Lyme disease is an infectious disease that’s found around the world—in the US it’s most commonly caused by the bacterium Borrelia burgdorferi, and cousins of this bacteria, Borrelia garinii and Borrelia afzelii are causes of Lyme disease in Europe and Asia. And new ones are still being found. In fact, in 2015, researchers from Mayo clinic discovered a new bacterial strain causing Lyme disease and decided to name it Borrelia Mayonii. So these Borrelia bacteria are all spirochetes which means that unlike other bacteria, they are long, thin, and spiral-shaped, and they spin or twist to move around. Lyme disease is classified as a zoonosis, meaning it’s it’s spread to humans from animals that exists as natural reservoirs, reservoir meaning that the bacteria typically doesn’t cause serious disease to the animal. And Borrelia species can infect a wide range of animals, including small mammals like mice, lizards, and birds. The bacterium isn’t known to spread directly from animals to humans, but instead it needs a vector, meaning some sort of intermediate organism to spread from the animal to the human. Depending on the region, there are different vectors, for example, in the northeastern U.S. it’s spread via Ixodes scapularis, commonly known as the black-legged deer tick, but other types of Ixodes ticks transmit Lyme Borrelia in western North America and Eurasia: like the sheep tick, the taiga tick, and western black-legged tick. Ticks need blood to survive, and I don’t mean they have blood already, they need blood from a host, or a blood-meal—just like mosquitoes, leeches, vampires, and other not-so-pleasant creatures. Literally being blood-suckers, it makes them obvious candidates for spreading blood-borne disease, right? And ticks need to go through life stages—larvae, nymph, and adult, not too different from us: children, adolescents, and adults. The larval tick will most likely get the bacteria while feeding on something like a mouse, since deer ticks in the larval stage prefer smaller animals. After larval deer ticks molt to the nymphal stage they feed on a broader range of animals, meaning that they can spread the bacteria they picked up to new reservoirs. After molting again to the adult phase, they focus mostly on deer, which actually aren’t the best hosts for Borrelia. So since the larval and nymphal deer ticks spread Borrelia to more suitable hosts, these two stages are very important for Borrelia. Now, both nymphal and adult-stage deer ticks, although not their preferred meal, occasionally feed on the unknowing human. If you’ve ever had a tick on you, you’d probably agree that the first thing you want to do is get it off. The tough part about deer ticks, especially nymphal stage deer ticks, is that they’re really small--about the size of a poppyseed--, and therefore sometimes hard to notice. This means they can be allowed to feed for long periods of time, thus allowing the tick to transmit the disease. The Borrelia bacteria are transmitted within the saliva of the tick as its feeding., and it typically takes about 36-48 hours of attachment time for the bacterium to move from the tick’s gut into the saliva and into the human.
If Borrelia infects a human it causes disease in three stages. The early localized stage of Lyme disease is usually days to weeks after the initial infection. As the bacteria spreads from this initial point, redness and inflammation expands as well. Sometimes, the space between the initial bite and outer radius of the rash is cleared of bacteria, leading to a bulls-eye shaped rash, also known as erythema migrans—which is a classic early sign of Lyme disease. In addition, there might be some vague flu-like symptoms at this stage as well. Next is the early dissemination stage which is usually weeks to months later, when the bacteria starts to spread through the bloodstream, or disseminate to places like the heart, brain, and joints. In general, relatively few bacteria actually invade these various tissues, but the immune reaction is usually pretty severe and turns these tissues into a warzone, essentially killing the bacteria but damaging the tissue in the process. Other instances of erythema migrans might start to pop up in places that don’t relate to the original bite. This is where Lyme disease can become serious. When the bacteria infects the heart tissue, it’s known as carditis. Although heart tissue inflammation can affect all sorts of heart functions, it often clinically presents as AV heart block, meaning the electrical signal moving from the upper chambers to the lower chambers is held up or blocked, which changes the timing of the heartbeat.
