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The low down on Lyme disease

31530344-Lyme3Have you ever sat beneath a tree during the summer afternoon, and found yourself wondering if it might be raining? Saying “I just felt something land on me!” Only to realize it wasn’t rain, it was insects falling from the tree?
This actually happened as we were hosting our prestigious Wilderness Medicine Debate Society debates as part of a Wilderness Medicine Elective for medical students hosted by Wilderness Medical Associates International. Following the debate we informed students of the presence ticks and someone in the group let out a gasp, “Tick…OMG!” Apparently students had heard about tick borne illnesses.

Many participants were already aware of the connection between ticks and Lyme disease.  Thus we reminded participants about the importance of regular “Tick checks” after outdoor activities in tick endemic areas. A simple, yet effective way of reducing your risk of acquiring Lyme disease, this recommendation got a good giggle from the group, maybe because it was also noted to be “a great way to really get to know fellow travellers on a trip!”

This is the second in a series of collaborative blog posts related to insects and infectious disease with my good friend Scott Willis.

Ticks are small eight-legged arachnid parasites that need to feed on blood to grow and survive. They latch onto mammals, birds, reptiles, and humans by piercing the skin to get a blood meal. Usually people will find ticks attached to their body after walking through a forest, before the tick has started feeding. Once the tick has started feeding (sucking blood) it becomes engorged, meaning the abdomen becomes larger and turns greyish blue in colour. What makes ticks so medically relevant is that they can carry all sorts of diseases, such as Lyme disease, babesiosis, and anaplasmosis. Many species of ticks carry the Lyme disease causing spirochete bacterium Borrelia burgdorferi. Not all tick species carry Lyme disease however. The most common and widespread tick that can pass on Lyme disease in southern Ontario is the deer tick (Ixodes scapularis) – also known as the blacklegged tick.

Blacklegged ticks have a 2 year lifecycle, going from egg, larva, nymph, adult to egg. Each phase must get a blood meal and feed before maturing to the next stage. More often than not the nymph stage is the main source of transmitting Lyme disease, since they need the blood meals to grow and develop and are easily hidden on the body. They are most active during mid-May to August. The blacklegged tick’s range stretches from southern Ontario, Quebec and most of Eastern United States. They are most commonly found in deciduous forests, since this is where white-tailed deer are found- the tick’s animal host.

The risk of a patient contracting Lyme disease when bitten by a tick depends on many factors. First the longer the tick has been attached to the person, the greater a chance of transmission. People can feel the tick before it starts feeding and can easily get it off their body. Many however do not feel the tick bite and the tick can stay attached to the body and continue feeding for days. Studies suggest that it takes up to 36-48 hours for the bacteria to be transmitted when feeding. This can easily be prevented by tick checks at the end of the day. Not all blacklegged ticks contain the bacteria for Lyme disease, with an estimated 25% of nymph ticks having Lyme disease and 50% of adults.

One of the main tools in predicting whether or not someone has Lyme disease after a tick bite is to use entomological evidence. Identifying the species of tick that bites a patient as a blacklegged tick can help in diagnosing Lyme disease. After getting bitten, it is advisable to have your patient keep the tick and bring it in to be identified. It can be dead or alive and simply kept in a container, like a zip-lock bag. It is suggested though that when the patient is removing the tick, be as careful as possible to avoid damaging it and thus preventing proper identification. Also keep the tick in a container with damp wrapping to prevent dehydration of the sample. Dehydration of the tick makes identification extremely difficult.

The primary means by which Lyme disease is diagnosed based on physician-observed clinical manifestations and a convincing history of exposure to an infected tick.

Identifying ticks is done by process of elimination. The only other common tick that might be confused with a blacklegged tick is the dog tick, which is commonly found on pets. Dog ticks are not capable of transmitting Lyme disease since they are not very good hosts for the bacteria. You can identify blacklegged ticks from dog ticks by their size. Blacklegged ticks are very small, smaller than other ticks that they may be confused with. Usually the nymphs are only 1 to 2mm in diameter, compared to the dog tick, an equally common tick, which is 3mm. The size difference is very noticeable. Also dog ticks have very definitive white markings on their back that the blacklegged ticks lack. Examine the white markings in the picture below on the dog ticks.

31530335-Lyme2This picture is a good indicator of the size difference. On the top are unfed adult blacklegged ticks and on the bottom are adult dog ticks. You can also note the white pattern on the “back” of the dog tick.
If you are trying to identify a tick, the internet has many wonderful resources!

http://www.tickencounter.org/tick_identification

This is a wonderful place to start! There are pictures of all stages of ticks for different regions (Southern Ontario would be Northeast/Midwest). It evens offers the different tick’s abundance.

http://www.idph.state.il.us/envhealth/tickkey.htm

This site offers a dichotomy key of-sorts. A bit more entomology lingo is present though, so this is recommended for the more seasoned tick identifier.

