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Human Rabies -- Montana and Washington, 1997

On January 5 and January 18, 1997, respectively, a man in Montana and a man in Washington died of neurologic illnesses initially suspected to be Creutzfeldt-Jakob disease (CJD) but diagnosed as rabies encephalitis during subsequent histologic examination on autopsy. The cases were not linked epidemiologically, and no secondary cases occurred. Postexposure prophylaxis (PEP) was administered to 113 potential contacts. This report summarizes the clinical presentations of the cases and the epidemiologic investigations by the Montana Department of Public Health and Human Services and the Washington State Department of Health; nucleic acid sequencing indicated that the silver-haired bat (Lasionycteris noctivagans) and the big brown bat (Eptesicus fuscus), respectively, were the probable sources of exposure. Case 1

On December 20, 1996, family members of a 65-year-old male resident of Blaine County, Montana, observed him experiencing apparent visual hallucinations. This behavior recurred, and he subsequently had slurred speech and complained of diffuse left-arm pain and weakness. He was admitted to a northern Montana hospital on December 23 and was evaluated for a possible transient ischemic attack or worsening of pre-existing Parkinson's disease. A computerized tomography (CT) scan of the brain was normal. On December 24, he developed respiratory arrest and was intubated and mechanically ventilated. During the following 2 days, he developed increased myoclonic activity of his left leg and trunk and was transferred to a second hospital for further evaluation.

On admission to the second hospital, he had diffuse total body myoclonic spasms. However, an electroencephalogram (EEG) was negative for epileptiform discharges suggestive of seizure activity, and a magnetic resonance imaging study of the brain was normal. He developed fever, and treatment with antibiotics was initiated for diagnoses of parasinusitis and left lower lobe pneumonitis. Sustained diffuse myoclonic activity persisted, and complete muscle paralysis was maintained with medication until January 3, 1997, when poorly reactive pupils and absent corneal reflexes were noted. When cerebrospinal fluid (CSF) was obtained on January 3, the opening pressure was 46 cm of H2O (normal: 10-20 cm of H2O). CSF analysis indicated a glucose level of 211 mg/dL, total protein level of 67 mg/dL (normal: less than 40 mg/dL), a red blood cell (RBC) count of 30 cells/mm3 (normal: 0 cells/mm3), and a white blood cell (WBC) count of 10 cells/mm3 (normal: 0-5 cells/mm3) with a differential of 50% polymorphonuclear neutrophils (PMNs) (normal: 0 PMNs). All subsequent viral and bacterial cultures of the CSF were negative. Laboratory findings on January 4 included a blood urea nitrogen of 28 mg/dL (normal: 9-19 mg/dL), a serum creatinine of 1.8 mg/dL (normal: 0.3-1.3 mg/dL), peripheral WBC count of 15,500 cells/mm3 (normal: 4800-10,800 cells/mm3), a hematocrit of 27% (normal: 42%-52%), platelets of 264,000/mm3 (normal: 150,000-450,000/mm3), and a negative serum rapid plasmin reagin test.

On January 5, the myoclonic spasms ceased spontaneously, cranial nerve reflexes were absent, and the patient could not breathe without the aid of a ventilator. The family elected to discontinue mechanical ventilation, and he died. An autopsy was performed to confirm the suspected diagnosis of spongiform encephalopathy, or CJD. Microscopic examination of brain tissue was delayed until February 10 because of a prolonged formalin fixation and decontamination protocol required in the preparation of specimens suspected to contain elements capable of transmitting spongiform encephalopathy.

Gross examination of the brain initially was negative for areas of focal necrosis, tumor, and hemorrhage. However, microscopic examination revealed diffuse pan- encephalitis with neuronal necrosis and mononuclear infiltration of the meninges, and Negri bodies throughout the brain tissue with highest density in the cerebellum and hippocampus. No findings were consistent with spongiform encephalopathy.

Paraffin-blocked brain tissues and formalin-fixed hippocampus were sent to CDC for confirmation and on February 14 tested positive for rabies by the direct fluorescent antibody (DFA) test and reverse transcriptase polymerase chain reaction (RT-PCR). Nucleotide sequence analysis of the viral nucleic acid implicated a variant associated with the silver-haired bat, with 99% homology with a variant identified in a previous case of human rabies in Montana in 1996 (1).

