Report purpose

This document provides Utah partners with a concise summary of this season’s major mosquito-borne disease results. Information displayed in this report has been compiled by the Utah Department of Health and Human Services (DHHS), but reflects information obtained from joint efforts. All activities related to the mosquito-borne diseases seen in Utah during the 2023 season involved major contributions from many different agencies. These include: Utah blood banks, local health departments (LHDs), Utah Department of Agriculture and Food (UDAF), Utah Division of Wildlife Resources (UDWR), Utah Mosquito Abatement Association (UMAA), the Utah Public Health Laboratory (UPHL), and the Utah Veterinary Diagnostic Laboratory (UVDL). In addition to the direct contribution of surveillance data, these entities were also involved in systematic planning and preparation for the 2023 season. The intent of this report is to document the results of the efforts put forth by these entities during the 2023 season. For more information about each disease described in this report, please visit our disease-specific webpages to learn more:https://epi.utah.gov/atozlist/

NOTE: This report describes the general trends that occurred during the 2023 season. Specific surveillance counts may be subject to change as data are reconciled.

Introduction

This report historically focused on each season’s West Nile virus results, but was expanded in 2023 to incorporate other mosquito-borne diseases for which Utah conducts surveillance. Since West Nile is the most common mosquito-borne disease in Utah, the majority of this report will cover this virus. Utah Department of Health and Human Services (DHHS) conducts surveillance for endemic and travel-associated mosquito-borne diseases. Mosquito-borne diseases considered endemic in Utah include West Nile virus (WNV) and St. Louis Encephalitis (SLE). Travel-associated diseases Utah DHHS monitors include chikungunya, dengue, malaria, and Zika. Public health investigations of travel-associated mosquito-borne diseases are important to determine the locations of exposure and help us monitor any potential locally transmitted events of these diseases. Malaria is transmitted by the Anopheles mosquito, which has been detected in almost every county in Utah since the establishment of Utah’s mosquito abatement districts (MADs). Chikungunya, dengue, and Zika are all transmitted by the Aedes aegypti mosquito, which has been detected near St. George and Moab. Both of these mosquito species are detected in low numbers, and the risk of locally acquired transmission of these diseases is small. However, due to the recent reports of local transmission of dengue in Arizona (2022) and California (2023) and malaria in Florida, Texas, Maryland, and Arkansas (2023), Utah DHHS has enhanced surveillance and monitoring of all reported cases of these mosquito-borne diseases for proactive awareness and response. SLE is transmitted to humans from the bite of an infected Culex species mosquito. A SLE human case has not been reported since 2016. However, mosquito pools have been positive for SLE in 2022 and 2023. WNV is also transmitted by the bite of an infected Culex mosquito. Birds are the natural host of the disease with humans and horses serving as accidental hosts. WNV is the most common disease acquired in Utah with a 10-year average reported human case count of 16. The majority of people infected with WNV never develop symptoms. A small percentage of infected individuals will display West Nile fever symptoms (fever, headache, and body aches). A more serious form of the disease, West Nile neuroinvasive illness, may also occur when the virus infects the central nervous system. People with this form of the disease experience high fever, severe headache, neck stiffness, and mental confusion. Hospitalization is often required and death is possible. This type of infection can also cause long-lasting neurological symptoms. WNV is the most common mosquito-borne disease found in Utah. The remainder of this report will primarily focus on WNV. For more information about each disease described in this report, please visit our disease specific webpages to learn more:@https://epi.utah.gov/atozlist/

2023 season national highlights

West Nile virus case maps present data reported to the Centers for Disease Control and Prevention’s (CDC) ArboNET surveillance system by state and local health departments. Figure 1 shows the WNV human reported cases by state of residence for 2023 with shading, ranging from 1–5, 6–8, 9–25, and >25 cases.

Figure 1: