Vital Signs

Trends in Reported Vectorborne Disease Cases — United States and Territories, 2004–2016

Ronald Rosenberg, ScD; Nicole P. Lindsey, MS; Marc Fischer, MD; Christopher J. Gregory, MD; Alison F. Hinckley, PhD; Paul S. Mead, MD; Gabriela Paz-Bailey, MD; Stephen H. Waterman, MD; Naomi A. Drexler, MPH; Gilbert J. Kersh, PhD; Holley Hooks, MPH; Susanna K. Partridge, MPH; Susanna N. Visser, DrPH; Charles B. Beard, PhD; Lyle R. Petersen, MD


Morbidity and Mortality Weekly Report. 2018;67(17):496-501. 

In This Article

Abstract and Introduction


Introduction: Vectorborne diseases are major causes of death and illness worldwide. In the United States, the most common vectorborne pathogens are transmitted by ticks or mosquitoes, including those causing Lyme disease; Rocky Mountain spotted fever; and West Nile, dengue, and Zika virus diseases. This report examines trends in occurrence of nationally reportable vectorborne diseases during 2004–2016.

Methods: Data reported to the National Notifiable Diseases Surveillance System for 16 notifiable vectorborne diseases during 2004–2016 were analyzed; findings were tabulated by disease, vector type, location, and year.

Results: A total 642,602 cases were reported. The number of annual reports of tickborne bacterial and protozoan diseases more than doubled during this period, from >22,000 in 2004 to >48,000 in 2016. Lyme disease accounted for 82% of all tickborne disease reports during 2004–2016. The occurrence of mosquitoborne diseases was marked by virus epidemics. Transmission in Puerto Rico, the U.S. Virgin Islands, and American Samoa accounted for most reports of dengue, chikungunya, and Zika virus diseases; West Nile virus was endemic, and periodically epidemic, in the continental United States.

Conclusions and Implications for Public Health Practice: Vectorborne diseases are a large and growing public health problem in the United States, characterized by geographic specificity and frequent pathogen emergence and introduction. Differences in distribution and transmission dynamics of tickborne and mosquitoborne diseases are often rooted in biologic differences of the vectors. To effectively reduce transmission and respond to outbreaks will require major national improvement of surveillance, diagnostics, reporting, and vector control, as well as new tools, including vaccines.


Vectors are blood-feeding insects and ticks capable of transmitting pathogens between hosts. Wide varieties of pathogens have evolved to exploit vector transmission, including some viruses, bacteria, rickettsia, protozoa, and helminths. Dengue viruses are estimated to infect nearly 400 million persons worldwide each year,[1] and malaria[2] is a major cause of pediatric mortality in equatorial Africa. Plague[3] and rickettsioses[4] cause deadly epidemics abroad. In the United States, 16 vectorborne diseases are reportable to state and territorial health departments, which are encouraged to report them to the National Notifiable Disease Surveillance System (NNDSS). Among the diseases on the list that are caused by indigenous pathogens are Lyme disease (Borrelia burgdorferi); West Nile, dengue and Zika virus diseases; plague (Yersinia pestis); and spotted fever rickettsioses (e.g., Rickettsia rickettsii). Malaria and yellow fever are no longer transmitted in the United States but have the potential to be reintroduced. As a group, vectorborne diseases in the United States are notable for their wide distribution and resistance to control. A Food and Drug Administration–approved vaccine is available to prevent only one of the notifiable diseases, yellow fever.

Despite the dissimilarities among vectorborne pathogens and the many vector species that can transmit them, commonalities exist. Vectorborne disease epidemiology is complex because of environmental influences on the biology and behavior of the vectors. The longevity, distribution, biting habits, and propagation of vectors, which ultimately affect the intensity of transmission, depend on environmental factors such as rainfall, temperature, and shelter. Most vectorborne pathogens are zoonoses, often with wild animal reservoirs, such as rodents or birds, making them difficult or impossible to eliminate. Arthropod vectors can bridge the gap between animals and humans that would not ordinarily intersect, as happens in Lyme disease, plague, and West Nile virus (WNV), facilitating the introduction of emerging animal pathogens to humans.

The pace of emergence of new or obscure vectorborne pathogens through introduction or belated recognition appears to be increasing. Since 2004, these have included two previously unknown, life-threatening tickborne RNA viruses, Heartland[5] and Bourbon,[6] both reported from the U.S. Midwest. A tickborne relapsing fever agent, Borrelia miyamotoi, first described in Japan, has been found widely distributed in the United States[7] and another bacterial spirochete, Borrelia mayonii[8] was discovered in the upper U.S. Midwest. Two tickborne spotted fever Rickettsiae, R. parkeri[9] and Rickettsia species 364D,[10] and a tickborne Ehrlichia (E. muris eauclairensis)[11] were discovered to be pathogenic to humans. The mosquitoborne viruses chikungunya and Zika were introduced to Puerto Rico in 2014 and 2015, respectively. Zika virus is emblematic of the dangers of emergence. Zika was one of a number of obscure, mosquitoborne viruses known to be pathogenic to humans that are rarely encountered or studied.[12] In the 60 years following its discovery in a monkey in Uganda, it was seldom reported as a human pathogen. In 2016, there were >36,000 cases reported in Puerto Rico, limited autochthonous, or local, transmission in Florida and Texas, and nearly 5,000 cases among travelers to the United States.[13] The teratogenic consequences of the 2015–2017 epidemic in the region of the Americas were unexpected.

CDC examined trends of reported vectorborne disease cases in the United States during 2004–2016; this report discusses the challenges of prevention and control and highlights opportunities for vectorborne disease preparedness at the state and local level.