Fatal Degenerative Neurologic Illnesses in Men Who Participated in Wild Game Feasts --- Wisconsin, 2002

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Creutzfeldt-Jakob disease (CJD) is a fatal neurologic disorder in humans. CJD is one of a group of conditions known as transmissible spongiform encephalopathies (TSEs), or prion diseases, that are believed to be caused by abnormally configured, host-encoded prion proteins that accumulate in the central nervous tissue (1). CJD has an annual incidence of approximately 1 case per million population in the United States (1) and occurs in three forms: sporadic, genetically determined, and acquired by infection. In the latter form, the incubation period is measured typically in years. Recent evidence that prion infection can cross the species barrier between humans and cattle has raised increasing public health concerns about the possible transmission to humans of a TSE among deer and elk known as chronic wasting disease (CWD) (2). During 1993--1999, three men who participated in wild game feasts in northern Wisconsin died of degenerative neurologic illnesses. This report documents the investigation of these deaths, which was initiated in August 2002 and which confirmed the death of only one person from CJD. Although no association between CWD and CJD was found, continued surveillance of both diseases remains important to assess the possible risk for CWD transmission to humans.

Case Reports

Case 1. In December 1992, a Wisconsin man aged 66 years with a history of seizures since 1969 sought treatment for recurring seizures, increasing forgetfulness, and worsening hand tremors. Electroencephalographic (EEG) examination demonstrated focal epileptiform activity and nonspecific diffuse abnormalities, but no specific diagnosis was made. In February 1993, he was hospitalized for increasing confusion, ataxia, and movement tremors of his extremities. A magnetic resonance image (MRI) demonstrated mild, nonspecific enhancement along the inferior parasagittal occipital lobe. A repeat EEG showed bifrontal intermittent, short-interval, periodic sharp waves, suggesting a progressive encephalopathy; a diagnosis of CJD was suspected. The man died later that month; neuropathologic examination of brain tissue during autopsy indicated subacute spongiform encephalopathy, compatible with CJD.

The man was a lifelong hunter who ate venison frequently. He hunted primarily in northern Wisconsin but also at least once in Montana. He hosted wild game feasts at his cabin in northern Wisconsin from 1976 until shortly before his death. Fixed brain tissue obtained during the autopsy was sent for analysis to the National Prion Disease Pathology Surveillance Center (NPDPSC) and reexamined at the institution where the autopsy was conducted. Histopathologic examination did not substantiate the diagnosis of prion disease. In addition, 27 brain tissue sections were negative for prions by immunostaining despite positive antibody reactions against other proteins (controls), which indicated that other epitopes in the tissue samples were preserved.

Case 2. In May 1999, a Minnesota man aged 55 years with no previous history of a neurologic disease sought evaluation and treatment following a 3-month history of progressive difficulty in writing and unsteadiness of gait. A computerized tomography (CT) scan and MRI examination of his head did not indicate any abnormality. In June 1999, he was hospitalized following onset of dementia, speech abnormalities, and myoclonic jerking. An EEG indicated left-hemispheric periodic sharp waves and moderate generalized background slowing; CJD was diagnosed clinically. In July 1999, following worsening symptoms and development of right upper extremity dystonia, the patient died. Neuropathologic evaluation of brain tissue during autopsy demonstrated widespread subcortical spongiform lesions, consistent with CJD.

The man was not a hunter but had a history of eating venison. He made an estimated 12 visits to the cabin where the wild game feasts were held, but he participated in only one feast during the mid-1980s. Sections of fixed and frozen brain tissue obtained during autopsy were analyzed at NPDPSC, and prion disease was confirmed by immunohistochemical and Western blot testing. The Western blot characteristics and prion disease phenotype in this patient were consistent with the most common form of sporadic CJD, classified as M/M (M/V) 1 (3). Subsequent genetic typing confirmed the presence of methionine homozygosity (M/M) at codon 129 of the patient's prion protein gene.

Case 3. In June 1992, a Wisconsin man aged 65 years sought treatment for progressive slowing of speech, worsening memory, and personality changes. By January 1993, his speech was reduced to one-word utterances. Neurologic examination showed a flat affect, decreased reflexes, and apraxia. A CT head scan showed mild atrophy, and an EEG was normal. Pick's disease was diagnosed. By May, he was unable to perform any daily living activities; he died in August 1993. Neuropathologic evaluation of brain tissue during autopsy showed symmetrical frontal lobe cerebral cortical atrophy and mild temporal lobe atrophy. No Pick's bodies or spongiform lesions were observed.

The man had a history of eating venison and participated regularly in wild game feasts held at the cabin owned by patient 1. He was a lifelong hunter and hunted mostly in Wisconsin but also in Wyoming and British Columbia. No game was brought to the wild game feasts from his hunting trips outside of Wisconsin. Examination of fixed brain tissue sent to NPDPSC demonstrated no lesions indicative of CJD, and immunohistochemical testing with antibody to the prion protein did not demonstrate the granular deposits seen in prion diseases.