Lyme disease is also known to cause swelling around the nerves that control the facial muscles, essentially pinching the nerve and causing facial nerve palsy, where facial muscles become weak or even paralyzed, which can make it hard to smile or close the eye. With Lyme disease, this condition is often bilateral, meaning it happens on both sides of the face. If the disease spreads to the joints, it can cause arthritis in the knee, the wrist, and the ankles. Lyme disease can also spread to the meninges, which is the lining of the brain, causing meningitis and sometimes terrible neck stiffness and headaches. Not surprisingly, inflammation in various parts of the body can also cause fevers, fatigue and other flu-like symptoms just like we saw in the early localized stage. If the disease is allowed to progress further to the late dissemination stage, which can emerge months or years after infection typically be up to a year after infection, symptoms can vary widely. They may include neurologic manifestations like sleep disturbances and fatigue, cognitive problems, and neuropsychiatric symptoms. Patients often present with chronic arthritis involving one joint (a knee is especially common) or a few joints.the major symptom is chronic arthritis of either one joint or a few joints, commonly involving the knee. The diagnosis of Lyme disease is clinical, based on signs and symptoms and on a history of exposure to infected ticks. Physicians look to blood tests to support their diagnosis. Usually blood testing for Lyme is doneNow the diagnosis of Lyme disease is usually made by looking at antibodies against Borrelia proteins. via a test called a Western Blot. This test, called a Western Blot, is not always reliable. There are some antibodies that sometimes cross react; they form against a normal bacteria but cross react with a Borrelia protein. This raises the possibility of “false positives.” There are also patients infected with the Borrelia bacteria who do not produce enough specific Borrelia antibodies to pass the threshold on a standard blood test--this raises the possibility of “false negatives.” The CDC surveillance criteria for identifying Lyme cases is a two-tiered test with strict intThe tricky thing is that sometimes antibodies cross-react. In other words, an antibody that is formed against a normal bacteria that lives in the gut might suddenly cross-react with a Borrelia protein because it looks similar. To help tease apart who really has Borrelia and who doesn’t, there are criteria about how many different types of antibodies a person needs to have in order to make the diagnosis more specific and weed out what can be considered “false positives.”Both the CDC and the FDA advise that Lyme disease is a clinical diagnosis and serologic testing is supportive.
To treat Lyme disease, antibiotics like doxycycline are the first-line choice of treatment, and they are most effective in the earliest stages of the disease. and if given early on in disease, are oftenvery effective at wiping out the bacteria, The although the specific antibacterial medication given often depends on things like the stage of the disease and the age of the patient. It’s also important to monitor patients being treated with antibiotics because they can develop a Jarisch-Herxheimer reaction, which is where they develop fevers, sweating, and muscle pains in response to the spirochetes breaking open and releasing a lot of antigens all at once—which is just super immunogenic. Ultimately, once patients are treated for Lyme disease they do really well—there can be a few weeks or months of ongoing symptoms of fatigue and muscle or joint pains which is normal, but this resolves and is not generally thought to be related to ongoing persistence of the Borrelia bacteria in the body. Having said that,In fact, there Some patients continue to have symptoms after treatment. Doctors and researchers are currently debating about why this is. One view holds that after treatment the Borrelia bacteria is eradicated and thus not responsible for ongoing illness, and instead symptoms result from autoimmune processes. There is nowongoing research into whether “persister bacteria” might be able to live dormant and cause thea clinical condition sometimes calledknown as Post Ttreatment Lyme Ddisease Ssyndrome. Currently, the infectious disease society of America suggests that there is ’s actually no evidence that the bacteria does not lives on chronically in the body after treatment, and there is no evidencereason to recommend usinge prolonged courses of antibiotics or other medications to treat any chronic symptoms attributed to Lyme disease.
Treatments for patients with persistent symptoms after standard therapy have not been successfully tested or approved by the FDA, and researchers and physicians are actively exploring clinical tools for the treatment of post-treatment Lyme symptomatology. In terms of prevention, people who work or explore wooded areas or areas with brushes, leaf litter, and tall grass are most at risk of picking up a deer tick and being infected with Lyme disease. That said, taking preventative measures are important for everyone, like wearing hats and long-sleeved shirts, as well as using bug spray in areas where ticks are known to spread Lyme disease. Treating footwear and clothing with the chemical permethrin has been found to be especially useful.
Resources edit
http://emedicine.medscape.com/article/330178-clinical
https://en.wikipedia.org/wiki/Lyme_disease#cite_note-pmid15117014-42
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2440571/
http://circ.ahajournals.org/content/127/7/e451.full
https://en.wikipedia.org/wiki/Ixodes_scapularis
http://www.hopkinsrheumatology.org/specialty-clinics/lyme-disease-clinical-research-center/research/