Tick-borne Diseases Are on the Rise in the United States

As tick-borne disease cases continue to rise in the United States, it is becoming increasingly clear that there is a greater need for new prevention and control methods.

Investigators from the National Institute of Allergy and Infectious Diseases, part of the National Institutes of Health, have released a new perspective piece in the New England Journal of Medicine suggesting that current diagnostics are not enough to control the growing problem of tick-borne infections.

From 2004 to 2016, the number of disease cases caused by ticks doubled in the United States, with Lyme disease accounting for the majority of those infections. Approximately 30,000 cases of Lyme disease are reported per year, according to the Centers for Disease Control and Prevention (CDC), but the actual incidence could be up to 10 times that number.

Authors of the perspective piece postulate that limitations in surveillance and reporting systems along with constraints imposed by the diagnostics currently available may contribute to the discrepancy. The authors detail several issues associated with the current diagnostics.

“Diagnostic utility is affected by variability among laboratories, timing of specimen collection, suboptimal sensitivity during early infection, imperfect use of diagnostics (particularly in persons with low probability of disease), inability of a single test to identify coinfections in patients with acute infection, and the cumbersome nature of some assays,” the authors write.

Furthermore, current diagnostics are unable to distinguish between past and acute infection, which can lead to nonspecific clinical findings. Tests can also remain positive, even after the infection has resolved, the authors add.

Powassan virus (POWV) is the only known North American tick-borne encephalitis causing flavivirus which saw a significant increase in cases from 2006 to 2016. Diagnosis requires serological testing, which can only be performed in specialized laboratories and is unable to identify novel tick-borne organisms.

The limitations of current diagnostics have led to the exploration of new technologies. One development includes a multiplex serologic platform that can detect antibodies to more than 170,000 distinct epitopes and distinguish between 8 different tick-borne pathogens, offering enhanced detection in specimens that are collected during early disease. Additionally, the use of nonserologic platform technologies may also improve the capability of diagnostics. For example, with the use of next-generation sequencing investigators discovered emerging pathogens such as Heartland virus and Bourbon virus by linking organisms with sets of unexplained symptoms.

Currently, prevention and management measures to reduce tick infection rely on reducing exposure to ticks or promptly treating infections; however, there are no current effective therapies for tick-borne viruses such as POWV.

Authors of the piece indicate that the largest gap in prevention is that there are no licensed vaccines for humans targeting any tick-borne pathogens in the United States. The only vaccine for Lyme disease, LYMErix, was withdrawn from the market.

Historically, vaccines have targeted specific pathogens, but investigators shifting towards the use of a new strategy that would involve targeting the vector instead. Doing this could reduce transmission of multiple pathogens at the same time through the exploitation of a common variable, such as vector salivary components. Phase 1 clinical trials are currently assessing the use of mosquito salivary-protein-based vaccines in areas where mosquito-borne diseases are not endemic. The approach is being explored for multiple tick-borne diseases since tick saliva also contains proteins common among various tick species.

The authors postulate that the burden of tick-borne diseases will continue to grow significantly. Research is necessary to improve prevention and management of these diseases and to address the lack of treatment options, vaccines, and diagnostics.

Until research can provide better preventive guidelines, individuals should use insect repellent, wear long pants while active in the woods or in gardens, and check for ticks following these activities.