Ticks are the arthropod ride of choice for vector-borne diseases in the United States, but the Zika virus and its mosquito minions gave the ticks and their bacterial passengers a run for their money in 2016, according to the Centers for Disease Control and Prevention.
There were 41,680 cases of Zika virus that year, more than any other vector-borne disease, including Lyme disease, which had been the most common transmissible pathogen going back to at least 2004, when arthropod-borne viral diseases became nationally notifiable, said Ronald Rosenberg, ScD, and his associates at the CDC’s National Center for Emerging and Zoonotic Infectious Diseases in Fort Collins, Colo.
All those cases of Zika virus were not, however, enough to put the mosquito-borne diseases – dengue, Zika, West Nile virus, malaria, chikungunya, and a few other rare viruses – ahead of the tick-borne diseases – Lyme disease, anaplasmosis/ehrlichiosis, spotted fever rickettsiosis, babesiosis, tularemia, and Powassan virus – for the first time. The tick-borne total for 2016 was 48,610 cases, compared with 47,461 for the mosquito-borne pathogens, the CDC investigators reported in the MMWR.
Since 2004, there have been 643,000 reported cases of vector-borne disease in the United States: 492,000 cases of tick-borne disease, of which over 402,000 were Lyme disease; 151,000 cases of mosquito-borne disease; and 89 cases of plague carried by the third type of vector, fleas, Dr. Rosenberg and his associates said based on data from the National Notifiable Disease Surveillance System.
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In 2004, there were 22,527 cases of tick-borne disease and 4,858 cases of mosquito-borne disease, and the increases since then reflect the dynamics of the pathogens and vectors involved. Growth of tick-borne disease has been gradual: “Tick-borne pathogens rarely cause sudden epidemics because humans are typically incidental hosts who do not transmit further, and tick mobility is mostly limited to that of its animal hosts,” the researchers explained.
The number of mosquito-borne disease cases, on the other hand, varies considerably from year to year: There were 5,800 cases in 2015, almost 15,000 in 2013, and only 4,400 in 2011. Unlike ticks, which may feed on blood only once in a year, the more mobile mosquitoes feed every 48-72 hours and transmit their pathogens “directly between humans … resulting in explosive epidemics,” the investigators wrote.
SOURCE: Rosenberg R et al. MMWR 2018 May 4;67(17):496-501.
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