Human sarcocystisJA Thomas
Department of Pathology, St. John's Medical College, Bangalore-560034, India
The nineteenth authenticated report of human sarcocpstis is made and all available literature reviewed on the subject.
Miescher  in 1843 for the first time described a peculiar parasite of mouse skeletal muscle, which came to be called "Sarcocystis".  These organisms were later, however, not only found to parasitise mice but also other mammals, birds and reptiles.
The first human case observed, was described by Lindemannl  in 1868 and in 1898, this parasite was named "Sarcocystis lindemanni", by Rivolta,  in honour of its discoverer. Several cases were subsequently published by Leuekart,  Koch and Gaffky,  Rosenberg  and Kartulis.  Babudeiere  and Kean and Grocott  believed that these reports, including that of Lindemann's, were doubtful, incorrect or lacked sufficient data for review. Thus, the first authenticated case involving Man and Sarcocystis lindemanni, was published only in 1894 by Baraban and Saint-Remy.  This report was followed by seventeen others, in the next 82 years. ,,,,,,,,,,,,,,,,,
The case presented here is the nineteenth and differs in some respects from those already published. An evaluation with comparisons of all available data, is presented in [Table 1].
A 54 year old Hindu vegetarian female, belonging to the middle-income-group complained of dull aching pain in both lower limbs of four months duration. She also complained of difficulty in walking and standing up. There was no history of a burning sensation over the lower limbs, no intermittent claudication or hypoasthesia. Her personal and family histories were noncontributory.
General physical examination of the systems showed no significant deviation from normal. Local examination of both lower limbs showed bilateral pedal oedema, with marked tenderness over the bellies of the left gastrocnemius muscle. A hard mass was palpable in the bulk of this muscle mass and measured 2.5 x 3 cms in area. The sensory and motor components of this limb and the other lower limb appeared normal.
Routine laboratory investigations were all within normal limits, The stool examination in particular showed neither ova nor cysts.
A biopsy of the hard mass in the left gastrocnemius muscle was done.
The specimen received by this department consisted of three pieces of white fibromuscular tissue, the largest piece of which measured 2.5 cms in greatest dimension.
One of the pieces was felt gritty on cutting.
Several sections from these tissues were examined and showed many skeletal muscle bundles. These bundles were however, widely dispersed and had interposed between them large tracts of collagenous tissue which showed evidence of heterotopic ossification See [Figure 1] on page 184B and evidence also of small islands of embryonic-type cartilage. A few thick-and-thin-walled blood vessels were scattered here and there. The Alcian-Blue Periodic-Acid Schiff Reaction (AB-PAS) showed Alcian Blue positivity in the collagenous tissue, especially around the areas of heterotopic ossification.
Examination of the skeletal muscle fibres of the widely dispersed bundles showed evidence of wide variation in size with evidence of atrophy, fragmentation and vacuolation See [Figure 2] on page 184B. Some of the vacuolated muscle fibres showed PAS-positive granules within which were rounded structures that measured about two microns in greatest dimension. Most of the fibres appeared moderately PAS-positive and showed cross striations with the Phosphotungstic -Acid-Hematoxylin (PTAH) stain. Many of the fragmented and vacuolated skeletal muscle fibres did not show such cross striations, with the PTAH stain.
One skeletal muscle fibre contained a cyst See [Figure 3] on page 184B. This cyst measured, on an average estimation on several consecutive 5 micron sections, 91 x 243 microns in cross-section and exhibited a capsule that was 0.5 to one micron in thickness, was pink with the Haematoxylin-Eosin stain, nonstriated with the PTAH stains, PAS-negative and separate from the sacrolemmal sheath of the involved skeletal muscle fibre See [Figure 4] on page 184B. No septae were seen. It was not possible to assess the ,length of the cyst. Within the cyst numerous interweaving bundles of vaguely sickleshaped organisms were seen, measuring on an average 7.3 x 1.25 microns. These organisms had PAS positive granules, at both poles, which were better visualized with the Iron-Haematoxylin stain. The involved skeletal muscle fibre showed patchy PAS positivity and showed crossstriations with the PTAH stain.
Although scattered aggregates of lymphocytes and plasma cells were seen around small blood vessels, no inflammation was seen involving the affected skeletal muscle fibre.
