Ticks belong to the arachnid family, which means they are related to spiders, mites, and scorpions. They are parasites that feed by latching on to an animal host, embedding their mouthparts into the host’s skin and feeding on its blood.
The deer tick (Ixodes scapularis) in the eastern United States and the Western black-legged tick (Ixodes pacificus) on the Pacific Coast are the two tick species known to transmit Lyme disease in the United States. In Europe, Ixodes ricinus, also known as the castor bean tick, can transmit Lyme disease as well as other pathogens causing encephalitis. Ixodes persulcatus, the taiga tick, which is distributed throughout Europe and Asia, can transmit borrelia and babesia.
Ticks go through four growth stages: egg, six-legged larva, eight-legged nymph, and adult. In order to grow, ticks must feed at every stage after hatching. The entire life cycle of an Ixodes tick takes two years.
[Image courtesy of http://www.bayarealyme.org]
Because they hatch from eggs, larval ticks are not born with infection. Ticks become infected by feeding on a reservoir animal which carries the bacteria. Animals carrying the infection include small mammals such as the white-footed mouse, eastern chipmunk, short-tail shrew, migrating birds, and deer. Host mammals can infect ticks with multiple pathogens, increasing the probability of co-infection.
[Image courtesy of the CDC]
The small size of the nymphal tick, about the size of a poppy seed, often allows it to go unnoticed. When the tick latches on to a host, it secretes the compound cementum, which enables the tick to adhere to its prey. By releasing a series of anti-inflammatory chemicals and antihistamines, the tick numbs the skin where it attaches and the bite becomes difficult to detect. A tick can remain attached for up to a week.
Like syphilis, Borrelia bacteria may remain latent for a long period of time because the bacteria often harbor in parts of the body that have few circulating antibodies. At least four pathogens, in addition to Lyme, can be transmitted into the bloodstream and lead to co-infections. Each pathogen requires a different drug regime, which in turn complicates treatment.
In addition to Borrelia burgorferi, the bacterium responsible for the Lyme outbreaks in Connecticut in the 1970s, other species of Borrelia can cause Lyme disease in the U.S. In 2013, a correspondence from members of the Yale School of Public Health and Yale School of Medicine (New England Journal of Medicine) described the outbreak of a new tick-borne infection in the United States. Blood samples taken from eighteen patients in southern New England presented evidence of infection by the bacterium, Borrelia miyamotoi, which was first identified in deer ticks in Japan in 1995. The infection causes relapsing fever and symptoms similar to Lyme disease.
Lyme Disease Prognosis
Most people with Lyme disease recover if given six weeks of antibiotics, if the disease is diagnosed immediately upon discovery of a tick or infected bite. If the disease remains undiagnosed for months or years, a full recovery becomes less likely. However, remission is possible and many people can live a full and productive life if the right treatments and support are given.
While the majority of people that are diagnosed immediately recover with antibiotics, roughly 36% of patients remain ill. The reasons they don’t recover are varied: 1) the course of antibiotics or other treatment were not long enough (a two-week course is typical, but insufficient for most), 2) the type of antibiotics or other prescribed remedies were not effective and/or 3) there may have been multiple co-infections or other underlying conditions that were not diagnosed or adequately treated.
Lyme infections, including Borrelia, Babesia and Bartonella, among others, are notoriously difficult to eradicate. When the tick or other insect injects these organisms into its host, it also injects substances that inhibit the host’s immune response. This is particularly true of Borrelia. The Borrelia spirochete can hide from the immune system by embedding itself in tissues that are not under normal immune surveillance, such as scar tissue, the central nervous system, the eyes, and joints and other tissues.
Like parasitic amoebas, Borrelia can also transform itself into cysts that evade both the immune system and antibiotics. According to Virginia Savely, DNP, the cyst form “allows the spirochete to hide undetected in the host for months, years, or decades until some form of immune suppression initiates a signal that it is safe for the cysts to open and the spirochetes to come forth and multiply.”
Each of Borrelia’s forms is targeted by different types of antibiotics, herbal remedies and other treatments, but because the spirochete can quickly change form, a number of antibiotics or different types of treatments may need to be administered in order to entirely eradicate the infections. Treatment regimens are often rotated, pulsed and changed every four to eight weeks so that the organisms don’t develop resistance to the medications or other antimicrobial remedies.
Treatment may take many months, or even years, but many adult patients are able to attain remission. Children may have long-lasting neurological injury if the infections are not treated promptly. No test exists to prove that a person can be “cured” from Lyme disease, and no test can prove that the infections are definitively gone. Even patients who go into remission can sometimes experience relapses when under extreme stress, although these are usually more easily managed than the initial outbreak of infections.
What Causes Lyme Disease? – Bay Area Lyme Foundation
A detailed article about the causes and transmission of Lyme disease.
Victoria Cairns, and Jon Godwin. Post-Lyme borreliosis syndrome: a meta-analysis of reported symptoms. Int. J. Epidemiol. (December 2005) 34 (6): 1340-1345.doi: 10.1093/ije/dyi129. First published online: July 22, 2005
Krause, Peter J. M.D. et al. Human Borrelia miyamotoi Infection in the United States. N Engl J Med 2013; 368:291-293January 17, 2013 DOI: 10.1056/NEJMc1215469
Judith Miklossy, Sandor Kasas, Anne D Zurn, Sherman McCall, Sheng Yu, and Patrick L McGeer. Persisting atypical and cystic forms of Borrelia burgdorferi and local inflammation in Lyme neuroborreliosis. J Neuroinflammation. 2008; 5: 40. Published online 2008 Sep 25. doi: 10.1186/1742-2094-5-40. PMCID: PMC2564911
Virginia Savely, RN, FNP-C. Controversy continues to fuel the “Lyme War.” Clinical Advisor, May 18, 2007
Kit Tilly, PhD, Patricia A. Rosa, PhD, and Philip E. Stewart, PhD. Biology of Infection with Borrelia burgdorferi. Infect Dis Clin North Am. 2008 Jun; 22(2): 217-234.doi: 10.1016/j.idc.2007.12.013 PMCID: PMC2440571 NIHMSID: NIHMS52288
Last Updated: 4/23/15
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