Acute muscular sarcocystosis: an international investigation among ill travelers returning from Tioman Island, Malaysia, 2011-2012

Abstract

Background: Through 2 international traveler-focused surveillance networks (GeoSentinel and TropNet), we identified and investigated a large outbreak of acute muscular sarcocystosis (AMS), a rarely reported zoonosis caused by a protozoan parasite of the genus Sarcocystis, associated with travel to Tioman Island, Malaysia, during 2011-2012.

Methods: Clinicians reporting patients with suspected AMS to GeoSentinel submitted demographic, clinical, itinerary, and exposure data. We defined a probable case as travel to Tioman Island after 1 March 2011, eosinophilia (>5%), clinical or laboratory-supported myositis, and negative trichinellosis serology. Case confirmation required histologic observation of sarcocysts or isolation of Sarcocystis species DNA from muscle biopsy.

Results: Sixty-eight patients met the case definition (62 probable and 6 confirmed). All but 2 resided in Europe; all were tourists and traveled mostly during the summer months. The most frequent symptoms reported were myalgia (100%), fatigue (91%), fever (82%), headache (59%), and arthralgia (29%); onset clustered during 2 distinct periods: "early" during the second and "late" during the sixth week after departure from the island. Blood eosinophilia and elevated serum creatinine phosphokinase (CPK) levels were observed beginning during the fifth week after departure. Sarcocystis nesbitti DNA was recovered from 1 muscle biopsy.

Conclusions: Clinicians evaluating travelers returning ill from Malaysia with myalgia, with or without fever, should consider AMS, noting the apparent biphasic aspect of the disease, the later onset of elevated CPK and eosinophilia, and the possibility for relapses. The exact source of infection among travelers to Tioman Island remains unclear but needs to be determined to prevent future illnesses.

Keywords: Malaysia; infectious disease outbreak; parasitic disease; sarcocystosis; travel.

Figure 1

Tioman Island, Malaysia, and locations visited by 68 case patients with acute muscular sarcocystosis, 2011–2012. Marker color represents the frequency of visitation to each village or attraction for the 61 case patients with these data available; each patient may have visited multiple locations. Other locations visited but not mapped include “south of Tekek” (n = 4), “between Ayer Batang and Salang” (n = 3), “between Ayer Batang and Genting” (n = 1), “Tekek to Juara” (n = 1), “northwest of island” (n = 3), and a snorkeling trip circumnavigating the island by boat with multiple stops (n = 1). Tioman Island is not drawn to scale relative to the mainland.

Figure 2

Date of departure from Tioman Island, Malaysia, by week, of 68 travelers with probable and confirmed acute muscular sarcocystosis, 2011–2012. The date of departure from Tioman Island reflects the last possible point of exposure of the traveler to the Sarcocystis species parasite. The earliest departure date was 1 May 2011, and the latest was 5 September 2012.

Figure 3

Symptoms among 68 patients with acute muscular sarcocystosis, Tioman Island, Malaysia, 2011–2012. Shown are the proportions of patients experiencing each symptom at any time during the course of their illness. Symptoms reported in <5% of the case patients are not shown and include throat pain* (3%), loss of appetite (3%), and stiff neck* (1%). *Unsolicited symptom spontaneously reported in the questionnaire narrative.

Figure 4

Timing of specific elements of acute muscular sarcocystosis. A, Onset of the 5 most frequently reported symptoms of acute muscular sarcocystosis relative to the number of weeks since departing from Tioman Island; onset clustered during the second (early) and the sixth (late) postdeparture weeks. More than 1 onset date for at least 1 of these symptoms was reported by 15 patients (myalgia [n = 10], fever [n = 7], headache [n = 2], fatigue [n = 1]; none for arthralgia). For 25 (37%) patients, the illness was described as phasic, intermittent, or waxing–waning in character, with periods of symptoms separated by a period of relative improvement. B and C, All blood absolute eosinophil counts and serum creatinine phosphokinase (CPK) levels, respectively, for all patients relative to the number of weeks since departing Tioman Island. Each case patient may have had >1 of each laboratory determination. One absolute eosinophil count of 6200 cells/μL and 1 CPK level of 3900 U/L, each from a different patient, is not included in B and C, respectively. *Based on the case definition, >500 cells/μL is considered elevated. ^†Based on the case definition, >200 U/L is considered elevated.

Figure 5

Histopathology and electron microscopy. A, Skeletal muscle (SM) with inflammation (arrows) adjacent to a small vessel (v). Inflammation composed of lymphocytes and macrophages with small numbers of plasma cells, eosinophils, and rarely neutrophils. Original magnification ×400, hematoxylin and eosin staining. B, SM with intramyocytic sarcocyst. Note the absence of inflammation surrounding the sarcocyst-containing myocyte. Original magnification 400×, hematoxylin and eosin staining. C, Portion of a cyst within SM, containing abundant bradyzoites (arrow). D, Higher magnification of the cyst wall, showing short protrusions (arrow) and a fairly thin granular layer (GL). Bars = 2 μm (C) and 500 nm (D). Abbreviations: GL, granular layer; SM, skeletal muscle; v, small vessel.