Tick-Borne Diseases, and How to Avoid Them

2018 December 29

Today, I wanted to talk a bit about (a) why ticks are such a festering mass of disease and pestilence, and (b) what you can do to avoid catching something from them.

(tick nymph)

To start with, ticks are obligate blood-feeders. The have to get a blood meal for every growth stage, and in the process they ingest whatever horrible disease their victims might happen to have. So far, this isn’t too unusual. Lots of things like to suck blood, and would therefore pick up disease organisms. The thing that spreads the disease is if the blood-sucker bites more than one victim, which means they can pick it up from one and transfer it to the next.

(deer tick)

So we can rank blood-sucking organisms by their likelihood of carrying diseases:

Almost no risk
Lowest risk are blood feeders that only bite once, which basically wouldn’t spread disease at all (like this opportunistic bug that normally sucks plant juices, but apparently isn’t averse to a bit of blood when the opportunity arises). Unless I am susceptible to some plant disease like chestnut blight[1], the odds of picking up anything are negligible.

(plant bug, genus Deraiocoris)

Small risk
There is slightly higher risk from the ones that tend to stick with a single host their whole lives, like bedbugs, fleas, and lice. They can spread disease if their hosts live in crowded conditions, but are limited in how far they will travel;


Fairly high risk
The risk elevates significantly with those that habitually bite multiple hosts over a short lifespan, like mosquitos and other biting flies. They are good at acting as vectors for diseases (spreading them from infected individuals to uninfected ones), but don’t act as a reservoir for the disease (maintaining the disease in the environment even when all the hosts have recovered from it) because they don’t survive through the winter after they pick up the disease[2];

(mosquitos trying to get through our window screen

Very high risk
And then there are the real bad actors, that bite multiple hosts over their lives (acting as vectors), and also live through the winter with infectious organisms in them so that they can infect new victims in the spring (acting as disease reservoirs).[3]

Ticks fall into that last category, in spades. They hatch, find some small animal for their first blood meal, molt and grow, find additional animals, feed again, molt and grow to adulthood, and then the females feed massively one last time before laying a few thousand eggs and repeating the cycle.

(unidentified engorged tick, maybe a nymph?)

(engorged wood tick)

This whole process can take several years, so the disease organisms that they pick up from an infected mouse as a newly-hatched larva can be spread by them to other mice when they are nymphs, and then persist in them until they reach adulthood and bite a deer, dog, or human.

Given their proclivity for multiple hosts, it is pretty good odds that any given adult tick will be carrying some disease. So, what diseases should we expect, and how are they transmitted?

While the big ones in the news are Lyme Disease and Rocky Mountain Spotted Fever, they aren’t the only ones by any means. The Centers for Disease Control has a list of 16 diseases carried by ticks in the United States, and there are others outside of North America. They can be divided up based on the type of organism that causes them.

Parasites: Babesiosis is caused by a parasitic organism that infects red blood cells, similar to the much-more-famous disease, malaria. There are treatments available, and it is not as severe of a disease as malaria.

Bacteria: Many tick-borne diseases are caused by bacteria – Anaplasmosis, Borrelia, Ehrlichiosis, Lyme Disease, Tick-Borne Relapsing Fever, and Tularemia. Some of these are life-threatening and need to be treated promptly. On the plus side, bacteria are susceptible to antibiotics, and so effective treatment is possible, although it is important to start treatment before the bacteria cause permanent damage.

Rikettsia: These are basically stripped-down bacteria that have lost the ability to live outside of host cells, and are kind of intermediate between bacteria and viruses. The various spotted fevers, including Rocky Mountain Spotted Fever, are this type. They are reported to respond to treatment with doxycycline.

Viruses: Viruses are basically bits of rogue DNA and RNA that get into cells and co-opt the cell machinery to manufacture more viruses. The ones carried by ticks include Bourbon Virus, Colorado Tick Fever, Heartland Virus, Powassian Disease, and maybe Southern Tick-Associated Rash Illness (STARI). Viruses are not susceptible to antibiotics, and once you have them they are basically untreatable, although it may be possible to develop vaccines to keep people from catching them in the first place.

The best way to avoid getting these diseases is obviously to avoid getting bitten. This means that if you go into an area where there may be ticks, constant vigilance is important. The ticks climb up on stalks of grass and grab onto you as you walk by, so avoid walking through tall grass. Wearing long pants that are either tucked into your boots or held tight around your ankles with a blousing strap might help keep them from crawling up your pants. After possibly being exposed to ticks, at the first opportunity you should remove and inspect all of your clothing, and if there is someone available to inspect the places that you can’t see, you should check each other. In particular, check your hair, around the waistline, and behind/inside your ears. Any ticks that you find can be killed easily by dropping them into a glass of soapy water or alcohol, or by cutting off their heads with a pair of scissors. Don’t bother trying to squash them to kill them, it is pretty hard to do. I also don’t advise throwing them in the trash or toilet, because they can crawl back out and have another try at you later. And brush your dog thoroughly, too. They can carry an incredible number of ticks if you don’t pay attention.

