Trends in tickborne diseases
In June, 2016 professionals from the Health and Human Services (HHS) Working Group on Lyme and Other Tickborne Diseases presented a joint webinar to discuss recent trends in tickborne diseases and their transmission.
Lyme disease is caused by the Borrelia burgdorferi bacterium, which is carried by the deer tick (Ixodes scapularis) in the northeast and north central United States and the western blacklegged deer tick (Ixodes pacificus) in the Pacific coastal regions. Infection is spread through the bites of tick nymphs.
Dr. Rebecca Eisen and Dr. Kiersten Kugeler of the Center for Disease Control and Prevention (CDC) in Fort Collins, Colo., described how tick presence has increased 45% since the mid-1990s and is now documented in at least 49% of contiguous United States counties. Ixodes scapularis (or blacklegged tick) has been expanding in all directions with the northeast and north central populations likely to merge in the Ohio Valley to form a single focus. As the spread of ticks is limited only by natural barriers such as rivers or lakes, continued range expansion is expected.
Yet despite widespread tick presence, most instances of Lyme disease remain focused in the northeast and upper Midwest. But the instances of reported Lyme disease demonstrate that the disease, like the ticks, is on the move. Between 1993 and 2012 the number of counties documented to be at high risk for Lyme disease has increased by almost 300%. The expansion of both the range of the vectors and the instances of Lyme disease make careful documentation and effective prevention methods high priorities.
New cause of Lyme disease
Elitza Theel, Ph.D., director, Infectious Diseases Serology Laboratory, Mayo Clinic, Rochester, Minn. reported on the identification of a novel species, Borrelia mayonii, which appears to be carried by the same tick groups responsible for Lyme disease. But unlike B. burgdorferi, the B. mayonii spirochete is found in whole blood, and grown and cultured blood samples reveal an average bacterial load 180-fold higher than in instances of B burgdorferi.
The patients infected with B. mayonii were residents of the upper Midwest and all had extensive exposure to ticks, although several reported no tick bites. The disease appeared similar to Lyme disease but symptoms were more severe and also included signs of neurologic involvement — confused speech, somnolence, and visual defects. All patients recovered completely with antibiotic therapy.
Alan Barbour, M.D., professor of medicine and microbiology & molecular genetics, University of California, Irvine, Calif. presented an update on Borrelia miyamotoi, a relapsing fever agent carried by hard ticks that was first reported over 100 years ago in cattle and other ungulates. Studies in Japan in 1995 described the presence of B. miyamotoi in the taiga tick (Ixodes persculatus), with subsequent studies also confirming B. miyamotoi in United States and European ticks. Unlike B. burgdorferi, which is transmitted by the bites of nymphs, B. miyamotoi is found in unfed larval ticks, confirming a transovarial transmission route for this Borrelia. And because the organism is already present in the salivary glands of larval ticks, transmission time may be considerably faster than the usual 24 to 36 hours.
In the United States B. Miyamotoi is present in both I. scapularis and I. pacificus ticks, but in I. pacificus the ratio of B. bergdorferi to B. miyamotoi has been documented at 1:1, meaning there is an equal chance of contracting HTRF as Lyme disease in western locations. HTRF can be difficult to distinguish from anaplasmosis but is marked by relapses of fever and viral-like illnesses including high temperature, a severe headache, low platelet count, and abnormal liver enzymes. Treatment of HTRF is similar to that of Lyme disease and other relapsing fevers.
Tickborne viral diseases
Dr. Nicholas Komar, S.D., CDC Arbovirus Diseases Branch, Division of Vector-Borne Diseases, Fort Collins Colo., presented information on tickborne viral diseases. There are no more than 10 cases of any of these diseases in a single year so there is a lack of knowledge about them in both the medical community and the public. Because of this they can be easily overlooked as a cause of disease.
Colorado tick fever is the most of common tickborne virus in the United States, with the Rocky Mountain wood tick acting as the vector. Symptoms of biphasic fever, chills, head and body aches, fatigue, and, occasionally, sore throat, vomiting, abdominal pain, or skin rash are usually mild, non-life threatening, and resolve without treatment.
Powassan disease has appeared most recently in New York, Minnesota and Wisconsin and is associated with both the woodchuck tick (Ixodes cookei) and I. scapularis. Powassan is a more severe disease, with patients displaying the neurologic symptoms associated with encephalitis in addition to the viral symptoms seen in Colorado tick fever. Approximately 10% of these cases are fatal and of the survivors, half usually display some form of persistent neurologic sequelae.
Heartland virus was discovered in 2009 appears to be transmitted humans via the lonestar tick (Ambylomma americanum). So far, it has only affected a few men who spent large amounts of time in tick infested habitats. In addition to the usual viral symptoms patients displayed low white blood cell count and decreased platelets. The fatality rate seems to be approximately 10%, although the total number of cases may be under-reported. Another strain, Bourbon virus, was isolated in 2014 from the blood of a patient who died after receiving a tick bite. Studies suggest that it is similar to Heartland virus and distantly related to influenza; however, much more research is needed.
Tick bites and meat allergy
Galactose-alpha-1,3-galactose, or Alpha-gal, is present in the tissues of all lower mammals, and the Alpha-gal allergy is caused by the production of IgE antibodies to the presence of mammal meat, including beef and pork.
Scott Commins, M.D., Ph.D, University of North Carolina, Chapel Hill, N.C., reported instances of patients who presented with sudden symptoms of headache, urticaria, angioedema, palmar edema, hives or GI distress within three to six hours after eating red meat. Each of these patients had eaten meat all of their lives and had never displayed these symptoms. Investigation revealed that geographic overlays of both the distribution of Rocky Mountain spotted fever (RMSF) and the range of the lonestar tick corresponded with the locations of the affected patients, and the patients themselves reported significant history of recent insect bites. Further testing revealed a rise in the Alpha-gal-specific IgE and the total IgE levels of these patients. This suggests that tick bites can affect total and specific IgE levels in some patients and that additional bites may lead to a larger increase in IgE response. Over time, sensitization to alpha-gal did decrease in these patients.
There are few options that reduce the likelihood of disease once exposure has taken place so, when possible, behavior should be altered to minimize contact with ticks. When contact is suspected, the body should be checked thoroughly and any ticks removed immediately to minimize the possibility of transmission of disease. The use of insect repellant on clothing, include DEET and Permethrin, should be encouraged. The EPA also offers on online tool that can identify appropriate repellants and their effective dosages.
The HHS Working Group on Lyme and Other Tickborne Diseases is available for viewing online.
Dr. Ben Beard: No relevant disclosures
Dr. Rebecca Eisen: No relevant disclosures
Dr. Kiersten Kugeler: No relevant disclosures
Dr. Elitza Theel: Dr. Theel is employed by the Mayo Clinic which offers serologic and molecular testing for Lyme disease through their reference laboratory, Mayo Medical Laboratories.
Dr. Alan Barbour: No relevant disclosures
Dr. Nicholas Komar: No relevant discosures
Dr. Scott Commins: Support from the NIH_NIAID (K08 AI085190, R21 AI087985 and R56 AI113095); unrestricted support from Blue Ridge Bread; NIH research grant UpToDate