Friday, October 11, 2013

13 24 Hours Of Attachment Is An Estimate - Not a Safety Blanket

By now you may have heard the news that the CDC announced that there are over 300,000 estimated cases of Lyme disease in the United States each year.

For many people, this estimate came as a shock, but it really shouldn't be - the CDC itself has stated in the past that reported cases are a fraction of actual case numbers - especially in highly endemic areas - and researchers have also stated a case count of 30,000 was an underestimate.

Many Lyme disease patients and advocacy groups felt vindicated by the announcement, as it confirmed their position that the number of people contracting Lyme disease was always much larger than official numbers which were originally reported. The below chart, for example, was created by Open Eye Pictures, which produced the controversial film on Lyme disease, Under Our Skin:

Lyme Disease in the US as of 2009 - 0ver 461,000 estimated cases
Click to zoom in for a closer look.

Open Eye Pictures created this chart back in 2011, based on data directly from the CDC but without direct access to the insurance study, patient survey, and other information the CDC used recently to adjust their new estimate to 300,000 annual cases of Lyme disease. As one can see, their estimate managed to come pretty close to the CDC's - if not potentially higher.

With this announcement, news outlets, park rangers, and medical experts began warning the public once again to take proper precautions to prevent tick bites and to do body checks for ticks after being outdoors.

Some are also informing people that if they don't spot a tick right away, not to worry - if a tick is removed properly within 24 hours, it is highly unlikely to transmit any tickborne disease.

While there is truth in that statement, unfortunately it isn't exactly accurate and doesn't cover all kinds of ticks and any tickborne infections they might be carrying.

This chart shows only a small fraction of tickborne infections currently known to be pathogenic to people along with their transmission times (and in some cases, typical attachment times):

Sample of Well-known and Newly Emerging Tickborne Diseases in North America and Europe and Their Estimated Transmission Times

Tickborne Infection
Tick Species
Estimated Transmission Time
Upon Attachment
Lyme disease BorreliosisBorrelia burgdorferi sensu strictuIxodes scapularis,
Ixodes pacificus
North America36-48 hrs;
24 hours or more;
potentially less 
Borrelia burgdorferi Ixodes ricinusEuropeLess than 24 hours
Borrelia afzeliiIxodes ricinusEuropeLess than 24 hours
Borrelia gariniiIxodes ricinusEuropeLess than 24 hours
Relapsing Fever
Borrelia miyamotoiIxodes scapularis, Ixodes pacificusNorth Americaunknown
Ixodes ricinusEuropeunknown
Borrelia turicataeOrnithodoros turciataNorth America30 seconds with a total tick attachment time 15-90 minutes
Borrelia hermsiiOrnithodoros hermsiiNorth America30 seconds with a total tick attachment time 15-90 minutes 
Human Monocytic EhrlichiosisEhrlichia chaffeensisAmblyomma americanum, Ixodes pacificus,
possibly Dermacentor variabilis 
North America12 to 24 hours 
Human Ewingii EhrlichiosisEhrlichia ewingiiAmblyomma americanumNorth Americasuspected 12 to 24 hours
(formerly HGE)
Anaplasma phagocytophilum (formerly Ehrlichia phagocytophilum)Ixodes scapularis, Ixodes pacificus, Dermacentor variabilisNorth America12 to 24 hours
BabesiosisBabesia duncaniIxodes pacificusNorth America24 to 36 hours
Babesia divergensIxodes ricinusEurope24 to 36 hours
Babesia microtiIxodes scapularisNorth America24 to 36 hours
Rocky Mountain Spotted FeverRickettsia rickettsiiDermacentor andersoni, Dermacentor variabilisNorth America4 to 6 hours
Q FeverCoxiella burnetiiDermacentor
andersoni (rare*)
North Americaunknown - suspected fast as highly infectious
Ixodes ricinus, others  (rare*)Europeunknown - suspected fast as highly infectious
Powassan Virus or Powassan EncephalitisLineage 1 or 2 FlavivirusIxodes cookei, Ixodes scapularisNorth America~15 minutes
Heartland VirusGroup V PhlebovirusAmblyomma americanumNorth Americaunknown
Tickborne Encephalitis (TBE)Flaviviridae FlavivirusIxodes ricinusEuropeWithin minutes

* Q fever is usually transmitted to people by exposure to contaminated raw dairy products, inhalation of aerosol fluids from pregnant animals, blood transfusions, and in utero. Tickborne infection with Q fever can happen - either through a tick bite or exposure to tick fecal matter - but along with cases of sexual transmission,  this is rare compared to other methods.

