Bad Bugs of Summer: Ticks
In our second post on the bad bugs of summer, we’ll be talking about ticks. Or, as I like to think of them, those bloodsucking disease spreaders.
First of all, I really shouldn’t call ticks “bad bugs.” Technically, they’re not bugs at all. Of course, mosquitoes aren’t either. But ticks aren’t even insects. They’re arachnids. And, worldwide, there are approximately 900 different tick species – around 25 of which can be found in North Carolina. Fortunately, only a few of those 25 species pose a problem for humans; the rest are content to pester other species.
All biting ticks belong to the Ixodidae family of so-called “hard ticks.” These ticks go through four life stages: egg (in which the tick pretty much just sits there), larval, nymph and adult. During those last three stages, the tick is a bloodsucking parasite.
One of the worst ticks in North Carolina (or anywhere) is the lone star tick, or Amblyomma americanum. This species gets its name from the white spot found on the back of females, and is such a nuisance because it is known to feed on human blood during its larval, nymph and adult stages. Worse still, americanum is a known vector for at least two diseases that affect humans – and it has been found from Maine to Oklahoma.
Because it is so common, and so dangerous, we’ll use americanum to illustrate how ticks suck. Literally. During its larval and nymph stages, americanum latches on to a passing mammal. Most ticks are very specific about the type of animals they feed from, but not americanum. It will feed on anything from a squirrel to a man. Once it has latched on, it climbs to exposed skin and begins to feed. In the larval stage, it feeds for 2-3 days before becoming engorged. As a nymph, it will feed for 4-5 days. Once sated, it falls off its host and molts into the next stage.
When they molt into adulthood, ticks exhibit sexual dimorphism for the first time. In other words, the males are distinct from the females. Most hard ticks, including americanum, mate on the host. The female won’t fully engorge with blood until after mating. But, in the 4-5 days after mating, a female will increase in weight 100-fold(!) over her unfed weight, amassing lipids and proteins from the host’s blood and secreting excess water and salts back into the host.
Hard ticks feed more slowly than mosquitoes, but their bites also result in pain, itching and swelling due to the physical injury caused by their mouthparts and the injection of a biochemical cocktail that prevents blood from clotting at the bite site.
But ticks are more than just disgusting pests. They also serve as vectors for numerous diseases. The three types of tick-borne diseases most commonly found on the Atlantic seaboard are all bacterial pathogens: Rocky Mountain Spotted Fever, Ehrlichioses and Lyme Disease.
Here’s how ticks can spread disease. If a tick in its larval stage feeds on a white-tailed deer that is infected with Ehrlichiosis, it will ingest a species of the Ehrlichiosis bacteria. Those bacteria colonize the tick and reproduce in its salivary glands. When the tick molts into a nymph, and later into an adult, it injects the bacteria into its hosts when it feeds. The same would hold true if the tick was exposed to the bacteria only during its nymph stage.
For human-specific cases of Ehrlichioses, americanum is the only vector (I told you they were bad news). For Lyme Disease, the black-legged tick is the only vector. For Rocky Mountain Spotted Fever, the vector has historically been the American dog tick, but there is some concern that a family of similar diseases are being spread by other tick species – including americanum.
So what can you do to protect yourself? Ticks need a moist environment to survive, so eliminating leaf litter in your yard can make it less hospitable to ticks by drying out the soil. And, when hiking in the woods or other tick-friendly environments, you can limit access to your skin by wearing long pants, tucking your pant legs into your socks and tucking in your shirt. And apply repellent. The CDC has a good list of repellants that will actually work.
When you get home from an outdoor excursion, check yourself carefully for ticks. If you get a tick off your skin within 24-48 hours, the possibility of its having transmitted a pathogen into your bloodstream is slim to none (they’re slow feeders, remember?).
If you do find a tick, shield your fingers with toilet paper, a paper towel or latex gloves and grab the tick as close as possible to the head. Pull directly away from the bite (perpendicular to your skin), gradually increasing the pressure until the tick comes off. Check the tick out. If it has a white plug around its mouthparts, you got the whole thing. If you don’t see that plug, look at the bite. If you see a black dot at the bite site, tease the mouthparts out with a sterilized needle. Here’s the CDC’s recommended approach.
Note: Many thanks to Dr. Charles Apperson, William Neal Reynolds Professor Emeritus of Entomology at NC State, for taking the time to talk to me about ticks. Apperson, whose work focuses on vector biology, ecoepidemiology and ecology of mosquitoes and ticks, was patient in his explanations, and kindly answered all of my questions (even the inane ones). Any errors in the above post are mine and mine alone.