It is important to note that if the tick is engorged, it makes the tick harder to identify, and you must focus on legs and upper part of the body. Identifying ticks can be challenging, if you are not comfortable with attempting to identify the tick then you can send it to an expert. Ticks that have been kept by the patient can be sent to a provincial laboratory for identification and Lyme disease testing. If the tick is identified as a blacklegged tick, it will be sent to the National Microbiology Laboratory (NML), where they will test it for Lyme disease using polymerase chain reaction along with any other potential pathogens. This service is provided by the Public Health Agency of Canada, and they use the data of Lyme disease positive ticks to monitor the tick’s spread. It is important to note that even if the tick tests positive for Lyme disease or that the tick that bit them was identified as a blacklegged tick, this is not a 100% guarantee that your patient has contracted Lyme disease. Additional blood tests should be ordered and symptoms must be considered.

31530328-Lyme_1
Blacklegged ticks becoming increasingly difficult to identify when they become engorged.
Generally IgM and IgG antibody blood tests are ordered for diagnosing Lyme disease in the patient, however it is often negative in the first weeks of the illness so if there is recent onset if symptoms or characteristic EM rash it may need repeating. Depending on lab resources, more sensitive PCR testing can also be done on the blood sample. If the patient is suspected of contracting Lyme Disease overseas its is important to test should using a C6 based assay as other serologic test may not detect infection with European species of Borrelia.

As always these tests are not 100% definitive and, as with all evidence-based medicine, everything must be considered before a diagnosis. Having entomological evidence as discussed in this blog can make ruling Lyme disease in or out much easier.

The concern is that Borrelia infection  (Lyme Disease) can result in dermatologic, rheumatologic, neurologic, or cardiac abnormalities. The typical incubation period is 3-32 days according to the CDC. It has been reported that anywhere from 70-80% of patients develop a rash, known as erythema migrans (EM) within 30 days of exposure to B. burgdorferi. EM is described as a red expanding rash (with or without central clearing) often accompanied by symptoms of fatigue, fever, headache, arthralgias or myalgias. Infection can also spread to causing more serious complications and conditions like meningitis or carditis with atrioventricular heart block. Untreated infection can progress to cause arthritis, peripheral neuropathy, or encephalopathy.

We must stress though that prevention is your most important tool in the fight against Lyme disease. If you are going into an area where blacklegged ticks are known to exist, stick to paths and wear long clothing. There are many commercial repellents available, but ones containing DEET or permethrin are your best bets. Perform tick checks at the end of the day. If you do find any ticks, use fine-tipped tweezers to remove it. Remember that the earlier you catch the tick, the less chance of Lyme disease transmission.

Knowledge is the best tool in the identification of blacklegged ticks and prevention of Lyme disease.

Sources:
http://www.cdc.gov/features/lymedisease/
http://www.phac-aspc.gc.ca/id-mi/tickinfo-eng.php
CDC Health information for International Travel 2010 – The Yellow Book

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Excellent Schoolmasters

30664776-Angel's landing
View of the main Zion canyon from Angel’s Landing… spectacular. Photo by Jonathan H. Lee.

“Earth and Sky, Woods and Fields, Lakes and Rivers, the Mountain and the Sea, are excellent schoolmasters, and teach some of us more than we can ever learn from books.” John Lubbock – The Use of Life (1894), ch. IV: Recreation

It wasn’t a Brown Recluse…

30669269-734px-Brown-recluse-2-editHave you ever heard some medicine or infectious disease keener throw out a “brown recluse bite” on their differential diagnosis for what looks like a simple insect bite? Have you seen a necrotic wound where a staff says it was likely due to a “spider bite”? Have you ever heard of Brown Recluse spiders? Do you live in Canada?
Below is an article about why it is exceedingly unlikely that your insect bite was a brown recluse, if you live in Canada. This is the first in a series of collaborative blog posts related to insects and infectious disease with my good friend Scott Willis.

To kick things off lets look at Table 1 from Swanson and Vetter, NEJM 2005 of conditions potentially misdiagnosed as bites from loxosceles spiders. This table always makes me smile.
30669276-Screen shot 2011-08-20 at 7.17.31 PM
David L. Swanson, M.D., and Richard S. Vetter, M.S. Bites of Brown Recluse Spiders and Suspected Necrotic Arachnidism. N Engl J Med 2005; 352:700-707. February 17, 2005.
Brown recluse spiders (Loxosceles reclusa) are small, brown spiders that have a potentially serious venomous bite that can cause skin necrosis (or at least that is what everyone is worried about). While this can be very startling, residents of Canada do not have to fear about being bitten by a brown recluse. The brown recluse spider can only be found in south Central/Midwest United States.

