Outbreak of Trichinellosis Caused by Trichinella papuae, Thailand, 2006

In 2006, the Thailand Ministry of Public Health studied 28 patients from a village in northern Thailand. All had myalgia, edema, fever, and gastrointestinal symptoms; most had eaten wild boar. A muscle biopsy specimen from a patient showed nonencapsulated larvae with a cytochrome oxidase I gene sequence of Trichinella papuae.


The Study
The investigation team reviewed medical records, interviewed hospitalized patients, and performed active case fi nding in the implicated village by visiting the houses of the known patients and inquiring about symptoms of fam-ily members and neighbors. A suspected case-patient was defi ned as a resident of village A who had myalgia and facial, periorbital, trunk, or limb edema during May-June 2006. A confi rmed case-patient was defi ned as a person who met the criteria of a suspected case-patient and who had eosinophilia and a positive serologic test or muscle biopsy result for Trichinella spp. A request for volunteers to serve as controls for the investigation was announced by the village president. A control was defi ned as a resident of village A who did not meet the case defi nition and who agreed to give an interview, allowed specimen collection, and had negative serologic results for Trichinella spp.
Physicians in the Thai Bureau of Epidemiology's Field Epidemiology Training Program and the Uthai Thani Provincial Health Offi ces conducted a case-control study to determine the source of infection. A questionnaire was used to collect demographic characteristics, signs and symptoms, date of illness onset, laboratory results, and suspected exposures before onset of illness. An environmental study was conducted to investigate suspected food items, the surrounding area, and wild and domestic animals. Data analysis was performed by using Epi Info 2002 version 2 (Centers for Disease Control and Prevention, Atlanta, GA, USA).
For laboratory investigation, samples were collected from case-patients and controls for complete blood counts and serologic testing. In the hospital, laboratory results, including complete blood counts and creatine phosphokinase (CPK), were reviewed and blood for detection of antibodies to Trichinella spp. was collected. A muscle biopsy of 1 case-patient was performed.
The investigation team also collected blood from domestic boar for antibodies to Trichinella spp. and a sample of fermented barking deer meat for larvae examination. No uncooked wild boar meat was available for laboratory analysis. All larvae and human serum specimens were sent to the Department of Helminthology, Mahidol University, Thailand. Immunoblot tests for human trichinellosis were conducted by using the 109-kDa diagnostic band (sensitivity 100%, specifi city 100%) (8). Boar serum specimens were also tested. Studies were exempted from human subjects review because they were conducted under the authority of the Ministry of Public Health to investigate outbreaks of illness.
The environmental study found that villagers were avid hunters of deer, boar, and other local game; they also raised domesticated pigs (the village had 8 domesticated pig sties, each containing 3-10 pigs). Villagers shared domesticated pig meat from various sties every 2-3 weeks. On May 20, a successful wild boar hunt resulted in distribution of wild boar meat to villagers. On May 21, domesticated pig meat was shared among villagers. A successful hunt for barking deer also obtained meat that was prepared in various styles, including cooked, raw, and fermented, and was distributed to villagers during April and May.
After eating suspected foods on May 20-22, the fi rst case-patient developed symptoms on May 24 (diarrhea and abdominal pain). Eighty-two blood samples were collected during the investigation; 32 (39%) had antibodies to Trichinella spp. Among 28 blood samples from casepatients, all had eosinophilia (>10% eosinophils, mean 28.6%, SD 13.5%) and 21 had leukocytosis, (mean 14,500 cells/mm 3 , SD 4,230 cells/mm 3 ). All 3 hospitalized casepatients had elevated CPK levels (median 830 U/L, range 506-1,208 U/L, reference <50 U/L). One domesticated pig was randomly selected from each of 8 pigsties and tested by ELISA for antibodies to Trichinella spp.; all pig samples were negative. A human gastrocnemius muscle biopsy specimen from a hospitalized case-patient was positive for nonencapsulated Trichinella spp. larvae (Figure 2), which provided a defi nitive diagnosis of trichinellosis. The parasite had a COI partial gene sequence of T. papuae (7). The case-patient had not traveled outside of Thailand. The fermented barking deer meat was negative for larvae.
Of 28 persons whose illness met the case defi nition, 24 (3 hospitalized case-patients and 21 villagers) had antibodies to Trichinella spp. and were included in the analytic    Table 2). Although the OR for becoming ill after eating cooked wild boar was increased, it was much lower than that for consuming raw wild boar (OR 2.9, 95% CI 0.4-19.5).

Conclusions
Eating undercooked wild boar meat was strongly implicated as the source of this trichinellosis outbreak. The villagers were instructed about the importance of thoroughly cooking meat potentially contaminated with Trichinella spp. These fi ndings indicate that the geographic range of T. papuae is greater than previously thought.