The patient had been retired for several years but performed odd jobs around the area where he lived. His main hobbies included hunting and trapping. His family could not recall any history of contact with ill animals during these activities but reported that he baited traps with decayed animals he had collected from roadsides, often removing meat from the carcasses without wearing gloves. They also recalled that a bat had entered their home through the bedroom window in late summer 1996. On subsequent days, the bat was observed to be roosting during the daytime and flying around the house at dusk, and the patient eventually forced the bat out of the house with a broom. The patient's wife denied known contact with the bat and did not recall her husband having reported direct contact with the animal at any time. The bat had been driven from the house approximately 4 months before the onset of the patient's illness.

Sixty persons (two family members and 58 health-care workers) received PEP because of possible percutaneous or mucous membrane exposure to the patient's saliva. Case 2

On December 30, 1996, a 64-year-old man from Mason County, Washington, was hospitalized because of an exacerbation of chronic back pain and new onset of weakness and numbness of his left arm. He had a history of atrial fibrillation, cardio-myopathy, and hypertension. The initial diagnosis was possible myocardial infarction (MI) or cerebrovascular accident. On admission, a CT scan of the head revealed mild brain atrophy, and diagnostic tests for acute MI were negative. On December 31, he developed profound generalized myoclonus that began in his left arm. Anticonvulsive medications were administered without effect, and he was intubated for airway control. A neuromuscular blocking agent was administered to control the diffuse myoclonus after an EEG revealed no seizure activity and CSF analysis was reported as normal. He developed increased lacrimation and hypersalivation requiring constant oropharyngeal suctioning. On January 5, 1997, he was transferred to a hospital in Seattle for further evaluation. A repeat CSF analysis revealed a glucose level of 85 mg/dL and a protein level of 93 mg/dL; WBCs and bacteria were not detected in the CSF. PCR evaluations of the CSF for herpes simplex virus and enterovirus were negative. Acute tetanus was considered as a diagnosis because of the intractable myoclonus and a history of hand wounds the patient had sustained while gardening, and tetanus immune globulin was administered.

On January 15, all antiseizure medications and neuromuscular blocking agents were discontinued. He remained obtunded, and a repeat CT of the head remained unchanged. At that time, a diagnosis of rapidly progressive CJD was suspected. His condition deteriorated to profound autonomic instability, and he died on January 18. On autopsy, brain tissue was collected for evaluation for CJD.

In late February 1997, examination of brain tissue showed round, eosinophilic, cytoplasmic inclusion (Negri) bodies, and a provisional diagnosis of rabies was made. Additional brain tissue sent to CDC for confirmation tested positive on February 28 for rabies antigen by the DFA test. Analysis of the viral RT-PCR sequence isolated from the brain tissue was consistent with a variant previously identified from the big brown bat in the western United States.

The patient lived in a heavily wooded rural area adjacent to a large lake. Although bats were common in the area, none were reported in the house or other buildings on the property. Inspections of the buildings on the premises after his death revealed no evidence of bat infestation. Before his illness, the patient's outdoor activities included landscaping, gardening, and cleaning out a well house; he often engaged in these activities after dark. Family members reported that the patient had no known history of exposure to bats or other animals during the months before his illness or during trips to MazatlĪn, Mexico, in February 1996, or Missoula, Montana, in September 1996.

PEP was administered to 53 persons at the two hospitals (34 nurses, nine physicians, nine respiratory technicians, and one laboratory worker), one family member, and one emergency medical technician working on the ambulance transport.

Reported by: R Geyer, DO, Benefis Hospitals, Great Falls; M Van Leuven, Fort Belknap Tribal Health Dept, Harlem; J Murphy, T Damrow, PhD, State Epidemiologist, Montana State Dept of Public Health and Human Svcs. L Sastry, MD, S Miller, MD, Univ of Washington Medical Center, Seattle; M Goldoft, MD, J Grendon, DVM, J Kobayashi, MD, PA Stehr-Green, DrPH, State Epidemiologist, Washington State Dept of Health. Div of Applied Public Health Training (proposed), Epidemiology Program Office; Viral and Rickettsial Zoonoses Br, Div of Viral and Rickettsial Diseases, National Center for Infectious Diseases, CDC.

Editorial Note

Editorial Note: This report describes the first two cases of human rabies documented in the United States during 1997 and the second case of human rabies in both Washington and Montana since 1995. Before 1995, neither state had had a reported case of human rabies for several decades. Before examination of tissue obtained on autopsy, the diagnosis initially suspected for both of these cases was CJD. However, illness for both patients was subsequently related to infection with variants of rabies virus associated with bats; since 1980, a total of 19 (56%) of the 34 cases of rabies diagnosed in the United States have been associated with these variants, and the silver-haired bat variant has accounted for 13 (68%) of the 19 bat-related rabies cases. Case 2 in this report is the first human rabies fatality in the United States ever to have been documented involving a rabies virus variant associated with the big brown bat species.

