What evidence is there, then, that it’s not just one type of tick that carries Lyme disease bacteria in the US? And what does that mean for your level of risk?
Lyme Disease Transmission
Writing in the May issue of The International Journal of Medical Sciences, researchers from the University of North Florida noted that not only do lone star ticks appear capable of transmitting Lyme disease bacteria to people but that two types of the bacteria that were previously thought not to infect humans may also be causing symptoms of the disease in the southeastern US. The paper could change the face of Lyme disease in North America, with potential ramifications for testing, diagnosis, treatment and vaccination against Lyme disease in the US and Canada. Diagnosing Lyme disease is made even more complicated by the fact that many different tick species also transmit coinfections of Lyme disease such as anaplasmosis, babesia and ehrlichiosis.
Explaining Cases of Chronic Lyme Disease in Non-Endemic Areas
Up until now, the predominant belief was that Lyme disease infections in humans in the US were caused by blacklegged tick bites that transmitted Borrelia burgdorferi sensu stricto and that other species of ticks, including the Lone Star tick did not cause such infections, nor did human patients contract the illness from any other Borrelia species unless they had travelled outside the country. This latest research, carried out by Dr. Kerry Clark and colleagues at the UNF found that patients symptomatic for Lyme disease were infected with two species of Lyme disease bacteria previously unknown to infect humans, Borrelia americana and Borrelia andersonii. If these Borrelia species are capable of causing Lyme-like illness then this could go some way towards explaining the large number of cases where patients continue to show symptoms of the disease but routinely test seronegative for B. burgdorferi antibodies.
Improving Maps of Lyme Disease Risk
In addition, Lyme disease risk maps tend to work on the basis of the population of so-called ‘deer ticks’ in a given area but there have been those who have long suspected that other types of ticks, aside from Ixodes scapularis, may be responsible for transmitting Lyme disease bacteria in the US. A recent Lyme disease risk map produced with almost $3 million in funding from the US Centers for Disease Control may turn out to be somewhat redundant if it turns out that other types of ticks are transmitting Lyme disease bacteria and that, in fact, other types of bacteria are causing Lyme disease.
Halting the Spread of Lyme Disease
The scientists looked at the lone star ticks, Amblyomma americanum, submitted as samples from human patients who subsequently tested positive for Lyme disease bacteria, namely Borrelia burgdorferi, sensu stricto. What they found was that some of the ticks also tested positive, despite the widespread assumption that Ixodes scapularis is the main, if not only, vector of Lyme disease in the US. In Europe and across Asia there are a number of other tick species and bacterial species known to be involved in Lyme disease but the US testing systems are set up on the premise that a single tick type and a single bacteria type are the culprits. Lone star ticks are, however, the most common types of ticks that bite humans in the southeastern US, with tick populations seen across half of the country and moving fast due to climate change and animal migration. They are found as far north as Canada and may present a major threat to public health if it does turn out that the ticks are capable of Lyme disease transmission. It may also explain why patients continue to suffer symptoms of Lyme disease in areas that do not appear to have ‘deer’ ticks.
Overcoming Problems Diagnosing Lyme Disease
The hope is that this groundbreaking Lyme disease research will help patients who have struggled for years to get a diagnosis because of the assumption that there is no Lyme disease present in their geographical area. Going through misdiagnosis after misdiagnosis can put patients at risk of permanent disability as well as chronic suffering, especially if Lyme disease is mistaken for an autoimmune disorder and treated with immunosuppressants that then allow an infection to run rampant. With recent appeals in Alberta for patients and doctors to send in ticks for assessment, it might be that the researchers would be wise to test a number of different species for the presence of bacteria, rather than simply assuming that Ixodes scapularis are the only tick capable of Lyme disease transmission. Evidence suggesting that the common lone star tick may transmit Lyme disease and that new Lyme disease bacteria are causing infections in humans will surely lead to some updated diagnostic guidelines and public health policies.
Kerry L. Clark, Brian Leydet, Shirley Hartman, Lyme Borreliosis in Human Patients in Florida and Georgia, USA, Int J Med Sci 2013; 10(7):915-931. doi:10.7150/ijms.6273