The incidence of tick infections in the United States has increased significantly in the last decade. It is therefore essential that public health officials and scientists build a robust understanding of the pathogenesis, develop improved diagnostics, and develop preventive vaccines, according to a recent commentary in New England Journal of Medicine by leading scientists of the National Institute of Allergy and Infectious Diseases (NIAID), part of the National Institutes of Health.
Bacteria cause most tick disorders in the United States with Lyme disease, which accounts for the majority (82 percent) of reported cases. The spirochete Borrelia burgdorferi is the main cause of Lyme disease in North America; It is borne by tough ticks, which feed on smaller mammals such as white-footed mice and larger animals such as white-tailed deer. Although there are likely to be many contributing factors to increased incidence of Lyme disease in the United States, greater tick densities and their expanding geographic extent have played a key role, the authors write. For example, the Ixodes scapularis tick, which is the major source of Lyme disease in the northeastern US, was detected in nearly 50 percent more districts by 2015 than in 1996. Although most cases of Lyme disease are affected disease successfully treated with antibiotics, 10 to 20 percent of patients report persistent symptoms after effective antimicrobial therapy. Scientists need to understand this ongoing morbidity better, the authors note.
Tick-borne viral infections are also increasing and could cause serious illness and death. For example, the Powassan virus (POWV), recognized in 1958, causes a feverish disease that can be followed by progressive and severe neurological conditions, causing death in 10 to 15 percent of cases and long-term symptoms in 70 percent of cases leads survivors. Only 20 US cases of POWV infection were reported before 2006; Between 2006 and 2016, 99 cases were reported.
The burden on the population from tick diseases is considerably underestimated, according to the authors. For example, the United States Centers for Disease Control and Prevention (CDC) report about 30,000 cases of Lyme disease annually in the United States, but estimate that the true frequency is ten times that number. This is partly due, in the view of the authors, to the limitations of current surveillance of tick-borne diseases, as well as to current diagnostics, which in some cases may be inaccurate and fail to detect new tick-borne pathogens when they occur. These limitations have led researchers to explore new, innovative diagnostics with multiple platforms that could bring clinical benefits in the future.
It is also critical that scientists develop vaccines to prevent disease, the authors write. A Lyme disease vaccine has already been developed but has been withdrawn from the market and is no longer available. Future protective measures could include vaccines specifically designed to elicit an immune response to a pathogen or to target pathogens within the ticks.
By researching the epidemiology of tick-borne diseases, improving diagnostics, finding new treatments and developing preventive vaccines, public health officials and researchers could counteract the growing threat of these diseases. In the meantime, according to the authors, health care providers should recommend their patients to use basic prevention methods: wear insect repellent, wear long pants while hiking in the forest or work outdoors and watch out for ticks.