Vector-Borne Diseases

**About Vector-Borne Diseases** **Overview** Mosquitoes, ticks, and fleas that spread germs (pathogens) are called vectors. A person who gets bitten by a vector and gets sick could have a vector-borne disease (VBD). Some VBDs, like plague, have been around for thousands of years. Others, like Heartland and Bourbon virus diseases, have been discovered recently. Some VBDs can become serious, life-threatening illnesses. **Increasing threat** Cases of VBDs have increased significantly since 2004, with more than 1 million cases reported between 2001 and 2023 in the United States[1](https://www.cdc.gov/vector-borne-diseases/about/#cdcreference_1). Annual reported VBD cases more than doubled during this period. Currently, states, territories, and freely associated states voluntarily report cases of 17 VBDs to CDC, plus additional cases that are not nationally notifiable but of interest to public health. However, reported cases tell only a portion of the story. For example, it is estimated that only 1 in 10 West Nile virus cases are reported, and the number of treated Lyme disease cases is possibly 10 times higher than the number reported to CDC. **Who is at risk** Certain groups of people are at a higher risk for disease than others. Understanding your risk can help you know when and where to expect ticks and mosquitoes. Those who may be at increased risk include: - Children - Older adults - Dog owners - Outdoor workers - Outdoor enthusiasts - [People with weakened immune systems](https://www.cdc.gov/vector-borne-diseases/risk-factors/immunocompromised-people.html) **Causes and spread** Several factors are driving the emergence and increased spread of VBDs, putting more people at greater risk. - **Changing land use patterns**, like reforestation, can lead to increased deer populations and suburban growth, exposing more people to more infected tick bites each year. - **Global travel and trade** play a role in introducing invasive vectors and pathogens throughout the Americas. - Travelers have inadvertently brought chikungunya and Zika viruses into the United States. - Almost every year, travelers have been associated with local spread of dengue in southern states. - **A changing climate** influences the geographic distribution and seasonality of VBDs. This includes: - Changing weather patterns and increased frequency of severe and unpredictable weather, such as heat waves and droughts. - Longer and warmer summers and shorter and milder winters lengthen vector seasons in the United States. - Temperature and precipitation affect disease transmission by impacting the replication, interaction, and survival of disease vectors. These factors, along with societal factors like housing conditions, occupational exposures, and access to health care, can contribute to worsening the already disproportionate impacts of VBDs in some communities.