In its “Vital Signs: Trends in Reported Vectorborne Disease Cases — United States and Territories, 2004–2016” published on May 1, 2018, the CDC reported that the data regarding the occurrence of nationally reportable vectorborne diseases during 2004–2016, which are most commonly transmitted by ticks or mosquitoes in the United States, including those causing Lyme disease, Rocky Mountain spotted fever, West Nile, dengue, and the Zika virus, indicate “persistent, locality-specific risks and a rising threat from emerging vectorborne diseases, which have increasingly encumbered local and state health departments tasked with preventing, detecting, reporting, and controlling them.”
The CDC reported that nearly 650,000 cases of vectorborne disease were reported during 2004–2016. Tickborne diseases, which accounted for >75% of reports, occur throughout the continental United States, but predominate in the eastern part of the country and in areas along the Pacific Coast. Reported cases of tickborne disease have doubled in the 13-year analysis period, with Lyme disease accounting for 82% of cumulative reported tickborne disease. The combined incidence of reported anaplasmosis and ehrlichiosis, which are tickborne bacterial diseases, rose almost every year, as did spotted fever; babesiosis, a tickborne parasitic infection that has been notifiable since 2011, also contributed to the rise. Endemic plague, a fleaborne disease that is transmitted mostly in the rural southwestern United States, did not exceed 17 cases in a year. Tularemia and ehrlichiosis are geographically widespread but more prevalent in the central United States.
The CDC reported that recent data from clinical and laboratory diagnoses estimate that Lyme disease infects approximately 300,000 Americans yearly, eight- to tenfold more than the number reported.
West Nile virus (WNV) was the most commonly transmitted mosquitoborne disease in the continental United States. Its most notable epidemic during 2004–2016 occurred in 2012, especially in Texas. Epidemics of dengue, chikungunya, and Zika viruses were mostly confined to the U.S. territories. All four dengue viruses were endemic in Puerto Rico, which was subject to cyclical epidemics, notably in 2010 and during 2012–2013. Puerto Rico’s first chikungunya virus epidemic peaked in 2014, followed by Zika virus in 2016. Travelers infected in the territories and Latin America accounted for >90% of the dengue, chikungunya, and Zika virus disease cases identified in the states and District of Columbia; limited autochthonous transmission of dengue occurred in Florida, Hawaii, and Texas, and of chikungunya and Zika viruses in Texas and Florida. Malaria is diagnosed in approximately 1,500 travelers yearly but no autochthonous transmission was documented during 2004–2016.
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.
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 CDC warns: “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 and Bourbon, 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 and another bacterial spirochete, Borrelia mayonii was discovered in the upper U.S. Midwest. Two tickborne spotted fever Rickettsiae, R. parkeri and Rickettsia species 364D, and a tickborne Ehrlichia (E. muris eauclairensis) 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. 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. The teratogenic consequences of the 2015–2017 epidemic in the region of the Americas were unexpected.”
The CDC concludes: “Reducing vectorborne disease incidence and responding to outbreaks is a large and complex challenge. CDC is using two strategies to mitigate vectorborne threats: advancing innovation and discovery and rebuilding comprehensive vector control programs that have eroded over time. CDC works with states, territories, and tribal councils to compile surveillance data, develop strategies and guidance, and educate the public about specific threats and prevention measures for populations at risk. Expanding sustainable vectorborne disease prevention programs is needed to respond to the ongoing and increasing threat of vectorborne disease.”
If you or a loved one suffered a serious injury (or worse) as a result of the misdiagnosis of Lyme disease in the United States, you should promptly find a Lyme disease lawyer who may investigate your Lyme disease claim for you and represent you in a Lyme disease malpractice case, if appropriate.
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