To evaluate transmission dynamics, we exposed 25 bird species to West Nile virus (WNV) by infectious mosquito bite. We monitored viremia titers, clinical outcome, WNV shedding (cloacal and oral), seroconversion, virus persistence in organs, and susceptibility to oral and contact transmission. Passeriform and charadriiform birds were more reservoir competent (a derivation of viremia data) than other species tested. The five most competent species were passerines: Blue Jay (Cyanocitta cristata), Common Grackle (Quiscalus quiscula), House Finch (Carpodacus mexicanus), American Crow (Corvus brachyrhynchos), and House Sparrow (Passer domesticus). Death occurred in eight species. Cloacal shedding of WNV was observed in 17 of 24 species, and oral shedding in 12 of 14 species. We observed contact transmission among four species and oral in five species. Persistent WNV infections were found in tissues of 16 surviving birds. Our observations shed light on transmission ecology of WNV and will benefit surveillance and control programs.

Powassan virus (POWV) disease is a rare human disease caused by a tick-borne encephalitis group flavivirus maintained in a transmission cycle between Ixodes cookei and other ixodid ticks and small and medium-sized mammals. During 1958-1998, only 27 POWV disease cases (mostly Powassan encephalitis) were reported from eastern Canada and the northeastern United States (average, 0.7 cases per year). During 1999-2005, nine cases (described herein) of serologically confirmed POWV disease were reported in the United States (average, 1.3 cases per year): four from Maine, two from New York, and one each from Michigan, Vermont, and Wisconsin. The Michigan and Wisconsin cases are the first ever reported from the north-central United States. Of these nine patients, 5 (56%) were men, the median age was 69 years (range: 25-91 years), and 6 (67%) had onset during May-July. All but one patient developed encephalitis with acute onset of profound muscle weakness, confusion, and other severe neurologic signs. In one case, no neurologic symptoms were present but the presence of pleocytosis, an elevated cerebrospinal fluid (CSF) protein concentration, and POWV-specific immunoglobulin M in CSF suggested neuroinvasion. All patients recovered from their acute disease, but most had long-term neurologic sequelae. Periresidential ecologic investigations were performed in three cases, including tests of local mammals and ticks for evidence of POWV infection. Woodchucks (Marmota monax), striped skunks (Mephitis mephitis), and a raccoon (Procyon lotor) collected at two of the Maine case-patients' residences had neutralizing antibody titers to POWV. I. cookei were found on woodchucks and skunks and questing in grassy areas of one of these residences; all were negative for POWV. Although POWV disease is rare, it is probably under-recognized, and it causes significant morbidity, and thus is an additional tick-borne emerging infectious disease entity. Because no vaccine or specific therapy is available, the basis of prevention is personal protection from ticks (or "tick hygiene") and reduced exposure to peridomestic wild mammals.

The 1999 New York epidemic of human West Nile virus (WN) encephalitis and meningitis was preceded by a crow die-off also caused by WN infection. As one component of the subsequently developed national surveillance system, crow mortality data were collected to detect WN activity before humans might become infected. However, predicting areas at risk for human WN disease likely requires assessment of multiple factors, including the intensity and timing of crow epizootics. To identify early season measures of WN activity in crows associated with subsequent WN disease in humans, county-level crow mortality data from seven northeastern states were analyzed. A predictive model was developed based on analysis of 2000 surveillance data and then assessed for 2001. To characterize the intensity of early season WN activity in crows, 15 variables were constructed from surveillance data of 52 counties that tested at least four crows during the early season (defined as June 17-July 28, 2000). County values for each variable were dichotomized at the 75th percentile into "high" and "low" activity. Multivariate analysis indicated that "high" early season activity of two variables-density of reported dead crow sightings (reported dead crows/area) and [(WN-infected crows/tested crows) x (human population)]--were associated with report of at least one human WN disease case (for each variable: adjusted odds ratio, 6.9; 95% confidence interval, 1.2-40.6). An assessment of this model using 2001 surveillance data from 61 counties yielded similar findings. With emphasis on early season WN activity, crow surveillance may allow timely targeting of interventions to protect the public health.

In 1999, the U.S. West Nile (WN) virus epidemic was preceded by widespread reports of avian deaths. In 2000, ArboNET, a cooperative WN virus surveillance system, was implemented to monitor the sentinel epizootic that precedes human infection. This report summarizes 2000 surveillance data, documents widespread virus activity in 2000, and demonstrates the utility of monitoring virus activity in animals to identify human risk for infection.

West Nile virus (WNV) can cause large outbreaks of febrile illness and severe neurologic disease. This study estimates the seroprevalence of WNV infection and assesses risk perception and practices regarding potential exposures to mosquitoes of persons in an area with intense epizootics in 1999 and 2000. A serosurvey of persons aged ≥12 years was conducted in southwestern Connecticut during October 10‐15, 2000, using household‐based stratified cluster sampling. Participants completed a questionnaire regarding concern for and personal measures taken with respect to WNV and provided a blood sample for WNV testing. Seven hundred thirty persons from 645 households participated. No person tested positive for WNV (95% CI: 0‐0.5%). Overall, 44% of persons used mosquito repellent, 56% practiced ≥ two personal precautions to avoid mosquitoes, and 61% of households did ≥ two mosquito‐ source reduction activities. In multivariate analyses, using mosquito repellent was associated with age <50 years, using English as the primary language in the home, being worried about WNV, being a little worried about pesticides, and finding mosquitoes frequently in the home (P <0.05). Females (OR = 2.0; CI = 1.2‐2.9) and persons very worried about WNV (OR = 3.8; CI = 2.2‐6.5) were more likely to practice ≥ two personal precautions. Taking ≥ two mosquito source reductions was associated with persons with English as the primary language (OR = 2.0; CI = 1.1‐3.5) and finding a dead bird on the property (OR = 1.8; CI = 1.1‐2.8). An intense epizootic can occur in an area without having a high risk for infection to humans. A better understanding of why certain people do not take personal protective measures, especially among those aged ≥50 years and those whose primary language is not English, might be needed if educational campaigns are to prevent future WNV outbreaks.

Autochthonous dengue virus transmission, last identified in the state of Hawaii in 1945, was detected again in 2001. A seroepidemiological survey in a high-incidence community (Nahiku) and a nearby low-incidence community (Hana Subdivision) was implemented. The two communities studied differed in median household size (two vs. four persons), median lot size (2.8 vs. 0.8acres), proportion of households with mosquito larvae (81 vs. 28%) and incidence of recent infection (39% [28/72] vs. 1% [1/131]). The average number of reported anti-mosquito actions by residents of both locations remained low, and approximately 50% (42/80) of the inspected houses had larvae, evidencing the need for more effective community mosquito control. Logistic regression analysis of risk factors for infection in Nahiku identified residing in properties with birds in the house or yard as significantly associated with infection (odds ratio 7.0, 95% CI 1.7-28.5), probably as an indicator of unspecified environmental characteristics that were attractive to the vector. We documented that nearly 40% of Nahiku residents had acquired dengue locally in 2001 and that undetected dengue outbreaks had occurred in Hawaii. Our data suggest that ecological characteristics may help Hawaii health officials identify communities at increased risk of dengue infection.