparison of microscopy and PCR for detection of 370
intestinal parasites in Danish patients supports an incentive for molecular screening 371
platforms. J. Clin. Microbiol. 50:540-541. 372
33. Xiang Z, Chen X, Yang L, He Y, Jiang R, Rosenthal BM, Luan P, Attwood SW, Zuo Y, 373
Zhang YP, Yang Z. 2009. Non-invasive methods for identifying oocysts of Sarcocystis 374
spp. from definitive hosts. Parasitol. Int. 58:293-296. 375
34. Habeeb YSM, Selim MA, Ali MS, Mahmoud LA, Hadi AMA, Shafei A. 1996. 376
Serological diagnosis of extraintestinal sarcocystosis. J. Egypt. Soc. Parasitol. 26:393-400. 377
35. Moré G, Abrahamovich P, Jurado S, Bacigalupe D, Marin JC, Rambeaud M, 378
Venturini L, Venturini MC. 2011. Prevalence of Sarcocystis spp. in Argentinean cattle. 379
Vet. Parasitol. 177:162-165. 380
on May 21, 2018 by guest
http://jcm.asm
.org/D
ownloaded from
Page 21
21
36. Pamphlett R, O'Donoghue P. 1992. Antibodies against Sarcocystis and Toxoplasma in 381
humans with the chronic fatigue syndrome. Aust. N. Z. J. Med. 22:307-308. 382
37. Heckeroth AR, Tenter AM. 1999. Development and validation of species-specific nested 383
PCRs for diagnosis of acute sarcocystiosis in sheep. Int. J. Parasitol. 29:1331-1349. 384
38. O'Donoghue PJ, Weyreter H. 1984. Examinations on the serodiagnosis of Sarcocystis 385
infections. II. Class-specific immunoglobulin responses in mice, pigs, and sheep. Zentralbl. 386
Bakteriol. Mikrobiol. Hyg. A 257:168-184. 387
39. Plotkowiak J. 1976. The results of continued investigations on the occurrence and 388
epidemiology of Isospora hominis (Railliet and Lucet, 1891) invasion. Ann. Parasitol. 389
22:137-147. 390
40. Gauert B, Jungmann R, Hiepe T. 1983. Relationship between intestinal disturbances and 391
infections with intestinal parasites in man, with particular reference to Sarcocystis 392
infections. Deutsch. Gesundheitsw. 38:62-66. 393
41. Giboda M, Ditrich O, Scholz T, Viengsay T, Bouaphanh S. 1991. Current status of food-394
borne parasitic zoonoses in Laos. Southeast Asian J. Trop. Med. Public Health 22 Suppl:56-395
61. 396
42. Meloni BP, Thompson RC, Hopkins RM, Reynoldson JA, Gracey M. 1993. The 397
prevalence of Giardia and other intestinal parasites in children, dogs and cats from 398
aboriginal communities in the Kimberley. Med. J. Aust. 158:157-159. 399
43. Soriano SV, Barbieri LM, Pierángeli NB, Giayetto AL, Manacorda AM, Castronovo E, 400
Pezzani BC, Minvielle M, Basualdo JA. 2001. Intestinal parasites and the environment: 401
frequency of intestinal parasites in children of Neuquén, Patagonia, Argentina. Rev. 402
Latinoam. Microbiol. 43:96-101. 403
on May 21, 2018 by guest
http://jcm.asm
.org/D
ownloaded from
Page 22
22
44. Boonjaraspinyo S, Boonmars T, Kaewsamut B, Ekobol N, Laummaunwai P, 404
Aukkanimart R, Wonkchalee N, Juasook A, Sriraj P. 2013. A cross-sectional study on 405
intestinal parasitic infections in rural communities, northeast Thailand. Korean J. Parasitol. 406
51:727-734. 407
45. Theis JH, Ikeda RM, Ruddell CR, Tay S. 1978. Apparent absence of Sarcocystis and low 408
prevalence of Trichinella in artificially digested diaphragm muscle removed during post-409
mortem examination at a Sacramento (California) medical center. Am. J. Trop. Med. Hyg. 410
27:837-839. 411
46. Greve E. 1985. Sarcosporidiosis--an overlooked zoonosis. Man as intermediate and final 412
host. Dan. Med. Bull. 32:228-230. 413
47. Troedsen C, Pamphlett R, Collins H. 1992. Is sarcocystosis common in Sydney? Med. J. 414
Aust. 156:136. 415
48. Wong KT, Leggett PF, Heatley M. 1993. Apparent absence of Sarcocystis infection in 416
human tongue and diaphragm in Northern Ireland. Trans. R. Soc. Trop. Med. Hyg. 87:496. 417
418
419
on May 21, 2018 by guest
http://jcm.asm
.org/D
ownloaded from
Page 23
������ � on M
ay 21, 2018 by guesthttp://jcm
.asm.org/
Dow
nloaded from
Page 24
on May 21, 2018 by guest
http://jcm.asm
.org/D
ownloaded from
