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Human Rabies -- Kentucky and Montana, 1996

In October and December 1996, a woman in Kentucky and a man in Montana died from rabies. This report summarizes the clinical courses and epidemiologic investigations of these cases, which indicate that a bat was the probable source of exposure for each case. Case 1

On September 28, 1996, a 42-year-old female resident of Cumberland County, Kentucky, visited a local emergency department (ED) because of dizziness, shoulder pain, and an inability to swallow; pharyngitis was presumptively diagnosed, and she was discharged. She returned to the ED that day and was admitted to the hospital. Findings on admission included an oral temperature of 100.6 F (38.1 C), a peripheral white blood cell (WBC) count of 7700/mm3 (normal: 5000-10,000/mm3), and the presence of ketonuria and bacteriuria. A lumbar puncture was performed to rule out primary neurologic involvement. The cerebrospinal fluid (CSF) contained 5 WBCs/mm3 (normal: 0-5 WBCs/mm3), 22 red blood cells (RBCs)/mm3 (normal: 0 RBCs/mm3), total protein of 45 mg/dL (normal: less than 40 mg/dL), and a glucose level of 111 mg/dL (normal: 70-110 mg/dL). Computerized tomography (CT) of the brain was within normal limits. During the next several hours, she gagged and vomited frequently, had continued difficulty swallowing and right arm pain, and became anxious and agitated; she was treated for anxiety, pharyngitis, pain, nausea, and vomiting.

On September 29, the patient was transferred to a referral hospital because of dysphagia and involuntary motor activity of her upper extremities, neck, face, and eyes. She had a temperature of 105.7 F (40.9 C), and a sample of CSF and complete blood counts were within normal limits. Viral encephalitis was presumptively diagnosed, and treatment with acyclovir was initiated. However, her condition continued to deteriorate, and on the evening of September 30, she was intubated because of progressive bulbar dysfunction.

On October 1, the patient was transferred to another referral hospital where she was treated with mechanical ventilation and cardiopulmonary stabilization for shock. Findings on physical examination included a temperature of 102.2 F (39.0 C), low systolic blood pressure (80 mm Hg), injected sclerae, bilateral proptosis, coarse thoracic breath sounds, and cyanotic extremities with pitting edema; in addition, her pupils were reactive, ocular-cephalic reflex was present, and all spinal reflexes were intact. An electroencephalogram (EEG) subsequently revealed status epilepticus, which required treatment with phenytoin, benzodiazepines, and pentobarbital. Chest radiographs obtained on October 2 revealed bilateral infiltrates consistent with pneumonia or adult respiratory distress syndrome, and broad-spectrum antibiotic therapy was initiated. CT revealed extensive diffuse cerebral edema. Although septic syndrome was considered, all cultures remained negative. Even though the EEG normalized, over the next 4 days there was no clinical improvement of neurologic function, and on October 10, there was no evidence of brainstem activity, and reflexes could not be elicited.

On October 10, a serum specimen was collected and submitted to a private laboratory for rabies testing; rabies neutralizing antibody subsequently was detected. On October 15, mechanical ventilation and vasopressor support were withdrawn, and the patient died.

The diagnosis of rabies subsequently was confirmed at CDC by detection of rabies antibodies in the serum sample obtained on October 10; however, a serum sample drawn on October 2 was negative for rabies antibodies. Vitreous humor fluid and serum obtained at autopsy on October 15 also were tested at CDC; both were positive for rabies antibodies by indirect immunofluorescence, and the vitreous fluid was positive for rabies virus nucleic acid by reverse transcriptase-polymerase chain reaction (RT-PCR) analysis. Nucleotide sequence analysis of the viral nucleic acid implicated a variant associated with the silver-haired bat (Lasionycteris noctivagans).

While hospitalized, the patient denied any history of animal bites, and an interview with the patient's husband on November 15 did not establish a history of contact with bats or other animals. The couple lived in an old house in a rural area and reported frequently hearing noises in the chimney that sounded like birds. However, investigation of the residence by the local health department did not detect evidence of bats in the house or chimney.

Rabies postexposure prophylaxis (PEP) was administered to 87 persons (five family members and 82 health-care workers) because of possible percutaneous or mucous membrane exposure to the patient's saliva. Case 2

On December 4, a 49-year-old male resident of Missoula County, Montana, was evaluated in a local ED because of fever, sore throat, productive cough, and severe right-sided supraorbital pressure and tenderness of several weeks' duration. An antibiotic was prescribed for sinusitis, and he was discharged. On December 9, he returned to the ED and was admitted to the hospital for evaluation of confusion, ataxia, persistent fever, cough, and sinus pressure. Findings on admission included an oral temperature of 102.9 F (39.4 C); pulse rate of 114 beats per minute; respiratory rate of 28 breaths per minute; and the presence of bilateral conjunctival suffusion, rhinorrhea, pharyngeal hyperemia, and bibasilar rales. A chest roentgenogram revealed bilateral interstitial infiltrates and a small left pleural effusion. A standard neurologic evaluation and brain CT were performed to rule out primary neurologic involvement: both were within normal limits. Abnormal laboratory findings included a peripheral WBC count of 17,500/mm3 and a serum sodium level of 120 mmol/L (normal: 135- 147 mmol/L). Pneumonia and severe hyponatremia were diagnosed; treatment included antibiotics and rehydration.

