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Prompt Medical Attention Important After Bat Encounter


The case report in the April 15th issue of the CDC’s MMWR, underscores the importance of prompt medical care after bat encounters even when unsure if a bite occurred.

The report highlights the case of a 55 year old man. On November 9, 2009 the Michigan hospital he had sought care from informed CDC of suspected rabies from an encounter with a bat 9 months earlier. He had reportedly awakened with a bat on his arm but had not sought medical evaluation.

The man was initially seen on October when he went to a local emergency department (ED) with complaints of 10 days of pain and progressive numbness in the left hand and arm and pain in his lower neck and upper back.

His initial exam revealed he was afebrile with normal blood pressure. A neurologic examination revealed normal strength and sensation of his lower extremities. His right arm showed normal strength, but the left hand showed no grip, and the patient could only lift his left arm a few inches.

Blood work was normal except for an elevated white blood cell count of 15,300/µL (normal: 3,600--10,000/µL) and elevated glucose of 155 mg/dL (normal: 70--99 mg/dL). A computed tomography scan of the brain without contrast revealed a cavernous sinus larger on the left than on the right and an area of slightly decreased density in the right basal ganglion and paraventricular areas.

During the ED evaluation, the patient's breathing became labored, and he had difficulty with respiratory secretions. He was placed on ventilation and transferred to a nearby tertiary-care facility. At the time of intubation, the anesthesiologist noted that the procedure was easy to perform because of lack of muscle tone in the patient's pharynx.

He was hospitalized, but died 12 days later. On November 14, CDC confirmed infection with a rabies virus variant that commonly infects the silver-haired bat (Lasionycteris noctivagans).

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Anyone who experiences contact with a bat and cannot confidently rule out a bite or scratch should seek prompt medical attention.

In this case, it wasn’t until November 8, a relative recounted an incident that had occurred approximately 9 months before onset of illness. The patient had told the relative about waking one night to a bat crawling on his arm. The relative did not know whether the patient had been bitten by the bat. The bat had been killed and discarded, and the patient did not seek medical care for the incident.

After obtaining the bat exposure history, the infectious disease physician contacted CDC on November 9 to discuss a diagnosis of rabies. The Michigan Department of Community Health Bureau of Laboratories also was contacted by the hospital regarding specimen collection. Serum, CSF, saliva, and nuchal skin biopsy specimens were collected and sent to CDC on November 10.

A total of 14 family members and friends were interviewed by the local health department regarding exposure to the patient's saliva during the 2 weeks before his illness onset and during his hospitalization. Eleven family members received rabies postexposure prophylaxis (PEP) at the advice of the local health department because of possible exposure to saliva through shared glasses or cups; an additional person also received PEP, although it was not recommended. Of 180 health-care providers from the two health-care facilities who were assessed for potential exposure to rabies virus based on their likelihood of saliva contact, six received rabies PEP.

Rabies is a viral disease of the central nervous system that is transmitted when broken skin or a mucous membrane is contaminated with saliva from an infectious mammal. Typically, after a 1--3 month incubation period, an acute, rapidly progressive encephalomyelitis develops, and death of the patient occurs within 20 days.

Rabies is preventable if exposure to the virus is promptly followed by wound cleaning, administration of rabies immune globulin, and rabies vaccination.

Clinical signs of rabies most often are associated with the encephalitic form of the disease and include hydrophobia, muscle spasms, and altered mental status. The patient described in this report exhibited characteristic signs of paralytic rabies, a less common presentation that manifests as flaccid paralysis relatively early in the illness course.

In the absence of a negative animal rabies diagnostic result, persons who come in contact with a bat and cannot confidently exclude a bite or scratch should be advised to seek medical attention. After the onset of symptoms, the clinical course of rabies is almost invariably fatal.

CDC MMWR; April 15, 2011