Four Human Cases of Eastern Equine Encephalitis in Connecticut, USA, during a Larger Regional Outbreak, 2019

Enhancing Eastern Equine Encephalitis Virus Surveillance in New Jersey: Optimized Collection of Culiseta melanura

Eastern equine encephalitis virus (EEEV) causes the most clinically severe neuroinvasive arboviral disease in the United States. The virus is endemic in eastern and Gulf Coast states and the Great Lakes region, causing cases annually. To detect EEEV circulation in its enzootic cycle before the virus infects humans and other mammals, mosquito control agencies in New Jersey have conducted mosquito surveillance using a series of permanent wooden resting box sites since 1975. We conducted 2 field studies, 1 evaluating resting traps and 1 evaluating efficacy of CO2 lures, to optimize collection of Culiseta melanura, the primary enzootic vector of EEEV. Resulting mosquito samples were subjected to molecular analysis to determine EEEV infection rates. Corrugated plastic boxes trapped more bloodfed Cs. melanura than other resting trap types (resting boxes, Centers for Disease Control and Prevention [CDC] resting traps, or fiber pots) and were similar to resting boxes in total number of female Cs. melanura caught. Further, non-baited CDC light traps were more successful in trapping host-seeking Cs. melanura than those baited with dry ice, a CO2 lure. The EEEV RNA was identified in Cs. melanura, Aedes vexans, Anopheles quadrimaculatus, and Uranotaenia sapphirina. Our findings indicate that corrugated plastic boxes and non-CO2 baited traps could improve detection of Cs. melanura. Mosquito control agencies are encouraged to periodically assess their surveillance strategy for EEEV.

Virology, ecology, epidemiology, pathology, and treatment of eastern equine encephalitis

Eastern equine encephalitis (EEE) was one of the first-recognized neuroinvasive arboviral diseases in North America, and it remains the most lethal. Although EEE is known to have periodic spikes in infection rates, there is increasing evidence that it may be undergoing a change in its prevalence and its public health burden. Numerous factors shape the scope of EEE in humans, and there are important similarities with other emergent viral diseases that have surfaced or strengthened in recent years. Because environmental and ecological conditions that broadly influence the epidemiology of arboviral diseases also are changing, and the frequency, severity, and scope of outbreaks are expected to worsen, an expanded understanding of EEE will have untold importance in coming years. Here we review the factors shaping EEE transmission cycles and the conditions leading to outbreaks in humans from an updated, multidomain perspective. We also provide special consideration of factors shaping the virology, host-vector-environment relationships, and mechanisms of pathology and treatment as a reference for broadening audiences.

Clinical Characteristics of the 2019 Eastern Equine Encephalitis Outbreak in Michigan

Background

Eastern equine encephalitis virus is a mosquito-borne alphavirus responsible for unpredictable outbreaks of severe neurologic disease in animals and humans. While most human infections are asymptomatic or clinically nonspecific, a minority of patients develops encephalitic disease, a devastating illness with a mortality rate of ≥30%. No treatments are known to be effective. Eastern equine encephalitis virus infection is rare in the United States, with an annual average nationwide incidence of 7 cases between 2009 and 2018. However, in 2019, 38 cases were confirmed nationwide, including 10 in Michigan.

Methods

Data from 8 cases identified by a regional network of physicians in southwest Michigan were abstracted from clinical records. Clinical imaging and histopathology were aggregated and reviewed.

Results

Patients were predominantly older adults (median age, 64 years), and all were male. Results of initial arboviral cerebrospinal fluid serology were frequently negative, and diagnosis was not made until a median of 24.5 days (range, 13-38 days) after presentation, despite prompt lumbar punctures in all patients. Imaging findings were dynamic and heterogeneous, with abnormalities of the thalamus and/or basal ganglia, and prominent pons and midbrain abnormalities were displayed in 1 patient. Six patients died, 1 survived the acute illness with severe neurologic sequelae, and 1 recovered with mild sequelae. A limited postmortem examination revealed diffuse meningoencephalitis, neuronophagia, and focal vascular necrosis.

Conclusions

Eastern equine encephalitis is a frequently fatal condition whose diagnosis is often delayed, and for which no effective treatments are known. Improved diagnostics are needed to facilitate patient care and encourage the development of treatments.