There Are Unknowns In Tickborne Disease Transmission Times

Note that in the above chart, some items are marked unknown. This is because - as far as could be determined, no lab animal model transmission studies for that specific organism have been completed.

Incubation research may have been conducted - and this can inform us how long it takes before animals show signs and symptoms of being infected - but it does not inform us how long a tick must be attached before an infection can occur.

For example, the chart above contains information on Borrelia miyamotoi as one causative agent of relapsing fever, but transmission time from a hard-bodied Ixodid tick is currently unknown.

Until recently, it was thought relapsing fever spirochetes only colonize soft-bodied ticks and persist in their salivary glands, where they can transmit infection to blood quickly. But does the same situation apply to all hard-bodied ticks Borrelia miyamotoi colonizes? Is it the organism, or the tick's physiology, or both which determines how quickly Borrelia miyamotoi can be transmitted on average?

Heartland Virus is another example where transmission time is unknown. Heartland Virus is so new, very little is known about it.

Transmission Time Varies Based On Pathogen And Tick Species

Some pathogens are transmitted from a tick to its host in a few minutes - not hours - and so the 24 hour guideline does not apply to them. Relapsing fever organisms and tickborne viruses often fall into this category.

Some pathogens are transmitted more rapidly from one tick than they are from another. In Europe, there is evidence Lyme disease spirochetes are transmitted to their host more rapidly due to Ixodes ricinus' physiology. So if you live in Europe or visit there and get bitten by Ixodes ricinus, if the tick was attached for under 24 hours you are more likely to contract Lyme disease than if you were bitten by an Ixodes tick in North America.

Note, too, that transmission times can be periodically revised based on new data - and if anything, the trend has been demonstrating infection transmission could take place in less time than originally determined.

Overview Of Risk Factors In Tickborne Disease Transmission

What your risk is for contracting particular tickborne infections can vary, depending on:

  • The geographic location you were in when you were bitten; 
  • The type of tick which has bitten you;
  • How recently the tick may have fed on another host;
  • How many infectious organisms it has in its salivary glands;
  • Whether or not the tick is carrying other pathogens;
  • How long the tick has been attached; 
  • How the tick has been removed.

Those are risk factors involving the tick. But there are also host factors as well. Different hosts - including humans - have different immune systems and responses to specific tickborne strains of pathogens, and this, too, can determine the outcome of how or even if an infection will occur.

The Bottom Line

So what does the 24 hour guideline mean? It means many tickborne infections are less likely to infect you if a tick has been removed within 24 hours, but it isn't an ironclad guarantee that you won't contract an infection.

The best thing to do, of course, is to prevent ticks from getting on you in the first place. Prevention is key. No ticks means no tick bites, and not having to worry about what kind of tick has bitten you and what disease it might be carrying.

Wear permethrin coated clothes and use DEET spray on exposed skin. Wear pants tucked into socks and long-sleeved shirts and stick to the middle of the trail when hiking.

The second best thing to do is to do a regular tick check outdoors with a friend and not wait until you come home. Brush off any loose ticks, and carefully remove ticks with tweezers or narrow forceps as soon as you find them. Clean the tick bite area and place antibiotic lotion on it, then save the tick(s) you find in a well-sealed container for identification and testing at a tick testing lab.

There is no 100% guarantee that even with early tick removal, you will avoid contracting a tickborne infection. But your odds of getting infected are greatly reduced the sooner you properly remove a tick.


Lyme disease. Centers for Disease Control. Downloaded September 28, 2013.
Lyme disease. Centers for Disease Control. Downloaded September 28, 2013.
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