Precipitin reactions were attempted using the patient's serum and homogenates of animal sarcocystis. They were not positive.
The patient was discharged, on the fourth postoperative day, her condition remaining unchanged.
Markus, Killick-Kendrick and Garnham  have attempted to establish the life cycle of Sarcocystis. These authors believed that two vertebrate hosts were required by the parasite and was essential for the completion of its life cycle. The sporocysts were excreted by Man, dog, or cat ("predators") in the faeces which when ingested by a bovine ("prey") developed asexually into merozoites that later became sarcocysts containing cystozoites. The "predators", on ingesting the infected bovine meat, developed male and female gametocytes in the intestinal epithelium. By the fifth day, isosporon oocysts were formed and escaped into the faeces, but being fragile, ruptured giving rise to sporocysts.
In the nineteen reports documenting human infections, in the last 82 years, Man has acted as the "prey". It is, therefore, possible that autoinfection or inhalation of infected material from unhygienic surroundings may play a part in the pathogenesis of these lesions. The latter possibility is further underlined by the fact that the patient reported here was a vegetarian Hindu, who, due to religious precepts was not likely to have consumed bovine meat.
On reviewing the nineteen authenticated reports of "sarcocystis", the cysts were located at the following sites:-upper limb-1 case, pectoral region-4 cases, leg and foot-5 cases, abdomen-1 case, mouth and tongue-2 cases, heart-6 cases, larynx-1 case, undetermined site in muscle-1 case. This distribution suggests that the parasite was predelected to locating itself in the more active muscles of the body.
The morphology of "Sarcocystis lindemanni" has been described, based on histological observations. It is to be therefore, expected that wide variations in descriptions would exist due to tissue shrinkage during processing. This fact is highlighted in the measurements cited in the various reports. The cysts varied in size from 10 to 53000 microns and have been shown to have a cyst wall in 4 instances which showed striations and varied in thickness from 0.5 to 16.1 microns. These striations in the cyst wall may have been due to skeletal. muscle fibre cytoplasm condensation. The organisms contained within the cysts were always described as slightly curved with lengths upto 14 microns and a width of 1.2 to 1.75 microns.
The presence of septae partitioning the cyst were noted in 5 cysts, were not seen in 7 cysts and not mentioned in 7 reports. Naidu  in 1929 suggested that such partitions tended to occur in only older cysts. This appears possible as seen in the reports of Baraban and Saint-Remy,  Vasudevan  and McGill and Goodbody  where the cysts with such septae measured over 1000 microns.
Bonne and Soewandi  and Feng  described a vascular host-stroma in relation to the parasite whereas Kean and Grocott,  Koberle,  Liu and Roberts,  Gupta et al  and the present author have seen atrophy of skeletal muscle fibres with degeneration and fibrosis with the occurrence of lymphacytes and polymorphs, in varying numbers in the connective tissue stroma. The present report, in addition, showed heterotopic ossification and embryonal cartilage formation. Whereas it would be difficult to discard these tissue reactions as just incidental findings, the relative paucity of parasites in the skeletal muscle fibres with no tissue reactions around would suggest just such a possibility. The vacuolation in some of the skeletal muscle fibres with a few PAS positive granules within were intriguing. Could this observation suggest that this parasite was capable of spreading from muscle fibre to muscle fibre? If this possibility were to exist the local tissue response could be explained. Another possible explanation for these host tissue responses could lie in the fact that the parasitised muscle fibre may have ruptured, resulting in the release of toxic products like "sarcocystin"  ,which may have not only produced the extensive tissue reactions but may have also been implicated in including weakness, and pain in the affected part.
The author thanks Dr. C. M. Francis;, M.B.B.S., Ph.D,, Dean of this Institution for permission to publish this report.
He further wishes to express his gratitude to the late Dr. Syed Mohideen, Professor of Veterinary Pathology, Veterinary College, University of Agricultural Science,Bangalore. Dr. S. J. Seshadri, Associate Professor of Veterinary Pathology and Dr. S. Sastry of that College for confirming his impression on the tissue sections.
[Figure 1], [Figure 2], [Figure 3], [Figure 4]