Wait, hold the press! What about a brown recluse which hitches a ride on a load of fruit shipped from the United States?

This question always gets raised and becomes a question of probabilities. I ask you to consider which is more likely…that a lone loxosceles spider hitch-hiked thousands of kilometers waiting stealthily to bite one unlucky soul…or that someone might not be using a suitably wide differential diagnosis (my money is on the later). Remember we should cast a wide net when formulating our diagnosis rather than settling on a diagnosis of convenience with little actual concrete evidence.

Brown recluse spider range
30669270-maps
http://dermatology.cdlib.org/DOJvol5num2/special/recluse.html

Despite this, many doctors in Canada still diagnose brown recluse bites. The belief that brown recluse spiders are in Canada is an urban legend; only 3 have been ever verified in Canada. Even having the spider accidentally transported from its natural habitat to Canada is extremely rare. The spiders themselves rarely bite, and are very shy in that they are only active at night. They prefer rocks and crevices, are not found in the open, and avoid human contact. They will only bite when trapped between you and a surface (putting on shoes with the spider inside for example).

Many times a patient will have their bite misdiagnosed as a brown recluse bite without anyone ever seeing a spider. Some states that do not have natural recluse populations have guidelines that state that if the spider is not seen in the act of biting then it should be treated accordingly and not as a necrotizing spider bite. Thus, it is important to have your patient bring in the offending spider if they are bitten, or at the very least they must report seeing the spider.

The diagnosis really comes down to whether the spider that bit the patient was a brown recluse or not. Brown recluse spiders are the most misidentified spider by amateurs and experts alike.

So you were bit by a spider, but was it a brown recluse?

Most people would consider the “violin head pattern” on the “middle” of the spider to be the most unique feature. Unfortunately most people identify the spider wrongly on this trait, as many other spiders have patterns that might resemble a violin head. The pattern itself on the recluse is not always vibrant or present, and can only be found on adult spiders. While brown recluse spiders are known for this pattern I would not recommend using it to identify the spider. If it is present, it can reinforce your identification, but it should not define it.

“Violin Pattern”
30669277-media_httpblogjimbail_vdrcp
The number of eyes and their arrangement on the spider is crucial to a proper identification. Most spiders have eight eyes. Brown recluse spiders only have six. This is rare, as there are few spiders that only have six eyes, none of which resemble the brown recluse. The arrangement of the eyes is also important.

Most other spiders have their eight eyes arranged in two rows of four like this:
30669273-Normal eyes

http://bugguide.net/node/view/84423

While the brown recluse has its six eyes arranged in pairs like this:

30669272-Recluse eyes

http://bugguide.net/node/view/84423
http://dermatology.cdlib.org/DOJvol5num2/special/recluse.html

One pair is in the middle, the other two are on each side. If you have a Web Frontal view Loxosspider with six eyes in this arrangement, you have a brown recluse.

There are a few other distinguishing characteristics that would help identify a brown recluse. Brown recluse spiders’ legs have a uniform light colour to them and there are no stripes or bands on the legs. Also, the legs have no spines, only fine hairs. The size of the spider is only about 6-20mm in size. If the spider meets all of these characteristics, it is a brown recluse spider. In a pinch though, the eyes are the key.

While the above information allows you to identify a brown recluse, we must stress that the bite isn’t a brown recluse bite. While the bites can be traumatizing, a diagnosis should only occur in regions and countries where Brown Recluses populate and live.

Consider other bugs as source of bite (unless presented otherwise); fleas, ticks, mites, bedbugs and assassin bugs. These bugs actually seek out humans, whereas spiders do not. If you can capture the spider, send it to an arachnologist for identification. Even if you get bit, a necrosis occurrence is very rare, occurring about 37% of the time. Most bites heal without any problems.

All of this, including the shyness and unwillingness of the spider to bite except in extreme circumstances makes a bite from a brown recluse in Canada – EXTREMELY UNLIKELY.

Wilderness Context

Forest

Wilderness medicine has been defined as any context that involves patient care in extreme environments, when resources may be limited or non-existent, and evacuation to greater medical care may be hours, days or longer. Applications of wilderness medicine may be in a remote corner of the planet, but also include environments such as urban disasters, severe weather conditions, multiple patients, police and military interventions or any situation that creates a context with minimal resources or extended scene patient management.

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