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Outbreak of Powassan Encephalitis Maine and Vermont, 1999-2001

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Outbreak of Powassan Encephalitis Maine and Vermont, 1999-2001 FROM THE CENTERS FOR DISEASE CONTROL AND PREVENTION nal fluid (CSF) contained 40 white blood Her clinical examination showed agita- Outbreak of cells (WBCs)/mm3 (normal: Ͻ4/mm3) tion without confusion, ataxia, bilat- (87% lymphocytes) with elevated pro- eral lateral gaze palsy, and dysarthria. Powassan tein (96 mg/dL; normal: 20-50 mg/dL). CSF contained 148 WBCs/mm3 (46% Encephalitis— Magnetic resonance imaging (MRI) neutrophils, 40% lymphocytes). Dur- revealed parietal changes consistent with ing hospitalization, she developed al- Maine and Vermont, microvascular ischemia or demyelinat- tered mental status, generalized muscle 1999-2001 ing disease. No causes for his apparent weakness, and complete ophthalmople- stroke were found. After 22 days of hos- gia. An electroencephalogram (EEG) in- MMWR. 2001;50:761-764 pitalization, he was discharged to a reha- dicated diffuse encephalitis, and a MRI bilitation facility. Nearly 3 months after showed bilateral temporal lobe abnor- POWASSAN (POW) VIRUS, A NORTH symptom onset, he remains in the facil- malities consistent with microvascular American tickborne flavivirus related to ity and is unable to move his left arm or ischemia or demyelinating disease. Af- the Eastern Hemisphere’s tickborne en- leg. Serum specimens and CSF col- ter 13 days, she was transferred to a re- cephalitis viruses,1 was first isolated from lected 3 days after hospitalization habilitation facility where she re- a patient with encephalitis in 1958.1,2 revealed POW virus-specific IgM; neu- mained for 2 months. Nine months after During 1958-1998, 27 human POW en- tralizing antibody (1:640 titer) also was onset of symptoms, she was walking and cephalitis cases were reported from found in serum specimens. Although had regained her strength, but the oph- Canada and the northeastern United some cross-reaction with WNV and St. thalmoplegia continued. A serum speci- States.3 During September 1999-July Louis encephalitis (SLE) virus occurred men collected 19 days after illness on- 2001, four Maine and Vermont resi- in the IgM assay, no neutralizing anti- set was positive for POW virus-specific dents with encephalitis were found to body was found. IgM and neutralizing antibody (1:640 be infected with POW virus. These per- The patient had not left Maine for 25 titer) and negative for WNV and SLE sons were tested for other arbovirus in- years. On ecologic investigation, over- virus antibodies. fections found in the northeast after test- grown bushes, leaf piles, and stacks of The patient had not left Maine in sev- ing for West Nile virus (WNV) infection old lumber and scrap metal covered his eral months before illness onset. Dur- was negative. This report describes these property. Family members reported see- ing two visits to a rural vacation home four cases, summarizes the results of eco- ing woodchucks, skunks, and squirrels in the month before illness onset, the pa- logic investigations, and discusses a po- on the property. During the 2 weeks be- tient removed several squirrel nests but tential association between ticks that in- fore illness, the patient’s main activi- reported no contact with ticks or ro- fest medium-sized mammals and the risk ties were lying on the ground repairing dents. One month after illness onset, an for human exposure to POW virus. The a boat hull and yard work. Approxi- ecologic evaluation of her primary home findings underscore the need for per- mately 6 weeks after illness onset, nine noted a well-manicured suburban prop- sonal protective measures to prevent tick medium-sized mammals were trapped erty near brush and woodlands. No evi- bites and continued encephalitis sur- on or near the patient’s property. Col- dence of medium-sized mammals was veillance. lections from these mammals and the found, and only three Ix. scapularis were grassy and brushy areas of the property collected; no POW virus was isolated. Case Reports yielded 31 ticks (Ixodes cookei). Tests for Nine months after illness onset, an eco- Case 1. In June 2001, a 70-year-old man POW virus infection were conducted at logic evaluation of the patient’s vaca- from Kennebec County, Maine, was CDC. Of the nine mammal serum tion home found several mammals, but taken to a local hospital with general- samples, four (two woodchucks and two none had ticks, and no serology samples ized muscle weakness, somnolence, diar- skunks) contained neutralizing anti- were collected. rhea, and anorexia. On clinical exami- body to POW virus, but no virus was iso- Case 3. In July 2000, a 25-year-old nation, he had a fever of 104.7°F lated from the ticks. man from Waldo County, Maine, sought (40.4°C), leukocytosis of 11,500/mm3 Case 2. In September 2000, a 53- medical care at a local hospital for fe- (normal: 4,300-10,800/mm3), decreased