They will usually crawl around on you for several hours before latching on, and even after they attach it appears to take a couple of hours before they start getting blood out. Once they are fastened, you can use the method recommended by the CDC to remove them with tweezers, or you can pop them off with a Tick Twister or Tick Key. The important things about removal are:

– Do it as soon as possible,
– Don’t squeeze the tick’s body, because that could force infected blood back into the wound, and
– Just pop it off mechanically. Don’t mess around with matches, or mineral oil, or cigarettes, or gasoline, or any of the other weird approaches that are supposed to make them “let go”. All of those are likely to make it vomit blood back into the wound, which is way worse than leaving bits of its mouthparts embedded in the skin.

Now, it’s one thing if you are not on your own property and have no control over its state of tickyness. But, if you have ticks on your own property, there are things you can do to get rid of them.

A good start is to make a “tick flag”, which is a sheet of fleece fabric (or similar wooly fabric) on the end of a stick. If you drag the fabric back and forth in the grass in front of you, the ticks will grab onto it, and get their legs tangled in the fleece until you pick them off and put them in the killing jar (the aforementioned jar of soapy water or alcohol). This is both a method for clearing them out, and a diagnostic tool to find the “hot spots” where the ticks are hanging out. The first year we did this, we killed about 50 ticks, and at the same time identified a patch of yard where the ticks were hanging out in unusual numbers. It turned out that any spot where there is a lot of small mammal traffic (mainly mice) is where you will find the greatest number of ticks.

Once you find the hot spots, there are some things you can do to knock them out. One suggestion I have seen is Tick Tubes. The way these work, is you take cotton balls, and treat them with permethrin, a powerful insecticide for ticks. Then you put the cotton balls in cardboard tubes (like toilet paper tubes), and leave them in areas where you suspect there may be mice or other small rodents. The mice then take the cotton back to their nests for bedding, and the permethrin kills the tick nymphs in their nests before they can mature. This is reported to knock back tick levels as much as 90%.

If you don’t want to deal with permethrin, there are other methods that are supposed to either repel ticks, or kill them. An approach that I think is intriguing is the use of parasitic nematodes to kill ticks. They apparently kill a lot of other small arthropods, too, but apparently don’t affect non-arthropods.

[1] James Thurber claimed in “My Life and Hard Times” that his great-uncle Zenas died of the chestnut blight (I am pretty sure he was joking . . .):
“Zenas had died in 1866. A sensitive, rather poetical boy of twenty-one when the Civil War broke out, Zenas had gone to South America–“just,” as he wrote back, “until it blows over.” Returning after the war had blown over, he caught the same disease that was killing off the chestnut trees in those years, and passed away. It was the only case in history where a tree doctor had to be called in to spray a person, and our family had felt it very keenly; nobody else in the United States caught the blight. Some of us have looked upon Zenas’ fate as a kind of poetic justice.”

[2] The short lifespan of mosquitos is, I think, why most mosquito-borne diseases are considered tropical diseases. There are probably more mosquitos in, say, Canada in the summer than there are in Africa. But the mosquitos aren’t able to spread diseases through the cold months, so the victims have a chance to recover from the diseases before the mosquitos come back. So unless a disease can persist in a victim that gets infected in the fall, and then is still contagious enough in the spring to pass it on to a new mosquito, then it will not persist in the temperate and arctic areas. Meanwhile, in the tropics, the mosquitos are available to spread disease all the time, and so the disease never goes away.

[3] There are some weird exceptions, though: even though leeches live for some years, and bite multiple hosts, it is evidently rare for them to actually spread diseases from host to host. I don’t know why this would be, it may just be that their between-bite interval is long enough that any disease organism that can’t actually reproduce in the leech is cleared out between feedings.

4 Responses
  1. Carole permalink
    December 29, 2018

    Interesting piece. Our State Foresters also report fire is a good way to control ticks. They usually try to have controlled burns in the long-leaf pine forests every 3 years to keep undergrowth down. Areas burned regularly have less ticks.

  2. January 3, 2019

    I wonder if that is only because the fire kills the ticks directly, or if it is also because the fire reduces the habitat for the small mammals that the ticks mature on?

  3. January 4, 2019

    Thanks for another interesting blog. I particularly liked your risk rankings based on feeding habits and life cycle.

    The new invasive tick found in 2017 in New Jersey – the Asian long-horned tick may increase the number of tick borne diseases beyond 16 in North America. . It is a known vector of many human diseases in Asia including SFTS (Severe fever with thrombocytopenia syndrome) a viral disease and Japanese spotted fever which is a rickettsia disease. There are concerns that this invasive tick might be capable of transmitting diseases that native North American ticks currently transmit including Lyme disease. see short blog if interested https://ticksurveillance.com/blog/

  4. January 11, 2019

    Great post, Tim. I learned quite a few things.

Comments are closed.