A definite history of animal bite could not be documented in either case in this report and has been documented for only one of the 19 bat-related cases of human rabies since 1980. Of the remaining 18 such cases, physical contact with a bat without an evident bite or other potential exposing event was reported for eight. A history of bat contact could not be established or excluded for the remaining 10 bat-related cases, including both cases in this report.

These data suggest that seemingly insignificant physical contact with bats may result in viral transmission, even without a clear history of animal bite (1). In all instances of bat-human contact in which rabies transmission is under consideration, the bat in question should be collected, if possible, and submitted for rabies testing. Rabies PEP is recommended for all persons with bite, scratch, or mucous membrane exposure to a bat unless the bat is available for testing and is negative for evidence of rabies. The inability of health-care providers to elicit information surrounding potential exposures may be influenced by the limited injury inflicted by a bat bite (in comparison with lesions inflicted by terrestrial carnivores) or by circumstances that hinder accurate recall of events. Therefore, PEP is also appropriate even in the absence of a demonstrable bite or scratch, in situations in which there is reasonable probability that such contact occurred (e.g., a sleeping person awakes to find a bat in the room or an adult witnesses a bat in the room with a previously unattended child, mentally disabled person, or intoxicated person). This recommendation used in conjunction with current Advisory Committee for Immunization Practices guidelines (2) should maximize a health-care provider's ability to respond to situations where accurate exposure histories may not be obtainable and minimize inappropriate PEP.

Although human rabies is rare in the United States, this infection should be considered in the differential diagnosis of persons presenting with unexplained rapidly progressive encephalitis. In both of the cases in this report, rabies was not suspected before death and, therefore, was not diagnosed until histologic examination of the brain tissue on autopsy. Because CJD was suspected in both cases, the process required to prepare histologic specimens (3) further delayed diagnosis and prophylaxis of health-care workers and family members who had had mucous membrane exposure to the patients' saliva. In both of these cases, the presence of myoclonus suggested the possibility of CJD; however, this feature is only rarely a presenting clinical sign and is less likely to be generalized as was reported in both cases. An elevated CSF protein also was present in both of these cases, suggesting a diagnosis other than CJD, which usually is not associated with CSF abnormalities. The progression of illness from onset of clinical symptoms to death also was more rapid (16 and 18 days) than that characterizing CJD (months) (4,5).

Bat rabies is enzootic in the contiguous United States (6); however, the reduction of bat populations is not a feasible or desirable strategy for rabies control in this reservoir. To minimize human and animal contact with bats, these animals should be physically excluded from houses and surrounding structures by sealing potential entrances (7). In addition, because of the risk for rabies associated with bats, they should never be handled by the public or kept as pets. Finally, rabies vaccination for dogs and cats should be kept current to provide a barrier to indirect human exposures to wildlife rabies through infected domestic animals.

References

  1. CDC. Human rabies -- Kentucky and Montana, 1996. MMWR 1997;46:397-400.

  2. CDC. Rabies prevention -- United States, 1991: recommendations of the Immunization Practices Advisory Committee (ACIP). MMWR 1991;40(no. RR-3).

  3. Budka H, Aguzzi A, Brown P, et al. Tissue handling in suspected Creutzfeldt-Jakob disease (CJD) and other human spongiform encephalopathies (prion diseases). Brain Pathol 1995;5:319-22.

  4. Kretzschmar HA. Human prion diseases (spongiform encephalopathies). Arch Virol 1993; (suppl 7):S261-S293.

  5. Gajdusek DC. Infectious amyloids: subacute spongiform encephalopathies as transmissible cerebral amyloidoses. In: Fields BN, Knipe DM, Howley PM, et al, eds. Fields virology. 3rd ed. Philadelphia, Pennsylvania: Lippencott-Raven Publishers, 1996:2851-99.

  6. Krebs JW, Strine TW, Smith JS, Noah DL, Rupprecht CE, Childs JE. Rabies surveillance in the United States during 1995. J Am Vet Med Assoc 1996;209:2031-44.

  7. CDC. Compendium of animal rabies control, 1997: National Association of State Public Health Veterinarians, Inc. MMWR 1997;46(no. RR-4).


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