On December 10, the patient exhibited ataxia and had diminished deep pain reflexes and decreased sensation in his right hand. A lumbar puncture was performed, and his CSF contained 121 WBCs/mm3 (51% macrophages, 48% lymphocytes, and 1% polymorphonuclear cells), a total protein level of 52 mg/dL, and a glucose level of 102 mg/dL. Magnetic resonance imaging (MRI) of the brain with gallium revealed no abnormalities. Later that day, severe hypercapnia developed, and intubation was required.

On December 14, the patient had multiple seizures followed by coma and loss of brain stem reflexes, doll's eye, and corneal reflexes; his pupils were mid-range and unresponsive to light. Analysis of a sample of CSF revealed 38 WBCs/mm3, a total protein of 49 mg/dL, and glucose of 136 mg/dL. Viral encephalitis was presumptively diagnosed, and intravenous acyclovir therapy was initiated.

Rabies was clinically suspected on December 17, and serum, saliva, and nuchal skin biopsy specimens were obtained and submitted to CDC for rabies testing. On December 18, rabies antibodies were detected in the serum specimen, and on December 19, the nuchal biopsy and saliva specimens were positive for rabies virus nucleic acid by RT-PCR analysis. Mechanical ventilatory support was discontinued, and the patient died. On December 20, nucleotide sequence analysis of viral RNA implicated a variant associated with the silver-haired bat (L. noctivagans).

The patient and his family lived in a rural area and reported occasionally seeing bats outside their home but denied having had physical contact with bats. In addition, the patient was employed as a custodian for a wood and paper mill and denied contact with bats at his workplace. Although coworkers reported that bats were sometimes observed near the mill premises, the Missoula City-County Health Department inspected the site after the patient's death and found no evidence of bats.

Rabies PEP was administered to 26 persons (three family members and 23 health-care workers) because of possible percutaneous or mucous membrane exposure to the patient's saliva.

Reported by: M Slocum, MD, P Disney, Cumberland County Hospital, Burkesville; S Rice, MD, L Martin, TJ Samson County Hospital, Glasgow; M Auslander, DVM, R Finger, MD, State Epidemiologist, Kentucky Cabinet for Health Svcs, Dept for Public Health. W Schaffner, MD, Vanderbilt Univ Medical Center, Nashville; G Swinger, DVM, W Moore, MD, State Epidemiologist, Tennessee Dept of Health. G Risi, MD, E Leahy, G Oliver, B Goode, Missoula City-County Health Dept, Missoula; T Damrow, PhD, State Epidemiologist, Montana State Dept of Public Health and Human Svcs. Viral and Rickettsial Zoonoses Br, Div of Viral and Rickettsial Diseases, National Center for Infectious Diseases; Div of Applied Public Health Training (proposed), Epidemiology Program Office, CDC.

Editorial Note

Editorial Note: In 1996, four cases of human rabies were documented in the United States, including the two cases described in this report. In both of these cases, the rabies virus variant was associated with the silver-haired bat, L. noctivagans, and in neither case, could a definite history of bat bite or contact be established. These findings are consistent with the emerging pattern in the epidemiology of human rabies in the United States: bat-related virus variants have been identified from 17 (53%) of the 32 cases of human rabies diagnosed in the United States since 1980. Of these 17 bat-related cases, 12 (71%) were infected with a rabies virus variant primarily associated with the silver-haired bat. A definite bite history could be documented in only one of these 17 bat-related cases; in eight of these instances, although contact with a bat was reported by the patient, a family member, or friends, in none of these cases was a bite recognized or a wound evident. These findings suggest that limited or seemingly insignificant physical contact with rabid bats may result in transmission of virus, even without a definite history of animal bite. Therefore, rabies PEP should now be conisdered in all situations in which there is reasonable probability that contact with a bat may have occurred, unless prompt laboratory testing of the bat has ruled out rabies infection. Examples of potential contacts include a sleeping person awakes to find a bat in the room, an adult finds a bat in the room with a previously unattended child, or a bat is detected in the presence of an unattended child or a mentally disabled or intoxicated person. Adherence to this recommendation and guidelines from the Advisory Committee for Immunization Practices (1) should maximize a health provider's ability to respond to situations in which there is difficulty in obtaining accurate exposure histories, while still minimizing the inappropriate administration of PEP. Persons with other exposures, including animal bite or scratch or mucous membrane contact with potentially infectious material, should continue to be considered for PEP.

Because bat rabies is enzootic in the contiguous United States (2) and reduction of bat populations is not a feasible or desirable strategy for rabies control in bats, human and domestic animal contact with bats should be minimized by physical exclusion of bats from houses and surrounding structures by sealing entrances used by bats (3). Bats should not be routinely captured or handled and should never be kept as pets. In addition, rabies vaccination should be kept current for all dogs and cats to provide a barrier to indirect human exposures to wildlife rabies through domestic animals.

References

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

  2. 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.

  3. CDC. Compendium of animal rabies control, 1997: National Association of State Public Health Veterinarians, Inc. MMWR 1997;46(no. RR-3).





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