year-old woman from York County, ver of 101.3°F (38.5°C), headache, vom- renal function, and anemia. He subse- Maine, sought medical care at a local iting, somnolence, and confusion. On quently developed left-sided hemiple- hospital for loss of balance, visual dis- clinical examination, the patient had dif- gia and marked confusion. Cerebrospi- turbance, and fever of 103°F (39.4°C). ficulty answering simple questions and 1962 JAMA, October 24/31, 2001—Vol 286, No. 16 (Reprinted) ©2001 American Medical Association. All rights reserved. Downloaded From: https://jamanetwork.com/ on 09/26/2021 FROM THE CENTERS FOR DISEASE CONTROL AND PREVENTION was intermittently uncooperative. He len, MD, Veterans Affairs Medical Center, White River fore they attach or as soon after attach- Junction; P Tassler, PhD, Vermont Dept of Health. Ar- had bilateral hand twitching, muscle bovirus Diseases Br and Bacterial Zoonoses Br, Div of ment as possible. Checking family pets weakness, and pronounced lip smack- Vector-Borne Infectious Diseases, National Center for also can prevent ticks from entering the ing. CSF contained 920 WBCs/mm3 Infectious Diseases; and an EIS Officer, CDC. home. Because Ix. cookei are often found (74% lymphocytes) with elevated pro- on woodchucks and skunks and may be tein (77 mg/dL). EEG showed diffuse CDC Editorial Note: These four cases the primary vector of POW virus, envi- background slowing consistent with en- of POW encephalitis are the first re- ronmental controls reducing human cephalitis. After 11 days of hospitaliza- ported in Maine and Vermont and the contact with small and medium-sized tion, he was transferred to a rehabilita- first in the United States since 1994.4 mammals should reduce risk for expo- tion facility. When discharged home 44 Since the introduction of WNV into the sure to POW virus-infected ticks. Per- days later, the patient required assis- northeastern United States in 1999,5 test- sons should keep areas adjacent to their tance to stand and perform daily activi- ing for POW virus and other arbovi- home clear of brush, weeds, trash, and ties. Serum specimens and CSF col- ruses that cause encephalitis has in- other elements that could support small lected 3 days after illness onset were creased (CDC, unpublished data, 2001). and medium-sized mammals. When re- negative for antibody to WNV and SLE These cases were identified as a direct moving rodent nests, avoid direct con- virus but positive for POW virus- result of requests for WNV testing. As tact with nesting materials and use sealed specific IgM antibody. The serum sample surveillance continues, knowledge of the plastic bags for disposal and to prevent also had neutralizing antibody (1:80 ti- epidemiology of POW virus in the direct contact with ticks. ter) to POW virus. At the time of ill- United States may increase. Because of the lack of awareness and ness onset, the patient worked as a log- In North America, POW virus has the need for specialized laboratory tests ger and lived in rural Maine where he been isolated from four tick species, in- to confirm diagnosis, the frequency of raised livestock. cluding Ix. cookei, Ix. marxi, Ix. spinipa- POW encephalitis may be greater than Case 4. In September 1999, a 66- lpus, and Dermacentor andersoni; a vari- previously suspected. POW encephali- year-old man from Washington County, ant POW virus also has been isolated tis should be included in the differen- Vermont, sought medical care at a hos- from Ix. scapularis; and evidence of in- tial diagnosis of all encephalitis cases oc- pital for somnolence, severe head- fection has been found in 38 mammal curring in the northern United States, ache, increasing confusion, and bilat- species, primarily woodchucks.1,6 Un- especially the northeast. Laboratory tests eral leg weakness that developed over like Ix. scapularis, the primary vector for for POW virus infection are not com- 6 days. On clinical examination, he was Lyme disease, Ix. cookei rarely search for mercially available but can be re- afebrile but had slow speech, memory hosts on vegetation and are often found quested through state public health labo- loss, a wide-based gait, and bilateral in or near the nests or burrows of me- ratories for testing at CDC. Awareness weakness in proximal lower extremi- dium-sized mammals. Infections have should be promoted among clinicians ties. CSF contained 54 WBCs/mm3 occurred from May to December, with and public health staff, and tick-bite pre- (95% lymphocytes) and elevated pro- a peak during June-September when vention strategies emphasized for the tein (67 mg/dL). An EEG showed dif- ticks are most active.1 Although nei- general public. fuse background slowing consistent ther the first or second patients re- with encephalitis. When discharged called tick bites, ecologic investiga- REFERENCES* home 11 days later, he could walk but tions suggest that their illnesses resulted 1. Artsob H. Powassan encephalitis.
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