Epidemiologic Investigation

Wild game feasts consisting of elk, deer, antelope, and other game that occurred at a cabin in northern Wisconsin owned by patient 1 began in 1976 and continued through 2002. These feasts typically involved 10--15 participants and usually occurred on weekends before or during hunting seasons in the fall and occasionally in the spring. Wild game brought to these feasts usually were harvested in Wisconsin, but three men who attended these feasts reported hunting in the western United States and bringing game back to Wisconsin. These activities took place in Colorado (near the towns of Cortez, Trinidad, Collbran, Durango, and Meeker), Wyoming (near the towns of Gilette and Cody), and Montana (near the town of Malta). CWD was not known to be endemic in these areas at the time that these hunting activities took place.

Information was obtained for 45 (85%) of 53 persons who were identified as possibly participating in the wild game feasts; all were male. Information was obtained by direct interview or from family members of decedents. Of the 45 persons, for whom information was obtained, 34 were reported to have attended wild game feasts. Seven of the 34 feast attendees were deceased, including the three patients. None of the four other decedents had a cause of death attributed to or associated with a degenerative neurologic disorder. None of the living participants had any signs or symptoms consistent with a degenerative neurologic disorder.

Reported by: JP Davis, MD, J Kazmierczak, DVM, M Wegner, MD, R Wierzba, Div of Public Health, State of Wisconsin Dept of Health and Family Svcs. P Gambetti, National Prion Disease Pathology Surveillance Center, Case Western Reserve University, Cleveland, Ohio. L Schonberger, MD, R Maddox, MPH, E Belay, MD, Div of Viral and Rickettsial Diseases, National Center for Infectious Diseases; V Hsu, MD, EIS Officer, CDC.

Editorial Note:

CWD was first described in the United States in the 1960s and classified as a TSE in 1978. Previously localized to a contiguous endemic area in northeastern Colorado and southeast Wyoming, since 2000, CWD has been found in free-ranging deer or elk in Illinois, Nebraska, New Mexico, South Dakota, Wisconsin, and outside the previously known endemic areas of Colorado and Wyoming. CWD has been identified also in captive deer or elk in Colorado, Kansas, Minnesota, Montana, Nebraska, Oklahoma, South Dakota, and Wisconsin (4). Because a variant form of CJD, with specific neuropathologic and molecular characteristics that distinguish it from sporadic CJD, has been associated with eating cattle products infected with a prion that causes bovine spongiform encephalopathy (5), concern has been raised about the possibility that the prion associated with CWD might be transmitted to humans in a similar way.

In this investigation, because only one of the three cases in Wisconsin had neuropathologic confirmation of a prion disease, no association could be made between case participation in the wild game feasts and the development of CJD. Although patient 2 had confirmed CJD, he was unlikely to have eaten CWD-infected venison at these feasts because venison and other game from outside Wisconsin that was served at these feasts did not originate from known CWD-endemic areas, and the man participated in the feasts only once. In addition, the prion disease in this case was consistent with the most common form of sporadic CJD, without apparent unusual neuropathologic or molecular characteristics that might occur if the prion related to CWD had been responsible for the disease.

The findings in this report are subject to at least two limitations. First, not all members participating in wild game feasts could be identified, and not all persons listed as participating could be contacted for interviews. Second, interviews that were conducted required recall of events that occurred up to 25 years ago, limiting the detail or accuracy of events. However, the similar responses obtained from different sources support the accuracy of the investigation findings.

A previous investigation of unusually young CJD patients in whom the transmission of CWD was suspected also did not provide convincing evidence for a causal relationship between CWD and CJD (2). However, limited epidemiologic investigations cannot rule out the possibility that CWD might play a role in causing human illness. Ongoing surveillance of CJD, particularly in states with CWD, is important to assess the risk, if any, for CWD transmission to humans. Because the confirmation of CJD and the detection of a new prion disease require neuropathologic study of brain tissue, physicians are encouraged to contact NPDPSC (http://www.cjdsurveillance.com; telephone, 216-368-0587) to confirm diagnoses of CJD and to distinguish its various subtypes. Because of the known severity of TSEs in humans and the possibility that the CWD prion can affect humans, animals with evidence of CWD should be excluded from the human food or animal feed chains. Hunters and wild venison consumers should follow precautionary guidelines available from the Wisconsin Department of Agriculture, Trade, and Consumer Protection (http://datcp.state.wi.us/core/consumerinfo) to prevent potential exposures to the CWD agent.

References

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Fatal Degenerative Neurologic Illnesses in Men Who Participated in Wild Game Feasts --- Wisconsin, 2002

Case Reports

Epidemiologic Investigation

Editorial Note:

References

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